球形容器内复合相变材料的约束熔化传热过程

为评估高导热填料对复合相变材料熔化传热过程的影响,采用实验方法定量分析典型球形容器中添加石墨纳米片的十二醇基复合相变材料的约束熔化传热过程.以熔化过程中的瞬时质量熔化率为比较对象,对石墨纳米片的质量分数和恒温加热边界条件进行参数化研究.实验结果表明,随着质量分数的增加,复合相变材料的熔化传热过程从以自然对流为主导逐渐转变为以导热为主导.在所研究的工况范围内,虽然复合相变材料的导热系数有一定程度的提高,但不足以弥补黏度增长所引起的自然对流削弱效应,反而使得熔化过程有所减缓.通过数据拟合得到了熔化率随傅里叶数、斯蒂芬数和格拉晓夫数等特征无量纲数变化的实验关联式,其预测结果的误差小于15%.

微能源系统中多能传输、存储与转换过程的影响机制

将用户侧电、热、气等多种形式能源集成构建微能源系统,能够综合考虑多能流的转换、存储与传输过程中的互补特性,有利于提升系统的整体能源利用效率。然而,系统中不同形式能量的物理属性和传输特性差异较大,现有模型在研究多能流的传输和转换过程时,难以完整考虑热量传输约束及其对能量转换的影响。针对微能源系统中的综合能量管理问题,构建了热力系统中换热器的非线性传热模型,并考虑了热量传输对能量转换效率的影响。同时,结合光伏电池、储能电池、热泵、燃气锅炉、太阳能集热器及相变储热装置建立了微能源系统中能量传输与转换的整体模型,并以系统投资与运行总成本最小为目标构建了优化模型,提出了一种以混合整数线性优化为基础的分层迭代优化策略,通过对系统进行优化设计,研究了热量传输、转换与存储过程间的相互影响。对比发现:未考虑热量传输对热泵和太阳能集热器效率的影响时,太阳能集热器总出力为考虑热量输传输影响的80.2%,储热装置最佳容量仅为考虑热量输传输影响的48.9%。

Modeling and Parametric Study of the Heat Transfer Inside a Lithium Bromide Flow Confined by Wire Screen

The present study deals with the numerical analysis of heat transfer inside a lithium bromide-water solution flowing down between finely meshed plastic wire screens. These screens confine the flow through capillary action while allowing the water vapour transfer inside an innovative absorber technology. The complex menisci shape formed on the confinement grid level, where the surface tension forces are of first importance, are reconstructed by a volume-of-fluid model. A continuum surface force model is used to account for the surface tension force. A static contact angle is used to define the wall adhesion. A new algorithm, consisting to set an unique constant temperature at the liquid/vapour interface and to determine the evolution of heat transfer characteristics over the simulation domain, has been implemented and validated by analytical solution. A parametric study has been conducted to determine the effect of the geometry, the contact angle and the shape of the wire on the heat transfer.