| 1. |
- Akkerman, V., et al.
(författare)
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Flow-flame interaction in a closed chamber
- 2008
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 20:5, s. 21-
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Tidskriftsartikel (refereegranskat)abstract
- Numerous studies of flame interaction with a single vortex and recent simulations of burning in vortex arrays in open tubes demonstrated the same tendency for the turbulent burning rate proportional to U-rms lambda(2/3), where U-rms is the root-mean-square velocity and lambda is the vortex size. Here, it is demonstrated that this tendency is not universal for turbulent burning. Flame interaction with vortex arrays is investigated for the geometry of a closed burning chamber by using direct numerical simulations of the complete set of gas-dynamic combustion equations. Various initial conditions in the chamber are considered, including gas at rest and several systems of vortices of different intensities and sizes. It is found that the burning rate in a closed chamber (inverse burning time) depends strongly on the vortex intensity; at sufficiently high intensities it increases with U-rms approximately linearly in agreement with the above tendency. On the contrary, dependence of the burning rate on the vortex size is nonmonotonic and qualitatively different from the law lambda(2/3). It is shown that there is an optimal vortex size in a closed chamber, which provides the fastest total burning rate. In the present work, the optimal size is six times smaller than the chamber height.
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| 2. |
- Prins, A. J., et al.
(författare)
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Visualization of Biomass Pyrolysis and Temperature Imaging in a Heated-Grid Reactor
- 2009
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 23:1, s. 993-1006
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Tidskriftsartikel (refereegranskat)abstract
- The main advantage of a heated-grid reactor for studying pyrolysis kinetics of solid fuel samples is that high heating rates of up to 1000 K/s can be obtained. However, one of the concerns is whether the temperature distribution over the grid material is uniform and whether the presence of a thermocouple welded to the grid causes any measurement errors. Biomass samples were placed on the heated-grid reactor, and the volatiles, emitted in the biomass pyrolysis process as hot gas plumes, were imaged with an infrared camera with a high framing speed. The temporal resolved infrared images indicate that the pyrolysis process does not take place at the same rate everywhere on the grid. Two-dimensional temperature images of a heated grid made of stainless steel were recorded using the method of laser-induced thermometry with thermographic phosphors. As expected from a heat-transfer model, measured temperatures were found to be significantly higher than temperatures indicated by a thermocouple welded to the bottom of the grid. It was also observed that there is a large temperature gradient between the two electrodes on which the grid is connected. It is shown that replacing a wire mesh by a foil as a grid material may lead to more homogeneous temperature distribution. The paper recommends additional research to demonstrate the suitability of the heated-grid reactor for carrying out accurate measurements.
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| 3. |
- Remie, Martin, et al.
(författare)
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Extended heat-transfer relation for an impinging laminar flame jet to a flat plate
- 2008
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 51:7-8, s. 1854-1865
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Tidskriftsartikel (refereegranskat)abstract
- Many industrial applications use flame impingement to obtain high heat-transfer rates. An analytical expression for the convective part of the heat transfer of a flame jet to a plate is derived. Therefore, the flame jet is approximated by a hot inert jet. In contradiction with existing convective heat-transfer relations, our analytical solution is applicable not only for large distances between the jet and the plate, but also for close spacings. Multiplying the convective heat transfer by a factor which takes chemical recombination in the cold boundary layer into account, results in an expression for the heat flux from a flame jet to the hot spot of a heated plate. Numerical and experimental validation show good agreement.
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| 4. |
- Remie, Martin, et al.
(författare)
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Heat-transfer distribution for an impinging laminar flame jet to a flat plate
- 2008
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 51:11-12, s. 3144-3152
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Tidskriftsartikel (refereegranskat)abstract
- Impinging flame jets are widely used in applications where high heat-transfer rates are needed, for instance in the glass industry. During the heating process of glass products, internal thermal stresses develop in the material due to temperature gradients. In order to avoid excessive thermal gradients as well as overheating of the hot spots, it is important to know and control the temperature distribution inside a heated glass product. Therefore, it is advantageous to know the relation describing the convective heat–flux distribution at the heated side of a glass product. In a previous work, we presented a heat–flux relation applicable for the hot spot of the target [M.J. Remie, G. Sa¨rner, M.F.G. Cremers, A. Omrane, K.R.A.M. Schreel, M. Alde´n, L.P.H. de Goey, Extended heat-transfer relation for an impinging laminar flame jet to a flat plate, Int. J. Heat Mass Transfer, in press]. In this paper, we present an extension of this relation, which is applicable for larger radial distances from the hot spot.
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| 5. |
- van den Boom, J.D.B.J, et al.
(författare)
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Active control of oscillations in a Rijke tube-like flat flame configurations
- 2007
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Ingår i: Proceeding of the European Combustion Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of low NOx premixed surface burners with a large modulation range in modern central heating systemsoften to noise problems. In order to make any further advance in the development of these systems the noise problemhas to be solved. Therefore, the possibility of suppression (and stabilization) of these instabilities is in investigatedusing active model-based control strategies. A model for the condensing gas-fired boiler is derived first. based on anacoustic network approach. Special attention is paid to the flame dynamics. Second, a H1 controller is synthesized,where also modelling uncertainties are taken into account. In the end the performance and the robustness of thecontroller is validated during experiments.
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