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Beskrivelse
The recently published book by the author, "Engineering Heat Transfer", already dealt with exact computation of heat exchangers and tube banks. In design c- putationthisisaccomplishedviacorrectivefactors;thelattermakesitpossibleto compute the actual mean temperature difference by starting from the logarithmic onerelativeto?uidsinparallel?oworcounter?ow. As far as veri?cation computation is concerned, corrective factors were int- ducedtocomputeacertaincharacteristicfactorcorrectly,asisfundamentalforthis typeofcomputation. Basedontheabove,theauthordecidedtoinvestigatefurther,re?ne,andwiden thistopic:theoutcomeofthisworkhasresultedinthishandbook. Newtypesofexchangerswereexamined;thecalculationwasre?nedtoproduce practicallyexactvaluesforthefactors. Thescopeoftheinvestigationwasincreased by widening the range of the starting factors. Furthermore, a greater number of valuestobeincludedinthetableswasconsidered. Finally,afewcharacteristicsof certainvaluesofthecorrectivefactorswerehighlighted. The?rstsectionisanintroduction;itsummarizesthefundamentalcriteriaofheat transferandproceedstoillustratethebehaviorof?uidsinbothparallelandcounter ?ow. Italsoshowshowtocomputethemeanisobaricspeci?cheatforsome?uids; itillustratesthesigni?canceofdesigncomputationandveri?cationcomputation. In addition,itillustrateshowtoproceedwithheatexchangersandtubebankstocarry outbothdesignandveri?cationcomputationcorrectly. AppendixAthenincludes36tablesasareferencefordesigncomputation,The tablescontainthecorrectivefactorsrequiredtoobtaintheactualmeantemperature differencebystartingfromthemeanlogarithmictemperaturedifferencerelativeto ?uidsinparallel?oworcounter?ow. Finally, Appendix B includes 35 tables for veri?cation computation. As far as heatexchangers areconcerned, itshowsthevaluesoffactor ? whichisrequired forthistypeofcomputation. Thevaluesofthecorrectivefactorsforcoilsandtube banksarealsopresented. Milano,Italy DonatelloAnnaratone v Notation c=speci?cheat(J/kgK) d=diameter(m) E=ef?ciencyfactor h=enthalpy(kJ/kg) k=thermalconductivity(W/mK) M=mass?owrate(kg/s) m=massmoisturepercentage(%) q=heatpertimeunit(W) 2 S=surface(m ) ? t=temperature( C) 2 U=overallheattransfercoef?cient(W/m K) x=thickness(m) 2 ? =heattransfercoef?cient(W/m K) ? =characteristicfactor ? =characteristicfactor ? =ef?ciency ? =correctivefactor ? =correctivefactor ? =characteristicfactor ? ?t=temperaturedifference( C) vii viii Notation Superscripts =heating?uid =heated?uid Subscripts c=counter?ow e=exchanger i=inside l=logarithmic m=mean o=outside p=constantpressure(isobaric),parallel?ow w=wall 1=inlet(forheatingorheated?uid) 2=outlet(forheatingorheated?uid) Contents 1 Introduction to Computation ...1 1. 1 GeneralConsiderations ...1 1. 2 MeanIsobaricSpeci?cHeat ...3 1. 2. 1 WaterandSuperheatedSteam ...4 1. 2. 2 AirandOtherGases...4 2 Design Computation...7 2. 1 Introduction ...7 2. 2 FluidsinParallelFloworinCounterFlow ...8 2. 3 TheMeanDifferenceinTemperatureinReality ...12 2. 3. 1 FluidsinCrossFlow...14 2. 3. 2 HeatExchangers...15 2. 3. 3 Coils...19 2. 3. 4 TubeBankswithVariousPassagesoftheExternalFluid . 21 3 Veri?cation Computation ...25 3. 1 Introduction ...25 3. 2 FluidsinParallelFloworinCounterFlow ...25 3. 3 Factor?inRealCases...33 3. 3. 1 FluidswithCrossFlow ...
