Abstract:

The phase change material (PCM)-based direct absorption/storage solar collector (DASSC) has the advantages of less heat transfer process, lower thermal energy loss, and higher photothermal conversion efficiency. The PCM exhibits limited light absorption capacity and low thermal conductivity, leading to significant temperature gradients and a low heat transfer rate in DASSC. Current research predominantly addresses the heat storage process in DASSC, with insufficient focus on the characteristics of the heat release process. To address this gap, a photo-thermal conversion shaped composite PCM (CPCM) is prepared using a melt blending method in conjunction with a vacuum adsorption technique. The DASSC is subsequently developed, leveraging the high absorption and substantial heat storage density properties of the CPCM. The light absorption and phase change characteristics of the CPCM are tested, and the effects of inlet temperature and Reynolds number of the heat transfer fluid on the heat release characteristics of the DASSC are investigated. The sensitivity and correlation of these two parameters on the heat release rate of DASSC are analyzed using the Morris method. The findings indicate that the absorbance of CPCM is 3.03 times that of pure PCM. Additionally, when the inlet temperature decreases from 16.0℃ to 10.0℃, the average heat release rate of DASSC increases by 47.7%. As the Reynolds number increases from 2462 to 5628, the average heat release rate of the DASSC exhibits a 15.0% enhancement. The sensitivity and correlation of the inlet temperature on the heat release rate of the DASSC are significantly higher than those of the Reynolds number. The optimal value of the inlet temperature should be calculated separately in the design and optimization of the heat release performance of DASSC, while the Reynolds number can be directly determined based on the positive and negative correlation.

Key words: phase change, solar energy, thermodynamic properties, photo-thermal conversion, storage solar collector

摘要：

基于相变材料（PCM）的太阳能直接吸收相变集-蓄热器（DASSC）具有传热环节少、热能损失低、光热转化效率高的优势。PCM自身吸光能力弱、导热性能差，导致DASSC温度梯度大、传热速率慢，且现有研究大多针对DASSC的储热过程，缺少对放热过程特性的研究。为此，采用熔融共混法结合真空吸附法制备了光热转化定型复合相变材料（CPCM），并基于CPCM的高吸收性和高蓄热密度特性构建DASSC。测试了CPCM的光吸收特性和相变特性，探究了传热流体进口温度和Reynolds数对DASSC放热特性的影响规律，基于Morris方法分析了两种参数对DASSC放热速率影响的敏感性和相关性。结果表明，CPCM的吸光度是纯PCM的3.03倍。当传热流体入口温度从16.0℃降低至10.0℃时，DASSC平均放热速率提高47.7%；当Reynolds数从2462增大至5628时，DASSC平均放热速率提高15.0%。进口温度对DASSC放热速率影响的敏感性和相关性都显著高于Reynolds数。进口温度在DASSC的放热性能设计和优化中应单独计算最优值，而Reynolds数可根据正负相关性直接确定。

关键词: 相变, 太阳能, 热力学性质, 光热转化, 集-蓄热器