Amirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190327Optimization and Thermodynamic Analysis of the Dual Mixed Refrigerant Process of the Natural Gas LiquefactionOptimization and Thermodynamic Analysis of the Dual Mixed Refrigerant Process of the Natural Gas Liquefaction23572368335810.22060/mej.2019.15191.6054FAMohsenKashi ParpinchiImam Khomeini international university, Qazvin, IranAlirezaSadeghimam Khomeini international university, Qazvin, IranMansourKhanakiImam Khomeini International UniversitySeyed AbbasSadatsakakImam Khomeini International UniversityJournal Article20181027Natural gas liquefaction processes require a lot of investment and operation costs and are part of the energy-consuming industries. In this research, parameters such as refrigerant component, inlet and outlet pressure to compressors were optimized in the dual mixed refrigerant system to reduce operating costs. The optimized system was then evaluated by exergy to obtain the amount of exergy loss in various components of the system, finding illustrate the highest exergy losses were in compressors, heat exchangers, aftercoolers and throttle valves, respectively. The reason for the high loss of exergy in the compressors is their low polytropic efficiency. Exergy analysis showed that exergy loss in the main cycle heat exchanger, is 4% higher than that of the pre-cooling cycle heat exchanger, which is due to the higher temperature difference between input and output flows in the main cycle heat exchanger. Analysis of the effect of the size of the heat exchanger, which highly affects investment costs, on the specific power consumption is carried out and the results showed that this effect is minimum at the optimum point and increases proportionally to the distance from the optimum point.Natural gas liquefaction processes require a lot of investment and operation costs and are part of the energy-consuming industries. In this research, parameters such as refrigerant component, inlet and outlet pressure to compressors were optimized in the dual mixed refrigerant system to reduce operating costs. The optimized system was then evaluated by exergy to obtain the amount of exergy loss in various components of the system, finding illustrate the highest exergy losses were in compressors, heat exchangers, aftercoolers and throttle valves, respectively. The reason for the high loss of exergy in the compressors is their low polytropic efficiency. Exergy analysis showed that exergy loss in the main cycle heat exchanger, is 4% higher than that of the pre-cooling cycle heat exchanger, which is due to the higher temperature difference between input and output flows in the main cycle heat exchanger. Analysis of the effect of the size of the heat exchanger, which highly affects investment costs, on the specific power consumption is carried out and the results showed that this effect is minimum at the optimum point and increases proportionally to the distance from the optimum point.https://mej.aut.ac.ir/article_3358_97108695bd93b6be52fa0334874c8722.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190430Study of the Natural Circulation Heat Recovery Steam Generator Unsteady Behavior Using One Dimensional Model for the Evaporator LoopStudy of the Natural Circulation Heat Recovery Steam Generator Unsteady Behavior Using One Dimensional Model for the Evaporator Loop23692386339610.22060/mej.2019.15234.6065FAOmidMahdavi KeshavarMaster of Science Graduate, Energy Conversion Department, Mechanical Engineering Faculty, Tarbiat Modares University, Tehran, IranAliJafarianAssociate Professor, Energy Conversion Department, Mechanical Engineering Faculty, Tarbiat Modares University, Tehran, IranSaberDeldarMaster of Science Graduate, Energy Conversion Department, Mechanical Engineering Faculty, Tarbiat Modares University, Tehran, IranJournal Article20181103Heat recovery steam generators as a vital part of cogeneration plants play a fundamental role in energy recovery processes. According to a necessity of accurate analysis of steam generators’ parameters variation rate to take a decision on steam generators processes such as start-up and shut-down, the present study aims to investigate the unsteady behavior of boilers using the dynamic simulation. In this respect, a one-dimensional model of the evaporator natural circulation loop along with boilers’ drum and heat transfer models are considered for simulation. Unsteady study scenarios include changes in the input heat to tube banks due to the change in the gas turbine load, feedwater flow rate and steam demand of the downstream cycle. A computer code has been developed to solve governing equations of a one- dimensional model and to demonstrate the response of boilers’ key parameters to different scenarios. Dynamic simulation results showed that a 5% increase in heat input to risers leads to an increase of 15% of the drum pressure as well as an increase of about 10 degrees of the tubes wall temperature. In addition, an increase of 20% in the heat input due to the change in the gas turbine load would increase the wall temperature of tubes by 35 degrees.Heat recovery steam generators as a vital part of cogeneration plants play a fundamental role in energy recovery processes. According to a necessity of accurate analysis of steam generators’ parameters variation rate to take a decision on steam generators processes such as start-up and shut-down, the present study aims to investigate the unsteady behavior of boilers using the dynamic simulation. In this respect, a one-dimensional model of the evaporator natural circulation loop along with boilers’ drum and heat transfer models are considered for simulation. Unsteady study scenarios include changes in the input heat to tube banks due to the change in the gas turbine load, feedwater flow rate and steam demand of the downstream cycle. A computer code has been developed to solve governing equations of a one- dimensional model and to demonstrate the response of boilers’ key parameters to different scenarios. Dynamic simulation results showed that a 5% increase in heat input to risers leads to an increase of 15% of the drum pressure as well as an increase of about 10 degrees of the tubes wall temperature. In addition, an increase of 20% in the heat input due to the change in the gas turbine load would increase the wall temperature of tubes by 35 degrees.https://mej.aut.ac.ir/article_3396_818de4d2ec21cfcb149ced7a5bed25ab.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190320Optimization of the Turbines Locating in the Wind FarmOptimization of the Turbines Locating in the Wind Farm23872402334910.22060/mej.2019.15150.6043FASeyed MojtabaVaredi Kulaee0000-0002-7427-2127MasoodAbdolmohammadiDepartment of Mechanical and Mechatronics Engineering, Shahrood University of TechnologyHabibAhmadiDepartment of Mechanical and Mechatronics Engineering, Shahrood University of TechnologyMostafaNazariDepartment of Mechanical Engineering, Shahrood University of Technology, Shahrood, Iran.Journal Article20181017Nowadays, with regard to the reduction of fossil fuels and the management of their use, wind power is now rising as one of the most efficient renewable energy sources. Moreover, wind farms, which include sets of turbines in a farm, have become more developed and their designs and optimizations have risen recently. In this paper, the wind turbines are located in the wind farm and the effects of their positions and arrangements on the production power of the whole system are investigated. For this purpose, a square farm is considered and, having information on how the winds and wind speeds in each case, will extract the optimum location of turbines in the farm using optimization algorithms. The main goal of this research is to increase the total amount of power extracted from the wind farm based on the changes in the locations and arrangements of the turbines. This optimization problem is subjected to some constraints, such as the maximum number of turbines in the farm, the minimum distance between turbines and the overall size of the farm. To solve this optimization problem, the genetic algorithm and particle swarm optimization methods are used and the results of these methods are compared.Nowadays, with regard to the reduction of fossil fuels and the management of their use, wind power is now rising as one of the most efficient renewable energy sources. Moreover, wind farms, which include sets of turbines in a farm, have become more developed and their designs and optimizations have risen recently. In this paper, the wind turbines are located in the wind farm and the effects of their positions and arrangements on the production power of the whole system are investigated. For this purpose, a square farm is considered and, having information on how the winds and wind speeds in each case, will extract the optimum location of turbines in the farm using optimization algorithms. The main goal of this research is to increase the total amount of power extracted from the wind farm based on the changes in the locations and arrangements of the turbines. This optimization problem is subjected to some constraints, such as the maximum number of turbines in the farm, the minimum distance between turbines and the overall size of the farm. To solve this optimization problem, the genetic algorithm and particle swarm optimization methods are used and the results of these methods are compared.https://mej.aut.ac.ir/article_3349_69f268fb2ba1068615b3219c6e8f57e8.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190320Performance Analysis of a Building Heating System using Underground Source Heat Pump and Photovoltaic Thermal CollectorPerformance Analysis of a Building Heating System using Underground Source Heat Pump and Photovoltaic Thermal Collector24032424334810.22060/mej.2019.15105.6025FAMaliheKaramiDepartment of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, IranFaramarzSarhaddiHead of Department of Mechanical Engineering
Research Laboratory of Renewable Energies and Electromagnetic Fluids, Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran0000-0002-5216-9823FatemehSobhnamayanDepartment of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, IranJournal Article20181007This study investigates the performance evaluation of a building heating system equipped to underground storage tank heat pump and photovoltaic thermal collector. The system consists of an underground spherical tank, a photovoltaic thermal collector and a heat pump. The performance evaluation of the combined system is carried out from the energy and exergy perspective. Developing energy balance for various components of the system, the analytical relations for water temperature of the auxiliary tank, solar cell temperature, absorber plate temperature and the useful heat gain of photovoltaic thermal collector are obtained. The output electrical power of photovoltaic module is calculated by the four-parameter current-voltage model. By writing the exergy balance for the various components of the system, their irreversibility is specified. The validation of the simulation results is carried. The obtained results indicate that the energy and exergy efficiency is maximum for the collector number of 65 and mass flow rate of 0.25 kg/s. The decrease in storage tank volume causes a decrease in water temperature. The increase of 30% in the collector number causes an increase of 25% in water temperature. The highest and lowest water temperature of the tank is observed on the ground of coarse graveled and granite, respectively.This study investigates the performance evaluation of a building heating system equipped to underground storage tank heat pump and photovoltaic thermal collector. The system consists of an underground spherical tank, a photovoltaic thermal collector and a heat pump. The performance evaluation of the combined system is carried out from the energy and exergy perspective. Developing energy balance for various components of the system, the analytical relations for water temperature of the auxiliary tank, solar cell temperature, absorber plate temperature and the useful heat gain of photovoltaic thermal collector are obtained. The output electrical power of photovoltaic module is calculated by the four-parameter current-voltage model. By writing the exergy balance for the various components of the system, their irreversibility is specified. The validation of the simulation results is carried. The obtained results indicate that the energy and exergy efficiency is maximum for the collector number of 65 and mass flow rate of 0.25 kg/s. The decrease in storage tank volume causes a decrease in water temperature. The increase of 30% in the collector number causes an increase of 25% in water temperature. The highest and lowest water temperature of the tank is observed on the ground of coarse graveled and granite, respectively.https://mej.aut.ac.ir/article_3348_333cb763facc6ce398ff83845f224d62.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190320The Importance of the Compatible Combustion and Sub-grid Scale Models on the Simulation of Large-Scale Pool FireThe Importance of the Compatible Combustion and Sub-grid Scale Models on the Simulation of Large-Scale Pool Fire24252442335010.22060/mej.2019.15288.6085FAGhassemHeidarinejadFaculty of Mechanical Engineering, Tarbiat Modares UniversityHadiPasdarShahriAssistant Professor, Faculty of Mechanical Engineering, Tarbiat Modares UniversityMohamadSafarzadehtarbiat modares universityJournal Article20181115In this paper, large-scale pool fire behavior has been investigated with large eddy simulation. In order to investigate the efficiency of various combustion models in the pool fire simulation, two combustion models of the eddy dissipation model and infinite fast chemistry in two sub-grid scale models of Smagorinsky and one equation was evaluated. The infinite fast chemistry model has an over- prediction in the reaction rate and flame temperatures in the simulation of pool fire. In addition, the eddy dissipation model, due to the use of time characteristic of turbulence and diffusion, has more accurate results in the prediction temperature field and flow behaviors. The eddy dissipation model with one- equation sub-grid scale model has better prediction for the velocity field and there is a difference of about 5–10 % with the experimental measurements. However, the infinite fast chemistry combustion model can better fit with the Smagorinsky sub-grid scale than one equation sub-grid scale model in the simulation of pool fire. The numerical results predicted by the different combustion models and sub-grid models for vertical velocity along the central line are in the range of experimental results, and almost all models predict the vertical velocity in this line, good.In this paper, large-scale pool fire behavior has been investigated with large eddy simulation. In order to investigate the efficiency of various combustion models in the pool fire simulation, two combustion models of the eddy dissipation model and infinite fast chemistry in two sub-grid scale models of Smagorinsky and one equation was evaluated. The infinite fast chemistry model has an over- prediction in the reaction rate and flame temperatures in the simulation of pool fire. In addition, the eddy dissipation model, due to the use of time characteristic of turbulence and diffusion, has more accurate results in the prediction temperature field and flow behaviors. The eddy dissipation model with one- equation sub-grid scale model has better prediction for the velocity field and there is a difference of about 5–10 % with the experimental measurements. However, the infinite fast chemistry combustion model can better fit with the Smagorinsky sub-grid scale than one equation sub-grid scale model in the simulation of pool fire. The numerical results predicted by the different combustion models and sub-grid models for vertical velocity along the central line are in the range of experimental results, and almost all models predict the vertical velocity in this line, good.https://mej.aut.ac.ir/article_3350_b7ee0d0d4d5ef995aae0fc691e6d840d.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190409Maps of Flame Dynamics for Premixed Lean Hydrogen-Air Combustion in a Heated MicrochannelMaps of Flame Dynamics for Premixed Lean Hydrogen-Air Combustion in a Heated Microchannel24432464336610.22060/mej.2019.14957.5997FAAlirezaAlipoorShahid Chamran University of AhvazKiumarsMazaheriFaculty of Mechanical Engineering, Tarbiat Modares UniversityJournal Article20180920In the present work, flame dynamics are extracted for combustion of premixed lean hydrogen-air in a heated microchannel using numerical simulation. In order to simulate the combustion phenomenon at this scale, Navier-Stokes equations along with energy and species conservation equations are considered by formulation of low Mach number and with consideration of detail chemical kinetics. Regarding different conditions, three dynamics is observed in the micro channel including periodic repetitive ignition-extinction, steady symmetric flame and steady asymmetric flame. Effects of different parameters such as inlet velocity, equivalence ratio, and channel width are investigated on the flame dynamics. .In the present work, flame dynamics are extracted for combustion of premixed lean hydrogen-air in a heated microchannel using numerical simulation. In order to simulate the combustion phenomenon at this scale, Navier-Stokes equations along with energy and species conservation equations are considered by formulation of low Mach number and with consideration of detail chemical kinetics. Regarding different conditions, three dynamics is observed in the micro channel including periodic repetitive ignition-extinction, steady symmetric flame and steady asymmetric flame. Effects of different parameters such as inlet velocity, equivalence ratio, and channel width are investigated on the flame dynamics. .https://mej.aut.ac.ir/article_3366_07f75d9144912970de5a09f5a305e10c.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190630Mathematical and Artificial Neural Network Simulation of NOx Selective Catalytic Reduction in a Monolithic ReactorMathematical and Artificial Neural Network Simulation of NOx Selective Catalytic Reduction in a Monolithic Reactor24652478348910.22060/mej.2019.15355.6102FAAliFarziFaculty of Chemical and Petroleum Engineering, University of Tabriz, Tabriz, Iran0000-0002-3416-894XParvanehKhalatiFaculty of Chemical and Petroleum Engineering, University of Tabriz, Tabriz, IranJournal Article20181128Worldwide development of industries and increase of energy consumption, have resulted fast increase in the emission of nitrogen oxides pollutants. Therefore, removal of nitrogen oxides is a very important issue. In this study, modeling and simulation of selective catalytic reduction of nitrogen oxides in a monolithic catalytic reactor at both steady-state and dynamic-state was performed. Steady- state results showed that because of intense effect of temperature on nitrogen oxides conversion and competition of the main reaction with ammonia oxidation reaction, conversion of nitrogen oxides requires a catalytic filter in the range 300-350°C. Results showed that nitrogen oxide conversion increases with decreasing gas hourly space velocity and increasing inlet nitrogen oxide concentration. At dynamic-state, the effect of changes in some parameters including gas hourly space velocity, inlet nitrogen oxide concentration, and ammonia /nitrogen oxide ratio were investigated. Also, steady-state simulation of the process was performed using an artificial neural network and conversions of nitrogen oxides and ammonia were estimated as a function of gas hourly space velocity, reactor temperature, and nitrogen oxide concentration. 96 networks with different neurons and two different activation functions in hidden layer were trained. The resulted optimum network showed maximum mean square error of about 0.01 compared to mathematical modeling results indicating high performance of neural network for prediction of process performance.Worldwide development of industries and increase of energy consumption, have resulted fast increase in the emission of nitrogen oxides pollutants. Therefore, removal of nitrogen oxides is a very important issue. In this study, modeling and simulation of selective catalytic reduction of nitrogen oxides in a monolithic catalytic reactor at both steady-state and dynamic-state was performed. Steady- state results showed that because of intense effect of temperature on nitrogen oxides conversion and competition of the main reaction with ammonia oxidation reaction, conversion of nitrogen oxides requires a catalytic filter in the range 300-350°C. Results showed that nitrogen oxide conversion increases with decreasing gas hourly space velocity and increasing inlet nitrogen oxide concentration. At dynamic-state, the effect of changes in some parameters including gas hourly space velocity, inlet nitrogen oxide concentration, and ammonia /nitrogen oxide ratio were investigated. Also, steady-state simulation of the process was performed using an artificial neural network and conversions of nitrogen oxides and ammonia were estimated as a function of gas hourly space velocity, reactor temperature, and nitrogen oxide concentration. 96 networks with different neurons and two different activation functions in hidden layer were trained. The resulted optimum network showed maximum mean square error of about 0.01 compared to mathematical modeling results indicating high performance of neural network for prediction of process performance.https://mej.aut.ac.ir/article_3489_1b318124e37af6d74a03501474f44ea1.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-6032529201902281-1- Two Phase Simulation of Droplets Motion in Cathode Channels and Manifolds of Polymer Electrolyte Membrane Fuel Cell1-1- Two Phase Simulation of Droplets Motion in Cathode Channels and Manifolds of Polymer Electrolyte Membrane Fuel Cell24792490331310.22060/mej.2019.13114.6001FASayed HosseinMasrouri SaadatFuel Cell Technology Research Laboratory, Malek Ashtar University of Technology0000-0002-2869-4935MazaherRahimi EsboeeFuel Cell Technology Research Laboratory, Malek Ashtar University of Technology, Fereydounkenar, Iran.MehrzadShamsFaculty of Mechanical Engineering
K.N. Toosi University of Technology
P.O Box: 19395-1999
Tehran, IranMajidGhasemiFaculty of Mechanical Engineering
K.N. Toosi University of Technology
P.O Box: 19395-1999
Tehran, IranJournal Article20181001Polymer electrolyte membrane fuel cell with a combination of oxygen and hydrogen and production of water converts the chemical energy of the fuel directly and through an electrochemical reaction to electrical energy. One of the most crucial issues for commercializing this technology is water management. In the present study, the motion of liquid droplets that emerged in the gas flow channels with inlet and outlet manifolds is investigated. Due to the small dimensions of these channels, the balance of surface adhesion and other dynamic forces influence the flow of fluid, therefore, the semi- empirical Hoffman model with a two-phase flow method for simulating physics in an applied geometry including gas flow manifolds are used. The effect of tapering the manifold cross-section on the liquid water droplets is also investigated. The physical model used for the dynamic contact angle is validated with data from an experimental study. Simulation results show that by changing the geometry of the input and output manifolds, the problem created in conventional geometry, which causes the obstruction of the last channel due to the accumulation of liquid water, will be resolved, thereby improving the geometry will improve the water management in the channels.Polymer electrolyte membrane fuel cell with a combination of oxygen and hydrogen and production of water converts the chemical energy of the fuel directly and through an electrochemical reaction to electrical energy. One of the most crucial issues for commercializing this technology is water management. In the present study, the motion of liquid droplets that emerged in the gas flow channels with inlet and outlet manifolds is investigated. Due to the small dimensions of these channels, the balance of surface adhesion and other dynamic forces influence the flow of fluid, therefore, the semi- empirical Hoffman model with a two-phase flow method for simulating physics in an applied geometry including gas flow manifolds are used. The effect of tapering the manifold cross-section on the liquid water droplets is also investigated. The physical model used for the dynamic contact angle is validated with data from an experimental study. Simulation results show that by changing the geometry of the input and output manifolds, the problem created in conventional geometry, which causes the obstruction of the last channel due to the accumulation of liquid water, will be resolved, thereby improving the geometry will improve the water management in the channels.https://mej.aut.ac.ir/article_3313_09060616068d2b9544dc33f2fbe4ce2d.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190410Effect of the Phase Change on the Flow Distribution in the Manifold of Fuel Cell StackEffect of the Phase Change on the Flow Distribution in the Manifold of Fuel Cell Stack24912506336710.22060/mej.2019.15136.6036FAAhmadRezaei SangtabiFerdowsi University of Mashhad, Mashhad, Iran.AliKianifarFerdowsi University of Mashhad, Mashhad, Iran.EbrahimAlizadehFuel Cell Technology Research Laboratory, Malek Ashtar University of Technology, Freydounkenar, Iran.MazaherRahimi EsboeeFuel Cell Technology Research Laboratory, Malek Ashtar University of Technology, Fereydounkenar, Iran.Sayed HosseinMasrouri SaadatFuel Cell Technology Research Laboratory, Malek Ashtar University of Technology0000-0002-2869-4935Journal Article20181015In this paper, the effect of water vapor phase change on the distribution of oxygen flow in the cathode side of a polymer electrolyte membrane fuel cell stack with 26 cells is investigated by using computational fluid dynamics. For this purpose, a code is developed in OpenFOAM software and validated with experimental data for the single-phase flow distribution. Three different boundary conditions are applied to the walls of the manifold: constant temperature, free and forced heat convection. The results indicate that water generated from condensation on the lower wall of the inlet manifold enters the first cell. Also, the accumulation of water in this area reduces the flow velocity at the entrance of the first cell. The condensed water vapor on the upper wall of the inlet manifold moves to the end of the stack. Part of the water enters into the last four cells, and the other part returns to the manifold due to the vortex. Therefore, the first cell and the last four cells receive less reactant than other cells. The non-uniform flow distribution parameter increases by up to 1425% on using saturated oxygen and under the forced convection condition.In this paper, the effect of water vapor phase change on the distribution of oxygen flow in the cathode side of a polymer electrolyte membrane fuel cell stack with 26 cells is investigated by using computational fluid dynamics. For this purpose, a code is developed in OpenFOAM software and validated with experimental data for the single-phase flow distribution. Three different boundary conditions are applied to the walls of the manifold: constant temperature, free and forced heat convection. The results indicate that water generated from condensation on the lower wall of the inlet manifold enters the first cell. Also, the accumulation of water in this area reduces the flow velocity at the entrance of the first cell. The condensed water vapor on the upper wall of the inlet manifold moves to the end of the stack. Part of the water enters into the last four cells, and the other part returns to the manifold due to the vortex. Therefore, the first cell and the last four cells receive less reactant than other cells. The non-uniform flow distribution parameter increases by up to 1425% on using saturated oxygen and under the forced convection condition.https://mej.aut.ac.ir/article_3367_0e7e05fa1026b0c5459267608ae320b8.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190223Numerical Investigation of Melting Nano-Enhanced Phase Change Materials in Triangular EnclosureNumerical Investigation of Melting Nano-Enhanced Phase Change Materials in Triangular Enclosure25072520331110.22060/mej.2019.14767.5934FAAbolfazlNematpourMasters student, Department of Mechanical Engineering, Noshirvani Babol, Babol, IranMohsenSheikholeslamiDepartment of Mechanical Engineering, Babol Noshirvani University of Technology, Babol, Islamic Republic of IranJournal Article20180731This paper presents a numerical study of the melting of nano-enhanced phase change materials inside a triangular container using N-eicosane and copper particles as base material and nanoparticle, respectively. Nanoparticles are used in the process of heat transfer and improve lubrication performance. To investigate the effect of nanoparticles on the heat transfer rate, various particles of copper nanoparticles have been added to the base phase change materials. The increase in the performance of the heat transfer of nanoparticles in the solid state was more than the liquid state in the laminar flow and the natural convection heat transfer. Also, the effect of entropy has been investigated. The simulation results show that the nanoparticles cause an increase in the thermal conductivity of nano-enhanced phase change materials compared to conventional phase change material. Increasing thermal conductivity by reducing the latent heat, increases the rate of melting of nanoparticles. The time of the melting of the phase change material has significantly decreased with increasing nanoparticles. Increasing the thermal conductivity effective in reducing the entropy production of the system is much more than the reduction of the specific heat and the heat of fusion of nano-enhanced phase change materials.This paper presents a numerical study of the melting of nano-enhanced phase change materials inside a triangular container using N-eicosane and copper particles as base material and nanoparticle, respectively. Nanoparticles are used in the process of heat transfer and improve lubrication performance. To investigate the effect of nanoparticles on the heat transfer rate, various particles of copper nanoparticles have been added to the base phase change materials. The increase in the performance of the heat transfer of nanoparticles in the solid state was more than the liquid state in the laminar flow and the natural convection heat transfer. Also, the effect of entropy has been investigated. The simulation results show that the nanoparticles cause an increase in the thermal conductivity of nano-enhanced phase change materials compared to conventional phase change material. Increasing thermal conductivity by reducing the latent heat, increases the rate of melting of nanoparticles. The time of the melting of the phase change material has significantly decreased with increasing nanoparticles. Increasing the thermal conductivity effective in reducing the entropy production of the system is much more than the reduction of the specific heat and the heat of fusion of nano-enhanced phase change materials.https://mej.aut.ac.ir/article_3311_bdd8817990ef209f0fb6b049f2d2ea0c.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190314The Effect of Surface Types on Bubble Dynamic Formation During Nucleate Pool Boiling by Use of Lee and Tanasawa Phase Change ModelsThe Effect of Surface Types on Bubble Dynamic Formation During Nucleate Pool Boiling by Use of Lee and Tanasawa Phase Change Models25212536333310.22060/mej.2019.15192.6055FASeyed AmirrezaHosseiniUniversity of GuilanRaminKouhi Kamali0000-0002-8004-0242Journal Article20181027Numerical simulation of boiling has always been a challenging problem in terms of the variety and effectiveness of two-phase models. Boiling is one of the efficient methods in high heat transfer. In the boiling simulation, in addition to choosing an appropriate heat and mass transfer model, it will be important to evaluate the surfaces in which boiling occurs on it. A problem of nucleate boiling of saturated liquid is numerically simulated in this investigation by use of volume of fluid model together with the geo-reconstruction of the interface. One-dimensional Stephan problem as sucking interface problem is solved for verification the numerical solver. Two-phase change models of the Lee model and the Tanasawa model are used in order to calculate the rate of phase change and source terms. The results of nuclear boiling are investigated on the hydrophilic surface, hydrophobic surface, and the surface with contact angle 90 degrees. The results show that boiling on hydrophobic surfaces causes the detachment of larger bubbles with a larger heat transfer rate. Besides, bubble merging depending on the density of nucleation sites leads the nuclear boiling on the hydrophobic surface to film boiling.Numerical simulation of boiling has always been a challenging problem in terms of the variety and effectiveness of two-phase models. Boiling is one of the efficient methods in high heat transfer. In the boiling simulation, in addition to choosing an appropriate heat and mass transfer model, it will be important to evaluate the surfaces in which boiling occurs on it. A problem of nucleate boiling of saturated liquid is numerically simulated in this investigation by use of volume of fluid model together with the geo-reconstruction of the interface. One-dimensional Stephan problem as sucking interface problem is solved for verification the numerical solver. Two-phase change models of the Lee model and the Tanasawa model are used in order to calculate the rate of phase change and source terms. The results of nuclear boiling are investigated on the hydrophilic surface, hydrophobic surface, and the surface with contact angle 90 degrees. The results show that boiling on hydrophobic surfaces causes the detachment of larger bubbles with a larger heat transfer rate. Besides, bubble merging depending on the density of nucleation sites leads the nuclear boiling on the hydrophobic surface to film boiling.https://mej.aut.ac.ir/article_3333_2be9bd7a3434f7038ca27d1918de58bd.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190702Numerical Simulation of Flow, Natural Convection and Distribution of Nano Particles inside Trapezoidal Cavity using Buongiorno’s ModelNumerical Simulation of Flow, Natural Convection and Distribution of Nano Particles inside Trapezoidal Cavity using Buongiorno’s Model25372550349310.22060/mej.2019.15442.6123FAMortezaBashirDepartment of Mechanical Engineering, Urmia University, Urmia, IranSamadJafarmadarDepartment of Mechanical Engineering, Urmia University, Urmia, IranSaberYekani MotlaghDepartment of Mechanical Engineering, Urmia University, Urmia, IranShahramKhalilaryaDepartment of Mechanical Engineering, Urmia University, Urmia, Iran0000-0002-6434-852XJournal Article20181213In the present study, natural convection of Al2O3–water nanofluid and nano-particles local distribution inside the trapezium enclosure has been investigated using non-homogenous two- phase Buongiorno’s model. The governing equations of the problem are momentum, energy and volume fraction of nanoparticles that are solved using the finite volume method and the SIMPLE algorithm. Diffusion and convective terms are discretized using a second-order central difference and upwind schemes. The left and right walls of cavity are kept at constant temperatures, while the other walls are thermally insulated. Simulations have been carried out for different inclination angles, including 0°, 30°, and 45°, Rayleigh number (102≤Ra≤104) as well as particle average volume fraction ranging from 0.01 to 0.04. Results show that at low Rayleigh number for a specific particle volume fraction, with increasing the inclination angle from zero to 45 degree, the average Nusselt number and heat transfer decreases 81%. On the other hand, optimum results were obtained for the inclination angle of 30 degree. The Nusselt enhancement percent was obtained 5.5 compared to the square enclosure and 6.8 compared to the inclination angle of 45 degrees. Results also showed a uniform distribution for nanoparticles in high Rayleigh numbers and in enclosures with different inclination angles.In the present study, natural convection of Al2O3–water nanofluid and nano-particles local distribution inside the trapezium enclosure has been investigated using non-homogenous two- phase Buongiorno’s model. The governing equations of the problem are momentum, energy and volume fraction of nanoparticles that are solved using the finite volume method and the SIMPLE algorithm. Diffusion and convective terms are discretized using a second-order central difference and upwind schemes. The left and right walls of cavity are kept at constant temperatures, while the other walls are thermally insulated. Simulations have been carried out for different inclination angles, including 0°, 30°, and 45°, Rayleigh number (102≤Ra≤104) as well as particle average volume fraction ranging from 0.01 to 0.04. Results show that at low Rayleigh number for a specific particle volume fraction, with increasing the inclination angle from zero to 45 degree, the average Nusselt number and heat transfer decreases 81%. On the other hand, optimum results were obtained for the inclination angle of 30 degree. The Nusselt enhancement percent was obtained 5.5 compared to the square enclosure and 6.8 compared to the inclination angle of 45 degrees. Results also showed a uniform distribution for nanoparticles in high Rayleigh numbers and in enclosures with different inclination angles.https://mej.aut.ac.ir/article_3493_ba036d228858d76fb89189853a5503bd.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190214Simultaneously Reconstruction of Radiation-Conduction Properties of Nanomaterial Thermal Insulators with Particle Swarm Optimization AlgorithmSimultaneously Reconstruction of Radiation-Conduction Properties of Nanomaterial Thermal Insulators with Particle Swarm Optimization Algorithm25512568329110.22060/mej.2019.14880.5966FAMehdiPakdamandepartment of mechanical engineering, University of Sistan and Baluchestan, Zahedan, IranSamiraPayanDepartment of mechanical engineering, University of Sistan and Baluchestan, IranSeyed MasoudHoseini SarvariShahid Bahonar University of KermanSohilaMohammadpourdepartment of mechanical engineering, university of sistan and baluchestan, iranJournal Article20180824In this paper, an optimization algorithm is proposed to simultaneously reconstruct radiation and conduction properties for thermal insulators constructed from Nanomaterial between two flat plates. The radiation problem is modeled using modified discrete ordinates method. The conduction and radiation problems are solved using the finite volume method and the inverse problem is solved using the particle swarm optimization problem. The various cases have been solved in this paper. Firstly a simple problem designs and solves. Next, a multi-stage algorithm with new objective functions is used for reconstruction of dependent-temperature properties of a nanomaterial. In the first case, constant absorption coefficient is reconstructed using the radiation intensity of boundaries, in the first stage and constant conduction-radiation parameter is reconstructed using the surface total heat flux in second stage. In the second section, the competency of the proposed multi-stage algorithm for the radiation and conduction temperature-dependent parameters is tested. In the numerical test a thermal insulator constructed from nanomaterial with 1cm thickness is used. The proposed algorithm and new objective functions are presented in this section to decrease sensitivity of Plank number and optical thickness to the measurement error.In this paper, an optimization algorithm is proposed to simultaneously reconstruct radiation and conduction properties for thermal insulators constructed from Nanomaterial between two flat plates. The radiation problem is modeled using modified discrete ordinates method. The conduction and radiation problems are solved using the finite volume method and the inverse problem is solved using the particle swarm optimization problem. The various cases have been solved in this paper. Firstly a simple problem designs and solves. Next, a multi-stage algorithm with new objective functions is used for reconstruction of dependent-temperature properties of a nanomaterial. In the first case, constant absorption coefficient is reconstructed using the radiation intensity of boundaries, in the first stage and constant conduction-radiation parameter is reconstructed using the surface total heat flux in second stage. In the second section, the competency of the proposed multi-stage algorithm for the radiation and conduction temperature-dependent parameters is tested. In the numerical test a thermal insulator constructed from nanomaterial with 1cm thickness is used. The proposed algorithm and new objective functions are presented in this section to decrease sensitivity of Plank number and optical thickness to the measurement error.https://mej.aut.ac.ir/article_3291_980a875ff6ef9c2d75e74307cbf5d205.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190311Geometric Optimization of Highly Conductive Inserts with Variable Thickness Embedded in a FinGeometric Optimization of Highly Conductive Inserts with Variable Thickness Embedded in a Fin25692580332410.22060/mej.2019.15293.6088FAMohammadAhmadian ElmiAmirkabir University of Technology, TehranMohammad RezaHajmohammadiAmirkabir University of TechnologySalmanNourazarAmirkabir University of Technology, TehranJournal Article20181117In the present study, it is proposed to reduce the thermal resistance of a straight fin by embedding highly conductive routes with variant thickness into a fin. Due to economic constraints, only a limited fraction of fin’s volume can be devoted to these materials. Therefore, in this research, an optimal geometric structure for the inserts is presented. The purpose of optimization is to maximize the heat transfer from the fin by increasing the degrees of the freedom-to-morph under the constraint of the fixed volume fraction of the inserts. The geometric structure of conductive materials is presented by distributing the inserts with variable thicknesses or a linear distribution. The effects of several parameters such as the aspect ratio of the fin, Biot number, the volume fraction of highly conductive materials and the thermal conductivity ratio on the optimization results are presented in detail. It is shown that the increment in the number of insert branches with different thicknesses results in higher heat transfer. It is also indicated that the linear distribution performs the best.In the present study, it is proposed to reduce the thermal resistance of a straight fin by embedding highly conductive routes with variant thickness into a fin. Due to economic constraints, only a limited fraction of fin’s volume can be devoted to these materials. Therefore, in this research, an optimal geometric structure for the inserts is presented. The purpose of optimization is to maximize the heat transfer from the fin by increasing the degrees of the freedom-to-morph under the constraint of the fixed volume fraction of the inserts. The geometric structure of conductive materials is presented by distributing the inserts with variable thicknesses or a linear distribution. The effects of several parameters such as the aspect ratio of the fin, Biot number, the volume fraction of highly conductive materials and the thermal conductivity ratio on the optimization results are presented in detail. It is shown that the increment in the number of insert branches with different thicknesses results in higher heat transfer. It is also indicated that the linear distribution performs the best.https://mej.aut.ac.ir/article_3324_3ce6d3c8830d27ec2e6a1936ecbaa514.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190318Analytical Solution of the Heat Transfer in Heterogeneous Composite Conical Shells with Temperature Dependent Conduction CoefficientsAnalytical Solution of the Heat Transfer in Heterogeneous Composite Conical Shells with Temperature Dependent Conduction Coefficients25812596334210.22060/mej.2019.15168.6050FABabakErfan ManeshMSc student, Faculty of mechanical engineering, Shahrood university of technologyMohammad MohsenShahmardanAssociated professor, Faculty of mechanical Engineering, Shahrood University of Technology, Shahrood, IranMahmoodNorouziAssociated professor, Faculty of mechanical engineering, Shahrood university of technology, shahrood, IranJournal Article20181024This paper presents an analytical solution for heat transfer in heterogeneous composite conical shells with temperature dependent conduction coefficients for the first time. The geometry of the shell is completely conical shaped and the fibers are winded around the laminate in the desired direction. In order to achieve the most general solution, the general boundary condition is considered at the basis of shell and the effect of heat convection resulted from flow motion around the body and different kinds of non-axisymmetric radiative heat flux at the outer side of the shell is modeled. The heterogeneous effect in this case is the results of the dependency in conduction heat transfer coefficient on temperature. Therefore, the heat transfer equation should first be transformed using the Kirchhoff transform to a solvable equation using integral transformation, then, the partial differential equation becomes an ordinary differential equation Fourier transformation. Finally, the transformed differential equation can be solved Green’s functions. In the end, the reversal integral transformation and reversal Kirchhoff conversion are applied to obtain heterogeneous temperature distribution. Validation of this analytical solution is performed by comparing the analytical results with the solution of second-order finite difference method and some applied cases are considered to investigate the capability of current solution for solving the industrial problems in the production of composite conical pressure vessels.This paper presents an analytical solution for heat transfer in heterogeneous composite conical shells with temperature dependent conduction coefficients for the first time. The geometry of the shell is completely conical shaped and the fibers are winded around the laminate in the desired direction. In order to achieve the most general solution, the general boundary condition is considered at the basis of shell and the effect of heat convection resulted from flow motion around the body and different kinds of non-axisymmetric radiative heat flux at the outer side of the shell is modeled. The heterogeneous effect in this case is the results of the dependency in conduction heat transfer coefficient on temperature. Therefore, the heat transfer equation should first be transformed using the Kirchhoff transform to a solvable equation using integral transformation, then, the partial differential equation becomes an ordinary differential equation Fourier transformation. Finally, the transformed differential equation can be solved Green’s functions. In the end, the reversal integral transformation and reversal Kirchhoff conversion are applied to obtain heterogeneous temperature distribution. Validation of this analytical solution is performed by comparing the analytical results with the solution of second-order finite difference method and some applied cases are considered to investigate the capability of current solution for solving the industrial problems in the production of composite conical pressure vessels.https://mej.aut.ac.ir/article_3342_14491b756b3a51daac41c24863285549.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920181120A New Index for Evaluating Thermal Sensation Based on the Principles of Non- Fourier Heat TransferA New Index for Evaluating Thermal Sensation Based on the Principles of Non- Fourier Heat Transfer25972608312810.22060/mej.2018.14472.5866FAAlirezaZolfaghariUniversity of Birjand0000-0001-9917-3400HaniehBijariDepartment of Mechanical Engineering, University of BirjandJournal Article20180520In recent years, the modeling of human thermal sensation based on thermoreceptors response has attracted the attention of many researchers. However, biological tissues do not usually follow the principles of Fourier heat transfer. So, this study tries to develop a new predictive index for a thermal comfort model based on cutaneous thermoreceptors obtained by using non-Fourier heat transfer in biological tissues. The mentioned index is in conformity with the ASHRAE standard thermal sensation scale. The model used in this study considers the concept of non-Fourier heat transfer to describe heat transfer in biological tissues. Since biological tissues consist of complicated and nonhomogeneous structures, it is important to describe the process of heat transfer in these tissues by non-Fourier heat transfer equation. The new index has been verified by extensive comparisons with the experimental and analytical results under steady-state and transient conditions where a good agreement was found. Results show that the new index can predict the thermal sensation with mean absolute errors of 0.31 and 0.49 under steady-state and transient conditions, respectively. Since the new index is based on the concepts of non-Fourier heat transfer, it can provide an accurate prediction of thermal sensation in terms of sudden change in temperature.In recent years, the modeling of human thermal sensation based on thermoreceptors response has attracted the attention of many researchers. However, biological tissues do not usually follow the principles of Fourier heat transfer. So, this study tries to develop a new predictive index for a thermal comfort model based on cutaneous thermoreceptors obtained by using non-Fourier heat transfer in biological tissues. The mentioned index is in conformity with the ASHRAE standard thermal sensation scale. The model used in this study considers the concept of non-Fourier heat transfer to describe heat transfer in biological tissues. Since biological tissues consist of complicated and nonhomogeneous structures, it is important to describe the process of heat transfer in these tissues by non-Fourier heat transfer equation. The new index has been verified by extensive comparisons with the experimental and analytical results under steady-state and transient conditions where a good agreement was found. Results show that the new index can predict the thermal sensation with mean absolute errors of 0.31 and 0.49 under steady-state and transient conditions, respectively. Since the new index is based on the concepts of non-Fourier heat transfer, it can provide an accurate prediction of thermal sensation in terms of sudden change in temperature.https://mej.aut.ac.ir/article_3128_dff8e9c2ac33381546d96deea9922999.pdfAmirkabir University of TechnologyAmirkabir Journal of Mechanical Engineering2008-603252920190320Analysis of the Heat Transfer in a Multilayer Living Tissue Using the Galerkin Weighted Residuals MethodAnalysis of the Heat Transfer in a Multilayer Living Tissue Using the Galerkin Weighted Residuals Method26092626335110.22060/mej.2019.15152.6044FAAli AkbarAbbasian AraniAssociate Professor of Mechanical Engineering, Mechanical Engineering Department, University of Kashan, Kashan, Iran0000-0003-3011-0297AliArefmaneshَAssociate Professor of Mechanical Engineering, Mechanical Engineering Department, University of Kashan, Kashan, IranArminEmamifarPh.D Candidate of Mechanical Enginerring, Mechanical Engineering Department, University of Kashan, Kashan, IranJournal Article20181021In this paper, the thermal behavior of living biological tissue during electromagnetic radiation thermal therapy is investigated. While a large number of studies devoted to the Fourier and non-Fourier heat transfer in living tissue are available for different boundary conditions, less analytical and semi-analytical works exist on the heat transfer in the multilayers tissue. In the present study, semi- analytical Galerkin weighted residuals method is used to solve the dual-phase lag non-Fourier heat transfer equation in the multilayer tissue with a tumor placed in. The results show that considering a multilayer tissue with distinct thermophysical properties for each layer has a remarkable effect on the temperature distribution in the tissue, so that 2°C difference in tumor temperature after 1800 s is observed. The effect of the Vernot number on the temperature distribution shows that increasing the flux relaxation time results in reducing the temperature signal velocity and the tumor temperature. Lowering the skin surface temperature, decreases the high values of temperature and forces the maximum temperature region deeper into the tissue. Moreover, the reduction in the blood perfusion rate that occurs in the hypoxic tumors results in the increase of the tumors temperatures during the thermal therapy.In this paper, the thermal behavior of living biological tissue during electromagnetic radiation thermal therapy is investigated. While a large number of studies devoted to the Fourier and non-Fourier heat transfer in living tissue are available for different boundary conditions, less analytical and semi-analytical works exist on the heat transfer in the multilayers tissue. In the present study, semi- analytical Galerkin weighted residuals method is used to solve the dual-phase lag non-Fourier heat transfer equation in the multilayer tissue with a tumor placed in. The results show that considering a multilayer tissue with distinct thermophysical properties for each layer has a remarkable effect on the temperature distribution in the tissue, so that 2°C difference in tumor temperature after 1800 s is observed. The effect of the Vernot number on the temperature distribution shows that increasing the flux relaxation time results in reducing the temperature signal velocity and the tumor temperature. Lowering the skin surface temperature, decreases the high values of temperature and forces the maximum temperature region deeper into the tissue. Moreover, the reduction in the blood perfusion rate that occurs in the hypoxic tumors results in the increase of the tumors temperatures during the thermal therapy.https://mej.aut.ac.ir/article_3351_0b6ace9e8971cf36f1782aa982a708db.pdf