【正文】 to the in?u ence of s on b. Summary and conclusions This study assessed an analytical formulation that con?ates two different heat exchanger design methodologies, the Kays and London’s (1984) εNTU approach and the Bejan’s (1996) method of entropy generation minimization. Expressions for optimum heat exchanger effectiveness, number of transfer units, ?ow path and heat exchanger surface area density are also devised. It was shown that there does exist a particular εNTU design for condensers and evaporators that minimizes the dimensionless rate of entropy generation. To this obser vation follows the conclusion that a high effectiveness heat exchanger has not necessarily the best thermalhydraulic design, as the effectiveness does not account for the pumping power studies considering a tube?n condenser for light mercial refrigeration applications and an evaporator for frostfree refrigerators were also carried out. In case of the condenser coil, where the entropy production due to viscous ?uid ?ow is of the same order of that due to ?nite temperature difference, the analytical formulation of Hermes (2021) showed to be suitable for thermodynamic optimizations. The analysis also indicated that a heat exchanger design with a high aspect ratio is preferable to a lowaspect ratio one as the former produces a dramatically lower amount of entropy. In addition, it was found that in case of a “nofrost” evaporator working under dry coil conditions, the pressure drop effect on the dimensionless entropy production is negligible in parison to the ?nite temperature difference, thus indi cating that Eq. (8) should be used with great care to avoid an economically unfeasible (high NTU) one hand, since the coil temperature is treated as a ?oating parameter during the optimization exercise, the design for heat transfer enhancement leads to lower average temperature differences and, therefore, to lower condensing temperature and higher evaporating temperature. On the otherhand, theoptimizationfor pressuredropreductionyields a higher mass ?ow rate for the same pumping power, thus improving the heat transfer coef?cient which also tends to reduce the condenser temperature or increase the evaporating temperature. Since the refrigeration system COP obeys the Tevap/(TcondeTevap) scale, it can be stated that the heat exchanger design that presents the best local (ponent level) performance in terms of minimum entropy generation also leads to the best global (systemlevel) performance. 冷凝器和蒸發(fā)器的熱力設計 : 制定和應用 摘 要 這份評估旨在用以前出版物中的最小熵產(chǎn)生法介紹的蒸發(fā)器及冷凝器中熱液的設計方法。 NTU/St (see Fig. 9a) and b 188。 ε(NTU), which the same for both surfaces, is also plotted to be used as a reference. It can be clearly seen that the (ε, NTU) design which minimizes the rate of entropy generation is (, ) for surface (, ) for surface . It can also be noted that the circular?n surface showed a higher rate of entropy generation for all NTU span,which is mostly due to the viscous ?uid ?ow effect assurface has a higher friction factor than surface 3/8T for the same Reynolds number (see Fig. 4). For low NTU values, where the entropy generation is ruled by NS,DT, both surfaces showed similar NS values as their jcurves are close (see Fig. 4).Fig. 6 pares three different condenser designs consid ering surface under the same working conditions. The heat exchanger length was also varied in order to acmodate the heat transfer surface area for different face areas. For a vertical, constant NTU line (. same heat transfer area), it can be clearly observed that a heat exchanger design with high aspect ratio (higher face area, smaller length in the ?ow direction) produces a signi?cantly lower amount of entropy in parison to a low aspect ratio design (lower face area, larger length). It can be additionally observed that the NS curves converge for low NTU values. This is so as the pressure drop effects, which rule the entropy generation for the low aspect ratio designs, are attenuated for low NTU values where the entropy generation due to ?nite temperature difference is Dominant. Now consider an airsupplied evaporator for household refrigeration appliances, prised of 10 tube rows in the ?ow