Study On Heat Transfer Characteristics Of Oscillating Jet Impingement In Confined Space With Uniform Heat Flux Boundary

Enhanced heat transfer technology is an important guarantee for the normal operation of high heat flux devices,which is widely used in high-power concentrated photovoltaic cells,multi-chip modules,aero-engines and other fields.Jet impingement heat transfer is one of the commonly used high-efficiency heat transfer technologies,which has experienced the gradual development from single hole to complex porous array impingement,from vertical impingement to oblique impingement,from static traditional jet impingement to dynamic pulsed jet impingement cooling,from passive jet impingement cooling to controllable active jet impingement cooling.Based on the idea of dynamic controllability,a novel oscillating array jet impingement heat transfer method is proposed on the basis of conventional array jet impingement heat transfer,which has the potential to realize efficient dynamic and uniform temperature control.Numerical simulation and experimental study were used to study the impingement heat transfer characteristics of oscillating jet with uniform heat flow boundary,and the influence laws of geometric parameters,oscillating motion parameters and flow parameters on its flow and heat transfer were analyzed.The main research contents are as follows:1)From the perspective of two-dimensional model,the characteristics of impinging heat transfer of oscillating jet are explored.The RNG k-εturbulence model is used to establish a two-dimensional numerical model of impinging cooling of oscillating jet,and the time-averaged Nusselt number Nu_t and the time-averaged Nusselt number nonuniformity factor C_Nu are used to evaluate its heat transfer intensity and uniformity.The effects of key parameters such as swing frequency,Reynolds number,slot width,impact spacing and maximum swing angle on the heat transfer performance are analyzed.Compared with the steady vertical jet cooling,the traditional jet impingement cooling can effectively improve the heat transfer uniformity of the target surface.2)A numerical model of oscillating jet impingement with uniaxial slot array in a three-dimensional rectangular cavity was established,and four oscillating motion modes,uniform angular velocity,linear angular velocity,up-throwing angular velocity and down-throwing angular velocity,were explored.The effects of key parameters such as maximum oscillating angle,oscillating cycle time,edge angular velocity,Reynolds number and boundary heat flux on its heat transfer performance were analyzed.It is found that Nu_t gradually increases with the increase of swing period,Reynolds number and boundary heat flux,but C_Nu gradually decreases.Generally speaking,the uniform angular velocity swing mode has the highest heat transfer intensity,the downward angular velocity swing mode has the best heat transfer uniformity,and the linear angular velocity swing mode has the best comprehensive heat transfer performance.3)The flow and heat transfer characteristics of different target width,impact distance,inlet and outlet configuration and cavity cross-section shape under linear angular velocity swing mode were further studied.It was found that Nu_t and heat transfer uniformity gradually decreased with the increase of target width.When the impact distance is 35 mm,the heat transfer performance is the best,and the Nu_t and C_Nu are 36.05 and 0.246,respectively.The outlet configuration has little influence on the heat transfer performance,and its symmetrical design has better heat transfer performance;The smaller the inlet area or the fewer arrays,the better the heat transfer performance.Nu_t will decrease when the cross-sectional area of the cavity is reduced.4)The design,manufacturing and device integration of the oscillating jet impact device were carried out,and the experimental study on the flowing law of oscillating jet was carried out preliminarily.The tracing effects of different colors of phosphor,ink and ink in the flow field were explored,and it was found that the black ink was the best.The corresponding numerical model is established and compared with the experimental results,which preliminarily verifies the effectiveness of the numerical simulation method in this paper.The flow characteristics of different swing shaft structures and swing frequencies are analyzed.It is found that when the swing frequency is large,the tail section of the jet has a directional delay with the nozzle,which reduces the impact effect of the jet on the target surface,while increasing the nozzle velocity can improve this phenomenon.