Problem description and geometric model 2.1 The geometric model is as shown. There are 5 rectangular electronic components distributed in a small space. The height of the small space is H = 25mm. = 15mm, width d = 5mm, the distance between electronic components D = l5mm, the distance between the electronic components and the inlet and outlet are 7.5mm, the size of each electronic component is 5mmX 15mm, the material is ceramic (the thermal physical parameters are : Density is 500 know / m3, specific heat is 0.84fc // know thermal conductivity is 0.21W / m ruler). The heating power of each electronic component is 30W (equivalent to a heat generation rate of 4xl05W / m3), and the height of the baffle is h. This paper divides the heat dissipation of electronic components in a small space at 0.2, 0.4, 0.5, 0.7, 0.9 discuss.
2.2 Control equations The control equations for fluid flow and heat transfer in a small space are: continuity equation: momentum equation: >> direction velocity component, pressure and temperature; Hanxin / are thermal expansion coefficient, gravity acceleration, viscosity coefficient, thermal diffusion Coefficient, density, and internal heat source terms.
Solution method This paper studies the fluid solid conjugate heat transfer problem, and simultaneously solves the continuity equation, momentum equation and energy equation.
The following assumptions are made in the calculation: the physical parameters of air are constant: the fluid has no slip on the wall surface: the flow of the fluid is a steady flow; the heat generation rate of electronic components is the isothermal generation rate; the influence of buoyancy is considered in the direction of gravity To satisfy the Boussinesq assumption.
The solution of the equation is based on the finite volume method in CFD for discretization, the standard Af turbulence model is selected, and the control equation is solved using the SIMPLEC algorithm. The inlet boundary conditions give the average inlet air velocity, inlet temperature, and equivalent values.
The outlet boundary condition is set to a relative pressure of 0, the heat generation rate of the electronic component is given, the other wall surfaces are insulated wall surfaces, and the wall surface adopts a non-slip boundary condition. In the rectangular space of 0lmX.25m of forced flow cooling system, there are 10,000 grid cells and 10251 nodes.
Analysis of the results 4.1 Analysis of the cooling effect of the electronic components It can be seen that the average Nu of the surface of the five electronic components when h / H = 0C without baffle) is lower than the average Nu of the surface of the electronic component when h / H = 0.2. In addition, the average Nu of the surface of the No. 1 electronic component near the entrance is the largest, the cooling effect is the best, the cooling effect of the No. 5 electronic component near the exit is the second, and the cooling effect of the No. 4 electronic component is the worst. This shows that the baffle can effectively reduce the temperature level of electronic components.
(C) Temperature field and velocity vector field diagram at h / H = 0.4 The synergy principle of the temperature field and velocity vector field diagram in a small space is expressed as follows: the performance of convective heat transfer depends not only on the velocity and physical properties of the fluid but also on the fluid and solid wall The temperature difference depends on the degree of synergy between the fluid velocity field and the fluid heat flow field. Under the same speed and temperature boundary conditions, the better their synergy, the higher the heat exchange intensity. The synergy between the velocity field and the temperature gradient field is as follows: the angle cosine of the velocity vector and the temperature gradient vector is as large as possible, that is, the angle between the two vectors is as small as possible. 0 The fluid velocity profile and the temperature profile are as uniform as possible (at the maximum flow rate Under certain conditions of temperature difference).
As shown in (a), when h / H = 0 (without adding baffles), the horizontal temperature of the air in the mainstream area in a small space is relatively uniform, and the lateral temperature gradient is small, but the longitudinal temperature is extremely uneven, and the longitudinal temperature gradient is very Large, the angle between the velocity vector and the heat flow vector is approximately 90. At this time, the speed field and the temperature gradient field of the air have the lowest degree of synergy, and the cooling effect of the electronic component is also the worst.
As shown in (b)-(f), after the baffle is installed, the horizontal temperature gradient of the air in the main flow area in a small space increases, while the vertical temperature gradient decreases; the angle between the velocity vector and the heat flow vector is less than that of the baffle The plate time is obviously reduced, and the degree of synergy between the velocity field and the temperature gradient field is improved. In addition, with the gradual increase of the baffle height, the lateral temperature gradient gradually increases, while the longitudinal temperature gradient gradually decreases, the angle between the velocity vector and the heat flow vector also gradually decreases, and the degree of synergy between the velocity field and the temperature gradient field increases , The cooling effect of electronic components has been greatly improved.
It can be seen that as the height of the baffle increases, the maximum temperature of the electronic component gradually decreases. It can be seen that as the height of the baffle increases, the average Nu number between the electronic component and the air gradually increases. This further shows that after the baffle is added, the degree of synergy between the velocity field and the temperature gradient field increases, and the heat transfer is strengthened.
The static pressure difference between inlet and outlet varies with the height of the baffle. Sr varies with the height of the baffle. 2 Analysis of inlet and outlet static pressure As shown, as the height of the baffle increases, the inlet and outlet static pressure difference increases first, then decreases, and then increases again. Without baffles, the minimum static pressure difference at the inlet and outlet is 36.65 Pa; with the increase of the height of the baffle, the static pressure difference at the inlet and outlet gradually increases, reaching a maximum value when the height of the baffle is h / H = 0.4 At this time, the static pressure difference between the inlet and the outlet is 159.37Pa; thereafter, with the increase of the baffle height, the static pressure difference between the inlet and the outlet gradually decreases, and the height of the baffle is h / H = 0. The static pressure difference between the inlet and the outlet is 146.77 Pa; thereafter, with the increase of the height of the baffle, the static pressure difference between the inlet and the outlet increases sharply.
4.3 Analysis of the cooling effect of electronic components To reflect the cooling effect of electronic components, while strengthening the cooling of electronic components, the resistance or power consumption should be as small as possible, which is more conducive to energy saving and engineering applications, because this is to describe and compare different convection In the case of heat exchange, the cooling effect of electronic components is quoted by a judging standard, that is, the cooling effect number of electronic components: Nu-which is the average Nusselt number of heat exchange on the surface of all electronic components, rmax is the highest of electronic components Temperature, AP is the static pressure difference between fluid inlet and outlet.
As shown, with the increase of the height of the baffle, the cooling effect number Sr of the electronic component first increases, and reaches a maximum value when h / H = 0.7, and then with the increase of the height of the baffle, the cooling effect of the electronic component The number Sr decreases. When h / H = 0. 7, the cooling effect number Sr of the electronic component is the largest. Therefore, the best size of the baffle is h / H = 0. Conclusion In this paper, the CFD software is used to discuss the flow and heat transfer in a small space with the heat dissipation of the microelectronic component as the background. The flow field and temperature field discuss the heat dissipation of electronic components in a small space without baffles and baffles. The conclusions are as follows: after adding baffles in a small space, it can obviously strengthen heat transfer, so it is a way to strengthen heat transfer that deserves attention; the degree of synergy between the velocity field and the temperature gradient field plays a very important role in heat transfer After the baffle is added, the synergy degree between the velocity field and the temperature gradient field is improved, which is beneficial to the cooling of electronic components.
After the baffle is installed, the static pressure drop at the inlet and outlet is increased while strengthening the heat transfer; C4) Considering the temperature level of the electronic components and the static pressure drop at the inlet and outlet, when the height of the baffle is h / When H = 0. 7, the cooling effect Sr of the electronic component is the largest, so the best size of the baffle is h / H = 0.
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