Influence of flow guiding conduit on pressure drop and convective heat transfer in packed beds

Packed beds with large tube-to-particle diameter ratios (D/d) suffer from poor lateral heat transport. Consequently, for applications with internal heat generation, fluid with high temperature concentrates in the center of packed beds, which is unfavorable to the design of high efficiency reactors. To address this problem, a novel method is developed: a free channel-flow guiding conduit (FGC)-is constructed in the center of a packed bed using highly fluid-penetrable material. Therefore, in the presented work, CFD simulations are carried out to study the influences of FGC to a conventional packed bed on packing structure, fluid flow distribution as well as heat transfer. It shows that cold fluid with high velocities is guided directly into the original hot zones where fluid temperature is generally higher in a conventional packing. Fluid flow in the lateral direction can be promoted with the Venturi effect. Moreover, with the FGC in proper sizes, pressure drop can be reduced about 16-26%; heat transfer coefficients merely drop 4-6%. However, although favorable effects could be achieved using the FGC, it is also observed that if an oversized flow guiding conduit was imposed into a packed bed, loss of effective cooling for particles would be also resulted since excess fluid could bypass through the conduit. Consequently, unexpected fluid temperature distribution could get some recovery. These findings are helpful for understanding of transport phenomena in packed beds as well as the design of high efficiency reactors. (C) 2019 Elsevier Ltd. All rights reserved.