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In this paper, a sensible Heat wheel is modeled as one-dimensional and unsteady using finite difference method implemented in a code. The governing equations include the energy conservation equations in the air stream and in the matrix are discretized and are solved in coupled form. Numerical results show that after about thirty to forty cycles, the wheel reaches steady state conditions and the wheel efficiency is shown to be constant. In steady state condition, the temperature distribution for both the air flow and the matrix is almost linear. Wheel temperature distributions are analyzed at different times and locations until steady state. Finally, investigation of the effect of different wheel parameters on wheel performance using the developed numerical model is done. Numerical results showed that the effectiveness of sensible wheel can be enhanced by an increasing the volume flow rate, decreasing the porosity of the matrix, increasing the number of transfer units (NTU). پرونده مقاله

Based on the available evidence, porous piezoelectric materials have great potential for the development of smart (active) structures with high strength, high stiffness and light weight such as ceramics and composites. Among the ceramic materials with porous piezoelectric compounds, can be mentioned Lead-zirconate-titanate (PZT), Lead-titanate (PbTiO2), Lead-zirconate (PbZrO3), Barium-titanate (BaTiO3), Cadmium-selenide (CdSe), etc. This study extracts the governing partial differential equations for steady- state and axisymmetric behavior of a circular solid plate is made of an undrained saturated porous piezoelectric hexagonal material symmetry of class 6 mm. The porosities of the plate vary through the thickness; thus, material properties, except poisson’s ratio, are assumed as exponential functions of axial variable z in cylindrical coordinates. Additionally, piezothermoelastic behavior of a circular plate subject to external thermal, mechanical and electrical loads is considered, so various concepts including three-dimensional linear elasticity theory and dielectric theory are used in combination to create a linear piezoelectric model. The extraordinary and special industrial properties of porous piezoelectric materials, their increasing use and the need to know the behavior of these materials, doubles the importance of this research. پرونده مقاله

In low-velocity areas, the Savonius turbine offers an attractive, economical, and ecologically beneficial method of generating electricity. However, due to the fact that scientists are still looking for a solution to the primary issue of the Savonius turbine's poor efficiency, this turbine has not yet been properly investigated. To increase the efficiency of the Savonius turbine the nozzle system can be utilized. In the present study, a 2-dimensional numerical simulation using the computational fluid dynamics (CFD) method was conducted for a Savonius vertical axis wind turbine (VAWT). This study aims to investigate the effect of different nozzle installation angles and nozzle wall lengths on the performance of the Savonius turbine and for this purpose, six different nozzle designs are investigated. In order to observe the performance of the mentioned turbine, the power coefficient (Cp) is calculated, and their values are compared in the different tip speed ratios (TSR). The results show that the highest efficiency of Savonius VAWTs is achieved with a nozzle installation angle of 55°. After that in optimum nozzle installation angle, the nozzle length of 1900 mm exhibits better performance compared to other nozzle lengths at a TSR of 0.5. پرونده مقاله

In the present study, a special model of geothermal heat exchangers called coaxial borehole heat exchanger (CBHE) was numerically analyzed. For this numerical solution, computational fluid dynamics (CFD) method was used. As the name of this system indicates, this system consists of two coaxial pipes. The parameters are studied in the research are the inlet velocity of the operating fluid into the inlet pipe, the groundwater seepage velocity, the soil porosity of the area and the use of nanofluids instead of pure water. Studies on each of the above conditions have shown that they can have a significant effect on increasing the temperature of the operating fluid flowing inside the outer pipe. The results show that when the operating fluid passes through the outer pipe at high speed, it does not have enough time to heat up and its temperature rises less. Also, the presence of groundwater seepage which is a natural factor, will reduce the temperature of the working fluid. The decrease in temperature is related to the velocity of groundwater flow. Clearly considering the porous medium and the amount of soil porosity and the empty space between particles affect on the thermal performance of CBHE. Obviously, high porosity increases thermal resistance and decreases thermal conductivity. The utilization of nanofluids as operating fluids instead of pure water was studied. With increasing thermal conductivity in nanofluids, the rate of temperature increase along the outer pipe increases. Therefore, the use of suitable nanofluids with high thermal conductivity is recommended as the operating fluid. پرونده مقاله