| With the development of the national economy,the energy consumption has continued to increase,and the problem of electricity supply contradiction has also become increasingly prominent.The central air-conditioning system is regarded as the biggest energy-consumption equipment in public building,which has been a key object of energy saving.In the field of air conditioning,the application of cold storage air-conditioning technology is one of the effective measures to solve this problem.At present,the ice-ball cold storage system is more widely applied.However,the phase change temperature of ice is low,which makes the evaporation temperature and COP of cool-storage air-conditioning is lower than conventional air-conditioning system.Therefore,it is significant to develop suitable phase change material(PCM)for conventional air-conditioning and improve the heat exchange efficiency of cool storage system.Compared with inorganic phase change materials,organic phase change materials have a low degree of super cooling and no phase separation phenomenon.However the phase change latent heat and thermal conductivity are relatively low.Therefore,this paper proposes using graft modification and nanocomposite technology to improve the latent heat and thermal conductivity of organic phase change materials.The phase change temperature of nanocomposite phase change material meets with air-conditioning condition.At the same time,the charging performances of nanocomposite PCM are investigated.The main research work and results are as follows:(1)A variety of organic PCM suitable for air-conditioning system were developed by step-cooling curve method.Then,the thermal performance of experimentally selected organic PCM was mearsured by differential scanning calorimetry(DSC).Finally,a new organic PCM YS-1 for use in air-conditioning system was selected for a further study.The phase change temperature and latent heat were 6.4? and 215.1 J/g,respectively.(2)The further study of using maleic anhydride(MAH)grafted method to the organic PCM YS-1 was made due to low latent heat of PCM.Or-thogonal test was used to determine the main factors that affect the grafting rate,and draw the best program of testing.The molecular structure of the grafted product YS-1-MAH was characterized by Fourier transform infrared spectroscopy(FTIR).The results showed that the characteristic peak of 5-membered ring vibration of MAH appeared on the infrared spectrum of grafted product,and the graft modification experiment was successful.The latent heat value of modified YS-1-MAH was higher than that of YS-1.(3)The modified YS-1-MAH was further studied by nanocomposite technology.A preparation method of directly blend by ultrasonic vibration,adding dispersant to prepare a new nano-composite phase change material was made.The effects of dispersant type,concentration and ultrasonic time on the dispersion stability of nanocomposites were investigated.Finally,the best preparation condition of graphene nanocomposites was determined.The thermal conductivity of nano-composite was measured by transient planar heat source method.The results show that the thermal conductivity of the nanocomposite phase change material YS-15(0.5wt%graphene/YS-1-MAH was increased by 26.8%and 30.4%,respectively,compared with the phase change material YS-1 at 8? and-10?.(4)The developed nanocomposite phase change material was applied to the direct contact latent heat thermal energy storage system.The physical model and mathematical model of direct contact thermal energy storage tank were established using ANSYS-FLUENT.he numerical simulation of the charging performance of nanocomposite phase change material in the tank was carried out.During the charging process,the volume fraction,charging capacity,charging rate and temperature distribution of the energy storage system with nanocomposite phase change material were studied and compared with those of umodified phase change material YS-1. |
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