CFD Analysis of Turbulent Heat Transfer through Rectangular Channel on Shape Optimization of Different Dimple Shape

Conventional sources of energy have been depleting at an alarming rate, which makes further sustainable fulfillment of requirement of energy very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry and solar energy heater. Convective heat transfer can be enhanced passively by changing flow geometry, or by increasing heat transfer coefficient between the heat transferring surface and the heat carrier fluid. Another possibility for increasing heat transfer to fluid is to employ extended surfaces. The use of dimple as fins in a duct increases the heat transfer area and breaks the laminar sub-layer creating local wall turbulence. The heat transfer rate is improved but pressure drops is increased as well. A numerical investigation has been performed to study the effects of different dimple shapes on heat transfer and fluid flow characteristics through transversely roughened rectangular channels for Reynolds number ranging from 10000 to 30000 and subjected to uniform heat flux of 1000 W/m2. Considering single-phase approach, the two-dimensional continuity, Navier-Stokes, and energy equations developed for the physical model have been solved by using the finite volume method (FVM). The optimization was carried out by using various dimple shapes (rectangular, triangular, wedge pointing upstream, and wedge pointing downstream) in in-line and six different aspect ratios (w/e = 5, 3.334, 2.5, 2, 1.667 and 1) to reach the optimal geometry of the dimple with maximum Performance Evaluation Criterion (PEC). The highest PEC was obtained for the triangular dimple channel with w/e = 1.667 (i.e. dimple height e = 6mm & w = 10mm) at Re = 10000.