Research On Cooling System Of Smart Phone Based On Phase Change Material

In recent years,the development of chips gradually tends to high frequency,miniaturization and integration.With the wide application of 5G technology in smart phones,how to effectively control the internal heat dissipation under high power consumption conditions or when the mobile phone battery is charging has become an important issue in mobile phone design.In this paper,5G chips and soft-pack lithium batteries in smart phones are taken as research objects.According to their different working temperature ranges,paraffin/graphite and lauric acid-myristate acid with suitable phase transition temperature are selected as phase transition media to cool them,and copper foil and graphene constitute a composite cooling layer to assist heat dissipation,which together constitute the thermal management system of smart phones.In the thermal analysis carried out by Fluent,the liquid phase volume fraction,melting rate and temperature change trend of 5G chip and soft pack lithium battery were studied.The results show that the melting rate of PCM can be increased and the temperature rise of PCM can be inhibited obviously.The use of 92% paraffin/graphite and 64:36 lauric acid-myristate acid in 5G chip and soft pack lithium battery respectively,compared with the use of no phase change material,can reduce the temperature of the maximum 8.67% and 10.49%,and the use of phase change material has obvious heat dissipation effect.The addition of the composite heat dissipation layer can effectively reduce the internal temperature of the mobile phone and improve the working reliability of the smart phone.Secondly,in order to verify the safety and stability of the thermal management system under different working conditions,combined with daily use scenarios,the cooling and heat dissipation effect of smart phones under different ambient temperatures was simulated.The results show that: With the increase of the ambient temperature,the temperature of 5G chip and soft-pack lithium battery also continues to rise.When the ambient temperature reaches40℃,the maximum surface temperature of 5G chip cooled by phase change materials reaches69.38℃,still in line with the appropriate temperature range,while the maximum surface temperature of soft-pack lithium battery reaches 42.06℃,exceeding the theoretical maximum temperature by 4.9%.The phase transition temperature of paraffin/graphite is higher,and the temperature inhibition effect is more obvious in the high temperature region,while the phase transition temperature of lauric acid-myristic acid is lower.When the temperature rises to the phase transition temperature,the temperature control effect shows a weakening trend.Finally,the temperature change of the soft pack lithium battery under different charging rate and cyclic attenuation is simulated.The results show that the temperature of the soft pack lithium battery rises obviously with the increase of the charging rate.When the charging rate is 2C,the maximum temperature of the battery reaches 45.48℃,which exceeds the maximum suitable temperature by 14.6%,indicating that the phase change material is not suitable for charging with a higher charging rate.When cyclic charging is considered,the SOH(State of health)of the soft pack lithium battery will continue to decay with the increase of charging times,and the battery temperature rise during charging will increase with the decay of SOH within a certain range.When SOH=80%,the battery temperature rise is 35.6% higher than the health state under the same working condition.When the cycle charge and discharge times reached 500 times,the temperature inhibition effect of paraffin/graphite on 5G chip decreased by 1.22% due to the loss of phase change materials,while the temperature inhibition effect of lauric acid-myristate acid on soft pack lithium battery decreased by 1.13%.