Numerical Study On Flow And Heat Transfer Characteristics Of Microchannel Heat Sink And Thermal-Stress Analysis

With the background of electronic device cooling techniques,this paper numerically studied microchannel heat sink for high power density chip cooling.Flow and heat transfer characteristics,thermal performance and cooling capacity were studied aiming to each microchannel heat sink model with different types and structures.Based on that,thermal stress distributions of microchannel heat sinks were also analyzed.Research in this paper mainly included: Firstly,flow and heat transfer characteristics,cooling capacity and thermal performance of traditional microchannel heat sink,rectangular micro pin-fin heat sink,jet-cooling heat sink and double layer microchannel heat sink were compared under various inlet velocity;the merits and demerits of each microchannel heat sink model were analyzed.Secondly,the effect of slot structure of microchannel heat sink on its flow and heat transfer characteristics were numerically studied.Thirdly,aiming to rectangular microchannel heat sink,the effect of rectangular pin fin geometric features on flow and heat transfer characteristics and cooling capacity were numerically studied and optimized from three respects,which are pin-fin distribution porosity,pin-fin section size and pin-fin located angle,respectively.Finally,thermal stress of rectangular micro pin-fin heat sink were analyzed;the optimized micro pin-fin heat sinks with different tip clearance were designed;and their flow and heat transfer characteristics,cooling capacity,thermal stress distribution were analyzed and compared.Characteristics of flow and heat transfer in four typical microchannel heat sinks and thermal performance were investigated by numerical method.The numerical results show that it is positive for improving thermal performance to fill metal foam in the inlet header by strengthening flow distribution uniformity.In comparison to traditional microchannel rows,the pin-fin array way of microchannels arrangement can strengthen the thermal performance of the overall heat sink with less pressure drop and better heat transfer capacity.Although the jetting cooling heat sink technology possesses the best chip cooling capacity,it is not proposed for the field of microchannel cooling because of a huge flowing resistant.Numerical results show that heat transfer performance in microchannel heat sink can be improved after slot structure was set up.Besides,slot structures have great influence on the flow and heat transfer.Overall,increasing rectangular slot width and trapezoid base angle are two effective ways to enhance heat transfer and improve thermal performance.Numerical studies on geometry features of micro pin fin heat sink were carried out and the characteristics of flowing and heat transfer in three types of micro pin fin heat sinks which are respectively optimized through different pin-fin porosity,equivalent diameter and pin-fin located angle were investigated.Numerical results indicated that there are apparent influences of both above geometry features on the characteristics of flowing and heat transfer in micro pin fin heat sink and there exist the optimum values for both porosity and angle.The optimum values of porosity and rotated angle are about 0.75 and 30 o respectively for the simulation cases.Moreover,model with smaller equivalent diameter at the same pin-fin porosity holds not only better flow and heat transfer characteristics,but also the feature of lower flow resistance and higher thermal performance.Aiming to traditional micro pin fin heat sink,the thermal stress concentration in cover plate of microchannel heat sink is distinctly in the corresponding heating area and the edge area of outlying pin fins.Micro pin fin heat sink with same pin-fin tip clearance holds better performance in decreasing the thermal strain and thermal stress in cover plate at the cost of lower cooling capacity.The ladder-shape clearance model can not only achieve good flow and heat transfer characteristic,cooling capacity,but also efficient in decreasing the thermal stress in cover plate.In general,the lower ladder-shape model processes best cooling capacity with good thermal performance and low thermal stress field in cover plate.