Subcooled flow boiling is used in many cooling systems due to its high cooling effect. In these systems, different substances such as water and refrigerants can be used as working fluid. However, most synthetic refrigerants such as CFCs and HCFCs have undesirable impact on the environment, so natural refrigerants like CO2 are often used in different refrigeration and heat pump systems worldwide. CO2 can also be used as working fluid in the cooling system based on subcooled boiling, and it is very important to accurately analyze the heat transfer behavior of CO2.
In contrast to previous Computational Fluid Dynamics (CFD) studies concerned with subcooled flow boiling of water or synthetic refrigerants in a vertical tube, Ma Kuk Chol, a researcher at the Faculty of Heat Engineering, has proposed a mathematical model to analyze subcooled flow boiling characteristics of CO2 in a horizontal tube.
He built a mathematical model by using the Eulerian multi-phase model coupled with the RPI model, and utilized the IAC model included in ANSYS FLUENT v.19.3 in order to consider the coalescence-breakup and evaporation-condensation effects of bubbles.
The important thing in building the CFD model for subcooled flow boiling heat transfer of CO2 was to determine correct values of bubble waiting time coefficient and critical Weber number. The analysis indicated that the former 0.8 and the latter 0.25 produced the most accurate results for subcooled flow boiling of CO2.
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