| With the development of the society and the improvement of living standards, the small electronic device has been widely used in all aspects of people's lives, and computers, televisions, mobile phones and other flooded with people's lives, has become an integral part of society today. At the same time, the reliability of these indispensable electronic products has become the focus of attention. According to statistics, the majority of component failure, or even damage to the electronic devices because the internal temperature is too high. Therefore, in order to meet the needs of our society and people's lives and allow small electronic devices to serve for our life better, the key to ensuring the reliability of electronic products is effective heat dissipation of small electronic equipments.Natural convection heat transfer problem in closed square cavity within heat sources which is abstracted out of the application background of small electronic devices cooling is studied by numerical simulation and experiment. The question were studied in several aspects by Fluent software, and the changes in the aspect ratio of the cavity, the height dimension of the heat source and the position in the horizontal and vertical direction were simulated. We analyzed simulation results, and summarized heat transfer rules. Choose typical works for experimental study by holographic interferometry photography and smoke visualization method, and analysis heat transfer mechanism by results. And then, by comparing the simulation results and experimental results we summarized the natural convection heat transfer law in the enclosed square cavity for providing technical reference for further optimization.Firstly, the question of natural convection heat transfer in closed rectangular cavity with double inner source was studied by numerical simulation, and we could get the following conclusions:When the temperature difference between the heat source and the low temperature of the wall is 5?, namely Ra is 3000, medium in closed cavity is a steady flow state. The scroll doesn't appear in velocity vector field which is perpendicular to the short axis and the temperature distribution changes more obvious with the smaller ratio of length, height and width. There are two scrolls in the cavity and distributed on both sides of two heat sources when the ratio of length, height and width is 2:1:1. And there are four scrolls in the cavity and distributed on both sides and in the middle of two heat sources when the ratio of length, height and width is 4:1:1, and the ratio is larger, the temperature distribution changes smaller. With the increase of the ratio, the scrolls in section perpendicular to the long axis widen. By monitoring the average Nusselt number of the top surface it can be drew that, with the increase of the ratio of length, height and width, the average Nusselt number of the top surface is decreasing, which shows that the ratio is smaller, the effect of the convective heat transfer in the top surface is better.The height of the heat source in the closed cavity is higher, the temperature distribution changes more obviously. No matter how highly heat changes, there aren't the complete scroll in the vector field of the velocity perpendicular to the short axis when the radio of length, height and width was 1:1:1; As the heat height increases, the two scrolls in the vector field of the velocity perpendicular to the long axis become larger gradually. By monitoring the average Nusselt number of the top surface it can be drew that, with the increase of the heat height, the average Nusselt number of the top surface is increasing, which shows that the height is bigger, the effect of the convective heat transfer in the top surface is better.With horizontal distance between heat source and the section of wide by height increases, the temperature distribution changes significantly, then blurs. No matter what changes the horizontal distance, there are two scrolls in velocity vector field of perpendicular to the short axis. When the horizontal distance is smaller, the scrolls appear in the middle of two heat sources, and narrow as the distance of the two became smaller. When the horizontal distance is bigger, scrolls appear on both sides of the two heat sources, and widen as the distance of the two become smaller. The scrolls on both sides of the two heat sources clear first, then there is a ablation trend with horizontal distance increasing in velocity vector field of perpendicular to the long axis. By monitoring the average Nusselt number of the top surface it can be drew that with the increase of horizontal distance, the average Nusselt number of the top surface decrease first and then increase, and the number take a minimum when the distance is 0.5H, which shows that the effect of the convective heat transfer in the top surface is worst at that time.With vertical distance between heat source and the bottom surface increases, the temperature distribution changes significantly. No matter what changes the vertical distance, there are two scrolls in velocity vector field of perpendicular to the short axis. The scrolls on both sides of the two heat sources clear first, and there is an upward trend with vertical distance increasing in velocity vector field of perpendicular to the long axis. By monitoring the average Nusselt number of the top surface it can be drew that with the increase of the vertical distance, the average Nusselt number of the top surface increase, which shows that the effect of the convective heat transfer in the top surface is better with the bigger distance.Then, the question of natural convection heat transfer in closed rectangular cavity with double inner source is studied by experiment with holographic interferometry photography and smoke visualization method, and it can be got the following conclusions:The Reynolds number is larger, the isotherm are steeper. There forms a scroll both sides of the double heat sources in velocity vector field of perpendicular to the short axis. The ratio of length, height and width increases, the scrolls widen and the rotation speed decreases. It also likes that in velocity vector field of perpendicular to the long axis. When the horizontal distance between heat source and the section of wide by height is 0.3H, there form a narrow scroll both sides of the two heat sources in velocity vector field of perpendicular to the short axis. a scroll is formed on the left and right sides of the heat source in velocity vector field of perpendicular to the long axis. When the horizontal distance is 0.7H, the scrolls in velocity vector field of perpendicular to the short axis are wider, and those in velocity vector field of perpendicular to the long axis are not obvious, which shows that the nearly flow field is influenced by the two heat sources due to the short distance between these. When the height of the heat source is 0.3H, there are two clear scrolls with upper position in velocity vector field of perpendicular to the short axis and two unclear and smaller scrolls with upper position in velocity vector field of perpendicular to the long axis which shows that the nearly flow field is influenced by the short distance between the two heat sources and the small space of the cavity. Through all the experimental results compared with the simulation results of the same working conditions, the flow field forms are almost identical, which validate the reliability of conclusions.The detailed study in the above aspects have some theoretical reference value to natural Convection in small space and small electronic equipment cooling problems. |
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