Experimental Study On Heat Transfer Characteristics Of A New Ultrathin Heat Pipe

With the emergence and rapid development of 5G technology,the power consumption of electronic chips has doubled,and the heat dissipation space has gradually been compressed.This has led to higher operating temperatures and heat flux densities in small fixed spaces,affecting the performance of electronic chips and devices,and restricting the further development of electronic products.Currently,ultra-thin heat pipes are an effective solution to the problem of high heat flow and heat dissipation in portable electronic devices.In order to overcome the heat transfer bottleneck problems caused by the simple structure and single size of the capillary core in traditional ultra-thin heat pipes,and further improve the heat transfer performance of ultra-thin heat pipes.This article innovatively proposes a micro column array multi scale capillary core,which is applied to a new type of ultra thin heat pipe with a total thickness of only 0.50 mm.The thermal performance of the new ultra-thin heat pipe was studied through experiments,and the gas-liquid flow of the Lshaped ultra-thin heat pipe was analyzed through visual experiments.The specific research content and achievements are as follows:A new type of micro column array multiscale capillary core was fabricated by sintering in an ultra-thin heat pipe.The capillary core can not only meet the support requirements,but also play a drainage role.And developed a packaging method with simple welding and high yield.The prepared capillary core was characterized and it was found that there were three scale structures of nano micro micro micro micro on the oxidized capillary core of the micro column array.The multi scale capillary core has good hydrophilic properties and large capillary suction,with a contact angle of 5° and a suction time reduction of 43.1%.A thermal performance test rig was built to study the effects of liquid filling rate,secondary degassing,inclination angle,and oxidation treatment on the thermal performance of ultra-thin heat pipes.It is found that the ultra-thin heat pipe has an optimal liquid filling rate φ=30%,at this time,the minimum thermal resistance of the ultra-thin heat pipe is 0.67K/W.When the liquid filling rate is low,the phenomenon of "burning out"occurs at high power.When the liquid filling rate is high,excessive working fluids can block the steam channel,reducing the thermal performance of the heat pipe.The secondary degassing process affects the thermal performance of the heat pipe by determining the residual degree of non condensable gas.A shorter secondary degassing time will cause non condensable gas to remain,increase the gas-liquid flow resistance of the heat pipe,and reduce the boiling limit of the ultra-thin heat pipe.A longer secondary degassing time will reduce the actual working fluid content in the ultra-thin heat pipe,reducing the heat transfer efficiency of the heat pipe.The inclination angle affects the heat transfer performance of ultra-thin heat pipes by changing the action of gravity θ=At 90° and 0°,gravity promotes the reflux of the working medium;stay θ=At 180° and-90°,gravity inhibits the reflux of the working medium.Oxidation treatment increases the phase change area of the capillary core,improves the wettability and liquid absorption ability of the capillary core,and greatly improves the operational performance of the ultra-thin heat pipe.The maximum evaporation heat transfer coefficient and the maximum condensation heat transfer coefficient of the ultra thin heat pipe after oxidation treatment increased by 77.2%and 108.5%.This ultra-thin heat pipe has excellent thermal conductivity,with a maximum equivalent thermal conductivity of 26482.3W/(m·K),approximately 66 times that of pure copper.Through infrared experiments,it was found that when the heat load was 10 W,adding this ultra-thin heat pipe to the traditional mobile phone cooling module reduced the central temperature of the heating zone and the maximum temperature difference between the backplane surface by 22.9%and 77.9%,eliminating the "hot spots" generated under high power consumption.After analyzing the climbing experiment results,it was found that the composite capillary core not only has the advantages of good fluidity of the wire mesh capillary core,but also has the advantages of high capillary force of the sintered capillary core,with a maximum climbing height of 250.7 mm.Using high-speed photography to visualize the gas-liquid flow of L-shaped ultra-thin heat pipes,it was found that sintered capillary core ultra-thin heat pipes are suitable for operation at low liquid filling rates,and the optimal liquid filling rate is φ=25%,and the composite capillary core ultra-thin heat pipe is suitable for operation under high liquid filling rate,and the optimal liquid filling rate is φ=35%。When the liquid filling rate is low and there is no excess liquid in the steam chamber,the sintered capillary core ultra-thin heat pipe has a smaller drying area,which can reduce the impact of "drying" on the thermal performance of the heat pipe;When the liquid filling rate is high and there is excess liquid in the steam chamber,the composite capillary core ultra-thin heat pipe can prevent excess liquid from blocking the steam channel and reduce the steam flow resistance.The composite capillary core can reduce the impact of excess liquid on the thermal performance of the heat pipe.