Assessment of flow pattern and temperature profiles by residence time distribution in typical structured packed beds

Abstract

The flow and temperature fields in packed beds are rather complex but are of great importance since they will influence macroscopic parameters and the overall performance of the packed bed system. Regions with either too high or too low velocity are not preferred since they will decrease the heat and mass transfer characteristics of packed beds. The residence time distribution (RTD) is a way to assess the characteristics of the flow maldistribution, where a narrower distribution is closer to the ideal plug flow with less dispersion. In this article, the RTD in three typical structured packed beds, namely, the simple cubic (SC) packing, the body-centered cubic (BCC) packing and the facecentered cubic (FCC) packing, are studied by using ANSYS FLUENT. Results show that, firstly, the RTD curve can be used to diagnose the flow pattern in packed beds where the skewed peak indicates the channeling effect and a long tail relates to recirculation. It is revealed secondly that, FCC packing has the narrowest RTD curve in the studied structures, BCC packing comes second and SC packing has the flattest RTD curve, which demonstrates that the flow uniformity in FCC packing is the best. For the same packing form, the flow is less maldistributed at higher velocity. Finally, it is shown that the packing form with less dispersion, which behaves more like the ideal plug flow, has a more uniform distribution of the particle-to-fluid heat transfer coefficient near the particle surface.

Numerical study of flow inhomogeneity and heat transfer enhancement in structured packed beds

“…The tracer concentration of the fluid domain is calculated and followed until it completely exits the outlet. The duration time of the tracer injection should be lower than 1% of the whole mean residence time [15]. The time step used in the present study is 5×10 -5 s. The convergence of each time step is reached when the residual of the tracer concentration is less than 10 -6 and the total time step of the calculation is 10000.…”

“…Guo et al [14] revealed that there is a relationship between the velocity distribution on a cross section and the RTD curve. Wang et al [15] studied the RTD in three typical structured packed bed and reported a relationship between the RTD and the heat transfer. Stepanov et al [16] studied the residence time by Lagrange particle tracking method in CFD to determine the influence of baffles in a combustion chamber.…”

Principles, technology, and application of transfer processes for energy saving and storage

“…纵向波纹内翅片管被用于空分系统冷却器(图10), 替 代原设计选用的整体轧制翅片管, 既提高了换热性 能, 又显著减小了换热器体积, 设备重量仅为原来的 1/4~1/3, 大幅降低了制造成本. [34,39] . 停留时间分布方差(VRTD)越小, 说明孔 隙结构中的流动越接近于理想推流, 对应的推流度越 高, 流动分布越均匀.…”

High-Throughput Routes to Biomaterials Discovery

“…The impacts of viscosity, velocity profile, and residence time gradients on outputs from thermal polymerization systems in continuous flow reactors has been investigated. , Based on these learnings, Corrigan et al investigated similar effects for PET-RAFT polymerization, aiming to tune and manipulate the shape of molecular weight distributions in PET-RAFT (Figure A). It was noted that several approaches could be used (e.g., the flow rates of the reactant streams, the chemical concentrations entering the reactor) to produce polymeric products with tailored molecular weights.…”