Djetel-Gothe Steve, Lanzetta François, Bégot Sylvie
FEMTO-ST, Energy Department, Univ. Bourgogne Franche-Comté, CNRS Parc technologique, 2 avenue Jean Moulin, 90000 Belfort, France.
Entropy (Basel). 2020 Feb 14;22(2):215. doi: 10.3390/e22020215.
The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate N S , the irreversibility distribution ratio and the Bejan number B e | N S based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K < < 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and B e | N S → 1 and → 0 for mass flow rates m ˙ → 0.1 kg.s.
应用热力学第二定律，通过三个因素来评估熵产生对实验型斯特林制冷机冷热交换器性能的影响：熵产生率(N_S)、不可逆性分布比以及基于我们引入的无量纲熵比的比詹数(Be|{N_S})。研究了这些因素随热交换器特征尺寸（水力直径和长度）、冷却剂质量流量和冷气体温度的变化情况。我们证明了这些因素对热不可逆性和流体摩擦不可逆性的作用。这些结论源自于在(240K\lt T\lt300K)温度范围内，由冷却剂液体（质量比为(55/45)的乙二醇/水混合物）穿过的双管式热交换器的熵产生因素关于传热和流体摩擦特性的行为。熵产生的数学模型包括压力、温度和冷却剂质量流量的实验测量值以及热交换器的特征尺寸。大的特征长度和小的水力直径会产生大量的熵产生，尤其是在低温时，因为冷却剂液体的高粘度值会增加流体摩擦。该模型和实验表明，在冷热交换器中传热比粘性摩擦占主导地位，并且对于质量流量(\dot{m}\to0.1kg\cdot s)，(Be|{N_S}\to1)且(\beta\to0)。
