A novel model for predicting wax deposition during turbulent and laminar flow of crude oil was developed. Experiments carried out using a mixture of toluene and an oil wax cut, in a laboratory flow loop, revealed model results on total mass of wax deposition showing a very conformity with experimental findings in the laminar flow regime. Molecular diffusion was the dominant mechanism during laminar flow. Sloughing effect was an important mechanism during wax deposition in the turbulent flow regime that should not be neglected. In the turbulent flow regime, there were critical flow rates for any system containing non-isothermal flow of waxy crude oil. These critical rates depended on the fluid (oil) characterization and pipeline characteristics, as well as operational conditions. Increasing flow rate beyond the critical flow rate decreased the amounts of wax deposit. These trends were similar to what were concluded in other experiments.
One of the problems faced by the petroleum industry is the wax deposition in pipelines during transportation of waxy crude oil. A comprehensive mathematical model for quantitative prediction of wax deposition for a multicomponent hydrocarbons mixture (oil) was developed. Deposition as a function of time was obtained as a solution of differential equations derived from the principles of mass and energy conservation, considering the thermodynamic of phase transition. Experiments were conducted using a mixture of toluene and an oil wax cut, in a laboratory flow loop. Model results on total mass of wax deposition showed conformity with experimental results in the laminar flow regime. These comparisons verified that molecular diffusion is the dominant mechanism during laminar flow.
Chemical Engineering Communications (00986445)189(7)pp. 959-973
A mathematical model is developed to study simultaneous heat and mass transfer in hot gas spray systems. The model is obtained by writing mass, energy, and momentum balances for both continuous and discontinuous phases. Governing equations along with suitable correlations for heat and mass transfer coefficients have been solved numerically. In order to develop a realistic model for such complicated systems, a droplet size distribution was implemented in the model instead of using an average size. A steady state spray-cooling problem is analyzed to illustrate the applicability of the model. To validate the mathematical model for this case, necessary data was collected and measured in commercial cement plants. A good agreement between plant data and the model was noticed in general, and results obtained from the model indicate that size distribution of water droplets and physical dimensions of the spray-cooling system are important parameters. This model is very useful in determining the so-called "critical operation condition" at which sludge formation at the bottom of spray-cooling systems will happen. The predicted parameters in spray-cooling systems both for droplet phase and gas phase aptly illustrate the ability of the model to treat the complex phenomena associated with two-phase flows.
A pilot scale fluidized bed dryer with an inert energy carrier (steel, glass beads ranging from 2.7 to 6.5 mm) was used to investigate the drying of carrots. The effects of sample diameter, inert material type, inert material diameter, amount of inert material, air velocity, and temperature on the rate of drying were studied. A mathematical model was proposed for predicting the drying rate and temperature of drying material. It was found that presence of inert particles enhance the rate of drying. The results of this study also revealed that, although the rate of drying increases with decreasing sample diameter, increasing the inert material thermal conductivity, and increasing air temperature, but the inert material diameter and air velocity have no significant effects on the rate of drying. The independence of rate of drying on air velocity especially in well-fluidized systems indicates that external diffusion is not a controlling step in this process. Also the presence of inert materials causes the drying material to reach more rapidly to its final internal temperature.
Chemical Engineering and Technology (09307516)26(1)pp. 43-49
A pilot scale fluidized bed dryer with inert particles as energy carrier was used to investigate the drying characteristics of carrot in this type of dryer. Glass beads, hollow steel balls and pieces of dry carrot were used as inert materials. The effects of sample diameter, inner material type, inert material diameter, amount of inert material, air velocity and temperature on the rate of drying were studied. It was found that the presence of inert particles enhances the rate of drying. The results of this study also revealed that, although the rate of drying increased with decreasing sample diameter, increasing of inert material thermal conductivity, and increasing of air temperature, but the inert material diameter and air velocity did not have any significant effect on the rate of drying. The independence of the rate of drying on air velocity in well fluidized systems, indicates that external diffusion is not the controlling step in this process. It was also found that the presence of inert materials caused the drying material to reach its final internal temperature more rapidly. The internal temperature of the drying material, also increased with increasing diameter and thermal conductivity of the inert materials.
Chemical Engineering Communications (00986445)190(4)pp. 508-518
In this paper some experimental results showing the influence of inclination of a cylindrical heating surface immersed in an air duct on heat transfer coefficient are presented. The experiments were performed in a laboratory-scaled apparatus of square cross section with dimensions 120 × 120 mm and 1400 mm in height. Heat transfer surface was an electrical heater made of brass tube with outer diameter of 19 mm and 110 mm length. In each experiment the temperatures of the front and rear side of the heating surface, inclination angle, air velocity, inlet air temperature, and heater power were measured. It was concluded that heat transfer coefficient depends on flow conditions and angle of inclination. The maximum Nusselt number (Nu) was observed to occur about 45° inclination relative to the horizon, for the range of Reynolds numbers used in experiments. The values of heat transfer coefficients in the vertical position were very nearly the same as they were in the horizontal position. Based on the experimental results, a correlation was proposed for estimation of Nu at the desired flow velocity and inclination angle, relative to Nu at zero inclination.
International Journal of Environment and Pollution (09574352)19(6)pp. 557-566
With the aim of the economic upgrading of natural resources, this investigation examined the hydrothermal synthesis of zeolite from perlite, and the ability of the synthetic zeolite to adsorb and retain cyanide. The hydrothermal treatment of perlite with aqueous sodium hydroxide results in the formation of Na-Pc zeolite. The cation-exchange capacity of zeolite for zinc, copper and silver was respectively 2.26, 1.86 and 2.44 meq g -1. The exchange was incomplete, but equilibrium was rapidly attained. Cyanide adsorption isotherms, constructed at three different temperatures, showed that the zeolite was very selective for cyanide. The solubility products of the cyanide precipitate and the exchange capacity of zeolite for individual cations governed the adsorption capacity of the zeolite. The method also remains selective in the presence of some other anions. Kinetic data for cyanide desorption in water and sodium chloride solution indicated that zeolite retains most of the adsorbed cyanide.
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025pp. 203-207
The role of diffusion in reducing the saturation pressure of oil in blocks located at different depths of fractured oil reservoirs has been studied. A model to describe unsteady state diffusion in a matrix block with a given geometry in fractured oil reservoirs has been developed and the results have been compared with the analytical solution. The delay time for solution gas drive due to diffusion in a block with a given shape has been calculated by using the data of Haft kel field. Copyright 2004, Society of Petroleum Engineers Inc.
The precipitation of waxy constituents in petroleum mixtures subjected to a cold environment gives rise to a variety of problems well-known in the petroleum industry. A revised multi-solid phase thermodynamic model for predicting wax precipitation in petroleum mixtures is presented in this article. The Peng-Robinson equation of state is used to evaluate the phase behavior of both liquid and vapor phases. The results predicted by this model agree with the experimental data of wax precipitating for several synthetic oils and crudes.
One of the problems faced by the petroleum industry is the wax deposition in pipelines during transportation of waxy crude oil. Oil companies dealing with waxy crude often spend millions of dollars in remedial procedures. An ideal design should use an accurate mathematical model that would include all salient features of wax deposition and waxy crude transport to predict wax deposition during crude oil transportation. In this article, a comprehensive mathematical model, both in laminar and turbulent flow regimes, is developed. The model couples energy equation with deposition and removal kinetics model and thermodynamic model. The k - ε turbulent flow model and energy equation were used to predict velocity and temperature distributions in the turbulent flow regime. Molecular diffusion of wax, as a mechanism of deposition and sloughing effect due to the hydrodynamic forces of fluid on deposited wax, have been considered. Parametric studies on the variation of the amount of wax deposition were performed for a mixture of toluene and oil wax cut in an experimental setup. Overall predictive ability of the proposed model is excellent for the laminar flow. For the turbulent flow regime, no necessary complete experimental data for model were available. Consequently, qualitative results were presented and discussed.
Canadian Journal of Chemical Engineering (00084034)83(3)pp. 401-408
A mathematical model consisting of differential equations for energy, momentum and material exchange is developed for a non-isothermal Venturi-type scrubber. By this model, the effects of heat and mass transfer on droplets concentration distribution and removal efficiency of particulate in a non-isothermal Venturi scrubber can be investigated. In order to approach a realistic model, the liquid film flow on the walls and droplet size distribution are considered. The model is validated by comparing the results of mathematical model by plant and experimental data reported in the literature. The Results section of this work reveals that the inlet humidity and temperature of the gas can affect the removal efficiency of the scrubber.
Polymer Engineering and Science (15482634)2005pp. 149-157
In this paper the rheokinetics of Polyurethane formation and the influence of shear rate on its kinetics have been studied. Two different linear polyurethane systems with 0% and 100% hard segments are examined in a cone and plate rheometer. The isothermal increase of viscosity during polyurethane formation has been measured at different shear rates and different temperatures and is modeled with an exponential function. The molecular weight vs. time curves and the reaction kinetic constants have been obtained for various shear rates and temperatures using gel permeation chromatography (GPC). It was concluded that kinetics of polyurethane formation is enhanced as the shear rate is increased. Phase separation is found to be responsible for irregularities in the viscosity build up due to formation of polyurethane with hard segments at high conversions.
Canadian Journal of Chemical Engineering (00084034)84(3)pp. 310-315
An analytical model using eddy diffusivity is applied for predicting droplet concentration distribution and liquid film formation in a Venturi scrubber. By comparing experimental data of film formation reported in literature (Viswanathan et al., 1984) and the results obtained from this model, a semi-empirical correlation for liquid droplets eddy diffusivity is obtained. The validity of this correlation is confirmed by obtaining good agreement between theoretical and experimental data of droplet concentration distribution and film formation in a Venturi scrubber (Viswanathan, 1998; Viswanathan et al., 1984).
