Modares Mechanical Engineering
Year:2018 | Volume:18 | Issue:5 |Papers Count:27

In a thermoelectric air-handling unit, a number of thermoelectric modules with forced convection heat sinks are used. In this research, it is tried to investigate the effect of module arrangement and air flow pattern on thermal performance of the system. For this purpose, the thermal performance of an air-handling unit including four thermoelectric modules with three different heat sinks layouts; parallel, series with unidirectional flow and series with counter flow were compared. The entropy analysis has been used to study the thermal performance and pressure drop imposed on the system. In addition, the effect of the electric current applied to the modules and the hot and cold air flows on the coefficient of performance of the system has been studied for three different layouts. Results indicated that, heat sinks layout and air flow pattern through the fins have significant effects on the thermal performance of a thermoelectric air-handling unit. The coefficient of performance for cooling and heating in the series arrangement are 1. 4 and 1. 1 times of those in parallel arrangement, respectively. The results of the entropy analysis showed that although the pressure drop imposed on the system in the layout of the series is greater than the parallel arrangement, this cannot reduce the advantage of using the series layout.

In this paper, the performance of three turbulence models, zonal k-ε , linear low-Reynolds k-ε and nonlinear low-Reynolds k-ε in the prediction of flow and heat transfer through a dimpled channel is investigated. Furthermore, the effect of YAP term replacement with NYP length scale correction term is studied. Dimples are heat transfer devices which are employed in gas turbine blades to increase the heat transfer levels. These devices do not act as an obstacle for flow, and thus they produce low pressure losses. In this study, the governing equations on flow and energy are solved using the finite volume method together with the SIMPLE algorithm. The results obtained with YAP term indicate that the nonlinear model predicts larger recirculation flow inside the dimple than zonal and linear models. Also, the intensity of impingement and upwash flow in this model is greater than other models. Heat transfer results show that the zonal model predicts the heat transfer levels lower than experimental measurement. Using the linear model leads to a better prediction of heat transfer inside the dimples and their back rim. Compared to these models, the nonlinear model yields a better prediction not only for the smooth area between the dimples, but in the back rim of the dimple. The replacement of the YAP term with the NYP term in linear and nonlinear models leads to more accurate results for heat transfer in dimple span-wise direction and back rim.

One of the concerns of designers of engineering structures is structural failure due to stress concentration caused by geometric discontinuities in the structures. Therefore, by considering that perforated composite plates are used in most engineering structures, their study is very important. The purpose of this paper is to present a new model based on the regression method for estimating stress concentration factor of a circular hole in orthotropic plates. One of the important applications of providing stress distribution around holes in terms of mechanical properties is the use of these relationships in the stress analysis of perforated viscoelastic plate using the effective modulus method or Boltzmann's superposition principle. First, using different values of the mechanical properties of the composites plates, and employing an analytical solution based on the complex variable method, the stress concentration factor of circular hole is calculated for a number of these materials. Then, using multiple linear regression, an explicit expression for the stress concentration factor is given in terms of mechanical properties. The results show that the multiple regression model is able to predict the circumferential stress with a maximum error of less than 1%.

Modified continuum models have been the essence of much attention in nanomechanics through their computational efficiency and the capability to produce accurate results which are comparable to the atomistic models ones. As the dimensions of a structure approach to the nanoscale, the classical continuum theory has not the capability to predict the behavior of nanostructures due to the size-dependent of their properties which is known as size-effects. In this work, the bending behavior of nanobeams with common sets of boundary conditions is investigated using state-space modeling on the basis of nonlocal beam theories. Both uniform load and point load are considered in this study. To this end, Eringen’ s equations of nonlocal elasticity are incorporated into the classical beam theories namely as Euler-Bernoulli beam theory (EBT) and Timoshenko beam theory (TBT). The maximum deflection of nanobeams corresponding to each set of boundary conditions is obtained using state variables and matrix algebra. The results are presented for different geometric parameters, boundary conditions, and the values of nonlocal parameter to show the effects of each distinctly. It is found that the non-dimensional maximum deflection corresponding to all boundary conditions and both loading cases will be increased for higher values of nonlocal parameter which show this fact that with increasing the nonlocal parameter, the stiffness of nanobeam decreases.

Evaluation of pressure oscillation of solid rocket motors in actual conditions requires static tests. These test have a large application in evaluation of motor various parameters effect on its operation. Using of these tests are very limited due to their high costs and so, evaluation of various parameters is nearly impossible. To solve this problem, sub scaled solid rocket motor must be designed. In this paper, designing process of space shuttle sub scaled solid boosters, called 1881, with scale 1: 31 has been proposed. Space shuttle and ariane 5 boosters have been argued to modeling and simulation. Sub scaled motor modeling and design parameters using Buckingham’ s Pi theorem and then, operation and dimensional properties have been presented. Three tests for evaluation of designed motor were done successfully and pressure and thrust history and its oscillations have been evaluated. Results show that for facility of fitting and reduction of test cost in subscale motors, using of Tan-Cu in throat instead of graphite and flange design of joints are very useful. Despite of using Buckingham’ s Pi theorem in solid motor scaling, propellant chemistry and its burning rate are affected of Crawford bomb and real flow of combustion products and in many case, error correction between Crawford and motor data is inevitable. On the other hand, existence of empty volume in forward segments and others, plays an important role in pressure oscillations and after end of burning or reducing, oscillations will be uniform.

Piezoelectric materials, in different shapes such as rectangular plate, annular plate, circular plate and cylindrical shell, have increasing application in industries in order to create smart structures. In this article, experimental and numerical analysis of free vibration of a two-layered cylindrical panel with metal and piezoelectric layer in different boundary condition is carried out. First, a single PZT-4 layer is polarized in radial direction. Using the Piezoelectric layer and an Aluminum layer, a two-layered smart panel is prepared. Then, the first natural frequency of the hybrid panel with free boundary condition is measured experimentally in three different ways. The hybrid panel is simulated in a finite element software (Abaqus). Results show good agreement between different experimental methods, as well as, between finite element model and experimental results. The accuracy, limitations and merits of different experimental methods are discussed completely. The results show that the natural frequency can be achieved accurately by excitation of actuator layer. Finally, the influence of different boundary conditions as well as geometrical parameter such as radios, length and thickness of smart cylindrical panel are investigated using the finite element software.

The effective bandwidth of a bi-stable electromechanical energy harvester is investigated. The Harvester’ s configuration is in the form of a cantilever beam in which the piezoelectric layers are attached on its two sides. The whole device undergoes sinusoidal base excitation. In addition an axial force is applied to the end of the beam. Post-buckling is caused by this force and system becomes bistable. The cantilever beam is modeled as a nonlinear Euler-Bernoulli beam and equations of motion are generated using Lagrangian method. The equations then discretize via Assumed Mode method and governing equations are solved via Complexification Averaging solution and compared with numerical results. Different attractors such as periodic, quasi-periodic and chaotic attractors are detected and their relative frequency domains are identified. Using semi-solution method, boundaries of different areas plotted in the base excitation-frequency domain. Finally, Uni-modal and multimodal cases are studied and compared with each other. It is shown that the uni-modal solution does not predict the behavior of the system correctly.

In this study, control design of a T shaped mass connected to the clamped-clamped microbeam excited by electrostatic actuation is investigated. The actuation force is generated by applying an electric voltage between the horizontal part of T shaped mass and an opposite electrode plate. In this model, the micro-beam is modeled by Euler-Bernoulli theory as a continuous beam. The T-shaped assembly connected to the the microbeam is assumed as a rigid body and nonlinear effect of electrostatic force is considered. Equations of motion and associated boundary condition are derived using the Lagrange’ s principle. The differential equation of nonlinear vibration around the static position is discretized using Galerkin method. . The discretized equations are solved by the perturbation theory. To improve the dynamics behavior of systems, nonlinear control feedback has been presented. The controller regulates the pass band of microcantilever and analytically approximate the nonlinear resonance frequency and amplitudes of the periodic solutions when the microcantilever is subjected to one point and fully distributed feedback forces. The results of paper may be used for improving the design of mass sensors based on nonlinear jump phenomena.

Rotational abrasive flow machining process (RAFM) is one of the modern surface polishing processes where in the material removal in micro and nano sizes is performed by tiny abrasive particles. Rotational abrasive flow machining is very effective in finishing of complex internal and external surfaces. in comparison with other finishing methods. In this study, the rotational abrasive flow machining process has been investigated in polishing of AISI H 13 hot work steel. The main objectives of workpiece rotation was increasing the material removal rate and decreasing the surface roughness of workpiece. So the effects of rotational speed and hardness of workpiece and the mesh size of abrasive particles as input variables on the output parameters including surface roughness and material removal rate have been studied. The results showed that applying of rotational speed of workpiece leads to higher material removal rate and lower surface roughness. Furthermore, the material removal rate is decreased and surface roughness is improved by increasing the mesh size of abrasive particles. Also, increasing the hardness of workpiece leads to decreasing the material removal rate, and in similar cutting conditions, the surface of workpiece with more hardness is better polished in comparison with the surface of workpiece with lower hardness.

To transport the natural gas from the producer sources to the consumers, gas pipelines are used. The extension of the pipelines reduces gas pressure and compression stations are considered to compensate for the loss of pressure in the transport path. At these stations, several compressor units usually work in parallel to share the gas inlet flow. The purpose of the present study is to investigate the load distribution method between parallel compressors in an optimal manner according to the capacity of each compressor. In this paper, a load sharing algorithm is proposed with the help of a model-based predictive controller (MPC) to achieve a stable and efficient operation at the compression station. In this algorithm, real-time optimization is used by an adaptive modifier method when faced with a variable demand from the consumer. The optimization is done according to the capacity of each compressor and using the approximated efficiency curve. In this way, the coordinates of the optimal working points for each compressor are obtained. The proposed algorithm is implemented in MATLAB software on the dynamics of centrifugal compressors in parallel arrangement. The results show that the load distribution using the proposed method has a much better performance than the old methods such as equal load balancing. This method results in the optimal operation of each compressor and thus storing and saving the natural gas.

To improve solar energy gain by the photovoltaic (PV) modules, a novel double-axis solar tracker was developed in the present study. The proposed system worked based on both active and passive methods of sun tracking using electromotor and gas actuator, respectively. The electromotor oriented the module in the east-west direction based on the principle of the chronology of the sun, and in the north-south direction, the change in the gas pressure, due to the temperature change, activated a pneumatic cylinder to rotate the module. The evaluation tests were carried out at the different modes of tracking (including east-west, north-south and double axis). The results showed that the available solar energy on the PV module increased by 5. 03%, 33. 75% and 38. 78% using the tracker at the north-south, east-west and double axis modes, respectively. This, finally, improved electricity generation of the PV module by 4. 82%, 31. 43% and 36. 25%, respectively. Moreover, employing the tracker system led to an increase in operating temperature of the PV module. Based on the operating temperature of the module with the tracking system, it was proposed for using in the photovoltaic-thermal collectors. The designed system could track the sun trajectory with the accuracies of 0. 6% and 8% in the east-west and south-north directions, respectively.

The main goal of this study is achieving thin-walled AZ31 magnesium alloy tubes with high ductility at elevated temperature. For this purpose, a combined severe plastic deformation method, including parallel tubular channel angular pressing (PTCAP) and tube backward extrusion (TBE) was used. First, PTCAP process was applied on tubular samples at 300° C and then, TBE process was performed at 300° C. After PTCAP, a necklace like microstructure, large gains surrounded by a large number of tiny recrystallized ones, was observed and the average grain size of the material decreased from 520 µ m to 11. 1 µ m. At the next stage, After TBE, an ultra-fine grain microstructure with an average grain size of 8. 6 µ m was formed. After performing this combined method, the hardness value of the PTCAP and TBE processed sample increased from 37 HV to 69 HV. Hot tensile testing studies at 300° C revealed an elongation to failure value of 181% for the PTCAP and TBE processed sample, while this value for as-received sample was 55%. Fractographic SEM images showed that predominately ductile fracture was occurred in all hot tensile specimens due to nucleation of microvoids and their subsequent growth and coalescence with each other.

In this paper, the effect of shape memory alloy on low-velocity impact response of rectangular sandwich plates with composite facesheets and soft auxetic cores is investigated using a new higher-order global– local hyperbolic plate theory. In order to obtain accurate results with the least error, non-uniform and time-dependent distribution for the phases of SMA and the transverse compliance of the soft core are considered. Also, a refined contact law is proposed instead of using the traditional Hertz law and different contact laws are considered for the loading and unloading phases. Stiffness effects of all layers along with the effect of plate thickness on contact stiffness are considered. The obtained nonlinear finite element governing equations are solved by making use of an iterative algorithm at each time step. The results of the present study are compared with the experimental results in other references, and it is proved that the results are valid. Finally, the effect of auxetic core, core Poisson's ratio, SMA wires, and indenter energy on impact response of composite sandwich plat are investigated. The results show that the auxetic core increases the apparent stiffness of the contact area that causes an increase in impact forces and a decrease in the lateral deflection and impact duration. Besides, the SMA can absorb a remarkable portion of the stored impact-induced strain energy due to the superelastic and hysteretic natures of the SMA material, which results in increasing impact strength of the sandwich plate and decreasing the damage caused due to the impact.

This article was carried out to investigate and compare fin-tube and plate-fin intercooler at different conditions (non-uniformity of velocity and non-uniformity of temperature of car inlet air with radiator effects) to optimize intercooler layout in cooling system. A tow-dimensional code for fin-tube heat exchangers (fin-tube intercooler and radiator) and a three-dimensional code for plate-fin intercooler were developed by ε-NTU method. Fin-tube model was validated with experimental tunnel test data and plate fin was validated by available data at literature. Results showed that plate-fin performance at least 6. 25% better than fin-tube intercooler. Doubling the aspect ratio caused 1. 5% and 5% increase of plate-fin and fin-tube intercooler heat transfer respectively. When non-uniformity of velocity increases to 0. 8, heat transfer decreases 13. 8% and 19. 6% for fin-tube and plate-fin intercooler respectively. This reduction in performance is the maximum value that is produced in planting intercooler along the wheels and above the engine. Applying radiator in system and planting block result in approximately 4. 5% and 2. 4% impairing performance of fin-tube and plate-fin intercooler respectively while changing position of block dose not effect on intercooler performance. The presence of shields and other obstacles in front of the car will create such an impact on the intercooler. Pressure drop of fin-tube intercooler 37. 5% lower than plate-fin intercooler.

In the present study, the effect of parameters of autogenous pulsed Nd: YAG laser welding process on the lap joint of a 316L stainless steel foil with a thickness of 100 µ m to be used as bipolar plates of polymeric fuel cell was investigated. For this purpose, the statistical tools, the analysis of variance and the various diagrams were used to analyze the data by response surface methodology. The peak power (130 to 650 W), pulse durability (1. 5 to 3. 5 ms), and welding frequency (14 to 18 Hz) were considered as input parameters. The mentioned statistical method was able to predict the effect of welding parameters by developing second-order polynomials, so that the total error including the repeatability error and the lack of fit error for shear strength model, weld undercut model, and weld underfill model obtained 2, 8 and 3, respectively. The defects of weld undercut and lack of penetration were identified as most important factors affecting the shear strength. The laser power is as the main parameter in this process and the impact of it on the shear strength of the weld, the weld undercut and the weld underfill is calculated 64, 62 and 66%, respectively. Finally, the maximum shear strength with the value of 522 MPa is achieved at a peak power of 260 W, pulsed duration of 3 ms and welding frequency of 17 Hz. In this case, the weld undercut is determined as 3 micrometers.

In orthopedic surgeries, the bone drilling is one of the most important biomechanic processes that has used.، This mechanical process is very important, sensitive and all-purpose in biomechanical engineering, because its complexity and special conditions. Bone drilling process has advanced by roboots and CNC machin entrance into the realm of orthopedic surgeries. The problematic issue during operation is the high increase in drilling process temprature which leads to the so-called thermal necrosis. It is not clear quality of enfluence of tool rotational speed and feed rate on the temprature and force responses and so it can be seen confilicts among different researcher results frequently. In this paper it is performed mathematical modeling and design of experiments on the input factors and output parameters of bone drilling. The effect of input factors and interaction of input factors have investigated. Increasing rotational speed the temperature increases where as the feed rate behavior is complex because contact duration between drill bit and bone so the increasing temperature take places because the low feed rate or increasing force and friction. In addition increasing the drill bit diameter increases the tempratures. Also the sobol sensitivity analysis method has used to investigate effect of each parameter in which rotational speed, feed rate and drill bit diameter have most effect respectiviely on temperature instantaneously. Also optimization process performed on temperature behavior, hence the minimum temprature is 37 0C when the diameter of drill bit 2. 5 mm, rotational speed 500 rpm and feed rate 30 mm/min.

The 2D position of a defect as well as its through-thickness length can be measured by ultrasonic time-of-flight diffraction technique (TOFD). By considering the methods used for detecting and positioning a target in radar, acoustic and sonar systems, an algorithm was developed for 3D positioning of defects in TOFD measurements. In this algorithm, the unknown parameter to be determined is the time difference of arrival (TDOA). While the developed algorithm is sufficiently fast, it suffers from various errors affecting the TDOA. The sensitivity of TDOA to errors is more noticeable when the distance between the receivers and the midplane (a plane with a minimum distance from the receivers) is small. This problem cannot be easily resolved when the receivers are coplanar. In this paper, using a closed form solution, a new algorithm is proposed for solving this problem. In this algorithm, by considering hypothetical locations for receivers, both the target (defect) and the positions of receivers are simultaneously verified. These hypothetical positions are obtained in such a way that their distances from the midplane is within acceptable limits. To validate the algorithm, it is used for determining the position of an artificial defect in a carbon steel block. The results prove that the algorithm is accurate and can be used in case of 3D TOFD measurements in which the receivers are usually coplanar.

In this study, numerically investigated effect of magnetic heat sources (residual and hysteresis) that can be useful in hyperthermia and their effects on cancerous tissue. The governing equations of continuty, momentum, concentration, energy and Arrhenius tissue destruction equation in the form of couplings are defined, solved and investigated in the finite-element COMSOL software. For blood flow inside the cancerous capillary, non-newtonian and temperature dependent model is used. The geometric model is simulated in three dimensions, including the capillary and cancerous tissue. Thermophysical properties of blood and tissue are also temperature dependent. Results indicated that the residual heat source plays a major role in increasing the temperature of the blood and tissue and can be ignored the effect of hysteresis heat source. The residual heat source has an inverse relation to the particle size and is ineffective in the particle size above 100 nm but hysteresis heat source is directly related to the size of the nanoparticles, and for particles with a size of 150 nm, it will result in a 1 degree increase in temperature for the tissue. The increase in blood temperature for 25 nm magnetic nanoparticles with the residual heat source can lead to the most destruction in cancerous tissue. Also, the viscosity of blood has an inverse relation with the concentration of magnetic nanoparticles in the capillary wall and blood temperature.

In addition to the operational and environmental loads, an offshore pipeline may be subjected to accidental transverse loads by falling heavy objects or trawl gears. As a result, the load bearing capacity of the pipeline may be significantly impared by the dents, gouges or other types of damages caused by the impact. Such damage to an offshore structure may have serious environmental and economic consequences. In this study, results of experimental investigations on the residual strength of plain and gouged dented steel pressurized pipes under monotonic axial compression are presented. Some series small-scale specimens were fabricated from API-5L-X80 steel pipes with (D/t) ratio of 22 for the purpose of experimental tests. The specimens were dented by a spherical indenter with (d/D) ratio of 0. 45 and gouges were applied along the pipe axis on the outer surface of the middle portion, whose cross section was rectangular. Defected and intact specimens were then collapsed by monotonic axial compression loading whilst subjected to constant internal pressure. In this research, effects of some key non-dimensional parameters such as dent depth, presence of the internal pressure and geometrical parameters of gouges have been studied.

Powder metallurgy process is commonly used to manufacture nanocomposite products, in which the product quality of this process depends upon Composite of reinforcement nanoparticle and distribution. In this article Metal Matrix Nanocomposite (MMN) by powder metallurgy with a base material stainless steel 316L, a material that is widely used in the industry, and reinforcement particles mixture of Carbide Titanium (TiC) as carbon-based reinforcing particles, and Hexagonal Nitride Boron (hBN) particles as the self-lubricating material is prepared. The reinforcement powders were micro Sized and mixed in high ball milling to reach Nano-sized, after 30 h mixing powders in high ball milling reach to Nano-sized, and then reinforcement Nanoparticles with 2 and 10 Wt. % Mixed with stainless steel 316L for 5 hours and compacted at 400 Mpa and sintered at 1400 C temperature and 3 Hours. Scanning electron microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) tests are performed on Powders to identify the nanocomposite microstructure. The Mechanical Properties such as Microhardness, Wear, and Bending Strength Were Analyzed. These results Compare with Results of stainless steel 316L without Reinforcement. Microhardness and abrasion resistance of Nanocomposite material have improved and flexural strength improved at the sample with 2 wt. % reinforcement and reduced at the sample with 10 Wt. %.

Tolerance analysis plays a crucial role in predicting the quality of products and reducing production costs. This procedure is generally complex and available methods for analyzing different types of assemblies are not always applicable. Accordingly, having a comprehensive approach to assess the effect of tolerances on the quality and cost of products is a fundamental requirement in the manufacturing industry. This paper proposes the improved second-order method for tolerance analysis of complex assemblies. The conventional second-order tolerance analysis (SOTA) is an accurate and applicable method for obtaining the statistical specifications of the assembly’ s key characteristic. However, determining the assembly function in SOTA entails forming vector loops and therefore, this method is limited to simple assemblies. On the other hand, in mechanical assemblies that are usually complex, creating vector loop may encounter some difficulties in practice. In this study, the mentioned issues have been overcome by linking SolidWorks and MATLAB software to employ the proposed methodology for any mechanical assemblies without creating vector loops. For this purpose, MATLAB software makes necessary changes in the SolidWorks model and calculates the derivatives of the assembly function, which are required for the analysis. Then, the statistical moments are computed and the probability distribution of the key characteristic is obtained using the Pearson system. The present study is appropriate for analyzing either linear or nonlinear assembly functions with any statistical distribution. Finally, the applicability of the proposed approach is investigated by some practical examples and the accuracy of results is confirmed by Monte Carlo simulation.

In this study, the buckling and postbuckling behavior of composite laminates with piezoelectric layers subjected to compressive in-plane loading have been investigated. The effects of coupled electro-mechanical field on the postbuckling and bifurcation point in cross-ply and general lay-up sequences have been studied using layerwise theory (LWT). The LWT used in this study for analyzing the piezo-composite laminate is based on the assumptions of the first order shear deformation theory (FSDT). In order to obtain the equilibrium equations, the principle of minimum potential energy has been employed. The obtained nonlinear equilibrium equations have been solved using Newton-Raphson iterative algorithm. Furthermore, the three dimensional finite element analysis has been performed to examine the accuracy of the results obtained using the proposed method. The obtained analytical results are in good agreement with those achieved through the finite element analysis. Obtained results showed that, location of the piezoelectric layers have significant effect on the buckling and postbuckling behavior of the composite plates. Moreover, number of degrees of freedom which is used in proposed method are less than finite element method which, decreased the computational time cost.

In this paper based on the Euler-Bernoulli beam model, the primary resonance a curved single carbon nanotube subjected to axial thermal force in the case of low temperature and high temperature and resting on a viscoelastic foundation is analytically investigated. The nonlinear partial differential governing equation is reduced to nonlinear ordinary differential governing equation by using of a single-mode Galerkin approximation along with the sinusoidal curvature for clamped-clamped single walled carbon nanotube under harmonic external force. The method of multiple scales is applied to determine the analytical primary resonance frequency response. Considering the curved geometry and the mid-plane stretching, a quadratic and cubic terms are presented in the governing equation. The effects of temperature change in high temperature and low temperature conditions, viscoelastic coefficients of medium, amplitude of sinusoidal curvature and excitation amplitude are investigated to study the property frequency response and development or elimination of forward and backward jumping phenomenon in primary resonance frequency response. The results show that these parameters have a significant effect on the frequency response of a curved single walled carbon nanaotubes under transvers harmonic force.

In this study, the thermoeconomic performance of absorption refrigeration cycle utilizing binary solution containing water-ionic liquid (1-Ethyl-3-Methylimidazolium Trifluoroacetate) is investigated and compared with the water-lithium bromide cycle. For this purpose, the thermodynamic and thermoeconomic analysis have been employed to simulation of the cycle and then, the effects of design parameters on the performance parameters like coefficient of performance, exergetic efficiency, solution circulation flow ratio, area of heat exchangers and cost of the streams are studied. The thermodynamic properties of the binary solution are predicted using Non-Random Two Liquids model. It has been found the system with ionic liquid has a lower coefficient of performance and exergetic efficiency (0. 66, 10. 15%) than aqueous solution of lithium bromide system (0. 78, 12 %). The total area and total cost of the ionic liquid system (49 m2, 4907 $/year) is larger than water-lithium bromide cycle (16 m2, 3347 $/year). Despite the Lower performance of systems with ionic liquid, the advantages of these liquids like no crystallization, negligible vapor pressure and weak corrosion tendency to iron-steel materials make the new working pair suited for the absorption refrigeration cycle.

In this research, using a thermomechanical constitutive model for shape memory polymers and employing the von Ká rmá n theory, a finite element analysis of a shape memory polymer beam is presented. The importance of introducing the von Ká rmá n theory for shape memory polymers is that the beam can have relatively high slopes during loading. Also, for optimization and designing processes we need to solve multiple problems and due to the high processing time the use of 3D model is not suitable. To validate the presented formulations, the reported results are compared with the 3D solution which was previously reported by the same authors. Accordingly, the effect of the hard segment volume on response of a thin beam has been investigated, and the results of the von Ká rmá n beam have been reported and compared with the 3D and Euler-Bernoulli solutions. As an example, the error of the beam response in one of the solved examples is 27% for Euler-Bernoulli beam and 1% for the von Ká rmá n solution compared to the three-dimensional solution. In general, the lower the beam thickness or the beam is longer, the Euler-Bernoulli beam error will be higher. The proposed finite element model can provide a reliable alternative response comparing to 3D modeling that requires a lot of processing time, and can be used for geometry and material parametric study.

Various numerical methods have been developed for solving morphodynamic systems, among which the finite-volume method has been widely employed in recent years. This paper presents an efficient finite volume technique for simulation of bedload sediment transport near dry interfaces. The equations governing sediment transport in channels and rivers comprise the shallow water equations and Exner equation. By considering a novel velocity for Riemann waves, shallow water and Exner equations are solved using a weakly-coupled scheme based on an augmented Riemann solver. In this approach the morphodynamic equation is first solved and the updated bedload changes with the same Riemann structure are used as a source term within the shallow water equations. Augmented Riemann solver is based on a decomposition of an augmented vector— the depth, momentum as well as momentum flux and bottom surface. The proposed numerical model is first used for the simulation dam break flow over a mobile bed. Then, dam failure due to over-topping flow is considered and the computed results are compared with the experimental data. These numerical results indicate that the defined weakly coupled method developed based on an augmented Riemann technique is able to be used for modelling bedload sediment transport near dry interfaces with highly accurate and exhibits a very good agreement with the experimental data for test cases.

The present study investigates the effect of the mixing chamber length on the effervescent atomizer internal two-phase flow and the liquid film thickness at the exit of the atomizer at different gas-to-liquid mass ratios. Therefore, the internal flow of this atomizer simulated for three different lengths of the mixing chamber, at the gas-to-liquid mass ratios of 0. 08%, 0. 32%, and 1. 24% and at the liquid flow rate of 0. 38 L / min by the volume of fluid interface following model. The simulation results show that the mixing chamber length does not have much effect on the dominant flow regime in the discharge passage. However, by increasing the mixing chamber length, the two-phase flow inside this chamber more expanded before entering into the discharge passage. Therefore, the two-phase interface instabilities in the discharge passage are lower for the atomizer with the longer mixing chamber. In addition, based on the measuring results of the liquid film thickness at the exit of the atomizer, the effect of the mixing chamber length on the thickness of this film depends on the gas-to-liquid mass ratio. Increasing the mixing chamber length at low gas-to-liquid mass ratio increases the liquid film thickness at the exit of the effervescent atomizer. While at high gas-to-liquid mass ratio, it's inverse. At middle gas-to-liquid mass ratio, the changes of the liquid film thickness at the exit of the atomizer with the mixing chamber length do not show a steady trend.