Computational study of fluid flow and heat transfer in composite packed beds of spheres with low tube to particle diameter ratio

• Published in: Nuclear engineering and design 2016-04, Vol.300, p.85-96
• Main Authors: Yang, Jian, Wu, Jiangquan, Zhou, Lang, Wang, Qiuwang
• Format: Article
• Language: English
• Subjects: Heat transfer; Laminates; Multilayers; Packed beds; Particulate composites; Tubes; Wall effects; Walls
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2015.10.030

•Flow and heat transfer in composite packed beds with low dt/dpe are investigated.•The wall effect would be restrained with radially layered composite packing (RLM).•Heat flux and overall heat transfer efficiency can be improved with RLM packing. The effect of the tube wall on the fluid flow and heat transfer would be important in the packed bed with low tube to particle diameter ratio, which may lead to flow and temperature maldistributions inside, and the heat transfer performance may be lowered. In the present paper, the flow and heat transfer performances in both the composite and uniform packed beds of spheres with low tube to particle diameter were numerically investigated, where the composite packing means randomly packing with non-uniform spheres and the uniform packing means randomly packing with uniform spheres, including radially layered composite packing (RLM), axially layered composite packing (ALM), randomly composite packing (RCM) and randomly uniform packing (RPM). Both the composite and uniform packings were generated with discrete element method (DEM), and the influence of the wall effect on the flow and heat transfer in the packed beds were carefully studied and compared with each other. Firstly, it is found that, the wall effect on the velocity and temperature distributions in the randomly packed bed of uniform spheres (RPM) with low tube to particle diameter ratio were obvious. The average velocity of the near-tube-wall region is higher than that of the inner-tube region in the bed. When the tube wall is adiabatic, the average temperature of the near-tube-wall region is lower. With radially layered composite packing method (RLM), smaller pores would be formed close to the tube wall and big flow channels would be formed in the inner-tube region of the bed, which would be benefit to restrain the wall effect and improve heat transfer in the bed with low tube to particle diameter ratio. Furthermore, it is also found that, with composite packing method (RLM, ALM and RCM), both the pressure drop and heat flux are higher than those in the uniform packing (RPM). And with radially layered packing method (RLM), the flow resistance would be reduced, and both the heat flux and overall heat transfer efficiency would be further improved for the composite packing with low tube to particle diameter ratio.