The Study Of Flow Visualization And Heat Transfer Characteristics In Micro-pin Fin Heat Sinks

With the rapid development of science and technology,the heat load of advanced equipment,such as solar panels,semiconductor laser,computer chips and guidance radar,is increasing quickly,which causes extremely high transient heat flux density.With the limitation of the heat transfer area,traditional cooling technology is hard to meet the requirements of the advanced system in thermal design,management and control.With the advantages of high specific area,compact structure and efficient cooling efficiency,micro pin-fin heat sinks come to be one of the most effective ways to solve the problem of high flux,and become a high-profile research by international scholars.In this paper,a variety of pin fin heat sink with complex structure are designed and processed.Heat transfer mechanism of micro pin fin heat sinks are researched,and structure of the heat sinks are optimized by using CFD numerical simulation software,Micro-PIV flow visualization experiment system and the single phase flow and heat transfer test experiment system.Firstly,staggered diamond pin fins with different tail angle,circular and dropshaped micro pin fin heat sinks were processed by secondary moulding process.Micro-PIV system was utilized for flow field visualization research.Micro pin fin heat sinks with the same structure were numerical studied.The results show as follows.Under Re = 20,flow field of different structure micro pin fin array remains stability.Under Re = 140,a pair of symmetrical vortex can be found at the wake region of diamond micro pin fin with 90° tail angle and circular pin fin with longitudinal spacing of 0.44?m.Under Re = 275,small asymmetric swings arise at the tail flow field of diamond micro pin fin with 60° tail angle.Under 75 ? Re ? 275,flow field of diamond micro pin fin with 45° tail angle and drop-shaped micro pin fin remains stability,which prove that tail structure can effectively weak the boundary layer separation and vortex formation.Then,flow and heat transfer characteristics of the micro pin fin heat sinks were researched by numerical simulation.Compared with the visualization results,it can be found that drop-shaped micro pin fin with 60 ° tail angle has the minimum wall temperature.Meanwhile,the pressure drop of the drop-shaped micro pin fin is the lowest one since streamlined shape decreases form drag,and the tail structure reduces pressure loss.Under the same pump power,the thermal resistance of drop-shaped micro pin fin is the smallest among all of the heat sinks.Among diamond micro pin fin heat sinks,the one with 45 ° tail angle has the minimum pressure drop since the tail structure reduces pressure loss,and it also has the smallest thermal resistance.Secondly,by utilizing CFD,numerical simulations and analyses were used to research the flow and heat transfer characteristic in different porosity staggered circular micro pin-fin heat sinks whose hydraulic diameter is 200 ?m.The results indicate that,heat flux influnces Nu number of heat sinks by effect the flow field of heat sinks.There is barely influence on Nusselt number under the porosity of 0.743 when heat flux changes,since the distance of pin fins reduces vortex shedding velocity.With the porosity of 0.836,the Nusselt number increases with the increase of heat flux,since the vortex shedding velocity increases with the increase of heat flux,which can enhance mixing in channel.Thirdly,wing-shaped heat sinks were designed and processed based on dropshaped micro pin fin.Flow field visualization was studied along with single phase flow and heat transfer characteristics.Flow velocity presents a periodic change along the flow direction since different velocity is found on each side of the wing-shaped pin fin,which promoted mixxing in channel and enhanced heat transfer effectively.Compared with SWP-0.36,SWP-0.44 has lower thermal resistance,and better comprehensive enhancement.