Abstract
Frost formation degrades the performance of heat exchangers greatly, thus influencing the cryogenic refrigerator. Different from frost formation on the evaporator surface, the growth and migration of frost layer inside the heat exchanger is of low temperature and humidity. In addition to the constantly changing boundary conditions, the effective prediction is difficult. In the present study, a numerical model was proposed to analyze the frost formation in the cryogenic heat exchanger of a reverse Brayton air refrigerator. Under small amounts of moisture, the growing of frost layer was simulated through the numerical heat and mass transfer by adopting semiempirical correlations. The frost formation model was inserted into the transient model of refrigerator, and numerical calculations were performed on heat and mass transfer rates, and growth and migration of frost layers in forced convection conditions. Experiments were conducted under different air humidity to investigate the frost formation and verify the numerical model. Through the model, the influences of frosting on the refrigerator were evaluated under different moisture contents and running time. It can be used to predict the performance of air refrigerators with low humidity and provide a basis for improving the system operation and efficiency.
Highlights
The heat transfer in reverse Brayton cycles has the characteristics of no phase change and the one between the cold and hot fluids in the cryogenic regenerator is gas–gas [1,2]
The frost growth model was newly proposed based on the numerical heat transfer and experimentally
The frost growth model was newly proposed based on the numerical heat transfer the semi-empirical correlations by adopting the Lewis analogy formula
Summary
The heat transfer in reverse Brayton cycles has the characteristics of no phase change and the one between the cold and hot fluids in the cryogenic regenerator is gas–gas [1,2]. As the gas–gas heat transfer coefficient is small, the cryogenic regenerator of the reverse Brayton refrigerator is required to have great heat transfer area. Great specific surface area, compactness and light weight, the plate-fin heat exchanger is widely used in the reverse Brayton refrigerator [3,4]. The cryogenic heat exchanger is a very important equipment in low temperature equipment. It affects the economy of the cryogenic equipment, and affects the possibility of process realization [5,6,7,8].
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