Research On Cooling Method Of Electronics Based On Jet Impingement

The cooling of generally complex electronic systems has become a tough challenge and a development bottleneck indeed, resulting from the combined effects of increasing high-power, heat fluxes, miniaturisation and the striving for zero defects. Electronic equipment overheating or thermal defect has become a major reason for electronic products' failure. The jet impingement heat transfer has become well established as a high performance technique for cooling comparing with normal heat transport methods. It has become a viable candidate for high-powered electronic cooling solutions. Numerous studies have been conducted to investigate the air impinging jet under condition of large aperture and high Reynolds number. However, Air jet coming from tiny diameter circular jet and impinging on the heat transfer surface with middle and low Reynolds number and its application to cooling electronics were studied in this paper. The main works are as follows:(1) Heat transfer of air impinging jet has been studied by experiment systematically. The experimental system was constructed which contains of jet generator, simulative test chip and temperature acquisition part. The experimental measurement error was analyzed and discovered that heat sink thermal resistance (θ_ab) and Nusselt number(Nu), respectively, the relative error not exceeding 3.43% and 8.77%. Heat transfer characteristics of confined single impinging jet with three small circular diameter which is lmm,2mm and 3mm, and multiple jets with arrangements of circular and square which every jet is circular and diameter is 1mm were experimental studied. Many physical and geometric parameters were changed to investigate their influence on heat transfer. Heat transfer criteria equation of confined impinging jet in stagnation region and average transfer coefficient of multi-jets is less than the single impinging jet with the same flow flux, heat transfer of the plate uphill part varied major with jet angle were concluded. Experiments were performed to investigate the turbulent fluid flow and heat transfer from three pin-fin heat sink geometries with air impingement cooling. Results for the average heat transfer coefficient were correlated in terms of Reynolds number and geometric parameters of the heat sinks. Parameters influencing to thermal resistance of heat sink were analyzed. The experimental results show that the method of air impinging jet combining with heat sink has a very significant advantage in comparison with the traditional air-cooling.(2) A detail numerical simulation study of heat transfer due to confined impinging small circular jet was presented. Numerical computations were performed by using several different turbulence models. The numerical results based on the RNG k-εturbulence model showed reasonable agreement with the experimental data for local heat transfer coefficient distributions. The confined air impinging jets with nozzle diameter from 1mm to 5mm, Reynolds number from 1000 to 15000 and swirling impinging jet with tiny nozzle were systematically and numerically simulated with RNG k-εmodel. Nusselt number correlations in both stagnation region and the whole heat transfer area were obtained. Numerical simulation results show that heat transfer characteristics of the tiny nozzle impinging jet represents scale effects, average heat transfer coefficient of swirling jet impingement is less than that without swirl velocity and heat transfer on the surface become uniform. RNG k-εmodel is also suitable for numerical simulation of heat sinks impingement. Minimizing thermal resistance of pin-fin heat sinks for impingement was studied. These calculations took into consideration design parameters including fin height, the number of rows and geometrical shape.(3) A theoretical methodology of optimization the geometry of the pin-fin heat sink was performed numerically. The methodology was integrated by the CFD and mathematical optimization method carried out by means of the sequential quadratic programming(SQP) which is widely used in the constrained nonlinear optimization problem. The flow and thermal fields are predicted using CFD. This method can solve the constraints with the single or multiple objective function optimization problems. The design optimization of the 8×8 pin-fins heat sink is performed. The fin height, fin width, and basement thickness are chosen as the design variables and the pressure drop and thermal resistance are adopted as the objective functions and minimized simultaneously. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: fin width is 4.16mm, fin height is 19.0mm and basement thickness is 3.73mm.(4) The air impinging jet for electronic cooling application is studied. A simplified heat transfer model of Flip-Chip BGA packaging was built up. The impinging jet cooling effect was analyzed by Thermal Profile method. When Re is 4000,8000 and 12000 respectively, The simulation results show that cooling effect of the single jet impinging on the surface of the chip is limited. The air jet impinging on heat sink is better and the chip power increases 118.8%, 116.7 % and 123.5 % respectively. Air jet impinging to heat sink can be directly applied to cooling of high-heat-flux electronic packaging with middle and low powerThe objective of the present study is to provide a physical insight into heat transfer effects and to facilitate the validation of electronics cooling. The research conclusions in this paper provide a systematic theoretical and experimental basis for impinging jet cooling used in electronics and have significant theoretical and practical value.This work was supported by the National Natural Science Foundation of China (No. 50376076).