جستجوی مقالات مرتبط با کلیدواژه « mass transfer » در نشریات گروه « فنی و مهندسی »
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The main goal is to build a mathematical model to describe the heat and moisture transfer process and experiment to determine the appropriate vacuum drying mode for Pyinkado wood material. According to the objective above, research has been conducted using the infrared vacuum drying method for Pyinkado, and a mathematical model has been developed to represent the heat and moisture transfer processes during the drying process. Solve mathematical models using the finite element method. Comsol Multiphysics software is used to simulate the drying process. Results are shown through images and temperature and humidity distribution charts. Experimental results recorded the distribution of temperature and humidity during the vacuum drying process of Pyinkado, compared with results calculated from a mathematical model with profiles and trends consistent with the drying experiment. The largest average error when drying using the infrared radiation vacuum method is less than 5%. Determine the appropriate technological parameters for the vacuum drying process of wood with a thickness of 50 mm. The parameters are as follows: drying temperature Ts = 58.9 °C, pressure p = 0.2 bar, and infrared radiation intensity Phn = 625– 641 W/m2.Keywords: Heat, Mass Transfer, Vacuum Drying, Pyinkado, Mathematical Model}
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The researchers have reported numerous numerical and analytical efforts in recent years to understand technological and industrial processes. Microelectronics, heat exchangers, solar systems, energy generators are just a few numbers of recent applications of heat and mass transfer flow. Two dimensional steady incompressible MHD flow of micropolar fluid over an inclined permeable surface with natural convection is investigated in this research work, with the contribution of thermal radiation under thermophoretic effects as a heating source. As a result of this infestation, mathematical model of the problem equations based on energy, momentum, angular momentum, mass, and concentration are developed. To convert the current problem into dimensionless ordinary differential equations, non-dimensional variables have been assigned. The evolved mathematical model is numerically solved aside utilizing Shooting technique along with 4th order R-K method solver in MATHEMATICA. The outcomes are displayed and analyzed through figures and tables. Finally, skin friction, Nusselt and Sherwood numbers are tabulated for distinct parameter-factors. To validate the accuracy of numerical method used in this problem, we compare the numerical results with available findings, and it is evident that the outcomes of current work are in good agreement with those reported in the literature. Improving the values of thermophoresis, radiation factors, and Schmidt number, declines the velocity. Higher values of radiation parameter, thermophoresis parameter, the microrotation increase near plane-surface and gradually diminishes far away from plane-surface. Profiles of temperature enhances with increasing the viscous dissipation parameter. Profiles of the concentration decreases by increasing the thermophoresis parameter and Schmidt number. Profiles of Skin friction and mass transfer rate decreases for magnetic field, thermal radiation and Schmidt number values.Keywords: Thermophoresis MHD, Mass transfer, Viscous Dissipation, Micropolar, Suction, injection, Heat generation, absorption}
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3-fluid liquid-to-air membrane energy exchangers (LAMEEs) are economic dehumidification systems; cooling tubes are put into dehumidifier liquid channels to regulate the internal temperature of the dehumidifier liquid. 3D computational fluid dynamics is used to simulate a 3-fluid LAMEE, and extra transfer of both heat and mass formulas, along with the essential equations that govern for viscous fluid flow, are compiled using external computer programs known as UDS (User Defined Scalar). This study thoroughly investigates the impact of the water inflow variables on system efficiency. The refrigeration fluid that runs inside the cooling tubes is water. The temperature distribution of the three fluids is investigated and the role of the refrigeration tubes based on their positions is evaluated on the desiccant solution cooling. Six tests are conducted to achieve the best arrangement of the inlet water conditions based on the tube’s geometrical location. At an intake water mass flow rate of 4.67 g/s, the latent and sensible effectiveness rise from51% to 78% and 60% to 130%, respectively, when the input water temperature drops from 24.6 °C to 10.1 °C.Keywords: 3-fluid LAMEE, Semi-permeable membrane, heat, mass transfer, Refrigeration tubes, Air dehumidification}
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In this study the effect of cooling load on the surface water of an open channel with different flow depths is investigated. The method, which was used, involves an experimental laboratory set-up that contains a well-insulated cooling load over a finite area of the water surface, without direct contact with the free water surface so that losses of load to the environment should be avoided. The different cooling loads for each experiment were achieved with the use of insulating films. The insulating film is placed at the bottom of the experimental set-up where there was an empty surface (gap - D), through which the cooling load is allowed to pass. The measurement of velocities was carried out at a two-dimensional (XZ) field, with the help of a digital camera. The recording of motion of the dye (rhodamine) along the channel per unit of time, allows the calculation of the values of the velocity fields. Measurements were conducted when the phenomenon becomes steady. The results for the determination of the cold mass length as a function of the flow depth, and the temperature difference ΔT, in a state of thermal equilibrium, led to the formation of a new mathematical relationship. Further study of the phenomenon is essential for the improvement of this study, in combination with other parameters that affect the aquatic ecosystem.Keywords: Open channel, Conductivity, Laboratory experiments, Cool transfer, Mass transfer}
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Journal of Oil, Gas and Petrochemical Technology, Volume:10 Issue: 2, Summer and Autumn 2023, PP 125 -137
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.
Keywords: Volume of fluid, mass transfer, Liquid-Liquid extraction, moving reference frame, surface tension} -
In this article, an analytical technique has been proposed for solving the model of heat and mass transfer in the unsteady squeezing flow between parallel plates. The procedure of combining the Fourier transform and the homotopy perturbation method to yield a new technique was successful. The similarity transformation idea has been used to transform the system of governing partial differential equations into the system of ordinary differential equations. The influence of the physical parameters on the velocity, temperature and concentration with different values are discussed. The numerical results of Nusselt and Sherwood numbers, coefficient of skin friction, were compared with previous published works. The convergence of the new method was also discussed theoretically and experimentally. Furthermore, tables and graphs of the new analytical solutions demonstrate possibility, usefulness to use the new algorithm to deal with many nonlinear problems, especially heat transfer problems.Keywords: Homotopy Perturbation Method, Fourier transform, heat, mass transfer, Unsteady squeezing flow, convergence analysis}
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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.Keywords: fuel cell, microfluidic, Mass transfer, Open-Foam}
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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.
Keywords: Bubble, Imaging, Mass Transfer, gas, liquid system} -
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.Keywords: Metoprolol, Extended-release tablets, HPMC polymer, Mass Transfer}
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Nanofluids find numerous applications in thermal engineering and industrial processes due to their effective thermal conductivity property compared to regular fluids. A nanofluid consists of containing nanometer-sized particles, called nanoparticles of metals, oxides, carbides, or carbon nanotubes etc. with water, ethylene glycol, and oil etc. serve as base fluids. The present study takes care of effects of Brownian motion and thermophoresis on unsteady Casson fluid flow, heat and mass transfer over a stretching sheet embedded in a porous medium. Moreover, the flow phenomena are subjected to heat source, thermal radiation, viscous dissipation, Joule heating and are associated with the diffusion of chemically reactive nanoparticles to base fluid. These two thermo mechanical aspects draw a little attention of the researchers as reported in literature. The governing equations of flow model admit similarity solution and are reduce to non-linear ordinary differential equations (ODEs) applying suitable similarity transformation and are solved numerically using Runge-Kutta-Fehlberg method with MATLAB code. The interesting outcomes are recorded as follows: The formation of inverted boundary layer, the consequence of flow reversal, is due to overpowering of shearing effect of the rigid bounding surface over the free stream stretching in the absence of suction. The higher magnetic field intensity as well as unsteady flow parameter leads to increasing skin friction coefficient may lead to flow reversal. Hence, regulating these parameters is a suggesting measure. The low Brownian motion in conjunction with high thermophoresis leads to upsurge of thermal energy (hike in temperature profile) near the bounding surface. The presence of nanoparticles considered in the base fluid, deduces the shearing stress at the plate surface is a desired outcome to avoid flow reversal.Keywords: MHD, heat, mass transfer, Casson Fluid, thermophoresis, Brownian motion, Chemical reaction}
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تاکنون بسیاری از محققین کار ریاضی روی چرخ های جاذب دسیکنت را ارایه کرده اند، اما اختلاف قابل توجهی بین مقادیر منتشر شده و مقادیر تجربی وجود داشته است. یک مدل ریاضی برای نشان دادن روند رطوبت زدایی جاذب رطوبت گیر دسیکنت با توجه به سرعت جریان هوا استخراج شده است. در این مدل تاثیر سرعت جریان هوا بر عملکرد چرخ به عنوان یک معادله اندازه حرکت همراه با انتقال حرارت و جرم مورد مطالعه قرار گرفته است. به این ترتیب یک مدل ریاضی بر اساس معادله دو بعدی ناویر-استوکس شرح داده شده است. مدل فعلی قادر به پیش بینی پدیده های انتقال گذرا و حالت پایدار در یک چرخ جاذب دسیکنت می باشد. این مدل رطوبت و دما را در کانال های جریان هوا و سطح جاذب با جزییات به عنوان تابعی از زمان نشان می دهد. نتایج پیش بینی شده در برابر داده های به دست آمده از نتایج تجربی، با دقت معقول تایید می شوند. بنابراین، مدل عددی ابزاری کاربردی برای درک و محاسبه فرآیند عملیاتی پیچیده درون چرخ است. در نتیجه، برای مطالعات پارامتر مفید است.A New Approach for the Heat and Moisture Transfer in Desiccant Wheels Concerning Air Stream VelocityMany investigators have presented mathematical work on desiccant wheels but there is a considerable discrepancy between published values and experimental values. A mathematical model based on the two-dimensional Navier-Stokes equation has been derived to show the dehumidification trend of desiccant dehumidifier concerning air stream velocity. In this model the effect of air stream velocity on wheel performance as a momentum equation combined with heat and mass transfer has been studied.
The current model is capable of predicting the transient and steady-state transport in a desiccant wheel. It reveals the moisture and temperature in both the airflow channels and the sorbent felt, in detail, as a function of time. The predicted results are validated against the data taken from experimental results, with reasonable accuracy. Therefore, the numerical model is a practical tool for understanding and accounting for the complicated coupled operational process inside the wheel. Consequently, it is useful for parameter studies.Keywords: desiccant wheel, Heat transfer, Mathematical model, Mass transfer, explicit program} -
در این پژوهش، جریان سه فازی گاز-مایع-مایع در یک میکروکانال بررسی و نقش فاز گاز در فرآیند استخراج مایع-مایع مورد مطالعه آزمایشگاهی قرار گرفت. مواد مورد استفاده شامل محلول آبی سدیم هیدروکسید به عنوان فاز آبی، استیک اسید در نرمال هگزان به عنوان فاز آلی و نیتروژن به عنوان فاز گازی بودند. میکروکانال مورد استفاده از جنس شیشه به عرض و عمق به ترتیب µm 800 و µm 700 بوده و فرآیند استخراج در حالت دو فازی مایع-مایع و سه فازی گاز-مایع-مایع مورد ارزیابی قرار گرفت. در حالت دو فازی (بدون حضور گاز)، الگوی جریان تشکیل شده لخته ای و الگوی جریان در حالت سه فازی به صورت امولسیون دوگانه یا لخته سه فازی گاز در آلی در آبی بود. طبق نتایج حاصل مشخص شد که با افزایش نسبت دبی فاز آبی به آلی از 5/0 به 2، ضریب کلی-حجمی انتقال جرم در حدود 50% کاهش پیدا می کند. همچنین با افزایش دبی کلی مایعات از mL/s 005/0 به mL/s 020/0، ضریب کلی-حجمی انتقال جرم حدود 140% افزایش پیدا می کند. نتایج نشان داد که افزودن گاز همواره باعث بهبود انتقال جرم در میکروکانال نمی شود. به عنوان مثال در دبی ثابت دو مایع برابر با mL/s 005/0، با افزایش دبی گاز از 0 تا mL/s 1/0، ضریب انتقال جرم کاهش و سپس با افزایش دبی گاز تا mL/s 2/0، ضریب انتقال جرم افزایش می یابد.کلید واژگان: جریان سه فازی, استخراج مایع-مایع, میکروکانال, فاز گاز, انتقال جرم}Petroleum Research, Volume:32 Issue: 124, 2022, PP 131 -145In this study, solvent extraction during gas-liquid-liquid flow in a microchannel was investigated. Sodium hydroxide aqueous solution, acetic acid dissolved in n-hexane and nitrogen were employed as the aqueous, organic and gaseous phases, respectively. The microchannel was made of glass with a cross sectional dimension of 800×700 µm2. In the two-phase mode (without the gas phase), the flow regime was slug flow, while in the three-phase flow mode, the flow pattern was a double emulsion (gas in organic in water) flow. By increasing the total fluid flow from 0.005 to 0.020 mL/s, the overall volumetric mass transfer coefficient enhanced on average by 140%. Using the gas phase did not always improve the mass transfer coefficient in the microchannel. For example, at a constant liquids flow rate of 0.005 mL/s, increasing the gas flow rate from 0 to 0.1 mL/s, deteriorated the mass transfer coefficient, however, increasing the gas flow rate up to 0.2 mL/s led to augmentation of the mass transfer coefficient.Keywords: Three-phase Flow, Liquid-Liquid Extraction, microchannel, Gas phase, Mass Transfer}
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یکی از چالش ها و پیچیدگی های شبیه سازی مسایل مرتبط با آتش استخری با سوخت مایع، تعیین نرخ تبخیر سوخت است. در این پژوهش تلاش شده تا با استفاده از الگوریتم متشکل از روابط ساده تحلیلی و نیمه تجربی، نرخ تبخیر سوخت متانول در مسیله آتش استخری کم عمق تحت اثر شار تابشی و دمای محیط گذرا محاسبه شود. در این الگوریتم، هر دو پدیده انتقال حرارت و انتقال جرم لحاظ شد و رفتار هر پدیده مطالعه شد. در مقایسه نتایج شبیه سازی ها با نتایج عددی پژوهش های دیگر، دقت قابل قبولی (کمتر از 3 درصد خطای نسبی) مشاهده شد. همچنین، در مقایسه نتایج شبیه سازی با نتایج تجربی، مشخص شد نتایج پایای شبیه سازی به نسبت نتایج تجربی، 1 درصد خطای نسبی دارد. با بررسی نتایج، مشاهده شد که نرخ تبخیر در حالتی که شار تابشی گذراست، به نسبت حالتی که شار تابشی پایا است 50 ثانیه تاخیر زمانی دارد. همچنین، عدد ناسلت و عدد گراشوف مستقل از شار تابشی و وابسته به دمای محیط اطراف می باشند.کلید واژگان: نرخ تبخیر, استخر سوخت کم عمق, انتقال جرم, آتش استخری, شبیه سازی عددی}Computing the evaporation rate of fuel is one of the challenges and complexities of pool fire simulations. In this study, the evaporation rate of methanol in a shallow pool fire problem is computed using an algorithm that includes analytical and empirical relations. Modeled radiative heat flux and surrounding air temperature are considered transient. Heat and mass transfer phenomena are included in this algorithm, and their effects are discussed. The relative error of results to other numerical studies was below 3 percent. Also, by comparing steady results to experimental results, the relative error was 1 percent. Results show that the evaporation rate in transient radiative heat flux case is delayed 50 seconds to constant radiative flux. In addition, Nusselt number and Grashof number are independent of radiative flux, and depend on surrounding air temperature.Keywords: Evaporation Rate, thin pool fire, Mass Transfer, numerical simulation} -
Iranian Journal of Mechanical Engineering Transactions of ISME, Volume:23 Issue: 1, Mar 2022, PP 46 -67
In this work, finite difference method is applied to two-dimensional transient heat and mass transfer of Casson nanofluid past an isothermal vertical conical plate embedded in a porous media under the influences of thermal radiation and magnetic field. The results of the numerical computations and simulations show that the temperature and concentration of the fluid increase as the Casson fluid and radiation parameters as well as Prandtl and Schmidt numbers increase. As the Grashof number, radiation, buoyancy ratio and flow medium porosity parameters increase, the velocity of the Casson fluid increases. However, it was recorded that the Casson fluid parameter, buoyancy ratio parameter, the Hartmann, Schmidt and Prandtl numbers decrease as the velocity of the flow increases. Also, the time to reach the steady state concentration, the transient velocity, Nusselt number and the local skin-friction decrease as the buoyancy ratio parameter and Schmidt number increase. Further investigations depict that the steady-state temperature and velocity decrease as the buoyancy ratio parameter and Schmidt number increase. Additionally, the results depict the local skin friction, Nusselt and Sherwood numbers decrease as the Schmidt number increases. Though, the local Nusselt number increases as the buoyancy ratio parameter increases. It was established that near the leading edge of the plate, the local Nusselt number is not affected by both buoyancy ratio parameter and Schmidt number.
Keywords: Finite difference method, Transient Free convection, Casson Nanofluid, Thermal radiation, Mass transfer} -
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.. . .Keywords: diffusivity, Drying, Lemon, Mass Transfer}
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در مقاله حاضر، تاثیر استفاده از هندسه های مختلف دهانه و بالابرهای سوزنی بر انتقال گذرا جرم گرما و مقادیر نشان دهنده احتراق و گونه های آلاینده هوا در انژکتورهای سوخت سیستم محرکه دریایی با استفاده از کد AVL-Fire CFD مورد بررسی قرار گرفته است. تاثیر هر یک از پروفیل های هندسی پیشنهادی و حرکت سوزن (مثلثی، ذوزنقه ای و چکمه ای) با کمک یک مش متحرک سه بعدی به وسیله مدل عددی در نرم افزار AVL Fire که با داده های آزمایشی در هر قسمت تایید شده است، بر روی عملکرد و گونه های آلاینده هوا سیستم پیشران دریایی توسط ماژول ANALYZER بررسی شده است. نتایج عددی نشان می دهد که مخروطی همگرا با پروفیل بالابر سوزنی ذوزنقه ای عملکرد موتور، راندمان و آلودگی کمتر NO را دارد. اگرچه، مخروطی واگرا با پروفیل بالابر سوزنی ذوزنقه دارای آلودگی CO کمتری است. مصرف سوخت 18.5 درصد کاهش می یابد و قدرت و گشتاور آن 64 درصد افزایش می یابد. همچنین در این حالت آلاینده های مونوکسید کربن 14 درصد و آلاینده های اکسید نیتروژن 10 درصد کاهش می یابند تا وضعیت بهینه به دست آید. در این حالت راندمان نشان داده شده و بازده مکانیکی به ترتیب 22% و 41.5% افزایش می یابد.کلید واژگان: سیستم پیشرانش دریایی, انتقال حرارت و جرم, گونه های الاینده هوا, پروفیل ذوزنقه, حرکت سوزن}In the present paper, the effect of using Different Orifice Geometries & Needle Lifts on transient heat-mass transfer and Combustion Indicated Quantities & Air Pollutant Species has been investigated in Marine Propulsion System Fuel Injectors using AVL-Fire CFD code. The effect of each of the proposed geometry and needle movement profiles (triangular, trapezius & boot) with the help of a three-dimensional moving mesh by numerical model in AVL Fire software, which has been validated with experimental data in each part, on the performance & Air Pollutant Species of the Marine Propulsion System has been investigated by ANALYSER module. Numerical results show that converged conical with trapezius needle lift profile has better engine performance, efficiencies and lower NO pollution. Although, diverged conical with trapezius needle lift profile has lower CO pollution. Fuel consumption decreases by 18.5% and its power and torque increase 64%. Also in this case, carbon monoxide pollutants decrease by 14% and nitrogen oxide pollutants decreasing by 10% for optimum status. In these case, indicated and mechanical efficiencies are increasing 22% and 41.5%, respectively.Keywords: Marine Propulsion System, Heat, mass transfer, Air Pollutant Species, trapezius profile, Needle Lifts}
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Long mixing time, high power consumption, and small mass transfer coefficients are common problems in the photobioreactor design for microalgae culture which have a great effect on system efficiency and performance, CO2 stabilization, and biomass production. In this study, a special design of the triangular external loop airlift photobioreactor was studied. The bioreactor's geometry was such that the angle between hypotenuse and the horizontal side ( ) could vary. This configuration created an effective gas-liquid countercurrent flow in the downcomer section. In the present research, hydrodynamic and mass transfer of the reactor were investigated on the microalgae productivity under different design and operating parameters. The optimum conditions for the enhancement of Chlorella vulgaris productivity were explored by analyzing the mixing time ( ), volumetric power consumption (P/V), mass transfer coefficients ( ), bubble diameter (d), and gas holdup ( ) as responses. The results showed that the hypotenuse angle of = 59o and the superficial gas velocities of the = 0.0050 m.s-1 for the downcomer and = 0.008 m.s-1 for the riser of the reactor were the best conditions to achieve the highest biomass productivity. The responses’ values obtained in the optimum condition were as follows: = 19.67 (h-1), = 23.79 (h-1), = 23.76 (h-1), = 0.41, and = 62.83 , which had a smaller deviation than the actual values. The highest concentration of Chlorella vulgaris ( 1.4 g.l-1) achieved in this work was obtained in a shorter span of time (11th day of cultivation) based on the growth curve in optimized conditions.Keywords: Airlift photobioreactor, Chlorella Vulgaris, Hydrodynamics, Mass Transfer, Mixing time}
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در مطالعات کانال مرکب به منظور کنترل برقراری شرایط توسعه یافتگی کامل جریان، لازم است توزیع دبی در کانال اصلی و سیلاب دشت بررسی شود. هدف این تحقیق، بررسی اثر شرایط ورودی در کانال مرکب با طول کوتاه در برقراری شرایط توسعه یافتگی با استفاده از بررسی میدان جریان و پارامترهای آشفتگی است. بدین منظور از ابزار سرعت سنجی تصویری ذرات در یک کانال مرکب استفاده شده است. نتایج این تحقیق نشان می دهد که در کانال مرکب کوتاه با استفاده از آرام کننده ی یکسان در کانال اصلی و سیلاب دشت، حتی تا انتهای کانال انتقال جرم از سیلاب دشت به کانال اصلی وجود دارد. در این حالت تغییرات سرعت طولی در عرض سیلاب دشت بسیار کم است و فروافتادگی شدید در محل سرعت بیشینه در کانال اصلی (در نزدیکی ناحیه اندرکنش) رخ می دهد. در حالی که در کانال مرکب کوتاه با افزودن آرام کننده ی کمکی در سیلاب دشت، شرایط مناسب و مشابه با کانال مرکب توسعه یافته تشکیل می شود.
کلید واژگان: کانال مرکب روباز, اثر ورودی, انتقال جرم, میدان جریان, سرعت سنجی تصویری ذرات}A compound open channel is composed of the main channel and flood plain. In experiments with compound open channel conducted to ensure that the flow is uniform and fully developed, it is necessary to study the distribution of discharge in the main channel and flood plains. The purpose of the present study is to investigate the effects of channel inlet condition on flow uniformity by considering distribution of discharge in channels with length to flood plain width ratio lower than 35 (needed for fully developed flow condition) by analyzing the flow field and turbulence parameters. For this purpose, particle image velocimetry method has been used in a rectangular compound open channel. To provide correct measurement of secondary velocities, using a non-intrusive method such as particle image velocimetry is completely essential. The results of this study show that in short compound channels with the same screen installed in the main channel and flood plain, there is significant mass transfer from the flood plain to the main channel until the end of the channel length. It was found that in this case, a considerable downfall occurs for the maximum velocity position in the main channel. However, with a supplementary screen installed in the flood plain, in addition to the typical screen, expected conditions are established similar to the fully developed compound channels. In this condition, the time-averaged streamwise velocities vary considerably in the flood plain along the spanwise direction. On the other hand, in short compound channels with the same screen installed in main channel and flood plain, the streamwise velocities do not change significantly along the flood plain width duo to the imperfect interaction of main channel and flood plain. These observations express that to provide correct distribution of discharge, a supplementary screen should be installed in the flood plain of the compound channel.
Keywords: Compound Channel, Entrance effect, Mass transfer, Flow Pattern, Particle Image Velocimetry} -
شناخت ساختار مواد تاریخی، به ویژه ترکیبات بر پایه رس، علاوه بر جنبه های فنی و باستان شناختی، از منظر بررسی فرایندهای آسیب رسان نیز قابل توجه است. یکی از عوامل ساختاری حایزاهمیت در موادی مانند سرامیک ها اعم از سفال، آجر، و بدنه کاشی، پدیده تخلخل است که مجموعه ای از حفرات و فضاهای خالی را شامل می شود و برحسب ارتباط با محیط پیرامونی خود، به صورت باز یا بسته طبقه بندی شده و براساس زمان شکل گیری، به دو صورت اولیه و یا ثانویه تشکیل می شوند. مهم ترین نقش تخلخل های باز، عملکرد آنها به عنوان کانال های انتقال رطوبت و یا هرگونه محلولی است که می توانند عامل شروع و یا ادامه یافتن بسیاری از واکنش های شیمیایی باشند. وجود رطوبت پدیده های انتقال یون ها، انحلال، هیدراسیون و تبلور نمک های محلول را به همراه خواهد داشت. در این مقاله با رویکرد تحلیلی و براساس نتایج حاصل از مطالعه آزمایشگاهی با روش های تخلخل سنجی جیوه (MIP) و تخلخل سنجی به شیوه غوطه وری (براساس استاندارد ASTM C20-92)، مهم ترین پیامدهای ناشی از وجود تخلخل در بافت یک قطعه سرامیکی ارزیابی شده است. این پیامدها عبارت اند از: الف) رابطه دمای پخت، درصد تخلخل، حجم و شعاع حفرات، ب) ارتباط اندازه تخلخل با فرایندهای انتقال رطوبت درون ساختار، و ج) رابطه تخلخل و شعاع حفرات با فشار تبلور نمک ها. نتایج بررسی هایی از این دست در آسیب شناسی و فرایند مرمت اشیاء تاریخی حایز اهمیت است. ایجاد شوک رطوبت بلافاصله پس از حفاری ناشی از شستشوی قطعه به منظور تمیزکاری، نمک زدایی و... بدون توجه به شرایط اثر از منظر نوع حفرات موجود، ماهیت و میزان تخلخل، علاوه بر افزایش تراوایی و امکان نفوذ رطوبت و به دنبال آن ایجاد تنش های فشاری ناشی از تبلور مجدد نمک ها، می تواند به حبس رطوبت و فراهم آمدن فضایی برای واکنش های آتی از بستری پایا (ایستا) به روندی پویا (دینامیک) منجر شود.
کلید واژگان: سرامیک های باستانی, ساختارشناسی, فرسایش داخلی, تخلخل, انتقال جرم}Structural characterization of historical materials, especially clay-based compositions, as well as technical and archaeological aspects, has a significant role in the diagnosis of the deterioration process. One of the most important parameters in the structure of clay-base ceramics (such as pottery, brick, and tile ware) is porosity that includes all open and closed pores in the matrix of porous material and it is formed through primary (during the preparation of raw materials) or secondary processes (during firing process and/or burial condition). The main function of open porosity is its role as moisture or any electrolyte transfer channel that can launch or continue many chemical reactions. This function has consequences such as ions transfer, phases dissolution, hydration, and crystallization of soluble salts. Therefore, take note of the percentage of the object’s porosity, especially in the excavation process, is highly essential. In this paper, according to the analytical point of view, through porosimetric methods such as mercury intrusion porosimetry (MIP) and immersing method (based on ASTM C20-92), the most important effects of the presence of porosity in the ceramic matrix were investigated. These parameters are a) relation between firing temperature, percentage of porosity, volume, and radius of pores; b) relation between porosity and moisture transfer through the matrix; and c) relation between porosity and salt crystallization pressure. Without pay attention to the object’s condition like types and amounts of pores, the possibility of increased permeability and diffusion of humidity, moisture shock immediately after excavation can occur as a result of cleaning or desalination process as well as salt crystallization pressure, capillary condensation, and further chemical reactions and physical erosions.
Keywords: : historical ceramics, structure, internal erosion, porosity, mass transfer} -
ریزجلبک ها با داشتن ذخایر زیاد کربوهیدرات ها و سرعت بالای رشد، به عنوان یکی ازنوید بخش ترین منابع برای تولید بیواتانول معرفی شده اند. در این تحقیق، بعد از کشت گونه های مختلط ریزجلبک در فتوبیوراکتور، برای افزایش تجمع کربوهیدرات ها در ریزجلبک از راهبرد قحطی نیتروژن استفاده شد. سپس، استخراج قندهای موجود در زیست توده با استفاده از فرایند آبکافت آنزیمی به وسیله آنزیم سلولاز انجام شد. در این مقاله برای نخستین بار، فرایند آبکافت آنزیمی ریزجلبک با در نظرگرفتن شرایط هیدرودینامیکی سیال درون راکتور بررسی شد. نتایج نشان داد که افزایش همزدگی سامانه بیش از غلظت آنزیم، بر بازده آبکافت تاثیر می گذارد. در دورهای بالاتر از rpm 250 که رژیم جریان از آرام به متلاطم تغییر می کند، میزان قند آزادشده بسیار بیشتر از مقادیر در دورهای پایین همزن است. هم چنین، افزودن بافل با جلوگیری از تشکیل گردابه میزان انتقال جرم را و به تبع آن بازده آبکافت را افزایش می دهد؛ اما تغییر نوع همزن تاثیر قابل ملاحظه ای بر فرایند آبکافت ندارد. هم چنین در این تحقیق، تاثیر همزدگی در طول فرایند آبکافت از راه ارزیابی نرخ انتقال جرم بررسی شد.
کلید واژگان: انتقال جرم, بافل, ریزجلبک, شرایط هیدرودینامیکی سیال, همزن, آبکافت آنزیمی}Microalgae with reserves of carbohydrates, high growth rate have been introduced as one of the most promising sources for bioethanol production. In this study, after culturing mixed microalgae species in photobioreactors, a nitrogen starvation strategy was used to increase the accumulation of carbohydrates in microalgae. Then, the sugars in the biomass were extracted using enzymatic hydrolysis by cellulase enzyme. For the first time, the enzymatic hydrolysis of microalgae is investigated by considering the dynamic conditions of the fluid inside the reactor. The results showed that increasing the system agitation more than the enzyme concentration affects the hydrolysis efficiency. At high speeds of 250 rpm, where the flow regime changes from slow to turbulent, the amount of sugar released is much higher than the values at low speeds of the stirrer. Also, adding baffle increases the mass transfer rate by preventing the formation of vortices and consequently increases the hydrolysis efficiency. But changingthe type of stirrer does not have a significant effect onthe hydrolysis process. Also in this study, the effect of agitation during the hydrolysis process was investigated by evaluating the mass transfer rate.
Keywords: Baffle, Mixed microalgae, Hydrodynamic Fluid Condition, stirrer, Enzymatic hydrolysis, Mass Transfer}
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