Research on Effects of Vapor Injection on Twin-screw Compressor Performance

Twin-screw compressors have been widely used in refrigeration systems and heat pump systems due to their unique advantages. Vapor injection (VI) technique could effectively increase the cooling or heating capacity of a refrigeration system. But in the meantime, because the VI will increase power consumption, the efficiency of the compressor will not be equally increased with the VI pressure. The effects of VI pressure on the performance of twin-screw compressor are generally obtained by one-dimensional numerical simulations or experiments. In this paper, the working process of twin-screw compressor with VI is simulated by computational fluid dynamics (CFD) technology. A homogeneous multiphase flow model coupled with a volume-of-fluid (VOF) method for interface capturing has been applied to determine the shapes of the gas-liquid interface and to compute the turbulent flow fields in twin-screw compressor. The influences of the VI pressure and VI position on the performance of the twin-screw compressor are analyzed. Comparing the P-θ indicator diagram and the performance parameters of the compressor with the experimental results, it can be found that the results of the CFD simulation are consistent with the experimental data. At the same VI position, as the VI pressure increases, the power of the compressor will gradually increase, and the efficiency of the compressor will rise first and then drop. Therefore, an optimum VI pressure can be found to reach the peak value of compressor efficiency. Under the same VI pressure, there is also an optimal VI position to maximize the efficiency of the compressor.