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 component300.0400.0500.0600.0700.0800.0900.0Cold 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 Totallb/h396,000Temperature, inF90Temp, C32.00Temperature, outF77Temp, C25.00Heat(5,002,748)Btu/h(1,466,306)WattsPressure, inpsig29Press Drop Allowedpsig2Fouling Resistanceft-h-F/Btu0.0005Heat Transferred5,002,748Btu/hCold Side0Fluid nameRaw WaterFlow Totallb/h1,188,000Temperature, inF68Temp, C20.00Temperature, outF72Temp, C22.33Heat5,002,748Btu/h1,466,306WattsPressure, inpsig60Press Drop Allowedpsig10(0)Fouling Resistanceft-h-F/Btu0.0005mass 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 fractionlb/ft3cPMWBtu/lb-FBtu/h-ft-FBtu/lblb/ft3cPMWBtu/lb-FBtu/h-ft-FABCmm HgpsigpsigWi ln(visc)cPln(cP)cPln(cP)1Water161.910.774094394318.021.000.35971.6362.110.902496740518.021.000.358.031,706.13231.4935.69(14.01)1-0.2560614564-0.10259020040.9434695161-0.05819122410.9264498889-0.07639532122Methyl Alcohol00.00.515864405832.040.00.0472.910.00.562399229232.040.00.07.971,515.29232.99180.57(11.20)0000.576320918500.57058785960300.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000400.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000500.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000600.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000700.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000800.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000900.000.00.00.00.00.000.00.00.00.00.00.00.00.00000000OK61.910.77409439431.000.3562.110.90249674051.000.35-0.2560614564-0.10259020040.9434695161-0.05819122410.9264498889-0.0763953212Cold Side Fluid Components1Water162.251.0218.021.000.34971.6362.190.9618.021.000.348.031,706.13231.4935.69(14.01)10.0158571549-0.04040837470.94-0.05819122410.93-0.0763953212200.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00300.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00400.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00500.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00600.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00700.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00800.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00900.000.00.00.00.00.00.00.00.00.00.00.00.00.00.00000.000.00OK62.251.021.000.3462.190.961.000.340.0158571549-0.04040837470.9434695161-0.05819122410.9264498889-0.0763953212Shell SideTube SideParameterUnitsInOutInOutFluid NameDistilled WaterRaw WaterFlow Totallb/h3960001188000Vaporlb/hLiquidlb/hSteamlb/hWaterlb/hNoncondensablelb/hEvap/Condlb/hTemperature (In/Out)F89.668Densitylb/ft3ViscositycPMolecular Weight, vaporMolecular Weight, noncondensiblesSpecific HeatBtu/lb-FThermal ConductivityBtu/h-ft-FLatent HeatBtu/lbInlet Pressurepsig29.0075460Velocityft/sPress Drop Allowedpsig1.510Fouling Resistanceft-h-F/Btu0.00049968710.0004996871

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 UBtu/h-ft-F520Safety factor for fouling20%Tube ODin0.750Tube wall thicknessBWG14Tube lengthft15Tube Passes10Shell Passes1Data (from the Process Data and F Factor worksheets)Flow ratelb/h1,188,000Heat transferredBtu/h5,002,748Temp diff correction factor1.000Average viscositycP0.99Average densitylb/ft362.22Pressure at inletpsig60Pressure drop allowedpsig10Tube roughnessft0.0000067CalculationsTube inside diameterin0.584Flow area per tubeft0.00186Tube area availableft/ft0.1963Log-mean temp diffF12.74Mean temperature differenceF12.74Adjusted dutyBtu/h6,003,298Tube area requiredft906Total tube length reqft4,615Number of tubes308Tubes per pass308Actual areaft907Flow rate per tubelb/h3,857Velocity in tubeft/s9.26Reynolds Number42,215Friction Factor0.0221Pressure Drop, tubespsig3.92Pressure drop, enter/exitft fluidneglectEnter/exit tubesft fluid2.00End losses in bonnets/channelsft fluid0.0Subtotal, extra losses tube sideft fluid2.00psig0.86Total pressure drop, tube sidepsig4.780

Problem Statement:Calculate the tube side pressure drop based on process data and heat load, using rule-of-thumb heat transfer rate and safety factorResultStandard 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) U

F FactorInputs (copied from the Process Data and Tubes worksheets)Hot SideFluid nameDistilled WaterTemperature, inF89.60Temperature, outF77.00Cold SideFluid nameRaw WaterTemperature, inF68.00Temperature, outF72.20Tube 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 coefBtu/h-ft-F1,057Data (from the Process Data and Tubes Pressure Drop worksheets)Assumed overall UBtu/h-ft-F520.0Outside surface areaft907.1Tube outside diameterin0.750Tube inside diameterin0.584ft0.049Tube length (one path)ft4,620.00Bulk viscositycP0.99Viscosity at tube wallcP0.93Bulk heat capacityBtu/lb-F1.00Bulk thermal conductivityBtu/h-ft-F0.34Reynolds Number42,215CalculationsInside surface areaft706.36Overall U based on inside areaBtu/h-ft-F667.81Average temperature, shell sideF70.10Average temperature, tube sideF83.30Mean wall temperature, insideF74.96Temp, C23.87Sieder-Tate term (visc ratio^0.14)1.01Prandl Number6.98Laminar flow calculationInside heat transfer coefficientBtu/h-ft-F27Turbulent flow calculationInside heat transfer coefficientBtu/h-ft-F1,569Transition flow calculationInside heat transfer coefficientBtu/h-ft-F7,778Choose which oneInside heat transfer coefficientBtu/h-ft-F1,569

Problem Statement:Calculate the tube side heat transfer coefficientResult

Shell GeometryInputsNumber of shells1Shell inside diameterin21.25