相变微胶囊悬浮液传热特性实验研究

Experimental investigation on heat transfer characteristics of microencapsule phase change suspension

相变微胶囊(microencapsulated phase change material,MPCM)在建筑节能领域应用广泛,为研究其传热特性,搭建了以水为换热流体(heat transfer fluid,HTF),微胶囊悬浮液为储能介质的潜热储能(latent thermal energy storage,LTES)系统。在实验过程中,通过改变换热流体的进口初始温度以及搅拌器的搅拌速率,获得了MPCM悬浮液的温度变化规律并计算了MPCM悬浮液的平均充放冷速率。实验结果表明:在充冷过程中,MPCM相变时温度变化速率减缓,相变温度区间较大,而在放冷过程中,MPCM相变时温度保持恒定,相变温度区间较小;未搅拌时,MPCM悬浮液中温度梯度较大,传热能力较差;搅拌时,MPCM悬浮液混合均匀,其温度梯度很小,传热能力较强;增加搅拌器的搅拌速率及水与相变微胶囊悬浮液的温差均可以提高MPCM的充放冷速率。

Microencapsulated phase change materials(MPCM) have been widely used in building energy conservation systems. In order to investigate the heat transfer characteristics of MPCM, the latent thermal energy storage(LTES) tank system, adopting MPCM slurry as the thermal storage medium and water as heat transfer fluid(HTF), was constructed. A series of experiments were carried out under different initial inlet temperatures of HTF and stirring rates of an axial stirrer. The temperature evolutions of MPCM slurry were obtained and the mean charging and discharging rate were calculated to evaluate the performance of the LTES tank. The experimental results indicate that, during the charging process, the temperature change rate of MPCM slurry decreases slowly during the phase change stage and the temperature range of phase transition is larger. During the discharging process, the MPCM slurry temperature is nearly kept constant and the temperature range of phase transition is smaller. A significant temperature gradient is observed in the LTES tank at a stirring rate of 0 rpm and the heat transfer capacity is weakened. The MPCM slurry is mixed uniformly with the stirring operation and there is insignificant temperature gradient in the LTES tank, and the heat transfer capacity is enhanced accordingly. Larger stirring rate and temperature difference between the HTF and MPCM can increase the mean charging and discharging rate of MPCM slurry.