Double pipe heat exchangers are widely used in various heat transfer applications starting from oil refineries to automobile radiators because of simplicity in design. The rate of heat transfer in a double pipe heat exchanger can be increased by using various heat transfer augmentation techniques out of which dimples is identified as a passive method with least value of pressure drop in comparison with other techniques. In the present work, the performance of double pipe heat exchanger with dimples of various shapes and configurations are investigated using the CFD package ANSYS® FLUENT 16.0 and the arrangement providing efficient heat transfer is identified through CFD results and experimentally validated along with the plain tube model. The inline arrangement with counter flow is chosen for the study with dimple dimension of depth to diameter ratio 0.26. Out of the various pitches ranging from 300mm to 100mm and dimple shapes considered such as hemispherical, square, triangular and elliptical, the hemispherical dimpled tube with a pitch of 150mm arranged in two rows is identified to be the most efficient. The experimental results are in good agreement with the CFD results and hence the studies show that performance of double pipe heat exchangers can be enhanced with the selected dimpled configuration which improves the heat transfer rate by creating turbulence in the flow at a minimum pressure drop.
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