Simulation Study On The Physical Mechanism Of Enhanced Heat Transfer In Bubble Periodic Bounce Disturbed Flow

With the rapid development of microelectronic chip technology, total chip size is reduced and the corresponding heat flux increases exponentially. Instead of conventional heat dissipation methods, micro-channel heat sinks could be used in chip cooling. The multiphase fluids flow in micro-channel is one of the research hotspots in micro-channel heat sinks. This study is based on the micro-channel model also includes the fluid of bubbles. The water is used in liquid phase and the air is used in gas phase. We also establish the physical model of micro-channel with serrated surfaces. The cyclical movement of bubbles is also simulated. The main research contents are as follows:The establishment of coupled physical model. According to the features of motion of bubbles, a micro-channel with serrated surface was established. In comparison to planar micro-channel, the serrated surface is found to disrupt the temperature boundary layer near the wall. Four kinds of angles of micro-channel with serrated surface are also established. According to the analysis of the velocity field and the bubble field, the micro-channel with 15° serrated surface is chosen as the final physical model of the numerical simulation of bubble movement.Analysis of influencing factors of bubble flow. This study simulates the flow and heat transfer of a single bubble and divides the single motion cycle of the bubble crossing the micro-channel into two stages(bubble collision and upspring). After each stage is analyzed, we found that the heat transfer is greatly strengthened when the bubble moves in the part of collision. Also, bubble moves along the wall and push the temperature boundary away from the wall in such stage, thus it can enhance the performance of the heat transfer near the wall. While the time-dependent changes of the pressure drop and the average temperature of heating surface were analyzed.Analysis of influencing factors of bubble flow. The difference in average temperature of heating surface between time beginning and end of the movement of bubble is analyzed through the change of initial velocity of liquid phase. We found that the heated surface temperature decrease, while the rate of flow increase, which verified the enhancement of heat transfer by the movement of bubbles. By comparing the change of temperature boundary layer near the wall before and after bubble collision in the liquid field of different flow velocity, we found that the high liquid velocity is beneficial to the enhancement of heat transfer. For the case of the thickness of the temperature boundary layer further increased when single bubble is in micro-channel, we proposed a multi bubble flow model. In this model, the temperature boundary layer was analyzed. And we also analyzed the time-dependent change of the pressure drop as well as the average temperature of heating surface. The analysis result shows that multi bubbles keep in a cycle movement which results in a greater heat transfer.