板翅式换热器不同气液入口分配方式的分配性能对比分析

采用计算流体动力学方法对换热器单层通道处的气液相"先混合、后分配"的传统入口分配方式(方式A)和气液相"先分配、后混合"的新型入口分配方式(方式B)分别进行数值模拟。通过分析气液总流量在0.078~0.291 kg/s和液相质量分数在7.8%~91.4%内的换热器入口气液流量分布的不均匀度和流量标准方差等评价指标,对两种入口分配方式的分配性能进行评估。结果表明:相同流量条件下,方式B比方式A的气液分配不均匀度更小。流量的增大会导致两种方式的气液分配不均匀度升高,其中方式A的气液分配不均匀度增幅更大。随着液相质量分数增加,方式A的气液不均匀度降低,方式B的气液分配不均匀度小幅升高,但方式B的气液分配不均匀度一直比方式A小,且保持较低值。方式B比方式A更能有效地提高板翅式换热器的流体流动分配均匀性。

Analysis and comparison of distribution performance of two entrance forms used in plate-fin heat exchangers

For the traditional entrance form (form A) used in plate-fin heat exchangers, gas and liquid flows were mixed together before entering the header to be distributed. A novel form (form B) was designed, in which distribution was prior to mixing by using a gas-liquid distributor. Numerical simulation of the gas-liquid flow distribution was carried out for the two different entrance forms by computational fluid dynamics method, respectively. The non-uniformity and standard deviation of the gas-liquid flow distribution in entrances of the plate-fin heat exchanger were analyzed under different conditions of flow rate (0.078-0.291kg/s) and liquid mass fraction (7.8%-91.4%). The calculation results show that the non-uniformity of gas-liquid flow distribution is smaller for the form B than that for the form A under the same flow conditions. The non-uniformity is more serious with the increase of mass flow rate, and the non-uniformity for the form A increases even greater. For the form B, the non-uniformity of gas-liquid flow distribution slightly rises with the increase of liquid mass fraction. Conversely, it reduces for the form A. The non-uniformity of gas-liquid flow distribution for the form B remains a lower value, which is smaller than that for the form A. The way of "distribution prior to mixing" can improve the uniformity of the fluid flow distribution in plate-fin heat exchangers effectively.