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| 2. |
- Baskakov, A.P., et al.
(författare)
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Complex Heat Transfer in Furnaces with a Circulating Fluidized Bed
- 2001
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Ingår i: Heat Transfer Research. - 1064-2285. ; 37:7-8, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- Intensity of heat transfer to screen surfaces in the furnaces with a circulating fluidized bed (CFB) is determined by both radiation and convection of particles. Due to the formation of a thermal boundary layer near the screens the role of radiation decreases and that of convection increases with an increase in concentration of particles in the furnace. Generalization of the data obtained in pilot-full-scale and industrial furnaces with a CFB allowed one to obtain a simple empirical dependence of the furnace-mean coefficient of heat transfer α (W/(m2·K) on the volumetric-mean concentration of particles c (kg/m3): α = 85·c0.3.
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| 5. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace
- 1998
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 41:8-9, s. 1013-1024
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Tidskriftsartikel (refereegranskat)abstract
- A heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace hasbeen formullated in order to calculate the heat transfer to the walls. The convective heat transfer is relatedto a horizontal particle flow from the core to the wall region, and an additive radiative heat transferconstituent is calculated for the particulate medium. An empirical description of the vertical distributionof solids and the transversal temperature profile are needed for the evaluation. The calculated heat transfercoefficients were compared with measurements in three commercial boilers and the deviation was less than40%, which is in the same order as the uncertainty of the experimental data.
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| 6. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Heat transfer in circulating fluidized bed boilers - do we know sufficiently?
- 1997
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Ingår i: Trends in heat mass and momentum transfer. - 0973-2446. ; 3, s. 85-104
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Tidskriftsartikel (refereegranskat)abstract
- A considerable amount of work, mostly measurements, has been dedicated to heat transfer in circulating fluidized bed combustors. The results show that the radiative constituent of heat transfer varies between limits depending on the optical thickness of a particle boundary layer, and that the convective constituent can be related to the average cross-sectional suspension density. Based on this information reasonable estimates of heat transfer coefficients can be made. Experimental data from boiler conditions and ambient conditions are compared introducing a compensation for thermal radiation and changes in the properties of the gas with temperature. A good agreement is achieved between the two sets of data, except for cross-sectional average suspension densities below about 5 kg/m3. Locally there is a variation in heat transfer across the membrane-tube wall, and the heat transfer to the tube crest can be twice that to the adjacent fin. Heat transfer models are reviewed and applied to a hot (boiler) case and a cold (laboratory) case. The deviation of computed heat transfer coefficients from the measured ones was larger than the scatter in the measured data. The differences in the results from the models are primarily explained by uncertainties in the fluid-dynamic model parameters. For refined estimates and optimisation, knowledge of the detailed behaviour of the fluid-dynamics of the combustor is necessary. In this field the thickness of the a gas-gap between wall and particle suspension, the cover factor of the time-resolved fluctuating particle concentration, and the in-flow of particles towards the wall are insufficiently known and further work is necessary. In addition, further work is needed concerning the local heat transfer to membrane-tube walls
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| 7. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Translation of Heat Transfer Measurements from Laboratory CFBs to the Conditions of CFB-Boilers
- 2003
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Ingår i: Heat Transfer Research. - 1064-2285. ; 34:3-4, s. 252-269
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work is to find a method for translation of heat transfer data from cold laboratory units to boiler conditions. From a compilation of existing data on heat transfer to walls in hot and cold circulating fluidized beds it is concluded that the results can be translated approximately by compensating for changes in the thermal conductivity of the gas and thermal radiation. A more general methodology is developed by deriving the criteria for thermal similarity. The only criterion that was added to those for fluid-dynamic similarity was the ratio of heat capacity of gas and particles. The thermal scaling is tested by comparing heat transfer measurements in a boiler with measurements in a scaled laboratory model. The results show that the Nusselt numbers were not the same in the boiler and the scaled model, which can be a result of the characteristic length-scale chosen, a too low heat capacity of the scaled particles or a failure to scale the local fluid-dynamics at the wall.
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| 8. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Translation of heat transfer measurements from laboratory CFBs to the conditions of CFB-boilers
- 2000
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Ingår i: IV Minsk Int Heat and Mass Transfer Forum,. / V.A. Borodulya, Teplitsky, J.C., Vinogradov, L.M., Palchonok, G.I.. - 9856456126 ; 6, s. 12-23
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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