Abstract:

To promote the application of ejector expansion work recovery technology， the research on the comprehensive performance of cooling and heating of the compression-ejection CO₂ heat pump system under the operating conditions of the wide temperature range of -30~50 ℃ and the expansion work recovery characteristics of the ejector is carried out in this paper. The focus is placed on analysis of the effect of the working nozzle on the adaptability of the fixed ejector to variable working conditions. The results show that under the cooling conditions， the injection coefficient decreases while the pressure lift ratio increases with the increase of the ambient temperature. Under the heating condition， with the decrease of the ambient temperature， both the injection coefficient ratio and pressure lift ratio increase first and then decrease. Under the cooling conditions， the recovered expansion work of the ejector accounts for 16.7%-37.2% of the maximum recoverable expansion work， while under the heating conditions， it accounts for 9.9%-41.3%. However， the fixed ejector designed for high-temperature cooling conditions is difficult to adapt to low-temperature heating conditions. When deviating from the design conditions， over-expansion at the nozzle outlet will result in shock wave energy loss， while under-expansion at the nozzle outlet in low-temperature heating conditions will cause the ejector to lose its entrainment effect.

Key words: electric vehicles, ejector, CO₂, adaptability, heat pump system