Longitudinal Air Flow Research Articles

Fire and Smoke Management in a Uni–Directional Road Tunnel for aCongested Traffic Condition

Emergency smoke ventilation for a uni–directional traffic road tunnel is studied using a CFD modelling approach. Fire scenarios in an uphill ramp for congested traffic conditions have been considered. Based on a longitudinal smoke ventilation system with a damper smoke–extraction device on the ceiling soffit, the impact of longitudinal ventilation (LV) control, operation of fire suppression intervention and emergency response delay have been quantitatively investigated.An assessment conducted with CFD modelling quantitatively shows to what extent the visibility is influenced. It has been revealed that longitudinal airflow velocities can influence the performance of damper smoke–extraction. Different longitudinal airflow velocity should be maintained for fires in different tunnel locations under congested traffic conditions. This is important for tunnels with a fire suppression system, as smoke flows to the lower location when hot layer stratification is disturbed by the application of water. Fire suppression can cool down the smoke temperature significantly, but the visibility in the downstream portion of the tunnel can be impacted if longitudinal ventilation is not properly controlledFor the modelled conditions with a heavy goods vehicle (HGV) fire in a 5% uphill ramp section of a tunnel, an LV flow velocity of 2 m/s can maintain tenable conditions upstream and downstream for congested traffic conditions.

Investigation on the Performance of Fire Detection Systems for Tunnel Applications––Part 2: Full-Scale Experiments Under Longitudinal Airflow Conditions

This paper presents the results of the full-scale experiments conducted in a laboratory tunnel facility under longitudinal airflow conditions and in the Carre-Viger Tunnel. The performance of nine fire detection systems representing five types of the fire detection technologies for road tunnel applications was investigated using representative tunnel fire scenarios. The changes in fire characteristics caused by longitudinal airflow, such as fuel burning time, fire growth rate, temperatures and smoke spread in the tunnel, were measured and analyzed. The experimental results showed that the detection time of the fire detection systems under longitudinal airflow conditions could be increased or decreased, depending on the fuel type, fire size and location, airflow velocity and detection method.

Investigation on the Performance of Fire Detection Systems for Tunnel Applications––Part 1: Full-Scale Experiments at a Laboratory Tunnel

A two-year international road tunnel fire detection research project (Phase II) was completed recently. As part of this project, a series of fire tests were conducted in a laboratory tunnel facility under minimum and longitudinal airflow conditions. In addition, fire tests were also conducted in the Carre-Viger tunnel in Montreal. This paper presents the results of the full-scale experiments conducted in the laboratory tunnel under minimum airflow conditions. The performance of nine fire detection systems representing five types of fire detection technologies was investigated using representative tunnel fire scenarios. Test results showed that the response of fire detection systems to a tunnel fire was dependent on the size, location and growth rate of the fire, the type of fuel as well as the method of detection.

Experimental study on burning rates of square/rectangular gasoline and methanol pool fires under longitudinal air flow in a wind tunnel

Square pool fires with length of 5, 7.5, 10, 15, 20, 25 and 30 cm and rectangular pool fires with dimensions of 10 cm × 20 cm and 10 cm × 40 cm were burned in a wind tunnel, under a longitudinal air flow ranged from 0 to 3 m/s with incremental change of about 0.5 m/s. Methanol and gasoline were burned and compared, with results indicated that their burning rates showed different response to the longitudinal air flow. With the increase of the longitudinal air flow speed, the burning rates of methanol pool fires, except the 5 cm square one, first decreased and then increased, but those of the 5 cm methanol square one and the gasoline pool fires increased monotonously. The burning rate of smaller square pool fires increased more significantly than that of the larger ones, as well as the enlargement of their flame attachment length along the ground. The burning rate of a rectangular pool fire with longer rim parallel to the longitudinal flow increased faster, but the flame attachment length seemed to increase more gradually, with the increase of the longitudinal air flow speed than that perpendicular to.

A one-dimensional analytical model for airborne contaminant transport in airliner cabins

Quick information on airborne infectious disease transmission in airliner cabins is essential to reduce the risk of infection of passengers and crew members. This investigation proposed a one-dimensional analytical model that can predict the longitudinal transmission of airborne contaminants or disease viruses inside an airliner cabin. The model considered both diffusive and convective transport of contaminants in the longitudinal direction of the cabin but assumed complete mixing of contaminants in the cabin cross-section. The effect of recirculation of the cabin air and efficiency of the high-efficiency particulate air (HEPA) filters is also considered in the model. The analytical solution for the one-dimensional contaminant transport model is obtained by using the principle of superposition and the method of separation of variables. The analytical solutions agree well with the computational fluid dynamics (CFD) results. The coupling of a CFD model with the one-dimensional analytical model could capture the impact of local airflow on contaminant transport. This analytical model has been used for analyzing contaminant transport in a 30-row all-economy-class airliner cabin with minimal computing effort. The paper presents a new one-dimensional analytical model that can provide quick information on global airborne contaminant transmissions in airliner cabins for effective response plans. The model can be used to study the effects of air exchange rates, recirculation, efficiency of the high-efficiency particulate air (HEPA) filters and longitudinal airflow on airborne contaminant transport in airliner cabins with minimal computing effort.

Findings of the International Road Tunnel Fire Detection Research Project

Fire detection systems play a crucial role in ensuring safe evacuation and firefighting operations in road tunnels, but information on the performance of these systems in tunnels has been limited and guidelines for their application in tunnel environments are not fully developed. Recently, the National Research Council of Canada (NRC) and the Fire Protection Research Foundation completed a 2-year international research project, with the support of private- and public-sector organizations, to determine some of the strengths and weaknesses of the various types of fire detection systems and the factors that can affect their performance in tunnel environments. The project included both laboratory and field fire tests combined with computer modeling studies. Although this research was conducted on road tunnels, the findings should apply to other tunnels, such as those used in subway systems. As part of the project, the NRC conducted two series of tests in the Carleton University-NRC tunnel facility to investigate the performance of detection systems under minimal and longitudinal airflow conditions. In addition, NRC conducted tests in the Carré-Viger Tunnel in Montréal, as well as a computer modeling study. The project studied nine fire detection systems that covered five types of currently available technologies. The performance of the detection systems, including response times and ability to locate and monitor a fire in the tunnel and the effect of the tunnel environment, were evaluated under the same conditions. This article provides an overview of the findings of the project. Fire detectors, fire scenarios and test protocols used in the test program are described. A summary of the research results of the full-scale fire tests conducted in a laboratory tunnel facility and in an operating road tunnel as well as of the computer modeling activities is reported.

Influence of Stationary Vehicles on Backlayering Characteristics of Fire Plume in a Large Cross Section Tunnel

This study is a part of an investigation project to examine emergencies in a large cross sectional tunnel, to be constructed on the New Toumei Expressway in Japan. Backlayering characteristics, the most important behavior in tunnel fires, are investigated through large-eddy simulation for various longitudinal air flows and fire sizes. The accuracy of this simulator has been previously confirmed by comparing with experimental results. In this study, specifically, stationary vehicles in a tunnel are considered in the simulation for the first time. Their presence induces turbulence in the longitudinal air flow and greatly affects the backlayering characteristics. However, earlier studies have not yet considered these effects. The results show that the presence of stationary vehicles reduces the backlayering length. Furthermore, the ratio of large-sized vehicles to total traffic is found to have little effect on fire behavior.

The dynamic characteristics and migration of a pyramid dune

AbstractThe results of wind tunnel experiments and field observations show that when the intersection angle between airflow direction and dune crest (ridge) line is > 30°, a reverse vortex is formed. Because of the convergence of sand streams from the windward and lee slopes at the crest, sand accumulates in the crestal region, causing vertical growth. Nevertheless, studies also show that the common asymmetry of the two slopes of a dune may significantly influence the evolution of arms of a pyramid dune. The migration rates of pyramid dunes are mediated by the interplay of their arms moving transversely and the vertical growth in response to the variations in wind regimes. Comparing the effects of airflow transverse to a given arm with longitudinal airflow, it is indicated that the transverse airflow is more significant in controlling the arms of pyramid dunes. The whole body of the studied pyramid dune, particularly the upper quarter section, migrated SE direction during the monitoring period. The patterns of wind erosion and deposition change alternately with seasonal variations in wind directions. The W, NE and SE sides undergo constant erosion, deposition and both erosion and deposition, respectively. The results of long‐term monitoring of a pyramid dune show that southerly winds, resulting from a local circulation, markedly affect the transverse migration of the whole pyramid dune.

Definition and experimental evaluation of the smoke “confinement velocity” in tunnel fires

An experimental study is carried out on a reduced scale tunnel model (scale reduction is 1:20). The main objective is to evaluate the longitudinal velocity induced into a tunnel when a fire plume continuously released is confined and extracted between two exhaust vents located on both sides of the fire source. For the experimental simulations, fire-induced smoke is simulated by an air and helium mix release. Smoke flow is symmetrical as regards the fire location and experiments are realized for an half tunnel with only one vent activated downstream the source. The vent extraction flow rate is step by step increased and the length of the stratified smoke layer downstream the vent as well as the longitudinal fresh air flow induced, are measured. A confinement velocity is then associated to the minimum value of the longitudinal air flow needed to prevent the smoke layer propagation downstream the vent. This velocity is evaluated for several values of the fire heat release rate and finally compared with the corresponding critical velocity obtained for a longitudinal ventilation system.

Equivalent thermophysical properties and surface heat transfer coefficient of fruit layers in trays during cooling

Experimental engineering data and predictive equations are established for the equivalent thermophysical properties (thermal conductivity, thermal diffusivity, specific heat capacity and density) and surface heat transfer coefficient of bulk layers of fruits (strawberries, raspberries, apricots, peaches, grapes and apples) in trays. Both packed layers and uncovered trays are considered as a system of fruits and air. In the first case the influence of air inclusions and free convection in closed space is taken into account, while in the second – special attention is devoted to the effect of air infiltration between the fruits placed in trays and pallets. The regression equations derived give the relationship between the considered equivalent values and the velocity of longitudinal air flow between the trays. The results are appropriate to be used for mathematical modelling and engineering calculations in real industrial heat transfer scenarios.

Similarity of plasmatron characteristics for longitudinal vortex flow around the arc with variations in the gas flow rate

The volt-ampere charateristics (VAC) of an elecric arc are correlated with longitudinal vortex air and nitrogen flows in plasmatrons with a rod-like cathode and two tubular electrodes. Two types of exponent approximations are used: a simple empirical formula and a relationship between generalized variables. It is shown by methods of regression analysis that the use of generalized variables provides similarity of the VAC upon variations in the gas-flow rate.

The Tensile Strength of Fiber Bundles in Longitudinal Air Flow

The tensile strength of twistless fiber bundle in longitudinal air flow was investigated in comparison to that in still air. First, the tensile strength of twistless fiber bundle in still air is obtained by integrating the frictional forces between adjacent fibers, under the condition that a fiber contacts closely with each other. Secondly, the frictional force in still air flow is considered to be the value of the frictional force in still air multiplied by the coefficient (k) which indicates the reduction of contact area between fibers by the air flow. Further, the tensile strength of the fiber bundle in the air flow is obtained by subtracting air drag force of fiber bundle from total frictional force between fibers in logitudinal air flow. The results of the experiment on the tensile strength of fiber bundle in longitudinal air flow.The results of the experiment on the effect of several faftors on the tensile strength of fiber bundle in longitudinal air flow are as follows : (1) The tensiles strength of fiber bundle in longitudinal air flow decreases with increasing air speed.(2) While the tensile strength of fiber bundle in longitudinal air flow is considerably lower than the one in still air in the range of low elongation speed, the former approaches to the latter in higher elongation speed.(3) The elongation of fiber bundle decreases with increasing air speed.

Water-Vapor Trasfer from Leaf-Like Surfaces within Canopy Models

Water vapor transfer from a model leaf set in a wind tunnel and that from citrus leaves formulating a canopy in the field were measured by using the leaf-like surface evaporimeter method due to HASESA and TAKECHI (1973), in order to make clear the wind dependence of forced convection water-vapor transfer coefficients over leaves within plant canopies. Local evaporation rates (w) at the point of 2cm from the leading edge of a leaf-like surface evaporimeter were determined respectively in the model and citrus canopies.The following relation was used to separate the effect of buoyancy term from the measured evaporation rates and to determine the local transfer coefficient due to forced convection(Df)Df, EXP=w/ΔC-Dn, CALCwere, ΔC is the departure of water-vapor concentration at the wet surface of the model leaf from that in the general air flow and Dn, CALC the water vapor transfer coefficient due to free convection. Because the leaf-like surface evaporimeter is flat, smooth and rigid, it is possible to assum that the influence of three factors such as leaf-fluttering, surface roughness and leaf curvature upon the transfer coefficient can be disregarded. The comparison between measured water-vapor transfer coefficients and standard coefficients (Df, STD) calculated from theoretical relations for a flat plate (in longitudinal flow) similar to the evporimeter in the size and surface temperature distribution enabled us to make clear the influence of canopy air-flow on the transfer coefficient over leaves.The results obtained for the surface evporimeter in longitudinal air flow are as follows:1. The water vapor transfer coefficient due to forced convection over the model leaf set in the front of model canopy agreed satisfactorily with those calculaled from the laminar boundary layer theory, because the air flowing on the model leaf was free from the air disturbance by the model canopy.2. Although the wind dependence of transfer coefficients over the model leaf set within and behind the model canopy was expressed by the 1/2 power law, the absolute values were to some extent larger than theoretical values. The difference between measured and calculated transfer coefficients was gradually large with the increment of leaf area density of the model canopy. When the leaf area density was retained constant throughout experiments, the values of transfer coefficient were independent of the tion of the model leaf within the model canopy along the direction of air-flow.3. Under the conditions that the model leaves were oriented so as to shelter behind windward leaves, values of exponent of the wind-transfer coefficient ranged betweeh 0.6 and 0.7. In this case, the fetch-dependence of the watervapor concentration over the surface of the model leaf was quite similar to that over a flat plate on which turbulent boundary-layer was built up.4. When the model leaves were set at different distances behind the model canopy, the influence of air-flow disturbance due to the canopy upon the water vapor transfer coefficient diminished gradually with increasing the distance from the canopy.In order to study the effect of the angle of attack of air flow on the water vapor trasfer, experiments with the model leaves inclined against the horizontal plane at different angles were carried out in the model canopy. As can be seen in Fig. 4, in the range of inclination angle between 10° and 20° the values of transfer coefficient were somewhat larger in comparison with those over a flat plate in longitudinal air flow. However, the effect of inclination angle on the transfer coefficient over the model plate decreased rapidly with departure from that inclination range and the values of transfer coefficient became nearly equal to or slightly smaller than the standard transfer coefficient.

Investigation of the intensification of heat transfer in a dense tube bundle washed by a longitudinal air flow

Experiments have been performed to investigate the intensification of heating and cooling obtained by periodically grooving the tubes of a staggered bundle with S/D=1.2 washed by a longitudinal air flow in the range Re=2 · 103–105. Tubular heat exchangers with longitudinal flow through the intertube space are widely used in a number of branches of technology. To develop more compact exchangers it is necessary not only to intensify heat transfer in the intertube space by creating turbulence in various ways but also to use dense bundles of tubes (relative pitch S/D ≤1.2).

Investigation of heat transfer in longitudinal air flow over a staggered tube bundle

Results are presented of an investigation of heat transfer in a longitudinal blow of air over a staggered tube bundle with s/d=1.2 and with heating and cooling in the range Re=2 · 103–105.