Analysis and intensification of the thermal performance in packed beds based on simulation and experiment
The presence of walls has a significant influence on the flow and heat transfer in packed beds, which are widely used in the chemical industry. It may lead to uneven flow and temperature distribution, thus reducing heat transfer performance. To suppress the wall effect, the present study proposes four different composite-packed structures by the discrete-element method (DEM), including the radially layered composite-packed model (Radially-LM), axially layered composite-packed model (Axially-LM), randomly composite-packed model (Randomly-CM), and randomly uniform-packed model (Randomly-UM). These flow and heat transfer characteristics are investigated by numerical simulations and a confirmatory experiment. Among the four models, Randomly-UM showed the most obvious wall effects on the velocity and temperature distributions. The velocity near the wall is higher and the temperature is lower than those of central area. The flow and temperature fields in the Radially-LM are more uniform than the other models. By analyzing the variations in the pressure drop with the inlet flow velocity and the Nusselt number with Reynolds number, the Radially-LM achieves a lower flow resistance and higher heat transfer efficiency. Therefore, the novel packed structure is reliable at reducing the flow resistance and improving the heat transfer efficiency in packed beds by suppressing the wall effects.
Keywords: Wall effect, Packed beds, DEM, Flow and heat transfer, Radially layered composite-packed model,