Showing 6 results for Stack
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Volume 13, Issue 2 (5-2013)
Abstract
In this paper, pollutants flows coming out of stacks or cooling towers with different outlet shapes have been numerically studied. The effects of exhaust outlet on plume rise, and the pollutant dissipation are investigated. To simulate the flow turbulence, realizable k – ε model is employed for the case of a stack flow with more than one exhaust outlet on the influence of wind condition. The plume rise and dissipation of pollutant are depending on the direction of the wind and the shape of exhaust outlet. Depending on wind direction and shape of exhaust outlet, higher or lower levels of plume rise can be obtained with various kind of pollutant dissipation. These changes are due to the influence of high pressure upstream and low-pressure downstream flow fields of outlet from stacks on the counter vertex rotating pair. The maximum concentration and dissipation of pollutant for various wind directions and output configurations are examined.
Volume 13, Issue 2 (6-2023)
Abstract
Aims: Today, the energy crisis has become a global problem, and all countries are involved in this crisis, so solutions with small results can lead to significant changes on a macro scale. Passive cooling strategies are a method to reduce energy consumption in buildings and help improve and promote energy management in hot climates.
Methods: The current study analysis ventilation performance related to constructing four-story buildings. Furthermore, there is a heavy investigation into the mechanical aspects of ventilation; hence this research is going to fill the gap in the architectural view of the ventilation system. The modeling uses energy software (Design-Builder).
Findings: Studies have been conducted to investigate the position of the stack, and the earth's rotation, in addition to changes in the materials of the stack in the residential area of Dezful city. The most frequent residential land size in the residential area of Dezful is 10x20 square meters. In addition, changing materials has a direct impact on stack ventilation.
Conclusion: The simulation outcomes demonstrated that material and site rotation changes could alter the stack's performance, meaning that glass can be more effective than aluminum. Still, the position of the stack in the plan does not make a significant difference in the stack's performance. The result is outstanding for architects and all people working in this field, which can be a guideline in designing energy-efficient.
Ahmad Rezaei Sangtabi, Ali Kianifar,
Volume 16, Issue 2 (4-2016)
Abstract
A thermoacoustic refrigerator is a device that transfers heat from a low temperature reservoir to a high temperature reservoir by utilizing acoustic wave. Due to using no moving parts, no exotic and poisonous materials, Thermoacoustic refrigerators have been considered by many researchers. In this paper, the OpenFOAM package is used to simulate a thermoacoustic refrigerator. The unsteady compressible Navier-Stokes equations and equation of state are solved with PIMPLE algorithm. The effects of driver pressure ratio, frequency and heat exchangers temperature differencing for air and helium have been studied. Length of heat exchangers and stack remains constant throughout the analysis process. The results are shown that the coefficient of performance (COP) is decreased and cooling power is increased due to rise of driver pressure ratio. Helium cooling power is greater than air, but their COP is equal because of its need greater input power. The cooling power for both air and helium are increased with enhance of temperature difference of heat exchangers. Also, COP of air refrigerator is decreased, but COP of helium refrigerator is increased. The longer device length, smaller COP and cooling power are the resultants of driver’s frequency reducing. When frequency is increased, the length of cold heat exchanger will be greater than gas particle displacement of air. Therefore, cold heat exchanger absorbs heat from the air instead of heat transfer to it and COP will be zero.
Sharif Gharib, Hassan Hassanzadeh,
Volume 17, Issue 8 (10-2017)
Abstract
To get the real answer a PEM fuel cell system to load changing, dynamic modeling is necessary because static modeling independent of time and it shows the system performance in just one or a few points. In this study, the dynamic performance of a PEM fuel cell stack is modeled in the Matlab Simulink and is validated by the data available in the literature. Modeling is done in two parts; in the first part, the input gases to the fuel cell stack are dray and the second part, the gases entering to the stack are humidification. In order to investigate dynamic response of system to rapid changes in electrical current, the variable electrical current is entered into the system step by step then the effect of this change on output voltage, consumption of reactants, temperature and pressure are obtained. Analyzing results of first part indicates that the time delay of system response to electrical current changes. With increasing the electrical current, the temperature of cell body, consumption of reactants and amount of input gases into the anode and the cathode channels are increased. The temperature of anode and cathode channels and fuel cell body are different and with increasing the stack power are more differences. Analyzing the results of second part indicates that with increasing the relative humidity of input gases the ohmic loss and so on the body temperature of fuel cell is decreased.
Volume 18, Issue 3 (8-2018)
Abstract
Some economists believe that economic crises and problems, such as economic volatility, high unemployment and inflation and the social losses, stem from the government's economic intervention and the implementation of its imperative policies. In this regard, the lack of implementation of the government’s imperative policies by central bank and its independence is still a controversial issue. In the present paper, using Stackelberg model and game theory approach, the efficiency of bond issuance is evaluated as a result of central bank independence and its effect on social loss. For this purpose, a 3-player game including government, central bank and speculators having different objective functions, is designed for Iran. Modeling and numerical analyzing are performed using softwares GAMS and MAPLE during 2005 to 2009. According to minimization of social loss, the results indicate if the government does not play a dominant leadership role, and conversely, if the central bank exerts its leadership in making monetary policy via open market operations (central bank independence), the social loss can be reached to its minimum level.
Alireza Moradi, Fathollah Ommi, Zoheir Saboohi, Mohsen Bahrami,
Volume 21, Issue 11 (9-2021)
Abstract
Thermoacoustic engine is an energy conversion device that uses the energy carrying capacity of sound waves to generate sound power from thermal energy. Although it is not difficult to build thermoacoustic engines due to having no moving parts, many researchers have always tried to reduce the temperature difference required to run thermoacoustic engines, so that these devices can be used in most industries. To investigate the onset conditions of the system, temperature changes in the stack section of a standing wave Thermoacoustic engine were investigated.
Numerical analysis of temperature changes along the stack, was performed using the rotts thermoacoustic equations. The temperature was calculated instantaneously along the stack, and this process continued until the thermal equilibrium was established in the system. A standing wave with an open end was designed and built to validate the temperature curves obtained at different moments. This thermoacoustic engine was able to display the temperature instantaneously along the stack with parallel plates structure. The data obtained from the experimental tests and the temperature changes diagram resulting from the numerical solution method, showed a good agreement with each other for the onset process in the system.
