Experimental Study On Flow And Heat Transfer Characteristics In Spiral Microchannels

Microchannel has become the research focus of many scholars because of its high surface to body ratio,light weight and high heat transfer efficiency.Compared with the conventional straight microchannel,the curved microchannel has compact structure,small thermal resistance and more uniform temperature distribution.However,there are few researches on the curved microchannel at present.The existing researches mainly use numerical simulation and theoretical analysis,and there is still no experimental research on the system in the curved microchannel.In this paper,the Archimedes double helix microchannel with rectangular cross-section is designed and fabricated by machining.The experimental study on the single-phase flow and heat transfer characteristics of eight helix microchannels with different helix pitch,hydraulic diameter,height width ratio of cross-section and different helix diameter is carried out at room temperature using deionized water as working fluid.It provides theoretical basis for microchannel design and optimization,which is of great practical significance.In order to study the flow mechanism in the spiral microchannel,firstly,the flow characteristics in the spiral microchannel are studied under the conditions of cold and heating respectively,and the variation rules of pressure drop characteristics,friction coefficient and Poiseuille number in the microchannel are analyzed.The experimental results show that the pressure drop in the spiral microchannel with different structural parameters increases obviously with the increase of Reynolds number.The larger the diameter of spiral and the ratio of height to width of cross section,the larger the pitch of spiral,the heat flux and the hydraulic diameter,the smaller the pressure drop.The friction coefficient in the microchannel decreases with the increase of Reynolds number.The influence of secondary flow on the flow is more obvious with the increase of Reynolds number Based on the experimental data,the correlation prediction formula of Poiseuille number in spiral microchannel is established.More than 95% of the data are in the18% error range,which can well predict the Poiseuille number in Archimedes spiral microchannel.Secondly,in order to study the heat transfer characteristics in the spiral microchannel,the temperature distribution and the overall heat transfer characteristics of the surface,the axial and the cross-section of the spiral microchannel are tested and analyzed with the infrared thermal imaging technology.It is found that the temperature of the working medium increases gradually during the axial flow of the spiral microchannel.In the first half of the channel flowing in clockwise,the temperature of the channel wall and the working medium increases rapidly,reaching 78.1% of the whole heating process.In the second half of the channel flowing out anticlockwise,the temperature increases significantly.The heat transfer coefficient and Nusselt number of the microchannel are increasing with the axial position point moving backward,while the heat flux density is decreasing with the axial flow of the working medium.The inner wall and the inner working medium temperature of the channel section are significantly higher than the outer side,and the lowest point of the working medium temperature on the section is slightly away from the center line near the outer side of the channel.The overall average heat transfer coefficient and Nusselt number of the spiral microchannel At the same Reynolds number,the smaller the helix diameter is,the higher the heat transfer coefficient is and the better the heat transfer performance is.The smaller the aspect ratio and the equivalent diameter are,the larger the heat transfer coefficient is and the smaller the Nusselt number is.In this paper,the flow and heat transfer characteristics in the spiral microchannel are studied by means of experiments.Combined with the infrared technology,the influence factors of experimental working medium under different working conditions are studied,which makes a useful exploration for the research of spiral microchannel.