Heat transfer enhancement on a flat surface with axisymmetric detached ribs by normal impingement of circular air jet

摘要

An experimental investigation is carried out to study the heat transfer enhancement from a flat surface with axisymmetric detached rib-rougheners due to normal impingement of circular air jet. A single jet from nozzle of length-to-diameter ratio (l/d) of 83 is chosen. Effect of rib width (w), rib height (e), pitch between the ribs (p), location of the first rib from the stagnation point and clearance under the rib (c) on the local heat transfer distribution is studied. Local heat transfer distribution on the impingement surface is investigated for jet-to-plate distances (z/d) varying from 0.5 to 6 using thermal infrared camera. Turbulence intensity using hot-wire anemometer and wall static pressure measurements are reported for the rib configuration in which maximum heat transfer was observed. Contrary to the results of smooth surface, there is a continuous increase in the heat transfer coefficient from the stagnation point in the stagnation region. This trend is well substantiated by the flow distribution in this region. The ratio of average Nusselt numbers of ribbed and smooth surface is seen to increase with Reynolds number. Correlation is developed for Nusselt numbers averaged upto an r/d of 1.5. Enhancements in heat transfer decrease for higher z/d s.