Research On Liquid Flow And Heat Transfer Characteristics In Narrow Slits

With the rapid development of modern technology and the requirement of electronic industry,high heat flux and space restriction on diversification,there are increasingly investigations focusing on the reduced the size of heat exchanger and the heat transfer mechanism in these high efficiency structures in recent years.Compared with traditional size in heat exchangers,the obvious advantages of minichannel are small size,which can be widely used in various fields,especially in the cooling of electronic devices;liquid in mini-channel can rapidly develop into nucleate boiling,which has high efficiency and powerful heat transfer;it is mass production and low cost.Therefore,it is widely used in microelectronic engineering,chemical industry,aerospace,bioengineering and other fields.A numerical investigation has been carried out in this paper,the laminar flow model and the finite volume method are used to discretize the equations,SIMPLE algorithm is used to deal with the coupling problem of velocity and pressure to examine the characteristics of flow and heat transfer in rectangular minichannel.On the basis of physical model,the effects of flow velocity to aspect ratio and inclination angle on flow resistance and heat transfer performance have been presented.The results show that the Nusselt number and pressure drop increase and flow resistance decrease with flow velocity,as well as aspect ratio.The optimal thermal performance of minichannel has been found at aspect ratio 10.In the low Reynolds number,because the effect of gravity is too small relative to the wall effect,the inclination of the channel has little effect on the heat transfer performance and flow resistance.Compared with the conventional scale,the minichannel enlarges surface area of water which is easier to contact with the heating wall.The heat transfer coefficient is much higher than that of the conventional channel.In order to further enhance the heat transfer performance of minichannel,micropillars are added into the rectangular channel.The effects of the height,ratios of pitch to diameter,inclination angle,shape and arrangement of micropillars on the heat transfer characteristics and flow resistance of the channel are studied.The results show that with the increase of h,the clearance velocity has been increased,as well as the high temperature area,Nusselt number and resistance has been increased.By changing S/d,it is found that when the interaction between micropillar and micropillar affects the near wall,the heat transfer effect is the best.When the inclination of micropillar is the same as the direction of water flow,the disturbance flow is also generated and the heat transfer performance is enhanced.The rhombus micropillar's edges are exposed to the fluid,which are more likely to cause intense collision and develop vortex.The optimum height is 0.75 mm,the ratio of pitch to diameter is 2,the inclination angle is 60°,the shape is rhombus,and the arrangement is staggered.Finally,the water and ethylene glycol in minichannel are investigated under non-uniform heat flux.It is found that because of the good thermal conductivity and low viscosity,the heat transfer performance of water is better.Then the flow and heat transfer effects in three shapes of micropillars are analyzed with non-uniform heat flux.It is found that the Nusselt number is increased under uniform heat flux,and the rhombus micropillars have the best heat transfer effect.This is due to the concentration of micropillars in high heat flux regions.The comparison between natural convection and forced convection shows that the heat transfer performance of the former is far inferior to that of the latter.In order to achieve higher heat transfer effect,a certain inlet velocity is required.