ACERC
Abstracts - 1996 |
ACERC
Abstracts - 1996 |
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Thrust Area 4: Turbulent Reacting Fluid Mechanics and Heat Transfer |
Shirolkar, J.S.
Modeling Turbulent
Particle Dispersion in Pilute, Non-Reacting Flows, Ph.D./BYU, August 1996.
Advisor: McQuay
Black, D.L. and McQuay,
M.Q.
HDT Vol. 238, 6:19-26, 1996. (Presented at the 31st National Heat
Transfer Conference, Houston, Texas, August 5, 1996.) Funded by ACERC and
Brighan Young University Mechanical Engineering Department.
To improve understanding of the complex phenomena involved in pulverized coal combustion in utility boilers and to develop information suitable for model validation of comprehensive combustion codes a series of measurements was taken on 160 MW corner-fired, pulverized-coal fired boiler operated by New York State Electronic and Gas (NYSEG). Data taken during the complete series of tests consisted of particle size and velocity measurements, gas temperature and velocity measurements, species concentration, wall heat flux, and solid sample composition at locations in the radiant section and the convective pass of the boiler. The measurements discussed here include those of particle size, velocity, concentration, and data rate for the full-load, baseline operating condition firing the boiler on different coals. The types of coals used during this test were three bituminous coals, one with a relatively high fixed carbon and low volatiles, labeled coal type B, one with a lower fixed carbon and higher volatiles content, labeled coal type A, and coal similar to the type A coal in composition, labeled coal type C.
The particle size velocity data were collected using the laser-based PCSV (Particle Counter Sizer Velocimeter) probe. Measurements for this test series were collected primarily in the radiant section of the boiler. Data were collected at four ports in the vertical line along the north wall of the boiler on the east wall. Significant variations in particle size and velocity were observed due to the change in coal type at the nose of the boiler, while measurements lower in the radiant section showed smaller differences. Vertical trends in the mean particle sized in the upper part of the radiant section show larger variations when using the type B coal than are seen when the boiler was fired on the type A coal. Profiles of volume mean diameter and velocity taken at the nose of the boiler for all three coals used show also show significant differences due to coal type. The maximum values in the rate Probability Density Functions (PDF's) for the type A coal shows an increase toward higher data rates with increasing vertical location in the boiler, while the maximum value in the PDF's shows a decrease toward lower rates for the type B coal.
Guilkey, J.E.; Gee, K.R.;
McMurtry, P.A. and Klewicki, J.C.
Experiments and Fluids, 21:237-242, 1996. Funded by National Science
Foundation.
The non-intrusive initialization of flow field with distinct spatially segregated scalar components represents a significant experimental difficulty. Here a new technique is described which makes possible the non-intrusive initialization of spatially binary passive scalar field in a laminar or turbulent flow field. This technique uses photoactivatable (caged) fluorescent dyes dissolved in the flow medium. The scalar field within the flow field is tagged or initialized by "uncaging" the appropriate regions with an ultraviolet excimer laser. Mixing between the tagged and untagged regions is quantified using standard laser induced florescence techniques. The method is currently being used to study mixing in a turbulent pipe flow.
Krueger, S.K.; Su, C. and
McMurtry, P.A.
J. Atmos. Sci, (in press), 1996. Funded by National Science Foundation
and Office of Naval Research.
The model used by Krueger (1993) to study entrainment and mixing of thermodynamic properties in the stratus-topped boundary layer has been extended to study these processes in cumulus clouds. The new model, called the "explicit mixing parcel model" (EMPM), represents the fine-scale internal structure of a rising thermal in a cumulus cloud using 1D domain. The internal structure evolves in the EMPM as a consequence of a sequence of discrete entrainment events and an explicit representation of turbulent mixing based on Kerstein's (1988) linear eddy model. In this version of the EMPM, a simple parameterization is used to determine the local condensation or evaporation rates. However, the EMPM can incorporate a droplet growth model to allow prediction of droplet spectra evolution.
The EMPM was used to predict the characteristics of Hawaiian cumulus clouds observed by RAGA, et. Al. (1990). All of these quantities required by the EMPM, except for the entrained blob size were obtained form the observations. Profiles of in-cloud mean and variances of thermodynamic properties calculated by the EMPM for entrained blob sized of 50 m, 100 m, and 200 m and by a parcel model with instantaneous mixing were compared to those both mixing representations, but the observed mean liquid water mixing ratio and buoyancy profiles and all of the observed variance profiles are better reproduced by the EMPM. The measurements were not accurate enough to allow further conclusions regarding the entrained blob size.
Additional results from the EMPM suggest that the characteristic entrained blob size may be more precisely determined from aircraft measurements of the clear-air segment size distribution. The model results also demonstrate that the fine-scale structure represented by the EMPM's 1D domain can be directly compared to high-frequency aircraft measurements.
Guilkey, J.E.; Kerstein,
A.R.; McMurtry, P.A. and Klewicki, J.C.
Physics of Fluids, (in press), 1996. Funded by National Science Foundation.
An experimental investigation of passive scalar mixing in turbulent pipe flow is carried out using a new non-intrusive scalar initialization technique. The measurements support a recently predicted similarity scaling of concentration spectra in flows that are unbounded in one direction. Reflecting this scaling, the scalar variance exhibits a power-law rather than exponential decay, indicating that the traditional plug-flow reactor picture of turbulent pipe-flow mixing omits key physical mechanisms.
Tree, D.R. and Webb, B.W.
Fuel: (in press), 1996. Funded by ACERC.
Gas temperature and effluent NOx measurements have been obtained in a full scale, 169 MWe, pulverized coal, corner fired, utility boiler with separate overfire. The measurements are the first of this kind in a full-scale boiler operated with overfire air and low NOx burners. A test matrix of seven operating conditions was used to compare temperature and NOx with changes in overfire, coal type, load, and burner tilt. Peat temperature were between 1500 and 1600°C and occurred just above the top burner. The measurements detail the profile of temperature through a traverse of a coal burner, close coupled overfire air port and separate overfire port. The data in the near burner and overfire air regions show evidence of reduced swirl as overfire are is increased. Little difference is seen in the temperatures of two coals with volatile fractions of 28 and 36%. Temperature changes are quantified in the overfire air region for changes in burner tilt and load. Temperature is approximately the same in the overfire air region as load is decreased, but temperature increased in the overfire air region as the burners were tilted from +5° to -5°.
Denison, M.K. and Webb,
B.W.
Proceedings of the First International Symposium of Radiative Heat Transfer,
1:193-208, 1996. (Presented at the First International Symposium of Radiative
Heat Transfer, Kusadasi, Turkey, August, 1995.) Funded in part by ACERC.
This paper reviews the development and validation of the Spectral-Line Weighted-Sum-of-Gray-Gases (SLW) model for the prediction of radiation transfer in high temperature gases. The parameters in the model are obtained directly from the line-by-line spectra of H2O and CO2. The Model allows the absorption coefficient to be the basic radiative property rather than a transmissivity or band of absorptance etc., and can therefore be used with any arbitrary solution method for the Radiative Transfer Equation (RTE). The model is base on a novel absorption-line blackbody distribution function. Predictions from the model compare well with the spectral line-by-line benchmarks.
Denison, M.K. and Webb,
B.W.
Proceedings of the First International Symposium of Radiative Heat Transfer,
1:228-238, 1996. (Presented at the First International Symposium of Radiative
Heat Transfer, Kusadasi, Turkey, August, 1995.) Funded in part by ACERC.
The previously published mathematical correlations of the absorption-line blackbody distribution function, central to the spectral-line based weighted-sum-of-gray-gases model (SLW), have been extended to elevate pressures by introducing a dependence on an effective broadening pressure. Comparison between experimentally determined total emissivities and those calculated with the model show good agreement. Agreement at elevated pressure between line-by-line benchmarks and model predictions is also demonstrated.
Ma, J.; Fletcher, T.H. and
Webb, B.W.
Twenty-Sixth Symposium (International) on Combustion, Naples, Italy,
July 1996. Funded by ACERC.
Coal pyrolysis experiments were performed in the post-flame region of CH4/H2/air flat flame burner running in fuel-rich conditions, where the temperature and gas compositions were similar to those in the near burner region of a large-scale coal-scale coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles at high temperatures in the absence of oxygen. The soot particles in the cloud were collected at different residence times using a water-cooled, nitrogen-quenched suction probe. The test variables included the reaction temperature and coal type. Soot yields in terms of weight percentage of dry ash-free coal were measured based on the bulk soot collection experiments. The measured soot yields were related to coal rank, reaction temperature, and residence time. Size changes of soot particles due to soot agglomeration were also observed. The information obtained about coal-derived soot is useful in predictions of rediative heat transfer and pollutant formations in the near-burner region of pulverized coal-furnaces.
Flores, D.V.
The Use of Two Mixture Fractions to Treat Coal Combustion Products in Turbulent
Pulverized-Coal Flames, M.S./BYU, April 1996. Advisor: Fletcher
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