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711.
二次风口的合理布设是实现炉膛内气体混合均匀、反应完全的有效措施之一,运用CFD技术进行二段往复炉排焚烧炉二次风口的辅助设计,借助PHOENICS软件模拟二次风口对炉内流场的影响。通过模拟发现,二次风口的布设可明显提高烟气的湍流程度.前后墙各设一排直径为0.04m的二次风口可以实现最佳的炉膛流场工况。 相似文献
712.
表面活性剂冲洗法是一种治理土壤与地下水非水相流体(NAPLs)污染的有效技术。在简要介绍表面活性剂冲洗法去除作用机理的基础上,总结了近些年来与表面活性剂冲洗法多相流相关的国内外试验研究和模型研究成果,主要包括表面活性剂作用所引起的混溶驱替和不混溶驱替多相流问题,并指出目前研究中存在的问题和进一步探讨的方向。 相似文献
713.
714.
Weisbrod N Niemet MR Rockhold ML McGinnis T Selker JS 《Journal of contaminant hydrology》2004,72(1-4):109-133
Migration of concentrated NaNO3 solutions in homogeneous packs of pre-wetted silica sands was investigated using a light transmission system. Solutions of 5 molal NaNO3 were found to migrate downward 24-62% faster than pure water, in an unstable, fingered manner. This behavior was attributed primarily to a surface tension induced, non-zero apparent contact angle between the imbibing and the resident fluids. For saline solutions of similar surface tension to that of pure water (achieved by the addition of 2% methanol), the migration rates and plume shapes were comparable to that of water, demonstrating that density was not the primary source of the observed differences in migration patterns. At depths where resident saturation increased above residual, the migration process appeared to occur via film flow with slight changes in saturation (<4%), rather than in a series of abrupt jumps, as observed at shallower depths. A method for contact angle scaling was used to illustrate the effects of non-zero contact angles on capillary pressure-saturation curves. 相似文献
715.
Fuster G Schuhmacher M Domingo JL 《Environmental science and pollution research international》2002,9(4):241-249
Substance Flow Analysis (SFA) is an important instrument that allows for the undertaking of environmental management for a specific contaminant. 'Control Analysis' is a tool that assesses the effect on a target flow of changes in flows forming part of a control basis set. The purpose of the present study was to perform a modeling of the annual PCDD/F flows in Tarragona Province and to apply the model for human health risk assessment. The validation of the model has been evaluated by comparing estimated fluxes with experimental values. Eleven subsystems, as well as a set of 88 flows of the system in Tarragona Province were considered. The total PCDD/F accumulation in Tarragona Province was between 62.6 and 159.5 g I-TEQ/y. Accumulation in sediments (27.9-74.6 g I-TEQ/y) and soils (35.0-80.8 g I-TEQ/y) are the two principal modes of deposition. Estimated flow in human adipose tissue means a mean intake of PCDD/F (via ingestion and inhalation) of 243 pg I-TEQ/person/day. The food chain pathway accounts for 99% of the total daily intake. As a result of the simulation, a 100% decrease in industrial emissions would cause a 1.7% reduction in the PCDD/F accumulation in humans. In turn, a 100% reduction of PCDD/Fs in the industrial waste waters would cause only an insignificant 0.1% decrease in the accumulation of PCDD/Fs in humans. 相似文献
716.
In this study, a three-dimensional model was used to numerically study the buoyant flow, along with its mixing characteristics, of heated water discharged from the surface and submerged side outfalls in shallow and deep water with a cross flow. Hydraulic experimental data were used to evaluate the applicability of the model. The simulation results agree well with the experimental results, particularly, the jet trajectories, the dimensions of the recirculating zone, and the distribution of the dimensionless excess temperature. The level of accuracy of the simulation results of the present study is nearly identical to that of the results conducted by McGuirk and Rodi (1978). If the heated water is discharged into shallow water where the momentum flux ratio and the discharge densimetric Froude number are high, the submerged discharge method is better than the surface discharge method in terms of the scale of the recirculating zone and the minimum dilution. In deep water, where the momentum flux ratio and discharge densimetric Froude number are low, however, the submerged discharge method had few advantages. In shallow water, the discharge jet is deflected by the ambient cross flow, while forcing the ambient flow to bend towards the far bank for the full depth. For a submerged discharge in shallow water, the recirculating zone is the largest in the lowest layer but becomes smaller in the upper layer. As the water depth increases, the ambient flow goes over the jet and diminishes the blocking effect, thereby decreasing the bending of the jet. 相似文献
717.
Tamara Fraizer 《Behavioral ecology and sociobiology》1997,41(6):423-434
I develop a state-based dynamic model of behavior to demonstrate that size-dependent differences in temperature tolerances
are not necessary to account for the activity of small male digger wasps late in the day. In the model, males defend or patrol
the nesting area, wait near nests, or feed away from the nesting area depending on time of day, energy reserves and size rank.
I assume a large male competitive advantage, so mating opportunities decrease with size rank for territorial or patrolling
males and are rare for all waiting males; the costs of patrolling or defense are higher than the costs of waiting. If energy
reserves of all males are initially small, all males alternate feeding and territorial or patrolling behavior. If energy reserves
are initially large, large males patrol or maintain territories until they risk starvation and leave the area to feed. At
this time, smaller males that have conserved their resources by waiting and feeding may defend territories or patrol. I simulate
the behavior of three populations representing two species of Microbembex by assuming large initial energy reserves for populations in which males were territorial and small initial reserves for
populations in which males patrolled, and then convert the predicted time of activity to temperature using local regressions
from field studies. Temporal patterns in the activity of large and small males were similar to those actually observed, and
relationships between size and temperature predicted by the model corresponded to most observations and were sometimes positive.
Thus, the delayed activity of smaller males does not correspond to activity at higher temperatures and is probably not attributable
to size-dependent thermal tolerances, but may represent a temporal displacement of mating activity due to intra-sexual competition
and mediated by energetics. The model makes testable predictions on the timing of feeding and depletion of energy reserves
in relation to size and initial energy state, and suggests how differences among species may influence the temporal and spatial
organization of male mating behavior.
Received: 27 February 1997 / Accepted after revision: 26 July 1997 相似文献
718.
The Kelvin–Helmholtz (KH) instability is traditionally viewed as an initial-value problem, wherein wave perturbations of a
two-layer shear flow grow over time into billows and eventually generate vertical mixing. Yet, the instability can also be
viewed as a boundary-value problem. In such a framework, there exists an upstream condition where a lighter fluid flows over
a denser fluid, wave perturbations grow downstream to eventually overturn some distance away from the point of origin. As
the reverse of the traditional problem, this flow is periodic in time and exhibits instability in space. A natural application
is the mixing of a warmer river emptying into a colder lake or reservoir, or the salt-wedge estuary. This study of the KH
instability from the perspective of a boundary-value problem is divided into two parts. Firstly, the instability theory is
conducted with a real frequency and complex horizontal wavenumber, and the main result is that the critical wavelength at
the instability threshold is longer in the boundary-value than in the initial-value situation. Secondly, mass, momentum and
energy budgets are performed between the upstream, unmixed state on one side, and the downstream, mixed state on the other,
to determine under which condition mixing is energetically possible. Cases with a rigid lid and free surface are treated separately.
And, although the algebra is somewhat complicated, both end results are identical to the criterion for complete mixing in
the initial-value problem. 相似文献
719.
Laboratory experiments have been carried out to investigate the effects of a sloping wall headland on the flow characteristics and the associated concentration distributions from a point source around the headland. A semi-conical headland with a slope of 1:2 was set up in a flow basin, 4.8 m long and 3.8 m wide. In this paper, the experimental results of a steady shallow-water current are reported. Three dimensional flow velocities in the basin were measured using Sontek-ADV instrument. The dye concentration levels in the basin were measured by two fluorometers. The experimental results showed a large-scale re-circulation region behind the semi-conical headland. The peak turbulence energy, at about 53% of the local kinetic flow energy, coincides with the region of high velocity gradient. Significant vertical flows were observed around the area near the downhill slope of the headland, with a maximum ratio of vertical to horizontal velocities being about 22%. Such relatively significant vertical scouring velocities, coupled with strong turbulence energy and high horizontal velocity gradients in the same region, could cause severe bed erosion. The experimental results have also been compared with the predicted results of a depth-averaged numerical model. The predicted eddy structure and the concentration distribution in the re-circulation area were found to compare favourably with the experimental results. However, the discrepancies in the flow velocities and the concentration levels near the headland were apparent. It was observed that the dye concentration continued to spread in the cross-stream direction after passing the headland, whereas only a limited extent of the lateral spreading was predicted by the numerical model further downstream of the headland. 相似文献
720.
稻麦轮作田氮素径流流失特征初步研究 总被引:12,自引:0,他引:12
针对近年来氮素化肥施用量大而利用率较低现状,在江苏太湖地区设计田间试验,研究稻麦轮作田全年氮素流失特征。结果表明,在本试验条件下稻季和麦季径流中氮损失量相近,麦季略高,约占施氮量的2%左右。麦稻轮作田径流氮损失中氨态氮较少,以硝态氮和其他形态氮为主,其中氨态氮损失以稻季为主,硝态氮损失稻季和麦季相近,其他形态氮损失麦季较多。不同作物田径流氮组成存在差异,麦季径流氮以硝态氮和其他形态氮为主,氨态氮极少,而稻季在施肥后短时间内径流氮中氨态氮、硝态氮和其他形态氮大致相当,其他时间以硝态氮和其他形态氮为主。 相似文献