Study On Structure Optimization Of Micro-pin Fin For Heat Transfer Enhancement And Single And Two Phase Flow Visualization Based On Micro-PIV System

With the development of technology, the higher integration degree of electronicdevices results in more heat flux. The traditional cooler design and production hasbeen unable to meet the rapid development of modern technology. As themicro-processing technology is getting more sophisticated, more complex,micro-channel heat sink has become goes into the international heat transfer academicresearch. The microscale flow test technology has become the focus of research athome and abroad.The content of this paper includes two parts: the flow and heat transfer of two kindmicro pin fin heat sink; microscale single-phase and two-phase flow testingtechniques.For the first part of the contents, we propose long-diamond shaped micro pin finheat sink and a combined micro pin fin heat sink.During the study, the silicon long-diamond shaped micro pin fin was processed.Experimental research and numerical simulation about the flow and heat transfer oflong-diamond shaped micro pin fin were performed. The results showed that: withinthe range of the number of experiments Re, the heat transfer coefficient of thelong-diamond shaped micro pin fin increases with Re. with same Reynolds number,the heat flux has no effect on heat transfer coefficient. Thermal resistance decreasedwith the increased pump power. The thermal resistance decreased faster when pumppower is small. And the thermal resistance becomes a certain value when the pumppower increases to a point. There is no total thermal resistance difference for differentheat fluxes. Nu increases with the increase of Re. Compared with the same sizecircular, and diamond micro pin fin,45o long-diamond micro pin fin has the bestrheat transfer performance. The long-diamond design avoids the vortex sheddingwhich will cause the resistance loss. Also, the long-diamond design extends the heattransfer area and conductivity of solid. Thereby it enhanced the heat transfer effect.A numerical simulation about the heat transfer characteristic for combined micropin fin has been done. The heat transfer effect of the combined micro-pin fin withdifferent angles decreased as the Re increasing among the present Re range. Therefore,this new structure was more appropriate for the condition of low Re. The combinedmicro-pin fin could damage the development of boundary layer by the little triangularmicro-pin fins, it could form longitudinal vortexs in the tail of circular micro-pin finand decrease backflow, enhance the effect of disturbance and mixing. The combinedmicro-pin fin improved the synergy of flow field and tempreture field; the heattransfer effect could be enhanced greatly for both the whole and the local. Thecombined micro-pin fin improved the synergy of flow field and tempreture field; theheat transfer effect could be enhanced greatly for both the whole and the local. The second part of this paper is mainly based on Micro-PIV flow visualizationexperimental system. Two parts of flow field testing were performed: the ingle-phasefluid flow field measurement of in-lined circular micro pin fin and liquid-liquidtwo-phase mixture flow field measurement of Y-import microchannel.In the course of the study, device of in-lined circular micro pin fin was processedusing PDMS material. And its internal flow field testing was performed. The resultsshow that: the velocity along the direction of the main channel at thefirst to secondrow of in-lined circular micro pin fin changes periodically. At lower Reynoldsnumbers, the vorticity distribution area is small. Vorticity mainly distributes at thearea along the flow of the left and right sides of the micropin fin, and the vorticitystrength is almost the same. At low Reynolds numbers, the vorticity diffusioncapacityin the direction perpendicular to the flow is greater than that at large Reynoldsnumber.A liquid-liquid phase flow field visualization test was performed in PDMS materialY imported micro channel. The results show that the slug flow in Y imported microchanne is regular shape, uniform size. The formation of the liquid projectile hasexperienced growth, scouring, and stretching, shedding process. With the constantflow rate ratio, the axial length of slug decreased with the increased continuous phaseCa; with the constant continuous phase Ca, the axial length of slug increase with theincreased flow ratio.