| The rapid development of electronic technology brings a growing challenge to the thermal management of the electronics.The thermal storage heat sink based on the solid-liquid phase change materials is supposed to be one of the most promising alternative cooling technologies to conduct high-performance and energy-saving thermal management for the devices who work with intermittent,pulsed or high-low cycle power,or the devices work under extreme environments.For the purpose of improving the thermal management performance and then promoting the application of the heat sink,in this thesis,the heat transfer and thermal storage characteristics of the heat sink,and the key factors which affect the thermal storage and release performance of the heat sink were investigated.In addition,the thermal storage and release performance of the heat sink were optimized by experimental and numerical methods.The main research contents and conclusions are summarized as follows:1.The heat transfer characteristics and the key parameters of the heat sink in each individual stage during the thermal management process were studied theoretically and experimentally.The results showed that:(1)there exist heat conduction,heat convection,heat storage and release during the thermal management process and all these heat behaviors influence with each other.The heat storage and release performance was affected by several factors and each factors had different influence effect at different stages.(2)as the thermal conductivity of the PCM increased,the thermal storage rate increased obviously,the thermal release rate increased slightly.When the heat conduction inside the heat sink and the heat convection with the environment were enhanced simultaneously,the safely heat storage time of the heat sink was extended and the re-solidify time of the PCM decreased.(3)the heat storage time extended and the heat release rate increased with the growing fo the melting temperature of the PCM.However,when the ambient temperature grew,the heat storage time decreased and the chip temperature increased.To reduce the influence of-the ambient temperature,measures should be taken to enhance the thermal storage performance.2.The thermo-physical properties of the PCM were modified and optimized experimentally to increase the thermal conductivity,latent heat capacity and thermal stability of the PCM.The results showed that:(1)The expanded graphite(EG)could effectively increase the thermal conductivity of the composite phase change material(CPCM)and enhance the thermal storage performance of the heat sink.Combined with the pillar fins,the EG could further improve the thermal storage performance inside the heat sink and the thermal storage rate increased by 17%.Meanwhile,the temperature of the heat source and sink wall decreased by 3.5 ? and 4.5 ?,respectively.(2)The ultrasonic exfoliation of the EG/paraffin composite could effectively increase the thermal conductivity and thermal stability of the CPCM.When the exfoliation time was larger than 5 minutes,the EG plate/paraffin suspension became thermal stable.The suspension showed the performance of shear thin non-Newtonian fluid and the shear thin characteristic became more obvious with the increasing of the mass percentage of EG plates.When exfoliated for 2 minutes,the therml conductivity of the composites increased by 102.36%.Moreover,as the exfoliation time increased,the CPCM thermal conductivity increased firstly and then decreased.3.To enhance the thermal storage performance of the heat sink and guide the thermal design of the heat sink,the thermal conductivity of the CPCM and the geometry of the heat sink were optimized.The results showed that:(1)the method based on the thermal resistance network proposed in this thesis could effectively solve the minimal thermal conductivity of the CPCM,while the numerical solution could effectively solve the optimal thermal conductivity of the CPCM.With the minimal and optimal thermal conductivity,the latent heat of the CPCM could be sufficiently extracted and the safely thermal storage time of the heat sink could be extended to its longest value.(2)the optimal thermal conductivity of the CPCM decreased with the increasing of the heat source safe operation temperature,and increased fast with the growing of the heat flux density absorbed by the heat sink.(3)To improve the transfer efficiency of the heat sink and decrease the mass fraction of the heat transfer enhancing fillers,the number of the heat storage units inside the heat sink should be increased,the ratio of the heat sink base thickness to the fin thickness should be decreased and the width-to-height ratio of the heat sink could be designed around 0.4-0.6.(4)With the plate fins un-uniformly distributed the influence of the thermal spreading resistance between the heat source and heat sink decreased.The temperature difference inside the heat sink decreased from 3? to 1 ? and the thermal storage rate increased by 14%.4.The "online thermal charging-offline thermal discharging" working mode of the heat sink was proposed to solve the problem of much too long re-solidify time of the thermal storage heat sink.The results showed that:(1)The paraffin could be well encapsulated by the epoxy resin though the special curing profile proposed in the thesis,realizing the modularization of the thermal storage unit(MTSU).The MTSU had good thermal storage performance and extended the safe operation time of the heat source with heating power of 2.5 W by 181%.(2)Adopting the new working mode,the heat sink could improve the on/off time ratio of the heat source from 1.02 to 14.86.The new working mode of the MTSU provides a fundamental solution to the problem of much too long re-solidify time of the heat sink and promotes the heat sink application.(3)The metal foam could efficiently improve the thermal management performance of the MTSU.Embedded with the copper foam and nickel foam,the effective thermal conductivity of the MTSU increased by 149.34%-404.64%,and the re-solidify time of the MTSU decreased form 118 minutes to 84 minutes. |
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