2011 Annual Meeting

(312b) CFD Based Simulation of Heat Transfer In a Fixed Bed Reactor Tube

Authors

Mohsen Behnam - Presenter, Worcester Polytechnic Institute
Anthony G. Dixon - Presenter, Worcester Polytechnic Institute


Low N (tube to particle diameter ratio) fixed bed reactors are commonly used in the chemical industry for extremely endothermic and exothermic reactions due to the better heat transfer. In the past, lots of researches have been carried out to simulate the heat transfer in fixed bed reactors by using kr/kf and hw. Most models for kr/kf and hw are based on a direct correlation with Re and N. Although most models seem to predict kr/kfvery well, but there is a lot of problem still exists to predict hw[1-2]. The main objective of this study was to develop a new heat transfer model with emphasis of industrial application for conduction and convection heat transfer in fixed bed tubes without using kr/kf and hw.

Fluid flow in a fixed bed of tube to particle ratio 3.96, 5.96 and 7.99 were obtained for packed bed column by solving the 3D Navier–Stokes and using commercial software FLUENT 6.3.26. The heat transfer was modeled by using pseudo-homogenous energy equation. COMSOL 3.5 was used to simulate heat transfer based on pseudo-homogenous equation in 2D. Effective radial thermal conductivity was calculated from Zehner-Schlünder model as function of bed porosity position, fluid thermal conductivity and solid thermal conductivity [3]. The convection heat transfer was calculated in the 2D flow fluid from the CFD run.

Results were obtained for Reynolds numbers in the range 240–1900. The accuracy of the new model has been validated by analytical solution. The temperature calculated by the pseudo-homogenous energy equation showed reasonable quantitative agreement with values predicted by CFD model.

[1] S. A. Logtenberg, A. G. Dixon, “Computational fluid dynamics studies of fixed bed heat transfer”, Chemical Engineering and Processing 37 (1998) 7–21.

[2] A.G. Dixon, “An improved equation for the overall heat transfer coefficient in packed beds”, Chem. Eng. Process. 35 (1996) 323.

[3] P. Zehner, E.-U. Schlunder, “Die Effective Warmeleitfahigkeit Durchstromter ugelschuttungen bei Massigen und Hohen Temperaturen”, Chem. Ing. Tech. 45 (1973) 272.