Jafar Mahmoudi - Academia.edu (original) (raw)

Papers by Jafar Mahmoudi

In this work, a new concept for cooling the electronic components using the copper-base heat sink... more In this work, a new concept for cooling the electronic components using the copper-base heat sink is proposed. The thermal performance and temperature distribution for the heat sink were analysed and a procedure for optimising the geometrical design parameter is presented. A three-dimensional model is developed to investigate flow and conjugate heat transfer in the copper-based heat sink. The model was produced with the commercial program FLUENT. The theoretical model developed is validated by comparing the predictions of the model with available experimental data. Several examples with different types of cooling methods and manufacturing processes are analysed to show the reliability and effectiveness in heat spreading of those. This report will also describe a modelling methodology that can be used to predict performance, with comparison to experimental data. The reliability of the presented model in optimising the copper-base heat sink design will be discussed.

Transactions of the Canadian Society for Mechanical Engineering, 2012

Bond strength of welded joints is an important factor in the explosive welding process. In such w... more Bond strength of welded joints is an important factor in the explosive welding process. In such welding process, stress waves produced by explosive energy propagate at the free surface and produce tension stresses. These waves result in spalling and scabbing at the edges of metals and reduce the tensile bond strength of explosive welding. The most common method for solving this problem is cutting and sizing the edges. However, this is not possible when the two metal parts to be joined are of unequal surfaces (a small plate to a large plate). This paper focuses on applying a new technique (Groove Method) for solving the strength problem at the edges for obtaining uniform welding. In this way, experimental and numerical analyses are performed to evaluate the Groove Method. The obtained results show the success and effectiveness of the groove method suggested in this paper.

Chemical Product and Process Modeling, 2012

One of the most important industrial processes is heat transfer, carried out by heat exchangers i... more One of the most important industrial processes is heat transfer, carried out by heat exchangers in single and multiphase flow applications. Despite the existence of well-developed theoretical models for different heat transfer mechanisms, the expanding need for industrial applications requiring the design and optimization of heat exchangers, has created a solid demand for experimental work and effort. This thesis concerns the use of numerical approaches to analyze and optimize heat transfer and fluid flow in power generation industry, with emphasis on pin fin technology. This research begins with a review on heat transfer characteristics in surfaces with pin fins. Different pin fins shapes with various flow boundaries were studied, and thermal and hydraulic performances were investigated. The impact of parameters such as inlet boundary conditions, pin fin shapes, and duct cross-section characteristics on both flow and heat transfer were examined. Two important applications in power generation industry were considered for this study: power transformer cooling, and condenser for CO2 capturing application in oxy-fuel power plants. Available experimental data and correlations in the literature have been used for models validation. For each case, a model based on current configuration was built and verified, and was then used for optimization and new design suggestions. All numerical modeling was performed using commercial CFD software. A basic condenser design was suggested and examined, supplemented by the use of pin fin technology to influence the condensation rate of water vapour from a CO2/H2O flue gas flow. Moreover an extensive review of numerical modeling approaches concerning this condensation issue was conducted and presented. The analysis results show that the drop-shaped pin fin configuration has heat transfer rates approximating those of the circular pin configuration, and the drop-shaped pressure losses are less than one third those of the circular. Results for the power transformer cooling system show those geometrical defects in the existing system are easily found using modeling. Also, it was found that the installation of pin fins in an internal cooling passage can have the same effect as doubling the radiator’s height, which means a more compact cooling system could be designed. Results show that a condensation model based on boundary layer theory gives a close value to experimental correlations. Considering a constant wall temperature, any increase in CO2 concentration results in lower heat transfer coefficients. This is a subsequence of increased diffusivity resistance between combustion gas and condensing boundary layer. Also it was shown that sensitivity of heat transfer rate to inlet temperatures and velocity values decreased when these parameters increased. The application of numerical methods concerning the condensation process for CO2 capturing required significant effort and running time as the complexity of multiphase flow was involved. Also data validation for the CO2/H2O condenser was challenging since this is quite a new application and less experimental data (and theoretical correlations) exist. However, it is shown that models based on numerical approaches are capable of predicting trends in the condensation process as well as the effect of the non-condensable CO2 presence in the flue gas. The resulting data, conclusions, applied methodology can be applied to the design and optimization of similar industrial heat exchangers, such as oil coolers which are currently working at low efficiency levels. It can also be used in the design of electronic components, cooling of turbine blades, or in other design applications requiring high heat flux dissipation. Finally, the finding on water vapour condensation from a binary mixture gas can be referenced for further research and development in this field.

Installed DCS system in Jajarm alumina production factory in Iran, help to us for transferred the... more Installed DCS system in Jajarm alumina production factory in Iran, help to us for transferred the signals from equipments to simulators. The simulators can help to operator for control, monitoring and training. Authors have tried to find a new simulator using ASPEN plusTM software and write a new protocol for discussed tasks.Aspen PlusTM by Aspen Technology is one of the major process simulators that arewidely used in alumina process industries today. It specialises on steady-state analysis.For implementation, simulation and interpretive of the alumina process flowsheet in jajarm factory was used from the Aspen Plus simulator. We have tried to be able to provide a list key operating and design parameters and equipment selection criteria for a limited set of unit operations and processes. And so for determinanation the economic potential of a process and to identify the operational variables that affect the economics we have studied the process and flowsheets.Using the general information of factory, process informations same as temperature, measuredpressure and so PFD, cinitic informations and finallay clin, bauxite and sodium sulphateinforamations we have design a new simulation method for digestion and control process in Jajarmfactory. The process has implemented on LCR1,PU08, PU10 and PU11 units.

Energy Procedia, 2009

Condensers for separation of CO 2 and steam are central devices in oxygen-fired power plants for ... more Condensers for separation of CO 2 and steam are central devices in oxygen-fired power plants for CO 2 capture. This work is the first part of a project aiming to optimize the design of a H 2 O/CO 2 Oxy-Fuel condenser. The project aims to achieve an in-depth understanding of the separation process at varying thermal conditions and with varying fluid compositions. COMSOL simulation tool has been used to study fluid flow, heat transfer and condensation process for H 2 O/CO 2 mixtures. The simulated condenser is a tank with all of its accessories. Boundary and initial conditions are set based on earlier works. H 2 O and CO 2 are considered as the main components for flue gas. The results show that with the proposed design, the condenser will be able to condense about 75% of water content in flue gas stream. The resulting flue gas stream after the condenser contains more than 97% CO 2. The information gained through the proposed project are important design data for improved condenser solutions that need to be implemented in order to reduce capital cost and increase the thermal efficiency of the power plants.

2007 IEEE Power Engineering Society Conference and Exposition in Africa - PowerAfrica, 2007

ABSTRACT Hot spot temperature (HST) is the most important parameter in the operation of power tra... more ABSTRACT Hot spot temperature (HST) is the most important parameter in the operation of power transformers. The HST has to be held under a prescribed limit. HST has a considerable effect on the insulation aging. Therefore detecting, monitoring and removing the HST could be a very important and necessary action for Utilities. A new design of oil spraying and its effect, along with a thermal management in a transformer cooling system has been studied in this paper. The effect of oil fluid flow on the HST problem has been considered in this paper; and the calculations and simulation have been performed by Ants algorithm. The simulation results have been validated based on a 230/63/20 kV, 250MVA transformer at the Sari substation in Iran, and the results indicate that the new design could mitigate the limitations of transformer loading due to the HST problem. The Ants algorithm have been proposed and applied for accomplishing this task and to give an improved level of accuracy.

2007 International Conference on Thermal, Mechanical and Multi-Physics Simulation Experiments in Microelectronics and Micro-Systems. EuroSime 2007, 2007

... Localized temperature rise in the winding takes place due to load current coupled with short ... more ... Localized temperature rise in the winding takes place due to load current coupled with short time over - loads, which the system is asked to cater to. Hot Spots, regions of inordinate temperature rise in the winding and top surface of insulating oil (Hottest spot temperature, HST ...

2007 8th International Conference on Electronic Packaging Technology, 2007

... need to a reliability working of power transformers, then correct performance of electronic d... more ... need to a reliability working of power transformers, then correct performance of electronic device due ... high cost, Dynamic thermal management and it is performance loss, Total power dissipation must ... Heat pipes A heat pipe is a device has an extremely high thermal conductivity ...

International Journal of Modelling and Simulation, 2013

A simulation model is developed to predict the performance of a tubular digestion process of a lo... more A simulation model is developed to predict the performance of a tubular digestion process of a low alumina/silica ratio diaspore bauxite type. The electrolyte-NRTL property method is used to calculate the equilibrium and thermodynamic properties of the slurry. The Aspen Plus simulator has been employed to solve the reaction and thermodynamic submodels. The model was validated with several sets of the industrial experimental data in terms of the flash tanks temperatures and close agreement was found. The simulation model has been utilized by the R&D department to predict the digestion process behaviour at various operation conditions. One practical output of this work is suggestion for a new design to increase the vapour and thermal energy recovery in the digestion process unit. As a result, the exhaust vapour from the last flash tank was directed to a new pre-heater section. The industrial output has been confirmed by the energy department that has decreased 8% in the furnace fuel consumption and leads to an increase of water recovery in the digestion unit.

There are many indoor pollutants in the residential buildings. Of those radon is a major and harm... more There are many indoor pollutants in the residential buildings. Of those radon is a major and harmful indoor pollutant in most countries. Radon sometimes entries to the house through building materials. High insulation and tightness in order to increase energy efficiency and to lower energy costs is led to the indoor air quality problems. Ventilation is a good method to dilute radon contaminant and maintain indoor air quality. The more fresh air is brought into the indoor environment, the better the indoor air quality can be achieved, if the fresh air comes from non polluted ambient source. However ventilation can consume a lot of energy (currently 29-59% of energy building use), especially in cold climate same as Sweden, energy consumption could be much more. Though for coping with high energy consumption the building tightness is acted very well, but for ventilation plays against. This contradiction makes a poor indoor air quality. The aim of this paper is to simulate and visualize...

The Journal of Chemical Thermodynamics, 2010

The experimental (liquid+liquid) equilibrium (LLE) properties for two ternary systems containing ... more The experimental (liquid+liquid) equilibrium (LLE) properties for two ternary systems containing (N-formylmorpholine+benzene+n-hexane), (sulfolane+benzene+n-hexane) and a quaternary mixed solvent system (sulfolane+N-formylmorpholine+benzene+n-hexane) were measured at temperature ranging from (298.15 to 318.15)K and at an atmospheric pressure. The experimental distribution coefficients and selectivity factors are presented to evaluate the efficiency of the solvents for extraction of benzene from n-hexane. The LLE results obtained

Materials Transactions, JIM, 2000

Management of Environmental Quality: An International Journal, 2013

CFD is widely used in indoor air quality, air flow pattern, indoor pollutant distribution and the... more CFD is widely used in indoor air quality, air flow pattern, indoor pollutant distribution and thermal comfort as a cost effective and powerful tool and it can be used to predict, estimate and visualize the indoor radon level.. The intention of this article is to use computational fluid dynamics (CFD), as a standalone tool to simulate indoor radon distribution and ventilation effects. This technique can be used to predict and visualize radon content and indoor air quality throughout a one family detached house in Stockholm.. In this study a mechanical balanced ventilation system and a continuous radon monitor (CRM) were also used to measure the indoor ventilation rate and radon levels. In numerical approach the FLUENT, CFD package was used to simulate radon entry into the building and ventilation effects. Results of numerical study indicated that indoor pressure made by means of ventilation systems and infiltration through door or window has significant effects on indoor radon content. It is observed that the location of vents can affect the indoor radon level, particularly in breathing (seating) zone. The analytic solution is used to validate numeric results at 3 distinct air change rates. The comparison amongst analytical, numerical and measurement results shows close agreement.

Korean Journal of Chemical Engineering, 2010

The extraction of benzene from a narrow cut of naphtha produced by the Iranian petrochemical comp... more The extraction of benzene from a narrow cut of naphtha produced by the Iranian petrochemical company has been studied at the operating temperatures of 40, 45 and 50 o C, and four solvent-to-feed ratios (S/F) varied over the range of 1-4. Two extraction solvents, sulfolane as a pure-solvent and (sulfolane containing 7 wt% 2-propanol) as a mixed-solvent have been investigated for selective removal of benzene from the naphtha cut. The experimental results demonstrated that the mixed-solvent at 40 o C is a suitable solvent to replace sulfolane for an industrial extraction process for the separation of benzene from the naphtha cut because of its lower price and energy savings.

Journal of Environmental Radioactivity, 2013

Radon is released from soil and building materials and can accumulate in residential buildings. B... more Radon is released from soil and building materials and can accumulate in residential buildings. Breathing radon and radon progeny for extended periods hazardous to health and can lead to lung cancer. Indoor air conditions and ventilation systems strongly influence indoor radon concentrations. This paper focuses on effects of air change rate, indoor temperature and relative humidity on indoor radon concentrations in a one family detached house in Stockholm, Sweden. In this study a heat recovery ventilation system unit was used to control the ventilation rate and a continuous radon monitor (CRM) was used to measure radon levels. FLUENT, a computational fluid dynamics (CFD) software package was used to simulate radon entry into the building and air change rate, indoor temperature and relative humidity effects using a numerical approach. The results from analytical solution, measurements and numerical simulations showed that air change rate, indoor temperature and moisture had significant effects on indoor radon concentration. Increasing air change rate reduces radon level and for a specific air change rate (in this work Ach ¼ 0.5) there was a range of temperature and relative humidity that minimized radon levels. In this case study minimum radon levels were obtained at temperatures between 20 and 22 C and a relative humidity of 50e60%.

International Journal of Green Energy, 2006

This paper describes a methodology used for designing louvered fins. Louvered fins are commonly u... more This paper describes a methodology used for designing louvered fins. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. Detailed measurements can be accomplished with computational models of these louvered fins to gain a better understanding of the flow field and heat distribution. The particular louver geometry studies for this work have a louver angle of 23° and fin count of 17 fpi. The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with louvered fins are analyzed numerically. A three-dimensional model is developed to investigate flow and conjugate heat transfer in the copper-based car radiator. The model was produced with the commercial program FLUENT. The theoretical model has been developed and validated by comparing the predictions of the model with available experimental data. The thermal performance and temperature distribution for the louvered fins were analyzed and a procedure for optimizing the geometrical design parameter is presented. One fin specification among the various flat tube exchangers is recommended by first considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected radiator are investigated also. The results will be used as fundamental data for tube design by suggesting specifications for car radiator tubes.

International Journal of Green Energy, 2006

International Journal of Energy Research, 2008

ABSTRACT Transformers are complex devices consisting of an iron core around which are wrapped var... more ABSTRACT Transformers are complex devices consisting of an iron core around which are wrapped various coils of insulated wires, inside a tank filled with insulating oil, along with connectors, bushings and various other small components.Overloading causes excess heat in a transformer, the negative effects of which are degradation of the kraft paper insulation around the wires (leading to internal failures of the coils), excessive tank pressure or degradation of the insulating oil (either of which can cause catastrophic failures, even explosions), and leaking gaskets and seals. (Since the copper used in the windings is already soft (annealed) and is not under tension, overheating of the conductors is generally not a concern.) Thermal cycling contributes to mechanical damage by loosening connections. Because of hysteresis in the transformer core, overloading generates harmonics and these can cause mechanical vibration of the transformer, contributing to physical damage. Overloading also assumes that faults near the transformer, when they occur, will be greater than normal, so there is the increased likelihood of damage to the transformer from fault currents; such damage can be manifested by coil failures, bushing flashovers, blown gaskets and seals, connector failures, oil explosions and fires, and physical displacement of internal components due to electromechanical torques. In addition, the world consumes millions of barrels of oils to cover the electrical losses, which then produces green house gases. With the introduction of new method for loss reduction, authors found a new method that is presented in this paper. In this paper we assess the impact of losses on final cost of transformer and green house gases. It is proved that losses cost is equal to the capital investment of the transformer. Emissions of CO2 in the electrical network is 0.4 kg CO2 kWh−1, which is (11 500 billion kilowatts hours of electricity produced) around 46 billion tons of transformer losses. This can be reduced to 23 billion ton using loss management. It is obvious that to cover losses generation of extra electricity is needed. Extra production leads to more CO2 emission. Installation of CO2 capturing device utilities at least can prevent more pollution emissions. For these reasons, a CO2 capturing condenser applicable in power station is presented here. It was simulated using COMSOL software. Copyright © 2008 John Wiley & Sons, Ltd.

In this work, a new concept for cooling the electronic components using the copper-base heat sink... more In this work, a new concept for cooling the electronic components using the copper-base heat sink is proposed. The thermal performance and temperature distribution for the heat sink were analysed and a procedure for optimising the geometrical design parameter is presented. A three-dimensional model is developed to investigate flow and conjugate heat transfer in the copper-based heat sink. The model was produced with the commercial program FLUENT. The theoretical model developed is validated by comparing the predictions of the model with available experimental data. Several examples with different types of cooling methods and manufacturing processes are analysed to show the reliability and effectiveness in heat spreading of those. This report will also describe a modelling methodology that can be used to predict performance, with comparison to experimental data. The reliability of the presented model in optimising the copper-base heat sink design will be discussed.

Transactions of the Canadian Society for Mechanical Engineering, 2012

Bond strength of welded joints is an important factor in the explosive welding process. In such w... more Bond strength of welded joints is an important factor in the explosive welding process. In such welding process, stress waves produced by explosive energy propagate at the free surface and produce tension stresses. These waves result in spalling and scabbing at the edges of metals and reduce the tensile bond strength of explosive welding. The most common method for solving this problem is cutting and sizing the edges. However, this is not possible when the two metal parts to be joined are of unequal surfaces (a small plate to a large plate). This paper focuses on applying a new technique (Groove Method) for solving the strength problem at the edges for obtaining uniform welding. In this way, experimental and numerical analyses are performed to evaluate the Groove Method. The obtained results show the success and effectiveness of the groove method suggested in this paper.

Chemical Product and Process Modeling, 2012

One of the most important industrial processes is heat transfer, carried out by heat exchangers i... more One of the most important industrial processes is heat transfer, carried out by heat exchangers in single and multiphase flow applications. Despite the existence of well-developed theoretical models for different heat transfer mechanisms, the expanding need for industrial applications requiring the design and optimization of heat exchangers, has created a solid demand for experimental work and effort. This thesis concerns the use of numerical approaches to analyze and optimize heat transfer and fluid flow in power generation industry, with emphasis on pin fin technology. This research begins with a review on heat transfer characteristics in surfaces with pin fins. Different pin fins shapes with various flow boundaries were studied, and thermal and hydraulic performances were investigated. The impact of parameters such as inlet boundary conditions, pin fin shapes, and duct cross-section characteristics on both flow and heat transfer were examined. Two important applications in power generation industry were considered for this study: power transformer cooling, and condenser for CO2 capturing application in oxy-fuel power plants. Available experimental data and correlations in the literature have been used for models validation. For each case, a model based on current configuration was built and verified, and was then used for optimization and new design suggestions. All numerical modeling was performed using commercial CFD software. A basic condenser design was suggested and examined, supplemented by the use of pin fin technology to influence the condensation rate of water vapour from a CO2/H2O flue gas flow. Moreover an extensive review of numerical modeling approaches concerning this condensation issue was conducted and presented. The analysis results show that the drop-shaped pin fin configuration has heat transfer rates approximating those of the circular pin configuration, and the drop-shaped pressure losses are less than one third those of the circular. Results for the power transformer cooling system show those geometrical defects in the existing system are easily found using modeling. Also, it was found that the installation of pin fins in an internal cooling passage can have the same effect as doubling the radiator’s height, which means a more compact cooling system could be designed. Results show that a condensation model based on boundary layer theory gives a close value to experimental correlations. Considering a constant wall temperature, any increase in CO2 concentration results in lower heat transfer coefficients. This is a subsequence of increased diffusivity resistance between combustion gas and condensing boundary layer. Also it was shown that sensitivity of heat transfer rate to inlet temperatures and velocity values decreased when these parameters increased. The application of numerical methods concerning the condensation process for CO2 capturing required significant effort and running time as the complexity of multiphase flow was involved. Also data validation for the CO2/H2O condenser was challenging since this is quite a new application and less experimental data (and theoretical correlations) exist. However, it is shown that models based on numerical approaches are capable of predicting trends in the condensation process as well as the effect of the non-condensable CO2 presence in the flue gas. The resulting data, conclusions, applied methodology can be applied to the design and optimization of similar industrial heat exchangers, such as oil coolers which are currently working at low efficiency levels. It can also be used in the design of electronic components, cooling of turbine blades, or in other design applications requiring high heat flux dissipation. Finally, the finding on water vapour condensation from a binary mixture gas can be referenced for further research and development in this field.

Installed DCS system in Jajarm alumina production factory in Iran, help to us for transferred the... more Installed DCS system in Jajarm alumina production factory in Iran, help to us for transferred the signals from equipments to simulators. The simulators can help to operator for control, monitoring and training. Authors have tried to find a new simulator using ASPEN plusTM software and write a new protocol for discussed tasks.Aspen PlusTM by Aspen Technology is one of the major process simulators that arewidely used in alumina process industries today. It specialises on steady-state analysis.For implementation, simulation and interpretive of the alumina process flowsheet in jajarm factory was used from the Aspen Plus simulator. We have tried to be able to provide a list key operating and design parameters and equipment selection criteria for a limited set of unit operations and processes. And so for determinanation the economic potential of a process and to identify the operational variables that affect the economics we have studied the process and flowsheets.Using the general information of factory, process informations same as temperature, measuredpressure and so PFD, cinitic informations and finallay clin, bauxite and sodium sulphateinforamations we have design a new simulation method for digestion and control process in Jajarmfactory. The process has implemented on LCR1,PU08, PU10 and PU11 units.

Energy Procedia, 2009

Condensers for separation of CO 2 and steam are central devices in oxygen-fired power plants for ... more Condensers for separation of CO 2 and steam are central devices in oxygen-fired power plants for CO 2 capture. This work is the first part of a project aiming to optimize the design of a H 2 O/CO 2 Oxy-Fuel condenser. The project aims to achieve an in-depth understanding of the separation process at varying thermal conditions and with varying fluid compositions. COMSOL simulation tool has been used to study fluid flow, heat transfer and condensation process for H 2 O/CO 2 mixtures. The simulated condenser is a tank with all of its accessories. Boundary and initial conditions are set based on earlier works. H 2 O and CO 2 are considered as the main components for flue gas. The results show that with the proposed design, the condenser will be able to condense about 75% of water content in flue gas stream. The resulting flue gas stream after the condenser contains more than 97% CO 2. The information gained through the proposed project are important design data for improved condenser solutions that need to be implemented in order to reduce capital cost and increase the thermal efficiency of the power plants.

2007 IEEE Power Engineering Society Conference and Exposition in Africa - PowerAfrica, 2007

ABSTRACT Hot spot temperature (HST) is the most important parameter in the operation of power tra... more ABSTRACT Hot spot temperature (HST) is the most important parameter in the operation of power transformers. The HST has to be held under a prescribed limit. HST has a considerable effect on the insulation aging. Therefore detecting, monitoring and removing the HST could be a very important and necessary action for Utilities. A new design of oil spraying and its effect, along with a thermal management in a transformer cooling system has been studied in this paper. The effect of oil fluid flow on the HST problem has been considered in this paper; and the calculations and simulation have been performed by Ants algorithm. The simulation results have been validated based on a 230/63/20 kV, 250MVA transformer at the Sari substation in Iran, and the results indicate that the new design could mitigate the limitations of transformer loading due to the HST problem. The Ants algorithm have been proposed and applied for accomplishing this task and to give an improved level of accuracy.

2007 International Conference on Thermal, Mechanical and Multi-Physics Simulation Experiments in Microelectronics and Micro-Systems. EuroSime 2007, 2007

... Localized temperature rise in the winding takes place due to load current coupled with short ... more ... Localized temperature rise in the winding takes place due to load current coupled with short time over - loads, which the system is asked to cater to. Hot Spots, regions of inordinate temperature rise in the winding and top surface of insulating oil (Hottest spot temperature, HST ...

2007 8th International Conference on Electronic Packaging Technology, 2007

... need to a reliability working of power transformers, then correct performance of electronic d... more ... need to a reliability working of power transformers, then correct performance of electronic device due ... high cost, Dynamic thermal management and it is performance loss, Total power dissipation must ... Heat pipes A heat pipe is a device has an extremely high thermal conductivity ...

International Journal of Modelling and Simulation, 2013

A simulation model is developed to predict the performance of a tubular digestion process of a lo... more A simulation model is developed to predict the performance of a tubular digestion process of a low alumina/silica ratio diaspore bauxite type. The electrolyte-NRTL property method is used to calculate the equilibrium and thermodynamic properties of the slurry. The Aspen Plus simulator has been employed to solve the reaction and thermodynamic submodels. The model was validated with several sets of the industrial experimental data in terms of the flash tanks temperatures and close agreement was found. The simulation model has been utilized by the R&D department to predict the digestion process behaviour at various operation conditions. One practical output of this work is suggestion for a new design to increase the vapour and thermal energy recovery in the digestion process unit. As a result, the exhaust vapour from the last flash tank was directed to a new pre-heater section. The industrial output has been confirmed by the energy department that has decreased 8% in the furnace fuel consumption and leads to an increase of water recovery in the digestion unit.

There are many indoor pollutants in the residential buildings. Of those radon is a major and harm... more There are many indoor pollutants in the residential buildings. Of those radon is a major and harmful indoor pollutant in most countries. Radon sometimes entries to the house through building materials. High insulation and tightness in order to increase energy efficiency and to lower energy costs is led to the indoor air quality problems. Ventilation is a good method to dilute radon contaminant and maintain indoor air quality. The more fresh air is brought into the indoor environment, the better the indoor air quality can be achieved, if the fresh air comes from non polluted ambient source. However ventilation can consume a lot of energy (currently 29-59% of energy building use), especially in cold climate same as Sweden, energy consumption could be much more. Though for coping with high energy consumption the building tightness is acted very well, but for ventilation plays against. This contradiction makes a poor indoor air quality. The aim of this paper is to simulate and visualize...

The Journal of Chemical Thermodynamics, 2010

The experimental (liquid+liquid) equilibrium (LLE) properties for two ternary systems containing ... more The experimental (liquid+liquid) equilibrium (LLE) properties for two ternary systems containing (N-formylmorpholine+benzene+n-hexane), (sulfolane+benzene+n-hexane) and a quaternary mixed solvent system (sulfolane+N-formylmorpholine+benzene+n-hexane) were measured at temperature ranging from (298.15 to 318.15)K and at an atmospheric pressure. The experimental distribution coefficients and selectivity factors are presented to evaluate the efficiency of the solvents for extraction of benzene from n-hexane. The LLE results obtained

Materials Transactions, JIM, 2000

Management of Environmental Quality: An International Journal, 2013

CFD is widely used in indoor air quality, air flow pattern, indoor pollutant distribution and the... more CFD is widely used in indoor air quality, air flow pattern, indoor pollutant distribution and thermal comfort as a cost effective and powerful tool and it can be used to predict, estimate and visualize the indoor radon level.. The intention of this article is to use computational fluid dynamics (CFD), as a standalone tool to simulate indoor radon distribution and ventilation effects. This technique can be used to predict and visualize radon content and indoor air quality throughout a one family detached house in Stockholm.. In this study a mechanical balanced ventilation system and a continuous radon monitor (CRM) were also used to measure the indoor ventilation rate and radon levels. In numerical approach the FLUENT, CFD package was used to simulate radon entry into the building and ventilation effects. Results of numerical study indicated that indoor pressure made by means of ventilation systems and infiltration through door or window has significant effects on indoor radon content. It is observed that the location of vents can affect the indoor radon level, particularly in breathing (seating) zone. The analytic solution is used to validate numeric results at 3 distinct air change rates. The comparison amongst analytical, numerical and measurement results shows close agreement.

Korean Journal of Chemical Engineering, 2010

The extraction of benzene from a narrow cut of naphtha produced by the Iranian petrochemical comp... more The extraction of benzene from a narrow cut of naphtha produced by the Iranian petrochemical company has been studied at the operating temperatures of 40, 45 and 50 o C, and four solvent-to-feed ratios (S/F) varied over the range of 1-4. Two extraction solvents, sulfolane as a pure-solvent and (sulfolane containing 7 wt% 2-propanol) as a mixed-solvent have been investigated for selective removal of benzene from the naphtha cut. The experimental results demonstrated that the mixed-solvent at 40 o C is a suitable solvent to replace sulfolane for an industrial extraction process for the separation of benzene from the naphtha cut because of its lower price and energy savings.

Journal of Environmental Radioactivity, 2013

Radon is released from soil and building materials and can accumulate in residential buildings. B... more Radon is released from soil and building materials and can accumulate in residential buildings. Breathing radon and radon progeny for extended periods hazardous to health and can lead to lung cancer. Indoor air conditions and ventilation systems strongly influence indoor radon concentrations. This paper focuses on effects of air change rate, indoor temperature and relative humidity on indoor radon concentrations in a one family detached house in Stockholm, Sweden. In this study a heat recovery ventilation system unit was used to control the ventilation rate and a continuous radon monitor (CRM) was used to measure radon levels. FLUENT, a computational fluid dynamics (CFD) software package was used to simulate radon entry into the building and air change rate, indoor temperature and relative humidity effects using a numerical approach. The results from analytical solution, measurements and numerical simulations showed that air change rate, indoor temperature and moisture had significant effects on indoor radon concentration. Increasing air change rate reduces radon level and for a specific air change rate (in this work Ach ¼ 0.5) there was a range of temperature and relative humidity that minimized radon levels. In this case study minimum radon levels were obtained at temperatures between 20 and 22 C and a relative humidity of 50e60%.

International Journal of Green Energy, 2006

This paper describes a methodology used for designing louvered fins. Louvered fins are commonly u... more This paper describes a methodology used for designing louvered fins. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. Detailed measurements can be accomplished with computational models of these louvered fins to gain a better understanding of the flow field and heat distribution. The particular louver geometry studies for this work have a louver angle of 23° and fin count of 17 fpi. The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with louvered fins are analyzed numerically. A three-dimensional model is developed to investigate flow and conjugate heat transfer in the copper-based car radiator. The model was produced with the commercial program FLUENT. The theoretical model has been developed and validated by comparing the predictions of the model with available experimental data. The thermal performance and temperature distribution for the louvered fins were analyzed and a procedure for optimizing the geometrical design parameter is presented. One fin specification among the various flat tube exchangers is recommended by first considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected radiator are investigated also. The results will be used as fundamental data for tube design by suggesting specifications for car radiator tubes.

International Journal of Green Energy, 2006

International Journal of Energy Research, 2008

ABSTRACT Transformers are complex devices consisting of an iron core around which are wrapped var... more ABSTRACT Transformers are complex devices consisting of an iron core around which are wrapped various coils of insulated wires, inside a tank filled with insulating oil, along with connectors, bushings and various other small components.Overloading causes excess heat in a transformer, the negative effects of which are degradation of the kraft paper insulation around the wires (leading to internal failures of the coils), excessive tank pressure or degradation of the insulating oil (either of which can cause catastrophic failures, even explosions), and leaking gaskets and seals. (Since the copper used in the windings is already soft (annealed) and is not under tension, overheating of the conductors is generally not a concern.) Thermal cycling contributes to mechanical damage by loosening connections. Because of hysteresis in the transformer core, overloading generates harmonics and these can cause mechanical vibration of the transformer, contributing to physical damage. Overloading also assumes that faults near the transformer, when they occur, will be greater than normal, so there is the increased likelihood of damage to the transformer from fault currents; such damage can be manifested by coil failures, bushing flashovers, blown gaskets and seals, connector failures, oil explosions and fires, and physical displacement of internal components due to electromechanical torques. In addition, the world consumes millions of barrels of oils to cover the electrical losses, which then produces green house gases. With the introduction of new method for loss reduction, authors found a new method that is presented in this paper. In this paper we assess the impact of losses on final cost of transformer and green house gases. It is proved that losses cost is equal to the capital investment of the transformer. Emissions of CO2 in the electrical network is 0.4 kg CO2 kWh−1, which is (11 500 billion kilowatts hours of electricity produced) around 46 billion tons of transformer losses. This can be reduced to 23 billion ton using loss management. It is obvious that to cover losses generation of extra electricity is needed. Extra production leads to more CO2 emission. Installation of CO2 capturing device utilities at least can prevent more pollution emissions. For these reasons, a CO2 capturing condenser applicable in power station is presented here. It was simulated using COMSOL software. Copyright © 2008 John Wiley & Sons, Ltd.