An Experimental Study On Phase Change Materials Used As Low-temperature Cool Storage And Their Characteristics Of Cool Charge

Developing cool thermal energy storage technology is an important measure to realize shifting electrical energy demand from peak period to off-peak period. At present, cool storage technology is applied mainly to air-conditioning in buildings, but it's potential to extend its application range with the development of technology. Therefore, R&D of low-temperature cool storage has important theoretical and practical significance.Some binary eutectic salt systems were tested by experiment, and a sort of binary eutectic salt was found whose phase change temperature is - 8.6C, which is most possible to use as cool storage material. In addition, a part of thermophysical properties of this material was tested. It's also analyzed for the phenomena of super-cooling and phase segregation of this material. The results show that this material is hopeful to apply in the field of beer freeze plant, freezing store and some chemical industry.It's used widely for internal melting ice-on-coil storage tank, so a cool storage experimental apparatus with internal melting ice-on-vertical-coil was set up, and the characteristic of cool charge and discharge of the above material are experimentally investigated in this apparatus, which is a basis in the design of cool storage project.The factors influencing cool charging and discharging properties include the structure and size of heat exchanger, the initial temperature and thermophysical properties of the cool storage material, the temperature and volumetric flux of coolant et al. The later is primarily studied in this thesis, and the experimental results show as follow:(1)The temperature of coolant at the cool storage tank inlet strongly affect the charging and discharging properties, In the charging process, the lower the inlet temperature, the quicker the freezing rate, the larger the cool charging rate, the less the time required for the same charging capacity. In the discharging process, the higher the inlet temperature, the quicker the melting rate, the larger the cool discharging rate, the more the cool energy supplied in the definite time.㏕he charging and discharging properties is weakly influenced by the volumetric flux of coolant. Adding the volumetric flux will appreciably quicken the freezing rate of the charging process and the melting rate of the discharging process in the initial stage,but the increment is small.(3)The heat transfer in the charging and discharging process are unsteady, and the heat transfer capability of the system will change against time, and the charging rate and discharging rate decreases gradually with time, as should be noticed in the design.(4)It's a dominant part of the total thermal resistance for the one of the ice layer in the charging process and the solution layer in the discharging process outside the coils. So the emphasis of heat transfer enhancement lies in increasing the conduction coefficient of the cool storage material outside the coil.(5)It's was concluded for a empirical correlation of natural convective heat transfer along the vertical tubes based on the experimental data.Nu = 0.2994(GrPr)03029 for the similar conditions to this experimental apparatus and 107