Experimental and numerical study of constrained melting of n-octadecane with CuO nanoparticle dispersions in a horizontal cylindrical capsule subjected to a constant heat flux
Experimental and numerical study of constrained melting of n-octadecane with CuO nanoparticle dispersions in a horizontal cylindrical capsule subjected to a constant heat flux
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DOI：
10.1016/j.ijheatmasstransfer.2013.08.001
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发表时间：
2013-12
影响因子：
5.2
通讯作者：
N. Dhaidan;J. Khodadadi;T. Al-Hattab;Saad M. Al-Mashat
中科院分区：
文献类型：
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作者：
N. Dhaidan;J. Khodadadi;T. Al-Hattab;Saad M. Al-Mashat
采用实验和数值模拟相结合的方法研究了正十八烷作为相变材料（PCM），CuO纳米颗粒作为导热增强剂（TCE）在水平圆柱形容器中的约束熔化过程。这些实验需要记录测试单元内不同径向和角坐标处的温度，从而允许在各种热通量速率和多个纳米颗粒重量浓度下监测熔化前沿的进展。同时控制守恒方程求解计算利用有限元方法。对计算模型进行了验证，结果与前人的相关工作吻合较好。模拟结果与实验结果吻合较好。的纳米粒子的重量浓度和施加的热通量（瑞利数）的熔化特性的影响进行了检查。熔化过程的特征在于固体-液体界面的形状、熔化速率、熔体分数和充电时间的进展。实验和数值计算结果表明，有一个增强的熔化特性与纳米粒子负载（加强有效导热系数）和瑞利数（增强自然对流的作用）的增加。熔化过程中的这种增强可以通过增加熔化速率来指示，这导致熔化时间的加速。在熔化的早期阶段，传导是主导的，导致同心等温线和高熔化速率。随着时间的推移，自然对流将发展并增加圆柱形容器顶部区域的熔化速率。另一方面，熔化在底部区域是由传导和二次再循环流动，由于热不稳定性，这是由波度的界面有记录。随着瑞利数的增加，熔体分数、熔化速率和充注时间的增加速率都有所提高。此外，对于低纳米颗粒浓度，熔化的加速速率非常高，并且随着纳米添加剂的量增加，其将降低，因为粘度、团聚和沉淀的增强效应可能抵消热导率的增强。
Constrained melting ofn-octadecane as phase change material (PCM) dispersed with CuO nanoparticles as thermal conductivity enhancer (TCE) that was contained and heated in a horizontal cylindrical vessel under a constant heat flux is investigated experimentally and numerically. The experiments entailed recording of temperatures at different radial and angular coordinates inside the test cell, thus allowing for monitoring the progress of the melting front under various rates of heat flux and multiple nanoparticle weight concentrations. The simultaneous governing conservation equations are solved computationally by utilizing the finite element approach. The computational model is validated and the results showed a good agreement with previous related work. The agreement between the experimental and simulated results is reasonable. The effects of the nanoparticle weight concentration and the amount of applied heat flux (Rayleigh number) on the melting characteristics are examined. The melting process is characterized by progress of the shape of the solid–liquid interface, melting rate, melt fraction and charging time. The experimental and numerical results reveal that there is an enhancement in melting characteristics with the increase of both nanoparticle loading (intensifying the effective thermal conductivity) and the Rayleigh number (augmenting the role of natural convection). This enhancement in the melting process can be indicated by increasing the melting rate which leads to acceleration of the melting time. In early stages of melting, conduction is dominant leading to concentric isotherms and high melting rate. As time progresses, natural convection will develop and increase the melting rate in the top region of the cylindrical container. On the other hand, melting at the bottom region is governed by conduction and secondary recirculation flow due to thermal instabilities which are recorded by waviness of the interface there. The melt fraction, melting rate and rate of enhancement in charging time are improved with the increasing of the Rayleigh number. Additionally, the rate of acceleration of melting is comparably high for low nanoparticle concentration and it will degrade as the amount of nano-additives increases as the augmentation effect of viscosity, agglomeration and precipitation may be negating the enhancement in thermal conductivity.