Experimental Study On Heat Transfer Performance And Theoretical Model Analysis Of Bent Flat Micro Groove Heat Pipe

The flat groove heat pipe is suitable for thermal management of thin,flat and compact electronic products and can be used in aerospace and ground applications.In the aircraft or spacecraft,the limited space leads to bending or deformation of the flat heat pipe.Also,the change of gravitational acceleration or gravitational angle may enhance or weaken the heat pipe heat transfer performance.According to the background above,in this work,experimental study on heat transfer performance and theoretical model analysis of flat trapezoid groove heat pipe with aluminum shell and acetone working fluid was conducted,laid the foundation for further research.Heat transfer testing rig for bending flat heat pipe was set up.The flat heat pipes of which the leak rate was tested at 1.56×10-8Pa·m3/s were chosen to conduct steady state heat transfer performance test.The effect of bending angle and gravitational angle of 0° to 90° on heat transfer was studied.The experimental result showed the flat heat pipe could reach to steady state in 10 minutes in horizontal state.Bending and positive gravitational tilt angle did not prevent heat pipe from starting up.When heat transfer limit occurred,temperature in evaporator of the heat pipe would rise sharply and made steady state hard to reach.Positive gravitational tilt angle could increase heat pipe heat transfer limit.Heat transfer limit rose from 40 W to 90 W when tilt angle rose from 0° to 30°.When flat heat pipe was under adverse gravity position,heat transfer limit reduced to less than 10 W.The change of bending angle did not have significant influence on heat transfer limit.Thermal resistance results showed that thermal resistance decreased with increasing heat input until reaching the heat transfer limit.At 30°tilt angle,thermal resistance could be lower than 0.1K/W with high heat input.Under the same heat input,the increasing tilt angle did not affect thermal resistance distinctly.The bending of flat heat pipe could increase effective thermal conductivity up to 14000Wm-1K-1,the higher the heat input,the more distinct the effect of bending.Bending and positive gravitational tilt angle both benefited the heat transfer performance.According to experimental result,a method using complementary groove structure to compensate heat transfer performance was presented.Analysis for heat transfer process and related characteristic parameters was made.Axial hydrodynamic model in groove and heat pipe thermal resistance model was presented for calculation of flow parameters and thermal resistance.The results indicated that in horizontal position,the heat transfer limit could be predicted by means of minimum meniscus radius and was determined by capillary limit.The total thermal resistance of heat pipe decreased with the increasing heat input.The main thermal resistance existed in evaporator and condenser wick.Last,the theoretical model was modified on the basis of experiment to explore the influence of working temperature.The computation results indicated that the difference on working temperature mainly affect axial liquid and vapor pressure and vapor velocity distribution,making thermal resistance increased after modification.But heat transfer limit was not affected.The theoretical model result had the trend compared to experimental result.Furthermore,bending effect on momentum equation and thermal resistance equation was introduced.The model result showed that bending changed meniscus distribution in groove and pressure variation trend in condenser,and reduced the thermal resistance.