Performance Investigation And System Simulation Of Pump-assisted Capillary Phase Change Loop

In order to solve the drawbacks of startup failure,limited heat transport distance and operational temperature oscillation due to the miniaturization of flat loop heat pipes,a novel two-phase cooling loop called pump-assisted capillary phase change loop is designed in this thesis.The loop,which combines the active and passive,mainly utilizes the latent heat of working fluid to transport heat.With the assistant of the micro-pump in the loop,the robustness and heat transport distance of the loop has a notable improvement.Pump-assisted capillary phase change loop possesses the advantages of strong heat transfer capability,low startup heat load,stable operation and high reliability,therefore it can be used in the fields of cooling high heat flux electronic devices and spacecraft thermal control.The thesis mainly pays attention to the performance investigation of pump-assisted capillary phase change loop.Based on the loop structure and operational process,the flow and heat transfer characteristics of the loop is theoretically analyzed.Loop I with methanol as working fluid and magnetic drive gear pump as the pumping source is then fabricated to investigate the influences of heat load,pumping power and heat sink temperature.The experimental results validate that pump-assisted capillary phase change loop could notably improve the startup characteristics and operational stability.According to the filling process used in loop I,a superior liquid charging system is designed,considering to decrease the non-condensable gas leaking in loop during the liquid filling process.When the superior liquid charging system is used in the methanol loop ?,the evaporation temperature of loop? has an obvious decrease.This results in a better startup characteristics and a lower operational temperature for loop ? in low heat load range.Aiming at decreasing the total weight and volume of the loop,loop ? and loop IV are set up,using the impeller pump designed by our school replacing the traditional gear pump.Loop ? is charged with methanol,meanwhile ammonia is selected for loop IV.The startup characteristics of loop ? indicate that initial liquid vapor distribution in the evaporator has great impact on the startup profile.When the vapor channel and vapor chamber are partially or completely occupied with liquid,the working fluid suffers from different state variation during startup.Moreover,the initial accumulated liquid in the vapor channel would increase the vapor.flow resistance,leading to a higher operational temperature.But,after the accumulated liquid vanishes,the operational temperature decreases.The experimental performance of loop IV indicates the heat transport capability of the loop has a notable increase by using ammonia as working fluid.Specifically,when the heater wall temperature is limited in 60?,the maximum heat load the loop can transfer is 250W and the corresponding heat flux is 24.6W/cm2.When the heater wall temperature is controlled in 80?,the maximum heat load and heat flux is 340W and 33.4W/cm2,respectively.Based on the relations of mass and energy conservation,a 1D steady state model of pump-assisted capillary phase change loop is built and solved numerically.The investigation shows that the model result coincides with the experimental result,which verifies the validity of the model.Based on the proposed model,a parametric study on heat load,liquid flow rate,heat sink temperature and evaporation temperature are further conducted to investigate the impact on the steady state operation.The model results give a better understanding on the operational characteristics of pump-assisted capillary phase change loop.In this thesis,an extensive investigation is conducted to study the startup and steady state operational characteristics of pump-assisted capillary phase change loop through theoretical analysis,experimental investigation and loop simulation.The research results indicate that pump-assisted capillary phase change loop overcomes the issues of startup and instability in traditional loop heat pipe.The present research work has certain guidance significance for understanding the operation law and achieving practical engineering applications of pump-assisted capillary phase change loop.