Single-phase and boiling heat transfer and pressure drop from dimpled vertical surfaces.

摘要

An experimental study of convective heat transfer to water from flat and dimpled vertical copper surfaces has been performed. Two configurations were investigated. The first configuration was conducted between parallel plates spaced 35 mm apart, while the second occurred in a short rectangular channel having a depth, width, and length of 2, 12 and 229 mm, respectively. Both configurations employed one-sided, asymmetric heating over an area 10 mm wide and 150 mm long with an unheated starting length of 38 mm. The principal effects on internal heat transfer and pressure drop for dimple depths of 0.51 and 0.89 mm and dimple spacings of 5, 10, and 20 mm have been determined. The dimples, or spherical depressions, measured 5 mm in diameter at the surface and were arranged in a single, in-line column. Single-phase laminar free and turbulent forced convection were investigated for the parallel plate case, while single-phase forced convection and thermosiphonic nucleate boiling were examined in the rectangular channel.;Experiments of natural convection from the vertical surfaces showed no distinguishable difference in heat transfer between the flat surface and the dimpled surfaces for either the external or internal configuration. Conversely, results from the forced convection experiments showed substantial heat transfer enhancement for the dimpled surfaces compared to that of the flat surface in both external and internal flow. For external flow, the dimpled surface with 5 mm spacings and 0.89 mm depths enhanced heat transfer by as much as 62% in comparison to the correlation