Experimental research on the pull-down performance of an ejector enhanced auto-cascade refrigeration system for low-temperature freezer

This paper presents an experimental investigation on pull-down performance of an ejector enhanced auto-cascade refrigeration cycle for low-temperature freezer application. The pull-down performances of the freezer established on the ejector enhanced cycle and conventional auto-cascade refrigeration cycle were compared. Additionally, operation behaviors of the ejector and the new cycle based freezer at different mixture concentrations and throttle valve openings were investigated. The results indicated that ejector enhanced system exhibited shorter pull-down time and lower freezer air temperature after continuous operation in comparison with the conventional system. And the pull-down time was saved by 34.4% and the energy consumption of the compressor was reduced by 29.6% at the desired freezing temperature of −40 °C.The largest time average values of the pressure lift ratio and entrainment ratio reached up to 2.854 and 1.340, and the time average compression ratio of the compressor was reduced by 11.6% due to the effective pressure lifting effect of the ejector. The optimal mass fraction ratio of 30%/70% for the mixture R23/R134a was proposed with respect to the shortest pull-down time. This research may offer good guidelines for further improving the performance of the auto-cascade refrigeration system in low-temperature freezer.