M.H. saidi
Sharif University of Technology, Mechanical Engineering, Faculty Member
ABSTRACT In this chapter, a comprehensive thermodynamic modeling of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) is conducted. A heat recovery steam generator is used to produce saturated water for the heating purpose. This... more
ABSTRACT In this chapter, a comprehensive thermodynamic modeling of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) is conducted. A heat recovery steam generator is used to produce saturated water for the heating purpose. This saturated hot water can be used in an absorption chiller system to meet the cooling load of the system. In order to model the hybrid system, chemical and electrochemical analyses of SOFCs and other components are carried out through energy and exergy analyses. The results of a hybrid system are compared to a gas turbine power generation system in order to investigate the effect of fuel cell on the system performance. Based on the model results, exergy efficiency of a hybrid SOFC-GT is higher than the one for conventional gas turbine and steam generator cycle. To enhance the understanding of the results in this study, a complete parametric study is performed and the results are presented. The results of this study, show that an increase in fuel cell stack temperature and compressor pressure ratio increases the efficiency; however an increase in fuel cell current density and gas turbine inlet temperature (GTIT) decreases the efficiency. In addition, an increase in HRSG steam pressure and a decrease in HRSG pinch point temperature results in an increase in system exergy efficiency.
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ABSTRACT Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex... more
ABSTRACT Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex engine are compared with a similar axial flow type engine. A detector sensitive to emission from C2 * excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2 * emission from flame. Mixtures of Propane and Butane with air enriched by oxygen are used as fuel and oxidizer. The effects of equivalence ratio and oxidizer mass flow rate are investigated as well.
ABSTRACT In this chapter, a comprehensive thermodynamic modeling of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) is conducted. A heat recovery steam generator is used to produce saturated water for the heating purpose. This... more
ABSTRACT In this chapter, a comprehensive thermodynamic modeling of a hybrid solid oxide fuel cell-gas turbine (SOFC-GT) is conducted. A heat recovery steam generator is used to produce saturated water for the heating purpose. This saturated hot water can be used in an absorption chiller system to meet the cooling load of the system. In order to model the hybrid system, chemical and electrochemical analyses of SOFCs and other components are carried out through energy and exergy analyses. The results of a hybrid system are compared to a gas turbine power generation system in order to investigate the effect of fuel cell on the system performance. Based on the model results, exergy efficiency of a hybrid SOFC-GT is higher than the one for conventional gas turbine and steam generator cycle. To enhance the understanding of the results in this study, a complete parametric study is performed and the results are presented. The results of this study, show that an increase in fuel cell stack temperature and compressor pressure ratio increases the efficiency; however an increase in fuel cell current density and gas turbine inlet temperature (GTIT) decreases the efficiency. In addition, an increase in HRSG steam pressure and a decrease in HRSG pinch point temperature results in an increase in system exergy efficiency.
The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In... more
The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer. The method consists of a finite difference based numerical approach for non-uniform grid which is applied to the dimensionless form of the governing equations, including the modified Poisson–Boltzmann equation. The results reveal that, neglecting the ionic size at high zeta potentials gives rise to the overestimation of the mixing length, because the steric effects retard liquid flow, thereby enhancing the mixing efficiency. The importance of steric effects is found to be more intense for channels of smaller width to height ratio. It is also observed that, in sharp contrast to the conditions that the ions are treated as point charges, increasing the zeta potential improves the cross stream diffusion when incorporating the ionic size. Moreover, increasing the EDL thickness decreases the mixing length, whereas the opposite is true for the channel aspect ratio.
ABSTRACT Heat transfer phenomenon in a recently developed vortex engine has been surveyed. Cooler walls, better combustion performance and more stable relative to the other engines, make these engines very interesting. These advantages... more
ABSTRACT Heat transfer phenomenon in a recently developed vortex engine has been surveyed. Cooler walls, better combustion performance and more stable relative to the other engines, make these engines very interesting. These advantages have been obtained by using a bidirectional swirl flow, containing a cool outer and a hot inner vortex, traveling upstream and downstream respectively. The most eminent benefit of these combustion chambers, having highly reduced wall temperature, is the result of convective heat release from the wall by the outer vortex. A thorough numerically and experimentally investigation has been performed on radiation and convection heat transfer to realize the exact heat transfer behavior of this engine. Results from flame structure observation indicate that flame area is much larger in vortex engine in comparison to regular engines due to vortex stretching of the flame which increases radiation heat transfer to walls. In spite of this increase, heat removal by outer swirl flow is high enough not only to compensate for increased radiation but also reduces the wall temperature substantially.
ABSTRACT Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in combustion for scientists and combustion researchers. In this research some parts of the combustion chamber wall are insulated using... more
ABSTRACT Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in combustion for scientists and combustion researchers. In this research some parts of the combustion chamber wall are insulated using Blanket as a high insulating material. The rate of radiative heat transfer to the chamber wall is calculated using temperature difference between inner and outer surface of chamber. In the experiments this parts are protected from direct contact with hot combustion media using quartz window. The luminous radiative transfer per volume of chamber and also volume of flame in a vortex engine are compared with that in a similar axial flow type engine. A detector sensitive to emission from C2 * excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2 * emission from flame.
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In this paper, the effect of increasing the number of layers on improving the thermal performance of microchannel heat sinks is studied. In this way, both numerical and analytical methods are utilized. The analytical method is based on... more
In this paper, the effect of increasing the number of layers on improving the thermal performance of microchannel heat sinks is studied. In this way, both numerical and analytical methods are utilized. The analytical method is based on the porous medium ...
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ABSTRACT The present study attempts to use the methanol–silver nanofluid filled heat pipe heat exchanger and compares the effectiveness as well as the energy saving with pure methanol. A heat pipe heat exchanger has been tested in a test... more
ABSTRACT The present study attempts to use the methanol–silver nanofluid filled heat pipe heat exchanger and compares the effectiveness as well as the energy saving with pure methanol. A heat pipe heat exchanger has been tested in a test rig under steady-state conditions. The lengths of both the evaporator and the condenser sections of the heat exchanger were 700 mm, and its central adiabatic section had a length of 160 mm. The heat exchanger had 36 plate finned copper thermosyphons arranged in three rows. The inlet air temperature across the evaporator section was varied in the range of 33–43 °C while the inlet air temperature to the condenser section was nearly constant to be 13 °C. First, pure methanol was used as the working fluid with a fill ratio of 50 % of the evaporator section length, and then dilute dispersion of silver nanoparticles in methanol was employed as the working fluid. The nanofluid used in the present study is 20 nm diameter silver nanoparticles. The experiments were performed to compare the heat pipe heat exchanger effectiveness and energy saving, using nanofluid and pure methanol. The inlet air relative humidity across the evaporator section was varied between 35 and 80 %. The sensible effectiveness of the heat pipe heat exchanger obtained from experiments varied about 5–22 % for pure methanol and 9–32 % for methanol–silver nanofluid. Based on these experimental results, using methanol–silver nanofluid leads to energy saving around 8.8–31.5 % for cooling and 18–100 % for reheating the supply air stream in an air conditioning system.
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Journal of Mechanical Science and Technology 23 (2009) 3448~3458 ... Approximate method of determining the optimum cross section of ... Omid Asgari* and Mohammad Hassan Saidi Department of Mechanical Engineering, Sharif University of... more
Journal of Mechanical Science and Technology 23 (2009) 3448~3458 ... Approximate method of determining the optimum cross section of ... Omid Asgari* and Mohammad Hassan Saidi Department of Mechanical Engineering, Sharif University of Technology, Tehran, 11365-9567, Iran
Research Interests: Mechanical Engineering, Applied Mathematics, Finite Volume Methods, Microfluidics, Heat Transfer, and 15 moreHeat Exchanger, Optimization, Laminar Flow, Heat Exchangers, Finite Volume, Cross Section, Length scale, Convective Heat Transfer, Method Validation, Fluidics, Forced Convection, Approximation Method, Heat Sinks, Heat Sink, and Constructal
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ABSTRACT Thermopneumatic micropump is one type of positive displacement micropump, which has many applications due to its relatively large stroke volume, low working voltage, and simple fabrication in microscale. In this paper, a... more
ABSTRACT Thermopneumatic micropump is one type of positive displacement micropump, which has many applications due to its relatively large stroke volume, low working voltage, and simple fabrication in microscale. In this paper, a numerical study of heat transfer and fluid flow in a valveless thermopneumatically driven micropump is presented. For rectifying the bidirectional flow, a nozzle and a diffuser are used as the inlet and outlet channels of the chamber. Since the fluid flow is induced by the motion of a diaphragm, the numerical simulation includes fluid structure interaction, which requires applying a dynamic mesh. The domain of solution is divided into two sections; the actuator unit, which contains the secondary fluid, and the main chamber through which the working fluid is passing. The temperature distribution, the pressure variations, and the center deflection of the diaphragm are obtained. In order to validate the model, the numerical results are compared with some experimental data, which shows fair consistency. According to the results of the three dimensional simulation, the rectification efficiency for the nozzle and diffuser channels depends on the frequency.
This paper describes the optimization of combustion chamber geometry and injection timing of new generation of EF7 engine that CNG is directly injected to the combustion chamber, with the aim of providing the best mixture at low and high... more
This paper describes the optimization of combustion chamber geometry and injection timing of new generation of EF7 engine that CNG is directly injected to the combustion chamber, with the aim of providing the best mixture at low and high speeds. The multi-objective genetic algorithm (MOGA) is coupled with the KIVA computational fluid dynamics (CFD) code, with grid generation in order to maximize the flammable mass of mixture. This would result in better combustion and improved fuel economy. The optimization variables related to the combustion chamber are seven geometry variables and injection timing. Through the present optimization, a great improvement in the mixture distribution is achieved. The optimization results show that early injection with the shallow bowl in shape can be advantageous at high speeds while late injection would result in better results at the low speed.