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EXPERIMENTAL AND NUMERICAL MODELLING OF ENHANCED THERMAL DIFFUSION IN A STRUCTURED PACKED BED

DOI: 10.1615/ICHMT.2012.CHT-12.1050
pages 1741-1753

Charl G. Jat Du Toit
School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa

Pieter G. Rousseau
North-West University, Department of Mechanical Engineering, University of Cape Town, Upper Campus, Rondebosch, 7701, South Africa

T.L. Kgame
School of Mech. & Nuc. Eng., NWU, Potchefstroom, South Africa

A.C.N. Preller
School of Mech. & Nuc. Eng., NWU, Potchefstroom, South Africa

要約

The effective thermal conductivity in high temperature packed bed reactors is usually derived by lumping all the relevant heat transfer mechanisms into a single representative value. It can be split into two or more contributing components. Here the focus is on the fluid effective thermal conductivity which characterises the enhanced thermal diffusion in the fluid due to the turbulent mixing that occurs due to the porous structure of the packed bed. A brief overview is given of the Braiding Effect Test Sections (BETS) with homogeneous porosities of 0.36, 0.39 and 0.45 that were constructed to investigate this phenomenon. To determine the thermal diffusion, sets of thermocouples were installed at two levels in the packed beds contained in the BETS. The BETS were mounted in the pressure vessel of the High Pressure Test Unit (HPTU) and the experiments were performed under suitable quality assurance certification. A thorough uncertainty analysis was performed on all measured variables and error propagation was used to determine the uncertainty associated with derived variables. Four test runs were performed to ensure repeatability. The measured temperature profiles were normalised to account for the varying ambient conditions between the test runs. A numerical model was generated of a quarter of the cross section and the lower half of the BETS36 test section. The grid was generated according to the findings of a thorough grid dependence study and LES was found to be the best to model the turbulent nature of the flow. The relevant data from one test case was used as the boundary conditions for the simulation. Good agreement was obtained between the simulated and the corresponding measured temperatures. Based on the uncertainty associated with the positions of the thermocouples and the temperature gradients in the bed, the simulation could explain the scatter in the measured temperatures.

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