Investigation Of The Heat Transfer And Cool Storage Characteristic Of Composite Shelf Filled With Phase Change Materials

As the terminal device of food cold chain, vertical open refrigerated display cabinet(VORDC) plays an important role in the food quality and safety. While, due to its own structure characteristics, there have some disadvantages in the VORDC, such as, the food package temperature is easily affected by the outside environment, and the temperature distribution is uneven inside the VORDC, especially the temperature fluctuation of food packages is larger, during the defrosting time. For the existing problems, the composite shelves filled with phase change materials(PCMs) are applied in VORDC to improve its performance, in this paper. Investigates the cool storage characteristics and heat transfer performance the of PCMs in experiment, and analyzes the temperature distribution of food packages after filling the composite PCMs in the composite shelf in VORDC. The research content is as follows:Firstly, in this paper, three kind of organic phase change materials(RT3, RT4 and RT5) are filled in the VORDC composite shelf, the cool storage and heat transfer characteristics of the materials are investigated. The results show that compared with the ordinary shelf, the food packages temperature difference on both side of the composite shelves(RT3, RT4 and RT5) are reduced by 40%, 80% and 40%, respectively; the average temperature of food packages are reduced by 13.7%-32%, and the temperature fluctuation of food packages are reduced by 53.3%-83.3%, during defrosting. In three kind of composite shelves, the lowest temperature of food packages is RT4 composite shelf, and the mean food packages temperature at each layers and rows are controlled in 5?.Secondly, besides the influence of outside environment, the low thermal conductivity coefficient of PCMs also affects the temperature distribution, therefore the food packages temperature difference is big, both on the horizontal and vertical directions in VORDC. In order to improve thermal conductivity coefficient of RT4, carbon nanotubes are mixed in RT4 to improve its thermal conductivity. The results show that with the increasing mass fraction of carbon nanotubes, the phase change enthalpy of composite PCMs is reduced, and the thermal conductivity coefficient of composite PCMs is improved. Compared with the pure RT4, the liquid thermal conductivity of 1%-CNT, 2%-CNT, 3%-CNT, 4%-CNT and 5%-CNT composite PCMs are increased by 12.8%, 22.6%, 22.6%, 39.2% and 44.0%, respectively, in the heating process.Thirdly, the thermal conductivity coefficient of composite PCM is increased with the increasing mass fraction of carbon nanotubes, but the increase amplitude is reduced. This is because the increasing carbon nanotubes can reunite in RT4. Therefore, the 3%-CNT composite PCMs are adopted to investigate the influence of the composite PCMs on the temperature of food packages in VORDC. The results show that the temperature difference of food packages on 3%-CNT composite shelf between left and right side is around 0.1?, and between front and rear row is around 3.2?, which are lower than that of RT4 composite shelf. The food packages temperature are all controlled in 4?, and maintaining the temperature level in refrigerated display cabinet relatively stable.