Heat transfer and flow visualization of conventional and swirling impinging jets.

摘要

A swirling impinging jet design was developed to enhance impinging jet heat transfer. Heat transfer and flow visualization of conventional and swirling impinging jets were experimentally investigated.;The heat transfer performance of the conventional impinging jets was experimentally studied under various working conditions: jet diameter from 3.17 to 12.7 mm; Reynolds number from ;A swirling impinging jet caused a saddle-shaped local Nusselt number distribution and significantly enhanced the heat transfer coefficient, with respect to both radial uniformity and local values, compared to a conventional impinging jet. The experimental parameters for swirling jets included: jet diameter, 12.7 mm; swirl angles, ;In order to further understand the impinging flow and heat transfer, a series of flow visualization experiments of conventional and swirling impinging jets were performed, employing three visualization techniques, smoke flow, smoke wires, and water jet simulation. The recorded images illustrated the causes of the measured saddle-shaped radial distributions of the local and average Nusselt numbers. The mechanism for heat transfer enhancement using a swirling impinging jet over a conventional impinging jet is that a "donut flow" is induced on the impinged surface by the swirl component in a swirling impinging jet, and it increases heat transfer coefficient while makes it more uniform.;Based on heat transfer measurement and the flow visualization, the models of the flow and heat transfer of both conventional and swirling impinging jets were developed.