积耗散最小换热器的优化设计外文翻译(编辑修改稿)

积耗散最小换热器的优化设计外文翻译(编辑修改稿)内容摘要：

[6–10]. The first approach can reducecosts, but possibly at the expense of sacrificing heat exchangerperformance [11]. As representative of the secondapproach, entropy generation minimization suffers fromsocalled “entropy generation paradox” [8,12]. By analogy with electrical conduction, Guo et al. defineda new physical concept, entransy, which describes heattransfer capability [13]. Based on this concept, the equivalentthermal resistance of a heat exchanger was defined toquantify heat transfer irreversibility in heat exchangers[14].Chen et al. applied entransy dissipation theory to thevolumetopointconduction problem[15]. Guo et al. defined anentransy dissipation number to evaluate heatexchangerperformance that not only avoids the “entropy generationparadox” resulting from the entropy generation number, butcan also characterize the overall performance of heat exchangers[12].Xu et al.[16] developed an expression of theentransy dissipation induced by flow friction under finitepressure drop in a heat exchanger. The present work, based on expressions of entransy dissipationfrom heat conduction under finite temperature differencesand flow friction under finite pressure drops [14,16], and on the dimensionless method proposed by Guo etal. [12], defines an overall entransy dissipation minimum overall entransy dissipation number is thentaken as an objective 10 function. Under certain assumptionswe attempt to prove that since the variation in the duct aspectratio or mass velocity has opposing effects on the twotypes of entransy dissipations caused by heat conductionunder finite pressure drop, respectively, there is a correspondingoptimum in duct aspect ratio or mass velocity. We also develop analytically expressions for the optimal ductaspect ratio and mass velocity of a heat exchanger that are useful for design optimization. 1 Entransy dissipation number The entransy is defined as onehalf the product of heat capacity and temperature [13]: 22121Eh TMCTQ pvh  (1) where T is the temperature, Qvh is the heat capacity at constant volume, and cp is the specific heat at constant , using the waterwater balanced counterflow heatexchanger as an example, we attempt to discuss the entransydissipation in heat exchangers. Assume that both the hot and cold fluids are inlet temperature and pressure of the hot andcold fluids are denoted as T1, P1 and T2, P2, the outlet temperature and pressure are T1,out, P1,outand T2,out, P2,out. For the balanced heat exchanger, the heatcapacity rate ratio satisfies condition 1)()( 12  mcmcC (where m is the mass flow rate). For the onedimensionalheat exchanger considered in the present work, the usualassumptions such as steady flow, no heat exchange withenvironment, and ignoring changes in kiic and potentialenergies as well as the longitudinal conduction are made. In the heat exchanger, there mainly exist two kinds of irreversibility:the first is heat conduction under finite temperaturedifferences and the second is flow friction under finite pressure drops. The entransy dissipation rate caused by heat conduction under a finite temperature difference iswritten as [14] ])(21)(21[])(21)(21[2,222,11222211outout TmcTmcTmcTmcEr (2) The corresponding entransy dissipation number is defined as [12] 221121 )()()( TTmc ErTTQ ErEr   (3) where Q is the heat transfer rate, is the heat exchangereffectiveness which is defined as the ratio of the actual heattransfer rate to the maximum possible heat transfer rate. The entransy dissipation due to flow friction under a finite pressuredrop is expressed as [16] 2,22,22221,11,1111 lnlnlnln TT TTpmTT TTpmEoutoutoutoutp   (4) 11 where P1 and P2 refer to the pressure drops in the hot and cold water, respectively。 1 and 2 are their corresponding densities. Putting in dimensionless form leads to ])1(1[ln1)()(])1(1[ln1)()(11221112221212211TTTTTTTpcpTTTTTTTpcpEp (5) which is called the entransy dissipation number due to flow friction. Assuming that the heat exchanger behaves as a nearly ideal heat exchanger, then (1ε) is considerably smaller than unity [17]. For a waterwater heat exchanger under usual operating conditions, the inlet temperature difference between hot and cold water， ΔT=T1T2，小于 100 K, is less than 100 K,hence )2,1(  iTT There fore, eq. (5) can be simplified to 212122212111ln1)()(ln1)()( TTTTpcpTTTTpc pEp  (6) Accordingly, the overall entransy dissipation number bees 212122212111ln1)()(ln1)()()1(TTTTpcpTTTTpcpEpErE  (7) For a typical waterwater balanced heat exchanger, the number of heat transfer units Ntu can be introduced, which approaches infinity as the effectiveness tends to unity. Since c=1, the effectiveness is [17] NtuNtu1 (8) where the number of heat transfer units is defined as pmcUANtu Here U is the overall heat transfer coefficient, and A is the heat transfer area. Assuming that the heat conduction resistance of the solid wall can be neglected, pared with the convective heat transfer, then it is appropriate to replace U with the convective heat transfer coefficient h. Therefore 21 )(1)( 11 hAhaUA  (9a) 12 or21111 Nt uNt uNt u  (9b) where h1 and h2 are the convective heat transfer coefficients of the hot and cold fluids, respectively, and )2,1()()(1  imchAN tu ii Ntu hA mc i i ii . In the nearly ideal heat exchangerlimit, Ntu＞ 1, that is [17] Ntu11 。