Iranian Journal of Chemical Engineering (IJChE)

Abstract In this paper, modeling approaches were given for explaining mass transfer during solid-liquid extraction in continuous fixed, expanded, and fluidized-bed extractors. The first approach utilizes a differential mass balance-based model, focusing on the differential mass conservation within an element of fixed and expanded-bed columns. The second approach employs a model by applying a mass balance concept to a control volume of the fluidized-bed column. The differential mass balance method segments the column into well-mixed stages, with the fluid flowing axially in an ideal plug flow regime. The solute diffusion inside the porous particles is modeled using Fick's second law of diffusion. Modeling parameters like the effective diffusivity and equilibrium concentration were estimated using the batch extraction experiments. These models were developed and validated using experimental column data involving the extraction of potassium bicarbonate from polyamide 6 pellets with distilled water as the solvent. The modeling results show a good agreement with experimental data.

Abstract The gelling of waxy crudes and the deposition of wax on the inner walls of pipelines present a costly problem in the production and transportation of oil. The object of the present study is to investigate the factors that affect the deposition of the paraffin wax on the pipe surface under different conditions using a flow loop system. A series of experiments on wax deposition from a mixture of waxy oil have been performed in a 65cm by 1cm ID flow loop in both laminar and turbulent flow regime. These experiments were done to study the effect of some important factors on the amount of deposited wax on the pipe wall. These factors consist of flow rate, residence time, wax concentration and temperature difference between mixture and pipe wall. It was found that the wax deposition increases with increasing temperature difference and residence time, but the effect of flow rate depends on flow regime. The other goal is mathematical modeling of wax deposition for a multi-component hydrocarbon mixture. The procedure for generating the model is described in detail. Finally, the results obtained from the model were compared with experimental data. It was found that there is an acceptable match between experimental and theoretical data and to some extent, this confirms the validity of the model and also the ability of the developed model to predict the wax deposition on pipelines under different operational condition.

Abstract Soil bioremediation, especially in the rhizosphere area, is the result of interaction between plant roots and microorganisms. It can be considered as one of the remarkable ways to eliminate pollutants. Various factors control the process with special relationships in the rhizosphere environment; changing each of them can impress on the system destination. With mathematical modeling, behavior of the process can be predicted and controlled, and improved by appropriate changes in the model. In this study, the effects of different parameters of a simple mathematical model, represented to predict microbial growth and necessary substrate changes in the rhizosphere have been studied using numerical finite difference method. Influences of the parameters on biomass and substrate concentrations were evaluated at different times. A number of variables directly, some negatively, and others neutrally impacted on the biomass and substrate concentrations. Investigating variables differently affecting on a model is important since perfectly tuning them can optimize the system performance, and achieve higher efficiency.

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 The presence of wall strengtheners in double-stage electrostatic precipitators affects gas velocity, electrical field and particle movement over the ESP. In this work we have used our previous mathematical model for double-stage ESP {Talaie et. al (2001) [10]] to study the effect of wall strengtheners on the performance of double-stage ESP. One of the important findings was that, due to the fact that wall strengtheners increase the degree of turbulence, the effect of gas turbulence on particle movement can not be ignored. The results of the calculations show that the simple Lagrangian model in which this effect is neglected is not suitable, whereas using an Eulerian approach provides much better results. The results of this model also revealed that the collection efficiency for small particles increases while that for large particles decreases when a baffle is used as wall strengthener.