Research On Thermophoretic And Inertial Aspects Of Ash Particle Deposition On Heat Exchanger Surfaces In Coal Fired Equipment
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| Total Pages | : 8 |
| Release | : 1986 |
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In support of the above mentioned objectives, we have initiated theoretical studies in the following three interrelated areas : (a) Interaction of inertial- and thermophoretic effects in well-defined laminar dusty-gas'' flows. (b) Self-regulated sticking and deposit erosion in the simultaneous presence of vapor or submicron glue'' (c) Use of packed bed and tube-bank heat transfer and friction correlations to provide the basis for future tube-bank fouling predictions. During the first three months of Grant DE-FG22-86 PC 90756, we have: (1) Designed and initiated construction of the microcombustor particle-laden jet facility described in Section 3.1. (2) Initiated theoretical studies of the interaction of inertial and thermophoretic effects, the role of simultaneous vapor arrival in determining particle sticking and erosion probabilities, and mass transport phenomena in deep tube banks.
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| Total Pages | : 8 |
| Release | : 1987 |
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In support of the above mentioned objectives, we are carrying out theoretical studies in the following three interrelated areas: (a) Interaction of inertial- and thermophoretic effects in well-defined laminar dusty-gas'' flows; (b) Self-regulated sticking and deposit erosion in the simultaneous presence of vapor or submicron glue''; (c) Use of packed bed and tube-bank heat transfer and friction correlations to provide the basis for future tube-bank fouling predictions. During this second quarter of Grant DE-FG22-86 PC 90756. we have: (1) done preliminary gas velocity and temperature calibrations of the micro-combustor exit gas flow jet and initiated the development of both a monodispersed droplet feed system and powder feed system to provide monodispersed particle laden jets covering a broad spectrum of particle sizes (ca. 0.5--50 m diameter); and, (2) demonstrated the ability of impacting supermicron particles to remove predeposited submicron particles on a platinum target, using real-time optical reflectivity methods. These preliminary experiments will be extended and discussed in our next Quarterly Technical Report.
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| Total Pages | : 8 |
| Release | : 1986 |
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In support of the above mentioned objectives, we have initiated theoretical studies in the following three interrelated areas : (a) Interaction of inertial- and thermophoretic effects in well-defined laminar ''dusty-gas'' flows. (b) Self-regulated sticking and deposit erosion in the simultaneous presence of vapor or submicron ''glue'' (c) Use of packed bed and tube-bank heat transfer and friction correlations to provide the basis for future tube-bank fouling predictions. During the first three months of Grant DE-FG22-86 PC 90756, we have: (1) Designed and initiated construction of the microcombustor particle-laden jet facility described in Section 3.1. (2) Initiated theoretical studies of the interaction of inertial and thermophoretic effects, the role of simultaneous vapor arrival in determining particle sticking and erosion probabilities, and mass transport phenomena in deep tube banks.
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| Total Pages | : 8 |
| Release | : 1987 |
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In support of the above mentioned objectives, we are carrying out theoretical studies in the following three interrelated areas: (a) Interaction of inertial- and thermophoretic effects in well-defined laminar ''dusty-gas'' flows; (b) Self-regulated sticking and deposit erosion in the simultaneous presence of vapor or submicron ''glue''; (c) Use of packed bed and tube-bank heat transfer and friction correlations to provide the basis for future tube-bank fouling predictions. During this second quarter of Grant DE-FG22-86 PC 90756. we have: (1) done preliminary gas velocity and temperature calibrations of the micro-combustor exit gas flow jet and initiated the development of both a monodispersed droplet feed system and powder feed system to provide monodispersed particle laden jets covering a broad spectrum of particle sizes (ca. 0.5--50 m diameter); and, (2) demonstrated the ability of impacting supermicron particles to remove predeposited submicron particles on a platinum target, using real-time optical reflectivity methods. These preliminary experiments will be extended and discussed in our next Quarterly Technical Report.
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| Total Pages | : 16 |
| Release | : 1990 |
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The overall goal of this research in the area of ash transport was to advance the capability of making reliable engineering predictions of the dynamics and consequences of net deposit growth for surfaces exposed to the products of coal combustion. To accomplish this for a wide variety of combustor types, coal types, and operating conditions, this capability must be based on a quantitative understanding of each of the important mechanisms of mineral matter transport, as well as the nature of the interactions between these substances and the prevailing ''fireside'' surface of the deposit. This level of understanding and predictive capability could ultimately be translated into very significant cost reductions for coal-fired equipment design, development and operation.
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| Total Pages | : 8 |
| Release | : 1988 |
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During the present reporting period, we have initiated work on (a) the interpretation of our recent data (see QTR5) on deposition rates under the simultaneous influence of inertia and thermophoresis, (b) the possible rate of particle photophoresis in environments characterized by high radiative heat loads. and (c) the influence of particle size distributions on total mass deposition rates. The fruits of these initiatives will be reported in subsequent quarterly technical reports. Here, we focus on our recent theoretical results in the important but previously uncharted area of the relations between particulate deposition mechanisms, deposit microstructure and deposit properties. Experimental verification of some of the most interesting predictions will be the subject of future HTCRE-Lab studies. Recent discussions with fouling engineers have convinced us that despite recent advances in our ability to predict particle deposition rates in convective-diffusion environments, the important connection between resulting deposit properties (effective thermal conductivity permeability, {hor_ellipsis}) and deposition mechanism remain poorly understood and only scarcely studied. Accordingly, as part of this DOE-PETC program we have developed a discrete stochastic model to simulate particulate deposition processes resulting from a combination of deposition mechanisms.
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| Total Pages | : 9 |
| Release | : 1987 |
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During this third quarter of Grant DE-FG22-86 PC 90756, we have obtained preliminary experimental results on the deposition behavior of submicron and supermicron solid particles (MgO, Al2O3) on a two-dimensional surface exposed to a high temperature/velocity particle ''laden'' atmospheric pressure jet. The uniform velocity (''plug flow'') jet, with temperatures up to about 1520 K, derives from a pressurized gaseous fuel microcombustion chamber (110 cc) equipped with a platinum guiding (exit) channel. Particles were generated by several methods (Berglund-Liu type aerosol generator, ultrasonic nebulizer, or syringe feeder with aerodynamic particle off-take) and were introduced into the combustion chamber with a carrier stream of nitrogen or air. Laser light scattering and reflectivity techniques were used for the study of particle deposition, supplemented by post-mortem microscopy on the exposed surface. We observed a linear deposition rate of submicron particles due to the thermophoretic mechanism (until the first layer was developed) under both high and low velocity conditions. On the contrary, supermicron particle deposits reach a steady-state, evidently due to a dynamic equilibrium between particle deposition and dislodging caused by the impacting particles. At several temperatures particle-free subsonic gas jets (up to 120 m/sec) were unable to remove the submicron particle layer.
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| Total Pages | : 11 |
| Release | : 1989 |
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Little is yet known (theoretically or experimentally) about the simultaneous effects of particle inertia, particle thermophoresis and high mass loading on the important engineering problem of predicting deposition rates from flowing ''dusty'' gases. For this reason, we investigate the motion of particles present at nonnegligible mass loading in a flowing nonisothermal gaseous medium and their deposition on strongly cooled or heated solid objects by examining the instructive case of steady axisymmetric ''dusty gas'' flow between two infinite disks: an inlet (porous) disk and the impermeable ''target'' disk -- a flow not unlike that encountered in recent seeded-flame experiments. Since this stagnation flow/geometry admits interesting self-similar solutions at all Reynolds numbers, we are able to predict laminar flow mass-, momentum- and energy-transfer rate coefficients over a wide range of particle mass loadings, dimensionless particle relaxation times (Stokes numbers), dimensionless thermophoretic diffusivities, and gas Reynolds numbers. As a by-product, we illustrate the accuracy and possible improvement of our previous ''diffusion model'' for tightly coupled dusty gas systems. Moreover, we report new results illustrating the dependence of the important ''critical'' Stokes number (for incipient particle impaction) on particle mass loading and wall/gas temperature ratio for dust-laden gas motion towards ''overheated'' solid surfaces. The present formulation and insulating transport coefficients should not only be useful in explaining/predicting recent deposition rate trends in ''seeded'' flame experiments, but also highly mass-loaded systems of technological interest.
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| Total Pages | : 10 |
| Release | : 1989 |
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Our results on photophoresis reveal significant transport effects, mainly for particles which are carbonaceous (char-like, soot-like) rather than ash-like. Figure 2 shows the predicted dimensionless transport coefficient (proportional to the ordinary Stanton number for mass transfer) as a function of radiation/convective flux ratio and carbonaceous particle radius for laminar boundary layer flow past a wall cooled to 70% of the mainstream temperature, subjected to a radiative energy spectrum appropriate to a black-body source at ca. 1800K. One sees that large effects on the particle deposition rate are produced if the radiative flux is comparable to or exceeds the ordinary (Fourier) energy flux. We are now extending this work to include the effects of inevitable particle asymmetries, including agglomerate (shape) effects, and the role that energy transfer (eg. radiative cooling of larger particles in a population) might play in the coagulation dynamics and deposition dynamics of such aerosol populations.
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| Total Pages | : 654 |
| Release | : 1993 |
| Genre | : Power resources |
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