CO_2蒸发器的性能模拟与优化计算

Performance simulation and optimization calculation for CO_2 evaporator

CO2蒸发器的结构和换热效果对CO2跨临界制冷循环的性能影响较大,为了能设计出高效的蒸发器,有必要对CO2蒸发器进行性能模拟和优化研究.首先采用稳态集中参数法建立了CO2蒸发器计算模型,对制冷量、冷冻水出口温度、压降以及CO2制冷剂的干度进行了模拟计算,并与实验值进行了比较,根据两者的比较结果对模型进行了修正.然后利用该模型对CO2蒸发器进行了优化计算,主要分析了换热管径和管长对冷重比及压降的影响.结果表明,冷重比和压降都随管径的增大而下降;而随着管长的增加,冷重比上升很快,并在1.4 m左右出现最大值,压降却随管长的增加而增大.综合考虑冷重比和压降两方面因素,CO2蒸发器适合选择小管径和长管长.

The structure and heat transfer performance of CO2 evaporator put great impact on the CO2 transcritical refrigeration cycle performance.In order to design high efficiency evaporator,it is necessary to implement performance simulation and optimization study for CO2 evaporator.Firstly,the calculation model based on steady state lumped parameter for CO2 evaporator is developed in this paper.And the cooling capacity,the outlet temperature of chilling water,pressure drop and CO2 mass quality are simulated and compared with the experiment values.The model is modified according to the comparison results.Then the model is utilized to do optimization calculation for CO2 evaporator.And the effect of tube diameter and tube length on the ratio of cooling capacity to weight and pressure drop are mainly analyzed.The results show that the ratio of cooling capacity to weight and the pressure drop both decrease with the increase of tube diameter.While with the increase of tube length,the ratio of cooling capacity to weight goes up quickly at first and reaches the maximum value at the tube length of 1.4m or so.And the pressure drop is raised with the increase of tube length.As the two factors of the ratio of cooling capacity to weight and pressure drop are considered comprehensively,it is suited to select small diameter tube and long tube length for CO2 evaporator.