Thermal and hydraulic characteristics of multiple row spiral finned tube heat exchangers

Abstract

An experimental investigation for the thermal and hydraulic characteristics of a spiral finned-tube heat exchanger was performed to understand its cooling performance for a developed novel defrosting technique. Two identical spiral finned-tube heat exchangers were manufactured; one having four rows and other having five rows. Both heat exchangers tubes were arranged inline. The heat exchangers had a tube diameter of 9.36 mm, spiral fins of 23.4 mm outer diameter, and 3.6 mm fin pitch (277 fins/m). The overall heat transfer coefficient was calculated using the measured temperatures and flow rates of each stream, and utilizing the logarithmic mean temperature difference method. The air-side heat transfer coefficient was determined using the calculated overall heat transfer coefficient and the tube-side heat transfer coefficient. The air-side pressure drop across the heat exchanger was also measured using a differential pressure digital manometer. The experimental data covered Reynolds number range of 1500 to 6000 and a Prandtl number of 0.7. Empirical correlations of Nusselt number, Colburn factor and friction factor versus Reynolds number were developed using least squares regression. The results showed that there is no significant variation in air-side heat transfer coefficient for the four and five rows spiral finned-tube heat exchanger and their Colburn factor is almost constant over the tested range of Reynolds number.