| As the Internet continues to develop,big data,artificial intelligence,and 5G are emerging and facilitating various aspects of human life.As a carrier of information,data centers are developing rapidly like mushrooms after rain,showing an upward trend in both quantity and scale.The development of technology has led to an increase in the heat flux density of heating elements per unit area,which poses a huge challenge to the cooling system of data centers.Traditional air-cooled and water-cooled methods are difficult to meet the heat dissipation requirements of high heat flux density data centers.Immersion phase-change liquid cooling is favored by people due to its low energy consumption,high efficiency,and low noise.Immersion phase-change cooling system mainly immerses the heating element in the liquid cooling cabinet,and uses a low-boiling-point,high-latentheat cooling medium to directly contact with the heating element for heat exchange,and transfers the heat to the external condensing system.This article conducts research on the immersion phase-change cooling system through a combination of numerical simulation and experimental methods.The immersion phase-change cooling system is physically modeled,and different cooling fluids are compared and analyzed.HFE-7100 produced by 3M is selected as the cooling medium for numerical simulation and experimental processes,which absorbs the heat emitted by the heating element and exchanges heat with cooling water of different temperatures to dissipate the absorbed heat to the outside of the system.The numerical simulation method is used to explore the effects of different cooling water inlet temperatures and flow rates on the heat dissipation performance of the entire immersion phase-change cooling system,monitoring changes in the surface temperature of the heat source,temperature rise of the inlet and outlet cooling water,gas-phase volume fraction of the HFE-7100 on the surface of the heat source,surface heat flux density,and heat transfer coefficient.The simulation results show that the surface temperature of the heat source reaches the steady state first under the condition of low cooling water inlet temperature,and the best inlet temperature for the entire immersion phase-change cooling system is 24°C.The optimal inlet flow rate for the entire system is 0.8 m/s.The effects of changes in internal system saturation pressure on the surface temperature and heat transfer coefficient of each server in the system are analyzed through numerical simulation,and the optimal operating saturation pressure of the system is 0.15 MPa.Furthermore,an experimental platform for the immersion phase-change cooling system is built to explore the effects of different cooling water inlet flow rates and inlet water temperatures on cooling performance.The experimental results are consistent with the simulation results,indicating that the lower the cooling water inlet temperature,the lower the temperature at which the system stops heating up and reaches a steady state,and the higher the cooling water inlet flow rate,the earlier the system reaches a steady state.The cooling water inlet temperature mainly affects the surface temperature of the heat source after stability is achieved,while the inlet flow rate mainly affects the heat transfer time.Finally,the physical modeling of the arrangement of server motherboards in both horizontal and vertical arrangements is simulated using numerical simulation methods.The simulation results show that the vertical arrangement of server motherboards is conducive to the detachment and upward process of bubbles,while in the horizontal arrangement,the bubbles generated by the lower layer of motherboards gather between the upper layers of motherboards,causing poor discharge of bubbles and affecting the heat transfer efficiency.The best distance between motherboards in the vertical arrangement is 15 mm,which ensures the heat dissipation effect of the system while maximizing the use of space. |
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