ghodrat ghassabi

The mechanical ventilation smoke management system involves the use of supply fan, jet fan, and exhaust fans, which are activated at different times after a fire is extinguished. This paper numerically investigates the effect of the priority and delay of smoke management systems on smoke distribution and visibility in a car park after a fire, using Fire Dynamic Simulation Code 6.7.6. The flow rates of the exhaust fan, supply fan and jet fan are 1.9 m³/s, 1.43 m³/s, and 1.67 m³/s, respectively. The fire, located near the supply fans, is modeled as a rectangle with dimensions of 2.0 × 0.8 m² and a power of 1.6 MW, lasting for one minute from ignition to extinguishment. Polyurethane is assumed as the flammable material. The priority and delay of the smoke management systems are evaluated through four scenarios over a period of 420 seconds. The results show that visibility reaches acceptable levels in all scenarios at all locations after 420 seconds. Additionally, the results indicate that the visibility of the upper half is highest for scenario a, at around 15 m. However, the visibility of the lower half is highest for scenario d, ranging between 20 and 30 m. It can be concluded that delaying the activation of smoke management systems is an effective strategy for facilitating smoke removal and fresh air intake.

Cyclones are widely used equipment in the industry for dust collection from fluid flows to reduce industrial pollution on the environment. In cyclones, the effect of the centrifugal force of the fluid and the difference in particle density compared to the fluid are used for particle and dust separation. The main criteria for evaluating the performance of a cyclone in dust separation are the pressure drop and the particle collection efficiency. In this study, the effect of the diameter of the cyclone cylinders, where the ratio of the upper to the lower cylinder diameter is 0.5, 1, 1.5, and 2, on the particle collection efficiency and pressure drop was investigated. The simulation was performed with ANSYS Fluent 2023 software. Turbulent flow was considered. The inlet velocity and cyclone cylinder were 1 m/s and 20 cm respectively. The results showed that by increasing the diameter of the cyclone cylinders up to 4 times, the efficiency increases by more than twice, and the pressure drop is not changed significantly.

Despite its great impact on economic progress, the cement industry produces a variety of environmental pollutants, including NOx, carbon dioxide, and carbon monoxide, the release of which can cause serious damage to the environment. In the meantime, the biggest impact of this industry on the environment is related to its burners, and the present research was written with the aim of investigating the effect of the location of calciner burners on reducing the emission of environmental pollutants in Qaen Cement Factory. The research method in the current research is quantitative, and in order to numerically investigate the effect of two positions for calciner burners in the lower part (main position) and in the upper part on the emission of pollutants, was used Ansys Fluent 2022 software. The findings of the research show that the Qaen cement factory in the calciner section is facing the problem of incomplete combustion, which has led to the production of carbon monoxide instead of carbon dioxide. In addition to reducing temperature and increasing fuel consumption, this incomplete combustion causes the production of significant carbon monoxide, which destroys the environment. Also, the results indicate that in the upper burner mode, due to the reduction in the chance of fuel and air mixing, the combustion becomes incomplete and the emission of carbon monoxide increases, but the production of Nox decreases due to the decrease in the combustion temperature.

Temperature management in turbomachines is a critical factor for improving power plant efficiency and service life. Air gap clearances between combustion chamber rings assist its installation and expansion while partially modifying the inlet air path to stave off mixing in the flame tube of the combustion chamber. Changes in clearance dimensions can cause geometric asymmetry and result in asymmetric flow and temperature distribution imbalances in the combustion chambers creating hot spots at the outlet of the combustion chamber. Hence, in this paper, the effects of four clearance dimensions with four values on temperature distribution in two combustion chambers attached to the compressor have been numerically studied using Ansys Fluent 17. Taguchi method is applied for optimization and decreasing the outlet semi-circles temperature difference using Minitab software. The optimization results illustrate that the radial clearance between the flame tube and the mixing chamber is the most significant variable in controlling the air flow rate and producing symmetrical temperature distribution in the two chambers. So, one-millimeter radial clearance between two chambers leads to an increase of the temperature distribution by 15oC and 100oC in average and point mode, respectively. Also, results show that as the average clearance of the combustion chamber decreases by 5 millimeters, the point mode temperature of its corresponding outlet semi-circle decreases around 100°C.

It has been demonstrated that thermal efficiency can be improved and Nox emission can be reduced in gas turbine cycles by inlet air evaporative cooling. For this method, few studies have been performed using numerical simulations due to the complexity of the combustion and evaporation process. This study numerically and thermodynamically investigated the effect of inlet evaporative cooling on the thermal efficiency and NOx emission of a V94.2 gas turbine. The compressor and turbine are simulated using thermodynamic modeling. However, thermodynamic modeling could be able to calculate the temperature only at the inlet and outlet of devices. Analysis of evaporating cooling effect on combustion chamber temperature distributions and species distribution could be achieved by numerical method. Therefore, the combustion chamber was simulated by numerical modeling using Ansys Fluent 16. The process was simulated at four humidity ratios, including, 0, 25%, 50%, and 75%. Combustion was assumed to occur in a diffusion-type flame. The mass flow rate of fuel and air was 3.64 kg/s and 214.2 kg/s, respectively. Results show that Numerical and thermodynamic solutions have a good agreement with the empirical result. Also, it is observed that the accuracy of the numerical solution is better than the thermodynamic solution. Results indicated a 0.44% improvement in thermal efficiency and a considerable 33.5% reduction of NOx emission at the highest humidity ratio.

Many researchers have experimentally and theoretically studied fresh water productivity in solar stills. In this regard, water preheating can play a noticeable role in enhancing the productivity of solar stills. In the present study, in order to study the effect of water preheating at the inlet of desalination system, a cascade solar still is built and integrated with two different solar collector in separated modes; an evacuated solar collector and a conventional flat plate solar collector. The mentioned solar still includes an external condenser, fin, and internal and external reflectors. It is worth noting that the embedded fins in the water passage are applied to induce hot spots and increase the evaporation rate and fresh water. The experiments were performed in August 2015 and summer 2017. The results showed that the combined desalination system with conventional flat plate collector and evacuated tube collector enhace productivity %60 and %13, respectively. In addition, efficiency of solar still in combination with conventional flat plate collector and evacuated tube collector was %81.8 and %59.1, respectively. The price of produced fresh water of solar still with conventional collector obtained 0.035 $/lit and for solar still with evacuated tube collector was 0.045 $/lit.

Gas turbine inlet air is filtered in multiple steps. First, the filtration step is used for removing the big things. Then, Sand and dust are removed using the inertial sand separators. Sand separators filtration system is composed of 30 rows of the inertial sand separators on 5 floors. In this paper, one floor of the inertial sand separators filtration system of Shahid Kave power plant has been simulated using Ansys Fluent 16. A computational server with 20 processing cores and RAM of 120 GB was used to carry out the calculations. The velocity and pressure fields have been studied and the effect of density and diameter of particles on inertial sand separators efficiency are investigated. Particle diameter and density are varied between 0.1 to 100 micrometer and 500 to 2000 kg/m3 respectively. The result shows that the collection efficiency of the inertial sand separators was reduced by increasing the particle diameter. However, the collection efficiency of the inertial sand separators was improved by increasing the particle density. Also, a few particles are collected by inertial sand separators, so that collection efficiency is less than 1%. Therefore, this system is inefficient and not cost-effective and elimination of the system fans could reduce the energy consumption of the gas power plant around 360 kW.

Over the past few years, researchers were carried out a conscious effort to explore various methods of improving the thermal efficiency of power plants. It was shown that the application of a recuperator is beneficial to improve the thermal efficiency of a gas power plant. Nevertheless, a few studies were done from a thermodynamic point of view and it is safe to say that few numerical simulation studies were performed using computational fluid dynamics. Therefore, in this study, the effect of using a recuperator was investigated to increase the temperature of the combustion chamber inlet air at four different temperatures (633, 643, 663 and 673 K) and to enhance the overall thermal efficiency. Furthermore, the effect of this approach on the emission of pollutants was explored. For this purpose, the compressor and turbine were numerically simulated using a developed MATLAB code while the combustion chamber of the gas power plant was simulated for various pre-heated temperatures in a thermodynamic analysis by ANSYS Fluent 16. The results indicated that in the case of the highest increase in the inlet air temperature to the combustion chamber (50°C) compared to the basic state (without recuperation), the thermal efficiency of the power plant and emission of nitrogen oxides were increased by 1.46% and by 44.17%, respectively.

In previous studies, there is no comprehensive experimental study that has evaluated dissimilarity between heat transfer and momentum transfer for all the interactions between effective variables. On the other hand, when a rectangular cylinder is located near a flat plate, skin friction coefficient and heat transfer coefficient are effected some variables that change in an extensive range. Therefore, testing all possible combinations of effective variables will not be reasonable. In this paper, maximum and minimum of skin friction coefficients and heat transfer coefficients were determined using robust Taguchi design. Design of experiments method was applied for decreasing the number of experiments without losing the required information in the first step. Then, experiments were performed in a wind tunnel, the maximum speed of which was 13 m/s. Finally, skin friction coefficient and heat transfer coefficient were optimized using Taguchi method and Minitab software. Results showed that dissimilarity between heat transfer and momentum transfer has occurred for all the possible combinations of the effective variables. Additionally, the gap height between the rectangular cylinder and flat plate was the most effective variable on generating the dissimilarity.