Micromilling Formation And Performance Of High Performance Reentrant Microchannels

With the rapid development of modern science and technology,the microminiaturization,multi-function and high-power of electronic chips have resulted in rapid increasing of heat flux.How to enhance the heat transfer performance and reduce costs has became the key questions in the development of microchannels.In view of this,this thesis proposed a pin fin-stagger reentrant microchannels and a micromilling method.The micromilling of microchannels,heat transfer performance of microchannels were symmetrically studied.The main contents in this thesis were as follows:(1)Designed the sizes of pin fin-stagger reentrant microchannels,reentrant microchannels,and rectangular microchannels,and proposed the scheme of micromilling for microchannels.The basic theories of micromilling were analyzed,it was found the size effect,minimum uncut chip thickness effects were caused by rounded cutting edge radius.Furthermore,the ideal instantaneous cutting thickness were calculated and it was found that the instantaneous cutting thickness will change in the micromilling process.(2)The burr formation locations and mechanisms by using the micro flat milling cutter were systematically assessed together with the Deform finite element analysis results.And experiments were performed to investigate the effects of processing parameters on burr,surface roughness of machined surface.Besides,the morphology of chips and tool wear were also studied.Finally,the optimum processing parameters were selected:n=15000r/min,f=90mm/min,ap= 100?m,and the rectangular microchannels was fabricated successfully.(3)The burr formation locations and mechanisms by using the ball end milling cutter were systematically assessed together with the Deform finite element analysis results.And experiments were performed to investigate the effects of processing parameters on machined surfaced quality.Furthermore,the morphology of chips and tool wear were also studied.Finally,the optimum processing parameters were selected:n=15000r/min,f=25mm/min,and the pin fin-stagger reentrant microchannels and reentrant microchannels were fabricated successfully.(4)The performance testing platform was set up,the heat transfer performance of the pin fin-stagger reentrant microchannels and reentrant microchannels were studied compared with rectangular microchannels.Results shows both the pin fin-stagger reentrant microchannels and reentrant microchannels can lower down the wall temperature(2.8?7.2? and 0.7?4.2?,respectively)and enhance the single phase convective heat transfer performance(1.2?2.0 times and 1.1?1.7 times,respectively).Besides,both two kinds of reentrant microchannels can lower down the incipient boiling point,enhance the two-phase heat transfer performance under certain conditions.Furthermore,it was found that the pin fin-stagger reentrant microchannels can mitigate the flow instabilities greatly.