جستجوی مقالات مرتبط با کلیدواژه « Stack » در نشریات گروه « مکانیک »

In this paper, the numerical simulation of combustion in one of the industrial furnaces of Kermanshah Oil Refining Company has been carried out in order to investigate the cause of high temperature damage to its damper and provide a solution to solve this problem. At first, the current situation has been investigated. For this purpose, the numerical model of furnace and burner has been produced and numerical simulations have been carried out to check the current situation. The agreement between the actual factory data and the numerical simulation data is acceptable. In the next step, by changing the burner and changing the shape of the flame, numerical simulations have been performed in order to solve the problem. The obtained results show that by changing the burner and using 4 smaller burners but with a longer flame, the shape of the flame becomes branched and with the increase of heat transfer caused by this situation, the temperature at the place where the damper is installed decreases by about 170 degrees Celsius. This decrease in temperature can solve the problem of damaging the damper and softening the structure connecting it to the flue.
 
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Today, due to the growing importance of polymer electrolyte membrane fuel cells in the production of clean energy, the diagnosis of this energy converter has become very important. Diagnosis can significantly increase the useful life and reliability of the fuel cell. A major part of the defects related to the polymer electrolyte membrane fuel cells is due to the disturbance of the moisture balance in them. Flooding is one of the most common defects associated with fuel cell imbalance, which is possible in both the cathode and the anode side of the cell. In previous works, the cathode has been considered as the only possible place for flooding, mainly because it is the source of water production. In this article, the anode is also considered as a possible place for this phenomenon. The method of this research is based on taking data from the stack under healthy operating conditions and trying to estimate the output parameters of stack voltage, cathode pressure drop, and anode pressure drop using related inputs using the adaptive neuro-fuzzy method. In conditions of uncertain operation in which the healthy or flooding operation of the stack is not known, comparing the deviation of the actual values of the outputs from the model with the allowable values of these deviations (0.735 [V], 0.0092 [bar] and 0.0047 [bar], respectively) can lead to determining flooding or normal conditions.

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.

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.

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.

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.

Cooling tower is one of the most important units used in the power plant. Thermal efficiency of the power plant is directly affected by thermal performance of the cooling system. Thermal performance of the Heller type cooling tower is significantly reduced in the wind condition as same as the other dry-cooling towers. Thermal performance of the cooling tower may be reduced up to %40 during high speed wind condition. It is due to separating flow around the radiators and deflected exit plume at the top of the tower stack. In the present research work, a special configuration was proposed for Heller-type cooling tower to reduce the undesirable wind effects. Numerical simulations of the flow field showed that, it could increase the thermal performance of the cooling tower up to %64 regarding the usual design configuration. This proposal is a cooling tower having 20×20 (m2) windbreakers and exit plane making angle of 27o with horizontal direction.