Abstract
Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry length of 66% and an overall heat transfer increase of up to 120% are found.
Highlights
Since the early 1950s, numerous authors have investigated fixed bed reactors regarding the packing structure [1], fluid flow [2] and heat and/or mass transfer [3]
discrete element method (DEM) is used for the generation of the fixed bed while the local flattening meshing strategy [15] is adopted for the mesh generation with some slight modifications
As expected for R1 the void fraction is constant over the radius while for R7, the tube without any wall structure, the well-known oscillating void fraction profile is obtained
Summary
Since the early 1950s, numerous authors have investigated fixed bed reactors regarding the packing structure [1], fluid flow [2] and heat and/or mass transfer [3]. Several mathematical models have been developed to predict the pressure drop and to describe heat and mass transfer phenomena. These models can be divided into three fundamentally different categories: . Pseudo-homogeneous models, in which particles are not explicitly resolved. Their impact on pressure drop and heat/mass transfer is considered by using effective transport parameters that incorporate all non-resolved phenomena. Several heat transfer correlations for pseudo-homogeneous reactor modeling were evaluated [4]
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