Experimental Heat Transfer And Flow Characteristics In A Square Section Mini-channel With Twisted Tapes

The high temperature of the electronic chip based on the highly integrated technology is easy to cause the problem of stability decline or even overheating and damage.In order to obtain a more efficient and stable cooling technology,more and more scholars began to engage in the research of mini-channel enhanced heat transfer technology.However,in the actual application process,the active heat transfer technology needs to consume a certain amount of energy,which can not be used in some specific occasions and is not easy to control.Therefore,passive heat transfer technology is widely used in production.The disturbance elements enhanced heat transfer technology is widely used in passive heat transfer enhancement technology,and the twisted tape has become the focus of the research of the disturbance elements enhanced heat transfer technology because of its easy manufacturing,low cost,strong anti-scaling ability.In view of this,this paper studies the heat transfer enhancementtechnology of the twisted tape insert.The study is divided into two parts:(1)Using deionized water as working fluid,the effects of twisted tapes with different twist ratios(Y=3,4,and 5)and twist lengths(L=50 mm,100 mm,and 150 mm)on friction factor,wall temperature,Nusselt number,entropy generation and performance evaluation criteria in the mini-channel under Reynolds number of 418.65-883.81 were studied.The results show that the addition of the twisted tapes make the wall temperature of the square-section mini-channel decrease significantly,the Nusselt number increase by 29%-149%,and the friction factor increases by 68%-372%.The wall temperature of the mini-channel decreases with the decrease of the twist ratio or the increase of the twist length.The Nusselt number and the friction factor increase with the decrease of the twist ratio or the increase of the twist length.The comprehensive performance analysis shows that the performance evaluation criteria of the mini-channel with twisted tapes are greater than unity,the twisted tape with twist length of L=150 mm and twist ratio of Y=3 has the highest performance evaluation criteria of 1.49.(2)The numerical simulation method is used to further study the effects of different arrangement and section number of twisted tape on the local pressure drop,local Nusselt number,velocity field,temperature field and field synergy in the mini-channel with square section.The results show that the velocity field and the temperature field are redistributed in the channel with the twisted tape,and the secondary flow is generated near the twisted tape,which greatlyenhances the mixing of the fluid.The field synergy angle between the velocity vector and the pressure gradient α around the twisted tape increased significantly,and the distribution of field synergy angle α alternations increases and decreases in the vicinity of the contact surface between the twisted tape and the fluid.The field synergy angle between the velocity vector and the temperature gradient βin the channel with the twisted tape decreased significantly,reaching a minimum of 19.5°.The area with a smaller field synergy angle β was mainly distributed at the back of the twisted tape.In general,the enhancement effect of segmental twisted tape on heat transfer performance is not as good as that of full-length twisted tape,but it is similar to that of full-length twisted tape.For the resistance loss caused by the twisted tape,the segmental twisted tape is far lower than that of full-length twisted tape,so it has the better performance.