Experimental study of single-phase pressure drop and heat transfer in a micro-fin tube

Abstract

The single-phase pressure drop and heat transfer in a micro-fin tube were measured using oil and water as the working fluids. The Prandtl number varied from 3.2 to 220 and the Reynolds number ranged from 2500 to 90,000. The results show that there is a critical Reynolds number, Re cr , for heat transfer enhancement. For Re < Re cr , the heat transfer in the micro-fin tube is the same as that in a smooth tube, but for Reynolds numbers higher than Re cr , the heat transfer in the micro-fin tube is gradually enhanced compared with a smooth tube. It reaches more than twice that in a smooth tube for Reynolds numbers greater than 30,000 with water as the working fluid. The Nusselt number is proportional to Pr 0.56 in the enhanced region and is proportional to Pr 0.3 in the non-enhanced region. For the high Prandtl number working fluid (oil, 80 < Pr < 220 ), the critical Reynolds number for heat transfer enhancement is about 6000, while for the low Prandtl number working fluid (water, 3.2 < Pr < 5.8 ), the critical Reynolds number for heat transfer enhancement is about 10,000. The friction factors in the micro-fin tube are almost the same as for a smooth tube for Reynolds numbers below 10,000. For Reynolds numbers higher than 30,000, the friction factor is about 40–50% higher than for a smooth tube.