فهرست مطالب moharram jafari

In this paper, mathematical model of different pumping plants including two or three centrifugal pumps in parallel connection is developed and simulated by MATLAB/Simulink. The effect of utilizing of variable speed (VS) and constant speed (CS) control on efficiency and energy is studied against different water consumption patterns. In according to results, in plants with double pumps, efficiency is a function of operating points as it varies by different consumption patterns, but in plants with three pumps it varies with a steady algorithm. It is recommended to implement (CS + VS + VS) strategy of control in pumping plant with three centrifugal pumps rather than (VS + VS + CS) as it costs lower in primary expenses of plant construction besides higher reliability, lower maintenance cost and shorter payback time. 10 to 15 percent efficiency increase by all VS control and 5 to 10 percent increase in efficiency is proposed by VS and CS compositional control strategies.

The Fans are the beating heart of the system and play an important role in the production process in industry. The objective of this paper is the numerical study of flow through an axial fan and examining the effects of fan design parameters on the performance of the fan. Fan design is done with SolidWorks software and the SST-k-ω and k-ε turbulence models are applied in the simulation which are done using CFX software. In the study of pressure distribution and current separation, occurs at the back of the blade attack edge, and as we get closer to the tip of the blade, the vortices resulting from the separation of the flow become decreasing. The effect of changing the length of the blades and their angle has also been studied. The results show that at different rotational speeds, the optimal blade is different and with increasing fan speed, the maximum fan efficiency percentage occurs at a smaller attack angle. By increasing the blade length by 20% the fan output increases 47.5% and the fan power consumption increases by 53%.

The application of guide blades is an appropriate method for improving the aerodynamic performance of Savonius wind turbines. Guide blades gather wind energy around the turbine and guide them into the concave side of the Savonius rotor. In this paper, a numerical investigation is conducted to evaluate the effect of the guide blades on the performance of Savonius turbines. ANSYS Fluent 16.0 software is applied for the simulation of turbulent and transient flow around the turbine. Suggested designs for guide blades are 4, 5, and 6 blades which are located in the angles of 30, 40, 50, and 60 degrees. The numerical results of power and torque coefficients show that guide blades have significantly improved the performance of Savonius turbines.  For a turbine with 5 guide blades located at the angle of 30 degrees, maximum power coefficient is 0.51, which indicates an increase of 183% compared to a single Savonius turbine without the guide blades. For turbines with 4 and 6 guide blades, maximum power coefficients are 0.42 and 0.49 respectively; this finding shows an increase of 133% and 171% in comparison with a single Savonius rotor without guide blades.

In the current paper, heat transfer in conduction pumping of n-hexane and n-decane dielectrics (as working fluids) using flush electrodes is investigated by conducting experimental tests. The Study has been carried out for different fluid film thicknesses and variable applied electric voltage, and the effects of various parameters such as physical properties (ion mobility difference, density and viscosity), as well as fluid working temperature on heat transfer performance of the conduction pump have been investigated. The results show that higher ion mobility difference, as well as lower density and viscosity, increases the flow rate and heat transfer in the conduction pump, due to the improvement of the vortices formation in the vicinity of the electrodes. Moreover, it significantly increases the heat transfer in the pump by creating turbulent flow around the electrodes. On the other hand, higher operating temperatures enhance the flow rate and heat transfer due to decreasing density and viscosity and also increasing the temperature gradient between the source and the destination of heat transfer. The intense heat transfer enhancement by using the conduction phenomenon compared to the ordinary fluid flow pumping through a simple duct (having no electrodes) is seen for all film thicknesses and working temperatures. Maximum observed enhancement of Nusselt number for n-hexane and n-decane are equal to 10401% and 568%, respectively.

Due to the capability of using exhausted gases of power plants directly in reforming process and producing high quality syngas, the tri-reforming process is a considerable kind of reforming process. In the present study, a power generation system based on solid oxide fuel cell with specific capacity and equipped to the external reforming is proposed and investigated form the viewpoint of thermodynamics. In order to conduct the external reforming process, exhausted gases from the system including the steam, carbon dioxide and oxygen are recycled and utilized as the reforming agents in the reactor. In order to model the proposed system thermodynamically, the principals of mass and energy balance are applied in Engineering Equation Software (EES). Effects of such important parameters as the current density and solid oxide fuel cell operating temperature on the system performance indicators including the various voltages, fuel mass flow rate, power generation and the energy as well as the exergy efficiencies of the system are investigated. The parametric study results shows that for the lower values of the current density and higher values of the SOFC operating temperature as well as the fuel utilization factor, the system energy and exergy efficiencies enhances.

In the current paper, performance of a conduction pump with flush electrodes has been experimentally studied using two dielectrics (n-hexane and n-decane) as the working fluids. The study is conducted for different liquid film thicknesses, and effects of changing the magnitude of applied electrical voltage, and other different parameters such as fluid physical properties (ion mobility difference, density and viscosity) and working temperature of the liquids on the performance and efficiency of the pump are investigated. Results show that while higher ion mobility difference increases electrical power consumption of the pump, since it leads to higher flow velocity, significantly enhances flow rate and efficiency. Therefore, using liquids with higher ion mobility difference is more appropriate in the industrial applications due to the simultaneous enhancement of flow rate and efficiency. On the other hand, although increasing the applied voltage decreases the pump efficiency, it raises flow rate, which is an important pump characteristic and even more important than efficiency for conduction pumps. Furthermore, it is observed that increasing the liquids temperature enhances the pump efficiency due to the reduction of fluids density and viscosity.

Injection system of a diesel engine is heart of the engine and could have significant effects on its performance. In this paper an annulus nozzle has been considered in the injection system of the Kubota V3300 diesel engine and the engine’s performance has been investigated by considering different fuel injection pressures and different pressure of the combustion chamber due to the turbocharging. Numerical results show that under turbocharging circumstances, increasing the injection pressure leads to more perfect combustion and the magnitude of SFC decreases to 0.195. Results also show that increasing the injection pressure during turbocharging lead to the increasing of engine’s power and torque and to the increasing of pollutants. It is found that in the absence of turbocharging, increasing the injection pressure leads to the increasing of SFC. It is also found that for the injection pressure equal to 60MP, SFC is equal to 0.21. Numerical results indicate that in the absence of turbocharging, increasing the injection pressure leads to the increase of the engine’s power, torque and its pollutants. Comparisons between both cases of presence and absence of turbocharging show that amount of soot in the case of turbocharging is less than its amount when the engine is naturally aspirated. These comparisons also show that NO emission in the absence of turbocharging is considerably less than generation of NO in the other case.

One of the important ways for improving performance of diesel engines is selecting of a proper and efficient fuel injection pattern. In this study six different patterns of fuel injection have been considered and performance of a diesel engine by using these patterns of fuel injection have been investigate numerically by employing AVL Fire. An annulus nozzle have been consider for the fuel injection system. It is expected that considering an annulus nozzle lead to increase of spry cone angle and proper distribution of the fuel inside the combustion chamber. Results show that employing proper and efficient patterns of fuel injection lead to increase of engine power and decrease of exhaust pollutants gases. Results also show that by employing a quasi-triangle fuel injection pattern, the diesel engine has better performance in competition with the case of using a constant fuel injection. It is found that by employing a quasi-triangle pattern of fuel injection, SFC reduces to 0.2043 kg/kJ, while the engine power increased by 27.5% and the magnitude of NO increases slightly. In the case of employing a constant-decreasing fuel injection pattern, the magnitude of SFC reduces to 0.2029kg/kJ whereas the magnitude of NO increases in comparison with the case of using constant fuel injection pattern. Numerical results show that by employing a constant-increasing pattern of fuel injection, the engine power is approximately equal to the engine’s power in the case of using a constant fuel injection pattern. But in this case the magnitude of NO reduces considerably.