跨临界二氧化碳压缩机热力性能仿真与分析

Modeling and Analysis of Trans-critical CO_2 Reciprocating Compressor

针对跨临界二氧化碳半封闭式往复式活塞压缩机建立了一个通用数学模型,既包括热力学模块,也包括机械模块。热力学模块主要描述气缸内部的气体压缩过程。机械模块包括运动学模型和曲轴连杆机构模型,考虑了轴承上的功耗损失。采用一台压缩机样机对模型进行了不同运行工况下的实验验证,结果显示压缩机流量和耗功的最大误差分别不超过5%和8%。通过仿真分析了变结构和变工况条件下的压缩机性能,结果表明:在不同的运行工况下,存在最佳缸径行程比;容积效率和等熵效率都随着转速的增加而下降;吸排气阀门内径存在最佳值;对于容积效率的影响,吸气阀间隙比排气阀间隙更大,活塞与汽缸间隙比活塞环与汽缸间隙更大。

A comprehensive physics-based model for a semi-hermetic CO2 reciprocating compressor is presented. The model is composed of two major sub modules, the thermal module and the mechanical module. The thermal module is used to simulate the vapor compression process inside the cylinder, while the mechanical module is to simulate the frictional loss happened in the bearing connected to the cylin- der. Extensive experimental validation of the compressor model were carried out for a CO2 prototype compressor under different operating conditions. The maximum deviations of mass flow rate and power consumption are within 3% and 8%, respectively. Furthermore, para- metric study was conducted to investigate the compressor performance as a function of the stroke-to-bore ratio and the gap between cylinder and piston under different operating conditions. The results indicated that there is an optimal stroke-to-bore ratio under different operating conditions. Both volumetric efficiency and isentropic efficiency fall with the increasing compressor speed. There are optimal diameters for suction and discharge valves. On the volumetric efficiency, the gap between suction valve and valve seat has heavier impact than the gap between discharge valve and valve seat, while the gap between piston and cylinder has greater impact than the gap between cylinder and cylinder ring. The analysis would help further improvement on the compressor design.