EXPERIMENTAL STUDY OF HEAT TRANSFER OF AXISYMMETRIC AIR IMPINGEMENT FROM AN ORIFICE ON A MODIFIED SURFACE

Abstract

Impingement cooling jet is widely used in different industrial applications due to high rate of heat removal on the surface being subjected to impinging. Ribs are used to enhance convective heat transfer by the promotion of higher turbulence levels. The aim of present work is to perform an experimental verification of the using modified surface with ribs on heat transfer enhancement. Experiments were performed to characterize heat transfer to a normally impinging air jet on uniformly heated surfaces modified with ribs from a single orifice of different diameters D of (5, 12, 20 mm). A centrifugal blower is used for air impinging with jet velocity in the range (18.4-36 m/s). Local heat transfer distribution on the impingement surface is investigated for orifice-to-plate spacing ratio (Z/D) of (4, 6, 8, 10) using thermal infrared imaging technique. Different configurations of modified surfaces in form of ribs surface are studied in the present work which are: rectangular ribs, and circular ribs with different sizes spaced at different pitch on the target ribbed surface. Heat transfer enhancement for five rib geometries is evaluated by comparison with results for a smooth flat surface. The enhancement ratio of heat transfer, as compared to the smooth flat surface is demonstrated by a factor ranging from 1.2 to 3. It is observed that the different shape of the ribs causes different effects on heat transfer coefficient between the impinging air jet and the target plate.