Pool boiling heat transfer on a reentrant cavity tube with R134a: Effects of saturation temperature under ice storage condition

Abstract

This study focused on the effects of saturation temperature under ice storage condition in heating, ventilation, and air conditioning or related industry for the R134a boiling heat transfer coefficients (HTCs) of a newly designed reentrant cavity copper tube. Experiments were conducted at saturation temperature ranging from −6.0 °C to 6.0 °C with heat flux ranging from 10.0 kW/m2 to 65.0 kW/m2 and the tube was heated with ethylene glycol–water mixture. The nominal outside diameter of the test tube was 25.14 mm, and the length in the test section was 1000 mm. Experimental results showed that the maximum increase in HTCs varies between 18% and 58% with the increase in saturation temperature by 12 °C. The enhancement factor, which is the ratio of HTC of the enhanced tube to that of plain tube, reaches its maximum at each saturation temperature. With the increase in saturation temperature from −6.0 °C to 6.0 °C, the maximum value increases from 2.2 to 2.5, and the corresponding optimum heat flux decreases from 40.0 kW/m2 to 20.0 kW/m2. The HTC shows different varying rates for experimental heat flux smaller and larger than the optimum heat flux. An exponent-function-form correlation well-fitted with the distinctive change rule is developed with a predicted error less than ±5.0%. The current study can serve as reference for industrial design and future academic studies.