JOURNAL OF MECHANICAL ENGINEERING
Year:2019 | Volume:49 | Issue:2 (87) |Papers Count:40

Experimental investigation of thermal efficiency in shell and helically coiled tube heat exchangers with 𝐅 𝐞 𝟑 𝐎 𝟒 magnetite nanoparticles

Thesubsonic flow fieldsperpendicular to AGARD-B standardwing-body model was investigated. Velocity distribution was obtained by using a hot wire anemometry on five sections at wing for investigating structure, size and position of vortexes. To investigate the effect of angle of attack, yaw angle and Reynolds number on flow structure on the wing the experiments were done at 5, 6, 8, 10 & 12 degree angels of attack 4, 8 &12 degree yaw angles and 250000 & 500000 Reynolds number in the close circuit subsonic wind tunnel of Malek Ashtar university of Isfahan. The innovation of the present study is to investigate the perpendicular flow structure of the Agard-B model in subsonic conditions and to investigate the effect of the yaw angle on the flow structurebecause previous experiments on this model are mainly carried out in supersonic conditions and without an examination of the yaw angle. Two vortex structures were formed around the wing, a longitudinal vortex which formed under the influence of the wing and a transverse vortex under the influence of body. Increasing the angle of attack caused the increase power of longitudinal vortex and increasing the yaw angel caused the increase of transverse vortex. In a certain range of Reynolds number increasing of Reynolds number had not anysignificant effect on the height of vortices.

One of the important factors for stabilization of autonomous underwater vehicles (AUV) is considering high nonlinearity of underwater environments. In this paper, firstly global finite-time stability of six DOF autonomous underwater vehicles without input dead-zone non-linearity based on adaptive finite-time proportional-derivative (AFPD) controller is proposed. The proposed controller doesn’ t refer to the modeling parameter and is much simpler; thus it is readily implemented. Stability of the system is guaranteed by the Lyapunov’ s direct method, LaSalle’ s invariance principle and geometric homogeneity techniques. Then global finite-time stability of the system with considering input dead-zone non-linearity, uncertainty and noise based on Lyapunov’ s direct method and a finite-time stability lemma is proven. Theoretical analysis also shows the finite– time stability of the AUV’ s states. Analysis results are confirmed via computer simulations.

Exergy analysis can be determining the actual amount of energy dissipation or thermodynamic inefficiencies for each component of a system. In this research, thermodynamic and exergy analysis of turbojet engine without afterburner has been presented to provide data and express ways to improve its performance. For modeling, a computer code has been written in MATLAB software and problem validation has been done with the GSP software. The results show that by increasing the flight altitude from the sea level up to 11 km, the compressor pressure ratio is equal to 40 and the exergy efficiency increases from 59. 16% to 63. 38%. At temperatures ranging from-93 ° C to 47 ° C, the exergy efficiency of a turbojet engine can vary from 51. 97% to 50. 78%. This means that if the flight of the airplane is carried out in a cool air, the exergy efficiency can be improved without applying the thermodynamic optimization in the engine. Other results indicate that with an increase in the flight speed of the aircraft from 50 to 300 m/s and at combustion temperature of 1850 K, its exergy efficiency increase from 51. 5% to 57. 53%.

In this paper, theoretical model of the contact between rigid spherical indenter with steel pipe API XB is presented to simulate dent on the pipes in working environments, and the results could be used to estimate the stress-strain distributions and as a result the useful life of pipes in denting area. Governing equilibrium equations for thin cylindrical shell is presented in the form of displacement components by the Navier method, which will be solved by higher order finite difference method. Richardson extrapolation technique and the effect of ChebyShev points on the convergence rate of responses in finite difference method will be discussed. Contact pressure between the pipe and indenter in each loading steps are estimated by contact mechanic theories and will be applied to the outer surface of the pipe. The finite element method will be used to compare the results. Finally, it can see that the results of two methods are in the good agreement with error less than 5% and theoretical model are applicable to variety of dimensions, material, boundary and loading conditions of pipe and indenter.

In this study, the performance of two-stage evaporative cooling system is evaluated under different conditions of temperature and flow of air and water inside the heat exchanger. For this purpose, a two-stage evaporative cooling system was designed and manufactured. In this system, the environment air is pre-cooled in the heat exchanger, before it enters the direct evaporative pad. The air is pre-cooled with cold water. This water is cooled by a compressive cooling system. With attention to compressive cooling system, it is possible to reduce the cold water temperature of the heat exchanger to less than the wet bulb temperature of the ambient air. The analysis of the results shows that, it is possible to reduce the outlet air temperature from the system to less than the wet bulb temperature of inlet air. In this system, the reduction of the water temperature in the heat exchanger and airflow in the system can increase the system effectiveness. The increase of water flow in the heat exchanger will increase the efficiency and reduce the outlet air temperature. Compared to the compression cooling system, the use of this two-stage cooling system can save up to 59% of energy consumption.

In this paper, numerical methods of the Adomian decomposition and the Modified Crank– Nicholson are used for solving the twodimensional Burgers’ equation, have been compared. These numerical methods have also been compared with the analytical solution. In contrast to the conventional Crank-Nicolson method, the MLCN method is an explicit and unconditionally stable method. This method leads to several block matrices through the transformation of the partial differential equation (PDE) into ordinary differential equations (ODE), which simplifies the calculations. The Adomian decomposition method includes the unknown function U (x), in which each equation is defined and solved by an infinite series of unbounded functions. In this study velocity parameters u in the direction of the X axis, and v in the direction of the Y axis, are examined at different times with different Reynolds numbers over a fixed time step. Also the accuracy of the Adomian and the Crank-Nicolson methods at different Reynolds numbers have been compared utilizing two examples of trigonometric and exponential functions with different initial conditions, which shows that the Adomian decomposition method is closer to the analytical method.

Erosion-corrosion usually occurs in the petrochemical, oil and gas industry and marine structures. Therefore, it is important to study the factors affecting. The severity of damage depends on various factors such as fluid velocity and microstructure of the material. The objective of this paper is to experimentally investigate the effect of fluid velocity on the erosion-corrosion of dual phase samples of Ck45. These were achieved by austenitising of samples at 740 oC for 45 min and then cooling in air, or quenching in water and/or austempering at 400 oC in salt bath for two hours. Erosion-corrosion tests were carried out in slurry composed of distilled water, 3 wt% NaCl and 1 wt% of alumina particles in flow velocities of 5, 9 and 16 m/s. The results revealed that the kinetic of erosioncorrosion was a linear. By increasing the velocity from 5 m/s to 16 m/s, the line slope is increased by a factor of 4-6, depending on the microstructures of samples. The erosion-corrosion rate increased by increasing velocity in accordance with a power relationship. The amount of power varied from 2 up to 3.

In this paper, the pH control solution is considered in a laboratory reactor. A prototype of an acid and an open stream is continuously coupled to the reactor tank in an appropriate proportions is used for PH process control then, according to the PEM table, the equation of the pH state is obtained after that with Optimizing the PI coefficients, the PI controller is designed. The classic PI controller was not able to control this process, so the state-of-the-art observer was used, which was able to control with high precision. The proposed observer estimates state variables with extreme precision due to linear design. In the design of non-linear observation, sliding mode control is used. This method is suitable for estimating the state variables of the non-linear nonlinear systems, but due to the occurrence of chattering, its efficiency is greatly reduced. In order to prevent chattering and also to increase the accuracy, the second-order slip-off theory of the flicker is used to design non-linear observation. Finally, a nonlinear viewer is designed and simulated by using of modeling theory.

In this study the laminar incompressible flow and the heat transfer from a rotationally oscillating circular cylinder with an attached splitter plate is investigated. Dynamic grid is used employing improved linear and torsional spring analogy which is coupled with the solver by the Arbitrary Lagrangian Eulerian (ALE) formulation for modeling the oscillation of cylinder by the aid of ANSYS FLUENT. The convection terms are discretized by QUICK, also diffusion terms have been discretized by second-order upwind scheme. For coupling the pressure and velocity fields, the PISO algorithm was employed. After verification of numerical solution with previous investigations, parametric studies were performed by changing oscillation frequency, splitter plate length and Reynolds number. It was observed that simultaneous usage of oscillation and splitter plate can have both positive and negative effects on drag reduction and heat transfer increment. Finally F=2 and L=0. 5 were chose as the best combination.

In this paper the crack growth process of the parts subjected to hot fluids has been studied. The fluid high temperature activates the creep process. In addition the effect of the fluid corrosion as an important factor in the crack growth has been considered. The effective factors are divided into two groups of developing factors and resisting factors. For calculation of the developing forces, the inherited mechanical model has been used and after deriving the creep function, the amount of these forces has been determined in two stages of crack concealment and crack growth. The resisting force has been calculated using Rabotnov method of accumulated small fractures in the crack region. The effect of corrosive environment has been considered in the calculations using penetration function and the fluid standard density variations. For solving the resulted equations, programming in the MATLAB software has been used. Then the effects of the crack initial length, the applied stress and the fluid corrosiveness have been investigated on the crack growth curve.

The real-world design optimization problems are complex and multidisciplinary. For example, design of a satellite system involves complex interactions between various sub-systems with a large number of design variables and constraints that limits application of conventional design optimization methods to this class of problems. In addition, design search space of such problems can be large and non-convex involving simulation of several interacting disciplines and hence it is time consuming or difficult to rapidly evaluate trade-offs between various disciplines. To address these difficulties, several research works are focused on the multidisciplinary design optimization methods. In this respect, this paper presents and efficient multidisciplinary design optimization framework using metamodels. The proposed method extends multidiscipline feasible concept using metamodels, design of experiments (DoE) and sequential quadratic programming (SQP) for solving large scale design optimization problems such as satellite systems. The proposed method is compared with the existing methods using a number of benchmark problems. The proposed method is implemented on a remote sensing satellite system. The results obtained show that the proposed method provides an effective way of solving large-scale design optimization problems.

In this study, effects of sintering time on the microstructural changes and electrochemical behavior of silver electrodes in the environment of silver-zinc cells was investigated. For this purpose, initially four Ag electrodes (positive plate) with composition of 95 wt% silver oxide, 4. 9 wt% carbon powder and 0. 1 wt% resin by powder metallurgy method was prepared. Then, four silver electrodes were sintered for 5, 10, 15 and 20 minutes at temperature 500° C. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were used in the 1. 4% KOH solution to evaluate the polarization resistance of Ag electrodes. Scanning electron microscopy was used to examine the microstructures of electrodes and point analysis was accomplished by EDX method. Electrochemical tests results showed that with increasing sintering time, polarization resistance of silver electrodes reduced in the KOH solution. SEM images were showed that with increasing sintering time, the amount and size of apparent pores increased in the electrodes. Also, point analysis results has implies on reduction carbon and oxygen in electrodes with the increasing sintering process time.

A problem associated with the aerodynamic design of high-speed trains is the air flow and slipstream effects caused by their passage. These effects can have some level of impact on fuel and energy efficiency of the train, but their other important consequence is the emergence of turbulent flows at higher speeds which can cause aerodynamic drag forces followed by noise and vibration. Thus, slipstream effects have significant importance in the design of trackside installations which necessitate unique safety measures. A high-speed train passing under a structure or object makes sudden impacts on aerodynamic forces acting on that object. So this issue needs to be considered in the design of structures and installations to be built around high-speed rails. In this study, a numerical simulation with moving mesh and k-epsilon turbulence model was carried out in FLUENT software to study the slipstream and aerodynamic effect of a passing high-speed train on overhead and trackside installations with the objective of preventing aerodynamics-induced damage. This simulation was conducted in two scenarios of absence and presence of aerodynamic brake on topside of the train. In the end, ABAQUS finite element software was used to determine the maximum stress exerted on objects (installations) positioned at different distances from the rail, and the results were compared with the maximum allowable stresses to determine a minimum permissible distance between installations and high-speed train.

In this study, to respect the shortage of water and consuming of the electrical power in the periphery of the Persian Gulf, generation of water and electricity is considered concurrently. In this paper, supplying the water, electricity as well as the cost of them in the city of Bashagard are investigated by using the system of MED+RO. Regarding to the ppm of the Persian Gulf’ s water 45000, the amount of supply water 10000 m3/day are considered. In this design, the RO system and final price recovery for the entire system are calculated equal to 42% and 2. 3 $/m3 consequently. Regarding the flow of outlet steam of HRSG, using the system of MED could not supply the required fresh water alone, but with the use of the GT+MED+RO hybrid system electricity and fresh water needed for this city are supplied. The utilizing of the hybrid system has also led to an increment in costs, which can be used with RO pumps using the more powerful gas turbine with the use of more electricity, and costs decreased from 2. 8 to 2. 3 $/m3.

Due to the importance of reducing energy consumption in today's world, the energy consumption should be separated from false claims. In this paper, higher than 98% efficiency claim in a "Condensation Package" is scientifically evaluated with few empirical indications in this field. The results show that, at least in countries where electricity is produced by natural gas, considering the actual operating conditions of the heating systems, not only the condensation package does not increase the efficiency, but the use of more electricity for the exhaust fan of combustion products in these packages also reduces efficiency. In fact, using electricity energy for exhausting the combustion product gases is the reason of efficiency decreasing. In addition, the problems arising from the distillation of water in the chimney flue perimeter wall of the building damage and environmental degradation as well and increase the air pollution. It is also noted that even for system operation under certain conditions, such as melting ice, thermal efficiency is never more than 98%.

In this paper, the effect of notch depth on the J-integral in the plates made of Bainitic functionally graded and weakened by U-notch under mode I loading was investigated. Functionally graded steels (FGSs) consist of ferrite (α ), austenite (M), bainite (β ) and martensite (M) co-existing in different configurations and produced via electro slag remelting (ESR). In the present work, a Bainitic functionally graded steel in the form of divider configuration was made and the J-integral was investigated. Moreover, the effect of notch depth on the critical load and critical J-integral was investigated. The results show a good agreement between the Finite element results taken from commercial ABAQUS software with the experimental ones. The results show that the critical fracture load decreases by increasing the notch depth. Moreover, the critical J-integral increases by increasing the notch depth.

To have a precise calculation of critical force and time of nano-manipulation, the effect of the different input factors on output parameters should be investigated. One of the exact sensitivity analysis methods is the statistical Sobol method. In this paper for the first time, the effect of the six environmental factors including cantilever elasticity module, cantilever Poison’ s ratio, particle’ s elasticity module, particle’ s Poison’ s ratio, surface energy and adhesion work have been investigated on eight output parameters including critical sliding force along x-axis, rolling about x-axis, sliding along y-axis, rolling about y-axis, and critical times of sliding along x-axis, rolling about x-axis, sliding along y-axis and rolling about y-axis, in 3D nano-manipulation based on Sobol statistical method. The final results of this paper showed that the cantilever elasticity module is the most effective factor on critical force and cantilever Poison’ s ratio is the most effective one on critical time in 3D nano-manipulation.

Energy absorbing systems are used in many engineering structures, especially in moving machines, to prevent or to reduce impact induced damages. The aim of this study is to survey deformation and energy absorption of sandwich structures consisted of two concentric aluminum tubes with EVA polymer foam between them. Two loading methods have been used; quasi-static loading and impact loading. Deformation mode, energy absorption and mean crush force were investigated as mechanical behavior parameters. Moreover, the effects of changes in tubes length and foam density on these parameters have been studied. For parametric study, finite element simulations carried out using LS-Dyna software. Results of the study show that using foam increases energy absorption; the higher the foam density the greater the energy absorption and mean crush force. Furthermore, comparison of folding mechanism between foam-filled structures and empty ones shows that using foam does not affect the folding mode.

In this paper presents the effects external pressures and stiffeners on vibration of sandwich cylindrical shell based on energy method under asymmetrical boundary conditions. The sandwich shell is formed by three layers where the inner and outer layers are stainless steel and the middle layer is aluminum. The sandwich cylindrical shell equations are established based on first order shear deformation theory (FSDT). The governing equations of motion were employed, using energy functional and by applying the Ritz method. The asymmetrical boundary conditions represented by end conditions of the sandwich cylindrical shell are clamped-free (CF), clamped-simply support (C-SS) and free-simply support (F-SS). The presented results are compared with those available in the literature and great agreement is observed. Finally, the effects asymmetrical boundary conditions, external pressures and stiffeners on vibration of sandwich cylindrical shell are studied.

In this paper, a biogas steam reforming system, ORC, is combined in order to produce hydrogen and power at the same time. The mixture of biogas contains a large percentage of Methane, Carbon Dioxide and negligible amounts of other gases. A thermodynamic comprehensive modeling was done on the proposed system. A parametric study is also done on the energetic performance combined system. The results show that by increasing the temperature in a constant molar ratio of carbon dioxide to methane, thereby hydrogen production rate, net generative power, and energy efficiency increased. Moreover, increasing the molar ratio of carbon dioxide to methane, resulted a decrease in hydrogen production per mole of methane and an increase in the net generative power, and so the energy efficiency of the combined system decreased. the most net generative power, energy efficiency of the combined system in the case of hydrogen production is maximum, achieved to 19. 24 kW, 44%; respectively; that compared to biogas, hydrogen production system through reforming, has 5% increased.

In this study, to present a formulation framework for thermal crack growth problems with moving boundaries, a cracked silica glass plate moving in a heterogeneous fluid has been investigated, using the extended finite element method (XFEM). For this purpose, the transient heat conduction with moving boundaries and simultaneously, convective heat transfer of moving boundaries with different ambient fluids, is formulated using XFEM and a system of transient heat conducting matrix equation is obtained. Furthermore, to accurately compute the temperature fields, by adjusting the Crank-Nicolson scheme and using the Von Neumann stability criterion, a numerical solution has been presented for the above-mentioned system. The formulation procedure has been coded in Matlab and it has been employed. In order to analyze the performance of the presented formulation, giving the mechanical and thermal properties for the soda-lime glass, obtained results are compared and verified with the experimental ones. After accuracy verification of results, the aforementioned process has been accomplished for other common silica glasses and the effects of thermal and mechanical properties of them has been analyzed on mode I stress intensity factor.

Researchesdone by researchers on the forced vibration analysis of rectangular plates based on the three-dimensional elasticity theory are limited to the analytical solutions for simply-supported boundary conditions or linear analyses. In this study, by eliminating the previous limitations, the forced vibration of functionally graded rectangular plates with different boundary conditions is examined based on three-dimensional theory of elasticity and taking into account the geometrically nonlinearity. The rectangular plate is made of the aluminum and alumina in which are distributed through the thickness direction according to a power law for functionally graded materials. In order to achieve the governing equations and corresponding boundary conditions in terms of displacements, Green-Lagrange, stress-strain relations and Hamilton's principle are used. The nonlinear coupled governing equations are discretized in the space domain using the generalized differential quadrature (GDQ) method. Then, utilizing the numerical-based Galerkin scheme, one can obtain a time-varying set of ordinary differential equations of Duffing type. The arc-length method is employed to solve the vectorized form of nonlinear parameterized equations. Finally, to have a comprehensive study on the effects of geometrical parameters, forcingamplitude and damping ratio on the frequency-response curve of functionally graded rectangular plateswith different boundary conditions are examined.

In this article, the modified dynamic path-planning algorithm is designed. The problem of overlapped obstacles (e. g., forbidden flight zones) is solved while the pervious dynamic path planning methods could not response to this problem. This modified introduced algorithm can be applied in the complex environment and complicated applications without any limitation on the states of obstacles and targets while the pervious dynamic path planning algorithm stops working when UAVs is inside the target circle. In this article, by considering a virtual obstacle, formation flying path planning is introduced. Numerical simulations are performed to verify the feasibility and ability of this proposed algorithm. This newly proposed algorithm performed for coordinated and group target tracking of multiple UAVs.

In this article, mechanical properties of dissimilar joints of austenite stainless steel AISI304, with low carbon steel St-37 fabricated with tungsten inert gas welding technique (GTAW) and 309 filler metal are investigated. By changing the arc heat input, welding speed and also inter-pass temperature, the effect of these parameters on the weld microstructure and tensile strength were investigated. Metallographic studies show that by increasing the arc heat input, solidification time was increased, so more transformation from ferrite to austenite was occurring and consequently the joint strength was increased and consequently. On the other hand, it was observed that by increasing the intensity of the current, the heat affected area was extended, the weld grain size was increased and consequently, the mechanical properties of the weld were decreased. Tensile test results showed that the weakest connecting zone of the samples is the carbon steel heat-affected zone. The highest tensile strength was obtained from the specimen welded with minimum current and most progressing speed without any inter pass time. This process condition led to recrystallization at the border of weld metal and part of the heat affected zone and resulted in significant reduction in the grain size and led to considerable improvement for the weld tensile strength.

In the current study, the non-Newtonian fluid over a stationary circular cylinder has been simulated using the lattice Boltzmann method. The regime of 2D and unsteady flow (Re=100) for different non-newotonian power-law indices (0. 4≤ n≤ 1. 8) and four different aspect ratios of 2, 4, 6 and 8 has been investigated. The power-law model was used for describing the non-Newtonian behavior of the fluid. The results have been compared with previous experimental and numerical results. The effects of the power– law index and aspect ratio on the vorticity contour, average drag coefficient, fluctuations of lift coefficient and time averaged of pressure coefficient have been studied in detail. The results show that the steady or unsteady fluid behavior depend on power-law index and aspect ratio. Generally, the average of drag coefficient deacreases by increasing aspect ratio at fixed power-law index. For all considered aspect ratio, except B=2, the average of drag coefficient increases when the fluid behavior changes from shear thining to shear-thickening.

In this article, a 2D simulation of mixing of nano drug particles has been performed for non-Newtonian fluid in a T-shaped microchannel. The effects of the applied electric field on the mixing behavior as a method for mixing enhancement as well as the effects of various parameters such as nanoparticle volume fraction, pressure gradient and rheological properties of the fluid have been investigated. The numerical method is based on the finite element method which has been performed using COMSOL Multiphysics software. All the physical properties of the fluid have been considered as a function of the local concentration of nanoparticles. It is expected that increasing the particle volume fraction in the inlet branch carrying nano drug, lead to the increase in the mean concentration in the outlet but the results show that mixing quality decreases for this case. The results also demonstrated the significant effects of electroosmotic phenomenon on the augmentation of mixing quality. Besides, it is found that applying higher pressure gradient results in a decrease of mixing quality, whereas changing the rheological index of the fluid has not any significant effect on the mixing quality for a pressure-driven flow.

A systematic design of the solid propellant rocket; Analysis of characterizes and components; Manufacture of a porotype and flight test are the main purposes of study. In rocket motor design process, the zero and one dimensional interior ballistic flow solution are used. The numerical solution is based on iterative approach for propellant combustion conditions and pressure estimation. Propellant grain geometry, combustion chamber, nozzle, motor bulkhead, joints analysis and sealing are most important subsystems; so the challenge is to develop a model for their convergence. The other highlight of this approach are parts building; make solid propellant and finally assemble the motor. This motor was used for real flight test of the sounding rocket. The experimental data and scientific process have good convergence and its results usable for other engineering research.

In this paper, the effect of coupled bending and membrane strains on the large plastic deformation of rectangular plates due to impact loading is investigated both analytically and experimentally. The energy approach based on upper bound solution has been used in order to predict the maximum permanent deflection of rectangular plates. By assuming a deformation shape function, two consecutive energy based analyses have been presented. In the first step, it has been shown that the longitudinal and transverse displacements do not affect the amount of plastic work as well as maximum permanent deflection. Hence, the analytical expressions are derived by excluding the longitudinal and transverse displacements from the analysis. Next, in the first analysis, the analytical models have been extracted for the case when membrane strain energy and bending one are considered. Thereafter, an analytical model has been presented for predicting midpoint deflection-thickness ratio of rectangular plates by incorporating the coupled interaction between membrane and bending strains. Eventually, the obtained analytical results have been compared with the experimental results and illustrate good agreement with experiments for different impact velocities, plate materials and plate thicknesses.

The rolling process is one of the most common processes of making the machinery parts and the workpiece cooling rate is one of the most important parameter in the improved of product properties. In this paper, the flow of nanofluids over a nonlinear stretching sheet with a magnetic field is studied as a simplified model of a rolling process. The stretching velocity of the sheet is assumed to vary as a power function of the distance from the origin. The governing equations are including continuity, momentum and energy balances that by using of similarity solution method are transformed to nonlinear ordinary differential equations and are solved. The similarity solution results of momentum and energy equations are compared with published data, and have achieved appropriate compliance. The results show that increasing the solid volume fraction of the nanoparticles φ , the thermal conductivity of the fluid has increases and Increment of the nonlinear stretching parameter n, decreases heat transfer. Also increment of magnetic parameters M, has reduced the cooling rate. In this paper, Bijan number is introduced as a normative for the qualitative cooling rate in the rolling process. Based on the results increase the solid volume fraction of the nanoparticles φ , the nonlinear stretching parameter n and magnetic parameters M, increased, decreased and decreased the number Bijan respectively. The results of this research can be extended for the increasing of the cooling rate in the rolling process of metals

In this paper, thermoelastic stress analysis of a laminated composite rotating disk has been studied using analytical and finite element methods. The governing equations of motion for a composite rotating disk are derived based on circular disk theory of plates in conjuncture with the minimum potential energy principle. The governed equations of motions are solved analytically using Differential Quadrature Method (DQM). Moreover, for the numerical simulations in FEM, ABAQUS software is used. Two models are considered in the numerical simulations for laminated solid and annular disks as, a) a disk with only one layer in longitudinal direction and layer wise in radial direction, b) a layer wise disk in both longitudinal and radial directions, respectively. After convergence study of the solutions, the results for stress distribution in radial and circumferential directions are obtained and then compared.

In this study, solid oxide fuel cell stack, biomass gasifier and heat pipes were integrated with each other. The rice husk and water steam were used as biomass and gasification agent, respectively. High temperature sodium heat pipes were selected for system. Unknown parameters were obtained using the balance of components, reaction equilibrium constant and the First Law of Thermodynamics. The integrated system model was prepared in EES and was described in detail. The results of gasifier, fuel cell stack and heat pipes have been validated in comparison to previous experimental results and researches. In this study, the performance of the system for STBR, current density, pressure and utilization fuel factor were investigated. The output parameters were composition of synthesis gas, the number of heat pipes, transferred heat by the heat pipes, the voltages and power of fuel cell, the power, efficiency and required biomass of system. The results indicated that in STBR=0. 7, utilization fuel factor of 0. 8 and current density of 4000[A/m2], the power and efficiency of integrated system were 233[kW] and 40%, respectively.

Natural convection of a two-dimensional laminar incompressible fluid flow in a ⅂-shaped cavity with rectangular heating obstacle on the upper wall has been investigated by LBM. The present study has been carried out for different aspect ratio and various cases of position of obstacle on the upper wall in different Rayleigh number. Water is chosen as a working fluid. Hydrodynamic and thermal behavior of fluid in the presence of rectangular heating obstacle was analyzed in form of streamlines, isotherms and the average Nusselt number. Results based on this numerical study showed that the rectangular obstacle considerably affect the hydrodynamic and thermal behavior of fluid in a ⅂-shaped cavity. By the increasing Ra number and the height of the obstacle, an increase in the average Nusselt number appeared. By analyzing the resulting graphs and figures, in Rayleigh number of 106 and aspect ratio of 0. 15, the best rate of heat transfer occurred. Also by analyzing the various cases of position of the obstacle toward the cavity, the maximum heat transfer rate was observed when the heating obstacle was located at Sx=0. 4. Results of this research are useful for designing the efficient position of electronic components location in the cavities.

In this study the failure analysis of austenitic stainless steel welded joints of fuel oil pipes have been investigated. Microstructure characterizations and fractography were performed on pipes and the crack initiation and fracture mechanism were studied. The results show that the fracture mechanism of pipes was fatigue and due to the early initiation and higher stress concentration in the overlap weld zone the fatigue life has been decreased. In order to increase fatigue life of pipes it is suggested to determine the initial crack created during service by NDT methods. It was recommended to provide additional support brackets in the affected pipe length to prevent the fuel oil return line from vibrating extremely.

In this study, a microvascular-based self-healing system has been introduced and employed in fibrous polymer-based composites. Microvascular channels were created using removable solid pre-forms which were placed in the structure of composite during specimen fabrication. Some of the channels were filled with epoxy resin+anhydride hardner as a healing agent and some others were filled by liquid catalyst. When the structure is subjected to the loading and micro-cracks created in the specimen, they will break the microchannels and then the healing agent flows in the damage area, leading to the elimination of the defects over a time span. This study aimed at investigating the role of healing time and healant volume fraction on the healing efficacy of structure after initial damage created through bending method. To do so, tensile strength of the specimens were assessed after passing the different time span from the initial damage creation. The observations indicated that the highest tensile strength recovery was 64. 9%after 7 days.

One of the defects resulted from working under high temperature and pressure in the rotor of rotary machines is local run out (bending). To remove this bending, flame straightening processcan be used. In this method, by heating the rotor at the maximum bent point, bending is fixed to some extent due to thermal gradient created and local plastic deformation. One of the serious limitations inresearch in this field is expensive and scarce hardware which has limited empirical and theoretical scope of the research. In this study, finite element simulations of the process on sample rotors are examined. In these simulations, heat flux on the heating point of the rotor is assumed as normal Gaussian distribution, while in previous studies, flame’ sheat flux was considered as constant. To verify the results of this study, experimental tests have also been arranged. Simulation results with the assumption of Gaussian flux show more consistency with the experimental results.

In this research, using a mesh free particle method based on Lagrangian formulation called smoothed particle hydrodynamics (SPH), sand behaviour on the transformation of sandy beaches was simulated. In this paper, weakly compressibility condition was used for SPH algorithm. This algorithm is based on the application of Tait equation of state rather than Poisson’ s equation for pressure calculation. In this research, sand behaviour was evaluated as a non-Newtonian fluid. In the validation process, flow under a gate, a dam break and sedimentation problem as a water-sediment two-phase flow were investigated. The results were validated with experimental data and numerical values and a good agreement was observed. The appearance of sandy beaches with given physical and rheological characteristics under the effect of a sinusoidal wave generator pedal was modeled under yield stress values of τ y = 200 Pa and τ y = 1000 Pa at different times. The shape of the simulated bed changed rapidly under the yield stress of τ y = 200 Pa, so that the form of the bed ripples reached a relative stability after 2-4 seconds.

Friction stir welding parameters such as is rotational speed, traverse speed and axial tool offset play as the main roles in achieving joint properties. In this research the effect of axial tool offset and depth of tool shoulder on the quality and mechanical properties of joint resulted from friction stir welding of 2 mm thickness to 4 mm thickness and 2mm thickness to 6 mm thickness of 6061-T6 Al alloy was investigated. It was shown that tensile strength of joints differs by varying the axial tool offset. When tool offsets there are in the thicker part, large discontinues particles could be observed in the stir zone which caused some cracks at the weld surface and therefore reduced surface quality and mechanical properties of joint. The best surface quality and mechanical properties were resulted from the tool offsetting in thinner part. The depth of tool shoulder is an important factor in heat generation, material extrusion under the shoulder and material flow during friction stir welding. At lower depth of shoulder weaker mechanical properties were observed which may be resulted from lack of sufficient heat generation and material flow at this situation.

In this study, the effect of warm air blowers on suppressing of heat losses and also downdraught for the buildings with exterior large windows was analyzed and compared. The air ducts were mounted at different locations besides the window at floor plenum, ceiling plenum and side walls. The simulation of flow and temperature fields for a two-person office room was carried out through computation fluid dynamic method. The thermal performance of these systems and analysis of thermal comfort were simultaneously accomplished based on ISO 7730 and ASHRAE standards. The inlet air temperature ranged 22-26° C for the three systems and the results were compared. The results show that the comfort air temperature was almost uniformly distributed the entire room for the systems with air ducts at floor and ceiling plenum. Also, the values of PMV and PPD for this system were lower than 15% in the occupied region.

Orifices are one of the common flowmeter for fluid flow measurement in industrial piping. Selection the suitable turbulence model has very important to achieve good accuracy of flow measuring in numerical simulation. This paper describes numerical simulation of the flow through a circular orifice in pipe by using computational fluid dynamics (CFD) with various turbulence modeling. Therefore the orifice in pipe is simulated in Ansys CFX 15 on 3D mode and different turbulence models such as standard 𝑘 − 𝜀 , 𝐵 𝑆 𝐿 , 𝑆 𝑆 𝑇 and 𝐵 𝑆 𝐿 𝑅 𝑆 𝑀 are employed. Via comparison of these results with experimental data and some valid numerical results, it can be found that the standard 𝑘 − 𝜀 model is the best agreement with experimental data. Also discharge coefficient of orifice is compared with standards ISO 5167 and ASME with about five percent error. In this model, maximum velocity is occurred downstream of orifice at distance of nearly one-time diameter of orifice hole. In this section the velocity of fluid is more than four times of the velocity at inlet the pipe.