ZnO对不同流态下相变微胶囊悬浮液对流换热特性影响研究*

相变微胶囊悬浮液（MPCS）可作为热交换介质和储热流体,但其导热率较低导致其应用受到一定的限制。以水为基液使用相变微胶囊（MPCM）制备MPCS,加入氧化锌（ZnO）颗粒以提高MPCS导热率。使用旋转流变仪、差式热量扫描仪、导热仪分别测定了MPCS的黏度、相变潜热和导热系数等物理性质。设计并搭建了试验台,在内径6 mm的圆管中,使用水、MPCS以及ZnO@MPCS在层流和湍流下进行强制对流换热实验,通过对比其换热情况分析ZnO对MPCS换热特性的影响。结果表明：加入ZnO的MPCS具有良好的储热性和导热性,1%ZnO@5%MPCS导热系数较5%MPCS提高了17.9%。层流条件下MPCS的平均局部换热系数低于水,1%ZnO@5%MPCS平均局部换热系数比水高6.5%;湍流时,1%ZnO@5%MPCS在相同质量流量和功率下的平均局部换热系数相较于水提高了15.7%。

Effect of ZnO on Convective Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry under Different Flow States

Microencapsulated phase change material slurry (MPCS) can be used as heat exchange medium and heat storage fluid. However, its low thermal conductivity limits its application. By using water as base liquid, the MPCS was prepared with microencapsulated phase change material (MPCM), and zinc oxide (ZnO) particles were added to improve the thermal conductivity of MPCS. Properties of the MPCS such as viscosity, phase change latent, heat thermal conductivity, etc., were measured by rotating rheometer, differential heat scanner and thermal conductivity instrument, respectively. A test-bed was designed and built. In a circular tube with an inner diameter of 6 mm, forced convection heat transfer experiments were carried out with pure water, MPCS and ZnO@MPCS under laminar flow and turbulence. By comparing the heat transfer conditions, the effect of ZnO on the heat transfer characteristics of MPCS was analyzed. The results showed that the prepared MPCS had good heat storage and thermal conductivity. The thermal conductivity of 1%ZnO@5%MPCS was 17.9% higher than that of 5%MPCS. The average local heat transfer coefficient of MPCS under laminar flow was lower than that of water, and the average local heat transfer coefficient of 1%ZnO@5%MPCS was 6.5% higher than that of water. In turbulent flow, the average local heat transfer coefficient of 1%ZnO@5%MPCS under the same mass flow and power was 15.7% higher than that of water.