Near-field Plume Research Articles

Dissolved and particulate Fe in a hydrothermal plume at 9°45′N, East Pacific Rise:: Slow Fe (II) oxidation kinetics in Pacific plumes

Production of Fe(III) particles in hydrothermal plumes is of fundamental importance to the long-term effect of hydrothermal circulation on seawater composition. To elucidate the fundamental controls on Fe redox kinetics and solution/particle partitioning in neutrally buoyant plumes, we sampled near-field (<3 km) plume particles at 9°45′N on the East Pacific Rise in 1996, returning in 1997 to sample both particulate and dissolved phases (0.40 μm filter). Concentrations of dissolved Fe varied from 320 to 20 nM in proximal (<0.3 km from vent site) to distal samples (1–3 km downfield), constituting ∼85–50% of total Fe, respectively. Based on vent fluid dilution factors calculated from dissolved Mn, a mass balance for vent fluid Fe at this site indicates that ∼65% of Fe is lost to particulate sulfide settling in the buoyant plume, and that particulate Fe in distal (1–3 km) samples is twice as concentrated as predicted from dilution of particles in proximal plume water. These observations are consistent with a calculated Fe(II) oxidation half-time of 3.3 h, long enough that Fe(III) colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions, preventing generation of high particulate Fe concentrations (11–56 nM observed). A general investigation of Fe(II) oxidation rates in plumes worldwide gives Fe(II) oxidation half-lives as short as 17 min at some Atlantic sites, and as long as 6 h at some Pacific sites. The calculations indicate that the distribution of Fe particles in plumes depends chiefly on inter-basin differences in ambient deep water chemistry (primarily pH and dissolved O 2) and on local currents driving plume dilution, and to a much lesser extent on variations in primary vent fluid composition. Long-term changes in thermohaline circulation or ocean biogeochemistry may therefore alter Fe dynamics and minor element fluxes associated with global hydrothermal activity, independent of variations in crustal production rates.

Microbial biomass in the hydrothermal plumes associated with the 1998 Axial Volcano Eruption

The Axial Response Team (ART‐1) documented greatly intensified chronic‐style hydrothermal plumes at Axial Volcano following a 1998 eruptive event. Significantly higher numbers of bacteria were found in the plume versus background stations and depths, due largely to 5 samples with high numbers (to 1.8×105 /ml) in far field stations. Highest ratios (0.20) of metal depositing capsuled bacteria to total bacteria were found in the near‐field (over caldera) plume. An unusual capsule form (FeCap), that dominated the near field plume capsule populations, was present in all plume samples, but were absent in background samples. Multi‐cell filaments, metal‐encrusted sheathed clusters and matrix‐enmeshed colonies, all uncommon in the water column, were also present in plume samples.

Effects of Micro- and Macroscale Turbulent Mixing on the Chemical Processes in Engine Exhaust Plumes

Abstract Turbulent mixing and chemical reactions in the near field of an engine exhaust jet plume have been investigated using a mixing model that explicitly incorporates both large- and small-scale turbulent mixing and the molecular diffusion effects. A reduced reaction mechanism that accurately reproduces results of a detailed mechanism for the lower stratosphere was used to simulate the exhaust plume dynamics of a typical high-speed civil transport aircraft. This study shows that, compared to predictions based on models that do not include small-scale mixing and/or molecular diffusion effects, 30% less O3 and 15% less NOx are depleted in the near field of the plume. This suggests that the lack of local mixing can have an inhibiting effect on ozone depletion in the near-field plume. Inclusion of heterogeneous kinetics involving the formation of nitric and sulfuric acid due to water condensation on soot particles showed that 15% of the available NOx is converted into its inactive form but has a negligibl...

Discrete wellbore simulations of pump-and-treat strategies for remediation of LNAPL-contaminated aquifers

The method for simulating wells screened over several computational nodes described in Wu et al. [Wu, Y., Forsyth, P., Jiang, H. (1996). A consistent approach for applying numerical boundary conditions for multiphase subsurface flow. J. Cont. Hyd., 23:157–184.] is applied to multiphase LNAPL remediation problems. Computational issues concerning modelling wellbore flow are discussed. Three-dimensional computations are presented using a multiphase, nonequilibrium mass transfer model, which show the effect of well placement and geometry on containment of the dissolved LNAPL plume and the dissolution of the NAPL phase. It is also shown that unless very small aqueous phase dispersion parameters are used, classical dispersion theory can produce unrealistic dispersion against the flow direction in the neighbourhood of a pumping well. Except in the long term, this may have implications regarding the prediction of near-field plume configuration and contaminant capture.

Modeling of microscale turbulence and chemistry interaction in near‐field aircraft plumes

The potential impact of aircraft exhaust gas on entrained ambient air in the stratosphere has been studied by using several numerical models to manifest the importance of mixing processes occurring at different scales. These models include perfectly stirred reactor (PSR), transient well‐mixed reactor (WMR), partially stirred reactor (PaSR), and joint scalar probability density function (PDF) simulation for the near‐field jet exhaust. Sensitivities of major species to chemical reactions are presented to illustrate the chemical transformation in the near‐field jet regime. An accurate reduced chemical mechanism that captures major reaction pathways has been systematically developed and tested. The predicted results with the reduced mechanism are found in good agreement with those from the detailed mechanism, but the computing time is decreased by a factor of 3. The effect of microscale turbulent mixing and chemistry interaction on species evolution is studied, and its impact is found most noticeable in the near field where the timescale of chemistry for highly reactive radicals, such as OH and HO2, is comparable or faster compared with that of microscale mixing. When microscale mixing is included, the predicted H2SO4 level increases at locations where sulfate aerosol formation may be important in the near field.

Modeling Emissions from Elevated Cylindrical Bins.

This paper demonstrates how wind tunnel modeling data that accurately describe plume characteristics near an unconventional emission source can be used to improve the near-field downwind plume profiles predicted by conventional air pollution dispersion models. The study considers a vertical, cylindrical-shaped, elevated bin similar to large product storage bins that can be found at many industrial plant sites. Two dispersion models are considered: the U.S. Environmental Protection Agency's ISC2(ST) model and the Ontario Ministry of the Environment and Energy's GAS model. The wind tunnel study showed that plume behavior was contrary to what was predicted using conventional dispersion models such as ISC2(ST) and GAS and default values of input parameters. The wind tunnel data were used to develop a protocol for correcting the dispersion models inputs, resulting in a substantial improvement in the accuracy of the dispersion estimates.

A Far-Field Hydrothermal Plume from Loihi Seamount

An extensive helium plume in the north central Pacific emanates from Loihi Seamount on the flanks of Hawaii. The maximum helium signal is found at a depth of about 1100 meters, the same depth as the near-field plume directly above Loihi Seamount. Although this helium plume is strongest near Hawaii, where the 3He/4He ratio at a depth of about 1100 meters reaches values 28 percent above the atmospheric ratio, it can be detected quite clearly at latitude 24&deg;N, over 400 kilometers to the north. Excess 3He is also present on the same isopycnal between 15&deg;N and 20&deg;N at 135&deg;W, some 2000 kilometers east of the Hawaiian Islands.

Microinstabilities in a 10-kilowatt self-field magnetoplasmadynamic thruster

Abstract : Theoretical studies indicate that a variety of microscopic and macroscopic plasma instabilities can significantly affect the performance of the magnetoplasmadynamic (MPD) thruster, yet experimental evidence for their existence is extremely limited. The objective of this research was to provide experimental evidence for the existence of microinstabilities in a 10-kW-class, self-field MPD thruster. The lower- bound of the range of thruster operating currents investigated in this study was set by the requirement that the electromagnetic thrust component be much greater than the electrothermal thrust component. The upper-bound of the operating current was set by the initial observation of high-frequency thruster voltage oscillations, which is usually associated with the onset of excessive thruster erosion. Experimental evidence for two microinstabilities was obtained in the near-field plume of the thruster: 1) the generalized lower hybrid drift instability and 2) the electron cyclotron drift instability.

Passive Fourier-transform infrared spectroscopy of chemical plumes: an algorithm for quantitative interpretation and real-time background removal

We present a ratioing algorithm for quantitative analysis of the passive Fourier-transform infrared spectrum of a chemical plume. We show that the transmission of a near-field plume is given by τ(plume) = (L(obsd) - L(bb-plume))/(L(bkgd) - L(bb-plume)), where τ(plume) is the frequency-dependent transmission of the plume, L(obsd) is the spectral radiance of the scene that contains the plume, L(bkgd) is the spectral radiance of the same scene without the plume, and L(bb-plume) is the spectral radiance of a blackbody at the plume temperature. The algorithm simultaneously achieves background removal, elimination of the spectrometer internal signature, and quantification of the plume spectral transmission. It has applications to both real-time processing for plume visualization and quantitative measurements of plume column densities. The plume temperature (L(bb-plume)), which is not always precisely known, can have a profound effect on the quantitative interpretation of the algorithm and is discussed in detail. Finally, we provide an illustrative example of the use of the algorithm on a trichloroethylene and acetone plume.

The dominant effect of alumina on nearfield plume radiation

Solid propellant rocket motors can achieve high specific impulse with metal fuel additives such as aluminum. Combustion of aluminum produces condensed alumina particles. Besides causing performance losses in the nozzle, the condensed Al 2O 3 particles are the major source of primary smoke in the exhaust plume. The particulate matter can also have major effects upon the plume i.r. signature. High number densities of particles can block gas-phase radiation from the plume. They can also be the source of radiation, especially the larger particles which exit the nozzle not in thermal equilibrium with the gas. In the past, the expected effects of particle size on the plume i.r. signature have been determined almost exclusively from predictions made with flow and radiation codes. The aim of the present work was to investigate the role of the Al/Al 2O 3 particles from a highly loaded solid propellant (up to 16% in weight) on the plume radiation of a small rocket motor (5 cm in diameter). The spatial variation of particle size distribution was simultaneously measured with the overall radiation of a portion of the plume in the i.r. band (3.5–5.0 μ). In micro-motors, operating with highly aluminized solid propellant, the condensed particles in the near exhaust plume were the major source of radiation in the 3.5–5 μ wavelength band. Motors with longer residence time and operating at medium chamber pressures produced more particles in the micron sized range. The role of afterburning was predominately confined to reheating of the alumina particles to a higher temperature, at which the condensed Al 2O 3 radiated more than gaseous species. Even with 30% Al 2O 3 in the plume, the plume of small motors can be considered as approximately conical in shape, with volume distributed radiating sources. Motor conditions producing larger particles in the plume core were thus found to increase plume radiation from that region. The overall apparent emissivity of the plume was between 0.15 and 0.25 (dominantly 0.16–0.19). Nearfield particle size distributions were tri- or quadra-modal and the farfield contained significantly fewer large particles. Thus, assumed monomodal distributions should not be expected to result in the correct prediction of the effects of particles onplume signature, nor can particle size data obtained in the farfield be expected to be applicable in the nearfield.

MIXING OF THERMAL DISCHARGES IN COASTAL WATERS

Mixing of thermal effluents, being discharged from thermal power plants on coastlines and which head into surface waves was investigated by analyzing extensive field and laboratory data on plume and ocean ambient conditions. Emphasis was given on the effect of waves and surf zone currents on the modifications of plume surface area and vertical temperature profile in the near-field area. The results of this investigation showed that large opposing waves increase the plume surface area, in the vicinity of the outfall, for all cases of tide level and wave direction. Moreover, waves focused cold bottom currents on the discharge outlet and consequently the temperature of the released warm water was decreased at the surface and near the bottom. Wave-induced cross flows decreased the plume cumulative surface area which corresponded to fractional excess temperature ranging between 0.8 and 0.5 normalized values. This decrease was shown to be contingent that there is no interaction between the far-field and near-field plume waters. Gradient of wave momentum flux across surf zone was found to be necessary parameter to characterize the incident wave field.

Interaction between two turbulent plumes in close proximity

This paper presents a systematic experimental study on stream-wise flow development and spatial structure of triple buoyant plumes. Two-dimensional Particle Image Velocimetry (2-D PIV) is employed to resolve velocity fields. Stream-wise axial velocity profiles, flow structure, flow region parameters, and self-similarity properties are analyzed at different configurations that are characterized by spacing ratios S/W (source spacing S divided by source width W).From velocity fields and axial velocity profiles, a similar stream-wise developing trend is identified in different source configurations. When near-field plumes travel downstream, axial velocities increase rapidly, off-center velocity peaks get merged with the central peak, and the number of velocity peaks reduces with the downstream distance. A compact source layout, comparing with the wide one, could enhance the near-field plumes interaction and promote the plumes deflection significantly.Fundamentally, the stream-wise spatial structure of the triple plumes initially consists of a converging region, followed by a merging region, and finally a combined region. By examining the averaged velocity fields, flow recirculation with negative axial velocities is found to scarcely exist in the converging region. Merging level Zm and quasi-combined level Zqc are analyzed quantitatively and statistically. Within the studied S/W range, the normalized Zm shows a linear increase with S/W in the formula of Zm/H=2.007(S/W)+1.173 and the normalized Zqc gives a power law increase with S/W in the formula of Zqc/H=6.035(S/W)0.4959. In addition, triple plumes are found to establish self-similarity approximately at Z = 3H with S/W of 0.2 and at Z = 4.5H with S/W of 0.5.

Cold shock: Biological implications and a method for approximating transient environmental temperatures in the near-field region of a thermal discharge

Biological data on the temperature preferences of fish indicate that, in general, they will be attracted to thermal discharges in the winter. This attraction to warmer temperatures increases their vulnerability to cold shock if the discharge heat source is discontinued. A scheme is proposed to predict the near-field thermal plume environmental temperatures during a power transient. This method can be applied to any jet discharge for which a steady-state model exists. The proposed transient model has been applied to an operating reactor. The predicted results illustrate how very rapidly the maximum temperatures decrease after an abrupt shutdown. This model can be employed to help assess the impact where cold shock may be a problem. Such predictions could also be the basis for restrictions on scheduled midwinter plant shutdowns.

Effects of oblique shock waves in the near field of rocket plumes

Rocket nozzle originated oblique shock waves effect on near-field plume inpingement flows, heat transfer and pressure distribution