Iranian Journal of Chemical Engineering (IJChE)

Abstract In the present study a mathematical model is developed in order to examine the effects of heat and mass transfers on removal efficiency of particulate matters in venturi type scrubbers. The governing equations including the variations of the particulate concentration, gas temperature, droplet temperature, diameter, and velocity are obtained based on the conservation laws and are solved numerically. In order to validate the model, necessary data was measured and collected in a commercial cement plant that uses these types of scrubbers in air pollution control applications. A good agreement between plant data and the model predictions is noticed in general. The results obtained from the model reveal that the existance of temperature difference between the gas and the liquid droplets decreases the overall removal efficiency of particulate matters. This is due to sudden reduction ofrelative velocity between the gas and droplets which is resulted from the existence ofheat and mass transfers between the two fluids, especially in the throat section. In addition, the effects ofvarious operating parameters on the extent ofreduction in the removal efficiency are examined. This study confirms that in most industrial applications ofventuri scrubbers it is necessary to use a direct or an indirect cooling tower in order to decrease the gas temperature before entering the venturi.

Abstract In this study a mathematical model is developed in order to simulate fluorination reaction of uranium dioxide which leads to the production of uranium hexafluoride. The model considers homogeneous reaction for intermediate solid and a heterogeneous one for unreacted shrinking core. Also, this study tries to clearly show the shortcoming of some of the well-known models that take heterogeneous reactions for both solids. In fact, one may not trust the accuracy of those models due to the importance of diffusion phenomena into the intermediate solid and the reaction taking place within it. On the other hand, neglecting the undeniable effects of some operating conditions such as temperature and particle sizes on gas concentration distribution and reaction rates may introduce large deviations. In this study, the governing equations are developed on the basis of the mass conservation law and solved numerically. Besides, for the first time,
some dimensionless equations and groups are introduced to predict reaction rates and amounts of the main and intermediate products for use in numerical procedures. Comparing the model results with corresponding experimental ones represents the desirable preciseness of the model. After validation of the model, the effect of some operating variables such as temperature and initial size of the particle are investigated on the reaction rates and conversions.