Numerical optimization study to install air curtain in a subway tunnel by using design of experiment

Subways are a major mode of public transportation in metropolitan cities. A proper ventilation system is required to maintain indoor air quality in subway tunnels. Platform screen doors improve the platform environment but degrade air quality in subway tunnels. Trains transport fine particles from the tunnel into the platform. An air curtain installation in the subway tunnel permits traffic and reduces the transfer of bacteria and fine particles. The existing tunnel of Seoul subway was investigated by using computational fluid dynamics and design of experiment method for optimum air curtain installations. The flow field of the subway tunnel was computed by using ANSYS CFX software. Minitab software was used to generate the design process and to analyze the computational results. The computational domain of the existing tunnel included two natural ventilation shafts, one mechanical shaft, and the twin tracks. The height, width, and length of each track were 6, 4, and 400 m, respectively. The air curtain installation area was located between the natural and the mechanical ventilation shafts of Rrack 1. The design variables for the optimization study were the width, velocity, and installation location of the air curtain. The object function for optimization was mass flow rate at the natural ventilation shaft. The length of the air curtain was fixed at 4 m. The predicted mass flow rates were analyzed with the design variables by using the response surface method (RSM). The optimum values of the design variables, i.e., velocity, width, and installation location were 25 m/s, 0.2 m, and 5.8195 m, respectively. The maximum mass flow rate with the optimum design values was 114.4447 kg/s. The optimum values of the design variables were validated by computing the tunnel with the optimum values from RSM. The mass flow rate in the natural ventilation shaft 1 was 114.2 kg/s, as predicted. The optimization study can be helpful to set the optimum design conditions for the subway ventilation system.     

A computational analysis of the airflow in a twin-track subway tunnel with a sliding-curtain to improve ventilation performance

A computational model of an actual Seoul subway tunnel was analyzed in this study. The computational model was comprised of one natural ventilation shaft, two mechanical ventilation shafts, one mechanical air supply, a twin-track tunnel and a train. The natural ventilation shaft discharges and supplies air due to the train’s movement. The mechanical ventilation shaft and the mechanical air supply discharges and supplies, respectively, the airflow from the axial flow fans in the middle of the ducts of the shafts. A sliding-curtain was installed in the tunnel. The objective of this study was to numerically investigate train-induced airflow in the twin-track subway tunnel with natural and mechanical ventilation shafts and an installed curtain. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The airflow velocity from the computational results was validated by experimental results. Understanding the flow pattern of the train-induced airflow in the tunnel is necessary to improve ventilation performance. The ventilation and aerodynamic characteristics in the tunnel, including train-induced airflow, were investigated by analyzing the volume flowrate at the exits of the ventilation shafts and the velocity in the tunnel. The computational results were compared to cases with and without a curtain installed in the twin-track tunnel. As the train passed the mechanical ventilation shafts, the quantity of discharged-air in the ventilation shafts decreased rapidly. The flowrate at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The airflow at the natural shaft and mechanical ventilation shaft 2, which was closest to the curtain, was increased. The computational results showed that the installed curtain can improve ventilation performance in the tunnel.     

A numerical simulation of train-induced unsteady airflow in a tunnel of Seoul subway

This study has been conducted to investigate numerically the characteristics of train-induced unsteady airflow in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train is applied. The validation of the present study has been carried out against the experimental data obtained by Kim and Kim [1] in a model tunnel. After this, for the geometries of the tunnel and subway train which are very similar to those of the Seoul subway, a three-dimensional unsteady tunnel flow is simulated. The predicted distributions of pressure and air velocity in the tunnel as well as the time series of mass flow rate at natural ventilation ducts reveal that the maximum exhaust mass flow rate of air through the duct occurs just before the frontal face of a train reaches the ventilation duct, while the suction mass flow rate through the duct reaches the maximum value just after the rear face of a train passes the ventilation duct. The results of this study can be utilized as basic data for optimizing the design of tunnel ventilation systems.     

开孔率对竖井型城市隧道阻滞工况自然通风影响的分析

为了分析开孔率对竖井型城市隧道在交通阻滞工况下对自然通风的影响,本文采用无量纲分析和模型试验的方法对其速度场、温度场和污染物浓度场进行了研究。通过对阻滞工况下隧道内空气所受的热压浮升力与重力的无量纲分析,得到了模型试验所需的热压通风相似准则数和温度分布相同所需散热量比例常数。利用所得相似条件搭建了开孔率分别为2.8%、3.7%、4.5%的3组试验模型进行试验。试验结果表明,随着开孔率的增大隧道内最不利通风段的通风效果得到改善,但竖井的建设费用大幅度提高。选择合适的竖井开孔率既能满足阻滞工况下隧道的通风要求,也能避免开孔率盲目增大导致的初投资浪费,对城市隧道建设具有重要意义。     

城市隧道竖井送排式通风优化

为了更有效地发挥送排风竖井在城市隧道中的通风作用,选择合理的送排风组合是一个重要的途径。本文采用CFD方法,对5种排风速度与5种送风速度的25种送排风组合进行了模拟,分析了不同送排风组合隧道内的通风效果。模拟结果表明:当送排比大于1时,隧道内会出现回流,且送排比越大,隧道回流效应越强,经济效益越低。隧道内气流分布和污染物浓度都与送排风组合有关,较大的排风速度虽有利于降低污染物浓度,但能耗也较大,过大或者过小的送风速度都会使隧道局部污染物浓度过高,降低通风作用。因此,综合考虑隧道通风经济性和实用性,确定排风速度为5~6m/s和送风速为8~12m/s为最优组合。选择合理的送排风组合,不仅能有效控制隧道污染物浓度,还能减少能量损失,对城市隧道的建设具有指导意义。     

Numerical study of air curtain systems for blocking smoke in tunnel fires

A tunnel fire is very dangerous to drivers because of generated poisonous gases. For dealing with this hazardous situation, ventilation systems for smoke control are installed so that drivers can be safely evacuated from the site of the fire. An air curtain system is one of these ventilation systems, and such a system in a tunnel generates an air wall to block the passage of poisonous gases. In this study, airflow discharge patterns of air curtain systems were analyzed using Computational fluid dynamics (CFD), with two design parameters—to predict the ability of the air curtain to block the contaminated adverse air-flow in the tunnel. The considered two design parameters were the installed angle of the slit nozzle (N_A) and the discharged air velocity at the slit nozzle outlet (N_V). The tunnel geometry for the CFD analysis was a two-lane type with a tunnel length of 100 m and an elliptical cross section. The height of the tunnel was approximately 7.3 m and the height of the installed air curtain was about 4.9 m from the road surface. In this study, the heat release rates of the fire, the distance from the fire site, and the temperature of the working fluid were respectively assumed to about 20 MW, 50 m and 473 K, on the basis of the NFPA 502. The CFD analysis demonstrated that an N_A of 0 deg could not block the adverse air flow due to a realistic tunnel inlet-outlet static pressure difference (ΔP_S). An N_A of 20 deg was required to effectively block the adverse flow. The blocking failure first formed at the sidewall of the tunnel, and it proceeded toward the center of the tunnel cross section when the adverse wind was strong. That aspect of the blocking failure was judged to be due to the fact that the tunnel cross section is elliptical. Anyway, when the tunnel ΔP_S was increased, that showed the need for a high N_V.     

Experimental study of a semi-passive ventilation grille with a feedback control system

The diffusion of window frames with low air permeability, due to the energy saving regulations, has implied in several cases the worsening of the indoor microclimate and air quality. On the other hand, air-tight window frames imply uncontrolled and too high air change rates. The mechanical ventilation not always is a practicable solution because of economic reasons and because it implies energy waste. Various Italian and European environmental and energetic laws take into consideration and promote the use of controlled natural ventilation, though this definition is not associated to well defined and tested technical solutions. An adequate solution can be achieved by using semi-passive self adjustable ventilation devices, able to ensure controlled changes of indoor air. In this paper, a semi-passive damper with a feedback control system is proposed and its behavior is investigated by means of experimental study. The presented semi-passive grille allows to control the air flow rate, injected into the room by natural or artificial pressure gradient, more effectively than the usual passive ventilation grilles made available by the present industrial production. However, since the semi-passive grille has a one-way flow, in the natural ventilation of a flat the proper functioning of the system could be ensured with a more complex configuration, with respect to the passive self-regulating grilles, able to limit the flow of fresh air in the presence of high levels of Δp; conversely, it could have widespread use in applications requiring a more accurate control of airflow in case of mechanical ventilation plants.     

Performance measurement of a smoke extraction system for buildings in full-scale hot smoke test

The current inspection method for a smoke extraction system in Taiwan measures whether the air flow of the smoke vent conforms to the design value. However, this method is inapplicable to natural smoke extraction systems. As the plugholing effect is disregarded, adequate air flow cannot ensure that the system will exhaust smoke effectively during a fire. Hence, a full-scale hot smoke test for smoke extraction systems is necessary. Some international test criteria are formulated using visible smoke and alcoholic fuel which is pollution-free after combustion. The effectiveness is judged only by visually observing the smoke’s flow direction, which is indeed unscientific. This study used a string of vertical smoke layer measuring instruments composed of several approved photoelectric smoke detectors, as well as a light attenuation measuring device composed of illuminance meters to conduct tests on the effect of makeup air. The results proved that the former one uses different height induction times to judge the position of the smoke layer effectively, while the latter one uses the light attenuation rate to distinguish the smoke density instantly and accurately. The obtained experimental data were consistent with the onsite smoke distribution. The two sets of equipment designed in this study can be used for full-scale hot smoke tests to obtain performance data for a smoke extraction system.     

Evaluation of optimal water flow and temperature in response to outdoor air temperature in plastic greenhouse with recirculated water curtain system

This study evaluated the optimal supply water temperature and flow rate in response to the outdoor air temperature in order to maintain a target indoor air temperature and minimize the amount of energy required to reheat a recirculated water curtain in a plastic greenhouse. This paper proposed a multiple regression model that estimated the indoor air temperature using the outdoor air and the inlet water temperatures, as well as the water flow rate, as independent variables. We also established a multiple regression model that estimated the average amount of energy required to reheat the recirculated water curtain. To this end, the study analyzed and quantified a reasonable inlet water temperature and water flow rate in response to the outside air temperature using isothermal and iso-energy curves. The results indicated that maintaining a higher water flow rate was preferable to maintaining a higher inlet water temperature for cultivation purposes.

     

Comparison of volume flow rate and volume-averaged local mean age of air for evaluating ventilation performance in natural ventilation

Evaluating the ventilation performance is an important part of natural ventilation studies. We considered the volume flow rate, which is used by many researchers, and the volume-averaged Local mean age of air (LMA) as the ventilation performance parameters to evaluate the performance of natural ventilation. Computational fluid dynamics (CFD) simulations were performed on an isolated building model of cross ventilation that contained two openings on the windward and leeward wall and single-sided ventilation model that consisted of a single opening. Parametric studies were performed to evaluate the ventilation performance of eight different building configurations in cross ventilation and single-sided ventilation. Using the volume flow rate it was difficult to evaluate the ventilation performance when the inlet and outlet were very close in cross ventilation and, in single-sided ventilation, it was difficult to evaluate when the airflow speed was fast near the opening but did not penetrate inside the building. While the volume-averaged LMA was an adequate parameter for representing the ventilation performance of the building, the LMA field was a more accurate representation of the local ventilation performance inside the building than the velocity vector field.

     

Estimation of appropriate capacity of ventilation system based on the air infiltration rate in Korean classrooms

The appropriate capacity of a ventilation system based on the air infiltration rate in Korean classrooms is investigated to obtain optimal design conditions for ventilation systems. Theoretical and the experimental analyses are performed to estimate the proper ventilation capacity with a consideration of the air infiltration, the indoor air quality, and the ventilation rate. The air infiltration rate of the classroom is measured within the range of 0.5–1.5 1/h, and the required ventilation rate should be decided not by the contaminants (Formaldehyde and TVOC) emitted from the construction materials but by the carbon dioxide (CO₂) emitted from human breath. The appropriate capacity of the ventilation system based on the air infiltration rate of the classroom for elementary schools is 500CMH and for middle and high schools is 800 CMH. The measured and the estimated values of CO₂ concentrations are very similar and the modeling equation of CO₂ concentration can be used as a reference for the proper estimation of ventilation rate in Korean schools.     

Measurement of indoor air quality for ventilation with the existence of occupants in schools

This paper evaluates the performance of ventilation for the removal of indoor pollutants as a function of ventilation rate and the number of occupants in a test room and school classroom. An experimental apparatus consists of a test room, a tracer gas supply system, a gas detector, and a fan for ventilation air supply with a controller. The ventilation performance is evaluated in a step-down method based on ASTM Standard E741-83 using CO₂ gas as a tracer gas in the test room of 35 m³. For the ventilation air flow rate of 1.0 ACH, a recommended ventilation flow rate of Korea school standard for acceptable indoor air quality in the case of one person, CO₂ gas concentration decreases up to 55% within 50 minutes without occupancy and increases up to 75% in the case of one occupant. Also indoor air quality at the school classroom is investigated experimentally.     

Experimental study of ventilation performance of a novel integral-type air conditioner with heat recovery using R290

The leaking safety of air conditioner using R290 has been a research hotspot in recent years, one method to lower the risk of explosion after leakage is utilizing ventilation. For fresh air conditioner, it's common to use thermal anemometry and differential pressure flowmeters to measure ventilation flow rate. However, there is non-negligible error especially under low air volume flow rate conditions. In this paper, a novel integral-type air conditioner with heat recovery using R290 is proposed. And the relevant influencing parameters are analyzed and experimentally studied. The results show that tracer gas method is an effective way to measure ventilation flow rate, and the novel integral-type air conditioner can meet the needs of the ventilation standards. The air volume flow rates of indoor unit fan and outdoor unit fan are dominant factors affecting ventilation flow rate. The outlet area of exhaust air duct is more sensitive than the inlet area of fresh air duct in exerting influence on ventilation flow rate, while the indoor temperature has a mild impact on ventilation flow rate.     

An experimental study on the performance of air/water direct contact air conditioning system

Direct contact air conditioning systems, in which heat and mass are transferred directly between air and water droplets, have many advantages over conventional indirect contact systems. The purpose of this research is to investigate the cooling and heating performances of direct contact air conditioning system for various inlet parameters such as air velocity, air temperature, water flow rate and water temperature. The experimental apparatus comprises a wind tunnel, water spray system, scrubber, demister, heater, refrigerator, flow and temperature controller, and data acquisition system. The inlet and outlet conditions of air and water are measured when the air contacts directly with water droplets as a counter flow in the spray section of the wind tunnel, and the heat and mass transfer rates between air and water are calculated. The droplet size of the water sprays is also measured using a Malvern Particle Analyzer. In the cooling conditions, the outlet air temperature and humidity ratio decrease as the water flow rate increases and as the water temperature, air velocity and temperature decrease. On the contrary, the outlet air temperature and humidity ratio increase in the heating conditions as the water flow rate and temperature increase and as the air velocity decreases.     

Feasibility of using thermal response methods for nonintrusive compressed air flow measurement

Robust, low-cost nonintrusive flow meters are of interest in many industries. In particular, a reliable nonintrusive flow measurement for the diagnosis of air leaks in compressed air systems is desirable. Measurement of the air flow due to leaks in the system ensures an accurate estimation of potential cost and energy savings. This study evaluates a novel method of using thermal responses to nonintrusively measure leakage rates in compressed air lines. The method uses heat and the resulting thermal response to calculate the flow rate inside the compressed air line. Compared to the current methods for flow measurement, this method can simplify flow measurement while decreasing the sensitivity to errors when measuring flow rates. In this study, the methodology of the proposed method is explained along with the potential advantages to the design. Two approaches are evaluated: a dynamic step response and sinusoidal frequency response. Simulated tests evaluate the feasibility of the proposed methods, followed by experiments that validate the simulation results. A clear correlation between the thermal step response and the flow rate indicate viability of the proposed method in simulation. Experimental results yielded similar results, confirming the validity of the proposed method. The results of a field test in an industrial environment demonstrate the capability of the approach to other flow rate measurement techniques.     

倾斜式太阳能烟囱强化自然通风理论研究

倾斜式太阳能烟囱利用太阳辐射增加烟囱内空气温度,烟囱内外空气温差形成的密度差提供了自然通风所需的驱动力。根据质量守恒和能量守恒方程给出倾斜式太阳能烟囱通风量计算方法,并将计算结果与文献试验测试值进行了对比,分析了烟囱长度、宽度、深度及倾角对通风量的影响,计算了倾斜式太阳能烟囱用于乌鲁木齐地区的通风量,并与竖直式烟囱进行对比,计算结果表明,相同结构尺寸下增加50°倾角可使通风量增加11.52%,是一种值得进一步研究的自然通风方式。     

地铁车辆轮轴修复加工新方法

对地铁车辆轮轴进行了疲劳分析,给出了轮轴必须修复的原因.采用工艺装备对地铁车辆轮轴进行动态仿真状况下修复的新方法,达到了预期的效果.     

Numerical analysis of particle concentration around the air-inlet of a train in a tunnel by using a discrete phase model

Subways are used for public transportation as a commuting medium in Korea. Subway trains operate mainly through tunnels. Fine particles generated by friction between rails and train wheels affect the air quality inside a train because the particles enter the ventilation system of the train passing through a tunnel. The PM₁₀ concentration has been mainly used to evaluate indoor air quality, and the PM_2.5 concentration has measured recently. Therefore, in this study, the concentrations of the particles entering the air-inlet with respect to particle sizes including 0.1, 1, 2.5 and 10 μm were investigated by using numerical analysis with ANSYS FLUENT software. The particle analysis was performed corresponding to 10, 40 and 80 km/h. It is expected that the numerical results would be helpful in studying the effect of particles corresponding to PM_2.5 on the ventilation system, to improve the air quality inside a train passing through a tunnel.     

Measurement of gas flow in short ducts,also rectangular

This paper presents a discussion of the system of the measurement of the gas flow (of air or flue gases) dedicated particularly for use in rectangular ducts with short straight sections and with considerable cross-section dimensions (above 1 m). The measurement is conducted at a necking – the duct inset – with a single-point sensor such as the Prandtl tube. The measuring method may be used in newly designed air and flue gas ducts, as well as in those already in service, such as air conditioning or ventilation systems and power boilers.     

新疆地区太阳能烟囱复合蒸发冷却通风降温系统

提出了太阳能烟囱复合蒸发冷却系统,对复合系统模型进行了理论分析及计算,得出通风量与烟囱高度、宽度及太阳辐射强度之间的关系。结果表明,太阳能烟囱的自然通风量随太阳能辐射强度及烟囱高度的增加而增加;在计算条件下,当宽度取1m时通风量取得最大值。在此基础上分析得到太阳辐射照度400W/m2、烟囱高度3m、宽度1m时,太阳能烟囱复合蒸发冷却系统应用于乌鲁木齐建筑时烟囱的理论通风量为0.21kg/s,该通风量基本满足乌鲁木齐夏季通风设计工况下,蒸发冷却降温时所需动力(0.23kg/s),且室内通风换气次数达到10次/h以上,是一种节能环保的自然通风降温技术。