传热学第九章

1HeatTransfer1/540%30300-5009-2HeatTransfer1.HeatTransfer2.1HeatTransferHeatTransfer2HeatTransfer32HeatTransfer)(21ffttAk−=ΦmtAk∆=ΦHeatTransfer1.1't2't2t1t't∆t∆xt∆0At∫∆=∆AmAtAt0xxd1dAtxtAkΦ∆=dd111ddtcqΦm−=222ddtcqΦm=HeatTransfer1qm1qm2c1c22341HeatTransferdA1't2't2t1t't∆t∆0Att∆AdxAtAkΦ∆=dd111ddtcqΦm−=222ddtcqΦm=21dd)(dttt−=∆ΦΦcqcqtmmdd11)(d2211µ−=+−=∆HeatTransfertAkΦ∆=ddΦΦcqcqtmmdd11)(d2211µ−=+−=∆∫∫−=∆∆∆′∆xxAttkt0dAtdµxxkAtµ−=′∆∆tln)exp(txxkAtµ−′∆=∆tAkt∆−=∆d)(dµdAtdktµ−=∆∆)exp(tkAtµ−′∆=∆HeatTransfer∫∆=∆AmAtAt0xxd1tttttm′′∆′∆′′∆−′∆=′∆′′∆′∆′′∆′∆=∆tlnt1-ttlnt()1-)exp(t)dAexp(t1x0kAkAkAAtxAmµµµ−′∆−=−′∆=∆∫3HeatTransfer20At1't2't2t1t't∆t∆21''ttt−=∆21'ttt−=∆minmaxminmaxtlnttttm∆∆∆−∆=∆'tt∆∆HeatTransfer2.7.1minmax≤∆∆tt2minmax,tttm∆+∆=∆HeatTransfer3.ctfmmtt)(∆=∆ψLMTDψ19-15~9-18ψHeatTransfer2-1312468…ψPψ22112122',ttttRttttP′−′′′′−=′−′′−′′=HeatTransfer4.(1)(2)(3)(4)4mt∆hctt′′′′ct′′ht′′HeatTransfer9-3(1)(2)mtkA∆=Φ)()(22221111ttcqttcqmm′−′′=′′−′=Φ4HeatTransfermtkA∆=Φ()11111ttcqpm′′−′=Φ()22222ttcqpm′−′′=Φ12Φ=Φcη0.97~0.98cηHeatTransfermtkA∆=Φ()11111ttcqpm′′−′=Φ()22222ttcqpm′−′′=Φ3835321ppcc221121ttttqqAkmm′′′′′′ΦHeatTransfer143kA21mmqq1kHeatTransfer34244A5Φmt∆HeatTransfer2A521mmqq't't21HeatTransfer1243k'1t'2t'Φ4Φ21hhmt∆'Φ5HeatTransfer52%5%(a)2—5'ΦΦ'ΦΦHeatTransfer1.ε0At1t′2t′1t′′2t′′2211cqcqmm≤)(2111maxttcqΦm′−′=1122cqcqmm≤)(2122maxttcqΦm′−′=HeatTransfer0At0At)()(21minmaxttcqΦm′−′=ε)()()()(21minmaxminttcqttcqmm′−′′′−′=ε1t′2t′1t′′2t′′1t′2t′1t′′2t′′HeatTransfer2.NTUmin)(NTUcqkAm=NTUKA3.εNTU=maxmin)()(NTU,cqcqfmmεHeatTransferεNTU11min)(cqcqmm=11222211maxmin)()(ttttcqcqcqcqmmmm′′−′′−′′==)(2111tttt′−′′′−′=ε()11221122ttcqcqttmm′′−′=′−′′)(2111tttt′−′=′′−′εHeatTransfer()11221122ttcqcqttmm′′−′=′−′′)(2111tttt′−′=′′−′ε()21221121211)()(ttcqcqttttmm′−′+=′′−′′−′−′εε+=′−′′′−′′−1)()(122112121cqcqttttmm6HeatTransfer)exp()()(2121KAttttttµ−=′∆′′∆=′−′′′−′′NTUmaxminmaxmin)()(1)()(1exp1cqcqcqcqNTUmmmm+−−−=ε9-229-27HeatTransfer4.011kkRf−=Rfkk0HeatTransferηo=19-1oofowioifiRhRAARhkη1111++++=HeatTransfer9-4mtkA∆=Φ(1)(2)(3)HeatTransfer4.08.0PrRe023.0ffNu=2.04.08.08.06.04.0023.0duchpηρλ=HeatTransfer1.()2.()7HeatTransferioifwooddhRRhk111+++=hiu0.88.0iiiuch=ioifwoodducRRhk8.0111+++=HeatTransferioifwoodducRRhk8.0111+++=8.011umbko+=u.b1/k01/u0.8arctanm8.0iiiuch=HeatTransfer1/k01/u0.8HeatTransfer9-89-139-179-219-269-279-59-119-189-359-59