Principal effective factors on the dynamic pull-down performance of a zeotropic mixture based ultra-low temperature freezer

Abstract

Abstract Cascade technology with less than -80℃ has risen sharply with the development of the biomedical industry. Although appropriate refrigerant-couples and corresponding improving-approaches have been presented, dynamic parameters of operating stability and security rather than COP are more important to evaluate an ultra-low temperature freezer. Refrigerant-couple R404A/R508A with pentane as oil carrier in the low stage is employed to be working fluids in this study, and the main dynamic parameters during the pull-down process are clearly discussed experimentally, especially the laws of highest discharge temperatures in both subsystems. Results demonstrate that the highest discharge temperature is generally appeared in the first half of the cooling-process, which should be the key-point of the discharge temperature protection. Additionally, the operating stability and security would be highly strengthened with decreasing charging amount, increasing zeotropic component fraction, and declining heat collector opening, however, corresponding negative effects will be definitely caused to a great extent.