مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 11 (بهمن 1402)

In this study, the effect of a water-based fire suppression system on fire control and extinguishment in a multi-story building was investigated using FDS software. The geometry consisted of a five-story building with a total of 25 units, where the fire room with heptane fuel was located on the third floor in the center of the ground floor room. Temperature parameters and species such as carbon monoxide and carbon dioxide were measured in each room, and the results were analyzed for two conditions with and without sprinklers from the start of combustion to 100 seconds. Validation showed that the numerical results of this study had an 8% relative error compared to experimental results. Additionally, in the condition without sprinklers, the temperature in the third-floor fire room reached 700 degrees Celsius within 30 seconds, but with sprinklers, extinguishment occurred in less than 20 seconds. This behavior also occurs for toxic species such as carbon monoxide and carbon dioxide, which are at risk on all floors above the fire room without sprinklers. Therefore, by considering minimum, maximum, and average values, the importance of sprinklers in extinguishing fires in the room and controlling toxic and hot gases in other rooms can be concluded.

Pollution and the distribution of dust in urban areas have caused a wide range of diseases. Dust is one of the environmental phenomena that has caused adverse effects on health and the environment. Contamination caused by dust of different origins is spread across a wide range of atmospheres. Our understanding of the mechanism of dust distribution and the turbulence in urban areas is very important, which helps us reduce the effects of these types of contaminants. Computational Fluid Dynamics models have been considered in this study due to the economical approach to research in the field of dust distribution. Due to the turbulence of the wind flow inside the city, we use the large eddy simulation method to model this turbulence, which is widely used in computational wind engineering. In this study, we have investigated the dust in the urban area. For this purpose, the effect of the wind direction angle and the urban environment as well as the height of the buildings on the speed distribution and dispersion of fine dust with time has been investigated in two separate computing spaces. By comparing the results between 0° and 10° angle, it has been observed that with the increase of the flow turbulence intensity angle, these turbulent characteristics lead to the dispersion and persistence of fine dust in the urban environment. By comparing the results, we conclude that by creating an angle in the urban area due to increased mixing, the amount of dust distribution in the urban area rises.

Enhancing fog collector efficiency can be achieved by increasing the number of layers in various collectors. This study scrutinized the influence of layers on efficiency for conventional collectors (Raschel and Aluminum mesh) through a meticulous analysis of theoretical relationships and the execution of experimental tests. In the laboratory phase, following the installation of the system, the output flow from the humidifier was directed toward the collecting plate. Subsequently, the efficiency of collectors with 1, 2, 5, and 7 layers was assessed and compared based on the amount of collected water post-fog extraction. The results of the investigation into the theoretical relations governing water extraction from fog revealed a significant trend. As the shade coefficient of the collector increases, aerodynamic efficiency demonstrates an initial increase, peaking at 50-60%, followed by a subsequent decrease. Furthermore, the efficiency of Raschel and Aluminum mesh is intricately linked to the number of layers, with the highest theoretical efficiency observed at 4 and 7 layers, respectively. Experimental findings indicated the highest water collection efficiency for Raschel mesh with 5 layers at 55.3% and for Aluminum mesh with 6 layers at 58.1%. In terms of cost-effectiveness, the optimal number of layers for Raschel and Aluminum mesh is determined to be 2 and 4 layers, respectively.

Microwave irradiation has been used to speed up chemical reactions in comparison to conventional reactions. Because the electromagnetic waves cause increasing molecular vibrations. Energy consumption is reduced by using electromagnetic waves. As a result, electrode corrosion rate is reduced. In this article, a numerical method has been used to compare saline water electrolysis (EL) and saline water electromagnetic electrolysis reactor (EMER). Axisymmetric geometry is considered in simulations and steady and frequency dependent analysis are conducted. Continuity equations and Navier-Stocks equation for fluid flow, and Nernest-Planck equation for mass transfer flow, and the maxwell equation for electromagnetic wave modeling are taken into account. At the first, the effect of electromagnetic waves on the ion separation has been investigated. Results have shown that an obvious enhancement has occurred in ion separation due to electromagnetic irradiation. The dechlorination in EMER process has been improved more than three times in comparison with EL process. Also, the ion separation has been enhanced linearly by increasing the cell potential and initial salinity. The quantitative results of each parameter are shown in the paper.

Leveraging artificial intelligence to forecast heat transfer characteristics across diverse industries holds significant potential for improving thermal equipment design, increasing heat transfer efficiency, optimizing cooling systems, and reducing energy consumption. The main contribution and purpose of the current study is predicting the Nusselt number in the context of turbulent flow-induced vibration around a heated cylinder experiencing unconfined oscillations along both streamwise and transverse axes. The anticipation of the Nusselt number relies on transverse and streamwise displacements of the oscillating cylinder and encompasses three distinct scenarios: displacement input in the x-direction, displacement input in the y-direction, and comprehensive amalgamation of both x and y inputs. This prediction is achieved through a sophisticated deep long short-term memory network, meticulously crafted and fine-tuned using a particle swarm optimization algorithm. The results highlight the effectiveness of the optimized networks across various inputs, with the highest predictive precision observed when employing combined x and y inputs. The correlation coefficients within the test segment are as follows: 0.967 for x input, 0.961 for y input, and 0.975 for combined x and y inputs. By applying the methodology elucidated in this study, the forecasting of heat transfer characteristics for structures subjected to fluid flow emerges as a feasible possibility.

Today's big cities are full of tall buildings requiring a lot of energy. On the other hand, dispersed electricity generation is an integral part of these cities in developed countries. To use small-scale wind turbines and dispersed electricity generation, the performance of such turbines in the vicinity of various buildings in the urban environment should be investigated. In this study, the power characteristics of a conventional Savonius wind turbine in the vicinity of a large circular cross-sectional building are assessed under a free-wind speed of 6 m/s. To this, the Savonius rotors are installed at a constant non-dimensional distance of 2 from the building envelope at different installation angles of 30°, 45°, 60°, and 90°. Additionally, to understand the effects of the rotation direction of the rotor, two possible rotations, namely, inward and outward rotations are studied. Computations are performed for tip speed ratios of 0.4, 0.8, and 1.2. The obtained results reveal the significant impacts of installation angle and rotation scenario. Examination of the obtained data shows that, depending on the for tip speed ratio, with inward rotation of the rotor at installation angles of 60° and 90°, the maximum improvements in the power coefficient are found compared to the reference case.