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H e a t P u l s e2007E X P L O R I N G T H E R M A L P R O P E RT I E S M E A S U R E M E N T O F N AT U R A L & E N G I N E E R E D M AT E R I A L S

7 Thermal Properties ofOils Measured With AField Portable Meter

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2Thermal Resistivityof Porous Materials(Soils) Change withChanges in Density, WaterContent, Temperature andComposition

4 Finding the R valueof Insulation usingthe KD2 8Beautiful JapaneseMurals Theatened byFungi

Preservation p8Artifact

5 How to Bake the Perfect Cheesecake Every Time

Blue Dragon ofTakamatsuzuka Tumulus

Japan

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Decagon's KD2 measures thethermal resistivity of materials.These measurements are fastand accurate, but there is a limit to thenumber of samples that can be tested,and the sampling and testing procedureitself may affect the reading obtained.Insight into the factors that may affectthermal resistivity of porous materialswill make the measurements made withthe KD2 as useful, representative and asaccurate as possible.

Soils and other porous materials vary indensity, water content, temperature andcomposition which affects the thermalresistivity of porous material. Table 1shows thermal properties of typical soilconstituents. These constituents occuras mixtures in typical porous materials.The thermal resistivity of the mixture isquite difficult to compute, since itdepends, not only on the thermalresistivities of the components, but alsoon their geometric arrangement.Methods for making this computationare given by Campbell and Norman(1998) and deVries (1963). Thesemethods were used to compute the

thermal resistivity of soils as they varywith water content, composition,density and temperature. The results ofthese computations are shown in Figures1, 2 and 3.

In general, the thermal resistivity of amixture is strongly influenced by thecomponent with the highest resistivity.Dry quartz sand and dry loam soil haveabout the same resistivity, even thoughthe resistivity of the minerals differs by a

factor of 3(Figure 1 andTable 1). Asthe limitingresistivitybecomeslarger,differencesin theresistivitiesof the othercomponentshave a largereffect. Forexample, dryquartz andloam differ in

resistivity by about 10%, while watersaturated quartz sand has about half theresistivity of saturated loam (Figure 1).

As the water content of unsaturatedporous materials increases, a threshold isreached where resistivity decreasesrapidly with increasing water content.This is evident in all three figures. Thisthreshold is more closely related tohydraulic than thermal properties ofthe material. It is the water content atwhich liquid water can flow acrossparticle surfaces to re-evaporate andtransport latent heat across pores in themedium.

Thermal Resistivity of Porous Materials (Soils)Change with Changes in Density, WaterContent, Temperature and Composition

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Therm. Resistivity(m K W-1)

0.40

0.33

0.11

1.00

4.00

1.65 @25C

0.45 @ 0C

38.8 @25C

Table 1. Thermal properties of soil materials (T is Celsius temperature) [modified from Campbell and Norman, 1998]

Material

Soil minerals

Granite

Quartz

Glass

Organic matter

Water

Ice

Air (101 kPa)

Density(Mgm-3)

2.65

2.64

2.66

2.71

1.30

1.00

0.92

(1.29-0.0041T * 10-3)

Specific Heat(J g-1K-1)

0.87

0.82

0.80

0.84

1.92

4.18

2.1+0.0073T

1.01

Thermal Cond.(W m-1K-1)

2.5

3.0

8.8

1.0

0.25

0.56+0.0018T

2.22-0.011T

0.024+0.00007T

Papers

� Campbell, G.S.,Huffaker, E.M., Wacker,B.T. and Wacker, K.C.2003. Use of the lineheat source method tomeasure thermalconductivity ofinsulation and otherporous materials. InWang, H. and Porter, W.(eds.) ThermalConductivity 27.DEStech Publications,Inc., Lancaster, PA.p.87–206.

� Fontana, A.J.,Wacker, B.T., Campbell,C.S. and Campbell,G.S. 2001.Simultaneous thermalconductivity andthermal diffusivity ofselected foods. InDinwiddie, R.B. (ed.)Thermal Conductivity26. DEStechPublications, Inc.,Lancaster, PA. p.38–44.

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In other words, the soil acts like a "heatpipe", an engineering device whichmakes use of latent heat transport forrapid and effective heat transfer. In amoist soil at room temperature 10 to20% of the total heat transport is aslatent heat through the pores. Thisportion of the heat transport is stronglytemperature dependent, roughlydoubling for each 10°Ctemperature rise.

The effective thermal resistivity ofmoist, air-filled pores is about the sameas the thermal resistivity of water at60°C, so, at this temperature, changingthe water content of the material doesnot affect its resistivity. In Fig. 3, the50°C curve shows almost no change inresistivity with increasing water contentonce the water content is high enoughto sustain the liquid return flow withinthe pores. �

References1. Campbell, G. S. and J. M. Norman.1998. An Introduction to EnvironmentalBiophysics, 2nd Ed. Springer Verlag, NewYork.

2. Campbell, G. S., J. D. Jungbauer, Jr.,W. R. Bidlake and R. D. Hungerford.1994. Predicting the effect of temperature onsoil thermal conductivity. Soil Sci.158:307-313

3. De Vries, D. A. 1963. Thermalproperties of soil. In Physics of PlantEnvironment. W. R. van Wijk (ed.) NorthHolland Pub. Co. Amsterdam pp. 210-235

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Figure 1The thermal resistivityof three soil materialsas a function of watercontent. The solidfraction in each was 0.5.

Figure 2Effect of density andwater content onthermal resistivity of aloam soil. The voidratio 1 curve is thesame as in Fig. 1. Thebulk densities are 1.06Mg/m3 for void ratio of1.5, 1.33 Mg/m3 forvoid ratio 1, and 1.59Mg/m3 for void ratio of0.67.

Figure 3Effect of temperatureand water content onthermal resistivity of aloam soil. The 25 Ccurve is the same as inFig. 1.

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The R value of a material is ameasure of its resistance to heatflow. The higher the R value, thelower the heat flow for a giventemperature difference. In winter, ahouse with an average R value of 10 willlose heat twice as fast as a house with anaverage R value of 20. Therefore, the Rvalue is critical for determining energyrequirements associated with heatingand cooling of homes and otherbuildings. The KD2 can’t measure theaverage R value of a building, but it canmeasure the thermal resistivity of thematerials that make up the building. Themost important andmost variable ofthese is theinsulating material.

We’ll start bydefining someterms. Thermalconductivity, K isthe amount of heat (Watts or BTU) thatflows across a plane of unit area (1 m2 or1 ft2) in unit time (1 s or 1 hr) when

Finding the R value of Insulation using the KD2there is unit temperature gradient (1 °C/m or 1 F/in). Units are W/(m °C) orBTU in/(ft2 hr F). Thermal resistivity isthe reciprocal of thermal conductivity(1/K), so units are m °C/W or ft2 hr F/(BTU in). Thermal resistivity is theresistance per unit thickness of thematerial (per meter or inch). Thermalresistance is the product of the resistivityand the thickness of the material, so itsvalue is specific not only to the materialbut also to its physical configuration.The R value, as used in U.S.building trades, is the thermalresistance in units of ft2 hr

F/BTU.

Determiningan R value withthe KD2 consists ofmeasuring the thermalresistivity of the material,converting it to Englishunits (the KD2 shows

m °C/W), and multiplying by theinsulation thickness in inches. Themultiplier for converting to Englishunits is 0.144.

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Application Notes

� Using the KD2 toMeasure ThermalConductivity

� The KD2 ThermalProperties Analyzer vsPublished Standards

� Simultaneous ThermalConductivity andThermal DiffusivityMeasurement ofFoods

� Finding the R Value ofInsulation using theKD2

� Thermal Resisitivity ofPorous Materials(Soils) Change withChanges in Density,Water Content,Temperature andComposition

� Using ThermalPropertiesMeasurements toPredict FoodTemperature DuringProcessing

� Underground PowerTransmission andDistribution Systems

� Reducing ContactResistance Errors inKD2 ThermalPropertiesMeasurements

CONTINUED ON TOP OF PAGE 5 >

REDUCE FOOD PROCESSING COSTS.Save energy and money by understandingheat flow in and out of your food products.

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KD2 directly display thermalconductivity of solids, gels, andpowders.

� Good R value reduces heat costs.

� KD2 fits inthe palm ofyour hand.

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Taking a measurementwith the KD2 issimple. Just insert theneedle into arepresentative sampleof the material to test,press the right buttonuntil the resistivityunits appear at the left

of the digits, press theleft button to start a

measurement, wait 90seconds for the measurement to

complete and record the reading.

As an example, assume we made ameasurement with the KD2 and foundthat the thermal resistivity of aninsulating material was 20 m °C/W.Converting this to English units gives

If the thickness of this insulation were 6inches, the thermal resistance would be

The R value of this insulation wouldtherefore be approximately 17.Doubling the thickness would, ofcourse, double the R value.

Using the KD2 to measure the thermalresistivity of insulation is a quick andportable method that anyone on a tightbudget can do. For more informationregarding the KD2, please contact theDecagon sales team at 509-332-2756 orvia email at sales@decagon.com. �

This cheesecake is not cooked inthe center. This cheesecake isover-cooked and has cracked.This cheesecake is just right. Why can’t Ibake the perfect cheesecake every time? Iuse the same recipe and carefullymeasure and add all of the ingredientsthe same way every time. I have evenmade sure the bake time is the same andthe oven is at the correct temperature,but the results are not always the same.Sometime it’s the perfect cheesecake,but other times the cakes are under orover cooked. Why?

The problem does not lie in the oven oryour recipe. Variation lies in the smalldifferences in the thermal properties ofthe cream cheese. Dairy products likemany other ingredients and foods varyslightly from lot-to-lot, season-to-

season, and supplier-to-supplier. Theimportant thermal properties are:thermal conductivity (k) and thermaldiffusivity (D). Simple definitions are asfollows: Thermal conductivity(k - W m-1 °C-1) is the ratio of heat fluxdensity to temperature gradient in amaterial. It measures the ability of asubstance to conduct heat. Thermaldiffusivity (D - mm2 s-1) is the ratio ofthermal conductivity to specific heat. Itis a measure of the ability of a materialto transmit a thermal disturbance.

The importance of thermal conductivityis to predict or control the heat flux infood during processing such as cooking,frying, freezing, sterilization, drying orpasteurization. It is necessary to ensurethe quality of the food product. Thermaldiffusivity determines how fast heat

How to Bake the Perfect Cheesecake Every Time.

CONTINUED ONPAGE 7

� All insulationshave differentR values.

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Thermal Properties of Oils Measured With AField Portable Meter

Statement of Work

Decagon Devices, Inc. iscurrently working inconjunction with the U.S.Government and the National Center

for Manufacturing Sciences (NCMS) inan effort to find a solution for measuringthe thermal properties of engine oil.

A primary function of engine oil is thetransfer and storage of the thermalenergy. Changes in thermal energytransfer and storage characteristics withuse are significant in themselves, interms of oil performance. However, theycan also be correlated with otherimportant properties, such as viscosity,fuel content, water content, impurities,etc. Measurement of thermal properties(conductivity and specific heat) may,therefore, provide a fast and accurateassessment of oil condition (need forchange) in a vehicle. Suchmeasurements are available in alaboratory setting, however, obtainingsufficient sample, transport of samples to

the laboratory, analysis and cost ofmaintaining the laboratory itself, as wellas returning the results to the relevantauthority is expensive and inefficient.

Decagon Devices, Inc.’s solutionproposal entails using a dual-probe lineheat source method that will providequick and accurate measurements ofthermal properties of fluids, even underfield conditions. The basis for theinstrument is Decagon’s existing KD2-Pro thermal properties analyzer. Newprobes were constructed to eithermeasure thermal properties of a fewdrops of oil from a dipstick. A fieldmeasurement provides an on-the-spotassessment of fundamental physicalproperties of the oil, which can be usedto assess oil quality. Thesemeasurements can be integrated withmeasurements from other hand-heldinstrumentation to provide a morecomplete picture of oil quality in thefield.

Decagon Devices, Inc. will be deliveringthermal properties measurements for awide range of oil samples, both new andused, and contaminated with addedwater, antifreeze, and/or fuel. Thermalproperties of the test samples will bemeasured over a range of temperaturefrom -20 °C to 80 °C. These tests willdetermine the range of thermalproperties and the KD2-Pro’seffectiveness in detecting contaminationor degradation. New probes for theKD2-Pro have been developed whichare suitable for oil thermal propertiesassessment under field conditions.Three production-ready prototypes ofthe KD2-Pro and probe will bedelivered along with the analysis ofthe data. �

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� Thermalproperties ofoil samplesbeing measuredwith KD2 Pro.

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DECAGON TRADESHOWS 2007

� Geo-Denver—February 18–21, Denver, Colorado

� PITTCON—February 25–March 2, Chicago, Illinois

� ANTEC 2007—May 6–10, Cincinnati, Ohio

� 2nd Int’l Conference of Porous Media—June 17–24, Kauai, Hawaii

� International Thermal Conductivity Conference—June 24–27, Birmingham, Alabama

� Institute of Food Technologists—July 28–Aug 1, Chicago, Illinois

� North American Thermal Analysis Society—August 25–29, East Lansing, Michigan

� American Society of Agronomy—November 4–8, New Orleans, Louisiana

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propagates or diffuses through amaterial. It helps estimate processingtime of canning, heating, coolingfreezing, cooking or frying. Watercontent, temperature, composition, andporosity affect thermal diffusivity. Theseproperties are necessary for calculatingenergy demand for the design ofequipment and optimization of thermalprocessing of foods (Polley et al., 1980).

To bake the perfect cheesecake everytime, you need to measure the thermalproperties on every batch of creamcheesecake batter using Decagon’s KD2Pro. Using these thermal propertiesvalues, the optimal cook time or beltspeed can be determined to bake theperfect cheese cake every time. No moreuncooked centers or dry, cracked cakes.�

Reference:Polley, S.L., Snyder, O.P. and Kotnour, P. 1980. Acompilation of thermal properties of foods. FoodTechnology 34(11):76-94.

Bake the PerfectCheesecake

CONTINUED FROM PAGE 5

You can use threeinterchangeable sensors tomeasure thermal diffusivity,specific heat (heat capacity),thermal conductivity and thermalresistivity with KD2 Pro. You cananalyze data and correct forsample temperature drift—providing accurate thermalproperties measurements.

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Read your thermal valuesdirectly or download rawvalues for analysis as requiredby IEEE and ASTM standards.

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Takamatsuzukatumulus is locatedin the Asukavillage, just southof Nara, Japan.This area is awonderfulcombination ofurban living andancient templesand tombs.Takamatsuzukawas named for thetall pine tree thatsits at the top of

the mound. Located within the tomb aresome of the most beautiful and famousJapanese wall paintings. Discovered in1972, the paintings are believed to havebeen made at the end of the seventh andbeginning of the eighth centuries.

Though it is unknown who is actuallyburied in the tomb, the murals areworthy of a nobleman. They depict asmall-scale universe, including starconstellations, the sun, the moon, andguardian gods, for the deceased.

This national treasure becamethreatened in 2001 with the appearanceof fungi growing on the interior limeplaster walls. Efforts began immediatelyto contain and stop the fungi growthwithin the tumulus. High humidity andhigh water content of the lime plasterwalls were believed to be a contributorof the fungi growth. Scientists usedDecagon’s KD2 to determine thethermal properties of the tumulus andsurrounding soil. As a result, it wasdetermined that the best short-term

KD2 determines thermal properties of theTakamatsuzuka tumulus and surrounding soil.

� A wall painting depicting a woman, found atthe Takamatsuzuka, is shown at left in a1972 photo; mold damage can be seen in thephoto on the right, taken in 2002

� Takamatsuzuka tumuluscooling system in background.

� Commorativestamp circa 1973.

� Mural on innerwalls of tomb.

solution would be to cool the entiremound to stop the fungi growth.

The monstrous cooling system wasinstalled over the mound, thus cooling itto a temperature where the fungi wouldbe dormant. The Agency of CulturalAffairs is investigating ways to preservethese beautiful murals for futuregenerations. �

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