Physical scale modelling of adhered spill plume entrainment

This work provides new experimental data to characterise entrainment of air into adhered thermal spill plumes using physical scale modelling. For the two-dimensional plume, the rate of entrainment with respect to height of rise is approximately half that of an equivalent two-dimensional balcony spill plume. For the three-dimensional plume, the rate of entrainment appears to be linked to the plume behaviour, which has been characterised in terms of the width and depth of the layer flow below the spill edge. In general, a layer flow below the spill edge that is shallow compared to its width will tend to adhere to the wall above the opening compared to flows whose depth approaches its width. This work proposes new empirical entrainment design formulae that have been developed on a more general basis compared to existing methods.     

Air entrainment into balcony spill plumes

New plume formulations have been developed for assessing air entrainment into thermal plumes that spill over a balcony edge into an atrium void.     

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Research on microclimate ventilation systems, which mostly involve free jets, points to delivery of better ventilation in breathing zones. While the literature is comprehensive, the influence of contaminant entrainment in jet flows and its implications on the delivery of supplied air is not fully addressed. This paper presents and discusses entrainment characteristics of a jet issued from a round nozzle (0.05 m diameter), in relation to ventilation, by exploring the velocity and temperature fields of the jet flow. The results show a trend suggesting that increasing the Reynold number (Re) reduces ambient entrainment. As shown herein, about 30% concentration of ambient air entrained into the bulk jet flow at Re 2541 while Re 9233 had about 13% and 19% for Re = 6537/12 026 at downstream distance of 8 diameters (40 cm). The study discusses that “moderate to high” Re may be ideal to reduce contaminant entrainment, but this is limited by delivery distance and possibly the risk of occupant discomfort. Incorporating the entrainment mixing factor (the ratio of room contaminants entrained into a jet flow) in performance measurements is proposed, and further studies are recommended to verify results herein and test whether this is general to other nozzle configurations.     

Predicting Spill Plumes with the Fire Risk Zone Model B-RISK

Recent experimental research on spill plume entrainment has developed a range of empirically-based formulae for smoke management design. These formulae form the spill plume entrainment model in B-RISK, a new fire risk zone model. This article describes the performance of B-RISK in predicting spill plume entrainment. Selected experimental data from the series of reduced-scale experiments used to form the new design formulae have been used for model validation, along with other full-scale experimental data from ‘hot smoke tests’ conducted to assess the performance of installed smoke management systems. B-RISK provides predictions of the plume clear-layer height that generally agree with experimental results within the range of experimental error. This gives confidence in its use to predict spill plume entrainment for smoke management design purposes.     

Calculation and design of tunnel ventilation systems using a two-scale modelling approach

This paper develops a novel modelling approach for ventilation flow in tunnels at ambient conditions (i.e. cold flow). The complexity of full CFD models of flow in tunnels or the inaccuracies of simplistic assumptions are avoided by efficiently combining a simple, mono-dimensional approach to model tunnel regions where the flow is fully developed, with detailed CFD solutions where flow conditions require 3D resolution. This multi-scale method has not previously been applied to tunnel flows. The low computational cost of this method is of great value when hundreds of possible ventilation scenarios need to be studied. The multi-scale approach is able to provide detailed local flow conditions, where required, with a significant reduction in the overall computational time. The coupling procedures and the numerical error induced by this new approach are studied and discussed. The paper describes a comparison between numerical results and experimental data recorded within a real tunnel underlining how the developed methodology can be used as a valid design tool for any tunnel ventilation system.This work sets the foundations for the coupling of fire-induced flows and ventilation systems where further complexities are introduced by the hot gas plume and smoke stratification.     

Entrainment by adhered two-dimensional plumes

Measurements are presented of the variation with height of the mass flux of two-dimensional, adhered smoke plumes created by horizontal smoke layers that flow below a ceiling and spill into a hall near one of its walls, and of the effect of the Froude number (Fr) of these horizontal layers on the shape of the rising plumes in the hall. The measurements suggest that such smoke layers would usually rise vertically; either adhered to the wall, when Fr is roughly <1, or as a free plume, when Fr is roughly >1, and that the entrainment of ambient air to these plumes is approximately proportional to their free perimeter. It is also shown that in both cases, the variation at large heights of the mass flux of these plumes varies approximately as that of a similar, weak plume from a virtual line source, whose location can be estimated by a previously suggested simple model. Possible effects of downstands in the ceiling and of boundary conditions in the hall are also discussed.     

Species Transport from Post-Flashover Fires

A study was performed to determine the use of an equivalence ratio to predict gas levels (CO, CO₂, O₂, and unburned hydrocarbons) transported to locations remote from a post-flashover compartment fire. A series of tests were conducted in a reduced-scale facility to measure the evolution of post-flashover compartment fire gases flowing down a hallway. Test variables included air entrainment into gases in the hallway, stoichiometry of the compartment fire gases entering the hallway, mass flow rate of compartment fire gases, and the presence of a vitiated smoke layer accumulated in the hallway. In cases with no layer accumulated in the hallway, species yields in the hallway were found to correlate with a control volume equivalence ratio. The control volume equivalence ratio is the ratio of the mass loss rate of fuel inside the compartment to the air flow into the compartment plus the air entrained into compartment fire gases flowing along the hallway. Layers that accumulate in the hallway were determined to limit oxidation, which in some cases resulted in CO yields transported to remote locations being 20% higher than those inside the compartment. Based on the experimental data, a methodology was developed for predicting species levels transported to remote locations.     

Carbon monoxide transport in an enclosed room with sources from a water heater in the adjacent balcony

This paper has presented a computational analysis of carbon monoxide (CO) concentration inside a typical enclosed room of a residential building in Taiwan. CO is produced from a house-used natural gas water heater installed in the balcony. It is then diffused into the adjacent bedroom, which often causes serious poisoning accidences. A general-purpose computational fluid dynamics (CFD) code is employed to predict the CO concentration and airflow fields inside a three-dimensional (3D) modeled house. The variation of CO concentration was simulated under different scenarios of vent air flow rates and exit openings. It was found that under the ventilation conditions of V>0.0003 m/s, the levels of CO concentration in the bedroom is significantly decreased due to the entrainment of fresh air into the bedroom from the inside door. The present results could be used as a base for ventilation design for enclosed rooms, aiming at a proper ventilation system selection for avoiding the CO poisoning.     

Application of FDS to Adhered Spill Plumes in Atria

In a recently published article (Poreh et al., Fire Saf J 43(5):344–350, 2008), Poreh et al. carried out a number of experiments in a small-scale atrium. They investigated the mass flow of the spill plume in case of fire emerging from an adjacent room or corridor. Based on these experiments, the equation for the mass flow rates of adhered spill plumes in atria was adjusted. In our article, we repeat the experiments in a computational fluid dynamics (CFD) program. The results agree well, both with the experiments and the suggested formula. After this first validation, large-scale CFD-simulations are carried out. It appears that the equation suggested by Poreh et al. is only valid in the case of a uniform smoke layer depth. If the smoke layer has a more complex configuration, the formula is no longer reliable for the design of the smoke and heat exhaust ventilation system.     

Enclosure smoke filling revisited

Building fires go through a series of stages. They start with a fire plume/ceiling jet period during which buoyant fire gases rise to the ceiling and spread radially beneath the ceiling. A second stage, the enclosure smoke-filling period, follows; this second stage is the subject of this paper. It has been more than 20 yr since Zukoski first addressed the smoke filling stage of enclosure fires in terms of thermodynamic control volume concepts and fire plume entrainment, yet his analysis remains pertinent. This paper reviews and extends fire modeling concepts related to enclosure smoke filling developed by Zukoski. The mass-based analysis of Zukoski is recast in terms of the volumetric flow rates typically used for ventilation system design; it is extended to consider global average temperature rise and the effects of oxygen consumption on the maximum global average temperature rise that can be achieved in a closed-room fire. A spreadsheet template is developed to compare hand calculations based on a global analysis with numerical smoke filling calculations. Results of this comparison suggest that there is little difference in conditions predicted with the global hand calculations and the numerical smoke filling calculations; consequently, the hand calculations are suitable for preliminary fire hazard analyses.     

On smoke control for tunnels by longitudinal ventilation

Two aspects of smoke control by longitudinal ventilation systems in tunnels is analysed. The first is the increase in air entrainment rate of the plume after operating the system, and the second is the increase in heat release rate as a consequence of increase in air supply rate for combustion. Computational fluid dynamics (CFD) was applied for verifying the study. Keypoints to consider in the design of longitudinal ventilation systems are noted.     

Detergents in drainage systems for buildings

Current soil waste vent (SWV) system design guides aim to produce ventilated drainage networks for buildings which protect attached water trap seals from unwanted air pressure effects. Such effects may cause trap seal failure that are caused by airflow induction during discharge. The ventilation design guides are based on steady-state experiments utilising cold clean water as a test media. However, most 'grey' and 'black' water sources are dosed with detergent, and are often warm, which significantly alters the behaviour when compared to clean water. Thus, current design standards provide only approximations of SWV system response. Results indicate that induced airflows in warm detergent-dosed water can be significantly higher than those measured in clean water systems, by a factor of more than 2. This paper quantifies the effect of detergents in SWV systems in terms of observed air entrainment rates and previously published research on the factors that contribute to air entrainment. Results of previous work are cast into dimensionless groupings suitable for inclusion into a mathematical simulation model based on a finite difference scheme. It utilises the method of characteristics as a solution technique to simulate drainage system operation via the equations that define unsteady partially filled or full bore pipe flows and the boundary conditions represented by water traps and other common system components.     

Air flows in dwellings—simulations and measurements

A study of the reliability of systems by considering the ability of different systems to maintain a required air flow rate over time is included in a subtask of IEA Annex 27 `Evaluation and Demonstration of Domestic Ventilation Systems'. Measurements and calculations were performed to determine the variation in ventilation rates due to variation in climate and variation in performance of the ventilation system. Dwellings with passive stack, mechanical exhaust and mechanical exhaust-supply ventilation, representative of the Swedish housing stock, were studied. Diagnostic tests were carried out, to discover if the installed ventilation system was functioning as designed e.g. air flows in mechanical ventilation systems and to determine certain values e.g. airtightness. The continuous monitoring included tracer gas measurements in dwellings of overall and local (individual rooms) ventilation rates, and measurements of boundary conditions, during three different periods, each lasting 1–6 days. Predictions of air flows were made for the measuring periods using COMIS, a multi-zone network model. This article presents and discusses the measurements and the calculations and compares the two. The predicted and measured average total outdoor air ventilation rates agree reasonably well. The agreement is less good for individual rooms.     

火源—竖井间距对自然通风隧道火灾烟气流动特征的影响

通过数值计算,研究顶部开口自然通风隧道火灾火源–竖井间距对烟气流动特征与竖井排烟效率的影响。考虑因素有火源–竖井间距、竖井断面尺寸。结果表明：随着火源–竖井间距的增大,竖井前方来流烟气的质量流量增大,且竖井的排烟效率逐渐降低,竖井内空气卷吸量减少;当火源–竖井间距较小时,竖井更有利于排出更多的热量,竖井后方的温度降低幅度更大,烟气可以被控制在更小的范围内。此外,随着竖井截面尺寸的增大,竖井的排烟效率增加,且增大竖井的宽度更有利于增加竖井的排烟量。因此建议当相邻竖井的间距较大时,可适当增加竖井的截面尺寸和竖井高度。     

Air flow and particle control with different ventilation systems in a classroom

Most ventilation and air conditioning systems are designed without much concern about how settling particles behave in ventilation air flows. For displacement ventilation systems, designers normally assume that all pollutants follow the buoyant air flow into an upper zone, where they are evacuated. This is, however, not always true. Previous studies show that high concentrations of settling respirable particles can be found in the breathing zone, and that the exposure rates can be a health hazard to occupants. The emphasis here is on how ventilation systems should be designed to minimize respirable airborne particles in the breathing zone. The supply and exhaust conditions of the ventilation air flow are shown to play an important role in the control of air quality. Computer simulation programs of computational fluid dynamics (CFD) type are used. Particle concentrations, thermal conditions and modified ventilation system solutions are reported.     

生态阳台的潮流设计

阳台既要满足生理要求,也要满足心理需求。文章从营造良好的建筑热工环境、强调阳台绿化的基本原则、重点研究绿色建筑中观景阳台的设计要点等三个方面探讨有关生态阳台的设计问题。     

Experimental studies on natural smoke filling in atrium due to a shop fire

How smoke spilling out of a shop fire would fill up an atrium has been studied experimentally in this paper. Full-scale burning tests were carried out in the PolyU/USTC Atrium constructed in Hefei, China. Since balcony spill plume expressions appeared in the literature might not be applicable for a shop fire with finite width, two plume models for smoke spilling out of a shop fire inside an atrium were proposed and assessed. An equation on studying the smoke layer interface height with a two-layer approach was derived.     

Air-water flows in circular drop manholes

Drop manholes, a typical element of urban drainage networks in steep catchments and in reaches of supercritical flow, enhance air entrainment and entrapment. The air flow across drop shafts can be remarkably high.

This paper discusses the air transport phenomena and the effects of ventilation absence in drop manholes. Based on an extensive experimental study, air entrainment mechanisms have been accurately described and air demand has been evaluated in different flow regimes. In addition, the effects of ventilation absence on the hydraulics of circular drop manholes, with emphasis on sub-atmospheric pressure onset and pool depth raising, have been investigated. The effects of a possible air flow recirculation have also been evaluated. Issues regarding any scale effects have been discussed.

The influence of the main hydraulic and geometric parameters on drop manhole performance was contemplated to provide improved design concepts for sewer systems.     

阳台漫谈

阳台是居住建筑中重要的半私有空间,是住宅必不可少的组成部分,以往人们常常过多地注意其立面造型而忽略了阳台应有的使用及其他功能。文章以漫谈方式对阳台的形式、功能和发展展望进行了剖析,以激发人们对阳台设计的激情和憧憬。     

Effects of the ventilation duct arrangement and duct geometry on ventilation performance in a subway tunnel

This study has investigated numerically the effects of the ventilation duct number and duct geometry on duct ventilation performance in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train, which was validated against the model tunnel experimental data in a previous study, is adopted to simulate train-induced unsteady tunnel flows. For the tunnel and subway train geometries that are exactly the same as those used in the model tunnel experimental test, but with the ventilation ducts being connected to the tunnel ceiling, the three-dimensional tunnel flows are simulated numerically under five different ventilation duct numbers and two different duct geometries. The numerical results reveal that: (1) for a given total area of openings, the ventilation duct number has little influence on the total mass flow of the air sucked into the tunnel through the ventilation ducts while the total mass flow of the air pushed out of the tunnel through the ducts increases remarkably with the increase in the duct number; (2) with the increase of the distance between a specific ventilation duct and the tunnel inlet the suction mass flow through the duct decreases significantly while the exhaust mass flow through the duct increases greatly, i.e., the location of a specific duct has a strong impact on the total suction and exhaust mass flows through the ventilation duct; (3) as the linkage angle between the tunnel ceiling and the upstream side wall of a duct is changed from 90° to 45°, the size of the re-circulation area inside the duct is much reduced when the train approaches the duct and thus the amount of air pushed out of the duct is greatly increased (i.e. the exhaust effect through the duct is remarkably strengthened).