Local heat transfer for finned-tube heat exchangers using oval tubes

摘要

This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted convection heat transfer in a narow rectangular duct fitted with either a cirular tube or an eelliptical tube in cross-flow. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddennly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat condition model. Heat transfer results were obtained over an airflow rate ranging f rom 1.56 x 10~(-3) to 15.6 x 10~(-3) kg/s. These flow rates correspond to a duct height Reynolds number range of 630 - 6300 with a duct height of 1.106 cm and a duct width-to-height ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is t. The elliptical tube had an aspect ratio of 3:1 and a/H equal to 4.33. Results presented in this paper reveal visual and quantitative details of local finsurface heat transfer distributions in the vicinity of circular and oval tubes and their relationship to the complex horseshoe vortex system that forms in the flow stagnation region. Fin surface stagnation-region Nusselt numbers are shown to be proportional to the square-root of Reynolds number.