Experimental Study On Flow Around A Single Cylinder In A Microchannel

With the improvement of the integration degree of micro electronic devices,the heat generated in unit space per unit time increases sharply,which greatly reduces the safety and stability of electronic devices.Microchannel heat exchanger is a kind of high efficiency heat exchanger with compact structure and high surface to body ratio,which has been concerned by scholars in the field of microelectronics heat dissipation.Adding fins in the microchannel can not only increase the heat transfer area,but also increase the disturbance of the fluid,thus enhancing the heat transfer.Although there are a lot of related studies on microchannels and flow around cylinder,these studies have focused on microchannels without pin fins,flow around traditional-scale cylinder and flow around microcolumn group.However,there are few studies on the flow around a single micro cylinder in a microchannel and there are few reports on the difference of different flow layers and the effect of aspect ratio on the flow around a micro cylinder.In this paper,microchannels containing a single micro cylinder are designed and processed,and a flow field visualization experiment bench is set up.Micro-PIV visualization technology is used to measure the flow around a single micro cylinder in the range of 0.3 to 62.28ml/min with deionized water as working fluid.In order to reveal the mechanism of flow around the micro cylinder,the streamline,velocity field,vorticity field,turbulence intensity field of the flow around the micro cylinder are studied.The results show that the first and second critical Re for flow around the micro cylinder which aspect ratio is 1 are about 10 and 430,respectively.With the increase of Re,the length and width of the vortex increase,the wake region expands,and the vortex center moves downstream.Because of the viscous friction of the bottom of microchannel,the closer to the bottom,the lower the velocity and the more uniform the distribution of the whole flow field.The vortex length is the same at different h from the bottom of the microchannel,and the flow separation is relatively early near the bottom of the microchannel.The vortex is not closed away from the bottom of the microchannel,and the center of the vortex shifts downstream.High vorticity areas and high turbulence intensity areas appear on both sides of the micro cylinder,and as Re increases,vorticity and turbulence intensity increase.The high turbulence intensity in the wake region first appears far away from the bottom of the microchannel,and then transits to vortex shedding.Secondly,the aspect ratio has an significant influence on the flow around the micro cylinder,which is studied in this paper.The flow characteristics of the flow around micro cylinder with different aspect ratio in the range of 7<Re<430 are compared.It is found that the aspect ratio has a great influence on the streamline,vortex structure,velocity field,vorticity field and turbulence intensity field.The results show that the aspect ratio has little effect on the first critical Re of the flow around the micro cylinder,but the second critical Re increases as the aspect ratio increases.With the increase of the aspect ratio,the flow velocity,vorticity and turbulence intensity of the fluid on both sides of the cylinder increase.At the same time the vortices in the wake area develop rapidly and the vortices are not closed at h=0.5H.At high Re,the vortex in the wake region is torn,and the sub-vortex zone appears.The high turbulence intensity area converges behind the wake region and approaches the micro cylinder.This paper uses experimental methods to study the flow around the micro cylinder.By changing the factors such as Re,shooting plane,and aspect ratio,and combining the flow visualization method,the flow mechanism of the micro cylinder is explored,which provided a reliable basis for the design and optimization of the micro-channel heat exchanger.