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As the coefficient of performance and the cooling power of adsorption chillers are low, the irreversibility calculation can identify the sources which limit the increase of performance parameters and effectively be used in association with current performance improvement techniques. Adopting the numerical modeling and calculating the temporal distribution of temperature in adsorber elements, this study measures the exergy destruction in different parts and processes of the adsorbent bed. The results show the maximum exergy destruction rate in isosteric phases, yet the total exergy destruction is low due to the short phase times. The highest total exergy loss is observed in isobaric heating phase due to the high irreversibility of desorption process and also long phase duration. Furthermore the effects of fin height and fin spacing on the exergy destruction of adsorbent bed are investigated. The results show that increasing fin height and fin spacing increase the total exergy destruction; however the dependency of fin spacing on exergy destruction is relatively low.

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In this paper the mixed convection and entropy generation in a square cavity filled with Al2O3-water nanofluid with the presence of a constant axial magnetic field, is analyzed. The upper and bottom walls are adiabatic. Discretization of the governing equations were achieved through a finite volume method and solved with SIMPLE algorithm. In this research the effects of the Rayleigh number (103- 106), Hartmann number (0 - 100) and also inclination angle (0 - 90°) are investigated. When the cavity is rotated, it is observed that the mean Nusselt number and total entropy generation increase when the Rayleigh number increases in cavity. In square cavity, regardless of the Ha number, by increasing of the inclination angel, the mean Nusselt number and entropy generation rate, increase until inclination angel 30°, then decreases. Also when the magnetic field is rotated, it is observed that the mean Nusselt number decrease when the Hartmann number increases. The mean Nusselt number when the cavity rotates with specific inclination angel is less than state that the cavity rotates with specific magnetic field. For finding optimum condition of heat transfer, Artificial Neural networks (ANN) were used. The results from optimization show that as the Rayleigh number increases, the optimum angel decreases. Whatever the Rayleigh number more increases, the decrement in optimum angel more intenses. Also in low the Rayleigh number, as the Hartmann number increases, the optimum angel decreases firstly then increases. In high Rayleigh number, as the Hartmann number increases, the optimum angel increases too.

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Taguchi method since 1980 is used as an effective way to optimize the design process engineering tests. In this paper by using of taguchi method optimal conditions of the mixed convection and entropy generation in a square cavity filled with Cu-water nanofluid is analyzed. For this purpose a L16 (43) orthogonal taguchi array is used. Discretization of the governing equations were achieved through a finite volume method and solved with SIMPLE algorithm. The effect of Richardson number (0.1-100 ), the volume fraction of copper nanoparticles (0-10%) and the wavelength of the wavy surface (0- 1) as an effective parameters for analyzing in four levels are considered. This analysis was performed for fixed Grashof number 104. The results show that the mean Nusselt number decreases by increase of the Richardson number, the volume fraction of nanoparticles and the wavelength of the wavy surface. It is found that the Flat plate (for wavy surface with the wavelength 0) and the volume fraction 0% in the Richardson number 0.1 is optimal design for heat transfer while the geometry with Ф=5%, Ri=100 and λ=0.25 is optimal design for entropy generation. Finally for maximum heat transfer and minimum entropy generation the geometry with Ф=0%, Ri =1 and λ=0.25 can be considered as an optimal design.

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Improvement of shooting accuracy with air gun pellets is very important in sport competitions which is always questioned by shooting enthusiasts. In this study, the performance of a transonic spherical projectile as an air gun pellet with 4.5 mm-caliber under a mechanism known as Hop-up is numerically examined. The motion of this projectile is assumed in four degrees of freedom including three translational motions and one transverse rotational motion. Hop-up mechanism is resulted in a rotational motion of spherical projectile, so a Magnus Force is generated which prevents the altitude loss of the projectile. The Navier-Stokes equations are solved in compressible non-stationary turbulent conditions with equations of the pellet motion in a coupled form and in a moving computational grid by a computer program. The present numerical simulation is based on “Roe” scheme with second-order accuracy using a finite volume method and because of the importance of time dependent parameters, second-order time accurate was applied. To validate the computer program operation, the results were compared to valid experimental data. The results obtained from these studies showed that proper rotation of the projectile for a certain distance prevents its height drop when hits the target. A relation was also obtained between the target location, shooting kinetic energy and proper angular velocity which can neutralize the projectile altitude loss at arbitrary distavces. It is also demonstrated that by increasing the angular velocity, the vortex shedding onset is accelerated and the projectile momentum is decreased.

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One of the important issues in shooting by air guns is to select the appropriate projectile for different distances of the target. In this paper, the performance of four samples of air gun projectiles (pellets) is studied. The motion of these projectiles is assumed in four degrees of freedom including three translational motions and one rotational motion. The considered projectiles have three calibers of 4.5, 5.5 and 6.35 mm, and four different types, namely flat nose, sharp nose, round nose and spherical. In order to numerical simulation of the problem, after these projectiles have been modeled geometrically, the 3-D compressible turbulent Navier-Stokes equations and dynamic equations of the projectiles motion are solved in a coupled form and in a moving computational grid. The numerical simulation is based on “Roe” scheme with second-order accuracy in space and time using a finite volume method. To validate the computer program operation, the results are compared to valid experimental data. Computed results describe the trajectory, velocity variations and altitude loss of the projectiles with time and location. Comparison of the projectiles performance including the trajectory, velocity variations and altitude loss indicate that the round nose projectile has the best performance in long distances compared to the other samples and the flat nose projectile has a great performance in short distances, while it has a weak behavior in long distances. Additionally, effect of nose shape on the performance of the sharp and round nose projectiles is investigated and the optimum nose shapes are obtained.

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