نشریه مهندسی مکانیک ایران
سال نوزدهم شماره 4 (پیاپی 49، زمستان 1396)

In this paper the laminar Bingham fluid flow through a converging conical duct is analyzed. The constitutive law of Bingham fluids is applied to model the yield dependent properties behavior of the fluid. An analytical solution is obtained for the pressure gradient assuming small conical angle of the duct. According to the yield dependent properties of the fluid, a region is developed in the fluid wherein the rate of deformation tensor is zero. This region is called plug region. According to obtained pressure gradient, the plug region is determined. Then, assuming the cylindrical symmetry, the governing equations are solved in cylindrical coordinate system and velocity field is obtained across the duct section. The results obtained in the paper is compared with the experimental data given in the literature search and Fluent numerical solution. The comparison of these two methods shows that the result of current paper is well compared with those given in the literature search. Finally, the effect of parameters such as yield strength and conical angle on velocity field and plug region is investigated.

With regard to the ever growing world population and the constant capacity of water resources, novel and trusted methods need to be implemented to preserve freshwater resources and also produce drinking water. In this study, an investigation was performed on a type of evaporation-based solar desalination system which was used to desalinate saline water. Among the aims of this study was the fabrication of a desalination system with the help of both solar panel and heat pipe technologies in a single system. After the fabrication of the desalination system, various parameters such as the amount of produced freshwater by distilled vapor on the glass covering and the surface temperature of the photovoltaic, heat pipe and glass cover were studied. Analysis of the effect of water depth in the basin and also the effect of the presence of a fan inside the reservoir were also performed and finally the amount of freshwater production was studied in passive and active situations. The results indicated that the optimum water depth was 5 cm and the freshwater production efficiency of the active configuration was 25% more than the passive state.

A solar electric-vapor compression refrigeration (SE-VCR) system has been proposed in this study. The SE-VCR system was investigated for different evaporating temperatures and months in Isfahan city. The system is simulated by software TRNSYS. the hourly cooling load capacities (heat gain) of a sample building during the different days were determined by using meteorological data such as hourly average solar radiations and atmospheric temperatures. The hourly total heat gain of the sample building and the hourly variations of various parameters such as coefficient of the performance, condenser capacity and compressor power consumption were calculated. the minimum photovoltaic panel surface area was determined to meet the compressor power demand according to the hourly average solar radiation data. also the economic calculations were performed for various sizes of solar system and It was found that adding solar system, is economically. also the annual consumption of carbon in the amount of 1241 kg for cooling saves.

Dielectric Barrier Discharge (DBD) plasma actuators are one of the most efficient and promising technique for active flow control. DBD plasma actuators are all-electric devices without need of pneumatic, hydraulic or moving parts. They are light and fast with low power consumption. All these features have attracted researchers to use these actuators in a variety of cases, such as turbulence flow control, laminar to turbulent transition suppression, separation control, drag reduction and mitigation of noise pollution. One of the models for simulation of plasma actuator effect on fluid flow is the electrostatic Suzen-Huang (S-H) model. This model adds the actuator effect as source terms to the Navier-Stikes equations by solving tow elliptic equations of the electrical potential and the charge density. In this study, a relationship between the independent electrical potential and charge density equations has been made in the form of a boundary condition for charge distribution on the dieleictic surface. The results show that the boundary layer structures on airfoil surface and flat plate is predicted with much higher accuracy by utilizing the modified model.

In this paper, square cavitywith air inside, two heaters situated at its lower wall, its upper wall insulated, and its two side walls kept at a constant temperature. The Lattice Boltzmann method has been used for simulation in this study; and the overall goals of this research are to optimize the installation length of heaters and to explore the effects of the amplitude and wavelength of thermal flux fluctuation and Riley’s number. The findings indicate that the flow within the cavity stabilizes more quickly by increasing the difference between the oscillation amplitude and period of thermal flux in heaters.In this paper, square cavitywith air inside, two heaters situated at its lower wall, its upper wall insulated, and its two side walls kept at a constant temperature. The Lattice Boltzmann method has been used for simulation in this study; and the overall goals of this research are to optimize the installation length of heaters and to explore the effects of the amplitude and wavelength of thermal flux fluctuation and Riley’s number. The findings indicate that the flow within the cavity stabilizes more quickly by increasing the difference between the oscillation amplitude and period of thermal flux in heaters.

Despite the fact that gas cyclones have simple geometry, there is a complex flow with high anisotropicity. Hence, In order to simulate such flow a good physical understanding is needed. In addition to high rotation intensity, there is also a high rate of stress-strain, so RMS turbulent model was used to study the gas phase behavior and Eulerian-Lagrangian statistical method was applied to evaluate the performance of calcium carbonate particles. Following results were obtained through the studying of separation part height effects on cyclone: With increase in height of the separation part of the cyclone for both cases, it is observed that the tangential velocity declines. Moreover, it decreases the Vertex Rankin area. On the other hand, it can be concluded that, the increase of this geometric parameter will rise the downstream flow rate in axial velocity. Therefore, the increase in height of the cylindrical cyclone results in pressure drop increment and improve the performance of the cyclone.