Research On Flow Boiling Heat Transfer Characteristics Of Complex Microchannels

The continuous development of the microelectronics industry has led to a sharp rise in the amount of heat generated by the chip,which has placed higher requirements on the performance of the heat sink.Micro-channel flow boiling cooling technology is based on the principle of phase change.heat is taken away by the phase change of the liquid phase.Compared with other cooling methods,micro-channel flow boiling cooling requires less mass flow under the s ame thermal load.Unit The space heat flux is large and the structure is compact.The flow boiling problem of microchannels involves the intersection of multiple disciplines.By studying the straight microchannels,researchers have obtained the correlation model of heat transfer and pressure drop.For complex micro-channel heat exchange devices,it is difficult to guide the design through the existing straight-channel heat exchange correlation and pressure drop models.This paper uses numerical simulation to study the flow boiling in microchannels,introduces a phase change mass transfer model through UDF module,and simulates the flow boiling in straight microchannels to complete the model verification.The common Z-shaped channel in the complex channel is selected as the research object to study the influence of structural parameters,working fluid velocity and heat flow density on the heat transfer and flow stability of the channel.The results show that the larger the angle of the Z-shaped channel,the better the heat transfer effect and the more uniform the temperature distribution on the wall.However,the increase of the angle will increase the piezoresistance,the stability of the two-phase flow will deteriorate,and the frequency and amplitude of the periodic pressure oscillations.Will increase.The influence of flow velocity on flow boiling was studied in the range of inlet velocity V = 0.3 ? 0.9 m / s.It was found that the increase of flow velocity promoted the heat transfer.Under the condition of low flow velocity,the liquid film on the wall is easy to evaporate and cause the heat transfer.Thermal deterioration,increasing the flow rate can improve the uniformity of the wall temperature distribution,reduce the average temperature of the wall surface,avoid the occurrence of local hot spots,and increase the flow rate.It will also increase the piezoresistance,strengthen the oscillation of the two-phase flow system,and reduce the reliability of the system.In the range of heat flux density q = 20 ? 80 W / cm2,the effect of heat flux density on flow boiling is studied.When the heat flux density increases to a certain value,heat transfer deterioration occurs.When the heat flux density increases,the piezoresistance increases and the flow increases.Increased instability.Aiming at the wall contact characteristics,the flow boiling heat transfer characteristics of the super-hydrophilic wall surface and the conventional wall surface under different heat flux densities were studied respectively.A s a result,the surface of the super-hydrophilic wall has no significant effect on the flow stability of the flow boiling,and enhances the heat transfer,and the higher the heat flux density,the more obvious the promoting effect.The study found that the volume fraction of gas phase in the channel is relatively small under low heat flow density,and there is a thick liquid film between the bubble and the wall surface.When the heat flow density increases,the gas phase in the channel increases,and the li quid film between the bubble and the wall gradually changes.Thin,even some areas will evaporate.Due to the excellent hydrophilicity of the superhydrophilic wall surface,the liquid phase is easy to gather at the wall surface,and the wall surface is not easy to evaporate,which improves the distribution of the liquid film and avoids deterioration of heat transfer.The occurrence of the phenomenon.