Study on Free Convection Heat Transfer in a Finned Tube Array

Abstract

We have been developing a free convection air cooled heat exchanger without power supply to improve economic efficiency and mechanical reliability. However, this heat exchanger requires a larger installation area than the forced draft type air cooled heat exchanger since a large heating surface is needed to compensate for the small heat transfer by natural convection. Therefore, we have been investigating a heat exchanger consisting of an array of finned tubes and chimney to increase the heat transfer coefficient. Since the heat transfer characteristics of finned tube arrays have not been clarified, we conducted experiments with a finned tube array to determine the relation between the configuration of finned tubes and the heat transfer coefficient of a tube array. The results showed that the average heat transfer coefficient increased with pitch in the vertical direction, and became constant when the pitch was over five times the fin diameter. The average heat transfer coefficient was about 1.4 times higher than that of a single finned tube in free space. The ratio of the average heat transfer coefficient of the finned tube array with chimney to that of a single finned tube was found to be independent of the difference in temperature between the tube surface and air.

An Experimental Investigation of Increasing the Thermal Efficiency of a Finned Tube Heat Exchanger by Using the Chimney Effect

“…Thanks to the use of a hydraulic coupling (5), it was possible to set different flows in the circulation pumps (18). The flow rate of the required volume of water, on the heat exchanger side, could be set using a manual setting valve (16). The heat exchanger (13) was thermally insulated with 80 mm-thick rock wool with a thermal conductivity coefficient of 0.036 W/(mK) so that all the heat supplied to the exchanger would be transferred to the environment through the extended surface.…”

“…One of the few articles that deals with the study of heat transfer from a bundle of finned tubes to air under free convection conditions was conducted by Katsuki et al [16]. They proposed a heat exchanger based on 25.4 mm diameter tubes with circular fins and a thickness of 0.8 mm and 58.4 mm in diameter that operate only under free convection conditions.…”

Natural convection heat transfer performance of additively manufactured tube bundle heat exchangers with novel fin design

“…One of the few studies dealing with the heat transfer from finned tube bundles under natural convection was performed by Katsuki et al [20]. The heat transfer of the tube bundle increased with the tube pitch in vertical direction and stays constant as the tube pitch is greater than five times the tube diameter.…”