Laminar flow and heat transfer in a finned tube annulus

Laminar flow and heat transfer magnitudes in a finned tube annulus are obtained numerically. External circular fins on the inner tube are periodic. Pressure drop and heat transfer characteristics of the fins are obtained in the periodically fully developed region by varying geometric and flow parameters. Geometric parameters are annulus radius ratio (0.3 to 0.5), fin height/annular gap (0.33 to 0.67) and fin spacing/annular gap (2 to 5). Flow parameters are Reynolds number (100 to 1000) and Prandtl number (1 to 5). Comparisons are made with a plain tube annulus having the same length, heat transfer surface area, volume flow rate, and Reynolds number. The entire inter-fin space was found to be occupied by recirculating flow except at Reynolds numbers less than 500. A major contribution to heat transfer is made from the fin side at the downstream end. At Prandtl numbers less than 2, the use of fins may not be justified because the increase in pressure drop is more pronounced than the increase in heat transfer. At a Reynolds number of 1000 and A Prandtl number of 5, the heat transfer increases by a factor of 3.1, while the pressure drop increases by a factor of 2.3. © 1989