JOURNAL OF MECHANICAL ENGINEERING
Year:2019 | Volume:48 | Issue:4 (85) |Papers Count:40

In this research, the effects of non-gray radiating gases on mixed forced and free convection heat transfer in an inclined duct with separation are studied. Distributions of absorption coefficients across the spectrum are obtained from the HITRAN2008 database. The full-spectrum k-distribution method (FSK) is used to account for non-gray radiation properties, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. In addition, the effects of duct inclination on the hydrodynamic and thermal behaviors of fluid flow are presented graphically for both gray and non-gray medium situations. The results show that increasing in the duct inclination leads to a considerable increase in the values of friction coefficient, and convective, radiative and total Nusselt numbers. Also, the results of gray medium are compared with non-gray results as a real case. This comparison illustratesthat the difference between the results of these mediums enhances by increasing the duct inclination, such that the highest difference between the results is related to the vertical ducts.

In the present study, block-diagram simulation of a reference horizontal axis wind turbine with pitch-regulated mechanism is presented. The aim of this simulation is modeling of wind turbine subsystems to investigate the transient behavior of the turbine under unsteady incoming wind. Analytical approximation model is used to estimate the output power coefficient. In addition, PID controller is imposed to regulate the output power via changing the blade pitch angle. Governing equations of the mechanical part (i. e. gearbox), electrical part (i. e. three-phase doubly fed induction generator), aerodynamic and controller models are implemented in LMS AMESim software package. The model uses a purely torsional multi-body simulation to show the dynamic behavior of gearbox. The proposed model is used to investigate the rotor transient behavior as well as the controller performance under the conditions that the wind speed changes linearly from 21 to 8 m/s during 130 seconds. The results show acceptable accuracy in comparison with the reference data.

The main purpose of this study is to predict the nonlinear dynamic behavior of a coaxial rotor system supported by two active magnetic bearings (AMBs) and contact with two auxiliary bearings. The system is modeled by ten degrees of freedom in two perpendicular lateral planes. In this model, gyroscopic moments of disks and geometric coupling of the magnetic actuators are included. The nonlinear equations of motion are developed using the Lagrange’ s equation and solved by the Rung-Kutta method. Then, the effects of unbalance, proportional and differential controller gain on the dynamic behavior of the coaxial rotor-AMB system are investigated by the dynamic trajectories, power spectra, Poincare´ maps and bifurcation diagrams. The results indicate that the unbalance and controller gains have significant effects on the dynamic responses of the coaxial rotor-AMB system. Also, the results of analysis reveal a variety of nonlinear behavior such as period-2, quasi-periodic motions, as well as jump phenomena that can give some insight to engineers and researchers in designing and studying coaxial rotor-AMB systems or some turbo-machinery in the future.

In this study, three kinds of gas turbine cycles coupled with multi effect evaporation thermal vapor compression desalination (METVC) are investigated. The first system is a simple cycle gas turbine (without steam injection). In the second and third system, a cycle gas turbine with steam injection into the combustion chamber (STIIC) and a gas turbine with steam injection before the combustion chamber (STIBC) are considered, respectively. At the first, design parameters such as compressor pressure ratio, the temperature of combustion product and pressure of motive steam was fixed and the performance of these three models are evaluated. Then, using a developed computational code, the effect of these parameters on exergy efficiency, output power, exergy destruction and important parameters of fresh water and power production are studied. The results show that exergy efficiency for models with steam injection increased 4% compared to the model without steam injection. In addition, for STIIC and STIBC, the rate of irreversibilities will reduce to 80. 22 and 81. 26 MW where this parameter is 82. 72 MW for without steam injection model.

Centrifugal pumps have many applications in various industries. Therefore, in this study, the effect of different blade numbers on the centrifugal pumps performance has been numerically investigated. The flow in impeller and volute has been investigated numerically by ANSYS-CFX commercial code. A numerical study has been done using Finite volume method and K-ω SST turbulence model. Rotating and stationary frames have been used to analyze flow in impeller and volute respectively and the results have been coupled by frozen rotor. Five impellers with 5, 6, 7, 8 and 9 blades were tested. Six-bladed H-Q curve of centrifugal pump was compared with a real model. Due to the small numerical error, we could use simulated pump with high reliability. The results indicate an increase in the head and a decrease in efficiency of the pump with increasing the blade number. Finally, the optimum number of blades for the pump has been obtained.

In this research, 3 layer composite weld containing Titanium diboride (TiB2) on low carbon steel (ST37) was carried out through flux cored arc welding via flux cored electrodes containing 100% TiB2 and 50-50 TiB2-Fe. Then, wear and microhardness tests were used for surviving hardness and wear behavior of samples. The obtained results showed that by increasing volume percent of TiB2 in microstructure, the hardness of layers increased. Also, the highest wear resistance belonged to third layer of sample with 50% TiB2 and thereafter, belonged to first layer of sample with 100% TiB2. The scanning electron microscopic investigation of samples wear surfaces indicated that by increasing volume fraction of TiB2 into layers, the depth wear scratches in the third and second layers decreased and segregation of wear debris in these layers increased, compared with first layer. Also, it was found that by increasing the layers, wear mechanism changed from ploughing to cutting.

The aim of this paper is the optimum design of a single circumferential groove for NASA Rotor 37, a transonic compressor. The design variables are the width, the depth and the position of the groove. Also the objective functions are the stall margin and the peak efficiency. The total pressure ratio at the near stall condition is used as a criterion to choose the optimum design. Neural networks are used to model the relation between design variables and objective functions. 123 various design points are simulated by CFD and the results are used to train the networks. Afterwards, a multi-objective genetic algorithm is used to optimize the design based on the maximum stall margin and the minimum reduction of the peak efficiency. After sorting the Pareto front according to the stall margin value, the first design point whose total pressure ratio is larger than the smooth wall condition, is selected as the optimum design. Simulation of the compressor with optimum groove shows the increase of the stall margin by 6. 2 percent with negligible effect on the efficiency.

During the past decade researchers have investigated vibrations of piezoelectric and piezomagnetic nanobeams. In addition to displacement fields, usually the electromagnetic fields are also considered one dimensional because the small ratio of height to length of the beam geometry. This makes the implication of electromagnetic boundary conditions on the upper and lower faces of the beam rigorous. In this study free vibration of Timoshenko beam having Magneto-Electro-Elastic properties laying on Elastic foundation has been studied considering one dimensional displacement fields and two dimensional electromagnetic fields. State equations which are a Integro-Differential couple has been discretized using a modified radial point interpolation function. Frequency response and the mode shapes have been queried for Dirichlet and Neumman boundary conditions with two conditions open circuit and closed circuit. . Obtained frequencies have been compared with results of the corresponding fully one dimensional problem.

In the present paper, the turbulent reacting flow within a porous media is modeled by developing a computer code. Separate energy equations for fluid and solid phases and the k-ε turbulence equations have been applied by non-thermal equilibrium and double decomposition methods, respectively and the fuel consumption rate is obtained from one-step Arrhenius equation. Turbulence modeling helped to obtain closer results compared with experimental data. Turbulence caused an increase to the effect of diffusion and heat transfer in the preheat zone which resulted in a lower maximum temperature in the combustion zone. In the case of excess air combustion, no temperature difference is observed in the upstream zone. The results showed that with decreasing porosity in the combustion zone, the fluid temperature along the burner decreases. That is, for the porosities of 0. 95 and 0. 7 the maximum temperature is decreased by 16% and 18% respectively. The maximum temperature difference in the case of excess air of 67% is about 400K which occurs at x=0. 01m and for the case of no excess air is about 200K at x=0. 045m.

In this paper design and manufacture of an experimental setup of rehabilitation device for isokinetic exercises, using pneumatic actuator, is presented. In isokinetic exercises, limb’ s movement must be provided at a constant speed. For this type of movements, the actuator should provide an accommodating resistance against patient effort. Therefor the main challenge is speed controller design for actuator in the presence of disturbances logged by patient. This goal is achieved by using electrical actuators at the commercial levels. But beside the high cost of this instruments, low softness of electrical actuators is the main problem of using them in rehabilitation devices. Using pneumatic actuators decrease the final price and benefits the system by pneumatic advantages such softness and high power to weight ratio. This requires overcoming speed control problems in presence of the considered challenges. In this research modeling and speed control of pneumatic actuator has been studied for contraction and expansion mode of muscle. Experimental results take advantages of servo pneumatic actuator for providing isokinetic trainings in leg rehabilitation as well.

In this paper a beta type Stirling engine for cogeneration of heat and electricity is proposed. The Stirling engines have advantages such as flexibility of fuels and heat sources, low noise level, and higher thermal efficiency than internal combustion engines. In these engines, in power production process, some heat is released to the environment, which can be recovered, and therefore the Stirling engine has a good potential to be used in combined heat and power systems. In this research, the non-ideal adiabatic analysis has been used for the Stirling engine and for enhance the accuracy of the model, the frictional and thermal losses have been considered. Non-ideal adiabatic analysis, was performed using a numerical code developed in MATLAB software. To validate of the model, the geometrical and operational specification of the GPU-3 Stirling engine was used and the results were compared with experimental results and other previous models. Then a beta type Stirling engine was proposed for the combined heat and power system in residential applications. Also, the effect of engine rotational speed, regenerator length and temperature of heat source on electrical and CHP efficiency were investigated and the appropriate amounts of operating parameters were selected. Finally, the electrical power and thermal power were obtained 11263 W and 21653 W, respectively with electrical efficiency of 27. 78% and CHP efficiency of 81. 19% efficiency for this cogeneration system.

Sliding mode control, due to its great robustness, is very effective approach for underwater vehicles. Due to complexity of underwater environment and existence of disturbance, robust controllers such as sliding mode control have appropriate results in experimental tests. In this paper, sliding mode control has been used for depth channel and steering channel. It has been used for linear and nonlinear systems with parametric uncertainty and sensor noise. Kalman filter observer has been applied to estimate the values of state variables of the underwater vehicle dynamic system that is excited by stochastic disturbances and stochastic measurement noise. Simulation results show that the proposed method is effective in control of depth and steering of the AUV and show that this method can obtain high precision tracking control performance.

In this research work, the effect of nanoclay addition on the flexural properties of E-glass/epoxy grid-stiffened composites (GSCs) was investigated. Firstly, in order to the formation of a stronger interface between the matrix and nanoclay particles, the nanoparticles were modified by a silan coupling agent (3-glycidoxypropyltrimethoxysilane/3-GPTS). Unidirectional glass fibers as rib reinforcement, plain glass fibers as skin reinforcement and a mixture of epoxy resin and 0, 1, 3 and 5 weight percent surfacemodified nanoclay as matrix part were used to produce GSCs. The surface modification trend of nanoclay particles was confirmed by Fourier transform infrared (FT-IR) and X-ray diffraction (XRD). Obtained results showed that the addition of the surface modified nanoclays caused the improvement of stiffness, maximum load and energy absorption properties of GSCs, and the maximum improvements was related to the specimen with 5 wt. % nanoclay. It was also found out that a considerable portion of energy absorption was occurred after the primary fracture at peak load, manifesting the high damage tolerance of the grid composite structures.

Internal thoracic artery and small saphenous vein are two options to be used as a coronary artery bypass grafts. The purpose of this paper was to investigate the viscoelastic properties of the small saphenous vein and internal thoracic artery under compression and tension at body temperature. The dynamic mechanical analysis was used to measure the viscoelastic properties of the ITA and SSV at each temperature and loading frequency range. Storage modulus, loss modulus and phase angle of the ITA and SSV were measured at the body temperature and under a periodic load with frequency ranging between 1 and 2 Hz. Storage and loss modulus of the SSV was higher than ITA. Furthermore SSV was stiffer and had higher internal friction in compression. While ITA was stiffer in tension, its compression and tension’ s loss modulus were about the same. Results of this research can help to improve the understanding of the mechanical behavior of ITA and SSV.

In the present paper the forced convection heat transfer of non-Newtonian Power-law fluid through an isothermal tube is studied analytically. Exact solutions for thermally developing and fully developed Power-law flows are presented. In the case of thermally developing flow, the energy equation is solved by applying the Separation Method resulting in a homogeneous system of differential equations including Sturm-Liouville equation. Temperature distribution of Power law flow through tube is presented for two states of shear thinning n=0. 2 and Newtonian n=1in closed form solutions. The diagram resulted of plotting the local Nusselt number versus the dimensionless tube length for both of two considered states, represents this fact that increasing of the Power law index the Nusselt number is decreased. For the fully developed Power law flow after solving the energy equation finally an ordinary second order differential equation is derived in which the flow temperature distribution is determined by Modal analysis. For different values of Power-law indices firstly, the Nussselt number is determined by wall thermal boundary condition and then the flow temperature distribution is presented by Frobenius method. The results show that the Nusselt number and maximum temperature are decreased by increasing the Power-law index meaning a decrease in the tube heat transfer.

In this paper, the behavior of energy absorption and maximum force of multi-walled and multi-cell tubes with different cross sections have been studied. Energy-absorption behavior has been simulated using finite element method in ABAQUS software. Numerical simulations with quasi-static load assumption for circle and square-shaped peripheral sections were performed. In the first step, the numerical results of applied force displacement curve caused by movement of the upper barrier have been compared with existing experimental results in different sources. In addition, the tube geometry has been changed to obtain better energy absorption. Then, several models of multi-cell sectins have been modeled. Using multi-cellular results indicating a high percentage of specific energy absorption, three types of adsorbents were designed with specified thickness parameters, vertex angle, tube spacing and number of cells. Using the design of experiments, the results of the simulation of these three absorbers were extracted with different parameters. The objective function equations are extracted from experimental design results according to the parameters considered using the response procedure method. Also, by using the genetic algorithm on the equations obtained by the response surface model, the optimal absorber characteristics were determined and correlated with the simulation results.

Increase of fuel price and limitation of carbon dioxide emission caused development of different techniques to enhance the thermal efficiency of internal combustion engines. One of these techniques is conversion of the waste thermal energy in the engine to mechanical or electrical energies. This investigation concentrated on simulation, examination and application of waste heat from exhaust gases of MTU-16V internal combustion engine in an organic Rankine cycle based on the efficiency of first and the second laws of thermodynamics. Using 862 kW power of exhaust gases waste heat, the net powers of working fluids including R600a, R600 and R245fa were evaluated and the highest net output power was calculated to be 37. 23 kW for R245fa working fluid. This working fluid increased the output power to approximately 2% and 6% in comparison with R600 and R600a fluids, respectively. Moreover, the mentioned working fluids were examined for volumetric flow rate and required volume contraction, where the lowest value was obtained for R600a. On the one hand, the effect of turbine inlet temperature on the volumetric flow rate, and effect of turbine inlet pressure on energy efficiency, exergy efficiency and irreversibility of the whole system were investigated. On the other hand, the influence of ambient temperature increase on irreversibility of each system component was studied. Based on the obtained results, R245fa fluid showed the best performance to be used in organic cycle from the viewpoint of the first and second laws of thermodynamics.

In this study, the effect of aluminum alloying element on the microstructural changes, mechanical properties and fatigue life of Hadfield steel was investigated. For this purpose, 2 blocks castings were prepared from Hadfield steel (without Al and with 1. 68 wt% Al addition) by using coreless induction furnace. After the casting, all the blocks were austenitized in 1100° C for 2 hours and immediately quenched in the pure water. In the next step, uniaxial tensile test, bending fatigue test and hardness test by vickers method were conducted on specimens. Microstructure evaluation was conducted by optical metallography and the fractured surfaces were observed by scanning electron microscopy. As a result, it was found that the sample containing 1. 68 wt% Al had more hardness and greater yield strength but tensile strength, flexibility and fatigue life of lesser compared to sample without Al addition. So, scanning electron microscopy images indicated the occurrence of ductile fracture in tensile test for both samples and was increased fatigue crack growth in the fatigue test due to the addition of aluminum to chemical composition of Hadfield steel.

The effect of magnetic fields on combustion is a well-known fact. In presence of magnetic field, the paramagnetic species change kinetics and equilibrium properties of chemical reaction in combustion. Because NO and O2 are paramagnetic species and other elements and methane are diamagnetic, applying a magnetic field on combustion cause to change its chemical reactions. In this study, the effects of uniform magnetic field on one stage methane combustion reaction has been studied numerically by means of Gibbs free energy minimization. The results suggest that the uniform magnetic field has significant effects on paramagnetic species and their production is influenced, dramatically. Methane combustion reaction with uniform magnetic field leads CO molar fraction to be increased and CO2 concentration to be decrease. The results indicate that the NO pollutant formation also can be decreased while the temperature is increased. Increasing the uniform magnetic field from 0. 06 to 0. 08 causes molar fraction of this pollutant to decrease by 88. 2%.

The behavior of concrete subjected to impact load, is different compared to the behavior under static loading. A test program was carried out to determine static and dynamic properties of rubberized concrete. In this study, waste tire rubber particles were replaced with fine aggregate in concrete mixture in 3 sizes, 0-1, 1-3 and 3-5 mm and in volume ratio of 0%, 10%, 20%, 30%, 40% and 50%. Static and dynamic tests are done with hydraulic and drop hammer machines. Results of compressive and flexural strength, velocity of ultrasonic wave, Static and dynamic modulus of elasticity, strain and Static and absorption energy of rubberized concrete are determined. The results indicated that: larger rubber particles in replacement of sand have better results than smaller sizes. Also increased in rubber content, decreased the unit weight, compressive strength and static and dynamic modulus of elasticity of rubberized concrete. Using rubber particles in concrete significantly increased the ductility and strain capacity of concrete. In addition in this study equation of impact test with using mass-spring modelling, was determined.

Deep drawing is an important and useful method to form different configurations like bath tub, shell box and etc from sheet metal. Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. In this process, the dimension and the blank of initial sheet metal must be obtained to reduce the material waste. The aim of this paper is to obtain the blank curve of rectangular plates. First, the actual simulation of deep drawing process is done by ABAQUS software. Then, by removing the non-deformed elements of the plate and exporting the remained sheet to the Solid Work software, the blank curve is determined. In order to check the method, the experimental deep drawing process was done on two sheet metals, one with rectangular configuration and the other with the obtained blank. The comparison shows the reduction of material waste (about 18. 75%) for the sheet with the suggested blank.

There is always a difference between the numerical, theoretical and experimental values of a physical quantity which is due to measurement errors. Electromagnetic hyperthermia using micro/nano particles is not an exceptional case. This deviation could affect the temperature distribution of domain. In this paper, the deviation of any effective parameter on temperature distribution, including concentration, injection area and radius of micro/nano particles, power and frequency of electromagnetic field are studied and uncertainty analysis is performed. The study was based on the induction heating by micro/nano particles in an electromagnetic field hyperthermia. The finite difference method was used to solve the equations numerically. Results show that the measurement of parameters such as electromagnetic field power, radius of micro/nano injection region should be done accurately.

In the present study, Al/Cu/Mg layered composite was produced through cold roll bonding (CRB). Also, mechanical properties, fractography, and microstructure were investigated through uniaxial tensile test, microhardness, scanning electron and optic microscope. Results of carried out tests, showed the value of tensile strength and microhardness for Al/Cu/Mg layered composite. Comparing to initial Al 1050, pure Cu and Mg AZ31B, the value of tensile strength increased. The main cause of this increase was applying high strain and cold working. Value of tensile strength for Al/Cu/Mg layered composite received 220. 3MPa that compared to initial Al 1050 and pure Cu and Mg AZ31B, enhanced 144%, 23%, and 29%, respectively. Results of SEM demonstrated that ductile fracture mechanism governed for Al and Cu layers, but fracture surface of Mg layer was a brittle fracture.

Clearances between cylinder and piston, and pressure difference between top and bottom of piston causes a flow through the crevices termed blowby. This phenomenon results in cylinder pressure and temperature drops; some unburned mixture remains in the crevices leading to inconvenient usage of the mixture in firing cycle and reduction in engine performance. In the current work a thermodynamic blowby simulation code validated in motoring condition has been used to study and predict the blowby of XU7JP/L3 engine in terms of engine speed and engine working life. Some geometrical measurements of cylinder-piston-ring pack were performed in two engine operations, 70000km and 200000km, to apply the code after required corrections. The obtained results showed that the values of the blowby geometry increased with enhancement of engine life and engine temperature. Increasing engine life enhanced cylinder leakage significantly so the leaking value of 200000km reached to 4 times greater than that for new engine life. Also the mass lost through second compression ring at 70000km and 200000km working durations increased to about 7 and 15 times of that for new engine one, respectively.

Dry electrical discharge machining is a sustainable machining process that is used gas medium such as air or Nitrogen instead of liquid dielectric mediums that are mainly based on oil derivation. In the current research, first each of three main responses including material removal rate (MRR), surface roughness (Ra) and radial overcut (ROC) have been optimized considering the effects of six main input factors including current (I), pulse on time (Ton), duty factor (D), spindle rotational speed (N), gas pressure (P) and the gas type. . Regarding the input factors, there are five quantitative and one qualitative input factor (gas type). So, in addition of air as most common dielectric medium, Nitrogen and mixture of Argon and air have been investigated as the other input factors of this parameter. The main purpose of this study is the multi objective optimization of dry electrical discharge machining responses by using the Grey relational analysis based on the Taguchi method. The results of this optimization method show the optimized level at I=12A, Pulse on time (Ton)=100  s, Duty factor (D) =66, Gas Pressure (P) = 3 bar and Spindle rotational speed (N)= 300 rpm and Nitrogen as the dielectric medium. The confirmation experiment at the optimized level by this method depicts that the optimized level has the maximum grey grade, hence it confirms the accuracy of the optimized level by Grey Relational Analysis method. . Also, regarding the equal weights of responses and considering the same effects of the surface roughness and radial over cut that both of them have the smaller the better characteristics, the optimization results in more effect on these responses in comparison with material removal rate.

Due to the cold air in the cold season, natural gas consumption will be greater than the standard mode and much higher than the normal. In this situation for networks comes a critical state, consumption increased as well as pressure reduced for natural gas, this condition has always been one of the main problems to deliver natural gas to various locations. In this study, a natural gas pipeline network in critical condition has been investigated. The proposed method for the analysis of pipeline network compared with previous studies, the validation results show the accuracy of 0. 37% for the proposed method. The effect of important parameters on the pipeline network in critical state such as: friction factor and natural gas composition have been studied. The results show, the friction factor has a great impact on the natural gas pipeline network, also natural gas with higher molecular weights have less pressure drop in the all of natural gas pipeline network’ s nodes.

In this manuscript, in-plane normal and shear interlaminar stresses in composite Timoshenko beam under transverse loading placed on the elastic foundation are studied. The elastic behavior of interlaminar stresses at the interface of adjacent layers is modeled by radial and tangential springs of high stiffnesses. In the first, governing equations and boundary conditions are derived by the virtual work principle and then they are solved by generalized differential quadrature method. By calculating the displacements of the beam laminates, the interlaminar stresses, which are the reaction of radial and tangential springs between adjacent layers of the laminated beam, are obtained. Also, the other stresses of the beam are calculated and drawn by equilibrium equations. Comparison between the results of presented analysis for a beam the and the results of three dimensional elastic solution is shown that the presented method has good accurate to predict the in-plane stresses. The results showed that Winkler effects on interlaminar stresses are lower than Pasternak effects. Also, the elastic foundation caused decrease and increase for interlaminar shear stress and normal stress, respectively.

Investigation of the effect of the STF on increasing of frictional energy on Kevlar fibers as one of the main factors of decreasing permeability in ballistic impacts is very important. In this study, for understanding the effect of STF on decreasing the permeability of fibers by increasing the frictional energy between fibers and projectile was modeled by ANSYS15 software. The projectile was impacted to the target with velocity of 350m/s. In both models the projectile penetrated and crossed the target. In modeling with Kevlar 29 fibers, the output velocity of projectile was about 341. 88m/s and in second modeling the output velocity was 306. 43m/s. This model was compared with previous experimental model; ballistic limit of Kevlar fiber without STF is also compared. The results demonstrated the effect of STF on decreasing the permeability of Kevlar fibers because of increasing the friction coefficient. According to the results, increasing the friction coefficient of more than 3 did not have significant effect on decreasing permeability.

In this study, the thermal characteristics of two impinging flame jets are investigated. For the flame structure and temperature field analysis, a non-contact method named Mach-Zehnder Interferometry is used. Mach zehnder method is utilized to determine the effective parameters of flame structure in different amount of Reynolds number and equivalence ratio. The hydraulic diameter of the burners is considered 1. 3 mm with 20 mm length and 10 mm width. The angle between two burners is 77 degree. The effect of fuel/air ratio is investigated, when Reynolds number is 70 and equivalence ratio varies between 0. 8 and 2. 5. Maximum temperature and velocity occurs in equivalence ratio of 1 but at this point, increasing of Reynolds number leads to enhance the maximum temperature and at the same time the growth of the maximum temperature domain

One of the goals of computational fluid dynamics for turbomachinery is the prediction of their performance such as the ratio of pressure, efficiency, and the nature of the flow. In this research, which consists of two parts, in the first part were performed steady and unsteady simulation methods on stage of the axial flow turbomachinery and results validated. In this regard, two numerical steady methods including a frozen rotor and stage, and three transitional numerical methods including standard transitions, time transformation, and profile transformation were used. Transient methods provided a more accurate prediction. In transient methods, it was observed that transient effects including wake, stator leading edge bubble and flow separation can be obtained more clearly, which were found to be weaker in other methods. In order to solve the numerical flow field used of structured grid and SST turbulence model was used for modeling turbulence. In the second part of the paper, 9 changes were investigated to the geometric changes, such as roughness in the blade surfaces, clockwise and counter-clockwise rotation of the foil sections, the creation of radius in the roots of the blades, and create of the axial distance between the blades.

In this paper, entropy generated during a continuous two-dimensional boundary layer flow on a porous flat plate surrounded by a variable heat flux is studied through a similarity solution. This study is presented for modeling of the cooling process of metal surfaces with porous coating that is widely used in industry. Using similarity variables, the continuity, momentum and energy equations are transformed into ordinary differential equations. To validate the proposed solution, results are compared to the existing studies. The effects of various parameters such as heat flux (q􀭵 ), suction parameter (S), Prandtl number (Pr), Stretch parameter on the plate velocity (U), temperature distribution (T) and dimensionless entropy (Ns) are shown and discussed in detail. Bijan number is used as an important parameter for qualitative study in cooling process on porous surfaces. The increase of Bijan number is introduced as a measure for the increase of cooling rate. The results of the study show that when Prandtl number increases, the entropy will decrease which leads to a decrease in Bijan number. However, an increase in permeability of surface causes to increasing suction parameter and Bijan number.

Natural convection of a two-dimensional laminar incompressible fluid flow in a square cavity with different corrugated on the bottom wall has been investigated by finite element method in Comsol software. The top and the bottom walls are insulated, the left and the right walls are maintained at a constant temperature Tc (TH> Tc). In this study, cavites with different corrugated by shapes of rectangular, trapezoidal, triangular and sinusoidal are studied for different amplitude of shapes of blocks, periodicity amplitude and aspect ratio and Rayleigh number. The air is chosen as a working fluid. Hydrodynamic and thermal behavior of fluid is analyzed in form of streamlines, isotherms and the average Nusselt number. Results based on this numerical study showed that the by increasing the Rayleigh number the rate of Nusselt number increases. There is an optimized range for increment rate of heat transfer by increasing the amplitude of shapes of blocks and periodicity amplitude. Also the maximum rate of heat transfer occurs in sinusoidal shape of cavity.

In this research, effects of introducing 0. 5wt% reduced graphene oxide (RGO) reinforcement on the creep behavior of the adhesively bonded joints are investigated at 25oC and 55oC. To this aim, uni-axial creep tests are conducted, and creep deformations of the bulk specimens produced via the neat adhesive and adhesive-RGO composite are recorded. Also, creep tests are performed to obtain creep behavior of the single lap joints. Furthermore, results of the bulk specimen tests are used in a finite element based numerical analysis to simulate the creep behavior of the joints. Results show that, a significant decrease in the creep deformations along with a remarkable increase of 30% in the creep life time occurs in the reinforced joints. Finally, comparing the numerical results and experimental data shows that the numerical analysis accurately simulates the creep behavior of the joints.

The mixed convection heat transfer and the entropy generation in a rhombic enclosure filled with the Cu-water nanofluid in presence of heat absorption or generation is investigated. The bottom wall is hot, the top wall is cold and the skewed walls are insulated. The top wall is moving from left to right at constant speed of U0. The computational grid is generated with the mapping of the geometry into a square domain. The governing equations are formulated in terms of the dimensionless stream function, the vorticity, and the energy and have been numerically solved using the finite difference scheme. The rhombic angle, the Richardson number, the volume fraction nanoparticles, and the heat generation or absorption coefficients effects on the heat transfer and fluid flow characteristics are examinated. The results show that the increase of the nanoparticles volume fraction leads to the increase of the average nusselt number, the total entropy, and Bejan number. When the Richardson number is 0. 1 and for all the nanoparticles volume fraction, the Nusselt number has maximum and minimum values at the angles of 120° and 30° , respectively. In addition, for all the volume fractions of nanoparticles and skew angles except the angle of 60 degree, the Nusselt number, the total entropy and Bejan number increase with the decreasing of the Richardson number. When Ri=0. 01, Nusselt number is increased and decreased by the heat absorption and generation, respectively.

Friction stir process (FSP) is a solid state process in which many parameters play important roles. Al 7075 is one of the strongest alloys. In this paper the effect of the traverse and rotational speed on the mechanical properties of Al 7075 are investigated in submerged and ambient conditions. The friction stir process is done with a threaded pin. The pin diameter, pin length and diameter of the shoulder were 8, 5 and 18 mm respectively. The experimental results showed that the normal and submerged friction stir process with optimum parameters can increase strength and elongation of Al7075. In the submerged and normal friction stir process tensile strength and elongation were increased 14. 85, 128. 57, 11. 71 and 138. 1 percent respectively. In most of the specimens Vickers micro hardness was increased regard to base metal. The submerged friction stir process generally showed better results than the normal friction stir process. In submerged friction stir process the maximum temperature was reduced about the 60 percent in comparison of the normal friction stir process.

Researches show that the water or steam injection and regeneration increase the thermal efficiency of the gas turbine cycles. However, there are very few computational fluid dynamics investigations for these methods. In this study, the effect of steam injection and regeneration on the thermal efficiency and Nox emission are independently investigated both numerically and thermodynamically. Ansysy Fluent 16 software has been used for numerical simulation. In this paper, combustion occurs in a diffusion type flame. Water steam 2000 C with flow rate 30 kg/s is injected into the combustion chamber and the combustion chamber inlet air temperature is 4600C by using regeneration. Results show that the thermal efficiency increases 4. 45% and 6. 9% with regeneration and steam injection, respectively. However, results show that Nox emission for the steam injection gas turbine cycle is 3. 5 times of regenerative cycle and 8. 5 times of simple cycle.

In this paper, a novel biogas steam reforming system for producing hydrogen is presented. The mixture of biogas contains a large percentage of Methane, Carbon Dioxide and negligible amounts of other gases. A thermodynamic comprehensive modeling (energy and exergy) was done on the suggested system. The impact of various system parameters in the mixture of biogas such as; temperature, and molar ratio of carbon dioxide to methane is also done on the hydrogen production rate, energy and exergy efficiencies of the entire system. The results show that by increasing the temperature of the steam reforming reaction in reactor, in a constant molar ratio of carbon dioxide to methane in the mixture of biogas, hydrogen production rate and energy and exergy efficiences are increased. Moreover, increasing the molar ratio of carbon dioxide to methane in the biogas combination at high temperatures, resulted a decrease in hydrogen production per mole of methane and so the energy and exergy efficiencies of the entire system (decreased). As well as the most energy and exergy efficiencies of the whole in the case of hydrogen production is maximum, achieved to 52% and 42%; respectively.

In today’ s world too much energy is consumed to provide comfort conditions inside the buildings and this makes it necessary to estimate the energy consumption and recommend appropriate strategy to reduce it. One way of calculating the amount of energy consumption for providing comfort conditions is to employ simulated programs such as EnergyPlus and DesignBuilder. In this paper one authentic case study has been chosen and by applying DesignBuilder program, the amount of energy consumption for its cooling condition on 1st of July in three different cities based on two different strategies has been simulated and their effects on electric energy consumption have been compared. The first strategy is to employ the equation of estimating heat transfer via solar radiation and using overhang shades (6 different thicknesses) to reduce the area of the building exposed to solar radiation and reducing the heat gained from it. The second one is to apply the equations of Fourier's law in which the amount of reduction in heat transferred to the building by utilizing heat insulations in 5 different thicknesses is calculated. The results showed that the second strategy has much more superiority over the first one considering in Ahvaz and Tehran cities, but for Tabriz, the difference between two strategies is less. Furthermore the results obtained in Ahvaz showed that our conception of reducing the energy consumption by employing overhang shades is not always right. And employing heat insulation even by the thickness of one centimeter is more effective.

In this study, an improved high-order theory is presented for buckling analysis of sandwich conical shell with thin FGM face sheets and homogenous soft core. First shear deformation theory (FSDT) used for the face sheets and cubic functions are assumed for the transverse and in-plane displacements of the core. The nonlinear Von-Karman type relations are used to obtain the strain components. The equilibrium equations are derived via principle of minimum potential energy. Analytical solution for static analysis of simply supported sandwich conical shells under axial in-plane compressive loads is performed by using Galerkin’ s solution. The comparisons show that the present results are in the good and better agreement with the results in the literature results.

An investigation has been carried out to study the heat transfer and pressure drop characteristics of MWCNT-Base oil Nano-fluid flow inside horizontal rectangular channels under constant wall temperature. The effect of different parameters such as mass velocity, aspect ratio of rectangular channels and Nanoparticles concentration on heat transfer coefficient and pressure drop of the flow is studied. Observations show that the numbers of Graz higher with increasing concentration of nanoparticles in oil, the increase is much higher heat transfer switch. And also shows that the pressure drop depends on the amount of nanoparticles and aspect ratio tube. By increasing the aspect ratio tube, the convective heat transfer coefficient increases very well.