Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Improvement of aerodynamic coefficients of the airfoil with free form deformation with the aid of Artificial Neural Networks and Genetic Algorithm Improvement of aerodynamic coefficients of the airfoil with free form deformation with the aid of Artificial Neural Networks and Genetic Algorithm 4113 4132 4267 10.22060/mej.2021.18982.6932 FA Mohsen Kazemi Department of mechanical engineering , faculty of engineering , Ferdowsi University of Mashhad , Mashhad , Iran Amirhossein Fardi Department of mechanical engineering , faculty of engineering , Ferdowsi University of Mashhad , Mashhad , Iran Mohammad Javad Maghrebi Department of mechanical engineering , faculty of engineering , Ferdowsi University of Mashhad, Mashhad, Iran Journal Article 2020 09 09 With the advent of morphing airfoils, the aerodynamics of wind turbines and wings underwent many changes. In this study, the aerodynamic coefficients of morphing airfoil based on NACA 0015 are optimized in the range of Reynolds number 105 to 106 and the angle of attack 0 to 12 degrees using Artificial Neural Network (ANN) and Genetic Algorithm (GA). First, the airfoils were created in MATLAB software by random control points and mesh generated in Gambit software, then in two-dimensional Ansys software were simulated. The simulation results, including lift and drag coefficients, separation point and pressure center, with control points were used to train the Artificial Neural Network (ANN). The trained function is given as an input function to the Genetic Algorithm (GA) to optimize the desired coefficients. Lift coefficient, center of pressure, separation point and lift to drag ratio were optimized as a single objective, In single-objective optimization, the lift coefficient was increased by 18% using the morphing airfoil. Also, the lift coefficient and the center of pressure, the lift coefficient and the drag coefficient were optimized as the dual-objectives optimization. In the optimization of the dual objectives, lift and drag coefficients were controlled by 0.8 and 0.03, respectively, by the morphing airfoils. With the advent of morphing airfoils, the aerodynamics of wind turbines and wings underwent many changes. In this study, the aerodynamic coefficients of morphing airfoil based on NACA 0015 are optimized in the range of Reynolds number 105 to 106 and the angle of attack 0 to 12 degrees using Artificial Neural Network (ANN) and Genetic Algorithm (GA). First, the airfoils were created in MATLAB software by random control points and mesh generated in Gambit software, then in two-dimensional Ansys software were simulated. The simulation results, including lift and drag coefficients, separation point and pressure center, with control points were used to train the Artificial Neural Network (ANN). The trained function is given as an input function to the Genetic Algorithm (GA) to optimize the desired coefficients. Lift coefficient, center of pressure, separation point and lift to drag ratio were optimized as a single objective, In single-objective optimization, the lift coefficient was increased by 18% using the morphing airfoil. Also, the lift coefficient and the center of pressure, the lift coefficient and the drag coefficient were optimized as the dual-objectives optimization. In the optimization of the dual objectives, lift and drag coefficients were controlled by 0.8 and 0.03, respectively, by the morphing airfoils.

https://mej.aut.ac.ir/article_4267_fb8e51c5c713f2aaf71f62e03c5298db.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Multiscale simulation of flow in fractured porous media using unstructured grids Multiscale simulation of flow in fractured porous media using unstructured grids 4133 4152 4072 10.22060/mej.2020.18399.6809 FA Zahra Mehrdoost Department of Mechanical Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran Journal Article 2020 05 10 In this paper for flow simulation in fractured porous media, a multiscale finite volume method on unstructured grids is developed. To this end, algorithms for generating coarse scale unstructured grids for the matrix and fracture networks are presented independently. The presented algorithms for generating coarse scale unstructured grids are adaptable based on local changes in permeability field. Unstructured grid adaption based on permeability field has significant effect on improving the multiscale solution results in highly heterogeneous permeability fields. For the first time in this research, applying adaptive unstructured grids in fractured porous media is done. Coarse scale grid cells are generated such that strong variation of permeability along their boundaries and also the placement of coarse scale vertices in low permeability region are prevented. To reduce the computational cost, fracture-matrix coupling is considered only for the calculation of basis functions in the matrix domain. In order to evaluate the proposed algorithms, various 2D test cases are designed and solved. Finally, it is shown that the multiscale finite volume method with the proposed algorithms is an efficient numerical method for flow simulation in heterogeneous fractured porous media. In this paper for flow simulation in fractured porous media, a multiscale finite volume method on unstructured grids is developed. To this end, algorithms for generating coarse scale unstructured grids for the matrix and fracture networks are presented independently. The presented algorithms for generating coarse scale unstructured grids are adaptable based on local changes in permeability field. Unstructured grid adaption based on permeability field has significant effect on improving the multiscale solution results in highly heterogeneous permeability fields. For the first time in this research, applying adaptive unstructured grids in fractured porous media is done. Coarse scale grid cells are generated such that strong variation of permeability along their boundaries and also the placement of coarse scale vertices in low permeability region are prevented. To reduce the computational cost, fracture-matrix coupling is considered only for the calculation of basis functions in the matrix domain. In order to evaluate the proposed algorithms, various 2D test cases are designed and solved. Finally, it is shown that the multiscale finite volume method with the proposed algorithms is an efficient numerical method for flow simulation in heterogeneous fractured porous media.

https://mej.aut.ac.ir/article_4072_27669f3f141da48bfe5e6b7aa37c38f9.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Experimental Study of the Effect of Fluid Jet Swirl on Circular Hydraulic Jump Experimental Study of the Effect of Fluid Jet Swirl on Circular Hydraulic Jump 4153 4170 4082 10.22060/mej.2020.18409.6811 FA Ali Asadi Department of Mechanical Engineering, University of Birjand, Birjand, Iran Seyyed Majid Malek Jafarian Shahid Avini Ali Reza Teymourtash Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran Journal Article 2020 05 11 When an axially symmetrical fluid jet impacts on a horizontal plate vertically, a hydraulic jump is formed. Numerous studies are conducted on circular hydraulic jumps. However, the effect of the important and key parameter of fluid jet swirl on hydraulic jumps is not investigated. The main purpose of this study is to investigate the effect of this parameter on the circular hydraulic jump. The results of this study, achieved by using experimental method, show that the higher the angular velocity, the higher the increase in the radius of the jump. Drawing the diagram of the dimensionless radius of jump based on the dimensionless number of swirl shows two categories of lines. The first category is the constant angular velocity lines with a negative slope and the second category is the constant flow rate lines with a positive slope. The results showed that increasing the angular velocity of the swirling jet has less effect on increasing jump radius than increasing the flow rate. Experiments also showed that the hydraulic jumps created by a swirling jet follow the trend results of modified Watson’s theory with a non-significant difference. When an axially symmetrical fluid jet impacts on a horizontal plate vertically, a hydraulic jump is formed. Numerous studies are conducted on circular hydraulic jumps. However, the effect of the important and key parameter of fluid jet swirl on hydraulic jumps is not investigated. The main purpose of this study is to investigate the effect of this parameter on the circular hydraulic jump. The results of this study, achieved by using experimental method, show that the higher the angular velocity, the higher the increase in the radius of the jump. Drawing the diagram of the dimensionless radius of jump based on the dimensionless number of swirl shows two categories of lines. The first category is the constant angular velocity lines with a negative slope and the second category is the constant flow rate lines with a positive slope. The results showed that increasing the angular velocity of the swirling jet has less effect on increasing jump radius than increasing the flow rate. Experiments also showed that the hydraulic jumps created by a swirling jet follow the trend results of modified Watson’s theory with a non-significant difference.

https://mej.aut.ac.ir/article_4082_02bf86214e264535e3412283e817deaa.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Numerical simulation of water hammer in various fluids due to a fast valve closure Numerical simulation of water hammer in various fluids due to a fast valve closure 4171 4188 4199 10.22060/mej.2020.18624.6865 FA Rafat Mohammadi Assistant Professor, Arak University Mohammad Aghaei Masters student, Arak University Journal Article 2020 06 22 The sudden changes of boundary conditions in the fluid transmission lines cause a transient flow, which is called water hammer. In this paper, the water hammer resulting from the fast closure of a valve in pipelines is simulated using numerical solution of continuity and Navier-Stokes equations. Simulation has been performed for a high-viscosity oil and for water. The initial flow regime for oil is laminar and for the water is turbulent. The obtained results are compared with the reported experimental data and a good agreement is observed. Velocity contours at different times show two regions with different behavior: the wall region and the pipe core region. In the wall region, the effects of fluid viscosity are dominant, the velocity gradients are sharper, and flow changes more rapidly. While the pipe core region is affected by fluid inertial forces. As the fluid viscosity decreases, the core region becomes more dominant. In addition, a parametric study has been conducted and the effect of different parameters on water hammer has been studied. The results show that by reducing the thickness or length of the pipe, or using a pipe with a lower elastic modulus, the water hammer effects can be significantly reduced. For example, by reducing the length of the pipe from 60 to 18 meters, the maximum pressure decreases by 11%. The sudden changes of boundary conditions in the fluid transmission lines cause a transient flow, which is called water hammer. In this paper, the water hammer resulting from the fast closure of a valve in pipelines is simulated using numerical solution of continuity and Navier-Stokes equations. Simulation has been performed for a high-viscosity oil and for water. The initial flow regime for oil is laminar and for the water is turbulent. The obtained results are compared with the reported experimental data and a good agreement is observed. Velocity contours at different times show two regions with different behavior: the wall region and the pipe core region. In the wall region, the effects of fluid viscosity are dominant, the velocity gradients are sharper, and flow changes more rapidly. While the pipe core region is affected by fluid inertial forces. As the fluid viscosity decreases, the core region becomes more dominant. In addition, a parametric study has been conducted and the effect of different parameters on water hammer has been studied. The results show that by reducing the thickness or length of the pipe, or using a pipe with a lower elastic modulus, the water hammer effects can be significantly reduced. For example, by reducing the length of the pipe from 60 to 18 meters, the maximum pressure decreases by 11%.

https://mej.aut.ac.ir/article_4199_e0c7ccc47b2613c82d1073a4214deecc.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Circumferential Casing Treatment in a Transonic Fan Circumferential Casing Treatment in a Transonic Fan 4189 4202 4284 10.22060/mej.2021.18660.6879 FA Hosein Khaleghi Department of Aerospace Engineering, Center of Excellence in Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran Martin Heinrich Institute of Mechanics and Fluid Dynamics, Technische Universität Bergakademie Freiberg,, Freiberg, Germany Mohammad Javad Shahriyari Department of Aerospace Engineering, Center of Excellence in Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran Journal Article 2020 07 09 This paper reports on a numerical simulation of circumferential groove casing treatment in a high-speed axial fan. Four circumferential grooves of the same geometry are located over the tip of a NASA Rotor-67 and unsteady calculations are performed from choke to near-stall. Results show that circumferential grooves reduce the incidence angle near the pressure surface at the blade leading-edge. Furthermore, the passage shock and the leakage flow are pushed rearward in the passage. It is found that circumferential grooves increase the momentum in the streamwise direction (fluid is absorbed by the grooves from their downstream part and is injected from their upstream section). The grooves also provide a flow path between the suction and pressure surface, leading to a reduction in the pressure difference between them. At the near-stall point the flow field near the grooves was found to be highly unsteady. Maximum unsteadiness was observed in the first upstream groove: the circulated mass flow rate changed as high as roughly 30 percent of its time-averaged value. As a result, in order to simulate circumferential groove casing treatment in compressors, unsteady computations are required. This paper reports on a numerical simulation of circumferential groove casing treatment in a high-speed axial fan. Four circumferential grooves of the same geometry are located over the tip of a NASA Rotor-67 and unsteady calculations are performed from choke to near-stall. Results show that circumferential grooves reduce the incidence angle near the pressure surface at the blade leading-edge. Furthermore, the passage shock and the leakage flow are pushed rearward in the passage. It is found that circumferential grooves increase the momentum in the streamwise direction (fluid is absorbed by the grooves from their downstream part and is injected from their upstream section). The grooves also provide a flow path between the suction and pressure surface, leading to a reduction in the pressure difference between them. At the near-stall point the flow field near the grooves was found to be highly unsteady. Maximum unsteadiness was observed in the first upstream groove: the circulated mass flow rate changed as high as roughly 30 percent of its time-averaged value. As a result, in order to simulate circumferential groove casing treatment in compressors, unsteady computations are required.

https://mej.aut.ac.ir/article_4284_41b0db49fd10d95920281dead0710f58.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Diagnostical and observational analysis of clear air turbulence over the middle east and Iran Diagnostical and observational analysis of clear air turbulence over the middle east and Iran 4203 4220 4268 10.22060/mej.2021.18770.6886 FA Reza JavanNezhad Graduate Center, Shahid Sattari Aeronautical University, Tehran, Iran. Mahmoud Safar Space Physics Department, Institute of Geophysics, University of Tehran Sarmad Ghader Institute of Geophysics, University of Tehran 0000-0001-9666-5493 Journal Article 2020 07 25 Turbulence forecasting started in World War II when scientists and individuals in the field of aviation began attempting to correlate observed clear air turbulence events with large scale synoptic features. Encounters with significant turbulence or simply bumpiness in flight, are a major concern not only for passenger comfort but also for safe, efficient, and cost-effective aircraft operations. Clear air turbulence represents disorganized fluid motions in the form of micro scale eddies that can take place within cloud-free or limited cloud patches in the free atmosphere, which causes in-flight bumpiness of aircraft. This study aims to present two case studies and comparison of the report of clear air turbulence over center, east and south east crossings over Iran region. Regional weather predictions are carried out using an ensemble forecasting system. In addition, the initial and lateral boundary conditions are taken from the global forecast system. For each member of the ensemble system, two nested computational domains with spatial resolutions of 27000 meters and 9000 meters are used. Case study of the predicted clear air turbulence indicates the proper performance of the predicted meteorological parameters. Turbulence forecasting started in World War II when scientists and individuals in the field of aviation began attempting to correlate observed clear air turbulence events with large scale synoptic features. Encounters with significant turbulence or simply bumpiness in flight, are a major concern not only for passenger comfort but also for safe, efficient, and cost-effective aircraft operations. Clear air turbulence represents disorganized fluid motions in the form of micro scale eddies that can take place within cloud-free or limited cloud patches in the free atmosphere, which causes in-flight bumpiness of aircraft. This study aims to present two case studies and comparison of the report of clear air turbulence over center, east and south east crossings over Iran region. Regional weather predictions are carried out using an ensemble forecasting system. In addition, the initial and lateral boundary conditions are taken from the global forecast system. For each member of the ensemble system, two nested computational domains with spatial resolutions of 27000 meters and 9000 meters are used. Case study of the predicted clear air turbulence indicates the proper performance of the predicted meteorological parameters.

https://mej.aut.ac.ir/article_4268_f0f6cc51dacebe556699ccb45e2d43a8.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Wind simulation in a complex terrain by numerical weather prediction method using large eddy simulation Wind simulation in a complex terrain by numerical weather prediction method using large eddy simulation 4221 4240 4291 10.22060/mej.2021.18863.6905 FA Shokoufeh Malek Mohamadi Department of Mechanical and Energy Engineering, Shahid Beheshti University, Exchange student with EPFL in Switzerland. Pooyan Hashemi Tari Department of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran Journal Article 2020 08 15 Researchers are interested in wind resource assessment studies for mountainous terrains using numerical weather prediction methods. In present study the wind over Martigny located in Switzerland has been simulated using weather research and forecasting model. Due to high resolution of the simulation (100 m), large eddy simulation is employed to perform turbulence modeling. The objective of this study is to assess the credibility of model in wind simulation and to examine the effect resolution and two different sub-grid scale turbulence models. The results reveal that model is able to properly generate the wind in comparison with the data obtained from wind measurement stations. The results also show a promising simulation for the region, located within a wide and flat valley. However, the discrepancies between the results and those obtained from the wind station are bold for regions at mountainous peaks. At the time at which the maximum wind speed occurs, it is found that the wind error decreases from 22m/s to 17m/s by changing the sub-grid scale model from Smagronisnky3D to turbulence kinetic energy 1.5 model. Also, the predicted wind speed declines from 17m/s to 7m/s by reducing the vertical size of the grid cells. Researchers are interested in wind resource assessment studies for mountainous terrains using numerical weather prediction methods. In present study the wind over Martigny located in Switzerland has been simulated using weather research and forecasting model. Due to high resolution of the simulation (100 m), large eddy simulation is employed to perform turbulence modeling. The objective of this study is to assess the credibility of model in wind simulation and to examine the effect resolution and two different sub-grid scale turbulence models. The results reveal that model is able to properly generate the wind in comparison with the data obtained from wind measurement stations. The results also show a promising simulation for the region, located within a wide and flat valley. However, the discrepancies between the results and those obtained from the wind station are bold for regions at mountainous peaks. At the time at which the maximum wind speed occurs, it is found that the wind error decreases from 22m/s to 17m/s by changing the sub-grid scale model from Smagronisnky3D to turbulence kinetic energy 1.5 model. Also, the predicted wind speed declines from 17m/s to 7m/s by reducing the vertical size of the grid cells.

https://mej.aut.ac.ir/article_4291_148d411aeffed8a6f6ad4ecd77d1f904.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Development of parametric and time dependent reduced order model for diffusion and convection-diffusion problems based on proper orthogonal decomposition method Development of parametric and time dependent reduced order model for diffusion and convection-diffusion problems based on proper orthogonal decomposition method 4241 4260 3849 10.22060/mej.2020.16936.6483 FA Mohammad Kazem Moayyedi Department of Mechanical Engineering, University of Qom 0000-0003-4016-1557 Farshad Sabaghzadeghan Department of Mechanical Eng. Univ. Qom Journal Article 2019 08 25 Simulation and numerical analysis of physical phenomena, especially for unstable problems, due to dependency of the numerical algorithms on the computer hardware to the increasing of the number of computational nodes, is the most important feature of their solutions. For this reason, increases the number of computations then increased computational costs. The order reduction method has been widely used in recent years to reduce computational time. In this way, by reducing the constraints of the system, without changing the inherent features of the problem, the computational efficiency will dramatically increase. In this study, using the basic concepts of dynamical systems, two problems of thermal diffusion and convection-diffusion are investigated independently and by using the proper orthogonal analysis method, a reduced order model is established for the equations governing these phenomena created. Accordingly, for each of the problems, based on the projection of the governing equation in the vector space of modes, by using more energetic modes, a reduced order model is obtained with respect to the orthogonal basis properties. The model obtained in order to simulate the process time variations can properly replace the original equation and predict the behavior of the system with very good accuracy. Simulation and numerical analysis of physical phenomena, especially for unstable problems, due to dependency of the numerical algorithms on the computer hardware to the increasing of the number of computational nodes, is the most important feature of their solutions. For this reason, increases the number of computations then increased computational costs. The order reduction method has been widely used in recent years to reduce computational time. In this way, by reducing the constraints of the system, without changing the inherent features of the problem, the computational efficiency will dramatically increase. In this study, using the basic concepts of dynamical systems, two problems of thermal diffusion and convection-diffusion are investigated independently and by using the proper orthogonal analysis method, a reduced order model is established for the equations governing these phenomena created. Accordingly, for each of the problems, based on the projection of the governing equation in the vector space of modes, by using more energetic modes, a reduced order model is obtained with respect to the orthogonal basis properties. The model obtained in order to simulate the process time variations can properly replace the original equation and predict the behavior of the system with very good accuracy.

https://mej.aut.ac.ir/article_3849_4f5a97cf06cf69028997db51d8726d28.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Numerical simulation of Holmboe waves in intrusive gravity current using LES method Numerical simulation of Holmboe waves in intrusive gravity current using LES method 4261 4278 4259 10.22060/mej.2021.19129.6954 FA Sadegh Rostami Dehjalali Department of Mechanical Engineering, University Of Zanjan, Zanjan, Iran Ehsan Khavasi Mechanical engineering department, University of Zanjan Parsa Nazmi Department of Mechanical Engineering, University Of Zanjan, Zanjan, Iran 0000-0001-6470-3272 Journal Article 2020 10 15 Gravitational currents are important currents in atmospheric and oceanic studies. Gravity current is caused when a fluid with different density moves into another fluid. If the fluid of a given density enters the stratified ambient, such that its density is lower than the underneath layers and higher than the upper layers, the gravity current is of the intrusive type. The Kelvin-Helmholtz and the Holmboe instabilities are seen in the interface. The decisive parameters in the type of instability are the Richardson number local and the ratio of shear layer thickness to the density layer. In this study, two-dimensional numerical simulation of Holmboe waves with the Eulerian-Eulerian approach on intrusive gravitational flow is investigated. OpenFOAM code was used to perform this simulation, and due to the turbulence of the flow, the LES method was used to model the turbulence. The obtained results show that with increasing the intrusive current density, the value of Richardson number decreases and the R parameter increases.Also, as the density increases, the frequency of the Holmboe waves first increases, then decreases. An increase in the wavelength of Holmboe waves is observed with increasing the intrusive current density. The phase velocity of Holmboe waves also does not have a specific trend with density changes. Gravitational currents are important currents in atmospheric and oceanic studies. Gravity current is caused when a fluid with different density moves into another fluid. If the fluid of a given density enters the stratified ambient, such that its density is lower than the underneath layers and higher than the upper layers, the gravity current is of the intrusive type. The Kelvin-Helmholtz and the Holmboe instabilities are seen in the interface. The decisive parameters in the type of instability are the Richardson number local and the ratio of shear layer thickness to the density layer. In this study, two-dimensional numerical simulation of Holmboe waves with the Eulerian-Eulerian approach on intrusive gravitational flow is investigated. OpenFOAM code was used to perform this simulation, and due to the turbulence of the flow, the LES method was used to model the turbulence. The obtained results show that with increasing the intrusive current density, the value of Richardson number decreases and the R parameter increases.Also, as the density increases, the frequency of the Holmboe waves first increases, then decreases. An increase in the wavelength of Holmboe waves is observed with increasing the intrusive current density. The phase velocity of Holmboe waves also does not have a specific trend with density changes.

https://mej.aut.ac.ir/article_4259_094bb65ef46d3eb4be0a87877ec333eb.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Control of droplet size in a two-phase microchannel using PID controller: A novel experimental study Control of droplet size in a two-phase microchannel using PID controller: A novel experimental study 4279 4292 4204 10.22060/mej.2020.18250.6783 FA Sina Mottaghi MSc of mechanical engineering, Shahrood university of technology Mostafa Nazari Department of Mechanical Engineering, Shahrood University of Technology, Shahrood, Iran. Mohsen Nazari Shahrood University of Tech, Shahrood, Iran Naserodin Sepehry صنعتی شاهرود-مهندسی مکانیک Amir Mahdavi Shahrood University of Technology Journal Article 2020 04 11 Precise droplet generation with controllable precise size is the target of this research. For this purpose, a flow focusing micro-channel is constructed using photolithography. Two syringe pumps are used, one for injecting discrete phase flow (DI water) and another for injecting continuous phase flow (oil). The Meros high speed camera is used for recording the image of droplets, and a fast image processing algorithm is used to calculate the size of the droplets. To regulate the size of the droplet, the PID controller is used due to its ease of implementation and robustness. The flow rate of the continuous phase flow is the control input and the size of the droplets is the output of the closed-loop system. Experimental tests are done by considering three desired droplet diameters, i.e. 100, 140 and 160 . To show the disturbance rejection characteristic of the designed closed-loop system, the flow rate of the discrete phase flow is changed stepwise. Due to this disturbance, the transient response of the system changed, but the controller attenuates this disturbance and regulates the system to the desired size. The experimental tests show that the designed closed-loop microfluidic system can generate droplets with desired precise size. Precise droplet generation with controllable precise size is the target of this research. For this purpose, a flow focusing micro-channel is constructed using photolithography. Two syringe pumps are used, one for injecting discrete phase flow (DI water) and another for injecting continuous phase flow (oil). The Meros high speed camera is used for recording the image of droplets, and a fast image processing algorithm is used to calculate the size of the droplets. To regulate the size of the droplet, the PID controller is used due to its ease of implementation and robustness. The flow rate of the continuous phase flow is the control input and the size of the droplets is the output of the closed-loop system. Experimental tests are done by considering three desired droplet diameters, i.e. 100, 140 and 160 . To show the disturbance rejection characteristic of the designed closed-loop system, the flow rate of the discrete phase flow is changed stepwise. Due to this disturbance, the transient response of the system changed, but the controller attenuates this disturbance and regulates the system to the desired size. The experimental tests show that the designed closed-loop microfluidic system can generate droplets with desired precise size.

https://mej.aut.ac.ir/article_4204_3335881e06d4d23091389226225e17c7.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 The effect of hole on the rectangular vortex generator on thermal-hydrodynamic performance of the minichannel The effect of hole on the rectangular vortex generator on thermal-hydrodynamic performance of the minichannel 4293 4308 4195 10.22060/mej.2020.18757.6885 FA Nadia Pahlevaninejad Department of Mechanical Engineering, Faculty of Mechanical Engineering, Babol Noshiravani University of Technology, Babol, Iran Masoume Rahimi Department of Mechanical Engineering, Faculty of Engineering, Golestan university, Gorgan, Iran Ali Akbar Ranjbar Department of Mechanical Engineering, Faculty of Engineering, Golestan University, Gorgan, Iran Majid Gorzin Department of Mechanical Engineering, Faculty of Mechanical Engineering, Babol Noshiravani University of Technology, Babol, Iran Journal Article 2020 07 24 There are several ways to increase heat transfer in mini-channels, like adding a vortex generator. In this paper, the effect of the presence of the hole on vortex generators on the heat transfer parameters is examined. In this study, a 50 mm long minichannel with eleven rectangular vortex generators, with holes with area of 5 to 60% of the vortex generator area, was analyzed with water-based fluid under constant flux in the range of Reynolds numbers 200-1000. The results showed the presence of holes on the vortex generators reduced the pressure drop resulting from the obstruction against the fluid flow and 34.7% decrease in pressure drop is observed for minimum and maximum area of holes in Reynolds number 1000. The Nusselt number is increased by existence of a hole in the Reynolds numbers range and then is decreased by increasing the size of the hole due to the reduction of the vortex size behind the obstacle, so that in the maximum Reynolds number by increasing hole size, 34.3% decrease is observed. There are several ways to increase heat transfer in mini-channels, like adding a vortex generator. In this paper, the effect of the presence of the hole on vortex generators on the heat transfer parameters is examined. In this study, a 50 mm long minichannel with eleven rectangular vortex generators, with holes with area of 5 to 60% of the vortex generator area, was analyzed with water-based fluid under constant flux in the range of Reynolds numbers 200-1000. The results showed the presence of holes on the vortex generators reduced the pressure drop resulting from the obstruction against the fluid flow and 34.7% decrease in pressure drop is observed for minimum and maximum area of holes in Reynolds number 1000. The Nusselt number is increased by existence of a hole in the Reynolds numbers range and then is decreased by increasing the size of the hole due to the reduction of the vortex size behind the obstacle, so that in the maximum Reynolds number by increasing hole size, 34.3% decrease is observed.

https://mej.aut.ac.ir/article_4195_a5e308070bd6dd3cc56283f2313522de.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Numerical analysis of the effect of baffle on heat transfer enhancement nanofluid flow over a backward facing step: A correlation for the average Nusselt number Numerical analysis of the effect of baffle on heat transfer enhancement nanofluid flow over a backward facing step: A correlation for the average Nusselt number 4309 4328 4154 10.22060/mej.2020.18564.6848 FA Hesam Moayedi Thermo-Fluids Department, Faculty of Mechanical Engineering, University of Guilan, Iran 0000-0002-8320-5292 Journal Article 2020 06 10 In this paper, the effect of baffle on the flow field and heat transfer enhancement of forced convection of Cu-water nanofluid flow in the laminar regime over a backward facing step is numerically investigated. Finite volume method is used to solve governing equations of flow and temperature. In this study, the influence of baffle geometrical parameters as height, width and number of baffles, as well as the Reynolds number and the volume fraction of nanoparticles on the flow filed and heat transfer are evaluated. Also, to evaluate the simultaneous of the heat transfer enhancement and pressure drop, the performance evaluation index is calculated. It is obvious that by increasing the Reynolds number and decreasing the volume fraction of nanoparticles, the performance evaluation index is increased. The average Nusselt number and the performance evaluation index for the width of baffle 2 are higher than other cases about 7.6% and 15% respectively. The results show that using 2 baffles must be more beneficial than other number of baffles. Finally, a correlation for the average Nusselt number as a function of Reynolds number, volume fraction of nanoparticles, number of baffles, baffle height and baffle width is presented with an average error of 2.88%. In this paper, the effect of baffle on the flow field and heat transfer enhancement of forced convection of Cu-water nanofluid flow in the laminar regime over a backward facing step is numerically investigated. Finite volume method is used to solve governing equations of flow and temperature. In this study, the influence of baffle geometrical parameters as height, width and number of baffles, as well as the Reynolds number and the volume fraction of nanoparticles on the flow filed and heat transfer are evaluated. Also, to evaluate the simultaneous of the heat transfer enhancement and pressure drop, the performance evaluation index is calculated. It is obvious that by increasing the Reynolds number and decreasing the volume fraction of nanoparticles, the performance evaluation index is increased. The average Nusselt number and the performance evaluation index for the width of baffle 2 are higher than other cases about 7.6% and 15% respectively. The results show that using 2 baffles must be more beneficial than other number of baffles. Finally, a correlation for the average Nusselt number as a function of Reynolds number, volume fraction of nanoparticles, number of baffles, baffle height and baffle width is presented with an average error of 2.88%.

https://mej.aut.ac.ir/article_4154_bd22c2ef9e6f0fa97825c6be879f8fa4.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Numerical investigation of the effect of thermophysical properties of nanofluid on fluid flow and heat transfer in a tube in presence of magnetic field Numerical investigation of the effect of thermophysical properties of nanofluid on fluid flow and heat transfer in a tube in presence of magnetic field 4329 4344 4261 10.22060/mej.2021.18936.6924 FA Yahya Malmir Chegini Faculty of Mechanical Engineering, University of Guilan, Iran Nima Amani Fard Journal Article 2020 09 02 In this paper, flow characteristics and heat transfer in a smooth horizontal pipe subjected to forced heat convection with constant wall heat flux in the presence of magnetohydrodynamic have been computationally analyzed. The effects of temperature-dependent density, specific heat capacity, thermal conductivity, and viscosity on heat transfer and frictional flow characteristics of transformer oil and local and average heat transfer coefficient have been numerically investigated. Firstly, to validate, the present numerical result has been compared with the analytical and experimental results through a smooth pipe, which shows a good agreement. A significant deviation between constant and variable properties has been achieved. Changes in fluid velocity profiles have led to changes in fluid characteristics including coefficient of friction and heat transfer coefficient. By considering the changes in the parameters, it was observed that the viscosity of the base fluid and the nanofluid have the maximum effect with approximately 30 and 25% increase in heat transfer coefficient and apparent friction coefficient relative to the fixed properties, respectively. Despite the dependence of the thermal properties of the nanofluid on temperature-dependent viscosity, the change in thermal conductivity leads to 35% increase in the heat transfer coefficient in the presence of a magnetic field. In this paper, flow characteristics and heat transfer in a smooth horizontal pipe subjected to forced heat convection with constant wall heat flux in the presence of magnetohydrodynamic have been computationally analyzed. The effects of temperature-dependent density, specific heat capacity, thermal conductivity, and viscosity on heat transfer and frictional flow characteristics of transformer oil and local and average heat transfer coefficient have been numerically investigated. Firstly, to validate, the present numerical result has been compared with the analytical and experimental results through a smooth pipe, which shows a good agreement. A significant deviation between constant and variable properties has been achieved. Changes in fluid velocity profiles have led to changes in fluid characteristics including coefficient of friction and heat transfer coefficient. By considering the changes in the parameters, it was observed that the viscosity of the base fluid and the nanofluid have the maximum effect with approximately 30 and 25% increase in heat transfer coefficient and apparent friction coefficient relative to the fixed properties, respectively. Despite the dependence of the thermal properties of the nanofluid on temperature-dependent viscosity, the change in thermal conductivity leads to 35% increase in the heat transfer coefficient in the presence of a magnetic field.

https://mej.aut.ac.ir/article_4261_13384ffc9d8bdb21c53c6f72d46f7866.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Measurement of subcooled flow boiling heat transfer coefficient in vertical annulus tube Measurement of subcooled flow boiling heat transfer coefficient in vertical annulus tube 4345 4360 4184 10.22060/mej.2020.18545.6841 FA Masoud Yarahmadi Fluid Mechanics Department, Shahrood University of Technology, Shahrood, Iran Mohammad Mohsen Shahmardan Associated professor, Faculty of mechanical Engineering, Shahrood University of Technology, Shahrood, Iran Mohsen Nazari Alireza Asgharzadeh Fluid Mechanics Department, Shahrood University of Technology, Shahrood, Iran Journal Article 2020 06 05 The boiling heat transfer, especially the subcooled flow boiling, is one of the cooling systems being used in industries due to their high heat transfer coefficient. The subcooled flow boiling happens when the bulk flow temperature and the interface temperature are lower and higher, respectively than the saturated temperature corresponding to the flow pressure. In the current study, an experimental apparatus was constructed, and subcooled flow boiling in an annulus tube was investigated. The annulus tube is in the vertical direction, and the internal and external diameters are 50.7 and 70.6 mm. The operating pressure was 1 atm, and the working fluid was water. In this investigation, heat flux, mass flow rate and the inlet subcooling effectiveness on heat transfer coefficient are considered. The experiments were performed in the mass flow rate range of 0.012 kg/s to 0.0286 kg/s in which the flow consists of both forced convection and flow boiling. The results show that the heat transfer coefficient is highly dependent on heat flux in a direct relationship. The mass flow reduction causes heat transfer coefficient increments to 30% in subcooled boiling regions. The use of porous media also increases the subcooled flow boiling heat transfer coefficient up to 30%. The validation of empirical results has also been done with valid previous reports. The boiling heat transfer, especially the subcooled flow boiling, is one of the cooling systems being used in industries due to their high heat transfer coefficient. The subcooled flow boiling happens when the bulk flow temperature and the interface temperature are lower and higher, respectively than the saturated temperature corresponding to the flow pressure. In the current study, an experimental apparatus was constructed, and subcooled flow boiling in an annulus tube was investigated. The annulus tube is in the vertical direction, and the internal and external diameters are 50.7 and 70.6 mm. The operating pressure was 1 atm, and the working fluid was water. In this investigation, heat flux, mass flow rate and the inlet subcooling effectiveness on heat transfer coefficient are considered. The experiments were performed in the mass flow rate range of 0.012 kg/s to 0.0286 kg/s in which the flow consists of both forced convection and flow boiling. The results show that the heat transfer coefficient is highly dependent on heat flux in a direct relationship. The mass flow reduction causes heat transfer coefficient increments to 30% in subcooled boiling regions. The use of porous media also increases the subcooled flow boiling heat transfer coefficient up to 30%. The validation of empirical results has also been done with valid previous reports.

https://mej.aut.ac.ir/article_4184_de043a5e421240eb846da8effe472ff1.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Comparison of axial and radial soil temperature distribution in U-tube and coaxial borehole heat exchangers Comparison of axial and radial soil temperature distribution in U-tube and coaxial borehole heat exchangers 4361 4378 4185 10.22060/mej.2020.18276.6799 FA Sepehr Sanaye Professor of departement of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran Fateme Mousavi Department of mechanical engineering, Iran university of science and technology Journal Article 2020 04 27 Dynamic variation of surrounding soil temperature in axial (depth) and radial directions of vertical type geothermal heat pump (heat exchangers are investigated here. This soil temperature distribution for borehole heat exchangers plays an important role in thermal operation, electricity consumption and coefficient of performance of geothermal heat pump. Thus the transient 3-dimensional numerical modeling of U-tube and coaxial borehole heat exchangers are investigated to find the temperature distribution around the buried pipes. The simulation is performed using ANSYS FLUENT 16.0 software based on the finite volume method. The effects of various parameters are studied and modeling results for the cooling application of heat pump are obtained for different mass flow rates of condenser cooling water. Results show that the injection heat transfer rate to the ground in summer, in the coaxial borehole heat exchanger at mass flow rates of 0.8, 1, 1.2 kg/s are 5.34%, 11.9%, 16.5% higher than U-tube borehole heat exchanger respectively. Moreover, after 93 days, the vertical temperature distribution of the soil for U-tube heat exchanger shows a significant variation mainly at depths less than 36.6 meters while the coaxial heat exchanger greatly affects the soil temperature distribution even in higher depths. Dynamic variation of surrounding soil temperature in axial (depth) and radial directions of vertical type geothermal heat pump (heat exchangers are investigated here. This soil temperature distribution for borehole heat exchangers plays an important role in thermal operation, electricity consumption and coefficient of performance of geothermal heat pump. Thus the transient 3-dimensional numerical modeling of U-tube and coaxial borehole heat exchangers are investigated to find the temperature distribution around the buried pipes. The simulation is performed using ANSYS FLUENT 16.0 software based on the finite volume method. The effects of various parameters are studied and modeling results for the cooling application of heat pump are obtained for different mass flow rates of condenser cooling water. Results show that the injection heat transfer rate to the ground in summer, in the coaxial borehole heat exchanger at mass flow rates of 0.8, 1, 1.2 kg/s are 5.34%, 11.9%, 16.5% higher than U-tube borehole heat exchanger respectively. Moreover, after 93 days, the vertical temperature distribution of the soil for U-tube heat exchanger shows a significant variation mainly at depths less than 36.6 meters while the coaxial heat exchanger greatly affects the soil temperature distribution even in higher depths.

https://mej.aut.ac.ir/article_4185_b207f5c56605a9d1a22e1e134fe95ba9.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Investigation on the effect of addition of nano-titanium oxide particles to phase change material in a hybrid system for battery cooling under constant heat flux Investigation on the effect of addition of nano-titanium oxide particles to phase change material in a hybrid system for battery cooling under constant heat flux 4379 4396 4280 10.22060/mej.2021.18825.6897 FA Mohsen Malekipour Faculty of Mechanical Engineering, University of Kashan Majid Sabzpooshani Faculty of Mechanical Engineering, University of Kashan Ehsan Houshfar School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran 0000-0001-6216-1182 Journal Article 2020 08 05 Increasing lithium-ion batteries temperature is known as a challenge. In this research, by completing a hybrid heat management system, the effect of adding Nano-titanium oxide particles to paraffin phase change material was investigated on the cooling performance of battery in two constant heat flux, 4.5 and 14 Watts. The hybrid system consists of nano-paraffin and copper metal foam with two working fluids as air and water. For air as working fluid, battery temperature in pure paraffin and nano-paraffins 1, 2, 3 and 4% became 56.2°C, 51.8°C, 50.7°C, 49.3°C and 48°C, respectively. From investigated cases, nano-paraffin 4% had the most decreasing temperature comparing to pure paraffin which was about 17%. Hybrid system with copper foam, nano-paraffin and working fluid as pure water tested in Reynolds numbers 420, 600 and 720. It is shown that the battery temperature reached stable temperatures of 48°C, 46°C and 44°C respectively, which comparing to the pure paraffin case, temperatures reduced by 11%, 12% and 12.5% respectively. Therefore, due to the low thermal conductivity of paraffin, the addition of nanoparticles to phase change materials is beneficial. Increasing lithium-ion batteries temperature is known as a challenge. In this research, by completing a hybrid heat management system, the effect of adding Nano-titanium oxide particles to paraffin phase change material was investigated on the cooling performance of battery in two constant heat flux, 4.5 and 14 Watts. The hybrid system consists of nano-paraffin and copper metal foam with two working fluids as air and water. For air as working fluid, battery temperature in pure paraffin and nano-paraffins 1, 2, 3 and 4% became 56.2°C, 51.8°C, 50.7°C, 49.3°C and 48°C, respectively. From investigated cases, nano-paraffin 4% had the most decreasing temperature comparing to pure paraffin which was about 17%. Hybrid system with copper foam, nano-paraffin and working fluid as pure water tested in Reynolds numbers 420, 600 and 720. It is shown that the battery temperature reached stable temperatures of 48°C, 46°C and 44°C respectively, which comparing to the pure paraffin case, temperatures reduced by 11%, 12% and 12.5% respectively. Therefore, due to the low thermal conductivity of paraffin, the addition of nanoparticles to phase change materials is beneficial.

https://mej.aut.ac.ir/article_4280_55603a5f239e435c642244be3e891b85.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Experimental investigation of personalized ventilation effects on temperature, velocity, and draught discomfort distribution in an office Experimental investigation of personalized ventilation effects on temperature, velocity, and draught discomfort distribution in an office 4397 4410 4166 10.22060/mej.2020.18478.6825 FA Alireza Zolfaghari University of Birjand 0000-0001-9917-3400 Peyman Ebrahimi Naghani Department of Mechanical Engineering, University of Birjand, Iran Mehdi Maerefat Department of Mechanical Engineering, Tarbiat Modares University Journal Article 2020 05 22 In this research, it has been tried to experimentally investigate the effect of a personalized ventilation system on airflow and temperature distribution in a room for two inlet air temperatures (24 and 32°C) and two different arrangements of the inlet diffusers (desk-mounted and under-desk air terminals). The results showed that the penetration depth of heat and momentum due to the inlet diffusers were not the same; So that the effect of inlet diffusers’ temperature on the room temperature distribution is significant up to a distance of about 60 cm. However, the effect of inlet velocity is noticeable up to a distance of about 110 cm. Therefore, the occupants’ thermal sensations up to the distance of about one meter from the inlet diffusers will be affected by the inlet conditions. Also, the results indicated that the draught discomfort along with the diffusers’ centerline is significant to a distance of about 180 cm. Based on the results, the air velocity and turbulence intensity are the two main factors in determining the draught discomfort in the personalized ventilation system and due to the rapid thermal mixing of inlet air with the room air, the effect of inlet temperature on the draught discomfort is not significant. In this research, it has been tried to experimentally investigate the effect of a personalized ventilation system on airflow and temperature distribution in a room for two inlet air temperatures (24 and 32°C) and two different arrangements of the inlet diffusers (desk-mounted and under-desk air terminals). The results showed that the penetration depth of heat and momentum due to the inlet diffusers were not the same; So that the effect of inlet diffusers’ temperature on the room temperature distribution is significant up to a distance of about 60 cm. However, the effect of inlet velocity is noticeable up to a distance of about 110 cm. Therefore, the occupants’ thermal sensations up to the distance of about one meter from the inlet diffusers will be affected by the inlet conditions. Also, the results indicated that the draught discomfort along with the diffusers’ centerline is significant to a distance of about 180 cm. Based on the results, the air velocity and turbulence intensity are the two main factors in determining the draught discomfort in the personalized ventilation system and due to the rapid thermal mixing of inlet air with the room air, the effect of inlet temperature on the draught discomfort is not significant.

https://mej.aut.ac.ir/article_4166_65ae450c5536606c266f49f1c08321f2.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Numerical simulation simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels Numerical simulation simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels 4411 4428 4239 10.22060/mej.2020.18513.6832 FA Seyyed Omid Haghani Department of Mechanical Engineering, khayyam university, mashhad, Iran Ebrahim Barati Mechanical engineering, Khayyam university Journal Article 2020 05 30 Ventilation is essential to provide a smoke-free path for safe passenger evacuation and effective rescue services in case of a tunnel fire, because the closure tunnels increase consequences of accidents significantly. In the present study, the simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels and physical phenomena has been investigated. Fire dynamics simulator will be used as a CFD tool. This simulation was performed to investigate the effect of the longitudinal distance of the smoke extraction system from the fire source on the smoke back-layering length and the maximum temperature in the two operating conditions used by this system downstream and upstream the fire source. In the present work, the smoke extraction system is located on the ceiling of the tunnel. The results show that using a smoke extraction system upstream of the fire source will increase the maximum temperature, but using the same system downstream will reduce the temperature throughout the tunnel and prevent smoke back-layering. However, attention to the smoke extraction velocity prevents the plug-holding phenomenon. The results also show that the simultaneous use of two smoke extraction systems at the upstream or downstream of the fire source will have a better result and The maximum temperature is reduced by 10%. Ventilation is essential to provide a smoke-free path for safe passenger evacuation and effective rescue services in case of a tunnel fire, because the closure tunnels increase consequences of accidents significantly. In the present study, the simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels and physical phenomena has been investigated. Fire dynamics simulator will be used as a CFD tool. This simulation was performed to investigate the effect of the longitudinal distance of the smoke extraction system from the fire source on the smoke back-layering length and the maximum temperature in the two operating conditions used by this system downstream and upstream the fire source. In the present work, the smoke extraction system is located on the ceiling of the tunnel. The results show that using a smoke extraction system upstream of the fire source will increase the maximum temperature, but using the same system downstream will reduce the temperature throughout the tunnel and prevent smoke back-layering. However, attention to the smoke extraction velocity prevents the plug-holding phenomenon. The results also show that the simultaneous use of two smoke extraction systems at the upstream or downstream of the fire source will have a better result and The maximum temperature is reduced by 10%.

https://mej.aut.ac.ir/article_4239_887a185b1a4080193d5cf63873ac6d70.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Investigation of using hybrid nanofluid-phase change material spectral splitter in photovoltaic/thermal system Investigation of using hybrid nanofluid-phase change material spectral splitter in photovoltaic/thermal system 4429 4454 4073 10.22060/mej.2020.18326.6800 FA Farideh Yazdanifard Department of Mechanical Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran Mehran Ameri Professor/Department of Mechanical Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran Robert Taylor Associate Professor/ School of Mechanical and Construction Engineering, University of New South Wales, Sydney, Australia Journal Article 2020 04 27 The photovoltaic/thermal system is capable of generating both heat and electricity simultaneously. The purpose of using spectral filters is to make full use of the solar radiation spectrum and thermal separation of photovoltaic and thermal units. The purpose of this paper was to investigate a new hybrid spectral filter consisting of phase change material and nanofluid to achieve a filter close to the ideal spectral filter. In this regard, the photovoltaic/thermal system with a combined nanofluid-phase change material spectral filter was simulated using energy balance equations in MATLAB software and its performance was compared with two conventional and nanofluid-based spectral splitting photovoltaic/thermal systems from energy and exergy viewpoints. Also, the optical properties of nanofluid and phase change material were simulated and the models were validated with the experimental data available in the literature. The results showed that by using a combined filter the photovoltaic temperature can be reduced by up to 50% and the output fluid temperature can be increased by twice. The exergy efficiency of the system with the combined filter was about 14% and 22% higher than conventional and nanofluid-based spectral splitting photovoltaic/thermal systems, respectively. The system also achieved the highest exergy efficiency at concentration ratios greater than 15. The photovoltaic/thermal system is capable of generating both heat and electricity simultaneously. The purpose of using spectral filters is to make full use of the solar radiation spectrum and thermal separation of photovoltaic and thermal units. The purpose of this paper was to investigate a new hybrid spectral filter consisting of phase change material and nanofluid to achieve a filter close to the ideal spectral filter. In this regard, the photovoltaic/thermal system with a combined nanofluid-phase change material spectral filter was simulated using energy balance equations in MATLAB software and its performance was compared with two conventional and nanofluid-based spectral splitting photovoltaic/thermal systems from energy and exergy viewpoints. Also, the optical properties of nanofluid and phase change material were simulated and the models were validated with the experimental data available in the literature. The results showed that by using a combined filter the photovoltaic temperature can be reduced by up to 50% and the output fluid temperature can be increased by twice. The exergy efficiency of the system with the combined filter was about 14% and 22% higher than conventional and nanofluid-based spectral splitting photovoltaic/thermal systems, respectively. The system also achieved the highest exergy efficiency at concentration ratios greater than 15.

https://mej.aut.ac.ir/article_4073_350a3797caea1668d227c8cbe52c793e.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 53 7 2021 09 23 Kinematic Optimization of the Stirling engine for Maximum Output Work and Constraint of Occupied Space Kinematic Optimization of the Stirling engine for Maximum Output Work and Constraint of Occupied Space 4455 4480 4230 10.22060/mej.2020.18822.6900 FA Abbas Rahmati Shahrood University of Technology Seyed Mojtaba Varedi Kulaee 0000-0002-7427-2127 Habib Ahmadi Shahrood University of Technology Mohmmad Hossein Ahmadi Shahrood University of Technology Journal Article 2020 08 05 The Stirling engine has attracted researchers' attention in recent years due to some advantages such as low noise, external combustion, and the ability to use solar and other new energy sources. Moreover, these engines can also be used in applications with low or high-temperature differences. The type of cylinders, their arrangement, and the transmission mechanism can affect this engine's performance. On the other hand, engineers and designers are always looking to increase the efficiency and effectiveness of mechanical systems, which in engines can lead to increasing the engine's work or power. In the current study, firstly, the dimensional analysis of different types of Stirling engines is done. Then, by defining the engine's geometric parameters as the design variables, the engine's output work will be maximized using optimization algorithms. Also, in order to prevent the increase of the dimensions of the engine and its occupied space, a new constraint in the problem will be used. Kinematic optimization is applied to four different types of Stirling engines. Three algorithms, namely genetic algorithm, particle swarm optimization, and imperialistic competition algorithm, have been used to solve the optimization problem. The results of kinematic optimization show that the output work of the engine with optimal dimensions has increased approximately 1.45 to 4.59 times. The Stirling engine has attracted researchers' attention in recent years due to some advantages such as low noise, external combustion, and the ability to use solar and other new energy sources. Moreover, these engines can also be used in applications with low or high-temperature differences. The type of cylinders, their arrangement, and the transmission mechanism can affect this engine's performance. On the other hand, engineers and designers are always looking to increase the efficiency and effectiveness of mechanical systems, which in engines can lead to increasing the engine's work or power. In the current study, firstly, the dimensional analysis of different types of Stirling engines is done. Then, by defining the engine's geometric parameters as the design variables, the engine's output work will be maximized using optimization algorithms. Also, in order to prevent the increase of the dimensions of the engine and its occupied space, a new constraint in the problem will be used. Kinematic optimization is applied to four different types of Stirling engines. Three algorithms, namely genetic algorithm, particle swarm optimization, and imperialistic competition algorithm, have been used to solve the optimization problem. The results of kinematic optimization show that the output work of the engine with optimal dimensions has increased approximately 1.45 to 4.59 times.

https://mej.aut.ac.ir/article_4230_c0e19ce0dbabbc0d17a4f8d4324cc8e3.pdf