Sharif Digital Repository

Real loading- unloading behavior of an A5083 aluminum alloy was recorded experimentally. This real behavior was incorporated in the variable material properties (VMP) numerical algorithm to predict residual stresses resulted from autofrettage and shrink fit in two kinds of autofrettage compound tubes. Using an analytical method, residual stresses induced by bore material removal via machining were calculated. Using developed VMP code and isotropic hardening rule in both autofrettage compound tubes, residual stresses resulted from shrink fit and autofrettage processes and via post machining, were estimated. Machining process simulation was performed for 10 mm bore material removal. ANSYS... 

Radial forging is an open forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, as well as for creating internal profiles for tubes such as rifling the gun barrels. The radial forging of tubes is usually performed over a mandrel to create an internal profile and/or size the internal diameter; but the process can also be used without a mandrel when workpiece geometry does not allow it or the internal surface quality is not critical. In some industrial applications, it may not be possible to use a mandrel inside the tubular workpiece, e.g., due to geometrical limitations of the workpiece. In this study, finite element modelling is applied to model the... 

When properties of the displacing fluid are considered, the rising profile of the penetrating fluid in a capillary tube deviates from its classical Lucas-Washburn profile. Also, shape of capillary tube can affect the rising profile in different aspects. In this article, effect of capillary tube's shape on the vertical capillary motion in presence of gravity is investigated by considering the properties of the displacing fluid. According to the fact that the differential equation of the capillary rising for a non-simple wall type is very difficult to solve analytically, a finite element simulation model is used for this study. After validation of the simulation model with an experiment that... 

Swage autofrettage process is used for internal forming and sizing of thick-walled tubes designed to withstand high internal pressures. In this process, a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. This paper presents an experimental and numerical study of this process. Two dimensional axi-symmetric and three dimensional finite element analyses are used to investigate the effects of workpiece and mandrel geometry on the forming load and part quality. Experiments are carried out to validate the numerical results. © 2005 Elsevier Ltd. All rights reserved  

Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. Among parameters affecting process variables, the die geometry is of fundamental importance and greatly influences variables such as forging load, stress distribution on the dies, metal flow during deformation, and surface finish of the forged product. In this paper a generalized slab method analysis of radial forging process is presented which can handle this process with curved shape dies. Results for dies with various curves are presented and it is shown that the analysis reduces to that of Lahoti and Altan [2] when the die... 

The failure analysis of a ruptured superheater tube after 20. years service in the oil-fueled boiler, as the typical problems in power plants, was investigated. A thin-lipped rupture at failed region was observed in superheater tube. By measuring the tube's wall thicknesses far from failed region, non-uniformity was seen. The suggested main root cause of failure was fireside corrosion of the tube during the service. Because of low grade of used fuel, sodium, sulfur, and vanadium elements were observed at the outer surface, which caused continuously scale formation and reduction of wall thickness, by metal consumption. In addition, it seems that it has been worsened by occurrence of long-term... 

This paper presents an efficient way for overcoming the inaccurate path error encountered in ray tracing for site-specific indoor propagation modeling. The source is modeled using triangular ray tubes each of which consists of three rays which do not lie in the same plane. Each possible source ray inside an arbitrary ray tube is expanded in terms of the three rays defining that ray tube. The variations of the expansion coefficients during the intersections of the ray tubes with dielectric media are derived and used for correcting the paths of the rays toward the receiver. A verification example is presented which proves that the presented method has the ability to be efficiently used in... 

In this paper, entropy generation in heat exchangers used in Indirect Evaporative Coolers (IDECs) is studied. First, expressions for the rate of entropy generation in tube-type and plate-type cross-flow heat exchangers used as IDECs are obtained. Then, by introducing appropriate geometric constraints and employing thermohydraulic design equations, the variation of the rate of entropy generation within the heat exchangers is investigated. The maximum EER, outlet temperatures and the optimum sizes are obtained for several cases. The results of several experiments conducted on an optimum tube-type experimental prototype are presented and compared with the numerical data. Copyright © 2009... 

The current study examines different arrangements of vortex tubes (VTs) to get higher performances for cooling and heating. The effects of thermo-physical parameters such as inlet feed temperature and inlet/outlet vortex tube pressure on generated temperature gradient are investigated. To estimate the cold outlet temperatures, the available equations in the literature are verified against our experimental data. Moreover, we propose a new equation to estimate the hot outlet temperature based on the upper limit of hot temperature (ULHT) and the lower limit of cold temperature (LLCT), verified with experimental data as well. Further, several arrangements are simulated to obtain the minimum cold... 

Radial forging is an open die forging process used for reducing the diameter of shafts, tubes and axels. In the present research, a new velocity field was developed to analyze the radial forging process by the upper bound method. The forging load was predicted by minimizing the deformation power with regards to the location of neutral plane. The accuracy of the model was verified by comparing the predicted forging loads with experimental results published by the previous researcher. A good agreement was found between the two sets of results. © 2007 Elsevier B.V. All rights reserved  

The life prediction of equipments guarantees reliable, safe, efficient and continuous operation of thermal power plants. In this paper wall thickness of reheater tubes of boiler number 3 of Neka power plant in north of Iran are measured at several points during maintenance shut down periods. Thickness dependency vs. time has been investigated. Artificial Neural Network (ANN) as a tool has been acquired to determine this dependency. Extrapolation of thickness function vs. time applying maximum normal stress criteria results in corresponding thickness. The maximum wall reduction rates have been calculated by two schemes namely Fuzzy function (FF) and Neural Network (ANN) applying numerical... 

Velocity distributions in (r,θ) directions are evaluated by solving simultaneous simplified Navier-Stokes equations (NSE) and continuity equation (CE) in polar coordinate. The analysis is based on steady state laminar flow of thin falling liquid film on a horizontal circular tube, for cases in which traction on the film surface is considered negligible. It is a common geometry for part of engineering problems such as evaporator, condenser, absorber, generator of absorption chillers and other similar units in mechanical and chemical engineering. Knowledge of the velocity profiles is usually needed for: 1 - solving governing energy and species equations 2- estimating the average and film... 

In this paper, the internal ballistics of a solid rocket motor (SRM) including a blast tube is investigated, numerically. Effects of the blast tube presence on the performance of the SRM are studied in detail using unsteady quasi one-dimensional conservation equations. These equations are discretized and solved using upwind Roe's scheme. Any two-dimensional grain configuration can be accounted for if an appropriate geometrical input file is generated using a grain analysis program. The results are presented for several blast tube geometries  

A considerable amount of energy is lost in the parabolic trough solar collectors due to the poor capability of working fluid in full absorption of the concentrated solar irradiation across the receiver tube. A new hybrid method is recommended here to cover up such deficiency by simultaneously using a rotary absorber tube and magnetic field inducer with nanofluid. Results showed that the combination effects of the receiver rotation and the magnetic field improve the convection mechanism in the absorber and increase both energetic and exergetic performance of the collector. The study reveals that there is an optimal rotational speed in the each magnetic field intensity for different... 

Recent research indicates that accurate material behavior modeling plays an important role in the estimation of residual stresses in the bore of autofrettaged tubes. In this paper, the material behavior under plastic deformation is considered to be a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. The yield surface is assumed to depend on the first stress invariant and the Lode angle parameter which is defined as a function of the second and the third invariants of the deviatoric stress tensor. Furthermore for estimating the unloading behavior, the Chaboche's hardening evolution equation is modified. These... 

A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics... 

Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br - H2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier - Stokes equations and continuity equation in polar and Cartesian coordinates. The analysis is based on steady state laminar flow of falling liquid film of Li Br - H2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (Ar),... 

In this article a double-inlet pulse-tube refrigerator (DIPTR) is modeled using the nodal analysis technique. The main complexity of the problem is oscillatory and unsteady characteristics of the flow. Solving the flow field in the regenerator section of the system as a porous medium with nonlocal thermal equilibrium is challenging. Governing equations are developed applying mass, energy, and momentum equations to different finite volumes in each component of DIPTR. A numerical code (SharifPTR), with graphical user interface, has been developed to investigate the influence of geometrical and working parameters on performance. The governing equations are a system of boundary value problems.... 

A stress-based forming limit diagram for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K model has been represented and used in tube hydroforming. In this study, the finite element model for bulge forming of straight tube has been constructed and verified with published experimental data. The adaptive simulation technique is based on the ability to detect the onset and growth of defects (e.g., wrinkling, and bursting) and to promptly readjust the loading paths. Thus, a suitable load path has been obtained by applying Adaptive Simulation Method in ANSYS Parametric Design Language (APDL)  

The deformation behavior of solid solution-treated AA6061 tubes in a novel severe plastic deformation process named Tube Channel Pressing has been assessed. In order to do so, an analysis based on the finite element method and dislocation density model is utilized, and microhardness measurement is carried out to verify the trends of analysis results. By comparing FEM results with experimental data, the optimized geometrical parameters controlling the deformation behavior of the tube in tube channel pressing are determined to obtain the best strain homogeneity and minimum dimensional changes in tube