Preparation, thermal performance and potential application of micro encapsulated PCM slurry and phase change micro-emulsion in the field of HVAC

Microencapsulated phase change material (PCM) slurry and phase change micro-emulsion are two kinds of novel two-phase heat transfer fluids. Compared with convectional single-phase heat transfer fluid such as water, their apparent specific heat in the phase change temperature range is greatly increased. Due to that, the heat transfer ability and energy transport ability can be obviously improved. Therefore, they have many potentially important applications in the fields such as heating, ventilating, and air-conditioning (HVAC), refrigerating and heat exchangers etc.. In the present paper, the preparation methods and conditions of microencapsulated tetradecane slurries and tetradecane micro-emulsions are investigated and their thermophysical properties are measured. The convective heat transfer enhancement mechanism of such two-phase heat transfer fluids is analyzed. Two kinds of models, i.e., the effective specific heat model and the internal thermal source model, are developed. By using them respectively, the influences of each factor on the heat transfer enhancement of such fluid flow in a circular tube are quantitatively analyzed. The simulated results are validated with the results available in the literature. Besides., this paper states the flaws of conventional Nusselt number in describing the heat transfer characteristics of such fluids and presents a modified Nusselt number for overcoming the flaws. Based on the thermophysical properties of the tetradecane micro-emulsion developed by us, the application of such fluid in the field of HVAC is primarily studied.