Numerical Simulation Study Of Heat Transfer Enhancement In Micro-channel Heat Exchanger

With the rapid development of devices such as semiconductor technology and micro-electromechanical technology?which is abbreviated as MEMS?,large-scale or larger-scale integrated circuit devices have emerged,and the integration of devices is getting higher and higher,resulting in an increase in heat output per unit area severe,seriously affecting the working performance of equipment and shortening the life of equipment.The traditional cooling technology more and more can't meet the requirements,so the micro-channel heat exchanger came into being.In order to enhance the heat transfer efficiency of the micro-channel heat exchangers,fluent numerical simulation was used to study the influence of different flowing media?water and different concentrations of Al₂O₃-H₂O Nano-fluid?within the micro-channel flow resistance and heat transfer characteristic.First of all,the flow and heat transfer characteristics in a single laminar flow channel with different cross-sections in micro-channels were investigated.Their diameters are between 0.1 and 0.4 mm and their length is 40 mm which were selected with 12 kinds of single micro-channels.The effects of geometric parameters such as equivalent diameter,cross-section type on the flow and heat transfer characteristics in micro-channels are studied in order to get the curve of the change characteristics with Nu number,frictional resistance coefficient and so on.In the last,the best single micro-channel model with smaller flow resistance,stronger heat exchange capacity and smaller pumping power is obtained:a square cross-section micro-channel whose diameter is 0.4 mm.Secondly,in order to make a comprehensive analysis of the work situation in the best structure of single micro-channel model.The optimal micro-channel structure model is obtained by changing the spacing between the adjoining micro-channels?using three kinds of pitches:0.2 mm,0.3 mm,0.4 mm?under the condition of certain size of 8 mm×800?m×40 mm.It is found that the micro-channel heat exchanger with the interval of 0.4 mm is the best.Within the allowable range of pump power,the higher the flow rate of working fluid is,the stronger the heat exchange effect will be.Finally,on the basis of the study of micro-channel heat exchanger,a single square cross-section micro-channel with the wall thickness of 0.2 mm,the hydraulic diameter of 0.4 mm and the length of 40 mm was selected,and the concentration of the internal working fluid is 0%,0.1%,0.5%,1%.It is concluded that the Al₂O₃-H₂O Nano-fluid can not only make the micro-channel heat transfer capacity enhanced,and make the heat transfer capacity increased with the increase of volume fraction but also with the addition of the Al₂O₃-H₂O Nano-fluids didn't lead the frictional drag coefficient too much change.In the last,Nu of square cross-section micro-channels,heat transfer characteristics,the flow correlation which is between friction coefficient and each dimensionless parameter are fitted.