Simulation And Experimental Research On Heat Transfer Characteristics Of Nano-Silver Fluid In A Flat Plate Pulsating Heat Pipe

Pulsating heat pipes(PHP)are widely used due to their advantages of small size,simple structure,and high heat transfer efficiency.However,the common structures face severe challenges due to their shortcomings such as low heat transfer coefficients and complex working mechanisms during heat-mass transfer.At present,by optimizing the structure and changing the working medium to improve the overall performance of the PHP has become a hot research topic.In this paper,the silver nanofluid with strong ion activity,low viscosity,and excellent thermal conductivity is applied to the flat plate pulsating heat pipe(FP-PHP).The three-dimensional geometric model of the FP-PHP with micro-channels at the condensation section is mainly established.The volume distribution and thermal performance of two-phase flow of FP-PHP under different liquid filling rate,heating power and pressure are analyzed and calculated.The characteristics of two-phase flow are observed through the volumetric distribution cloud diagram,and the change rules of heat transfer are judged according to the thermal performance indexes such as thermal resistance and heat transfer coefficient,and the trend of temperature changes at the evaporation and condensation section is analyzed to study the structure start-up characteristics.The simulation results show that the silver nanofluid can effectively improve the heat transfer ability of FP-PHP.At the same time,the visual experiment platform is built independently to verify the reliability of the simulation results.There are three main research conclusions:1.Visual phenomenon analysis.Simulations and experiments show that the flow pattern of the water is relatively single,but the bubble types of silver nanofluid include bubble flow,plug flow,annular flow,semi-annular flow,and staggered cluster flow in the visualization phenomenon.With the increase of heating power,the stable cycle time is gradually shortened,the flow pattern changes rapidly,and the cycle is short.2.Thermal characteristics analysis.Under different filling rates,with the increase of heating power,the thermal resistance of the silver nanofluid gradually decreases,and the heat transfer coefficient gradually increases.When the heating power reaches 110 W,the thermal resistance of the silver nanofluid is the smallest,it is only 0.40 K/W.At this time,the heat transfer coefficient is 33% higher than that of the water.The starting temperature of the silver nanofluid is low,it is only 46 ?.The temperature uniformity is excellent,after the heating power reached 70 W,the overall temperature ripple is only 1.2 ?.3.Pressure effect analysis.In order to further explore the effect of pressure on the FP-PHP,the fluctuating pressure and flow velocity of the channel of ethanol and water at different pressures are analyzed through simulation.It is found that the thermal properties of the working fluid of ethanol vary greatly with pressure.At 0.1 Pa,the pressure oscillation in the channel is stable and efficient,and the performance is optimal.The water has the best oscillation effect at 101,325 Pa.However,the channel pressure is mostly maintained at negative pressure under high vacuum and low vacuum.The flow pattern is relatively single,which seriously affects the conversion of two-phase flow.