مجله مهندسی مکانیک
سال چهل و هفتم شماره 3 (پیاپی 80، پاییز 1396)

In this research, the amount of natural gas leakage from a small hole located on the lateral surface of the above-ground or buried distribution gas pipe lines is estimated. The geometry was designed and meshed by GAMBIT software and then numerical calculation is carried out by FLUENT software. The working fluid was considered as compressible ideal gas. The fluid flow was assumed turbulent and soil considered as a porous zone. The results indicate that for small hole diameters, discharge speed reaches to the sound speed and at the so-called, choking occurs at exit position. Also, the volumetric flow rate of leaked gas has a linear relation with pressure of initial point and second order relation with hole diameter. In the case of buried pipes, permeation depth of gas in soil at the small diameter holes, is more than large holes but volumetric rate of leaked gas is lower. Finally, with the goal of making the results applicable for the natural gas industry, two correlations were developed for estimating the amount of leaked gas in aboveground and buried pipelines.

Pumps are used in reverse direction as hydraulic turbines due to their simple structure but use of a pump as a turbine changes its characteristics. In this study reverse operation of a centrifugal pump is numerically investigated so Best Efficiency Point (BEP) and performance diagrams are obtained. Splitter blades as a passive flow control were used in many turbo machineries and are suggested in this study for pumps as turbines. Governing equations including continuity and momentum equations were employed in time-averaged form due to turbulent behavior of flow. Source term of momentum equation was used to consider rotating effect of impeller such as Coriolis acceleration and centrifugal force. Proposed numerical method uses k-ω SST turbulent model with standard wall function .To simulate the flow in rotating and stationary parts of the turbo machine, Multi Reference Frame (MRF) analysis was employed along with Frozen Rotor technique. Results showed that efficiency was improved and BEP tends to occur at higher flow rates in splitter bladed impellers, which results in higher energy production. On the other hand cavitation risk is reduced by means of splitter blades.

In many industrial applications, fluids have non-Newtonian behavior and it is essential to access appropriate analytical models to study them. The Maxwell fluid model is one of the various models, proposed for the approximation of the non-Newtonian fluid behavior, which is used to study some of the industrial applications. In this research, the analytical investigation of a Maxwell flow on flat plate subjected to magnetic field in a porous media has been studied. For this purpose, the governing non-linear partial differential equations, are transformed to the ordinary non-linear equations by similarity variable and then analytically solved by the HPM. The results of the proposed method are compared to the numerical solution and validated. According to the results, increasing the magnetic field parameter, causes the velocity distribution decrement and increment of the boundary layer thickness. The most significant effect of the magnetic field parameter is observed for the stress on the plate. By increasing magnetic field parameter, the stress distribution on the plate substantially increases. Also increasing the magnetic field parameter, increases the skin friction coefficient on the surface and the velocity distribution.

This study deals with the solution of an inverse problem in a living tissue to estimate the time-dependent heat flux. The thermal properties such as thermal conductivity, blood perfusion and metabolic heat generation are considered temperature dependent. The Pennes bioheat model is applied to simulate thermal behavior. The Sequential Function Specification Method (SFSM) and Conjugate Gradient Method (CGM) with adjoint problem are applied to obtain the unknown surface heat flux. Two examples are considered to examine the accuracy and ability of the inverse analysis. A comparison of two methods in the solution of the nonlinear inverse bioheat transfer problem is done. Results confirm the accuracy of both methods in estimating unknown surface heat flux for exact data. The effects of measurement error, initial guess and measurement location upon the precision of the estimated results are evaluated. Results demonstrate that the accuracy of conjugate gradient method is more than the sequential method .However, in both methods; the precision of the inverse solutions decrease by increasing measurement error. Results show the time-dependent surface heat flux can be obtained by any arbitrary initial guess. In addition, the conjugate gradient method is more sensitive to measurement location than the sequential method.

In this research, the plunging motion of wing in unsteady incompressible and laminar flow is simulated by a numerical method based on finite volume technique and using dynamic mesh. The effects of amplitude, reduced frequency and aspect ratio on the trust generation in MAVs and Fishes Reynolds number region, are investigated. For simulating this oscillating wing, dynamic mesh with rigid body motion is applied. The simulation results are compared with published data to confirm the validity of this research. In this simulation, the effect of reduced frequency, amplitude, their simultaneous effect of them and the effect of aspect ratios investigated. These simulations are in Reynolds 3000 and some aspect ratios, reduced frequencies and amplitudes. This simulation results show that by increasing reduced frequency and amplitude, relative angle of attack increases, which increase pressure deference around the wings. Results showed that increase in reduced frequency is of more importance than the increase in the amplitude because of more acceleration. Low aspect ratio of the wing has negative effect on the production of trust force due to backflow of wing tips.

The present research is mainly devoted to investigate the effect of pressure ratio (ᴨ) on the Shock Wave-Boundary Layer interaction phenomena along the wall surface in internal compressible flows. The implicit Reynolds Average Navier-Stokes equations and k-ω turbulent model have been used to numerical simulation and investigation the effect of pressure ratio on location, structure of the shock train and the boundary layer specification. The obtained results show that the present numerical results are in good agreement with the experimental data. On increasing ᴨ, not only the shock train moved toward the upstream flow but also the shock structure changed from X-shape to λ. Furthermore with increasing ᴨ the displacement of shock train along the duct is increased. With decreasing ᴨ the shock train moved to the downstream so that the length of the duct isn’t enough for complete recovery pressure. The flow separation bubble is formed near the wall, when the shock was strong. The experimental results of supersonic blow down wind tunnel in Cambridge University have been used for validation.

In industrial natural gas burner, due to high temperature of flame, radiation is the most important mode of heat transfer and a main portion of heat must be transferred via radiation. However, the natural gas burner does not have suitable thermal efficiency, which leads to several commercial and qualitative problem. In the present study, the impact of different synchronous combustion ratio of gasoil-natural gas on flame structure and heat transfer was investigated. The structural and outward flame properties were determined by photography and processing technique. Also, a Solar Power Meter and calibrated thermopile were used to determine the luminous radiation and the total radiation of flame, respectively. Due to the important role of soot particles in flame radiation, the combination of yellow and red chemiluminescence and IR photography of flame were employed to determine the qualitative distribution of soot particles in flame. Also, the spectral radiative characteristics of soot particles were measured by BOMEM FTIR. The result indicated that synchronous combustion of gasoil droplets into natural gas create a volume flame with uniform temperature and enhance the radiation and thermal efficiency of flame. Increase in synchronous combustion from 0 to 35%, rises the average temperature of flame from 735 K to 1088 K and enhance the radiation heat transfer and thermal efficiency 1.55 and 2.35 times greater than pure natural gas, respectively.

In this paper a new method for object handling is presented. It is based on the use of an intelligent gripper to detect the object stiffness and then setting a programmable force for grasping the object motion. The main components of this system includes sensors (sensors for measuring force and displacement), electrical (electrical and electronic circuits, tactile data processing and force control system), mechanical (gripper mechanism and driving system for the gripper) and the display unit. The system uses a rotary potentiometer for measuring gripper displacement. A microcontroller using the feedback received by the load cell, mounted on the finger of the gripper, calculates the amount of stiffness, and then commands the gripper motor to apply a certain force on the object. Results of Experiments on some samples with different stiffness show that the gripper works successfully. The gripper can be used in Haptic interfaces or robotic systems for object handling.

Vortex tube or Ranque–Hilsch vortex tube is a mechanical device with a simple geometry and without any intricacy in its components, which can produce two colder and hotter streams from compressible inlet air. In this investigation, computational fluid dynamics (CFD) technique is used to study of key design parameter influence, i.e. inlet pressure on the performance of vortex tubes and energy separation phenomenon. The novelty of the present paper is the special focus on the Mach number inside vortex chamber and its changes due to the inlet pressure effect which has not been investigated in other papers yet. The governing equations have been solved by FLUENT code in 3D compressible and turbulent model using standard k-ε turbulence model. In this study on the basis of obtained results by the CFD study, different inlet pressures of vortex tube are studied. Finally in order to attain the more temperature separation in the vortex tube system, some suggestions and results is presented. This article believes that every vortex tube has an optimum pressure which is commercially optimized in heating and cooling processes. This optimum pressure was found to be 4.8 bar in the present research. The present obtained software results indicate that for cooling purpose, the cold mass fraction of about 0.3 will be recommended for higher cold temperature difference and for heating purposes in throughput of the cold mass ratio of about 0.8 is used. The obtained CFD results are validated by available experimental results. Also the inlet pressure increment reveals the increase of entropy generation and irregularity in the system.

In this paper, flat plate solar collector is modeled and verified. Then, the sensitivity analysis for three different water mass flow rate including 0.1, 0.2 and 0.3 /s are performed and the effect of tubes size, geometrical characteristics of collector, collector structure and absorber plate emissivity and cover emissivity on the thermal efficiency are investigated. The results of sensitivity analysis revealed that by increasing the water mass flow rate the collector efficiency increases. Then optimization is performed by considering collector efficiency as objective function and by selection of seven design parameters including number of tubes, tubes diameter, collector length, collector width, edge insulation thickness and bottom insulation thickness and three constraints including the rate of heat transferred to the fluid by the collector, aspect ratio and fluid temperature difference in the inlet and outlet of the collector. To obtain the optimum value of collector efficiency, Real Parameter Genetic Algorithm (RPGA) is used and the results of optimum design parameters and objective function are presented. Optimizing results show that best possible efficiency is 0.7362. Finally, optimization process is done for three different mass flow rates and results are reported.

In this article, the forced vibration analysis of viscoelastic microscale pipes conveying fluid resting on visco-Pasternak foundation under a harmonic moving load is considered. Based on the strain gradient theory and Euler-Bernoulli theory, the governing equation of motion and boundary conditions are derived using extended Hamilton principle. The viscoelastic behavior of the micropipes is modeled by using the Kelvin-Voigt linear viscoelastic theory. The displacement field in the space domain is approximated by trial functions and the equation of motion are reduced into the time domain using Galerkin method. The coupled equation system in the time domain is solved by differential quadrature element method (DQEM) and the results of numerical analysis are obtained for two different boundary conditions, namely pinned-pinned and fixed- fixed. In the present work, the effects of different parameters such as the mass ratio, diameter of micropipe, Pasternak and Winkler foundation moduli, different boundary conditions on the nondimensional deflection of viscoelastic micropipe are investigated. Also, results are in well agreement with the ones obtained in previous work.

In present study the effects of plasma actuation on the position of the separation point by using the different types of voltage functions including the sinusoid, square and triangular has been investigated. Also, the ability of this actuator for increasing the lift coefficient of airfoil NACA 0015 at angles of attack 0, 5.3, 11.5 and 17.5 has been studied and the best voltage function type for increasing of lift coefficient and removing or weakening the separation point has been determined. At first the pressure coefficient over the airfoil was calculated when actuation was applied and was validated by comparing with experimental data of Sosa. Then the variation of the velocity profiles and position of separation point in the three regions over the airfoil and a region behind the airfoil according to the voltage types sinusoid, square and triangular for different angles of attack have been predicted time-dependent numerically by COMSOL Multiphysics.

In this work, the effects of a splitter plate on the hydro-thermal characteristics around a circular cylinder in a channel was studied. The two-dimensional unsteady and incompressible flow and heat transfer was investigated numerically by solving the continuity, x - and y - momentum and energy equations using finite volume methodology by FLUENT. The second order upwind scheme is used to discretize convective and diffusive terms. The resulting algebraic equations are solved by PISO algorithm. The splitter plate length varies from 0.25D to 3D and it's angular position varies from 0° to 45° with Reynolds numbers 600, 800, 1000, 1200 and 1500. With increasing the splitter plate length Drag coefficient decreased continuously and the surface Nusselt number of cylinder is decreased with adding a splitter pale with length more than 1.5D. in this manner by increasing Reynolds number, effect of adding splitter plate decreases.

This work is devoted to find an appropriate criterion for thermal judging of nanofluids. The importance of this issue arises from the possible misleading which asserts an existence of extra heat transfer for nanofluid compared to the base fluid, neglecting the hydraulic effects such as increasing the pressure drop. To clarify the issue, an experimental apparatus with ability of making fixed Reynolds number and constant pumping power was constructed and thermal behavior of silicon oxide/ water nanofluid and distilled water are investigated in the laminar and developing regions. In this regard, heat transfer coefficient inside the finned air cooled heat exchanger is evaluated. Results are provided for different inlet temperatures and different nanofluid concentrations for two criteria of fixed Reynolds number and constant pumping .According to the results, the concentration of the nanoparticles in the base fluid will have a huge impact on the amount of deflection of these two measures, so that by increasing the concentration of nanofluids, the difference between these two measures becomes greater, hence in this work due to the low concentration of nanofluids, the use of any of the criteria did not make a significant difference in the results.

In this paper, penetration of drop and liquid film in layered porous media is studied by the two phase lattice Boltzmann-Shan and Chen model. Layered porous medium is generated by locating solid obstacles randomly, such that the amount of porosity in each layer and whole domain is a fixed value, making the porous medium more homogeneous. In this study, penetration pattern of liquid drop and liquid film in porous substrate is investigated and viscous fingering and capillary fingering regimes are considered and compared. The influences of porosity and the hydrophilicity or hydrophobicity property of surface are considered, too; generally, increasing the porosity and making the surface hydrophobic cause increasing the penetration rate. Because the porous medium being layered, the effects of using layers with different porosities and having an averaged-specified value in whole domain, on improving the penetration rate are discussed. Also, it is investigated how to change the penetration pattern from the viscous fingering to the capillary fingering regime by means of hydrophilic and hydrophobic surfaces inside the porous matrix. A unique feature of this research is to provide a mechanism to change the penetration path into specified one.

The wellhead pressure and temperature in the geothermal wells at a region are different. In this paper a new combined flash-binary cycle, considering the temperature and pressure differences of wells, for power generation from geothermal wells of Sabalan region in Iran, is proposed. Four appropriate working fluids are considered for the binary cycle and the proposed system is analyzed thermodynamically by the EES software using the real data of sabalan geothermal wells and the optimum pressure values are calculated for two flash chambers. The results show that to achieve the maximum output power, the optimum pressure for the first flash chamber is 800 kPa and for the second flash chamber is 92 kPa. Also, the results indicate that, among the considered working fluids for the binary system, R141b is the best fluid. For this working fluid the net output power of the proposed cycle is calculated as 17.11 MW. To compare the performance of the proposed cycle by cycle proposed in the previous research for geothermal sources of Sabalan by considering the well conditions as previous research, the results show that the net output power of the proposed cycle in this paper is 26.3 % higher than the corresponding value obtained for Sabalan geothermal sources in a previous research.

The bipolar plate is one of the most important components in a PEM (Proton Exchange Membrane) fuel cell .In this paper the mechanical behavior of the composite bipolar plates are studied and compared with Department of Energy (DOE) criteria. All specimens were prepared by casting under pressure and under the hot press. Phenolic resin powder was used as matrix of composite in manufacturing of bipolar plates. To increase the flexural strength and impact strength, the carbon fibers and carbon fabrics were used as filler. electrical conductivity of the samples was analyzed by adding natural graphite powder in the composite. In for the mechanical behavior of bipolar plates, samples with different weights of phenolic resin were produced and tested. The morphology of samples was conducted using a Scanning Electron Microscope (SEM). Finally, the results showed that increasing the percentage of resin, increases the flexural strength and impact strength of composite bipolar plates however the electrically conductivity reduces compare with DOE criteria.

In this article, the lattice Boltzmann method combines the immersed boundary technique to simulate the behavior and deformation of red blood cells with the primary different shape. Also, the blood flow inside an artery is simulated and some phenomena such as emboly and drug delivery have been analyzed. The results show that damage to the arterial wall will cause vortex flow and blood clotting. The quality of the drug injection in the arterial branch that is very impressive. Finally, comparing the results with other results show that the simulation accuracy is acceptable.

The Aquifers are underground porous formations containing water. Confined aquifers are surrounded by impermeable layers on top and bottom, called cap rocks and bed rocks. These aquifers are suitable for seasonal thermal energy storage.A confined aquifer with a very low groundwater flow velocity was considered to meet the annual cooling and heating energy needs of a residential complex located in Tehran, Iran.Three different alternatives of aquifer thermal energy storage (ATES) were employed to meet the heating/cooling demands of the complex. These alternatives were: using ATES for cooling alone, employing flat plate solar energy collectors for heating alone and employing a heat pump for cooling and heating. For the economical evaluation of the alternatives, a life cycle cost analysis was employed. For the environmental evaluation, Ret Screen software was employed. For the three considered operational alternatives, using ATES for cooling alone had the minimum payback period time of 2.41 year and life cycle cost of $16000. In the environmental consideration of the three alternatives, coupling of ATES with heat pump for cooling and heating had the minimum of CO2 generation, corresponding to 359 tons/year.

As nanotechnology develops, atomic force microscope Nano-robots attracted the attentions as an efficient instrument in order to Nano-structures transfer and construction. Lack of possibility of simultaneously observing the Nano-particles controlled pushing operation is one of the most important limitations on this method. In present research a virtual reality environment is used for observing the operation process in order to eliminate the limitations. At first, the images obtained from the AFM Nano-robots were processed in the simulation performed and then Nano-particles dimensions were determined. Then, the particles were transferred using Nano-particles transference dynamic simulation and simulating the critical time-force diagram. The simulations developed in order to make use of the rectangular, dagger and V-shaped cantilevers. The virtual reality environment provided allowed for the modeling applicability accurate process simulation for users.

In present paper, the modeling and optimizing of the combined cooling, heating and power (CCHP) system coupled with the reverse osmosis desalination are performed for a hotel. At the first step, operation strategy of two different configurations of combined cooling, heating and power system and reverse osmosis desalination is presented to provide the building demands, and the operation of these systems in comparison with traditional system will be optimized by genetic algorithm. In optimization process, multi criteria objective function (energetic, economic and environmental), called the Percent of Relative Annual Benefit (PRAB), and gas engine as prime mover (with in partial load), were used. Then, the environmental performance of these systems in comparison with traditional system is examined. Present results show that pollutant emission of CO2, CO and NOx reduce in an extensive range of nominal power of gas engine in both configurations. However, in CCHPW configuration system, by selecting 3250 kW nominal power for gas engine, a better performance is observed in relation with economic and environmental considerations, such that the highest annual benefit of 5.21×106 $/year is obtained, while the emission of CO2, CO and NOx pollutants reduces by 61%, 79% and 86%, respectively.

This paper develops open-loop optimal control approach for path planning of redundant manipulators with the last flexible arm and fixed base in trajectory tracking. In this method, regardless of flexibility, the space of joints answer is obtained for the rigid motion of manipulator. By proper selection of state vector, the cost function and system constraints are turned to classic form of optimization problem. By using Pontryagin’s minimum principle, the obtained equations are changed into two point boundary value problem. To verify the proposed method, simulation for three-link flexible manipulator is conducted. The results and surveys show the effectiveness of the proposed methods.

The performance of a proton exchange membrane fuel cell is expressed mainly by the polarization curve. Polarization curve is determined by calculating the thermodynamic potential and activation, ohmic, and concentration losses. Applying the curve fitting equations of the polarization curve, the cell output voltage can be calculated for a specific current density and for the specific operating conditions. Therefore numerous equations have been presented to predict or fit the polarization curve, due to the nonlinearity of the curve; their precision is the main challenge. Nevertheless, the comparison of these equations has been accomplished neither wholly nor in the entire range of the polarization curve. In this study, first of all, equations are categorized into analytical, semi-empirical, and empirical equations, and then their precision were compared as quantitative and qualitative by polarization curve and tools such as sum of squares due to error, coefficient of determination (r2), iterations and values of corresponding parameters, with the aid of Matlab software. The results show that among the investigated empirical equations, our equation is more precise. Akimoto’s equation and Haji’s equation were found as the best semi-empirical and analytical equation, respectively. Finally, the best equations were compared together with two sets of experimental data, our equation and Haji’s equation totally had the highest precision (r2> 0.999); therefore they were introduced as the best investigated equations.

In this paper, transient impact on a composite plate is studied using the spherical nose . The governing equations of the plate based on the first shear deformation, are discretized using the Galerkin finite element method. The mass, stiffness and force matrices are obtained such that the terms of bending and shear in the matrices are considered separately, and the Gaussian integration method is used to overcome the shear locking phenomena. The model is developed so that it is capable to taking frequent loading and unloading during the impact. The governing equations of the plate and the projectile are solved in the time domain using the Nikolson and Newmark integration methods. The results are compared with the results of other researchers and the accuracy of the model is verified. According to the numerical analysis, it is observed that the present model has accurate results for thick and thin plates. The low velocity impact on a composite plate with clamped and mixed boundary conditions is studied and the time history of response of the plate such as deflection, penetration, contact force and kinetic energy are presented.

In this paper the possibility of in-flight simulation of longitudinal and lateral dynamic of fighter aircraft by an unmanned aerial vehicle (UAV) is evaluated and the required controllers for in-flight simulation and tracking the flight profile of fighter aircraft are designed. Controllers design are based on the method of pole placement and tracking method, and the controllers are designed to adapt the UAV platform to track the longitudinal and lateral dynamic behavior of the fighter aircraft. After applying these controllers on the UAV platform, the fighter behavior is simulated and the simulation results showes that, dynamic behavior of fighter aircraft is appropriately tracked by UAV platform on a common performance envelope. To validate the results, the flight test data of the fighter aircraft is simulated by the UAV platform. Comparing the results of the flight simulation and the flight test profile, the capability of in-flight simulation of fighter aircraft by UAV platform is approved.

In this paper, forced vibration analysis of functionally graded (FG) nanocomposite cylinders reinforced by wavy carbon nanotubes (CNTs) subjected to time depended internal pressure is investigated by a mesh-free method. In the mesh-free analysis, moving least squares (MLSs) shape functions are used for approximation of displacement field in the weak form of motion equation. The applied nanocomposite is a mixture of wavy single-walled carbon nanotubes (SWCNTs) reinforced in isotropic matrix material. Material properties are estimated by a micro mechanical model and new extended rule of mixture. Micromechanics equations cannot capture the scale difference between the nano and micro levels. In order to overcome this problem, some efficiency parameters are defined. In this simulation, an axisymmetric model is used and three linear types of FG distributions of wavy CNTs and a uniform distribution are considered along the radial direction of cylinder. The results of mesh-free method and mechanical properties are verified by finite element method (FEM), experimental and theoretical results. Effects of the distribution kind, aspect ratio, waviness and volume fraction of CNT are investigated on forced vibration analysis of the FG nanocomposite cylinders. It's observed that CNT waviness and volume fraction have a significant effect on the vibrational behavior of the CNT-reinforced cylinders.

In this paper, added mass coefficients of an underwater vehicle were calculate using boundary element method. Fluid flow was solve using boundary element method on triangular meshes created by GAMBIT. For verification purposes, added mass coefficient of typical ellipsoid and sphere in various aspect ratios were considerd. The results for typical ellipsoid and sphere were compared with analytical results. As an applicable research, Suboff submarine was investigated. Added mass coefficients of Suboff submarine which was determine by boundary element method was compare with experimental results then. The results show good consistency in comparison with experimental one.

In this paper a single swirl injector has been investigated by writing a computer code and then its results have been validated by experimental work. The process of spraying and atomization of fuel and oxidizer in double swirl injector have been simulated steady state with same experimental conditions. Then, a single swirl injector with atonal fuel has been modeled time dependent and finally a single and double swirl injectors with different fuels, including oil, crosin, liquid nitrogen, liquid hydrogen as fuel, water and oxygen as the oxidizing simulated. The goal of this simulation is to compare the droplets diameters and velocity of swirl injectors. It can be noted that the output droplet diameter of double base swirl injector is less than a single one and the velocity of double swirl injector is greater than single swirl injector.

Solar air heater is a special solar collector that its working fluid is air. It is used for warming of inlet air in HVAC system, solar dryer and for regeneration of desiccant wheel in solar cooling system. In this paper, a new design of air heater collector is introduced and its mathematical model for heat transfer in collector elements like collector coating, absorber,… are derived. Then by simulation of this collector in Matlab software, the best dimension of collector is determined. The results are validated by experimental data. The behavior of this kind of collector is studied in humid and warm region in north of Iran. Carrier software is used for building thermal load calculation.

A thermodynamic analysis of a novel combined cycle which is combination of methane fired gas turbine cogeneration system (CGAM) with a Kalina cycle system (KCS) is reported In order to waste heat recovery. With the aim of detect irreversibility distribution in the cycle, exergy destructions and exergy efficiencies are calculated for components. Finally, a comprehensive parametric study is performed to investigate the effects of some important parameters i.e. air compressor pressure ratio, air compressor and gas turbine isentropic efficiency, maximum pressure of Kalina cycle and ammonia concentration of working fluid on energy and exergy performance of the proposed system. The results showed that, the cycle efficiency is maximized at a particular air compressor pressure ratio and its value depends on several operating parameters of the system. Maximum energy and exergy efficiencies are determined to be 85.8% and 52.5%, respectively, for the proposed system in air compressor pressure ratio of 15.26. The maximum net output power of Kalina cycle is 940 kW which occures in 45 bar and increase of ammonia concentration leads to net output power increasing.

Due to the noticeable stiffness and also very low deformability, brittle materials have vast application in the various industries such as automobile, navy, and aero. Therefore, investigation of failure behaviour and mechanical fracture of these materials is one of the most important challenges of the engineers and researchers. The main aim of this paper is to compare the performance of the extended finite element method (XFEM) with the conventional finite element method (CFEM) in prediction of crack initiation and propagation in a brittle material. For this purpose first, applying the damage models based on the CFEM and XFEM available in ABAQUS finite element software, crack onset and growth in a graphite specimen with keyhole notch is simulated. Then, values of crack initiation angle and maximum load capacity in the sample under different mixed mode loading conditions are predicted, compared with experimental results and validated. Comparison of the numerical results obtained from the CFEM and XFEM simulations with the empirical results reveals that the XFEM in addition to decreasing the computational costs and also reducing sensitivity to the element size in the mesh has higher accuracy and more performance in prediction of crack initiation and propagation in the brittle materials, compared with the CFEM.

Steady flows over a 60º delta wing with sharp leading edge are numerically studied at different sound regimes. In the numerical analysis using the Fluent software, an unstructured grid, Roe’s upwind scheme, k-ω SST turbulence model, implicit solution and parallel processing are utilized. Visualization results obtained by numerical simulations show that a leading edge vortex is formed on the upper side of the wing with or without the presence of the secondary separation which gradually expands and becomes closer to the wing surface with increasing Mach number. At Mach numbers higher than 2, the leading edge becomes supersonic and the expansion wave emanating from the leading edge accelerates the flow. At this condition, shock waves are formed on the wing which interact with the vortices. With increasing Mach number up to the hypersonic region, the shock waves above the primary vortex disappear and the vortex size and strength are decreased due to the severe expansion of the flow over the lee-surface of the wing. The effect of Mach number on the vortex core position, lift coefficient, surface pressure distribution, and vortex breakdown location is investigated. Increasing Mach number causes that aerodynamic coefficients increase in subsonic range and decrease in supersonic range. Also, vortex breakdown location moves downstream, and vortex core location gets closer to the wing surface until M = 3 and gets far from it at higher Mach numbers.

Wear is the main cause of reduced life expectancy and performance of spindle used in machine tools. To achieve high wear properties, the AISI 51XX series steel used as a spindle be applied in the carburized and tempered condition. In the current work, obtained properties from three different cycles of carburizing were compared with each other and the influence of tempering temperature on wear resistance of carburized samples were surveyed. The used wear test type was block on ring. Also, scanning electron microscopy, microhardness and metallography have been used for further investigation. The results show that; samples carburized at 920 °C for 5 hours, then normalized, next austenitized at 840 °C for 30 in, afterward quenched in oil and finally tempered at 100 °C has a good wear resistance compared with the other samples. Also, with increasing of tempering temperature to 250 °C, not only wear resistance of samples has not been improved, but also abrasion resistance, has been worsened rather to the raw samples.

In this research, the critical buckling temperatures of a 2-Directional FGM circular plate under the two types of temperature rise are calculated based on first order shear deformation plate theory (FSDT) in the cases of clamped support edge. The equilibrium and stability equations for 2-Directional FGM circular plate are derived according to FSDT and using the energy method and Euler equations and then the stability equations are solved by series method and computer programming and the critical buckling temperatures are derived. At the end, the results are illustrated by tables and graphs and the effect of various parameters such as the volume fraction indexes on the critical buckling temperatures are studied and compared with results of some other articles. The results show that for different values of volume fraction indexes in r-direction (µ), the volume fraction index in z-direction (n) has a little effect on the critical buckling temperatures. Also when µ is positive, the critical buckling temperatures are decreased by increasing µ but when µ is negative, vice versa. Also, for FGM thickness constant, critical buckling temperature is increased by increasing the aspect ratio (h/a), while decreased by increasing volume fraction exponent.

The purpose of this study is to model and predict the thermal conductivity of graphenenano fluid through the artificial neural network of multilayer perceptron. Nano Fluid temperature, volumetric fractions and thermal conductivity of nanoparticles are considered as network inputs. According to the experimental data of previous experiments on thermal conductivity of graphene nanoparticles at the temperature of 25 to 50 ° C and the volume fraction of 0.055-0.066, the network performance tests were performed.In order to evaluate the accuracy of the model in predicting the thermal conductivity of the nanofluid, the root mean square error indices, detection coefficient and absolute error percentage are used. These values are0.04 W/ mK, 99% and 0.26% , respectively.The results of the indicators show the accuracy and reliability of the proposed model in comparison with experimental results and theoretical models.

Limitation of fossil fuel resources together with commitment to conservation of environments have caused the views to be focused on the use of renewable energy resources. Biogas is produced by the anaerobic decomposition of organic matter in WWTPs (wastewater treatment plants) and is considered to be a sustainable energy resource due to permanency of wastewater flow. This research focuses the process of biogas fuel engine implemented in Kashan WWTPs. This system can reduce the fuel consumption rate and use renewable energies in production of heat and electrical power reliable a part of processing consumption of WWTPs. Specifications of biogas production in Kashan WWTPs is taken as sample and the necessary elements for installation and construction of biogas fuel engine are described and then two cogeneration units are designed for producing 466 kW electricity and 556 kW heat.. Costs of installations and total capital investment required for this power plant is calculated about 270,000$, which can be returned in 4 years through sales of electricity and other by-products. Also using wastewater for producing biogas reduces greenhouse emission such as methane and carbon dioxide.

In this paper, the effect of geometric parameters on the performance of tubes - finned heat exchanger is investigated. For this purpose, four triangular vortex generating process such as simple and angled types of triangle and square appendages are considered to increase the rate of heat transfer between the fluid and the fin and tube walls. Furthermore, the effects of these appendages on heat exchanger pressure, friction and its performance are demonstrated. The comparisons between numerical data with the published results show an accurate agreement with an error up to 5.3%. The maximum increasing the Nusselt number and pressure loss versus Reynolds number is concerned to base model and angled cubic appendages respectively with values of 80% and 2.95%.

In some copper, iron and zinc mines, the pipelines are used to transport the solid-liquid mixtures. In this case, the pipeline diameter is important in order to reduce energy consumption and costs. Therefore, the optimal diameter must be determined to minimize the sum of the aforementioned costs. Therefore, diagrams of the influence of significant parameters for slurry solid-liquid pipe diameter e.g. density of solid, size of solid particles, volumetric fraction of solid and dynamic viscosity have been represented. So, the optimal diameter of Sungun copper mine has been investigated, and the results are in good agreement with those obtained from the manufactured model.