m. vajdi

The global population increase and the depletion of fossil fuel reserves, along with environmental changes caused by the rising demand for renewable energy, have turned the sustainable, adequate, and cost-effective supply of these resources into a significant challenge. The current study examines the power generation cycle based on geothermal and solar energy, aiming to optimize operational procedures, increase efficiency, and reduce energy production costs. This study utilizes EES software for exergy and exergy-economic analysis and employs the Taguchi optimization method to identify optimal operational conditions. Results show that, under optimal conditions, this system can increase the first law efficiency by up to 17% compared to the average and reduce the total exergy destruction by up to 50%. Furthermore, the results indicate that the evaporator connected to the solar collector and the condenser temperature are the main factors affecting the efficiency of the first and second laws, reducing exergy destruction, and the cost rate of exergy destruction

The increasing energy demand in industrial and operational units and corresponding concerns about the limited fossil resources as well as environmental pollutions urge the researchers to generate electricity from renewable energy sources such as wind, geothermal, solar, and biofuels. In the present work, the use of solar and geothermal energy in producing electricity is investigated. The proposed cycle is capable of producing power by using both solar and geothermal energy sources simultaneously or can be used separately to generate electricity. Organic Rankine Cycles (ORCs), which benefit working fluids like refrigerants, have been employed. These cycles are able to produce electricity from low-temperature energy sources. The cycle is designed to employ two evaporators as high temperature and low temperature ones and, consequently, is equipped with two turbines as high and medium pressure ones. The governing equations of mass balance and first and second laws of thermodynamics were applied to each cycle component. A numerical code is written and solved by EES software. The performance of the proposed cycle was analyzed by energy and exergy viewpoints and the first and second law efficiencies were calculated. Therefore, the amount of exergy destruction and exergy efficiency of each component was defined. To evaluate the cost of the final product, which is electricity, exergoeconomic analysis, as an efficient tool, was carried out and the final cost of products was defined. Parametric study of the effect of different designing parameters, such as pinch point temperature difference and evaporator temperature on the energy and exergy performance and cost of the product was done. The obtained results showed that the best second law efficiency was related to high-pressure turbine, whereas the low-pressure turbine acquires the highest value of exergoeconimc factor. The average electricity production cost based on power generation in low- and high-pressure turbines was calculated as (0.102$/kwh).

Heat transfer enhancement from a flat plate in which a thin blade is rotating at a certain speed in the vicinity of the plate has been investigated in the present study. For this numerical study, the finite volume method was used in which the rotation of the blade was simulated by the definition of sliding mesh and interface boundary within the computational domain. The equations of mass, momentum, and energy were solved in two-dimensional and transient form for airflow with constant physical properties using Fluent commercial software and the details of the flow and thermal fields were obtained at the top of the plate. The rotational Reynolds number of the blade has been changed in the range of 1360-5460 and the dimensionless parameter of blade-end-to-plate distance to the blade length (d/D) was ranged from 0.105 to 0.420. The results indicated that heat transfer from the plate is improved by increasing the rotational speed of the blade, especially on the front side of the rotating blade, while the effect of the d/D was effective only over a limited area of the plate central section

An asymmetric numerical study has been performed to investigate the effect of utilizing circular porous fins on heat convection inside of an annulus enclosure. The walls are considered to be at a constant temperature. The porous fins are installed on the outer wall, and other walls are insulated. Governing equations discretized using the FVM based on the second-order upwind scheme. The effect of different parameters on heat transfer enhancement inside the annulus, such as annulus inclination angle, annulus aspect ratio, Darcy number, Rayleigh number, thermal conductivity, the position of fins, number, and length of fins, has been investigated. Results declared that increasing Darcy number from a certain value would enhance the average Nusselt number dramatically at both aspect ratios, even though annulus with an aspect ratio of 3:1 has a higher value of average Nusselt number compared to the aspect ratio of 2:1. It has been illustrated utilizing low relative solid to fluid phase thermal conductivity nullify the effect of the increasing number of porous fins on heat transfer enhancement but, by increasing relative thermal conductivity to Ke=100, installing four porous fins on the inner cylinder increases the average Nusselt number by 7 percent compared to using only one fin.

In this paper, forced, free, and mixed convections in incompressible flow were studied numerically. Nano-sized Al2O3, TiO2, MgO, and ZnO ceramics with water were considered as nano-fluids. Simulations were carried out for cavity flow with different boundary conditions and aspect ratios, as well as flow over stationary and rotating cylinders. The mean Nusselt number ((Nu) ̅) and friction factor for cavity flow and (Nu) ̅ for flow over a cylinder were compared for different nano-fluids. A new code was developed in FORTRAN 95 for numerical simulations. A fifth-order Runge-Kutta method for time discretization and a characteristic-based scheme for convective terms were used in this code. The averaging scheme on the secondary cells is used to obtain viscous fluxes. Primary results are validated with other researcher's outputs. Results showed that MgO-water and ZnO-water had maximum and minimum heat transfer rates, respectively. Moreover, maximum and minimum shear stresses were recorded for the Al2O3-water and TiO2-water, respectively. Using nanofluid increases the heat transfer rate between 15 and 37 percent depending on the Richardson number and selected nano-particles.

Solid propellant systems are basically two types: case bonded and cartridge. Liner, as a polymeric glue, is responsible for bonding propellant to casing in case bonded ones, therefore, it must have sufficient mechanical and adhesive strength. The type and amount of each component of polymeric composition plays an important role in liner strength. In this research, effect of chain extender content (4-6 percent) and fillers (9-17 percent) on tensile strength of liner based on HTPB and bonding strength of liner-propellant was investigated. The result showed that with increase in amount of chain extender, bonding strength between liner and propellant, tensile strength and elongation at break liner was increased. In addition, it was found that increase in fillers content up to 15 percent improve tensile strength and elongation at break, whiles increase in fillers, decrease bonding strength through decrease in permeability of liner into propellant surface.

Micro-mixers are one of the important components of micro-fluid systems. Micro mixers are small devices that are used to mix two different fluids which can be liquid or gas phases. Since the scale of these devices is very small and fluid flows with very low Reynolds. At lower Reynolds numbers, the fluid's diffusivity is the dominant parameter to mix the fluids. If the flow is forced to create vortices, mixing phenomena will improve considerably. So using the appropriate geometries to create vortices and accelerate the mixing process along the channel is essential. In this study, two cylinders are used to enhance the mixing which is a passive method.Despite other mixing accelerators, cylinders are better because of their smaller drag coefficient. Rotating cylinders can help the mixing phenomena by means of fluid no-slip boundary condition. Since a rotating cylinder can change the path lines of fluid particles and help the mixing process, both cylinders is used geometry rotate clockwise or counter clockwise. Simulation of mixing and fluid flow, accomplished with numerical methods and finite element. Governing equations are solved by means of COMSOL software and the results are shown as contours of pressure and concentration.Four different cases are considered base on the combination of rotation direction of cylinders. To verify the numerical method, simulation of a T-mixer is done by standard input data and compared with previous works, data. Results for a T-shaped mixer are in good agreement with reference data. Then, simulation of flow around stationary cylinders is done and results are compared with different rotating cases. It can be admitted that two rotating cylinders are better. However, two cases in which the rotational direction of cylinders are the same, improve mixing much better. In these two cases, cylinders force the fluid particles to enter the other fluids region and mix with each other.