用于低干度混合工质制冷的板翅式换热器传热系数

Overall heat transfer coefficient of plate-fin heat exchanger during a mixed refrigerant cryogenic process in low quality

对于中小型天然气液化装置,板翅式换热器被广泛应用于回热换热。然而,目前对低干度混合工质在板翅式换热器中低温换热性能优化等问题的研究甚少。因此,搭建一套采用单级压缩、一级回热的Linde-Hampson制冷循环系统,并以N_2-CH_4-C_2H_4-C_3H_8-i C_4H_(10)作为混合制冷剂制取-160℃低温,用以重点分析板翅式换热器中的总传热系数以及影响板翅式换热器传热系数的因素。实验结果表明:低干度下板翅式换热器中总传热系数在2.6~22.7 W·m^(-2)·K^(-1)之间,受制冷温度和循环浓度变化的影响不明显,而目前对低干度低流速下混合制冷剂的低温换热性能预测仍存在一定的偏差,其中Cavallini和Modified Granryd的计算模型经修正后可推荐使用;同时,也从制冷剂流速、压降等方面对板翅式换热器优化设计提出了相关建议。

Plate-fin heat exchangers（PFHEs） are mostly employed in medium- and small-sized LNG plants. However, works about the heat transfer characteristic optimization of mixed refrigerant in PFHE under low quality have been barely carried out nowadays. Thus, a Linde-Hampson cycle using single stage compressors and recuperative heat exchanger was established and mixed refrigerant（N2-CH4-C2H4-C3H8-i C4H（10）） was used to obtain the refrigeration temperature of-160℃. Meanwhile, the overall heat transfer coefficient and the correlational influence factor were mainly analysed. The experimental results showed that the overall heat transfer coefficient of the PFHE was about 2.6—22.7 W ·m^-2·K^-1 while the refrigeration temperature and the circulated composition had week influence on the overall heat transfer coefficient. Meanwhile, the existing correlations cannot accurately predict the heat transfer coefficient of the mixed refrigerant under low quality and low flow velocity. However, the correlation of Cavallini and modified Granryd can used to predict the HTC of mixed refrigerant under low quality and low flow velocity after modification in this work. Additionally, some suggestion have been proposed in the design and optimization of PFHEs considering the refrigerate flowrate and pressure drop.