| Based on the current social energy shortage,energy development and uneven distribution,energy storage technology has gradually become the core technology of supplementary energy form and energy economy application in China.The purpose of this paper is to develop a phase change cold storage material,which is applied to the air conditioning system in summer to provide cold water for the air conditioning system,so as to reduce the operating load of the air conditioning system or increase the energy coefficient of the air conditioning system.The phase variable storage material is used to store cold by night low energy,and the cooling amount is released for air conditioning system during the peak period of daytime electricity consumption.As an inorganic phase change material,mirabilite has the advantages of high latent heat,wide source,low price and no irritation.However,mirabilite also has the common problems of phase change materials of inorganic brine compounds,that is,phase separation and undercooling exist in the melting process,and the phase transition temperature is on the high side and the thermal conductivity is low.The eutectic phase change storage material(PCM)was prepared by modifying mirabilite with different proportion of phase change temperature regulator and nucleating agent,and the optimum eutectic phase change storage material was selected by experimental test.On this basis,porous medium expansion vermiculite was used as carrier to load eutectic phase change storage material to prepare composite phase change storage material(CPCM),and the thermal properties of composite material were further optimized to lay a foundation for industrial application.The main contents and conclusions are as follows:Firstly,borax with different mass fraction was selected as nucleating agent,and then mixed with mirabilite to test the step cooling curve,and the lowest supercooling ratio was selected.After determining the optimum addition ratio of borax,ammonium chloride with different mass fraction was added as phase change temperature regulator.The above experiments were repeated to screen out the that meet the phase change temperature required for cooling storage,which is the best PCM.The experimental results show that when the mass fraction of borax is 3% ammonium chloride,the undercooling degree of the material is less than 2? and the phase transition temperature is 16.2?,which meets the requirements.Second,the expanded vermiculite(EV)was used as the carrier to load the selected PCM,the material was loaded into the micropores of the expanded vermiculite by vacuum adsorption,the micro-scale locking was used to solve the PCM phase separation problem,the composite phase change material was prepared CPCM,and the thermal physical properties parameters of the CPCM were measured experimentally.The microstructure was observed.Finally,the mass ratio of the EV to the PCM reached the load limit at 1:6,and the internal thermal conductivity and cold storage were improved,The phase transition temperature is 16.2? and the total cooling capacity is 120.68 k J/kg.Thirdly,a thermal cycle test system is built to test the prepared CPCM and study its thermal cycle stability.When the inlet water temperature is 24? at low flow rate,the CPCM cooling release is more sufficient and more stable when the inlet water temperature is 24?,and the influence of the material packaging diameter on the material melting-solidification cycle is investigated,then the pipe diameter is 30 mm,the water bath temperature is 7?9;hence,the CPCM working parameters are determined for practical applications.Fourth,the theoretical derivation of the internal temperature distribution of the tube cooling storage element is helpful to understand,whether the phase transition in the tube is uniform during the actual heat transfer process.Finally,a large capacity heat storage and heat transfer device is designed with practical application,and its special structure is innovative.This paper provides experimental support and theoretical guidance for the practical application of cold storage technology. |
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