Abstract
In recent years, water (R718) as a kind of natural refrigerant—which is environmentally-friendly, safe and cheap—has been reconsidered by scholars. The systems of using water as the refrigerant, such as water vapor compression refrigeration and heat pump systems run at sub-atmospheric pressure. So, the research on water boiling heat transfer at sub-atmospheric pressure has been an important issue. There are many research papers on the evaporation of water, but there is a lack of data on the characteristics at sub-atmospheric pressures, especially lower than 3 kPa (the saturation temperature is 24 °C). In this paper, the experimental research on water boiling heat transfer on a horizontal copper rod surface at 1.8–3.3 kPa is presented. Regression equations of the boiling heat transfer coefficient are obtained based on the experimental data, which are convenient for practical application.
Highlights
As global warming has raised more critical concerns in recent years, refrigerants, such as R22, R410A and R134a with high global warming potential (GWP), are facing the challenge of being phased out
Experimental data indicated that when the heat flux was constant, the boiling heat transfer coefficient gradually decreased with decreasing pressure [3,4,5]
The boiling heat transfer coefficients of water on a horizontal copper rod at sub-atmospheric pressure are calculated by Equation (1) according to the experimental data
Summary
As global warming has raised more critical concerns in recent years, refrigerants, such as R22, R410A and R134a with high global warming potential (GWP), are facing the challenge of being phased out. Experimental data indicated that when the heat flux was constant, the boiling heat transfer coefficient gradually decreased with decreasing pressure [3,4,5] It plays a significant role for the optimization of the whole system that the evaporator heat transfer enhancement in refrigeration and heat pump systems working at sub-atmospheric pressure. It shows that there was correlation research, but the research that applies to work conditions of the evaporator in water vapor compression refrigeration or heat pump systems is still blank. The correlations of water boiling heat transfer coefficient on a horizontal copper tube surface at sub-atmospheric pressure are still unknown. This experiment will guide the heat transfer enhancement of the evaporator working at sub-atmospheric pressure
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