Microencapsulated phase change material suspensions have many potential applications in the fields of energy storage, air-conditioning and exchanger, etc. In this paper, stable microencapsulated phase change material suspensions are prepared with the water–propanol mixture as the base fluid and the addition of dispersants. The dependence of the specific heat, phase change enthalpy, rheological behavior and thermal conductivity of such fluids on the concentration and temperature is experimentally determined. And the heat storage and the natural convective heat transfer performance of tube immersed in the 10wt%–30wt% microencapsulated phase change material suspensions are experimentally studied. The result shows that the natural convection process can be characterized by three regimes: the pure conduction, the quasi-steady and the decay period. The convective heat transfer coefficient of a thick suspension is lower than the diluted one, although more heat can be stored by the thick suspension. And the increase of the temperature and flow rate of heat transfer fluid inside the tube is beneficial to the natural convective heat transfer performance.

Conclusions

In this paper, the experimental research on the natural convective heat transfer of a circular tube heat exchanger immersed in microencapsulated phase change material suspensions was performed. The 10~30wt% water–propanol based MPCMS with 0.2wt% SDS and 0.4wt% alginate as the dispersant was formulated and shows the best stability. And the thermo properties of such fluids were studied. DSC measurement of MPCM particles indicates that the onset temperature of melt/solidify is 50.85 °C/58.11 °C with the latent heat of 152.8 J/g. Tested with rheometer, MPCMS behaved as Newtonian fluid characteristics and the viscosity increased with mass fraction of MPCM and decreased linearly with temperature. And the thermal conductivity of MPCMSs was found to increase with temperature, but had a sudden decrease after the phase change region. An experimental rig is built to investigate the natural convective heat transfer characteristics of an immersed tube with the surrounding heat storage media by using 10wt%–30wt% MPCMSs and the base fluid as the heat storage media, and the effect factors including HTF flow rate and HTF inlet temperature are also studied. Conclusions from the experimental results can be summarized as below:

(1) More heat stored and smaller temperature rise are obtained by the MPCMS with higher concentration and 44% more heat was absorbed by the 30wt% MPCMS than the base fluid. But the natural connective heat transfer coefficient decreases with concentration due to the increase of viscosity.

(2) The transient heat transfer coefficient was found to decrease at the pure conduction process initially, then remained nearly constant at the quasi-steady process, and finally decreased during the decay period. Affected by the phase change latent heat, the quasi-steady period was prolonged and the decay period was delayed for the more concentrated MPCMS.

(3) The rise of HTF temperature and HTF flow rate is beneficial to both the charging process and the natural heat transfer performance.

The results have been published on Applied Thermal Engineering 99 (2016) 583–590.