Convective heat transfer study on the spiral finned tube heat exchanger under various fin pitch arrangements

Abstract

Tube-type compact heat exchangers are one of the most commonly used heat exchangers in the industry. Compact heat exchangers are known for their large surface area to volume ratios allowing more optimal heat transfer rate. This study examines both the coefficient and the rate of convective heat transfer on the outer surface of a tube-type compact heat exchanger. The heat exchanger was configured in the sharp turns and spiral fin which is varied in pitch. The Fin pitches were 1 cm, 2 cm, 3 cm, 5 cm, and 7 cm. The length of the heat exchanger pass was 30 cm with a turn length was 8.2 cm and the total length of the heat exchanger was 6 m. Heat exchangers were made using galvanized pipes with an inside diameter (Di) 20 mm and an outside diameter (Do) of 22 mm, fins are made using aluminium with a thickness of 0.3 mm. Water was maintained at a constant temperature of 80 °C and circulated into the heat exchanger with a flow rate of 0.4 L/s. The air was blown using a fan with varying speeds of 2.4 m/s, 2.8 m/s and 3.4 m/s (the ambient air temperature was 28 °C). The results showed that the highest convection heat transfer coefficient and heat transfer rate occurred in the heat exchanger with a fin pitch of 2 cm, because the turbulence was more optimal and fewer airflow losses. In the heat exchanger with a fin pitch of 3 cm, 5 cm and 7 cm has a large gap between the fins so that turbulence is not optimal while in the heat exchanger with a fin pitch of 1 cm the gap between the fins is too small so that it inhibits the rate of airflow.