Heat Exchangers

HomeChapter 2: Heat ExchangersRules of Thumb for Chemical Engineers, 5th Editionby Stephen HallUnits:This Excel workbook includes Visual Basic for Application function subroutines.Macros must be enabled for them to work.Guide to Using this WorkbookThe primary purpose of this workbook is to demonstrate the use of the Bell-Delaware method for rating shell-and-tube heat exchangers. The method is applicable to exchangers with NO PHASE change. The worksheets follow the text in the stepwise evaluation of a heat transfer problem that is defined by the hot and cold fluid properties. Input cells have RED text. Cells with black text are formulas.1. Define the components in the hot and cold streams on the Process Fluids worksheet. Store the properties for new (previously unknown) components on the Fluid Data worksheet.2. Define the mass fraction of the components, flow rates, and temperatures on the Process Data worksheet3. Use the Tubes Pressure Drop worksheet to determine the tube diameter, length and number of tube passes in the exchanger, based on a pressure drop criteria4. Calculate the inside film coefficient on the Tubes htc worksheet5. Determine the shell diameter and enter information about the tube bundle and baffles on the Shell Geometry worksheet.6. Calculate the outside film coefficient on the Shell htc worksheet7. Determine the pressure drop on the shell side on the Shell Pressure Drop worksheet8. Compute the overall heat transfer coefficient, clean and fouled, on the Overall U worksheet; iterate until the assumed overall U in Step 3 agrees with the calculated U-clean9. Complete a TEMA datasheet on the Shell-and-Tube worksheet10. The Conversions worksheet is used for data, including the status of radio buttons and checkboxes, and must not be deleted!ChemEng Software sells an Excel template called TANKJKTwww.chemengsoftware.comTANKJKT models heat transfer in vessels with jackets and/or internal coils. It includes a database of properties for glass-lined reactors, heat transfer fluids, and insulation materials. Order on-line or by telephone, 24-h/d; credit cards accepted.

Customary USSIwww.chemengsoftware.com

Process FluidsUse this worksheet to define the components present in the hot and cold streams for a heat transfer problem.Multiple components from the Fluid Data properties table can be specified, and their properties will be averaged.Averging properties for non-ideal solutions, such as polar mixtures (with water), gives poor results.A better approach is to define the properties for the mixtures at several temperatures and add them to the database.The composition (i.e., mass fraction of each component) is specifed on the next worksheet.Use the dropdown list to view the Fluid Data content:Methyl AlcoholTo add new materials to the Fluid Data, go to the Fluid Data worksheet tabHot Fluid ComponentsNamein Data Table?Description1WaterYESCity water2Methyl AlcoholYESpure component3Methyl AlcoholYESpure component4Methyl AlcoholYESpure component5Methyl AlcoholYESpure component600.0700.0800.0900.0Cold Fluid ComponentsNamein Data Table?Description1WaterYESCity water200.0300.0400.0500.0600.0700.0800.0900.0

Problem Statement:Define components for the hot and cold streamsAdd to Hot Fluid ListAdd to Cold Fluid List

Process DataInputsHot SideFluid nameDistilled WaterFlow Totalkg/h180,000Temperature, inC32Temp, C32.00Temperature, outC25Temp, C25.00Heat(5,289,269)kJ/h(1,469,242)WattsPressure, inkPa(g)200Press Drop AllowedkPa(g)10Fouling Resistancem-C/W0.0001Heat Transferred1,469,242WCold Side0Fluid nameRaw WaterFlow Totalkg/h540,000Temperature, inC20Temp, C20.00Temperature, outC22Temp, C22.33Heat5,289,269kJ/h1,469,242WattsPressure, inkPa(g)414Press Drop AllowedkPa(g)69(0)Fouling Resistancem-C/W0.0001mass fracmass fracViscosity Based on the Wall TemperaturesComponentDensityViscositySp HeatTherm CondH VapDensityViscositySp HeatTherm CondAntoine CoefficientsVPVPPartial PViscosity using Eq 27-3If Shell SideIf Tube SideHot Side Fluid Componentsmass fractionmole fractionkg/m3cPMWkJ/kg-CW/m-CkJ/kgkg/m3cPMWkJ/kg-CW/m-CABCmm HgkPa(g)kPa(g)Wi ln(visc)cPln(cP)cPln(cP)1Water1991.690.774094394318.024.200.612,260.00994.900.902496740518.024.200.608.031,706.13231.4935.69(96.54)1-0.2560614564-0.10259020040.9434695161-0.05819122410.9264498889-0.07639532122Methyl Alcohol00.00.515864405832.040.00.01,100.000.00.562399229232.040.00.07.971,515.29232.99180.57(77.23)0000.576320918500.570587859603Methyl Alcohol0.00.515864405832.040.00.01,100.000.00.562399229232.040.00.07.971,515.29232.99180.57(77.23)0000.576320918500.570587859604Methyl Alcohol0.00.515864405832.040.00.01,100.000.00.562399229232.040.00.07.971,515.29232.99180.57(77.23)0000.576320918500.570587859605Methyl Alcohol0.00.515864405832.040.00.01,100.000.00.562399229232.040.00.07.971,515.29232.99180.57(77.23)0000.576320918500.57058785960600.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000700.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000800.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000900.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000OK991.690.77409439434.200.61994.900.90249674054.200.60-0.2560614564-0.10259020040.9434695161-0.05819122410.9264498889-0.0763953212Cold Side Fluid Components1Water1997.191.0218.024.200.592,260.00996.120.9618.024.200.608.031,706.13231.4935.69(96.54)10.0158571549-0.04040837470.94-0.05819122410.93-0.0763953212200.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00300.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00400.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00500.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00600.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00700.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00800.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00900.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00OK997.191.024.200.59996.120.964.200.600.0158571549-0.04040837470.9434695161-0.05819122410.9264498889-0.0763953212Shell SideTube SideParameterUnitsInOutInOutFluid NameDistilled WaterRaw WaterFlow Totalkg/h180000540000Vaporkg/hLiquidkg/hSteamkg/hWaterkg/hNoncondensablekg/hEvap/Condkg/hTemperature (In/Out)C3220Densitykg/m3ViscositycPMolecular Weight, vaporMolecular Weight, noncondensiblesSpecific HeatkJ/kg-CThermal ConductivityW/m-CLatent HeatkJ/kgInlet PressurekPa(g)200413.6855452065Velocitym/sPress Drop AllowedkPa(g)10.342138630268.9475908678Fouling Resistancem-C/W0.0000880.000088

Problem Statement:Specify process conditions for a liquid-liquid heat exchange problem, and perform a heat balanceHot Side FlowHot Side Temperature InHot Side Temperature OutCold Side FlowCold Side Temperature InCold Side Temperature OutSolve Heat Balance

Tubes Pressure DropInputsFluid flowing in tubesRaw WaterAssumed overall UW/m-C2,953Safety factor for fouling20%Tube ODmm19.050Tube wall thicknessBWG14Tube lengthm5Tube Passes10Shell Passes1Data (from the Process Data and F Factor worksheets)Flow ratekg/h540,000Heat transferredW1,469,242Temp diff correction factor1.000Average viscositymPa-s0.99Average densitykg/m3996.65Pressure at inletkPa(g)414Pressure drop allowedkPa(g)69Tube roughnessm0.0000020CalculationsTube inside diametermm14.834Flow area per tubem0.00017Tube area availablem/m0.0598Log-mean temp diffC7.08Mean temperature differenceC7.08Adjusted dutyW1,763,090Tube area requiredm84Total tube length reqm1,410Number of tubes309Tubes per pass309Actual aream85Flow rate per tubekg/h1,748Velocity in tubem/s2.82Reynolds Number42,165Friction Factor0.0221Pressure Drop, tubeskPa(g)26.96Pressure drop, enter/exitm fluidneglectEnter/exit tubesm fluid5.96End losses in bonnets/channelsm fluid0.0Subtotal, extra losses tube sidem fluid5.96kPa(g)5.94Total pressure drop, tube sidekPa(g)32.900

Standard tube lengths in the US are 4, 8, 12, 15, and 20 ftMinimum = number of shell passes, or may be a multiple of 2 times the shell passes. This is the total number of tube passes, example: 3 shells, 2 tube passes in each shell = 6 tube passesTypical value is0.5 to 2.5 m/s or2 to 8 ft/sAfter stepping through all of the worksheets to "Overall U", come back here and iterate this assumption until it agrees with the calculated (clean) UProblem Statement:Calculate the tube side pressure drop based on process data and heat load, using rule-of-thumb heat transfer rate and safety factorResult

F FactorInputs (copied from the Process Data and Tubes worksheets)Hot SideFluid nameDistilled WaterTemperature, inC32.00Temperature, outC25.00Cold SideFluid nameRaw WaterTemperature, inC20.00Temperature, outC22.33Tube passes1Shell passesN1CalculationsIntermediate valueR2.999Intermediate valueP0.195Intermediate valueS1.581Intermediate valueW0.517Intermediate valueW'0.805General CaseNumerator(1.042)Denomenator(1.107)General Case AnswerF0.942R=1 CaseNumerator0.341Denomenator0.345R=1 AnswerF0.990Choose which oneF0.942

Problem Statement:Calculate the LMTD configuration correction factorResult

Tubes htcInputsFluid flowing in tubesRaw WaterAssumed inside heat transfer coefW/m-C6,000Data (from the Process Data and Tubes Pressure Drop worksheets)Assumed overall UW/m-C2,952.7Outside surface aream84.5Tube outside diametermm19.050Tube inside diametermm14.834m0.015Tube length (one path)m1,412.75Bulk viscositycP0.99Viscosity at tube wallcP0.93Bulk heat capacitykJ/kg-C4.20Bulk thermal conductivityW/m-C0.59Reynolds Number42,165CalculationsInside surface aream65.84Overall U based on inside areaW/m-C3,791.99Average temperature, shell sideC21.17Average temperature, tube sideC28.50Mean wall temperature, insideC23.87Temp, C23.87Sieder-Tate term (visc ratio^0.14)1.01Prandl Number6.98Laminar flow calculationInside heat transfer coefficientW/m-C152Turbulent flow calculationInside heat transfer coefficientW/m-C8,899Transition flow calculationInside heat transfer coefficientW/m-C44,069Choose which oneInside heat transfer coefficientW/m-C8,899

Problem Statement:Calculate the tube side heat transfer coefficientResult

Shell GeometryInputsNumber of shells1Shell inside diametermm539.75