| As the total amount of global data soars year by year,data centers are becoming more and more indispensable in today’s information era.The high data volume and high computing power carried by the data center make the thermal conditions of the server chips worse.At the same time,in order to solve the problem of the thermal conditions of the data center servers,the cooling system brings high power consumption of non-IT equipment,which is unfit for energy saving and emission reduction needs of the new era.Aiming at the dilemma of data center cooling,this thesis analyzes and summarizes the advantages of existing data center cooling solutions,proposes a two-phase flow cooling system for data center servers with active-passive mode switching,and describes the system level,component-level and chip-level of the cooling system in detail.Also,the cooling system in active and passive mode and the working principle of switching between the two modes are introduced.Then,the chip-level heat dissipation optimization based on the rectangular microchannel and the heat dissipation pillars scheme is proposed,and the flow characteristics of the two-phase flow in the microchannel and(micro)heat dissipation column scheme are qualitatively analyzed,and then the corresponding optimization design is proposed.Finally,analytical modeling and numerical simulations are carried out for the cooling system in the two modes of the system,and the performance of the component-level and chip-level cooling systems is verified.For cooling systems in passive mode,the two-phase flow in the loop thermosyphon can achieve zero-power dissipation under low heat flux conditions.Based on the pressure drop equation of the two-phase flow and the approximation of the evaporation-condensation flow,the numerical simulation is carried out using the C++.The results show that the non-microchannel scheme can stably dissipate heat under the condition of the heat flux density lower than 4.25 W/cm~2,and the mass flow rate of the working fluid in the loop thermosyphon is 5.293 kg/(m~2*s).However,the high frictional pressure drop of the microchannel will affect the heat dissipation performance of the passive mode.For active two-phase flow,this thesis uses computational fluid dynamics(CFD)method to simulate the influence of working fluid flow rate,inlet volume gas fraction and source heat flux density on thermal dissipation performance of active two-phase flow.The Ansys Fluent simulation results are verified by flow pattern analysis and interpretation.The results show that the maximum temperature at the heat source is 347.91K when the working fluid flow rate is 0.05m/s,the inlet volume gas fraction is 0.2,and the source heat flux density is 23W/cm~2.This thesis also numerically calculates the optimal working fluid flow rate under different thermal conditions,providing a guidance for mode switching of the heat dissipation system.In the rectangular microchannel scheme,the thermal power,the flow rate of the working fluid and the gas content of the inlet volume are kept unchanged,and the cross-sectional area of the flow channel is kept the same as that of the non-microchannel scheme.The results show that the 1mm-wide rectangular microchannel performs the best heat dissipation efficiency,the maximum temperature of the heat source is 339.15K;the heat dissipation pillar scheme also shows better efficiency than the non-microchannel scheme.For the cylindrical heat dissipation pillar scheme with the same fluid domain as the non-microchannel scheme,the maximum temperature at the heat source is stable at 342.17K.The multi-level two-phase flow heat dissipation system switching between active and passive mode proposed in this thesis could implement both the low power consumption and high heat dissipation efficiency.Schemes of microchannels and heat dissipation pillars are proposed.Each scheme is simulated,verified and optimized.The new concept prototype in this thesis supplies the sound theoretical and engineering foundation for data center server cooling. |
