Optimization of injection holes in symmetric and asymmetric scroll compressors with vapor injection

A simplified numerical model was developed to analyze the optimum injection-hole diameter and angle for symmetric and asymmetric scroll compressors with vapor injection. The present numerical model was validated by comparing the predictions with the measured data for a water-to-water heat pump. The optimized injection-hole angle in the symmetric scroll compressor was much lower than the intuitively observed optimal value of 360° because late injection caused significant backward flow to the injection port. The asymmetric scroll compressor showed a relatively short injection period compared with the symmetric scroll compressor, yielding an unfavorable effect on system performance due to the lower injection mass flow rate. Therefore, in the asymmetric scroll compressor, an increase in the total injection-hole area is a good solution to overcome the performance degradation from short injection periods by increasing the injection-hole diameter and the number of injection holes as well.