The Heat Transfer Coefficient During Pool Boiling of Refrigerants in a Compact Heat Exchanger

Marcin Kruzel (), Tadeusz Bohdal, Krzysztof Dutkowski, Krzysztof J. Wołosz and Grzegorz Robakowski
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Marcin Kruzel: Department of Power Engineering, Koszalin University of Technology, 75-453 Koszalin, Poland
Tadeusz Bohdal: Department of Power Engineering, Koszalin University of Technology, 75-453 Koszalin, Poland
Krzysztof Dutkowski: Department of Power Engineering, Koszalin University of Technology, 75-453 Koszalin, Poland
Krzysztof J. Wołosz: CERED Centre of Excellence, Warsaw University of Technology, 09-400 Płock, Poland
Grzegorz Robakowski: Department of Power Engineering, Koszalin University of Technology, 75-453 Koszalin, Poland

Energies, 2025, vol. 18, issue 15, 1-20

Abstract: The results of experimental data on the heat transfer coefficient during the boiling of pro-ecological refrigerants in a compact tube-shell heat exchanger are presented. The boiling process occurred in the micro-space of the exchanger shell on the surface of horizontal tubes, which were heated from the inside with warm water. The flow of the refrigerant was gravity-based. The heat exchanger was practically flooded with liquid refrigerant at a saturation temperature (ts), which flowed out after evaporation in a gaseous form. The tests were conducted for four refrigerants: R1234ze, R1234yf, R134a (a high-pressure refrigerant), and HFE7100 (a low-pressure refrigerant). Thermal characteristics describing the heat transfer process throughout the entire compact heat exchanger, specifically for the boiling process itself, were developed. It was found that in the case of micro-space boiling, there is an exponential dependence of the heat transfer coefficient on the heat flux density on the heated surface. Experimental data were compared to experimental and empirical data presented in other studies. Our own empirical models were proposed to determine the heat transfer coefficient for boiling in a mini-space for individual refrigerants. The proposed calculation models were also generalized for various refrigerants by introducing the value of reduced pressure into the calculation relationship. The developed relationship enables the determination of heat transfer coefficient values during boiling in a micro-space on the surface of horizontal tubes for various refrigerants with an accuracy of ±25%.

Keywords: pool boiling; heat transfer coefficient; refrigerants; heat exchanger (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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