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Refrigerated Seawater Spray:Its Application to Onboard Stowageof Pacific Shrimp (Pandalus jordani)
By Edward KolbeAssociate Professor of Agricultural Engineering
Oregon State University Marine Science Center, Newportand Jong S. Lee
Professor of Food Science and TechnologyOregon State University
Oregon State UniversityExtension Marine Advisory Program
A Land Grant / Sea Grant CooperativeSpecial Report 600 September 1980
,FG
REFRIGERATED SEAWATER SPRAY
Its Application to Onboard Stowageof Pacific Shrimp (Pandalus Jordani)
Refrigerated seawater spray has been developed and used by severalinnovative individuals in the West Coast fishing industry. Becauseof some continuing difficulties, researchers at Oregon StateUniversity have been involved in the study of this technique forchilling and holding Pacific shrimp on board the vessel. Thesenotes report progress and recommendations as of June, 1980.
Table of Contents
Chapter 1. Operation and Processing
Chapter 2. Seawater Pumping and Spray
Chapter 3. Refrigeration System Sizing . 19
Chapter 4. Tips on Cleaning and Sanitizing 32
Chapter 5. Fish Hold Construction 38
Chapter 6. Temperature Measurement 44
References 45
Other Literature of Interest 47
Appendix: Construction of the Canadian Temperature MeasuringDevice 49
List of Figures
Chapter 1
1. Workable RSWS circuit.
Chapter 2
2. Spray pipe layout in fish hold.
3. Tablespoon deflector sprayer.
4. Spray pattern with tablespoon deflector.
5. Operation of intersecting spray nozzles.
6. Spray patterns for a single Bete nozzle pair placed at twodifferent distances above the surface of the shrimp.
7. One design idea for a multiple diverging jet.
8. Example fish hold.
9. Distribution of Bete spray nozzles.
10. Pressure drop for fittings, in equivalent lengths of pipe.
, Chapter 3
11. Theoretical system temperatures resulting from design ofTable 1.
12. Example A - effect of varying compressor size.
13. Example B - effect of reducing the refrigeration reserve.
14. Example C - effect of using a smaller capacity chiller.
15. Example D - effect of operating with lower spray densities.
16. Predicted cooling rates resulting from "marginal design" ofTable 2.
Chapter 5
17. Theoretical heat leakage rate as a function of urethane foaminsulation thickness.
18. Insulation and hold lining in wooden vessels.
Appendix
19. Operational amplifier.
20. Characteristics of the Fenwal UUA35J1 thermistor.
21. Circuit of telethermometer.
22. Probe designs.
List of Tables
Chapter 3
L. Example RSWS design.
2. A marginal design.
ii
Chapter 4
3. Microbial load of fish hold surfaces.
4. Microbial counts in NMFS experimental RSWS system.
5. Microbial flora of RSW on two shrimp vessels using RSWS.
Appendix
6. Parts list for telethermometer.
iii
CHAPTER 1
OPERATION AND PROCESSING
Introduction
Refrigerated seawater spray (RSWS), as used on the Oregon coast,is a system in which seawater, chilled by mechanical refrigera-tion, is sprayed over shrimp in the hold. With proper sizingand design of the system, cooling rates can be more rapid andstowage temperatures colder than on boats using traditional icefor cooling.
For the fisherman, there appear to be several advantages forchanging from ice to RSWS:
1) freedom from lost time due to scarcity of ice in someports;
2) reduction of effort because there is no need to shovelice below deck;
3) elimination of the expense of ice and the fuel cost tocarry it;
4) ability to handle unexpectedly large catches during atrip;
5) possibility of quicker cooing rates and lower holdingtemperatures, especially in cases where ice is inade-quately applied;
potential of making longer trips than presently possiblewith ice and of delivering a better quality product.The potential of extending storage life could also bene-fit the processor and the consumer.
But there are several potential problems associated with RSWS.Among these:
1) The sanitary condition of the fish hold has a signifi-cant effect on the quality of RSWS shrimp. With ice,clean water from melting ice continually washes mud andbacteria from shrimp into the sump or bilge. From hereit is eventually pumped overboard. RSW spray is aclosed system. A small volume of water, which picks upmud and bacteria, circulates over and over. Worse yet,any initial spoilage in one small area of the hold willrapidly, spread to the whole load. Thus special designand operating procedures for adequate cleaning and sani-tizing of fish hold and plumbing are essential. Theseinclude proper construction (for example, an insulated,nonporous, water-tight fish hold) as well as propercleaning and sanitizing schedules and procedures;
PUMP
I BACK- FLUSHCIRCUIT
CLEANING
SPRAY
SHRIMP
DRAINAGE,
SUMP
There are still some uncertainties concerning properhandling and treatment of RSWS shrimp to ensure highrecovery and peelability;
3) Mechanical problems at sea without adequate repairmaterials, service skills, and/or backup systems couldmean loss of part of the catch or a trip cut short;
4) Initial expense of the system can be high. (In spiteof this, it pays to enlist the guidance of professionalrefrigeration specialists.)
The RSWS piping system is a closed circuit which continuallycirculates a given volume of water through a chiller (Figure 1).The chiller could be a closed box or shell-and-tube type, or itcould possibly consist of refrigeration coils immersed in thesump. The "backflush circuit" shown in Figure 1 enables periodicflushing of the closed chiller and strainer (if one is used).Addition of a "cleaning loop," "filler pipe" and "vent pipe" are
FILLER VENTPIPE PIPE
SPRAY PIPE
CHILLER
STRAINER
® INTAKE ® OVERBOARD
Figure 1. Workable RSWS circuit.
2
Canadian design practices (Ref. 1) to enable concentratedcleaners and sanitizers to be circulated in the piping and equip-ment.
The following sections describe both present practice and tenta-tive recommendations on the operation of these systems and onprocessing shrimp held on RSWS boats. Details on related subjectsare reported in subsequent chapters. These include design ofsprayers, sizing of piping and circulating pump (Chap. #2);sizing of refrigeration compressors and heat exchangers (Chap. #3);cleaning and sanitizing of the fish hold and equipment (Chap. #4);layout and construction of the fish hold and insulation (Chap. #5);and measurement of RSW temperatures in the fish hold (Chap. #6).
Operation
At the present time, RSWS systems are holding shrimp on the vesselaround three-four days*, or about the same time span allowed withice. The factors which limit the holding period are dictated bythe processing schedule and shelf life. They may be influencedby enzyme and/or bacterial action, water uptake, seawater temper-ature, and time of year that shrimp are landed. In two recentexperiments, batches of 600 and 400 pounds of shrimp were heldunder refrigerated seawater spray for periods of three and sevendays, respectively. The small scale RSWS system had been thor-oughly sanitized beforehand. Bacteria levels were low andremained fairly constant during the holding periods (see Chapter4 ) .
It appears that a rapid cooling rate and maintenance of constantlow temperatures are essential for good shrimp quality maintenance.We at OSU recommend a cooling rate sufficient to bring the shrimptemperature to around 32°F before the next tow is put down, oraround 1-1/2 hours. Sizing the system to do that is the topic ofChapter 3.
Spray temperatures should be maintained in the area of 30-31°F.Colder than that presents the risk of freezing up a chiller**;warmer temperatures accelerate bacterial growth. The systemmust allow some means of monitoring RSWS temperature from thewheelhouse (a topic of Chapter 6).
The rate at which the first tow of the trip is cooled will dependin part on the amount of pre-chilled water in the sump. Oneshould put down several hundred gallons and have it completelychilled to 31°F before putting any shrimp in the hold. Seawaterpumped into the sump at the beginning of the trip must be as
*Limited practice in Alaska might be to hold for a period greaterthan this.
**In addition, Canadian experience with finfish (Ref. 1) hasindicated that partial freezing can occur with RSW temperatureslower than 31°F.
3
clean as possible, taken on in areas away from harbors or ri-rermouths. Note that as more shrimp are put down during the trip,spray water will tend to be "held up" in the shrimp mass. Morewater will probably have to 1)e added to keep the sump level abovethe pump suction pipe.
During fishing, it is important to wash out as much mud as pos-sible before putting the shrimp down. Research has shown thatassociated with mud is a certain type of bacteria that coulddamage shrimp, even at the low temperatures existing in the hold.So washing out mud by dragging the cod end and hosing the catchon deck is important. A few fishermen have also noted thatremoval of particularly heavy twine cod ends or chafing bagswill greatly improve the washing action in the water.
It is impossible to wash all the mud out. As a result of thisand a certain enzyme produced beneath the shell of the deadshrimp, the circulating refrigerated seawater will tend to turndark. It appears that periodic (at least once a day) changeoverof sump water will help control this and perhaps reduce thebacteria levels as well. A disadvantage of changing water isthat the new, warm seawater will temporarily warm up some of theshrimp. It may prove to be important to modify the piping cir-cuit (Figure 1) by running a bypass line directly from spraypipe to sump. You could then cool the new seawater to 31°Fbefore spraying it on the shrimp. Another possible techniquewould be to continually change water at a low rate of flow.The use of a counterflow heat exchanger would perhaps be worth-while to prevent excessive load on the system. The advantagesgained by cleaner water and perhaps lower bacterial levelswould have to be weighed against the disadvantages, whichinclude complexity and expense of equipment, increased refrig-eration energy, and possible increase in salt uptake by theshrimp.
Processing
Experience with processing of shrimp held in RSWS has been bothgood and bad. Some have had consistently good success. Othershave run into problems of low recovery. These problems seem torelate to any or all of the following:
-type of peeling machine (i.e., one that peels raw shrimpvs. one that peels pre-cooked shrimp);
--skills of the peeling machine operator;
-manner of holding, treating, or cooking the shrimp beforepeeling;
-conditions in the fish hold of the boat.
It is extremely difficult to pinpoint a specific cause (if thereis one) for a run having low recovery. Our research has beenaimed at:
--identifying practices which adversely affect quality andrecovery; and
--recommending practices which will increase peelabilityand recovery.
Some experiments have indicated that freshwater soaking of RSW-held shrimp will increase peelability (i.e., ease of shellremoval--Ref. 2). The present practice of "aging" RSW-heldshrimp on ice may be mostly due to exposure to freshwater fromthe melting ice.
Currently, research is underway at the OSU Seafoods Laboratoryin Astoria, to identify the means to pretreat the shrimp toenhance peelability and yield. Recent tests on ice-held shrimphave shown that substantial increases in yield will result frompretreating with condensed phosphates. These and other strate-gies will be applied to RSW-held shrimp in future experiments.
Future Work
There are several other holding techniques that show some poten-tial. Among these:
1) CO 2 injection. Over the past few years, the NationalMarine Fisheries Service has run experiments on shrimpheld in flooded RSW tanks saturated with CO 2 gas (Ref. 2,3, 4, and 5). The results have been encouraging; shrimphave been held longer periods with good color and tex-ture. Some of the problems: titanium heat exchangerswere needed because of the corrosive nature of CO 2
-saturated seawater; CO2 gas, released from shrimp duringcanning, would occasionally cause cans to bulge; occa-sional low recoveries were encountered when peeling inPCA (pre-cooked) machines. It will be of value toexperiment further with this and one further variationsuggested by NMFS researchers: cool the shrimp quicklywith RSW--then drain and hold in a cold CO 2 atmosphere.
2) Use of potassium sorbate. Canadian researchers haveinvestigated the use of potassium sorbate for RSW-heldfish (Ref. 6). Increased holding times and enhancedproduct quality have resulted for various fish speciesin half-strength seawater.
3) Chilled seawater (CSW). CSW generally refers to seawaterthat is chilled by adding fresh water ice. Thus itssalinity is lower than RSW. The Canadian TechnologicalResearch. Labs have been experimenting with CSW forflooded fish tanks; cold water is continually circulatedby compressed air introduced at the bottom (Ref. 7).There may be some application to shrimp, held either incontinuously flooded CSW tanks or held in air after beinginitially cooled with a CSW rinse.
5
SLAUGHTER
HOUSE_J_J
CHAPTER 2
SEAWATER PUMPING AND SPRAY
A workable RSWS circuit appears in Figure 1. It is a closedcircuit which, in this case, pictures a tube-in-box chiller.(Some systems may locate the "chiller" in the sump by immersingrefrigerant coils.) The in-line strainer pictured in thisfigure may not be necessary or even desirable, depending onthe nature of the spray heads and/or chiller.
Piping Layout
Figure 2 shows the layout of the spray pipes in the fish hold.It, is important to lay out these pipes so they will (1) pro-vide adequate coverage, and (2) have the fewest possible deadends where debris will collect.
Drainage
The greater the volume of shrimp, the more water will beretained in the shrimp mass. It is desirable to minimize thisretention by allowing good drainage from the bins; this maymean screened or perforated floorboards, binboards with spacersor screened panels. It would be helpful to design the sump sothat a side channel (covered with screening or expanded metal)extends into each bin.
FROMPUMP
SPRAY PIPE
Figure 2. Spray pipe layout in fish hold.
6
Flow Rate
The design of the circulation and spray system involves a seriesof trade-offs. The major goal is to provide a cold, even, sprayPattern over all the bins holding shrimp. Too small a flow rate
--provides insufficient water flow to remove heat from theshrimp within a reasonable amount of time. Related tothis are uneven spray patterns resulting from low pres-sures and flows;
--may lead to a flow velocity in the chiller that is toolow to develop adequate heat transfer and/or cause freeze-up in the chiller;
-has a lower than necessary flow velocity in the pipes,which may allow sludge to build up in the corners.
Too large a flow rate
-adds additional heat of pumping to the water you aretrying to refrigerate;
-may erode baffle plates in the chiller;
--will create a pressure drop along the spray pipe thatcould lead to uneven spray patterns (or it necessitatespipe diameters that are larger than they need to be);
--may lead to a "washing out" of the shrimp color (althoughthe extent of this problem has not been checked out).
Obviously a large spray rate for fast cooling is needed only inthe one or two bins where warm shrimp have just been put down.Assume for the present time that no special valving systemexists and that a compromise design has a constant, uniformspray rate in all bins that will hold shrimp.
Based on experiments (Ref. 8, 9) and our present state of knowl-edge of bacterial growth and effects upon processing, the spray-ing density needed to achieve an adequate cooling rate is on theorder of 0.5 gpm/ft 2 ; it is also important that this spray beevenly distributed. A concentrated stream will not spread hori-zontally as it flows through loose, newly loaded shrimp. Thus,at least 0.5 gpm is needed over every square foot of horizontalsurface covering the shrimp. This number is based on our designphilosophy to size the system so that the largest tow (singlehaul of shrimp) is reasonably cold by the time the next tow isput down. In Oregon, this might mean 5,000 pounds cooled to 32°Fwithin 1-1/2 hours. The number also assumes that refrigerationequipment is properly sized (the subject of Chapter 3). Asresearch continues and more is learned about the control of shrimpquality using RSWS, these criteria may prove to be too rigid.But they are at present based on the best information available,and will therefore be used in these design recommendations.
7
HOLE DRILLED
\\IN PIPE
PVC PIPE
Figure 3. Tablespoon deflector sprayer.
Sprayheads
Oregon State University did some experiments to determine spraypatterns resulting from various pressures using several differentspray head designs (Ref. 10). We could not test all possiblecombinations but did learn a few interesting things. One thingwe learned was that the conventional tablespoon deflector(Figure 3) does not do a very good job of distributing spraywater. It does have the advantage of being inexpensive and notsusceptible to clogging. But many common spoons will easilydeflect off-center if the water pressure is high or if they arebumped while the fish hold is being cleaned. In addition, thespray pattern fora single spray head is very uneven--it isespecially weak near the center (Figure 4).
As an example, for a 1/2-inch diameter hole emitting 13.5 gpm,spray density near the center "low density" space (an area6 feet wide near the floor) was only around .06 gpm/ft 2 . Notethat if the 13.5 gpm flow rate were evenly distributed over abin measuring 6 feet by 5 feet, the resulting density would beslightly under the recommended 0.5 gpm/ft2.
So single tablespoon sprayers cannot provide an even distributionof water over the shrimp. An array of several sprayers might dothe job, but the total rate of spray and the plumbing necessaryin such a small space probably wouldn't be worth it.
We also learned about a type of spray head that gives a rela-tively even pattern. Manufactured by the Bete Company* (Ref. 11),it is actually two side-sprayers directed against each other(Figure 5). The result is a relatively dense rectangular pattern.
*Brand names are used in this publication for illustrativepurposes only; their mention does not constitute endorsementof these brands.
8
SPOON DEFLECTOR
PVC PIPE
\ ‘ \
t \ \ \\ N \HEAVY \ ‘ " \\ \DRIBBLE i \ \ \ \ \UN DER \\PIPE , \ ` \\
VERYLOWSPRAYDENSITY
HEAVYSPRAYDENSITY
Figure 4. Spray pattern with tablespoon deflector.
PIPEABOUT
[*-- 6" -61
Figure 5. Operation of intersecting spray nozzles.
9
FNOZZLE-TO-SHRIMP NOZZLE PAIR I S 20
I CLEARANCE = 41--8"
PRESSURE = 4 PS.I.
I DEN SITY = G.P.FT. 2 r-NOZZLE -TO--
SHRIMP I I-4 I
6 FT.APPROX.
Figure 6. Spray patterns for a single Bete nozzle pair placedat two different distances above the surface of theshrimp.
Figure 6 shows a very rough outline of this pattern for two dif-ferent distances above the surface of the shrimp. This indicatesa need to have a minimum of around 1-1/2 feet of clearance underthese nozzles to achieve adequate spray distribution. Flow rateat 4 psi (pounds per square inch)--close to the optimum pressurefor these nozzles--is around 14 gpm for a pair of 1/2-inchnozzles (Part Number i/2 I520). One can achieve a spray densityin a bin of at least 0.4 gpm/ft 2 by spacing the nozzle pairs at3-foot intervals. If more than two pairs were to go into onearea or bin, it would generally be easy to achieve the neededdensity.
1 0
Although the nozzles mentioned above have hole sizes that wouldpass most solids suspended in water, a potential problem mightbe clogging by shrimp "whiskers" picked up in the sump. Prelim-inary results of using these sprayers aboard a shrimp vesselindicated that while "whiskers" were not a problem, some cloggingoccurred when a lot of fish were held with the shrimp. A strainermay be necessary to prevent nozzles clogging with fish scales.
A multiple jet design showed some promise (although pattern wasnot as good as the intersecting spray type). Five divergingjets (Figure 7 is one idea), hit against the ceiling 6 inchesaway. Disadvantages are the small holes (potential for clogging)and a need to operate at a fairly high pressure (12-15 psi) toget a good distribution. At 15 psi, the hole pattern of Figure 7will emit around 20 gpm.
There are obviously dozens of other spray nozzles that would dothe job if placed correctly, and if driven with the right pres-sure. We tested some of these, which included single and multi-ple jets directed against the ceiling, fire sprinklers, andsprayers directed in from the side. Others, such as the flatperforated deflector slung underneath the pipe (produced byAnderson Refrigeration in Seattle), we did not get a chance totest. In any case it is impossible here to consider every com-bination. Hopefully, we will be able to test some more designs
SECTION A-A
Figure 7. One design idea for a multiple, diverging jet.
1 1
in the future. But based upon presently available information,the main points are:
1) Spray density should be around 0.5 gpm/ft2;
2) Tablespoon deflectors have an uneven distributionpattern and will generally fail to deliver the properdensity to all areas of the bin;
3) Intersecting spray-type nozzles gave by far the bestspray uniformity of all nozzles that we tested; and
4) Other nozzles and arrangements will have to be consid-ered by the designer for each individual case.
Assuming a need for 0.5 gpm/ft 2 , the next section outlines thesteps one might go through to size a circulating pump. Includedis an example design.
Sizing a Pump
1) The first step is to calculate a total spray rate neededto cover the surface of all bins at the rate of 0.5 gpm/ft2.This is simply the total surface area multiplied by 0.5gpm/ft2.
Example
Figure 8 is a hypothetical layout of a fish hold. Assumethat shrimp will be held in bins 1-6. The total surfacearea of these bins is 240 ft 2 . So a uniform spray densityof 0.5 gpm/ft 2 would require a total flow rate of at least (0.5 gpm/ft 2 ) x (240 ft z ) = 120 gpm.
Note the qualifier "at least." It is impossible to have atruly uniform spray density because of the way spray headsperform. This is the topic of step 2.
2) The next step toward sizing a pump might be selecting anozzle for distribution of the water. Consider two typesof nozzles for the hypothetical fish hold (Figure 8)--intersecting spray nozzles, and 1/2-inch holes with somekind of suitable deflector.
Example A
The spray coverage information of Figure 6 showed that 0.4gpm/ft 2 could result from a supply pressure of 4.0 psi.Flow rate is roughly proportional to the square root ofsupply pressure. So we could get a spray density of 0.5gpm/ft 2 by increasing supply pressure to around 6 psi.Using this kind of data supplied by the manufacturer(Ref. 11), the intersecting spray nozzle pairs should belaid out as shown in Figure 9. Adequate coverage resultsby installing the 1/2-inch size (1/2 IS20) in bins 1-5, and
12
SLAUGHTERHOUSE
BIN 2
BIN 3 BIN 6BIN 5
BIN I BIN4
-- I5-0
5-0
6-0 6-0 --I
Figure 8. Example fish hold.
the 3/8-inch (3/8 1514) in bin 6. If the former emits 17.5gpm at 6 psi and the latter 12 gpm at 6 psi, total flowrate (and thus pumping rate needed) will be 259 gpm. Notethat this is over twice the amount needed for the perfectlyeven coverage (120 gpm) found in step 1. This variationfrom perfect performance could be considered in terms of" efficiency." If 100% efficiency resulted from a perfectlyeven distribution, the intersecting spray pairs as laid outhere will operate at a spraying efficiency of around120/259 x 100% = 46%.
Example B
Nozzles made with 1/2-inch holes and some kind of suitabledeflectors will probably distribute spray water less
13
614- IL 6'
• • • •
BIN
• • • •
BIN 4
le •
BIN 2
BIN 3
• • • . • • • •
BIN 5 BIN 6
Figure 9. Distribution of Bete spray nozzles.
efficiently than intersecting spray nozzles. For calcula-tion purposes, assume this efficiency is at best 40%. Flowrate needed will thus be
120 gpm - 300 gpm40%
The flow rate from a sharp-edged orifice can be calculatedusing the formula (adapted from Ref. 12):
,--W = 18 d 2 vP
where W = flow rate, in gpmd = hole diameter, in inchesP = pressure in the pipe, in psi
(Note that if the inside edge of the hole wererounded off, the actual flow rate could be asmuch as 50% greater.)
14
Assuming a 6 psi average pressure, the flow rate from onehole will be
W = (18)(1/2) 2 1/T = 11 gpm
The number of holes needed will be
300 gpm 27 holes11 gpm/hole
The distribution of these nozzles along the pipe will dependon spray patterns and location of bulkheads.
Thus the inefficiency of nozzles requires the pump to supplya much greater rate of flow than calculated in step 1--infact, over 2 times as much.
3) The third step toward sizing a pump is to consider the flowrate needed through the chiller*. For the chiller to trans-fer the amount of heat it is rated for, the water flow ratemust be close to the rated value also. Assuming we need250 gpm, check two examples.
Example A
The small chiller manufactured by W. E. Stone & Company(Model 605--nominal 6 tons of refrigeration) is rated at250 gpm with a pressure drop of 7 psi.
Example B
The Canadian cylindrical chillers commonly used for RSWsystems are rated for 80 gpm at a pressure drop of 5 psi.Thus three in parallel would pass the recommended flowrate. If only two were needed for the necessary heattransfer, some kind of partial bypass might be designed.
4) The first three steps have determined a flow rate that thepump needs to supply. Step 4 determines the pressure atwhich the pump must work. To do this, add up all thepressure drops (AP's) that will occur in the circuit (see,for example, Figure 1), including:
--AP across the strainer (if one is used)--AP across the chiller--AP through piping and fittings--AP through the nozzles.
Consider first the piping and fittings. The ASHRAE Handook(Ref. 13) gives formulas for pressure drops through thermo-plastic pipe and fittings. Figure 10 summarizes this
*Consideration of chiller size and selection is the topic ofChapter 3.
15
< 2500 20-
w(lc 15-U)
Lux 10-
PRESSURE DROP PER100' OF LENGTH FORSCHEDULE 40 RIGIDPLASTIC PIPE. C REF. t3)
50 100 150 200 250
300FLOWRATE W C G.P.M.
PRESSURE DROP FOR FITTINGS, IN EQUIVALENT LENGTH( FT ) OF PIPE ( REF 13)
PIPE SIZEI -"
2"311
TEE, SIDE OUT 8 l2 16 22
90 0 ELBOW 4 6 8 12
45 0 ELBOW 2 2i 4 5
INSERT COUPLING 14 2 3 4MALE- FEMALE INSERT
ADAPTER32 44 64
Figure 10. Pressure drop for fittings, in equivalent lengthsof pipe.
16
information for schedule 40 pipe. Note that the curvesshow friction pressure drop occurring along a 100-footlength of pipe. For 250 gpm flowing through 100 feet of3-inch pipe, the pressure drop will be about 5 psi. If thelength is only 40 feet, the pressure drop will be 40 ft/100ft x 5 psi = 2 psi.
To calculate pressure drop (AP) across fittings, firstfind the "equivalent length." This is the length of pipewhich will have the same friction AP as that fitting. Nextfind the actual pressure drop for that length in the curvesof Figure 10. For example, 7 right angle bends in a 3-inchpipe circuit will have an equivalent length of 7 ft x 8 ft =56 ft.
For a flow rate of 250 gpm, the friction pressure drop in56 feet of pipe (and thus, across seven 90° elbows) will be
ft56(5 psi) x - 2.8 psi100 ft
Example
Consider the example system discussed in previous steps,and assume total flow rate to be 250 gpm with sprayersoperating at a pressure of 6 psi.
Using the information in Figure 10, we could show that atypical circuit made up of 3-inch pipe might have a pres-sure drop through pipes and fittings of around 5 psi, andthat the pressure drop through the spray pipes would beanother 1.5 psi.
If the Stone chiller of our previous example were used,the rated AP across it would be around 7 psi. For a linestrainer, estimate 6 psi drop. So the total pressure dropthat needs to be supplied by the pump will be
6 psi across the strainer +7 psi across the chiller +6 psi through piping and fittings +6 psi across the nozzles
TN psi total needed from the pump.
Be careful not to exceed the rated pressure of the chiller.The Stone chiller used in this example has a maximum allow-able operating pressure of 35 psi.
5) The final step is to select a pump that will supply thenecessary flow--250 gpm at 25 psi in the example. Recom-mendations can be obtained from any pump manufacturer. Asan example, performance curves show that a 3 x 3 inch Barnespump with 7-inch impeller turned at around 2,500 rpm woulddo the job.
17
Pump Heating
Pumping puts energy into the water. This energy will alwaysend up as heat, which must be removed by the refrigerationequipment. The amount of heat can be calculated using theformula
Q = (1.48) x (W) x (AP)
where Q = heat, in Btu/hrW = flow rate, in gpm
AP = total head pressure generated by the pump,in psi
Example
For 250 gpm pumped to 25 psi, the heat of pumping will be
Q = (1.48) x (250 gpm) x (25 psi)Q = 9,250 Btu/hr
This heat is equivalent to over 3/4 of a ton of refriger-ation, an amount that must be continuously supplied by therefrigeration machinery.
18
CHAPTER 3
REFRIGERATION SYSTEM SIZING
Introduction
How fast must shrimp be cooled down in the fish hold? The answeris probably "as fast as possible"; quality is better maintainedat low temperatures. But refrigerated seawater spray (RSWS)represents a closed system in which bacterial growth can be amore significant problem than in those systems using ice. Thusit is important not only to follow good cleaning and sanitizingpractices, but also to bring temperatures down fast and thenmaintain a steady, low temperature. Based on available informa-tion, researchers at OSU feel that the system should be sized tochill the largest expected tow (single haul of shrimp) to 32wFbefore the next tow is put down. In Oregon, we (OSU) will inter-pret this to mean that a 5 4000 pound tow put into an empty fishhold must be brought to 32F within 1-1/2 hours. (The recom-mended holding temperature is 30-31°F.)
Several things affect this cool-down rate. Assuming refrigerantcircuits, expansion valves and accessories are properly matchedto the compressor, some factors which can affect cool-down ratein a major way are:
-compressor size-chiller size--weight of shrimp-compressor speed
--refrigerant used-water flow rate through chiller (if a "closed" chiller)
--temperature and volume of pre-chilled sump water-water spray density (gpm/ft 2 ) on shrimp.
Some other factors which affect cool-down rate, but generallyin a minor way are:
-heat leakage into the fish hold--heat of pumping (see Chapter 2)--seawater temperature (affecting initial shrimp temperature
and condenser performance)-superheating and subcooling of refrigerant.
Sizing the System
The required effective cooling rate can be approximated usingthe formula:
(M) x (C) x (AT) Q At
where Q = coolie a rate, Btu/hrM = mass of shrimp, lbC = specific heat of shrimp, Btu/lb oF
19
AT = temperature change, 0FAt = time interval, hr.
To calculate the required cooling rate, use the following values:
M = 5,000 lbC = .86 Btu/lb 0F (Ref. 14)AT = 60°F - 32°F = 28°FAt = 1-1/2 hr.
Thus:
(5,000 lb) x (.86 Btu/lb 0F) x (28°) Q (1.5 hr)
= 80,300 Btu/hr.
Because 12,000 Btu/hr = 1 ton of refrigeration, this coolingrequirement represents almost 7 tons of refrigeration, plus someadditional refrigeration needed to account for pumping heat andleakage.
The next step would be to talk with refrigeration specialistsconcerning the right combination of compressor and chiller toachieve the needed cooling rate at the required operatingtemperatures. Table 1 summarizes an example design that wouldtheoretically meet the requirements.
System Performance
Using this design, it is possible to theoretically predict thetemperature of shrimp and spray water over the first few hoursof chilling. Because this involves such a large number ofcalculations, a computer program is helpful in speeding up theprocess. Such a program can demonstrate what might happen whenparameters and equipment sizes (as in Table 1) are changed.Although these calculations cannot predict exactly what willhappen on the boat, they can give a good indication. In twocases for which we have measured temperatures on the boat, thecomputer calculations were able to reproduce those temperaturesquite well (Ref. 9).
Figure 11 shows how these calculations predict fish hold temper-atures resulting from the equipment and conditions specified inTable 1. As you can see, the theoretical design comes close tothe goal of bringing average shrimp temperature to 32°F within1-1/2 hours. (Note that "average shrimp temperature" is plottedin Figure 11. Temperature of shrimp lying at the bottom would beslightly higher.)
Using the same type of calculations, it is also easy to show howa variation of one piece of equipment or one o perating conditionwill affect the cool-down temperature of the 5,000 pounds ofshrimp. Following is a description of this effect. Keep inmind that except for the one factor being varied in each example,
20
a_ 40 _ TEMP2L.LJ SPRAY
TEMP.
32—30—
60 —
AVE. SHRIMPTEMP.
1-` 50—
0 20 40 60
80
100TIME, MINUTES
Figure 11. Theoretical system temperatures resulting fromdesign of Table 1.
the conditions are all defined in Table 1. Also keep in mindthat these examples are not actual onboard measurements, but aretheoretical predictions.
Example A
What happens if you use a smaller compressor?
Instead of the specified 27 CFM compressor (Table 1), try twosmaller compressor sizes: 20 CFM (such as the Carrier 5F303-cylinder at 1,200 RPM), and 13 CFM (such as the Carrier 5F202-cylinder at 1,200 RPM).
21
Table 1. Example RSWS design.
Item Notes
Compressor size(Choose to allowpumping rate ofaround 27 CFM*)
An example of this might be a Carrier5F40 4-cylinder compressor turning @1,200 RPM. Under design conditionsspecified in this table (assumes theuse of R-22), around 10 hp will be neededto drive this compressor. It is assumedthat other refrigeration accessories (con-denser, thermal expansion valves, lines &controls) are properly designed.
Selection of this compressor is based onprevious calculation--that 7-8 tons ofrefrigation are needed. Later discussionwill show that you might get by with asmaller-sized compressor.
Chiller size(Should havenominal capacityof 6 tons refrig-eration with tem-perature differ-ence of 10°F**)
An example might be a WESCOLD Model 605,manufactured by W. E. Stone Co.
Weight of shrimp This is a given design criterion.(5,000 lb)
Compressor speed(1,200 RPM)
Although the example compressor is ratedfor 1,750 RPM (at which 40 CFM would bepumped), refrigeration specialists oftenrecommend operating at slower speed.(See, for example, Ref. 15.) Slowerspeed will lead to longer compressor life,less required maintenance.
Refrigerant(R-22)
R-12 seems more available in local marinesupply shops, but R-22 has been recom-mended to gain more power from the sameequipment, operate at higher efficiencies,perhaps require smaller line & valve sizing(Ref. 15).
Water flow ..tethrough chl(240 GPM)
This influences the performance of thechiller and should therefore be checkedwith manufacturer of the chiller used.The example W. E. Stone chiller is ratedat a water flow of 250 GPM.
(continued...)
22
Table 1 (continued):
Volume & temperatureof pre-chilled sumpwater(500 gal. @ 30°F)
For adequate chilling rate, especially forfirst shrimp dumped into hold, severalhundred gallons of water should be pre-chilled to lowest practical temperature.
Water spray over This value is indicated in Ref. 9.shrimp(0.5 GPM/ft2)
Heat leakage intofish hold(Calculated assumingtotal surface area,1,000 ft 2 & over-all heat transfercoefficient, .05(Btu/hr ft 2 °F))
With some variations, this results from4 inches of urethane foam in a fish holdapproximately 18 ft long, 15 ft wide.(This topic is covered in more detailin Chapter 5.)
Heat of pumping This flow and pressure drop resulted from(Calculated con- example calculations in Chapter 2.sidering 240 GPMpumped @ 25 psig***)
Seawater temperature Assumed(60°F)
Refrigerant Assumedsuperheat (15°F)
Refrigerant Assumedsubcool (15°F)
Saturated discharge Assumedtemperature (100°F)
*Cubic feet per minute.
**This "temperature difference" is equal to (average watertemperature) - (saturated suction temperature).
***Pounds per square inch gauge.
'23
13 CFM ( FOR EXAMPLECARRIER 5F 20 )
u_O
a:2ui 50-
02
I. 40-
11.1
60
32_ _ _ _30-
0 20 40 60 80 100TIME , MINUTES
Figure 12. Example A - effect of varying compressor size.
Figure 12 shows that the 3-cylinder (20 CFM) compressor coolsthe shrimp down almost as fast as the larger 27 CFM compressor,especially during early phases of the cooling cycle*.
There are two reasons why Figure 12 doesn't show a more dramaticdifference between the two larger compressors. One reason isthat they are both pushing the limits of the chiller used; that
*Two other parameters greatly affect compressor capacity: speedand refrigerant. As a rough estimate, the capacity will dropoff (or increase) proportionally to the speed. So increasing acompressor speed from 1,200 to 1,400 RPM will increase its capa-city by a factor of around 1,400/1,200 = 1.17, or a 17% increase.
Changing refrigerant from R-22 to R-12 will decrease capacity byaround 38%. The 4-cylinder compressor of Table 1 has a capacityof 8.1 refrigeration tons at 200F suction temperature. IfR-12 were used, its capacity would be 5.0 refrigeration tons.(Ref. 15 contains a few notes on switching refrigerants.)
24
is, they are a little large for the 6-ton chiller. The secondreason for such a small difference, especially in the earliercool-down period, is because a large amount of "reserve refrig-eration" was provided by the 500 gallons of pre-chilled sumpwater. In fact, if the compressor were not running at all,this reserve would bring the shrimp down to around 4.S°F. Thenext example shows what happens if that reserve is smaller.
Example B
What happens if the "refrigeration reserve" is smaller? Thatis, what if the water is not totally pre-chilled or is reducedin volume?
Instead of 500 gallons of seawater pre-chilled to 30°F, a smallerreserve might result from:
a) 200 gallons pre-chilled to 45°F,
b) 200 gallons not pre-chilled at all--that is, startingout at the same temperature as the ocean, assumed to be60°F,
c) 500 gallons unchilled at 60°F.
Figure 13 shows the effect of these three example conditions,again, with the other parameters as listed in Table 1. As youwould expect, a volume of water in the sump which is not pre-chilled to 30°F represents an additional load on the system andthis will slow down the cooling rate. Two hundred gallons ofwarm (60°F) water is just about like adding another 2,000 poundsof shrimp to the hold.
It is interesting to note that it is more important to get thepre-chill temperature down to 30°F than it is to get the volume up to 500 gallons. In fact, for the chiller and large compres-sor used in these calculations, the curve corresponding to 200gallons pre-chilled to 30°F will fall very close to the lower(design) curve of Figure 13.
Example C
What happens if you use a smaller chiller?
Chiller capacity depends to a large extent on length of pipe orheat transfer surface area and on velocity of refrigerant insidethe pipes. But there are other factors that can greatly reducethe rated capacity:
a) Reduced refrigerant flow, due to undersized compressoror expansion valve,
b) Reduced water flow,
c) Eroded baffle plates,
25
60
40—
32_
30 —
60
a: 50 —Ld
a_2L-I 40 —
32— — — ——
20 40 60TIME , MINUTES
Figure 13. Example B - effect of reducing the refrigeration reserve.
f III 120 40 60 80 100
TIME, MINUTES
Figure 14. Example C - effect of using a smaller capacity chiller.
200
d) Fouling or scaling on the heat transfer surfaces.
Figure 14 shows the effect of using a chiller around half thesize of that specified in Table 1. The effect is again lessthan dramatic due to the use of a hefty compressor and a largeamount of pre-chilled sump water.
Example D
What is the effect of reducing the spray density (gpm/ft 2 ) overthe shrimp?
Low spray density can result from a low pumping rate or poorlydesigned nozzles. The upper curve in Figure 15 indicates aninadequate cooling rate even though its spray density of 0.1gpm/ft 2 is greater than that measured in some laboratory testsof tablespoon deflectors (more fully discussed in Chapter 2).
I I I
40 60 80 100TIME, MINUTES
Figure 15. Example D - effect of operating with lower spraydensities.
27
Effects of Loosening the Design
The design described in Table 1 and the recommended rate ofchilling (32°F within 1-1/2 hours) are probably in some respectsboth a bit "conservative," that is, more rigid than necessary.However, it is wise to err in this direction because it appearsthat RSWS is a fairly sensitive system.
The example calculations shown in Figures 12-15 indicate thatshrimp cooling rates can be affected by:
a) Unchilled sump water,
b) Inadequate spraying,
c) Undersized compressor,
d) Undersized chiller.
Some of the effects on chilling rate were quite a bit less thanothers, but keep in mind that these examples considered whatmight happen if only one of the design parameters was changedat a time. In fact, several minor effects can add up andsignificantly slow down shrimp cooling rate. Consider whatmight happen if you made a series of minor changes to the designin Table 1. Table 2 describes this marginal design and Figure 16shows the predicted results.
A series of what appears to be minor design changes produces aninadequate cooling rate. Conceivably, after 1-1/2 hours or so,another 5,000 pounds of shrimp might go below, further delayingthe cool-down rate of the first batch.
Available Equipment
The two major components to be selected are the compressor andchiller. Carrier, Copeland, Dunham-Bush, Tecumseh, and Thermoking,among others, are manufacturers of compressors suitable for thesize operation considered in this report. The selection andmatch-up with other components and controls can be done by agood refrigeration contractor. Such an individual or company canalso give good recommendations on chiller selection and sizing.There are an increasing number of options on chillers, and itmight be of value to mention several of them here.
1) Box-type chillers
These are generally constructed of galvanized steel; refrig-erant flows through pipe coils which are stacked inside abaffled box. Two manufacturers are:
a) W. E. Stone & Co., Inc.4220 22nd Avenue, WestSeattle, WA 98199Phone: (206) 284-5710
28
Table 2. A marginal design.
Item Example designof Table 1
Marginaldesign
Compressor 27 CFM Same
Chiller 6 tons rated @ 4 tons rated @ This10°F temperature 10°F tempera- lowdifference ture difference due
Shrimp 5,000 lb 5,500 lb 10% increaseweight
Compressor 1,200 RPM Samespeed
Refrigerant R-22 R-12 R-12 is more com-monly available
Water flow 240 GPM 180 GPM Lower flowrate caused by small
pipe size, under-sized pump
Volume & 500 gal. @ 30°F 500 gal. @ 40°F Refrigerationtemperature not running longof pre- enough beforechilled first tow putwater down
Water spray 0.5 GPM/ft 20.3 GPM/ft2
Lower rate dueto inadequatepumping rate,sprayer design
Heat Based on coeffi- Sameleakage cient, 0.05 &
surface area,1,000 ft2
Pumping Based on 240 GPM Based on 180heat pumped @ 25 psig GPM pumped @
25 psig
Seawater 60°F Same
Refrigerant 15°F Samesuperheat
Refrigerant 15°F Samesubcool
Saturated 100°F Samedischargetemperature
Notes
considersperformanceto under-
sized chiller,low water flow,fouling, oreroded baffles
60
32—
30—
20 40 60 80 100TIME , MINUTES
Figure 16. Predicted cooling rates resulting from "marginaldesign" of Table 2.
b) Anderson Refrigeration, Inc.18811 Meridian Avenue, NorthSeattle, WA 98133Phone: (206) SU 4-4422
2) Shell-and-tube type
a) Canadian design: These have been widely used for manyyears on Canadian RSW systems. They consist of atinned copper or galvanized steel tube bundle insidea 6-inch by 10-foot plastic pipe. Several are gener-ally used in parallel. Two manufacturers are:
General Refrigeration Engineering, Ltd.1766 West 4th AvenueVancouver, B. C., Canada V6J 1M1Phone: (604) 738-5181
30
Trans-Cold Refrigeration, Ltd.2590 Douglas RoadBurnaby, B. C., Canada V5C 5B4Phone: (604) 291-9901
b) Bell & Gossett "REFA" Evaporators
manufacturer's address:
Bell & GossettFluid Handling Division, ITTMorton Grove, IL 60053
c) Bohn Heat Transfer Division1625 East Voorhees StreetDanville, IL 61832
d) Dunham-Bush, Inc.West Hartford, CN 06110
3) Open coil chillers
These consist of refrigeration coils lying in the sumpbeneath the surface of the circulating water. For somebrine-spray freezing systems on albacore tuna vessels, theyhave been recommended because of lower cost (Ref. 15). Theyseem also to have a good potential for RSWS on shrimpvessels. One hesitation is that RSW systems holding chilled,unfrozen produce demand more thorough cleaning and sanitizingthan brine spray systems holding frozen whole tuna. An opencoil chiller may make it difficult to do the proper cleaningbetween trips. It may be desirable to connect the coilswith flexible refrigeration hose, allowing them to be liftedout of the way for better cleaning of the sump. One furthercaution about design of open coil chillers: pipe diametersmust be small enough to allow high refrigerant velocitiescapable of returning oil to the compressor; yet for eachrefrigerant circuit, pipe diameters must be large enough toprevent excessive refrigerant pressure drop which would hurtperformance.
Pipe diameter also influences heat transfer. Under manycircumstances, the convection coefficient in the flowing,boiling refrigerant is the controlling factor; that is, itmost strongly influences the overall heat transfer charac-teristics. An excessive pipe diameter will cause a lowrefrigerant flow velocity and a low overall heat transfercoefficient, no matter how high the water velocity outsidethe pipes.
31
CHAPTER 4
TIPS ON CLEANING AND SANITIZING
Introduction
Cleaning and sanitizing are especially criticial for RSWS vessels,compared to the conventional ice-boat, for the following reasons:(1) shrimp in RSWS systems are no longer separated and insulatedfrom each other or from fish hold surfaces, (2) shrimp will nothave the benefit of melting ice that tends to wash bacteria away,and (3) RSW is recirculated, thereby exposing the entire catchin the fish hold to the same microbial condition, whether goodor bad.
This chapter describes and discusses the means to properly cleanand sanitize RSWS vessels and gives tips on how to maintain goodmicrobial quality of shrimp.
Why are we concerned with bacteria?
High numbers of bacteria in shrimp mean spoilage--either shrimpare already spoiled or will spoil very soon. In the process ofspoilage, bacteria increase in numbers in the fashion in whichbankers compound interest rates: one becomes two, two becomefour, four become eight, etc. If we start out with one bacteriumand assume it will multiply every 20 minutes (which they do,incidentally, under given conditions), we will have 64 bacteriain two hours, 4,096 in four hours, 262,144 in six hours, and16,777,216 in only eight hours. If we start out with 100 bacteria(as if bacteria had a 2-hour head start), numbers will reach the17 million level in less than six hours.
Aren't bacteria killed during blanchin•and peelin
Yes, most of them are killed during steam blanching and most areabsent from peeled shrimp. What we cannot remove by heating isthe damage already done by bacteria.
Don't b 4cter a hel a e RSW shrim so the el more Basil ?
This is a myth with no factual bampsis. We found fresh RSWS shrimpharder to peel, although they became quickly peelable after soak-ing up water from melting ice. We at OSU are presently studyingthe factors which affect peelability and recovery.
Where do bacteria on RSWS shrimp come from?
They originate from an unclean fish hold, wooden bin boards,blind ends of spray pipe, mud left on shrimp, and the shrimpitself. Bacteria that originate from the fish hold and RSWSpiping systems pose by far the greatest problem. Once RSW startscirculating, these bacteria become dislodged, contaminating thewater, and are absorbed by shrimp put down in such water. Mud
32
is rich with bacteria that produce foul smells--the typical sul-furous odor of a mud flat, for example. Therefore, mud should becleaned off shrimp before they are put down in the hold.
How do we build an RSWS s stem that is eas to clean and sanitize?
First order of business is to design the system to facilitatecleaning. Rough wooden surfaces can never be cleaned thoroughly;even a painted wood surface is too porous. Cement holds posesimilar problems. The fish hold, therefore, must be lined witha smooth fiberglass coating. For the same reason, wooden binboards need to be replaced with aluminum or high density plastic.
Spray pipe should have no dead-ends. Dead-ends accumulatedebris and become breeding grounds for bacteria. Figure 2 illus-trates a spray pipe layout with a minimum of dead-ends.
A cleaning loop (Figure 1) that will circulate concentrateddetergent and sanitizer solution from the chiller to the pipeand back is needed to properly clean the inside of the pipe.Spray heads must also be closed off during this operation.
Why do we clean AND sanitize--aren't they one and the same?
Detergent removes bacteria, along with the slime and debris thatserve as the breeding ground for bacteria. Detergent, however,still leaves at best one out of ten bacteria behind to multiplyin the fish hold overnight. Bacteria can multiply at a rapidrate because the refrigeration that checks their growth isturned off at night. Remember, one bacterium can multiply intonearly 17 million in eight hours! Sanitizing cleaned surfacesdelivers the knock-out punch.
Can we clean and sanitize in one step?
Life would be simpler if we could. The problem is that theeffectiveness of the sanitizer is quickly neutralized by slimeand debris. The alkaline nature of many detergents also cutsinto the effectiveness of some sanitizers. A SANITIZER ONLYWORKS WELL ON CLEAN SURFACES. Therefore, the fish hold must becleaned before applying the sanitizer.
How do we clean and sanitize the fish hold?
Immediately after unloading, the fish hold should be flushedwith potable water to remove as much slime and debris as possible.Following this, apply a foam type cleaner under pressure to allwalls, ceilings, floors, -Traes, and corners of the fish hold.Scrub with a stiff brush if necessary and wait ten minutes. Thefoam keeps the cleaner in contact longer and makes it easier toclean the ceiling. Rinse off detergent with potable water; THENAPPLY THE SANITIZER TO THE CLEAN SURFACE.
33
How do we clean and sanitize holding tank, chiller, and spray pipe?
With refrigeration off, circulate a non-foaming type detergentthrough the tank, chiller and pipe. After ten minutes, bleed-offthe detergent overboard and replace it with potable water untilthe returning water is clear. Add sanitizer and circulate thesolution through the cleaning loop for ten minutes. If you donot have a cleaning loop, it is almost impossible to cleaninside the pipe, chiller and holding tank.
Occasional Canadian practice is to leave a sanitizer in thecleaning loop overnight, although there is a potential problemif the sanitizer is chlorine. Manufacturers of galvanizedchillers caution that such a prolonged exposure to chlorinecan lead to accelerated corrosion of the chiller.
What can we do while under way?
Before leaving port, fill the sump with sanitizer solution andwhile under way, turn on the spray system for 20 minutes. Thenempty the sump and refill it with unpolluted clear seawater.
Flushing the system with sanitizer while under way is addedinsurance against bacteria that might have multiplied overnight.
What detergents should be used?
Any detergent used properly will do the job. A foam or jelly ty3e detergent* will work best for the fish hold because itclings to the ceiling and lifts out dirt and debris. You mustuse a non-foaming type* in pipes and chillers.
What sanitizers should be used?
A 50 ppm chlorine or iodophor solution will do the job**. Ifhousehold bleach is used to prepare the chlorine solution,remember that bleach is notoriously unstable; use the freshestavailable. It is not uncommon for an unopened bottle of bleachto contain half as much of the active chlorine contents asstated on the label. Because the active ingredient of bleach(sodium hypochlorite) is not effective in alkaline conditions,most detergents (alkaline) and bleach can not work together tosanitize effectively. (We use detergent and bleach together inlaundry for bleaching purposes, not for germicidal reasons.)
*Many detergent manufacturers provide the variety of detergentsmentioned above.
**Commonly recommended chlorine concentration for this purposeis 100 ti 200 ppm. Bleach added to increase chlorine concen-tration, however, will enhance scale formation. Iodophor,when used above 25 ppm, may impart undesirable flavor toshrimp.
34
Using too much bleach actually cuts down its germicidal effec-tiveness and could cc..ribute to scale formation. NEVER USEMORE THAN A TABLESPOONFUL PER 2 'JALLONS OF WATER. (The logic--"if a little is good, more will De better"--fails here.)
If scale is formed, apply aciu cleaner* at once. Since acidcleaners are more expensive and often less effective, switchback to the alkaline type once the problem is solved.
The following microbiological data we obtained should furtherreinforce the importance of cleaning and sanitizing the RSWSsystem.
We checked the cleanliness of two RSWS boats ready to leave theport. The microbial loads we obtained were as follows:
Table 3. Microbial load of fish hold surfaces.
No. Microor• anisms/s•. inchBoat 1 cement ho • Boat 2 (fiberglass hold)
12345
slimy331458181
90394445
>1,000871
The cleaning and sanitizing jobs were obviously inadequate.
When we applied our recommended cleaning and sanitizing procedureon an experimental RSWS system**, the microbial load on the fiber-glassed tank walls was below detection level; microbial load inthe circulating seawater was measured as 2 per ml.
We also analyzed the microbial load of the RSW in this experi-mental unit during a 3-day trip. The data revealed the following:
*Many detergent manufacturers provide the variety of detergentsmentioned above.
**This system, borrowed from the National Marine Fisheries Service(NMFS) in Seattle, was capable of spraying recommended rates ofRSW on shrimp sample loads on the order of 600 lb.
35
Table 4. Microbial counts in NMFS experimental RSWS system.
RSW Sample* Microbial Number per ml
1. Seawater at start of trip 23
2. RSW recirculated in clean fish hold
2(3 hrs. since start of trip)
3. Shrimp in hold (10 hrs. since start 240of trip)
4. Shrimp in hold for 2 hrs. 170
5. Shrimp in hold for 12 hrs. 430
6. Shrimp in hold for 20 hrs. 1,800
7. Shrimp in hold for 36 hrs. 960
8. Shrimp in hold for 46 hrs. 1,200
9. Shrimp in hold for 56 hrs. 1,300
10. Shrimp in hold for 67 hrs. 800(end of trip)
*RSW was chilled to constant 31°F.
The system was thoroughly sanitized as the low initial microbialnumber would show. Microorganisms were introduced by the shrimpand their number multiplied to nearly 5 times at the end of the3-day trip. This was with the experimental system and a shrimpload was put down only once.
A similar study was done with two RSWS shrimp boats and theresults were as follows:
36
Table 5. Microbial flora of RSW on two shrimp vessels using RSWS.
Boat No. 1 Boat No. 2Microorganisms (%) New RSW* Old RSW New RSW Old RSW
Pseudomonas 6.2 5.2 10.3 5.4
Moraxella 64.6 79.3 38.5 50.0
Acinetobacter 4.6 0 5.1 6.8
Flavobacterium-Cytophaga 16.9 9.5 21.8 16.2
Arthrobacter 1.5 4.3 23.1 20.3
Lactobacillus 0 0.9 0 0
Micrococcus 0 0 0 1.4
Unidentified 6.2 0.9 1.3 0
No. colonies identified 65 116 78 74
Count of sample per ml 7.7 x 10 4 1.5 x 10 6 8.3 x 10 4 7.3 x 105
*New RSW = RSW at the start of the trip before shrimp are intro-duced.
Old RSW = RSW at the end of the trip (3 days).
The cleaning and sanitization were not thorough, as indicated bythe initial microbial loads of around 80,000 per ml. The micro-bial loads at the end of the 3 day trips were on the order of1,000,000 per ml, compared to 1,000 for the experimental system.The microbial population of the new and old RSW revealed, however,that there was no drastic shift in its makeup, although thenumber had increased to 10 times the original number.
The study showed that: we can effectively clean and sanitizethe RSWS system; the microbial multiplication can be effectivelychecked; and, unless we clean the system and the shrimp reallywell, the use of RSWS can quickly invite troubles.
37
CHAPTER 5
FISH HOLD CONSTRUCTION
Introduction
To properly design a fish hold for stowage of RSWS shrimp, theselection of materials and layout must consider:
1) Proper water flow;
2) Heat transfer and control of temperatures;
3) Need for cleanable surfaces;
4) Handling of the catch.
This chapter discusses how the first three areas relate to thefinal design. Fish hold design and construction are basedlargely upon the experience and preference of individuals andshipyards; it is the intent of this chapter to cover only thosedesign problems that seem to be important to the success of RSWSsystems. Remember that RSWS is different than using ice onshrimp. Any spoilage in an isolated area will spread to theentire fish hold with recirculating RSW.
For more general design help, one should contact industryspecialists and perhaps consult some of the articles and reportsreferred to below.
Proper water flow
RSWS is based on good circulation of cold water through shrimp;Chapter 2 discusses spray head design that will allow an evendistribution of water on top of the shrimp. But as watertrickles down through the shrimp to the sump, it can be divertedor held up, and this can lead to problems.
The first circulation problem occurs if the bin is not welldrained. Water held up in the bottom of a shrimp-filled binwill likely be warm and thus allow rapid bacteria multiplication.If drainage is bad enough that shrimp become covered with water,then you may encounter another problem: as the boat rolls, shrimpcan slosh around and become broken; this can lead to low recoveryin the plant*. It appears desirable to have some kind of drain-age grid as part of the bin floor rather than rely on loosefitting bin boards. Several fishermen are presently experiment-ing with different drainage designs.
*This is due to the free surface. NMFS researchers have foundno such problem with shrimp held in a recirculating RSW tankwhich was completely flooded and had no free surface-.
38
A second potential circulation problem relates to flow withinthe shrimp mass. The density of a mass of shrimp depends on howtightly shrimp are packed; density can range from around 40 lb/ft3to 60 lb/ft 3 . In laboratory tests (Ref. 8), we found a very poorhorizontal spreading of a concentrated surface spray as it flowedthrough loosely packed shrimp. However, good horizontal spreadingoccurred when these shrimp were compacted into a density close to60 lb/ft 3 . Thus it is conceivable that water would tend to flowaway from those areas of the bin that have a higher densitypacking. One of these areas would occur directly under a man-hole where falling shrimp are hitting the pile; water might tendto flow toward the outer edges of the pile. A second region ofhigh density would occur at the bottom, where shrimp tend to becompacted. This packing could slow down circulation in the lowerregion and direct a greater share of the flow out between theupper bin boards. One solution might be intermediate screenedshelves. We do not presently know if poor circulation withinthe shrimp mass is a problem--it is something to be aware of.
Heat transfer and control of temperatures
Insulation around the fish hold slows the flow of heat from warm(say, 60°F) seawater into the 31°F hold. On some older woodenvessels, the "insulation" is often merely the air gap betweenhold liner and hull planking. On some flooded-tank RSW systemsused in Canada, this has been considered sufficient (Ref. 16).
But for steel-hulled vessels and especially for RSW spray sys-tems, insulation is important--perhaps not so much to preventoverall heat leakage as to prevent high shrimp temperatures atthe outer edges. As heat flows in, these outer shrimp can heatup to temperatures somewhere between 31° and 60°, especially inareas that do not receive adequate spray or during short periodswhen spray is shut down. The resulting growth of bacteria willbe carried to other parts of the hold by recirculating RSW.
How much insulation do you need? If one is using urethane foam,two to four inches is the range frequently recommended for iceuse (Ref. 17, 18, 19). One publication from Great Britain recom-mends four to six inches for RSW holding tanks (Ref. 20). Forboats stowing frozen products in tropical climates, the recommendedthickness is as high as twelve inches (Ref. 21). Figure 17 showspredicted heat leakage rates under the following conditions:
-steel hull;
-31°F fish hold temperature;
-urethane foam insulation with a density of 1.5 lb/ft 3 anda thermal conductivity of 0.16 Btu in./hr ft 2 °F (Ref. 13);
-total area (walls, floor, ceiling) of 1,000 ft2;
-no air gap between insulation and skin.
39
10000
8000-
7000-
I 6000-
DI-ca 5000_
4000-
_J
I- 3000-
I2000 -
1000 -
SEA TEMP.70°F
I 2 3 4 5 6 7INSULATION THICKNESS, IN.
NOTE: I REFRIGERATION TON =12,000 BTU/HR.
Figure 17. Theoretical heat leakage rate as a function ofurethane foam insulation thickness.
40
The curves show that heatthickness; a thickness ofa fairly low level. This,about shrimp temperaturesthis uncertainty, we feelwould be a safe design.
flow varies a lot with insulationtwo inches will limit total flow toof course, does not say anythingnext to the outer wall. Because ofthat four inches of insulation
This discussion concentrates on urethane foam. There arecertainly other types that will work. Their advantages anddisadvantages can best be presented by industry specialists.Installation, heat transfer characteristics, and coatings arealso discussed in Ref. 17, 18, 21, 22, 23, and 24.
There are a few other points concerning insulation worth men-tioning:
1) Urethane foam can be extremely flammable and should becovered with a suitable thermal barrier. Ref. 25 and26 discuss some problems and recommended solutions;
2) Most sources recommend that insulation in wooden boatsbe applied to the hold liner in such a way as to leavean air gap between liner and hull planking (Figure 18).Some new wooden boats can have insulation applieddirectly to the hull planking, completely filling thearea between frames (Ref. 22), and one Canadianresearcher reported that even a few older wooden vesselsin his area have had insulation sprayed between frames,directly onto hull planking (Ref. 27). However, hecautioned that the preparation on older boats shouldinvolve hauling them out of the water, stripping awaythe old hold liner, and leaving a heater in the fishhold for three to four months before applying insulation.Present industry practice prefers an air gap betweeninsulation and planking.
Need for cleanable surfaces
Thorough cleaning and sanitizing has been emphasized by many whohave studied RSW (Ref. 17, 19, and 1).
To repeat some recommendations of the previous chapter:
1) Avoid cement fish hold liners. They are difficult toclean, especially when cracks develop--fiberglass witha smooth surface preparation seems to be the best.
2) Avoid wooden bin boards--use aluminum or high-densityplastic.
One should also avoid corners, crevices, or other areas that arephysically difficult to reach for adequate cleaning.
Aluminum bin boards are very commonly used in Canada (Ref. 28)and are, in fact, required on new vessels receiving government
41
AIR SPACEBETWEENTIMBERS
EXISTING HOLDCEILINGI.E. LINING
Figure 18. Insulation and hold lining in wooden vessels (fromRef. 22).
42
financial assistance (Ref. 22). One possible problem that hasyet to be checked out: caustic soda (lye, sodium hydroxide)occasionally used in fish hold cleaning (Ref. 1) may damagealuminum surfaces.
We are not aware of any high-density plastic bin boards currentlyon the market, although we have been in touch with an individualin Norway who is trying to develop such a board with some assis-tance from the Norwegian government (Ref. 29). Replacement forwooden bin boards must be found, because no matter how clean therest of the fish hold, unclean bin boards will quickly spreadbacteria throughout.
43
CHAPTER 6
TEMPERATURE MEASUREMENT
Maintaining low temperature is important for landing a highquality product. A remote-reading sensor with a meter locatedin the wheelhouse can ensure that temperatures are being prop-erly maintained. It can warn of such things as a plugged intakeon the circulating pump, frozen chiller, failed compressor orcontrols. Also, by knowing the rate at which the system isdesigned to cool down, you can recognize when refrigerationperformance is beginning to drop (caused, for example, by ashortage of refrigerant or a clogged bank of chiller coils).
If only one temperature sensing probe is available, you shouldprobably locate it in the water line downstream of the chiller--or alternately, in the sump. Mount any additional sensors inthe floor or lower walls of different bins to monitor shrimptemperatures and distribution of spray water.
Very few meters on the market apply specifically to RSW systems.But at least one product, not widely advertised, comes close:it is a special "Brine Temperature Gauge" manufactured by theSea-Temp Company (Ref. 30). This is not the model commonly usedby trollers; it has a different thermistor and dial scale, allow-ing measurement of temperatures in the range of -20°F to +40°F.Unlike the trollers' ocean temperature model, this one willallow use of a selector switch, so you can locate severalthermistor sensors in the hold and read them all on the samemeter. The standard price (around $125 in 1980) includes onesensor with 30 feet of wire. Because the wire is vinyl-coatedand may not stand up to near-continuous immersion in seawater,it would probably be worth ordering special neoprene-coatedwire (around 50' per foot) for use in the fish hold.
Another meter has been developed in Canada specifically formeasuring RSW temperatures (Ref. 31). Its full range (10°F to60°F) is particularly accurate in the area of 32°F. It operateson its own batteries and has a built-in selector switch to allowmonitoring of several different thermistor sensors. The Appendixdescribes the construction of one of these devices as well asseveral temperature probe options. They have also recentlybecome commercially available from the General Refrigeration Co.in Vancouver, B.C. (Ref. 32).
This chapter describes two RSW temperature monitoring systemspresently available. Others can be built from commonly obtain-able electronic parts.
44
REFERENCES
1. Gibbard, G. A., S. W. Roach. 1976. Standards for an RSWsystem. Fisheries and Marine Service Technical ReportNumber 676. Dept. of Fisheries and Oceans. Canada.
2. Kolbe, E., J. S. Lee, J. K. Babbitt. An index of peelabil-ity for shrimp. Accepted for publication, Journal of FoodScience.
3. Nelson, R. W., H. J. Barnett. 1971. Fish preservation inrefrigerated seawater modified with carbon dioxide. Volume3 in: Proceedings, Thirteenth International Congress ofRefrigeration. Washington, D.C.
4. Bullard, F. A., J. Collins. 1978. Physical and chemicalchanges of pink shrimp, Pandalus borealis, held in carbondioxide modified refrigerated seawater compared with pinkshrimp held on ice. NMFS Fishery Bulletin 76(1):73-78.
5. Barnett, H. J., R. W. Nelson, P. J. Hunter, H. Groninger.1978. Use of carbon dioxide dissolved in refrigeratedbrine as a preservation of pink shrimp (Pandalus spp.).Marine Fisheries Review. Volume 40, Number 9.
6. Tomlinson, N., S. E. Geiger, G. A. Gibbard, D. T. Smith,B. A. Southcott, J. W. Boyd. 1978. Improving landedquality of groundfish by modification of refrigeratedseawater. Fisheries and Marine Service Technical ReportNumber 783. Department of Fisheries and Oceans. Canada.
7. Chilled seawater system data sheet. Available from libraryof the Technological Research Laboratory, Department ofFisheries and Oceans, 6640 Northwest Marine Drive, Vancouver,B.C., Canada V68 1X2.
8. Kolbe, E. 1979. Cooling Pacific shrimp (Pandalus jordani)with refrigerated seawater. Journal of Food Science 44(5):1418-1419, 1424.
9. Kolbe, E. 1979. Refrigerated seawater spray system modelfor shrimp vessels. Journal of Food Science 44(5):1420-1424.
10. Kolbe, E. 1980. Spray head design on fishing vessels usingsprayed refrigerated seawater. Transactions of the AmericanSociety of Heating, Refrigerating and Air ConditioningEngineers. Volume 86, Part 2.
11. Data sheet describing IS series (intersecting spray nozzles).Bete Fog Nozzle, Incorporated, 305 Wells Street, Greenfield,Massachusetts 01301.
12. Fairbanks Morse/Colt Industries. 1974. Hydraulic Handbook,8th Edition.
13. ASHRAE. 1972. Handbook of Fundamentals.
14. ASHRAE Handbook and Product Directory. 1974. Applications.
15. Kolbe, E. 1977. Marine refrigeration, some tips on design,installation and servicing. Special Report 488, OSU SeaGrant Marine Advisory Program. (This report summarizes manyrecommendations of Mr. Jack Appelt, Quality Refrigeration,Wilmington, California.)
16. Roach, S. W. 1973. Operating instructions for RSW systemson BC salmon packers. Available from library of the Tech-nological Research Laboratory, Department of Fisheries andOceans, 6640 North West Marine Drive, Vancouver, B.C. CanadaV6T 1X2.
17. Merritt, J. H. 1969. Refrigeration on fishing vessels.Fishing News (books) Ltd.
18. Angel, N. B. 1972. Insulating ice bunkers in fish holds ofolder fishing vessels. University of North Carolina SeaGrant Program. Report UNC-SG-72-05.
19. Ice in Fisheries. 1975. FAO/United Nations FisheriesReports Number 59. Available from UNIPUB, PO Box 433,Murray Hill Station, New York, NY 10016.
20. Kelman, J. H. 1977. Stowage of fish in chilled seawater.Torry advisory note number 73. Available from the Director,Torry Research Station, PO Box 31, Aberdeen, ScotlandAB9 8DG.
21. Mead, J. T. 1973. Marine refrigeration and fish preservation. Business News Publishing Company.
22. Prescott, B., G. M. Sylvester. 1974. Hold linings forCanadian fishing vessels. Publication 77. Technical ReportSeries, Industrial Development Branch, Fisheries and MarineService, Environment Canada.
23. Adams, B. W., R. B. Fisher. 1970. Plastics as a fish holdlining material. Circular of Information 631, AgriculturalExperiment Station, Oregon State University.
24. Stair, D. 1976. Refrigeration shop talk. Fishermen's News,February, First Issue.
25. Freeman, N. 1976. Hazards of foam insulation shown in hotblaze aboard big crabber. National Fisherman. September.
26. Hutton, M. 1976. Rigid polyurethane insulation - a guideto safe use. Alaska Sea-Grams. University of Alaska MarineAdvisory Program, November.
27. Kolbe, E. 1977. On board freezing of troll-caught salmon.Fisherman's News, February, First Issue.
46
28. Alcan Products Limited. Fish holds of Alcan aluminum penboards and stanchions. Alcan Products, 480-2609 GranvilleStreet, Vancouver, B.C. V6H 3H3.
29. Anon. 1977. Plastic fish room pound boards from Norway.Commercial Fishing. Volume 8, Number 1.
30. Sea-Temp Company, 19250 East Colima Road, La Puente,California 91748; (213) 964-0774.
31. Lee, F. N., S. W. Roach. 1976. The measurement of tempera-ture in refrigerated seawater storage tanks. InternationalInstitute of Refrigeration, Commission Bl, Washington, D.C.
32. General Refrigeration Company, 1766 West 4th Avenue,Vancouver, B.C. Canada; (604) 738-5181.
Other Literature of Interest
1. Hayes, K. M., W. E. Schumacher, C. J. Wilder. 1971. Clean-ing and sanitizing fish holds. Hawaii Fish'n Facts.Leaflet 165, Cooperative Extension Service, University ofHawaii.
2. Hayes, K. M., W. E. Schumacher, C. J. Wilder, R. E. Moser.1973. Cleaner boat - better fish. Hawaii Fish'n Facts.Leaflet 173, Cooperative Extension Service, University ofHawaii.
3. Lee, J. S. 1973. Cleaning and sanitizing agents for seafoodprocessing plants. Oregon State University Sea Grant Publi-cation SG21.
4. Lee, J. S. 1977. Hazard analysis and critical controlpoint application to the seafood industry. Oregon StateUniversity Sea Grant. ORESU-H-77-001.
5. Nickelson, R. 1972. Seafood quality control - boats andfish houses. Texas A&M University Sea Grant Program.TAMU-SG-72-508.
6. Stinson, W. S., J. Forwater. 1978. Selection guide -cleaning and sanitizing compounds. Food Processing,February. pp. 34-38.
Acknowledgements
The authors with to thank several individuals who have donatedsamples, advice and information used to perform the researchreported here. Among these individuals are:
Capt. Leo Kuntz, Garibaldi, OregonMr. Frank Lee, Canadian Technological Research Laboratories,
Vancouver, B.C.
47
Mr. Lowell Schreiber, President of Smith's Pacific Shrimp,Garibaldi, Oregon
Mr. Sid Shannon, Department of Agricultural EngineeringCapt. Mike Wheeler, Garibaldi, Oregon
48
APPENDIX
CONSTRUCTION OF THE CANADIANTEMPERATURE MEASURING DEVICE
Prepared byDouglas Cheney and Edward Kolbe
This Appendix describes the design of a telethermometer thatmight lend itself to construction at home or a local electricalshop. It was designed by the Canadian Technological ResearchLaboratories (Ref. 31); we at OSU have built a version which ispresently being demonstrated aboard an Oregon shrimper.
The telethermometer is a battery powered RSW temperature meterwith a built-in selector switch capable of monitoring 10 ther-mistor sensors from a remote location. The current fishingvessel tests include use of several different types of temper-ature sensing thermistor probes.
This Appendix includes: an explanation of the telethermometer'soperating principles, wiring schematic, parts list, constructionnotes, and photos to aid those interested in constructing ameter and temperature probes.
Operating Principles
As described by Lee and Roach (Ref. 31):
The principle of the measuring circuit of thetelethermometer is based on the characteristics of anoperational amplifier in the configuration illustratedin Figure 19. It can be shown that ideally the inputvoltage Vin and the output voltage Vout are governedby the equation
Vout = -- V R2 Vin
where R 1 and R2 are the feedback resistors. From theexpression, it can be observed that, if R 1 and Vin areheld constant, Vout is inversely proportional to R2 .
In the telethermometer circuitry, R2 will be the resistance ofthe temperature probe thermistor.
A typical resistance vs. temperature curve ofthermistors is shown in Figure 20. The resistance RTincreases exponentially as temperature decreases. IfRT is substituted into the [above] equation for R2[while Vin and R 1 are held constant], Vout will varynon-linearly with temperature. The non-linearity shouldnot pose any problem in this particular case since only
49
R
V IN
Figure 19. Operational amplifier (from Ref. 31).
22
cn2
0%." 18 —
(*)0
UZ 14 —
cr- 10 —i-
6 20 25 30 35 40 45 50 55 60
TEMPERATURE (°F )
Figure 20. Characteristics of the Fenwal UUA35J1 thermistor.
50
a small temperature range (30°F to 60°F) is of interestand linearization in this particular range is notnecessary.
The Fenwal UUA 35J1 precision curve-matchedinterchangeable thermistor was chosen for this appli-cation. Vin is provided by a mercury battery at 1.35volts. A 5 volt DC meter with .1 volt divisions wasselected to display temperature. In the neighborhoodof 32°F, .1 volt/°F provides the desired readability.A meter plate with temperature scale in 1°F divisionis specially manufactured by Armaco* for use on theirU411 DC panel meter [1 mA range; 1100 internal resis-tance].
The Fairchild** iA741 operational amplifier issuitable for this application because of its depend-ability, economy and ruggedness. For convenience,the amplifier is powered by two 9 volt batteries,independent of the ship's power.
As shown in Figure 21, ten stations are providedto accommodate ten probes***. An eleventh stationprovides a calibration feature. The calibratingresistor Rc is preadjusted to match the resistanceof the thermistor at 32°F.
This allows later recalibration of the meter (i.e. adjustmentof R 1 ) so that it will read 32°F whenever the selector switchis in the "Calibration" position.
The Canadian Technological Research Laboratory has tested thisdesign in the laboratory against a Westronics Thermocouple. Thereadings agree to within 0.5°F in the range from 25°F to 60°F.
The parts list for our telethermometer is given in Table 6.
Construction Notes
1) It is important that care be taken in the constructionprocess and that only good quality materials be used dueto the harshness of the shipboard marine environment.
*R. Mack & Co.Armaco Electronic Equip.820 SW Marine Drive, PO Box 58010Vancouver, B.C. V6P-6L6 Ph. 604-324-3866
**We used a Radio Shack operational amplifier.
***Note that the OSU model contains only 5 stations, with anoption to add more later.
51
5 K —ASelector0—~/N---0---A Switch
0-,AN^-0Calibrationt
R e
pA741
Meter
/!11 .35 v 9v 7_7 Batteries
Figure 21. Circuit of telethermometer.
2) We built our telethermometer in a commercially availablecarrying cabinet. For shipboard use, it may be desirableto mount components on a frame suitable for permanentinstallation in the wheel-house. A mounting method thatwill minimize the effects of vibration would be preferable.
Our selector switch is capable of handling 10 probes. Aswitch with more or less terminals may be chosen accordingto the boat's requirements. Be sure to reserve a positionfor calibration.
We had difficulty obtaining a 3 pole momentary contactswitch. A 4 pole switch would be more readily availableand could be used just as well.
52
Tabl€. ParL.s Hs i- for telethermometer.
Q ty Part Supplier Part No. Price(Aug. '77except
where noted)
1 5K metal film resistor
2 50K trim potentiometers5 miniature phone plugs5 jacks1 11 position switch1 switch dial (for above switch)1 pointer knob "1 contorn utility cabinet
AlliedElectronics*
831-2465 $ .60
822-87RL 2.96868R-3054 4.15868R-3066 2.75747-2503 6.35851-2503 .53543-R-2300 .19736-3609 15.30
1 U 411 panel meter ARMACO**-specify RSW face for above meter
1 3PDT momentary contact switch United RadioSupply***
U411
MPA-306F
30.51 (Aug.1979
price)
4.85
1 hook-up wire (spool)
2 battery connector clips1 "AA" battery holder1 solder1 drawer handle2 ring tongue connectors1 operational amplifier1 1.35 V "AA" mercury battery2 9 volt Alkaline batteries
RadioShack
1.69
996979
.65
.45276-007 .49
E12N Everready 2.853.00
TOTAL $79.79
Time used for fabrication of unit: locate and order parts 3 hrs.shop time 9 hrs.
TOTAL 12 hours
*Allied Electronics5901 4th Ave. SouthSeattle, WA 98108Ph. 800-426-4402
**ARMACO Dealer ***United Radio SupplyR. Mack Company 123 NE 7th Street820 SW Marine Dr. Portland, OR 97232PO Box 58010 Ph. 503-233-5341Vancouver, B.C.
V6P-6C6Ph. 604-324-3866
53
5) When assembling components, make sure that the batteriesare accessible for replacement. Battery life is said to beapproximately two years.
6) The adjustment screw on potentiometer R 1 should be acces-sible from the front of the meter. Potentiometer Rc isadjusted only once--when the meter is initially calibratedwith an ice bath. It should be mounted inside to avoidinadvertent adjustment which would render the meter read-ings inaccurate.
7) We had a little trouble initially with the meter driftingfrom its calibrated position, a possible characteristic ofthe mechanical contact in the variable potentiometers usedfor R 1 and Rc. Designer Frank Lee suggests a possiblesolution: replace the R I potentiometer we used (50 K2)with a 25 Kn resistor in series with a 10 Kc, 20-turn trimpotentiometer. Replace the 50 KO potentiometer we used forRc with a 14 Kc resistor in series with a 5 Kc, 20-turn trimpotentiometer.
8) The 5K metal film resistor must be wired in series with thepanel meter to make it into the necessary 5vDC meter (Figure21).
9) From the wiring diagram you will notice that the operationalamplifier terminals are numbered. To find the correspond-ing terminals on the device itself lay it on its back(terminals) pointing up. There will be a tab or indentation,usually circular, on one corner of it. Number the terminalsclockwise from this point.
10) Although we soldered wires directly onto the terminals ofthe operational amplifier, the designer warns that excessiveheat while soldering can destroy the component. He suggeststhat a better way is to use a socket, rather than solderingleads to the operational amplifier directly. Another advan-tage of this is that the operational amplifier can be easilyreplaced if accidently destroyed.
11) Most likely, one of the terminals on the phone jacks willground to the case. Make sure that this is the "common"terminal and not the one that connects to the selectorswitch.
To calibrate the meter:
Initial Calibration
a) Put a thermistor probe in a thermos of ice water thatis 32 deg. F. Check this temperature with a goodmercury thermometer.
b) Adjust R 1 to make the meter read 32 deg. •
54
c) Turn selector switch to "Calibrate" position.
d) Adjust Rc to read 32 deg. F.
e) Rc should not be changed again.
Suceeding Calibrations
a) Turn Selector switch to "Calibrate" position.
b) Adjust R 1 to read 32 deg. F.
c) Check calibration daily.
Thermistor Probe Construction
As described by Lee & Roach (Ref. 31),
The thermistors are provided in small epoxycoated beads, about .095" in diameter with two bareleads about 3 inches long. The leads are extendedto a convenient length with insulated wires; thejoints can be insulated with heat shrinkable tubing.These thermistors are ,.used in different typesof casings or moulded in clear plastic resin forinstallation in boats of different construction.
The Fenwal UUA-35J1 thermistor is available from the followingsuppliers:
Model UUA-35J1:
Allied Electronics5901 4th Ave. SouthSeattle, WA 98108Phone 800-426-4402Price: $3.99 each (1979 price)
R&R Associates5501 6th Ave. SouthSeattle, WA 98108Phone 206-762-7664$4.72 each - minimum $50.00
order (1977 price)
Figure 22 shows some designs of probes, the first three of whichwe are now testisong. Type (a) is a hand-held probe about threefeet long. It is intended to be plunged into the center of ashrimp mass to read the temperature there. It is made from 1/4"schedule 80 PVC pipe with the thermistor potted in quick-dryingindustrial strength epoxy at the very tip of the pipe. Caremust be taken to insure water-tight connections at both ends.Type (b) is intended for use in RSW piping. It is made from a1/4" PVC pipe plug that has been drilled out to accommodate thethermistor which was then soldered to the insulated lead in wire.This is epoxyed into the hole in.the plug as shown. Type (c) isthe'same type of setup only the thermistor is molded. into ablock or disk of clear plastic resin. This is intended to bescrewed or fiberglassed into the side of the fish bin. Thelead-in wires should be protected as much as possible from
55
3'
Drill out to OD of wire Thermistor
*-bead
Fill with quicksetting Epoxy Quick setting
PVC pipe Epoxy
Drill out to 0.D. of wireThermistor bead
Quick setting Epoxy
B
C
A
Insulation
Bulkhead
Figure 22. Probe designs.
56
physical damage and salt water by use of fiberglassing, woodstrips or conduit wherever feasible. Probe (d) is a through-the-bulkhead type installation. A good caulking compound shouldbe used in the void space around the thermistor tip to preventfish slime from accumulating.
The wire we used to connect probes to the telethermometer in thewheel house is standard #18 two-wire type SJ electrical cord.Electrical shielding is not necessary. And because its resis-tance is extremely small, it can be as long as necessary withoutaffecting the reading.
Because the wire runs through the fish hold, its coating mustresist penetration by the sprayed seawater. Vinyl, or Polyvinyl-chloride is OK for only a short term (a few days) immersion, andthen it should be thoroughly dried before immersing again.
Rubber coated wire (designated type "SJ") is what we are using.It will stand up if it is not exposed to oil, as in the engineroom. To be resistant to oil, the wire must be coated withneoprene. A wire having rubber over the two individual wiresplus a neoprene outer jacket, is designated type "SJO." Sourcesof wire include:
W. W. Grainger6335 North Basin Ave.Portland, OR 97217503-283-0366
Allied Elect.5901 4th Ave. SouthSeattle, WA 98108
Commercial Product Available
This article has described the construction of the Canadiantelethermometer. A Canadian firm has recently begun manufac-turing this unit which sells in Vancouver for $220 (1979Canadian dollars). Probes are made up to suit each installationand represent an additional cost.
The firm is:
General Refrigeration1766 W. 4th AvenueVancouver, B.C. Canada(604) 738-5181
157
Extension Service, Oregon State University, Corvallis, Henry A. Wads-worth, director. This publication was produced and distributed in fur-therance of the Acts of Congress of May 8 and June 30, 1914. Extensionwork is a cooperative program of Oregon State University, the U.S.Department of Agriculture, and Oregon counties.
Extension's Marine Advisory Program is supported in part by theSea Grant Program, National Oceanic and Atmospheric Administration,U.S. Department of Commerce.
Extension invites participation in its programs and offers themequally to all people, without discrimination.
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