A preliminary method to estimate the plume chimney height for a still ambient condition is presented here. The method predicts a negligible plume chimney effect on the laboratory-size test exchanger. ...Measurements from an industrial-size heat exchanger (2.4 2 6.0 m 2 ) in forced-draft mode have been compared with simulations incorporating the new method. The simulated heat loads agree with the 11 measurements to within +25/-40%, compared to an average of +70% if calculated by an existing formula and -75% by assuming negligible effective plume chimney height. Agreement between the new method and the measured exchanger performance did not appear to be affected by wind speeds in the range 2-6 m/s.
Fine bubble modelling of smoke flows Li, Yuguo; Shing, Vicent C.W; Chen, Zhengdong
Fire safety journal,
04/2003, Letnik:
38, Številka:
3
Journal Article
Recenzirano
This short note presents a simple experimental modelling technique for smoke spread and movement in enclosures and sloping tunnels by using fine hydrogen bubbles, which are generated by electrolysis ...in a water tank. Results obtained from two independent experiments agree very well with each other, demonstrating the consistency of the new experimental method. The experimental results for the stratification interface height are also in good agreement with both the experimental data and theoretical predictions available in the literature. The developed method is then used to study smoke spread in a tunnel fire, and the effect of tunnel slopes on smoke movement is visualised.
Long-term monitoring of two well-characterized, oxidizing septic system plumes (Langton and Long Point 2 sites) over periods extending two to four years after decommissioning, has revealed that ...ground water PO4(3-) concentrations (0.4 to 5 mg/LP) have persisted at levels virtually unchanged from those observed during active sewage loading. In addition, the frontal part of the PO4(3-) plume at the Long Point 2 site can he observed to continue to advance during the decommissioned period. At the Langton site, where an active regional ground water flow system is present, all major plume solutes (Na+, Ca2+, Cl-, NO(3) returned to background values within one year of decommissioning, with the exception of PO4(3-). This evidence suggests that phosphate behavior in the ground water zone at these sites is dominated by sorption reactions that are both rapid and reversible. Thus, if septic system phosphorus is not retained in the vadose zone, but is transported into the ground water zone, it has the potential to be persistent and to be mobile enough to constitute a threat to downgradient surface water environments. This evidence also shows that when a septic system is decommissioned, if an oxidizing PO4(3-) plume is present, downgradient P loading is not likely to diminish for many years thereafter.
The expansion of the plume generated by KrF laser irradiation of hydroxyapatite (HA) targets under a 0.1-mbar water atmosphere has been analyzed by means of fast intensified CCD imaging and ...time-resolved optical emission spectroscopy. Images obtained have revealed up to three different emissive components in the plume. The first and fastest one, whose expansion takes place at a velocity of about 10 super(4) m/s, shows the development of a shock wave in its front, resulting from the interaction between the species released from the target and the background gas. The water vapor slows down this component up to values of about 3x10 super(3) m/s following a behavior that can be well described by the dynamics of a spherical shock wave. The low intensity of emission of the second component has not allowed us to analyze its dynamics. The third and slowest component expands at a constant velocity of 5x10 super(2) m/s and is constituted by hot particulates leaving the target. Spectra recorded in the shock front have shown the presence of emission lines arising from Ca I, Ca II, P I and some impurities, and two strong emission bands that can be assigned to some sort of calcium oxide.
Rotation used to be thought as an effective method to prohibit the formation of freckles of a binary alloy unidirectionally solidified from below, which we will show in the present paper is true only ...under restrictive conditions. A linear stability analysis is implemented for the system consisting a dendritic mushy region underlying a bulk fluid region and rotating uniformly about a vertical axis. Emphasis is placed on the rotation effects on the competition between the convection modes, which has a direct influence on the formation of freckles. Results show that rotation generally enhances the stability of the convection modes, but the enhancement is not significant until the rotation speed is very high (such as 10
5 rpm), which in some sense agrees well with the previous numerical and experimental results. In spite of its ineffectiveness as an inhibitory method to the formation of freckles, it is found from the present parametric study that the effects of rotation on convection depend largely on the buoyancy ratio
A
of the alloy. Both the changes of the rotation speed and the buoyancy ratio may lead to a switch of the most critical convection mode, which may in turn influence the characteristics of the subsequent plume convection, and thus the formation of freckles.
Air pollution modelling at a regional scale Tulet, P; Crassier, V; Rosset, R
Environmental modelling & software : with environment data news,
01/2000, Letnik:
15, Številka:
6
Journal Article
Recenzirano
A mesoscale simulation system Meso-NH-C allowing for on line coupling between dynamics and chemistry is presented. Further advantages of this system lie in high vertical resolution, nesting ...capabilities and a full set of parametrization schemes. This system is applied from 9 to 11 August 1997 for a pollution episode over Western Europe. In this episode, both a European and a regional scale analysis have been performed (Greater Paris area). The possibilities of such a modelling system have been emphasized, particularly regarding the evaluation of transboundary fluxes.
The direct gamma dose rates due to a stationary Gaussian plume of radionuclides in the atmosphere have been calculated using different models Lagrangian dose model (LDM), Gaussian plume model (GPM), ...and uniform cloud model (UCM), and the results are compared.
The atmospheric parameters (used in the Lagrangian model) like mean and fluctuating wind components, etc., were obtained from the published field data on a neutral atmosphere. In the LDM, a continuous release of radionuclides into the atmosphere was simulated by liberating a large number of Lagrangian particles, whose trajectories were tracked for various hours in a three-dimensional computational domain. A point isotropic source formula was used for calculating the direct gamma dose contribution from all Lagrangian particles constituting the plume. Each particle represented a point source of radioactivity, whose strength was calculated from the known release rate and was subsequently allowed to decay as a function of time.
The comparison of the LDM results with the GPM indicated that both models predict comparable results in a homogeneous atmosphere. The LDM is, however, more versatile, as it can incorporate variation in meteorological data in space and time (of course when available). The UCM also compared well for ground releases; however, it cannot be used for elevated releases and short downwind distances. The purpose of this work was to test the LDM for simulating the transport, dispersion, and decay of a radionuclide plume. The LDM shall later be used for complex topographic and meteorological conditions, where the GPM is not suitable.
Five atmospheric transport models were evaluated for use in Phase II of the Historical Public Exposures Studies at the Rocky Flats Plant. Models included a simple straight-line Gaussian plume model ...(ISCST2), several integrated puff models (RATCHET, TRIAD, and INPUFF2), and a complex terrain model (TRAC). Evaluations were based on how well model predictions compared with sulfur hexafluoride tracer measurements taken in the vicinity of Rocky Flats in February 1991. Twelve separate tracer experiments were conducted, each lasting 9 hr and measured at 140 samplers in arcs 8 and 16 km from the release point at Rocky Flats. Four modeling objectives were defined based on the endpoints of the overall study: (1) the unpaired maximum hourly average concentration, (2) paired time-averaged concentration, (3) unpaired time-averaged concentration, and (4) arc-integrated concentration. Performance measures were used to evaluate models and focused on the geometric mean and standard deviation of the predicted-to-observed ratio and the correlation coefficient between predicted and observed concentrations. No one model consistently outperformed the others in all modeling objectives and performance measures. About 75% of the maximum hourly concentration predictions were within a factor of 5 of the observations. About 64% of the paired and 80% of the unpaired time-averaged model predictions were within a factor of 5 of the observations. The overall performance of the RATCHET model was somewhat better than the other models. All models appeared to experience difficulty defining plume trajectories, which was attributed to the influence of multilayered flow initiated by terrain complexities and the diurnal flow patterns characteristic of the Colorado Front Range.
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