Theoretical And Experimental Research On Solid-Liquid Phase Change Thermal Management Technique With Gradient Melting Point

Over-temperature operation is one of the main factors leading to the failure of electronic components.Developing an efficient thermal management system is crucial to ensure the stability and safety of electronic components.In recent years,solid-liquid phase change material(PCM)based passive thermal management technique has developed rapidly,especially suitable for the thermal management of electronic components with intermittent or pulsating operating characteristics.Due to the low thermal conductivity of most phase change materials,heat transfer enhancement is of important to improve the thermal performance of phase change material heat sink.Gradient melting point technique is commonly applied in efficient latent heat storage systems,while this technique is rarely researched in the field of thermal management.This paper proposes a novel thermal management method based on the Gradient melting point technique,and the structural design and optimization methods of the cascaded PCM heat sink are developed.The specific research contents are as follows:Firstly,a novel cascaded solid-liquid phase change material heat sink containing three layers of phase change materials is proposed.Three kinds of low melting point alloys(LMPAs)with different melting points were used as phase change materials.The thermal management performance of the PCM heat sinks with different combinations of phase change materials was experimentally tested under different heat source power conditions.A numerical model was established to simulate the working process of the PCM heat sink,and the heat transfer enhancement mechanism of the Gradient melting point technique was analyzed.Combining the numerical model with genetic algorithm,the PCM volume fraction ratio of the cascaded PCM heat sink were optimized and analyzed.The research results show that the overlapping melting is the key for cascaded solid-liquid heat transfer enhancement technique to improving the thermal performance of PCM heat sink.During the overlapping melting period,the inherent melting point difference between the solid liquid phase transition interfaces enhances the heat transfer inside the heat sink,thereby effectively reducing the temperature of the heat source.Optimizing the volume fraction ratio of cascaded PCM heat sink can effectively extend the duration of overlapping melting period,thereby improving the thermal management performance of the cascaded PCM heat sink.With a heat flux of 3.0 W/cm~2,the experimental temperature rise rate and protection time of the cascaded PCM heat sink is 3.09℃/min,which is 47.8%lower than that of the traditional PCM heat sink using only one PCM.The enclosure shape of the PCM heat sink also has a significant impact on the solid-liquid phase change process of the PCM within it.A morphological enclosure shape optimization method is developed and applied to the optimization the enclosure shape of the low melting point alloy based PCM heat sink.Through alternative execution of morphology operations(erosion and dilation),the material distribution within the design domain is continuously modified during the iteration process until the optimal enclosure shape is obtained.The research results show that the morphological enclosure shape optimization method is effective and significantly improves the thermal performance of PCM heat sink.With a heat flux of 3.0 W/cm~2,the experimental temperature rise rate of the optimized single PCM heat sink is reduced to 3.21℃/min,which is 15.2%lower than the theoretical minimum temperature rise rate of a conventional rectangular PCM heat sink.Combining the Gradient melting point technique with the morphological enclosure shape optimization method,and further considering the optimization of the PCM volume fraction ratio,a modified optimization method for the enclosure shape optimization of the cascaded PCM heat sinks is proposed.The research results show that the morphological enclosure shape optimization method significantly improves the thermal performance of cascaded PCM heat sink.With a heat flux of 3.0 W/cm~2,the numerical temperature rise rate of the optimized cascaded PCM heat sink is only 2.45℃/min,which is 35.3%lower than the theoretical minimum temperature rise rate of a conventional rectangular PCM heat sink..The advantages of low melting point alloys lie in their high thermal conductivity and high volume-latent heat storage density.However,its high material density increases the total weight of the heat sink.Based on the Gradient melting point technique,a lightweight thermal management technique using low melting point alloys and paraffin as phase change materials is proposed.By establishing a numerical model,the working processes of the cascaded PCM heat sink were simulated,and thorough structural parameters analysis performed.The numerical results show that the synchronization of the solid-liquid phase change processes of the paraffin and the low melting point alloy has an important impact on the thermal management performance of the cascaded PCM heat sink.The thermal management performance of this cascaded PCM heat sink is between pure paraffin heat sink and pure low melting point alloy heat sink.Its lightweight advantage is achieved by sacrificing thermal control performance and operational flexibility.