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

In this numerical study, the effect of the water_sprinkler system in controlling and extinguishing the fire in a multi-storey building was carried out using FDS_software. The geometry consists of a five_story_building with total of 25 units, the fire room is located in the third unit on the ground_floor, and the fuel_source is in the center of the room and is heptane type. In each room, the parameters of temperature and CO and CO2 were measured and the results were checked from the start of the combustion process up to 100 seconds for two cases of with_ and without_sprinklers. it was found that the numerical results of this study have a relative error of 8% with the experimental results. In addition, the temperature in the third room of the first_floor has reached 700 degrees Celsius (above critical conditions) within 100 seconds in the case of without_sprinklers; However, the extinguishing occurred in the fire room in less than 20 seconds using sprinkler. Such a behavior also happens to the toxic species of CO and CO2, so that they are in danger in all the upper floors of the fire room without_sprinklers. In a summary, taking into consideration the minimum, maximum and mean values of temperature and toxic species, can emphasize the importance of sprinkler in extinguishing fire in the fire_room and controlling toxic and hot_gases in rooms.

The pollution and spread of fine dust in the urban environment causes a wide range of diseases. Pollution caused by fine dust with different origins spreads in a wide range of atmosphere. Our understanding of the mechanism of fine dust distribution and its disturbance in urban areas is very important because it helps us to reduce the effects of this type of pollution. Due to the turbulent nature of the wind flow inside the city, the method of simulating large eddies has been used to model this turbulence, which is widely used in computational wind engineering. In this research, the investigation of fine dust in the urban environment has been investigated. For this purpose, the influence 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 have been investigated in two separate computing spaces. By comparing the results between 0° and 10° angle, it can be seen that increasing the angle increases the irregularity of the flow and as a result, more fine particles spread and remain in the urban environment. According to the results, it was observed that the method of simulating large eddies is a suitable method for simulating wind flow and fine dust concentration around buildings.

The low efficiency of water harvesting in conventional collectors has limited the development of its use in fog-prone areas. One of the ways to improve efficiency is to increase the number of layers in different collectors. For this purpose, the effect of the number of layers on the efficiency of conventional collectors was investigated based on theoretical relations and also by conducting experimental tests. In the laboratory section, after the installation and commissioning of the fog water harvesting system, the output flow from the humidifier hit the collecting plate and after the fog extraction, a percentage of it was transferred to the storage tank in the form of water droplets. By measuring the amount of collected water, the efficiency of collectors with 4 layers was estimated and compared. The results showed that with the increase in the number of layers, the theoretical efficiency of Raschel mesh first increases and then decreases, but in aluminum mesh, the increase in efficiency continues with the increase in the number of layers. The highest theoretical efficiency of Raschel mesh and aluminum mesh can be achieved in the case of 4 and 7 layers, respectively. According to the results of the experimental test, the highest water collection efficiency of Raschel and aluminum mesh was obtained in 5 and 6 layers, respectively.

The microwave irradiation has used to speed up chemical reactions in comparison of conventional reactions. Because the electromagnetic waves cause increasing the molecular vibrations. Energy consumption is reduced by using electromagnetic waves. As a results, electrodes corrosion rate is reduces. 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 maxwell equation for electromagnetic waves modeling are taken into the account. At the first, the effect of electromagnetic waves on the ion separation has been investigated. Results have shown that an obvious enhancement has been occurred in ion separation due to electromagnetic irradiation. The dechlorination in EMER process has been improved more than three times in compare with EL process. Also, the ion separation has been enhanced linearly by increasing the cell potential and initial salinity. Quantitative results of each parameters are shown in the paper.