Analyzing the Applicability of Procedures for Calculating the Coefficient of Heat Transfer in Boiling of Multicomponent Working Fluids
Multicomponent working fluids are widely used in refrigeration and cryogenic technologies. A recuperative heat exchanger, the device influencing the efficiency of the entire low-temperature installation, is one of the main elements of these systems. It serves to regenerate the cold: the reverse (low-pressure) flow cools the direct (high-pressure) flow. In the direct flow, the flow of working fluid condenses, and in the reverse flow it boils. Thus, it is important to know how the design of this heat exchanger shall be determined in designing low-temperature systems. However, the boiling and condensation of mixtures still remain poorly studied due to a small amount of available experimental data and, accordingly, due to a limited number of empirical correlations describing these processes. As a result, those who develop heat exchangers for low-temperature systems operating on mixed working fluids encounter certain difficulties in designing such devices. The article describes various existing correlations describing the boiling of multicomponent working fluids at low temperatures and compares the results obtained using these correlations with the existing experimental data on the boiling of mixtures. The values of the heat transfer coefficient calculated using the Mishra method have better agreement with the experimental data in comparison with the results obtained from other correlations. However, since the experimental data are available for a small number of experiments, in which mixtures having the same composition, with the same operating pressures and mass flowrates are used, it would be incorrect to make a final conclusion about the applicability of the correlations. The analysis carried out in this article paper is a step toward detailed understanding of the applicability of correlations for multicomponent mixtures. More complete experimental data obtained for the same composition under different conditions are needed in order to understand the effect of each parameter on the boiling heat transfer coefficient. Reliable data on the heat transfer coefficient are necessary in designing heat exchangers for low-temperature installations operating on a mixed refrigerant.