جستجوی مقالات مرتبط با کلیدواژه « Mass transfer » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Liquid-liquid extraction is one of the main separation processes which has many applications in different industries. Among different influencing parameters on Liquid-liquid performance, the surface tension effect was investigated in the present study. The mass transfer of a single droplet was simulated using the volume of fluid approach coupled with a single-field mass transfer approach.  Due to the high computational time, the moving reference frame approach was supplemented to computational codes in parallel processing mode assuming static droplet and moving zone. The results showed that with the reduction of surface tension coefficient, while the other parameters were kept constant, the regime change from spherical to oscillating occurred, the velocity decreased. In addition, along with an additional reduction in the surface tension coefficient, the droplet breakage happened. Despite a considerable reduction in terminal velocity, the reduction in mass transfer was not observed due to the interfacial area increase which enhanced mass transfer while velocity reduction negatively disturbed it. The concentration contour plots of droplets in various surface tension coefficients were reported in different droplet regimes starting from circulating to breakup.

The development of microelectronic devices has increased the need for a power supply with high power density for long-term operation. In this article, firstly, the microfluidic fuel cells (MFCs) have been introduced, secondly, due to the significant effect of mass transfer on their performance, mass transfer in these fuel cells has been investigated. MFCs have small dimensions and simple geometry, and usually, formic acid and oxygen dissolved in sulfuric acid are used as fuel and oxidizers, respectively. To model the MFC, the equations of continuity, momentum, and mass transfer have been solved in three-dimensional by Open-Foam open-source software and validated with the results available in the references. From Fick's equation has been used to calculate rate of diffusion and from the Butler-Volmer equation has been used to calculate rates of electrochemical reactions in catalyst layers. Preliminary results indicate that the performance of this fuel cell is greatly limited by poor fuel utilization, which is consistent with the experimental data. The flow is fully developed in this short distance from the inlet, and in the fully developed area, the ratio u_max⁄u ̅ is equal 2.1. The mixing zone located at the interface of fuel and oxidizer is in the shape of an hourglass in cross-section, and with increasing the inlet velocity, its thickness decreases along the channel. Also, as the flow moves along the channel, the thickness of the layer with a low concentration near the electrodes increases.

Most industrial operating units are basically in contact with two gas and liquid phases. Bubble characteristics over the last years have been determined through different methods. In this project a mass transfer system has been designed for absorbing gas bubbles by liquid phase. The mass transfer and hydrodynamic behavior in the wake of single rising air bubbles were investigated by using an image analysis method and empirical relations. By considering these methods, the overall bubble properties including the size of single bubble, shape, path, rising velocity and mass transfer coefficient were studied and measured. The investigation was developed with 0.15×0.15×0.35 m3 bubble column and nozzle diameter (0.5, 1, 1.5, 2, 2.5 mm) in different liquids considering viscose changes. Moreover, from the results obtained, it can be concluded that the increase of nozzle diameter increases the bubble diameter which results in reduction of velocity and mass transfer coefficient. This is a fact that, by raising the viscosity of liquid phase the bubble diameter stands at the highest level and on the contrary velocity and mass transfer coefficient stand at the lowest level. So according to these outcomes we can conclude that, the diameter of bubble depends on physical properties of fluids and has a direct relation with nozzle diameter.

Metoprolol has been widely used for controlling high blood pressure, preventing myocardial reinfarction, setting rate changes, setting heart rhythm, treatment of chronic angina and preventing excessive bleeding during surgery. The purpose of this research is formulation and manufacture of extended release tablets of metoprolol succinate that conform to all the in vitro physicochemical US Pharmacopoeia national formulary (USP32). For preparing the tablets, the hydrophilic HPMC(K100M) polymer was used in direct compression method. Release of metoprolol in phosphate buffer having pH=6.8 (USP32) was measured by HPLC. Also, using experimental correlation of diffusivity in buffer medium and Gurney-Lurie charts during tablet enlargement with time, diffusion coefficients of drug and partition coefficients were obtained at different time steps. The rate of drug release depends on the type, viscosity and polymer concentration. Drug release results over 20 hours for polymers of HPMC(K100M), HPMC(K4M), HPMC(K15M), polyethylene oxide, ethyl cellulose, Eudragit (RL100) were investigated and compared. The results demonstrated that HPMC(K100M) met the standards of USP32 very well and was superior over the other polymers tested.

Achieving the rate and the amount of mass transfer is of paramount importance in selecting optimum conditions for drying and affects the development of the quality of drying. Note that, to obtain the amount of mass transfer, the conditions of mass transfer such as temperature, pressure, geometry, and diffusion coefficient should be completely determined. In this research, an experiment is conducted in atmospheric conditions and then the amount of mass flow in a spherical body is measured. Utilizing the Newman equation and the experimental results, the diffusion coefficient is found to be in the range of 10-11 m2/s. Additionally, the experimental data reveal the linear and exponential variation of diffusion coefficient with a constant coefficient of 1306.8 and exponent of 2.0883 which is against size and time. Results show that findings are in considerably high agreement with the experimental data.Keywords: Diffusivity, Mass transfer, Lemon, Drying.. . .

Electrohydrodynamic (EHD) drying of Poly (vinyl acetate) latex films was investigated in a wind tunnel, experimentally. The influence of various conditions such as the air temperature, air velocity, and the concentration of latex solution, in the presence and the absence of a high electric field, was investigated. The effects of the applied voltage intensity, electrode gap, number of needle electrodes, and polarity of corona on the drying rate of polymer films were carried out. The drying behavior of films in a wind tunnel was obtained by the weighting method and analyzed based on heat and mass transfer. Results showed the role importance of EHD on the drying rate of the polymer film. Increasing the intensity of the electric field, number, and configuration of needle electrodes, and decreasing the electrode gap leads to a significant enhancement of the drying rate of a polymer film. Scanning electron microscope images (SEM) were used to analyze the effect of EHD on the morphology of dried films.

Forward osmosis (FO) is an energy-saving separation process that can be used in desalination applications. This work investigated the effect of mass transfer phenomenon on the FO desalination process. For this purpose, the water flux was studied through a bench scale system using a flat sheet FO membrane and feeds with various salinity. Then, the mass transfer resistances, which appear in the form of concentration polarization (CP) for the FO process, were evaluated qualitatively and quantitatively, using the collected experimental data and by employing a mathematical model. The results indicated that the increase in feed salinity led to a decrease in water flux due to the counteracted part of the draw solution osmotic pressure, thus leading to a lower effective osmotic pressure and driving force.  Also, according to the results, there was a significant difference between the theoretical and experimental fluxes, indicating the influence of the mass transfer effects on the osmotic pressure drop. The modeling results showed that the internal concentration polarization (ICP) still held more contribution to the osmotic pressure loss. Furthermore, it was observed that as the feed solution concentration increased, both the ICP and dilutive external concentration polarization (DECP) decreased, whereas the concentrative ECP (CECP) intensified. Therefore, increasing the CECP led to a significant reduction in the effective osmotic pressure. In addition, increasing the draw solution concentration was accompanied by a much more severe ICP that limited the enhancement of effective flux.

Understanding the kinetics of gas hydrate formation is essential to model and predict the hydrate formation (or dissociation) process. In the present paper, we investigated the formation of pure propane gas hydrate as a former gas. In this regard, several experiments were conducted to measure the rate of hydrate formation under various pressures (410 to 510 kPa) and temperatures (274 K to 277 K) in a controlled temperature stirred reactor. It was observed that propane consumption rate can be assumed constant with time. Mass transfer approach was used to estimate the mass transfer coefficient in the gas-liquid contact area as a function of pressure and temperature. Results indicated that mass transfer approach can predict the kinetics of propane hydrate formation. In other word, it is reasonable to assume that this process is a mass transfer limited phenomena and the mass transfer in the liquid side the gas-liquid contact area controls the hydrate growth.

A bioreactor refers to any manufactured or engineered device that supports a biologically active environment. These kinds of reactors are designed to treat wastewater treatment. Volumetric mass transfer coefficient and the effect of superficial gas velocity, as the most important operational factor on hydrodynamics, in three-phase airlift reactors are investigated in this study. The experiments for the external airlift reactor were carried out at a 0.14 downcomer to riser cross-sectional area ratio, and for the internal reactor at 0.36 and 1. Air and water were used as the gas and liquid phases, respectively, as well as activated carbon/sludge particles as the solid phase. Increasing the superficial gas velocity resulted in greater liquid circulation velocity, gas hold-up, and volumetric mass transfer coefficient; increasing the suspended activated carbon particles resulted in a decreased concentration of activated sludge, downcomer to riser cross sectional area ratio, liquid velocity, gas hold-up and volumetric mass transfer coefficient. The maximum gas hold-up was 0.178 which was attained in the external airlift reactor with a 1 Wt. % of activated sludge at a gas superficial velocity of 0.25 (m/s). The maximum volumetric mass transfer coefficient was 0.0485 (l/s) that was observed in the external airlift reactor containing activated carbon with a 0.00032 solid hold-up. A switch was observed in the activated sludge airlift reactor flow regime at gas velocities higher than 0.15 (m/s) and 0.18 (m/s) in the activated carbon airlift reactors.

The current research aims at conducting an experimental and theoretical investigation on the performance of air dehumidification system using a nanofluid of γ-alumina nano-particles in LiBr/H2O, as a desiccant. Comparative experiments organized using a central composite design are carried out to evaluate the effects of six numerical indices (air velocity, desiccant flow rate, air humidity ratio, desiccant solution concentration, air temperature, desiccant temperature) and one categorical factor (adding nano-particles), on outlet air humidity ratio and outlet air temperature as responses. Reduced quadratic regression models are derived for each response. The obtained results revealed that LiBr/H2O solution concentration and air temperature have the most significant effect on outlet air humidity ratio and outlet air temperature, respectively. It was found that the average rates of mass transfer and heat transfer increased to 12.23 % and 13.22 %, respectively, when γ-alumina nano-particles (0.02 wt %) were added to the LiBr/H2O solution. The average rates of mass and heat transfer coefficients increased to 22.73 % and 26.51 %, respectively.

This investigation attempts to evaluate and compare the effect of packing type on the mass transfer and pressure drop along the gas sweetening absorption column. To this aim, modern packings such as Super Ring, Ralu Ring, Ralu Flow and the second-generation packing (Pall Ring), have been used in simulated columns by using of Aspen HYSYS modeling software. Flooding calculation is made possible by linking Aspen HYSYS with MATLAB programing. The selected models validity is checked by comparison to empirical data from a real gas plant. It should be noted that empirical data is available just for second-generation packing. Comparison of these packings performance shows that Super Rings provide low pressure drop, Ralu Rings lead to high mass transfer and Ralu Flow packings can provide high mass transfer and low pressure drop in absorption columns. According to results, the capacity of gas treatment units can be significantly increased by replacing Pall Ring with Ralu Flow.

Liquid membrane processes have attracted many interests in recent years for removal of heavy metals such as cadmium from industrial wastewaters. In this study, a modified hybrid liquid membrane system is introduced. The setup is worked by applying the water-insoluble dioctyl phthalate as the organic solvent. N-octanol and tetra butyl ammonium bromide are added to the organic phase to increase the system efficiency. The effects of different parameters such as pHs of the feed and stripping phases, the complexing agent concentration, the organic film thickness, initial concentration of cadmium, and the carrier concentration on the cadmium removal are studied. The results demonstrate the increase in the removal rate and capacity comparing to those of previously studied hybrid liquid membrane system. An electrical potential is then applied to the hybrid liquid membrane system. The results show higher removal rate and capacity compared to the corresponded values in the system without applying electrical potential.