Theoretical And Experimental Investigation On Oscillation And Heat Transfer Of An Oscillating Heat Pipe

The Oscillating heat pipe(OHP)has potential for heat dissipation of higher integration equipment due to its high heat transfer capacity,simple structure,and low cost.Because the OHP can function well even under the severe conditions such as vibration,acceleration,it will have an impact on the electronics cooling or thermal management in the ocean-going ships.In order to better understand fluid flow and heat transfer mechanisms occurring in OHPs,experimental investigation and theoretical analysis have been conducted to investigate the effects of thin film evaporation,ultrasound,and electrical field,and oscillating flow on the heat transfer performance of an oscillating heat pipe.An experimental investigation on oscillating flow and heat transfer of an OHP without the external field has been conducted.Results show that its heat transfer capacity depends on heat load,operating temperature,tilt angle,filling ratio and work medium.The experiment demonstrated that an OHP has high heat transfer capacity that depends on the oscillating frequency,amplitude and thin film evaporation of internal working medium in an OHP.A mathematical model studying the bulk flow effect on thin film evaporation heat transfer was developed considering momentum conservation equation and bulk flow equation.Results show that bulk flow greatly hinders thin film evaporation heat transfer.In addition,it is found that the heat flux increases with the increasing of superheat and accommodation coefficient.The Volume of Fluid(VOF)model was employed to simulate and analysis vapor-liquid two phase flow in a capillary tube.Results show that when the contact angle becomes smaller,it is easy to generate circulation,which can enhance heat transfer.A mathematical model that considers electric field effect on thin film evaporation was also developed to investigate the effect of electric field on disjoining pressure,thin film thickness,interfacial temperature,and heat flux.Results show that electric field can decrease thin film thickness,extend length of thin film region,and effectively strengthen thin film evaporation heat transfer.Considering heat transfer mechanism of oscillating flow in an OHP,a high bubble generation rate can increase oscillating motion and strengthen heat transfer.Ultrasonic effect on nucleation and heat transfer performance of an OHP was experimentally investigated.Ultrasound can promote nucleation in deionized water.Compared to single frequency ultrasound,dual-frequency ultrasound can further promote nucleation,and effectively improve heat transfer performance of an OHP.In addition,it shows that a dual-frequency ultrasound can result in a better performance than single frequency ultrasound,which depends on operating temperature,inclining angle and physical properties of working medium.