SESSION 3
OPTICAL DIAGNOSTICS AND RADIATIVE TRANSFER
A PRECISE CALIBRATION TECHNIQUE FOR MEASURING HIGH GAS TEMPERATURES
Süleyman A. Gökoğlu and Donald F. Schultz
NASA Lewis Research Center
Cleveland, Ohio
ABSTRACT
A technique was developed for direct measurement of gas temperatures in the
range of 2050K-2700K with improved accuracy and reproducibility. The technique
utilized the low-emittance of certain fibrous materials, and the uncertainty of
the technique was limited by the uncertainty in the melting points of the
materials, i.e., ±15K. The materials were pure, thin, metal-oxide fibers whose
diameters varied from 601Mm to 400Mm in the experiments. The sharp increase in
the emittance of the fibers upon melting was utilized as indication of reaching
a known gas temperature. The accuracy of the technique was confirmed by both
calculated low emittance values of transparent fibers, of order 0.01, up to a
few degrees below their melting point and by the fiber-diameter independence of
the results. This melting-point temperature was approached by increments not
larger than 4K, which was accomplished by controlled increases of reactant flow
rates in hydrogen-air and/or hydrogen-oxygen flames. As examples of the
applications of the technique, the gas-temperature measurements were used (a)
for assessing the uncertainty in inferring gas temperatures from thermocouple
measurements, and (b) for calibrating an IR camera to measure gas temperatures.
The technique offers an excellent calibration reference for other gas-
temperature measurement methods to improve their accuracy and reliably extending
their temperature range of applicability.
INVESTIGATION OF RADIATIVE HEAT TRANSFER IN FREEBOARD OF A 0.3 MWt AFBC TEST RIG
Mehmet Kozan and Nevin Selçuk
Department of Chemical Engineering, Middle East Technical University, 06531 Ankara, TURKEY
Tel:+90 (312) 210 2603, Fax:+90 (312) 210 1264, E-mail:selcuk@rorqual.cc.metu.edu.tr
ABSTRACT
Based on the analysis of measured data on flow rates, concentrations and
temperatures taken during steady: state operation of a lignite-fired 0.3 MWt
Atmospheric Fluidized Bed Combustor (AFBC) test rig, radiative exchange in
freeboard of the combustor was modeled by using a well-stirred enclosure model
in conjunction with Radiosity-Irradiation Method (RIM). Radiative properties of
the particle laden combustion gases were calculated by assuming gray radiation
behavior for both particles and gas, and using Leckner's correlations for gas
and Mie theory for particles. The accuracy of the model was tested by comparing
its predictions with incident radiative heat fluxes measured on the freeboard
wall. Comparisons between the incident radiative heat fluxes predicted by the
present model and those measured show that this engineering approach can be used
with confidence by designers for the particle loadings typically encountered in
freeboards of bubbling fluidized bed combustors.
A RADIATION MODEL FOR THE NUMERICAL SIMULATION
OF COAL-FIRED FURNACES USING BODY-FITTED GRIDS
J. Strohle, H. Knaus, U. Schnell and K.R.G. Hein
Institute for Process Engineering and Power Plant Technology,
University of Stuttgart,
Pfaffenwaldring 23, D-70550 Stuttgart, Germany
ABSTRACT
A model for predicting radiative heat transfer in coal-fired furnaces is
presented. The radiative transfer equation is modelled by the discrete ordinates
method for body-fitted coordinates using the S4-approximation. The gas
absorption coefficient is determined by a weighted-sum-of-gray-gases model, the
radiative properties of coal and ash particles are derived from the specific
area and a mean efficiency factor of the particle cloud. The scattering phase
function is modelled by the Delta-Eddington approximation. The entire radiation
model is adopted for vector and parallel computers guaranteeing numerical
efficiency. It is tested at an idealized squared combustion chamber with black
walls filled by an emitting, absorbing medium with constant absorption
coefficient. The computations are carried out on several curvilinear non-
orthogonal grids using different boundary conditions. On all grids the computed
radiative source terms and wall heat fluxes are in very good agreement with the
analytic solution. Furthermore, the model is validated at a coal-fired test
facility. Apart from the near burner region the computed temperature
distribution only slightly deviates from the measured values.
PERFORMANCE OFDISCRETE ORDINATES METHOD IN
A GAS TURBINE COMBUSTOR SIMULATOR
Nuray Kayakol*, Nevin Selçuk+, Ian Campell' and Ömer L. Gülder'
* Glass Research Center Sisecam, Istanbul, Turkey
+ Department of Chemical Engineering Middle East Technical University
Ankara 06531, Turkey
Tel:+90 312 2102603, Fax:+90 312 2101264
E-mail: selcuk@rorqual.metu.edu.tr
' Combustion Group, ICPET, BCdg. M-9. National Research Council, Canada Ottowa,
Ontario, KIA ORG, Canada
ABSTRACT
Predictive accuracy of discrete ordinate method (DOM) was assessed by applying
it to the prediction of incident radiative fluxes on the walls of a gas turbine
combustor simulator (GTCS), and comparing its predictions with measurements.
Input data utilized for the DOM were measured gas concentration and temperature
profiles and inner wall temperatures of the GTCS which is a cylindrical
enclosure containing a turbulent diffusion flame of propane and air. Effects of
order of approximation (S4 and S6) and using uniform and non-uniform gas
absorption coefficients for the non-homogeneous medium on the accuracy of the
predicted heat fluxes were also investigated. Comparisons show that S4
approximation is adequate for the prediction of incident wall heat fluxes and
the use of an absorption coefficient profile based on measured gas
concentrations and temperatures improves the accuracy significantly.
Miguel Caldas and Viriato Semiâo
Mechanical Engineering Department,
Instituto Superior Tecnico - Technical University of Lisbon - Portugal
ABSTRACT
Adequate modeling of thermal radiation is an essential tool for the design of
real-live combustion systems. Predictive methods solving the radiative heat
transfer equation require the values of absorption and scattering coefficients
of the participating media. In the present paper, a compromise between accuracy
and computational economy is ensured in the evaluation of those coefficients, by
using the exponential wide band model for the gaseous components of the mixture.
a new curve fitting approach to the Mie theory for intermediate and large
particles and power series to represent the Mie coefficients for small
particles. Predicted results with those approaches are presented herein
demonstrate the proposed models' high accuracy and relatively low computational
costs.
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