Handbook for Heat Exchangers and Tube Banks Design

Donatello Annaratone

• 08 november 2014
• 9783642428869

Samenvatting:

The motion of fluids is never in parallel- or counter-flow in heat exchangers and tube banks, leading to complexities in the equations for calculating their transferred heat and temperatures. This review of the topic includes 70 design and verification tables.

When a heating fluid transfers heat to a heated fluid through a wall, if the fluids are in parallel flow or counter flow it is possible to compute exactly both the transferred heat and the temperatures of the fluids via well-known equations. This holds true both for design and verification computation. However, the motion of the fluids is never in parallel flow or counter flow in heat exchangers and in tube banks. Instead, it is rather complex and consists of a combination of various cross flows. Hence, a precise design of the above components requires, on a case-by-case basis, the availability of the value of certain crucial factors or of corrective factors so as to make it possible to use the equations relative to parallel flow or counter flow. This handbook contains the introduction to the problem, its design criteria, and about 70 tables for the exact design and verification computation. It also indicates how to proceed in the case of cross flow.

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 ...