Abstract
This research was aimed at studying the numerical and experimental characteristics of the air flow impinging on a dimpled surface. Heat transfer enhancement between a hot surface and the air is supposed to be obtained from a dimple effect. In the experiment, 15 types of test plate were investigated at different distances between the jet and test plate (B), dimple diameter (d) and dimple distance (Er and Eθ). The testing fluid was air presented in an impinging jet flowing at Re = 1500 to 14,600. A comparison of the heat transfer coefficient was performed between the jet impingement on the dimpled surface and the flat plate. The velocity vector and the temperature contour showed the different air flow characteristics from different test plates. The highest thermal enhancement factor (TEF) was observed under the conditions of B = 2 d, d = 1 cm, Er= 2 d, Eθ = 1.5 d and Re = 1500. This TEF was obtained from the dimpled surface and was 5.5 times higher than that observed in the flat plate.
Highlights
Heat exchangers, whether large or small, play an important role in industry and in everyday life
The thermal enhancement factor (TEF) represents the ratio of heat transfer and the power ability of the fluid to flow through the heat exchanger device
The results indicate that non-Newtonian fluid is the optimum choice to obtain high heat transfer rate for laminar flow
Summary
Whether large or small, play an important role in industry and in everyday life. Our study was focused on the improvement of the heat exchanger surface This has been developed from a flat plate to a dimpled surface for generating a vortex and high turbulence intensity on the surface. This can increase the heat transfer and reduce the pressure drop. Ribs or baffles are set on the heat exchanger plate for increasing the heat transfer This can increase the pressure drop and the friction factor, leading to the production of a low thermal enhancement factor (TEF). A higher TEF cannot be obtained at a higher heat-transfer rate with a high pressure drop
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