An experimental investigation of nucleate boiling heat transfer from an enhanced cylindrical surface

In this study, nucleate boiling of the refrigerant R123 on the enhanced surface with 3-D micro-structures of a cylindrical tube is experimentally investigated. Water flows inside the tube and provides heat to the refrigerant outside the tube to boil. Experiments were performed at three pressures corresponding to the saturation temperatures of 4.4, 11.1, and 17.8 degrees C respectively to obtain the quantitative temperature effect on the boiling heat transfer coefficient. The results showed that boiling heat transfer on the enhanced surface can be divided into the low-heat-flux region (q '' < 25 kW/m(2)) and the high-heat-flux region (q '' > 25 kW/m2). Within the low-heat-flux region, the boiling heat transfer coefficients increase linearly with increasing heat flux and the influence of the saturation temperature is insignificant. As the heat flux enters into the high-heat-flux region, the boiling heat transfer coefficients remain nearly flat as the heat flux increases within this region and the effect of saturation temperature is considerable. The boiling heat transfer coefficients at 11.1 and 17.8 degrees C are respectively 8.0-10.0% higher and 22.9-24.2% higher than the boiling heat transfer coefficients at 4.4 degrees C within the range of heat flux 25-62 kW/m2, which is equivalent to 1.2-1.8% increase in the boiling heat transfer coefficient per degree increase in the saturation temperature. In addition, for comparison with the enhanced tube, the experiments of boiling on the smooth surface of a plain tube were also performed for the saturation temperature of 4.4 degrees C. Results showed that the boiling heat transfer coefficients on the enhanced tube are 6-10 times those on the plain tube within the range of heat flux of 12-62 kW/m(2). (C) 2013 Elsevier Ltd. All rights reserved.