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ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

International Heat Transfer Conference 13
August, 13-18, 2006, Sydney, Australia

Heat Transfer and Flow Characteristics of Impinging Jet with Triangular Multi-tabs

Get access (open in a dialog) DOI: 10.1615/IHTC13.p16.170
12 pages

要約

The effect of triangular multi-tabs attached at the perimeter of a jet nozzle on the heat transfer enhancement was investigated experimentally. The flow structure modified by the tabs was visualized with a smoke-wire method. The heat transfer rate on the impinging plate under uniform heat flux condition was measured with fine thermocouples. Four different types of jet nozzle having 0, 4, 6 and 8 tabs were tested at a jet Reynolds number of Re = 15,000. The local and average Nusselt numbers were increased with increasing the number of tabs. At the nozzle-to-plate distance of L/D = 2, the average Nusselt number was increased about 9.5 % at Re = 15,000 in the impingement region for the case of 4 tabs attachment. As the nozzle-to-plate distance (L/D) increases, however, the heat transfer enhancement effect was reduced. As the protrusion depth of tabs into the jet flow increases, the heat transfer rate was also enhanced, when the nozzle-to-plate distance was smaller than L/D = 6. In order to reveal the mechanism of heat transfer enhancement, a stereoscopic PIV (SPIV) system was employed to measure the flow structure modification of the 3-D turbulent impinging jet quantitatively. The SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get the spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. The 4-tab jet flow accelerated along the tab lines and the turbulence intensity was increased in the regions just behind the tabs and highly turbulent flow motion is maintained up to the downstream location of L/D = 4. This indicates that the spacing between adjacent tabs in the 4-tab system was relatively sufficient to allow the vortices to develop independently and enhanced turbulent mixing effect. The entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet with 4 tabs, increasing the entrainment rate about 8.5%.