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CHEE 470CHEE 470HEAT EXCHANGERSHEAT EXCHANGERSHEAT EXCHANGERSHEAT EXCHANGERS
BOB HEASLIPBOB HEASLIP
AGENDAAGENDA
Types of Heat ExchangersTypes of Heat Exchangers
TEMA Type Shell & Tube Heat ExchangersTEMA Type Shell & Tube Heat Exchangers TEMA Type Shell & Tube Heat ExchangersTEMA Type Shell & Tube Heat Exchangers
Shell & Tube Exchanger ArrangementsShell & Tube Exchanger Arrangements
Selection of Exchanger Type & OrientationSelection of Exchanger Type & Orientation
Shell & Tube Exchanger Thermal DesignShell & Tube Exchanger Thermal Design
Estimation of Film CoefficientsEstimation of Film Coefficients
Pressure Drop CalculationsPressure Drop Calculations
Thermal DesignThermal Design –– Other Exchanger TypesOther Exchanger Types
TYPES OF HEAT EXCHANGERS
• DOUBLE PIPE HEAT EXCHANGERS
SIMPLEST TYPE
A PIPE INSIDE A PIPEA PIPE INSIDE A PIPE
SMALL HEAT TRANSFER AREAS
TYPES OF HEAT EXCHANGERS
• HAIRPIN HEAT EXCHANGERS
TUBES INSIDE A U SHAPED SHELL
GOOD FOR HIGH TEMPERATURES ANDPRESSURES
LIMITED SIZE
TYPES OF HEAT EXCHANGERS
• PLATE & FRAME HEAT EXCHANGERS
FLUIDS FLOW BETWEEN THINFLUIDS FLOW BETWEEN THINPLATES
COMPACT DESIGN
HIGH HEAT TRANSFERCOEFFICIENTS
GASKETS LIMIT PRESSURE &TEMPERATURETEMPERATURE
NOT USED WITH HAZARDOUSCHEMICALS
TYPES OF HEAT EXCHANGERS
• SPIRAL PLATE HEAT EXCHANGERS
FLUIDS FLOW BETWEEN TWOPLATES WOUND AROUND EACHOTHER
GOOD FOR SLURRIES
LOW PRESSURE DROP
OFTEN USED IN VACUUMOFTEN USED IN VACUUMSERVICE
TYPES OF HEAT EXCHANGERS
• SPIRAL TUBE HEAT EXCHANGERS
FABRICATED FROM BENT TUBINGFABRICATED FROM BENT TUBING
AVAILABLE “OFF THE SHELF”
SMALL SERVICES FOR EXAMPLE SAMPLE COOLERSAND PILOT PLANTS
TYPES OF HEAT EXCHANGERS
• AIR COOLED EXCHANGERS
USED WHEN WATER EXPENSIVE OR NOT AVAILABLE
MUST BE DESIGNED TO HANDLE SEASONAL AND DIURNALTEMPERATURE CHANGES
EXPENSIVE AND TAKE UP A LOT OF ROOM
SMALLER PACKAGED “RADIATOR” TYPE UNITS AVAILABLE
SHELL & TUBE HEATSHELL & TUBE HEATEXCHANGERSEXCHANGERS
• THE MOST COMMON HEAT EXCHANGER TYPE – BY FAR• THE MOST COMMON HEAT EXCHANGER TYPE – BY FAR
• A LOT OF HEAT TRANSFER AREA IN A SMALL VOLUME
• BEEN IN USE FOR OVER 150 YEARS
• CAN BE DESIGNED FOR ALMOST ANY SERVICE
• DESIGN PRINCIPLES WELL KNOWN
• MANY DESIGN & FABRICATION SHOPS AROUND THE WORLD• MANY DESIGN & FABRICATION SHOPS AROUND THE WORLD
• AVAILABLE IN MANY DIFFERENT MATERIALS
• CAN BE DESIGNED FOR ALL PRESSURES & TEMPERATURES
TEMA
TUBULAR
EXCHANGEREXCHANGER
MANUFACTURERS
ASSOCIATION
SHELL & TUBE HEATEXCHANGER COMPONENTS
TUBES
SIZE IS OUTSIDE DIAMETER
¾” IS MOST COMMON SIZE
BIRMINGHAM WIRE GAUGEIS THICKNESS
AVAILABLE IN MANY ALLOYS
LENGTHS IN 2’ INCREMENTSUP TO 24 FEET LONG
TUBE LAYOUTS
TUBES ARE ARRANGED INSPECIFIC PATTERNSSPECIFIC PATTERNS
TRIANGULAR LAYOUT ISTHE MOST COMMON
DISTANCE BETWEEN TUBESCENTERS IS THE PITCH
LAYOUT & PITCH AFFECTSHEAT TRANSFER AND
TRIANGULAR SQUARE
HEAT TRANSFER ANDPRESSURE DROP
TUBESHEETS
TUBESHEETS HOLD THE ENDS OF THETUBES AND PROVIDE A BARRIERBETWEEN TUBE & SHELLSIDE FLUIDS
TUBES ARE CONNECTED TO THETUBES ARE CONNECTED TO THETUBESHEETS BY “GROOVING &ROLLING” OR BY WELDING
TUBESHEET MATERIALS MUST BESUITABLE FOR BOTH FLUIDS
SHELL
THE SHELL IS THE CONTAINER FOR THESHELL SIDE FLUID
FABRICATED FROM PIPE OR ROLLED SHEETFABRICATED FROM PIPE OR ROLLED SHEET
THE LEAST CORROSIVE & LOWESTPRESSURE FLUIDS ARE PLACED ON THESHELL SIDE TO REDUCE COSTS
SEVERAL DIFFERENT STYLES ARE USEDFOR DIFFERENT SERVICES
BAFFLESHORIZONTALSEGMENTAL
VERTICALSEGMENTAL
BAFFLES SUPPORT TUBES ANDDIRECT SHELL FLUID FLOW ACROSSTUBES
BAFFLE CUT IS % OF SHELLDIAMETER REMOVED
BAFFLE SPACING IS THE DISTANCEBAFFLE SPACING IS THE DISTANCEBETWEEN BAFFLES
SINGLE SEGMENTAL SINGLE SEGMENTAL
SHELL SIDENOZZLES
IMPINGEMENTPLATE
TUBESIDENOZZLES
BONNET TYPECHANNELCHANNEL
CHANNEL WITHGASKETED
PASS DIVIDER
COVER
S&T HEAT EXCHANGERS&T HEAT EXCHANGERARRANGEMENTSARRANGEMENTS
3 BASIC ARRANGEMENTS3 BASIC ARRANGEMENTS
FIXED TUBESHEETFIXED TUBESHEET
FLOATING HEADFLOATING HEAD
UU--TUBETUBE
3 BASIC ARRANGEMENTS3 BASIC ARRANGEMENTS
UU--TUBETUBE
FLOATING HEAD
TEMA W TEMA T TEMA SExternally Sealed Pull Through Floating Head
Floating Tubesheet Floating Head with Backing Device
FIXED TUBESHEET
EXPANSION JOINT
U-TUBE BUNDLE
REBOILER TYPES
REBOILER TYPE SELECTION CHART
FILM THEORY OF HEAT TRANSFER
There are five layers through which the heatmust flow:
1. The inside boundary layer2. The inside fouling layer3. The tube wall
DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS
3. The tube wall4. The outside fouling layer5. The outside boundary layer
The quantity of heat flow is the same througheach layer.
Therefore (assuming that the outside area is equal to the inside area):
q = Q/A = h (T -T ) = h (T -T ) = h (T -T ) = h (T -T ) = h (T -T )q = Q/A = hi(TH-T1) = hfi(T1-T2) = hw(T2-T3) = hfo(T3-T4) = ho(T4-TC)
Where : q = heat flux, BTU/hr/ft2 or W/mQ = Total Heat Transfer, BTU/hr or WA = Heat Transfer Area, ft2 or m2
h = Heat Transfer Coefficient, BTU/hr-ft2-oF or W/m-oKT = Temperature, oF or oK
DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS
The thermal resistance to heat flow, r is the reciprocal of the heat transfer coefficient.i.e. r = 1/h
Where: r = thermal resistance, hr-ft2-oF/Btu or m2-oK/W
Therefore the above equation can be modified as follows:Therefore the above equation can be modified as follows:
q = Q/A = hi(TH-T1) = (T1-T2)/rfi = (T2-T3)/ rw = (T3-T4)/rfo = ho(T4-TC)
In terms of temperature differences one can write:
TH-T1 = q/hi & T1-T2 = q rfi & T2-T3 = q rw & T3-T4 = q rfo &T4-TC = q/ho
Substituting one gets: T -T = DT = q(1/h + r + r + r + 1/h )Substituting one gets: TH-TC = DT = q(1/hi + rfi + rw + rfo + 1/ho)
Since q = Q/A, the above equation can be rearranged to give the following:
Q = A (TH-TC)(1/hi + rfi + rw + rfo + 1/ho)
The term 1/(1/hi + rfi + rw + rfo + 1/ho) is referred to as the overall Heat TransferCoefficient, U which has the units BTU/hr-ft2-oF or W/m2-oK.
Substituting U into the previous equation gives:
DEVELOPMENT OF BASIC HEAT TRANSFER EQUATIONS
Q = U A (TH – TC) also written as Q = U A DT
Previously it had been assumed that the outside area is equal to the inside area.However, this is not the case when tubes are being used.Modifying the above equations to take into account differences in areas gives:
U = 11/ho + Ao/Aihi + rw + rfo + Ao rfi/Ai
Often when carrying out heat transfer calculations, the goal is to determinethe heat transfer area, A.
A = Q / U DT
TYPICAL OVERALL HEATTYPICAL OVERALL HEATTRANSFER COEFFICIENTSTRANSFER COEFFICIENTS
AREA = QAREA = QAREA = QAREA = Q
U xU x DDTT
PROCESS SIMULATION GIVES Q &PROCESS SIMULATION GIVES Q & DDT.T.
WE WANT TO KNOW THE AREA.WE WANT TO KNOW THE AREA.
BY USING TYPICAL U’s WE CAN ESTIMATE THE AREA.BY USING TYPICAL U’s WE CAN ESTIMATE THE AREA.
TYPICAL U’s ARE THOSE EXPERIENCED IN SIMILARTYPICAL U’s ARE THOSE EXPERIENCED IN SIMILAREQUIPMENT UNDER SIMILAR CONDITIONS.EQUIPMENT UNDER SIMILAR CONDITIONS.
COCURRENT & COUNTERCURRENT FLOW
T2
t1
t2
T1
T2 t2
t2
t1
COUNTERCURRENT FLOW
t2T2
T1
COCURRENT FLOW
LOG MEAN TEMPERATURE DIFFERENCE (LMTD)LOG MEAN TEMPERATURE DIFFERENCE (LMTD)
T1
T2t2 LTTD
GTTD
THE TEMPERATURE DIFFERENCE BETWEEN THE FLUIDSTHE TEMPERATURE DIFFERENCE BETWEEN THE FLUIDSUSUALLY VARIES IN DIFFERENT PARTS OF THE EXCHANGER.USUALLY VARIES IN DIFFERENT PARTS OF THE EXCHANGER.THE APPROPRIATE AVERAGE TEMPERATURE DIFFERENCE FORTHE APPROPRIATE AVERAGE TEMPERATURE DIFFERENCE FORCOUNTERCURRENT OR COCURRENT FLOW IS THE LOG MEANCOUNTERCURRENT OR COCURRENT FLOW IS THE LOG MEANTEMPERATURE DIFFERENCE CALCULATED AS :TEMPERATURE DIFFERENCE CALCULATED AS :
t1t2 LTTD
TEMPERATURE DIFFERENCE CALCULATED AS :TEMPERATURE DIFFERENCE CALCULATED AS :
GTTD - LTTDLMTD =
ln(GTTD/LTTD)
LMTD CORRECTION FACTORS
IN THIS REGION FLUID JUST ENTERING THESHELLSIDE IS EXCHANGING HEAT WITH FLUIDJUST ENTERING THE TUBESIDE. THEREFOREFLOW IS CO-CURRENT.
IN THIS REGION FLUID ENTERING THESHELLSIDE OF THE EXCHANGER ISEXCHANGING HEAT WITH FLUIDEXITING THE TUBESIDE. THEREFOREMOSTLY COUNTERFLOW FLOW ISBEING ACHIEVED.
MOST EXCHANGERS HAVE ACOMBINATION OF COCURRENTCOMBINATION OF COCURRENTAND COUNTERCURRENTFLOW. CORRECTION FACTORSARE APPLIED TO THE LMTDUSING A DIFFERENT CHARTFOR EACH EXCHANGERCONFIGURATION
NON-LINEAR TEMPERATURE PROFILES
WATCH OUT FOR THISSITUATION
CALCULATION OF THE OVERALL HEATTRANSFER COEFFICIENT
U = Overall Heat Transfer Coefficient
ho = Outside Film Coefficient
hi = Inside Film Coefficient
rw = Tube Metal Resistance
r = Outside Fouling Resistancerfo = Outside Fouling Resistance
rfi = Inside Fouling Resistance
Ao = Outside Area
Ai = Inside Area
METAL RESISTANCE IN TUBES
rw normally has little affect on the heat transfer coefficient
FOULING FACTORS
ESTIMATION OF FILM COEFFICIENTS
• SENSIBLE HEAT TRANSFER
• CONDENSING
THREE MECHANISMS
• BOILING
EACH CAN OCCUR INSIDE OR OUTSIDE THE TUBE.
EACH CAN OCCUR IN COMBINATION WITH ANY OTHER.
SENSIBLE HEAT TRANSFERINSIDE THE TUBE
1. Calculate Reynolds Number.
2. Read Nusselt Number, jH off Sieder and Tate chart.2. Read Nusselt Number, jH off Sieder and Tate chart.
3. Calculate the film coefficient, hi.
HEAT TRANSFER COEFFICIENTSFOR SENSIBLE HEAT TRANSFER
INSIDE THE TUBE - WATER
KERN METHODKERN METHOD
1. Calculate velocity in tubes.
2. Determine average watertemperature.
3. Read film coefficient off thechart.
4. Correct for tube inside4. Correct for tube insidediameter.
HEAT TRANSFER COEFFICIENTSFOR SENSIBLE HEAT TRANSFER
OUTSIDE THE TUBE
1. Calculate Reynolds Number.
2. Read Nusselt Number, jH off the Kern chart.
3. Calculate the film coefficient, hi.
USE OF FINNED TUBES FORENHANCED HEAT TRANSFER
IN CASES WHERE A LOW COEFFICIENTON THE OUTSIDE OF THE TUBES LIMITSON THE OUTSIDE OF THE TUBES LIMITSTHE HEAT TRANSFER, FINNED TUBESCAN BE USED TO INCREASE THEOUTSIDE AREA.
CONDENSING COEFFICIENTSOUTSIDE TUBES & INSIDE HORIZONTAL TUBES
1. Calculate Condensing Load
2. Read Condensing Coefficient of f Chart
CONDENSING COEFFICIENTSINSIDE VERTICAL TUBES
1. Calculate Reynolds Number.
2. Read Nusselt Number off chart.
3. Calculate the film coefficient, hi.
VAPORIZATION
HEAT TRANSFER IN VAPORIZING OPERATIONS ISLIMITED BY MAXIMUM FLUX
ABOVE THE MAXIMUM FLUX HEAT TRANFER IS HINDERED BY ALAYER OF VAPOUR INSULATING THE SURFACE.
VAPORIZATION
Btu/hr-ft2MAXIMUM FLUX
ORGANIC FLUIDS – NATURAL CIRCULATION 12,000
ORGANIC FLUIDS – FORCED CIRCULATION 20,000
WATER & AQUEOUS SOLUTIONS 30,000
MAXIMUM FILMCOEFFICIENT
ORGANIC FLUIDS 300
WATER & AQUEOUS SOLUTIONS 1000
Btu/hr-ft2-oFCOEFFICIENT
PRESSURE DROPTUBESIDE – THROUGH TUBES
PRESSURE DROPTUBESIDE – THROUGH HEADS
PRESSURE DROPSHELLSIDE
CHEE 470HEAT EXCHANGERSHEAT EXCHANGERS
ASSIGNMENT