Effective cooling of electronic equipment has emerged as a challenging and constraining problem of the 21st century. This paper reports the experimental and numerical investigations carried out to study the feasibility and effectiveness of steady and unsteady air jet impingement cooling used in high-power electronics. The results obtained from numerical studies are validated with the values obtained from experimental studies. Studies have been conducted to see the effects of parameters such as the Reynolds number, the period of pulse, and the ratio of jet spacing to diameter (Z/ D) on the heat transfer characteristics. The Reynolds number is varied between 10 000 and 20 000 and the period of pulse is varied between 2 and 10 s. It is found that in both steady and unsteady jets, an optimum cooling is obtained when the Z/ D ratio is 5. For a Reynolds of 20 000, the stagnation heat transfer coefficient increases by 25% when an unsteady jet is used instead of a steady jet. A correlation is proposed for the Nusselt number in terms of the Reynolds number and this is valid for air as the cooling medium.Index Terms-Convergence of numerical methods, power electronics, pulse generation.

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Cooling of electronics and micro-electronics devices is an important task in our present world. Synthetic jet is a relatively new technique for electronic chip cooling which synthesizes stagnant air to form a jet resulted from periodic oscillations of a diaphragm in a cavity. Synthetic jet cooling increases the rate of heat transfer as compared to other cooling techniques. The impingement heat transfer characteristics of a synthetic jet is studying in this work. Synthetic jet is driven by a piston-cylinder arrangement a through circular nozzle for the impingement of jet on the heated surface. Air is considered as the cooling medium. Heat flux is taken as 8000W/m2. Numerical simulations and experimental methods are conducted to study the effect of various distance between the orifice and the heated plated(Z). A circular orifice is used to study the characteristics of convective heat transfer. The results are verified by the time history of convective heat transfer characteristic and validated with experimental results. The model was simulated to investigate the dispersion of heat flow on the walls using a mathematical turbulent model of k- ω SST. The Reynolds number (Re) is in the range of 4000-8000 based on average velocity, while the normalized impinging distance varies between 2D to 10 D The results shows the significant influence of Z/D ratio and sinusoidal wave frequencies to the heat transfer rate obtained. Experimental and numerical investigations is carried out to study the variation of Nusselt number with jet velocity. It is found that the Z/D ratio at 6 gives the maximum amount of cooling for a flat plate.

Jet impingement is one of the best methods for achieving high heat transfer coefficient in a single phase and has been a topic of active research for several decades, involving both experiments and computations. Most of the research on multiple jets have been carried out for an array of jets in the high Reynolds number regime. Experimental and numerical investigations were carried out to study the effect of inline three jet array impinging on a flat plate with varying Reynolds Number. Air was considered as the cooling medium. This study investigates the fluid flow and heat transfer characteristics of circular and square jet arrays impinging orthogonally on a flat-plate with inline arrangements. The number of jets is 3. The Reynolds number is varied from 3000 to 6000. The numerical methodology is validated using the experimental local Nusselt number distribution for inline three jet array with the same geometry and boundary conditions. In this work, circular and square of equal hydraulic diameters were selected for a comparative study. The results reveal that square jet array has better heat transfer characteristics compared to a circular array. The optimum value of jet to target plate distance is 6 times the jet diameter for both circular and square jet array. Also, the optimum value of pitch to diameter ratio is 2.