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.     

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.     

On the upward movement of smoke and related shopping mall problems

The data of Morgan and his co-workers for the movement of smoke in 1/10 scale shopping malls are re-examined. This has been done to see how far a simple theoretical treatment based on plume theory and virtual sources (a basis for many calculation methods) can be exploited instead of the more complicated theory of sources of finite sizes. The work follows and extends the work of Law.

A number of theoretical relationships are used to correlate data and, in particular, they confirm Law's view that the data can be used to give plausible values for the positions of the virtual sources. Some of the complexities of the theory for finite strip sources may be bypassed if experiments are used for estimating the position of effective virtual sources. Experiments to locate the effective virtual source and the limiting asymptotic form of the theory (appropriate to line sources) can correlate and scale data to an accuracy satisfactory for fire engineering purposes. Various aspects of theory are discussed including the method of allowing for the ‘ends’ of finite strip sources, and the use of the theory of weak plumes for strong plumes.

There remains however a problem in reconciling the ‘near’ field of the plume rising around the balcony edge to the ‘far field’, but it is shown that the introduction of an exceptionally high local entrainment could — for these data — be avoided if: (a) the mass at any level in the plume is about 45% larger than expected from other laboratory experiments on plumes; or (b) there is extra entrainment due to the deflection and consequent disturbance as the plume strikes the ceiling; or (c) there is extra upward flow owing to radiation heating up the lower walls and floor as suggested by recent investigations. These matters await further investigation.     

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.     

A phenomenological model of near-field fire entrainment

A phenomenological model of air entrainment into combusting regions of axisymmetric fire plumes is developed and compared with some existing experimental entrainment data. The model considers engulfment of ambient air into a fire plume due to the action of the toroidal vortices that are formed periodically close to the source of an axisymmetric fire. It is shown that the diffusive entrainment rates of air towards a wrinkled flame sheet representing the turbulent diffusion flame severely underpredicts the entrainment rates by at least two orders of magnitude, suggesting that the turbulent large-scale engulfment is the primary mechanism of entrainment. By describing the entrainment process as periodic engulfment of ambient air around the toroidal vortex rings and the frequency of formation and passage of these vortex rings in combusting regions of fire plumes, it is shown that the modeled entrainment process gives good agreement with the experimentally determined fire plume entrainment or plume mass fluxes. This model accounts for the physical processes of unsteady fire plume dynamics, including the effects of pulsations for the first time. The model predicts the plume mass flux to grow linearly with height above the fire source and to be independent of the fire heat release in the visible flame region. The predicted scaling with respect to the source diameter appears to be in the range suggested by the experimental data. Overall, this new model provides a better foundation for the scaling of entrainment rates in the near-field of fire plumes. The methodology can be extended to predict entrainment rates in other periodic unsteady vortex dominated flows, such as pulsating buoyant non-reacting plumes.     

Entrainment in fire plumes

A new technique for measurement of mass flow rates in buoyant fire plumes is described. The characteristics of 10–200 kW methane diffusion flames stabilized on porous-bed burners of 0.10–0.50 m dia. are described. A transition in the dependence of flame height on heat input and burner size was observed when the flame height was about four times the burner diameter. The mass flow rates in the buoyant plumes produced by the fires were measured for a range of elevations starting just below the time-averaged top of the flame and extending to six times this flame height. The mass flow rates in this region of the plume were correlated by the use of a simple plume model. Atmospheric and forced disturbances in the air being entrained increased the entrainment rate of the plume.     

Comparison of plume rise models against water tank experimental data for neutral and stable crossflows

The evaluation of the trajectories of plumes rising into a crossflow is relevant for the correct modelling of pollutant dispersal in the atmosphere. Plume rise models are therefore an important part of several dispersion models. There is a general consensus on the formulation of plume rise through solution of equations describing the conservation of energy and momentum in the plume closed with an empirical formulation of the entrainment rate of fresh air into the developing plume. However, there are differences in the entrainment coefficients found in different studies. In this work the trajectories of sixty plumes, simulated at small scale in a towing water tank, have been analysed in order to test the performance of widely used dispersion codes and to find statistically the best entrainment coefficients for the different models. The plumes simulated cover a wide range of scenarios from pure jets to buoyant plumes developing in both neutral and linearly stable stratified crossflows. A new analytical model for stable crossflows, representing an extension of an existing model, has been presented and tested. Results show that the entrainment coefficients are different for neutral and stable crossflows, especially for approximate analytical codes. In contrast, the coefficients of the integral model seem to be less sensitive to the stability of the crossflow. The entrainment coefficients found by the fitting of the analytical models are significantly lower than the measured spread rate of the plumes. In neutral crossflows the generalised Briggs model and the integral model give statistically similar performances. In stable crossflows the new analytical model as well as the integral model are able to predict the oscillation of the plumes around their equilibrium height; however, there is an underestimation of both the oscillation frequency and the downwind position of the maximum height. The use of an added mass coefficient allows, with almost the same entrainment coefficients, improved prediction of the oscillation frequency and of the maximum rise position. Measured plume height oscillations are more strongly damped than predicted ones.     

Dispersion in flow from a continuous source at sea

Diffusion experiments, using a continuous release of fluorescent dye from an anchored source, were carried out in the Holy Loch and two coastal areas of the Irish Sea. In each case the dye distribution was sampled by a vessel making a series of crossings of the plume. The data were analysed in terms of σ_y, the standard deviation of the dye distribution at right angles to the axis of the plume, as a function of the diffusion time t₁ and the corresponding eddy diffusion coefficient K_y. In general the value of K_y increased with t up to a diffusion time of at least 2 h. In many cases the relation between K_y and t was approximately linear, corresponding to spreading with a constant diffusion velocity B such that K_y = B²t. The observed median values of B for the Holy Loch, Red Wharf Bay and the area of the Irish Sea off the Cumberland coast were 0·4, 1·1 and 1·4 cm s⁻¹ respectively. The vertical diffusion was also analysed, but in less detail, and other features of the plumes, including their variability, are discussed. In general the rates of diffusion in the Holy Loch are similar to those reported by other workers for the Great Lakes and for coastal sea areas with weak currents and high stability. In the two Irish Sea areas the diffusion rates are similar to one another but considerably greater than in the Holy Loch.     

Swelling properties and coefficient of permeability of friction-reducing polymer for pull-out of temporary sheet piles

Harmful cracks and settlements occur after the pull-out removal of temporary sheet piles. This is because a large amount of soil is discharged from the ground due to the significant skin friction at the steel surface. In order to prevent these cracks and settlement problems, a friction-reducing polymer was developed. After a sheet pile coated with the polymer is installed into the ground; the polymer absorbs ground water and transforms to a swollen gel layer which separates the soil and the sheet piles. In this investigation, a newly designed column type test apparatus was used to simulate ground conditions. The swelling test was carried out, followed by a continuous permeability test. Based on the obtained test results, the swelling properties and coefficient of permeability of the friction-reducing polymer in the ground were determined. The main conclusions are as follows. The values of the water-absorbing ratio, Ra_max, decrease with increasing earth pressure, p′, independent of the pore water pressure, u. Equations to determine the values of Ra_max are proposed as functions of p′ only. The maximum swelling pressure, at which the friction-reducing polymer cannot absorb water and swell, is p′_max?=?560?kPa. Even at a depth of approximately 100?m, the polymer absorbs ground water, and the swollen gel layer forms. The approximate range of coefficient of permeability, k, of the swollen gel layer is 10^?13–10^?11 m/s; these are extremely small values. The swollen gel can be considered an impermeable material. Depth distributions of the thickness and the coefficient of permeability of the swollen gel layer are illustrated in practical charts, based on the test results.     

The activated sludge process—3 single sludge denitrification

The general aerobic bi-substrate active-site death-regeneration activated sludge model including nitrification of Dold et al. (Prog. Wat. Technol.12, 47–77, 1980) is extended to include the kinetic behaviour of the denitrification process in single sludge systems. The extension requires a change in the value of only one of the kinetic constants (K′_mp) in the expression for the particulate substrate utilization rate when the environment becomes anoxic. The extended model simulates very closely the response of the multi-reactor nitrification-denitrification process configurations under both constant and cyclic flow and load conditions. Under constant flow and load conditions, the denitrification response predicted can be reduced to that approximated by a zero order reaction dN/dt = ?KX_a with two rates in the primary and one in the secondary anoxic reactor respectively.     

Effect of ash disposal ponds on groundwater quality at a coal-fired power plant

The impact of fly and bottom ash disposal ponds on groundwater quality was investigated at the coal-fired Columbia Power Plant at Portage, Wis. Groundwater sampling was conducted utilizing a network of piezometers and multilevel wells located at various cross-sections of the ash disposal facility. Analyses were performed for 16 major and minor elements, pH and conductivity. Data for a 3-yr monitoring program established the existence of large B, Na and SO₄ plumes in the groundwater system surrounding the ash disposal area. Substantial amounts of B, Na and SO₄ were present in the plume and portions were discharged into an adjacent wetland as the plumes moved with groundwater flow. The secondary fly ash settling pond was the major source of B and SO₄, while the main source of Na was from previous releases to the aquifer from the use of Na₂CO₃ to condition fly ash to enhance removal of SO₂ from flue gas by electrostatic precipitation. Movement into the groundwater of heavy metals such as Cu and Zn was not observed and their concentrations are likely attenuated in the pond.     

CO2 transport by urban plumes in the upper Spanish plateau

CO₂ transport from two cities, Valladolid, over 20 km away and Palencia, over 40 km away from a rural site is analysed through three years of detrended CO₂ concentrations obtained near the surface. Meteorological data were obtained from a RASS sodar. Directional analysis by histogram of concentrations above the 95th percentile revealed three differing sectors, one associated to a rural origin and two linked to both cities. Modes indicated anticyclonic turning during plume travel, confirmed by the daily evolution of the wind direction. At night, the Valladolid concentration median was 6 ppm above the Palencia median, which was 2 ppm higher than the rural sector median. Monthly evolution of daily maxima evidenced the Valladolid plume influence in spring and September, whereas the Palencia plume was noticeable in October and November. Skewness analysis showed almost symmetric distributions in the Valladolid plume and right skewed distributions in the Palencia and rural sectors. This result was attributed to the different mixing of both plumes. Vertical gradients of wind speed, direction and potential temperature were also calculated, and evidenced a stratified structure of the lower atmosphere at night and an almost uniform layer during the day. Finally, the median gradient Richardson number showed the highest values, occasionally above 0.8 for the Valladolid sector, implying lower mixing with the environment in the Valladolid plume than in the Palencia plume.     

Ausbreitung von Kältefahnen im Grundwasser bei Erdwärmesonden

Shallow geothermal energy installations, especially ground source heat pump (GSHP) systems are increasingly being used for air conditioning and temperature control in buildings. Heating applications, for example, result in cold temperature anomalies (cold plumes) in the subsurface. To avoid interactions between adjacent cold plumes, authorities recommend minimum distances of about 10 m between installations. The length of these plumes can be simulated analytically and numerically. The presented analytical solutions are valid for steady-state conditions and consider conduction, convection and dispersion. The results show that the length depends on different parameters, especially flow velocity. The plumes in gravel aquifers become temporarily longer than in less permeable aquifers. Even under average energy extraction rates, they can exceed 10 m in length after one heating period. In the presented example the plume has a length of 10 m after 100 days under a continuous energy extraction rate of 55 W?m^?1. However, these plumes can regenerate quickly. Finally, the analytical results are discussed in a legal context.     

Defluorination of water by modified ceramic membranes from clayey minerals

Investigated are main regularities of the process of defluorination of water by nation-made ceramic membranes from clayey minerals, modified by a dynamic layer from aluminum hydroxycompounds and demonstrated its high efficiency. It was proposed to use specified membranes for defluorination of water to MAC standards in drinking water at the initial concentration F^– up to 22.0, Al³⁺—4.0–6.0 mg/dm³ in the additive forming the dynamics, pH_ini 6.5–7, P—1.0 MPa.     

An Approach for Assessment of Compaction Curves of Fine Grained Soils at Various Energies Using a One Point Test

Compaction curves of soils are essential for establishing practical and reliable criteria for an effective control of field compaction. This paper deals with the development of a practical method of assessing laboratory compaction curves of fine-grained soils. It is found that for a given fine-grained soil compacted at a particular compaction energy, the relationships between water content (w) and degree of saturation (S) are represented by power function, which are w=A_dS^B_d and w=A_wS^B_w for the dry and the wet sides of optimum, respectively (where A_d, A_w, B_d and B_w are constant). The B_d and B_w values and optimum degree of saturation (ODS) are mainly dependent upon soil type irrespective of compaction energy. The A_d and A_w values decrease with the logarithm of compaction energy and the decrease rates are practically the same for any compacted fine-grained soil. This leads to a simple and rational method to assess the compaction curve wherein the compaction energy varies over a wide range using a one point test (a single test). Assuming that fine-grained soils compacted under standard Proctor energy behave in agreement with Ohio's curves, the modified Ohio's curves for the other three compaction energy levels (296.3, 1346.6 and 2693.3 kJ/m³) are developed based on the proposed method. These curves can be used to assess the entire compaction curves at the required compaction energy based on a single set data of dry unit weight and water content.     

Flow generated by a thermal plume in a cooled-ceiling system

The transient and steady states of the flow generated by a heat source inside a closed room provided with a cooled-ceiling system at constant temperature are experimentally studied. During the transient regime the plume generated by the source interacts with the ambient fluid and, after it reaches the top contour, spreads under the latter giving place to the formation of a horizontal thermal front that eventually descends affecting the whole room. It is found that the formation and velocity of the descending front are determined by the filling-box model in an insulated space but with a smaller temperature difference between both sides of the front. The steady state is established when the heat supplied by the source is completely absorbed by the ceiling allowing a convective process to take place characterized by a turbulent flow in the major part of the room and by a thermal boundary layer developed below the ceiling, where vortexes and little plumes form, the detection of which is allowed by the application of synthetic schlieren technique. Analogies with the results obtained in the classical Rayleigh-Benard experiments allow an insight of the mechanisms of heat transfer in order to improve the indoor comfort in buildings under similar conditions to those discussed here.     

Influence des panaches ionisés sur le champ électrique terrestre

Several months of measurements of atmospheric electrical parameters, in particular of the earth's electric-field, using a mobile laboratory, have made possible an extension of previously obtained results (Laurent and Peyrous, 1979) to the industrial area of Pardies-Nogueres.This study confirms the presence of a negatively charged aerosol in the plume emitted by factory chimneys. Down-wind, under the chimney plume, the earth's electric field is inverted and takes on large negative values and, if fall-out occurs, the space charge density due to large ions becomes negative.In the first theoretical part of our paper, we reduce the chimney plume to an equivalent charged line whose charge varies with distance as a result of recombination and diffusion. Atmospheric turbulence is neglected, and only the vertical component of the electric field is measured.By mapping charts (Fig. 5) which give cross-sections of the electric field measured along-lines perpendicular to the wind direction one measures the distance (OP) between the inversion maximum (O) and the beginning of the inversion (P) and one can thus calculate the height of the chimney plume (equations (11), (12) and (13)). Then, using equation (6), and knowing the wind speed and the distance from the source one can calculate the charge. Furthermore, if the width of the chimney plume is assumed to be the same as that of the inversion indicated on the chart, and knowing the original diameter of the plume, one can calculate the mobility k of the negative particles by using the relationship indicated by Jones and Hutchinson (1976) (equation (16)).The experimental results were obtained by using a Field Mill installed on the roof of the laboratory van with the recording synchronized to the vehicle speed (Fig. 6, 7 and 8). Two sites were studied: the Lacq gas treatment plant and a plant producing aluminium by electrolysis from molten alumina at Nogueres.The distance over which the chimney plume can be localized depends on the plume charge and the wind speed. From the measurements made, it was estimated that the recombination coefficient of positive and negative charges was 6.8 m^?3 s^?1 and the mobility of negative ions in the chimney plume was 5 · 10^?5 m² v^?1 s^?1.Our calculations of the height of the chimney plume correspond well with the increase in height of the plume above the chimney outlet given by the HOLLAND formula. The measurements made on the fixed site of Lacq (Fig. 14) show the effect of wind and the relationship between the chimney plume and the electric charge.The measurements of the earth's vertical electric field to detect chimney plumes permits the localization of charged aerosols and the calculation of the charge and its altitude. It also allows one to follow the plume and, with space charge measurements, to determine where fall-out occurs. A study of the mechanism of charge separation at the source together with that of diffusion and recombination can be envisaged.A comparison between calculations using diffusion theory and results obtained from our measurements of the height of the plume is underway.     

Mechanical Behavior of Bentonite-Sand Mixtures as Buffer Materials

For the purpose of establishing the method for estimating in-situ mechanical behavior of artificial buffer materials, stress-deformation behavior of bentonite-sand mixtures were investigated through oedometer test, consolidated undrained triaxial compression test and expansive stress-strain measuring test by changing the clay content as 30, 50, 70 and 100%, and by changing the range of initial dry density of mixture from 1.4 to 1.8 g/cm³. Oedometer test results suggest that the magnitude of consolidation yield stress almost coincides with the maximum expansive stress (p′_s)_max irrespective of bentonite-sand mix proportion, initial density of mixture and the magnitude of molding stress at the specimen making. Strong correlation between consolidation stress and initial tangent modulus during undrained triaxial compression test is observed, and it is found that the reduction rate of rigidity is hardly dependent on the specimen making method, molding stress and the consolidation stress. From the two series of expansive stress-strain measuring tests, it is recommended to perform the measurement of expansive stress by feed back system with the load cell installed at the base of the specimen. A unique relationship is found between the maximum expansive stress (p′_s)_max versus bentonite specific volume v_b, which is defined as the specific volume calculated by excluding the volume of sand particles. The line showing the unique log v_b versus log (p′_s)_max relationship can be recognized as the state boundary line prescribing one-dimensional expansive stress-strain behavior of the bentonite-sand mixtures.