Employing an ejector to recover the expansion work of the auto-cascade refrigeration cycle is a feasible method to improve the system performance. The system operation characteristics are closely relevant to the ejector geometry parameters. In order to obtain the critical structure parameters influencing the freezer's pull-down performance, experimental research was conducted on an ejector-enhanced auto-cascade refrigeration cycle applied in a low-temperature freezer. The impacts of the ejector nozzle throat, mixing chamber diameter and length, and the nozzle exit position on the system's pull-down and steady operation characteristics were explored. The experimental results illustrated that the cooling rate and the attainable freezing temperature were mainly influenced by the nozzle throat and mixing chamber length instead of the nozzle exit position and mixing chamber diameter. The nozzle throat diameter of 0.52 mm and the mixing chamber length of 25 mm was optimal concerning the fastest cool-down rate and lowest freezing temperature of -61.2 °C. At the early phase of the pull-down process, a small mixing chamber diameter would cause the ejector malfunction of the pressure lift. There was a worst nozzle exit position of slowing down the pull-down speed, rising the freezing temperature, and reducing the system COP and exergy efficiency at the given operations. The ejector yielded the maximum pressure lift ratio of 1.196 and the entrainment ratio of 0.523 at the optimal ejector geometries. This work would be helpful to guide the ejector structure optimization for the ejector-enhanced auto-cascade low-temperature freezers.

采用喷射器回收自复叠制冷循环的膨胀功是提高系统性能的一种可行方法。系统运行特性与喷射器几何参数密切相关。为了获得影响冷冻机下拉性能的关键结构参数，对应用于低温冷冻机的喷射器增强自复叠制冷循环进行了实验研究。探讨了喷射器喷嘴喉部、混合室直径和长度以及喷嘴出口位置对系统下拉和稳定运行特性的影响。实验结果表明，冷却速度和可达到的冷冻温度主要受喷嘴喉部和混合室长度的影响，而不是喷嘴出口位置和混合室直径。喷嘴喉径 0.52 mm 和混合室长度 25 mm 是最佳冷却速度和最低冷冻温度 -61.2 °C。在下拉过程的早期阶段，较小的混合室直径会导致压力提升的喷射器故障。在给定的操作中，存在一个最差的喷嘴出口位置，即降低下拉速度、升高冷冻温度并降低系统 COP 和火用效率。在最佳喷射器几何形状下，喷射器产生了 1.196 的最大压力提升比和 0.523 的夹带比。