Heat transfer correlation for boiling flows in small rectangular horizontal channels with low aspect ratios

In the present experimental study, a correlation is proposed to represent the heat transfer coefficients of the boiling flows through horizontal rectangular channels with low aspect ratios. The gap between the upper and the lower plates of each channel ranges from 0.4 to 2 mm while the channel width being fixed to 20 mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200 kg/m(2) s and the channel walls were uniformly heated up to 15 kW/m(2). The quality range covers from 0.15 to 0.75 and the flow pattern appeared to be annular. The modified Lockhart-Martinelli correlation for the frictional pressure drop was confirmed to be within an accuracy of 20%. The heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely to be with the smaller gap size, the heat transfer rate is primarily controlled by the liquid film thickness. A modified form of the enhancement factor F for the heat transfer coefficient in the range of Re-LF less than or equal to 200 well correlates the experimental data within the deviation of 20%. The Kandlikar's flow boiling correlation covers the higher mass flux range (Re-LF > 200) with 10.7% mean deviation. (C) 2001 Published by Elsevier Science Ltd.