Boiling flow and heat transfer in rectangular periodic expansion-constriction microchannels
In order to explore the boiling flow and heat transfer characteristics in the rectangular periodic expansion-constriction microchannel,rectangular periodic expansion-constriction microchannels of different sizes are established,and deionized water is used as the working fluid to carry out numerical simulation under the conditions of inlet velocity of 0.2 m/s and heat flux of 50 W/cm2.The results show that there are enlarged and contracted cross-sectional structures in the rectangular periodic expansion-constriction on microchannels.The enlarged part of the microchannel provides a nucleation site,which is conducive to bubble nucleation and increases the heat exchange area.With the increase of the periodic frequency of the expansion-constriction structure,the more intense the coupled heat transfer between cavitation and boiling in the microchannel,there are still more small bubbles in the middle and downstream regions of the channel.The number of small bubbles along the channel increases,the gas content increases,and the heat transfer performance continues to improve.In addition,the maximum temperature of the wall along the microchannel gradually decreases,and the temperature distribution along the channel become more uniform.The rectangular periodic expansion-constriction microchannel reduces the contact area between the bubble and the wall,and reduces the frictional pressure drop between the two phases.But the expansion-constriction of the microchannel increases the resistance to flow in the channel.The pressure drop in the expansion-constriction microchannel increases with the increase of the y of the structural parameters.At the same time,the comprehensive performance of flow heat transfer in the microchannel increases first and then decreases with the increase of the frequency of the expansion-constriction channel.When the structural parameter of y is 0.2,the comprehensive performance of the rectangular periodic expansion-constriction microchannel is the best,which is 34％higher than that of the rectangular straight microchannel.
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