Smoke Exhaust Efficiency Research Articles

Effect of Platform Screen Doors on Mechanical Smoke Exhaust in Subway Station Fire

Abstract In subway station fires, the most immediate threat to passengers’ life is not the direct exposure to fire, but the smoke inhalation with hot air and toxic gases. Thus, the study on efficient smoke control is of theoretical and practical significance. In this paper, the fire dynamics simulator (FDS) is used to study the effects of open mode of platform screen doors (PSDs) on mechanical smoke exhaust in subway station fire. The fires is located on the middle of the platform. And the results indicate that open platform screen doors on both sides of the platform, can not only reduce the gas temperature, but also improve the efficiency of mechanical smoke exhaust, which are beneficial to safety evacuation.

Particle Size Distribution and Diffusion for Simulated Cooking Fume

Studying particle size distribution and dispersion characteristics of cooking oil fume can help to analyze the influence of the particles on indoor air quality and the health of the residents.Electrical low pressure impactor (ELPI) was employed to measure the number and mass concentration of the particles size range of 0.03-10 μm at two different locations in the kitchen space with smoke exhaust on and off,respectively.The cooking particles were mostly located at below 655 nm.The smoke exhaust with open condition could remarkably decrease the kitchen's cooking fume.The number concentration of particles decreased from 2.8×106 cm-3 to 2.3×105 cm-3,and PM2.5(aerodynamics diameter ≤2.5 μm particulate matter) mass concentrations decreased from 85.9 mg·m-3 to 6.2 mg·m-3.The sucking efficiency of smoke exhaust for PM10 was higher than PM2.5.The number concentration of particles could be declined by 65%,and the cooking fume of PM2.5 could be declined by 75% during the diffusion process detected at the area of 3 m far away from the area where cooking took place.The distribution of PM2.5 mass concentration field of oil fume was simulated by computational fluid dynamics.The temperature field distribution of oil fume was monitored by infrared camera,presenting sector diffusion with the temperature decreasing from 70℃ to room temperature.

Full-scale fire experiments and simulation of tunnel with vertical shafts

Based on the data gained from the full-scale experiments and Computational Fluid Dynamics theory, the fire characteristic in tunnel with natural ventilation systems is researched. The system consists of groups of openings with vertical shafts on tunnel roof. Firstly, the temperature, concentration, spread and sedimentation characteristics of smoke are simulated using CFD software under full-scale experiments’ conditions. Plug-holing and adhered spill plume can be observed from the simulation results. These special phenomena decrease the efficiency of smoke exhaust. Nevertheless, most smoke can be exhausted through the shafts in the condition of natural ventilation systems. Furthermore, the simulation results are compared with the data gathered from full-scale experiments and the simulation results agree well with the experimental data. Lastly, the conclusion is drawn and the future trends are proposed. It provides theoretical support to adopt this innovative tunnel with vertical shaft in future.

Effects of Supply-exhaust Ratio on Smoke Exhaust Efficiency in a Large Machinery Space

The effects of supply-exhaust ratio on smoke exhaust efficiency in a large machinery space were studied numerically. The simulation model used was a certain machinery space on a naval ship and two types of fire source are provided. Various parameters, such as the smoke layer height, smoke concentration and gas temperature were considered. Results show that the mechanical exhaust system could decrease the gas temperature and smoke concentration, and increase the visibility in a machinery space fire. With the increase of supply-exhaust ratio, the smoke control efficiency is improved. Considering both of smoke control efficiency and consume of energy and cost for the typical machinery space, a value about 70% of supply-exhaust ratio is suggested to be used in mechanical exhaust system.

An experiment and simulation of smoke confinement and exhaust efficiency utilizing a modified Opposite Double-Jet Air Curtain

Fires in high-rise buildings often result in tremendous property losses and heavy casualties. Smoke has been reported to be the main cause of these casualties. A modified Opposite Double-Jet Air Curtain (ODAC) is introduced in order to confine smoke movement and to exhaust smoke during a high-rise building fire. Here, a study including an experiment and a numerical simulation, was performed to determine the efficacy of a modified ODAC. The experiment was conducted on a 1:12 scale model of a high-rise building. A complementary Fire Dynamics Simulator (FDS) simulation was conducted on a full scale building. The influences of the air curtain discharge velocity and heat release rates (HRRs) were examined.The results of this study show that given the same supply air volume and HRR, the carbon monoxide (CO) concentration with the ODAC is clearly lower than the levels found with a traditional air curtain in a high rise building fire. The gas temperatures in the hallway increased significantly with the increase of HRR, and when the HRR reached 1.5MW or more, a significant increase in the temperature of the smoke in the stairwell entrance was observed. When HRR reaches 2MW, and the velocity has increased to 9m/s, the CO concentration in the entrance of stairwell just meets the minimum Safety and Health standards.

Preliminary Study on Exhaust Efficiency of Smoke Management System in Tunnel Fires

Exhaust efficiency in tunnel fires with mechanical means was discussed. Heat exhaust efficiency and smoke exhaust efficiency were defined and studied under two different exhaust modes (longitudinal exhaust and transverse exhaust) respectively. Exhaust efficiency depends on smoke generation rate, exhaust rate, heat loss through walls of tunnel, configuration of extraction installations and so on. Under smoke extraction, smoke exhaust efficiency equals 1 if a quasi-steady vented stage without upstream outflow forms, otherwise smoke exhaust efficiency is less than 1. Heat exhaust efficiency is always less than 1 since part of the heat released by the fire is lost through the solid boundaries of tunnel by radiative and convective heat transfer between the smoke and ceiling lining. Based on experimental data obtained from a series of fire tests in a model tunnel, heat exhaust efficiency was estimated and influencing factors were discussed. In tunnel fires with transverse mechanical exhaust system, heat exhaust efficiency varies from 20% to 50%. Heat exhaust efficiency increases along with the reduction of the number of exhaust inlets turned on while extracting and decreases along with the increase of the area of exhaust inlet. However, quantitative influence of inlet position on exhaust efficiency still need further study and will be reported later.

A Numerical Study on the Influence of Smoke Vent Height on Mechanical Smoke Exhaust Efficiency for Platform Fire in a Subway Station

A Numerical Study on the Influence of Smoke Vent Height on Mechanical Smoke Exhaust Efficiency for Platform Fire in a Subway Station

Experimental studies of mechanically exhausted smoke within the transport passage of the main transformer of an underground hydropower station

Scale modeling experiments were conducted in a 1/12th scale model of the underground transport passage of the main transformer of a hydropower station model. The influence of heat release rate and smoke exhaust rate on the smoke exhaust efficiency was investigated. Results showed that the smoke exhaust process was less efficient when the heat release rate was larger, and that better smoke control may be obtained with larger smoke exhaust rates. The results of the scale modeling experiments have been compared with full-scale experimental results in other studies. Through comparison, it can be concluded that the results of the scale modeling experiments may be extrapolated to full scale, and the spill plume has similar characteristics to the smoke generated directly from fires that had spread along the passage.

Experimental study of air entrainment mode with natural ventilation using shafts in road tunnel fires

A set of burning experiments with n-heptane pool fire were conducted to investigate the air entrainment mode with natural ventilation using shafts in road tunnel fires. One criterion was proposed to determine the critical shaft height of the plug-holing occurrence in our previous work whereas this study quantificationally analyzes the effect of plug-holing on the smoke exhaust efficiency. The disturbance of smoke exhausting on the smoke–air interface, which causes different amounts of fresh air exhausted directly and indirectly, is investigated. Results show that using vertical shafts to discharge smoke leads to a strong mixing process between the smoke layer and the fresh air. Consequently, about 2/3 of the smoke exhausting rate of the shaft is air. Moreover, some of the entrained air mixes into the smoke layer downstream the shaft, resulting, in a small reduction amount of the spilling smoke, which also proves an inefficient smoke exhausting process. Hence, for the sake of improving effectiveness of natural ventilation, some significant improvements are needed in practice.

Numerical Simulation of Smoke Exhausts Function of Roof Vent in Compartment Fires

The influence of roof vent area and fire source area on smoke exhaust function of roof vent is provided in this paper. Numerical simulation results show that the temperature of hot smoke layer increases with the increases of heat release rate and decreases as the roof vent area increases. For the evaluation criterion with temperature difference, with the increase in roof vent area and fire source area, the smoke exhausts function of roof vent was enhanced. But for the evaluation criterion with efficiency of smoke exhaust, the smoke exhaust efficiency increases as the roof vent area increase and decreases with the increases of fire source area.

A study of the effect of plug-holing and boundary layer separation on natural ventilation with vertical shaft in urban road tunnel fires

A set of burning experiments were conducted to investigate the effect of vertical shaft height on natural ventilation in urban road tunnel fires. Two special phenomena, plug-holing and turbulent boundary-layer separation were observed, both of which will influence the effect of smoke exhaust. When shaft height is relatively small, the boundary layer separation is significant and vortexes form in the upstream region inside the shaft, causing the backflow of gas mixture and preventing the throughflow of smoke. With the increasing of shaft height, the boundary layer separation becomes inconspicuous and the plug-holing occurs, leading to the ambient fresh air beneath smoke layer being exhausted directly, which will strongly decrease the smoke exhaust efficiency. Therefore, it is not the case that the higher the vertical shaft, the better the smoke exhaust effect, there exist a critical shaft height in which the boundary layer separation can be diminished to a large extent and overmuch entrainment of fresh air such as plug-holing can be avoided. In addition, the critical shaft height related to better effect can be determined by the new criterion of Ri′(Ricritical′=1.4) proposed in this paper.

Influences of Smoke Exhaust Effect by Setting Atria Buffer Zone in Straight Corridor of Building

In high-rise building fires, a great deal of fresh air will be sent into the fire floor when pressurization is taken. Smoke is diluted by the fresh air, and the efficiency of mechanical smoke exhaust is reduced. The assumption that set atria buffer zone in straight corridor of high-rise building is put forward, and mathematic model of smoke flow in high-rise building. The results show that, for straight corridor, setting atria buffer zone the efficiency of mechanical smoke exhaust is about 3.6% higher than which atria buffer zone is not set, and smokeless zone is formed in the corridor nearby atria, and it is helpful to escaping from fire floor for people.

Numerical Simulation Study of Smoke Exhaust Efficiency in an Atrium

The influence of multiple parameters on smoke exhaust efficiency in an atrium is the subject of this article. Detailed information is obtained through a series of four numerical simulations, all but one case involving a mechanical exhaust system. Quantitative smoke exhaust efficiencies in various cases are evaluated and compared. The investigated parameters include the activation time of the smoke exhaust system, the mechanical fan capacity, the elevation of make-up air inlets and the horizontal location or distributed arrangement of the inlet distribution. It is revealed that all these parameters have impacts on smoke exhaust efficiency to different degrees and hence on the performance of the smoke exhaust system. Improper design and operation may lead to a significant reduction in efficiency. The mechanism that causes the reduction of efficiency is discussed. Velocity and temperature fields are analyzed to reveal the interactions between the fire plume and the inlet jet flows.

Experimental investigation on influence of smoke venting velocity and vent height on mechanical smoke exhaust efficiency

A set of burning experiments were conducted to investigate the influence of smoke vent height and exhausting velocity on mechanical smoke exhausting efficiency. Results have shown that the smoke exhausting process becomes more efficient due to the increased smoke vent height and the decreased exhausting velocity, which eliminate the plug-holing issue with fewer disturbances on the smoke layer interface. For each certain exhausting velocity, there is a critical value of distance between the vent and the bottom of the smoke layer. When the distance is less than the critical value, the smoke exhausting is inefficient, and the efficiency decreases sharply as the distance decreases. Contrarily, when the distance is greater than the critical value, a good efficiency can be acquired and the exhausted smoke increased relatively slowly as the distance increases. A critical Froude number, proposed by Hinkley to predict the onset of plug-holing effect in gravity venting systems, was validated in the experiments. However, the experimental results indicate that in the tests without the plug-holing, the fresh air entrained due to smoke exhausting is up to 48% of the mechanical exhausting rate.

Two typical phenomena from the numerical simulation of fire and smoke transport in a gymnasium fire

Navier-Stokes equations are solved to simulate a gymnasium fire. The equations are simplified by weakly compressible low Mach number assumption. Turbulence effect is simulated using Smagorinsky large eddy simulation (LES) model. The mixture fraction combustion model is adopted to simulate the burning process. With the analysis of computed velocity and temperature field, two important phenomena, named door effect and smoke plug-holing, are found to be responsible for the deterioration of smoke exhaust efficiency when natural ventilation or forced ventilation is present. Some explanations are made to elucidate these effects’ mechanism. An improved design of smoke ventilation system is suggested.

Full-scale experimental studies on mechanical smoke exhaust efficiency in an underground corridor

Full-scale burning tests were conducted in a full-scale underground long corridor with beamed ceiling and smooth ceiling. The influence of air-supply opening position on the smoke exhaust efficiency was studied. The operation time of the smoke exhaust fan was also discussed to obtain a better smoke exhaust. Results showed that the smoke exhaust would be more efficient when air-supply openings were some distance away from the smoke exhaust openings. When the air-supply opening was near the smoke exhaust opening, even with larger smoke exhaust rate, it still gave poor smoke control results. Two comparing tests on the effects of operation time indicated that it would give poor smoke control ability when the smoke exhaust system operated too early. Finally, some future research topics were also discussed in this paper.