| 1. |
- Leckner, Bo G, 1936
(författare)
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Heat transfer in the entrance region with fully develped turbulent flow between parallel plates
- 1972
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 15, s. 35-42
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Tidskriftsartikel (refereegranskat)abstract
- An analysis is made of local heat transfer in a thermal entrance region with a fully developedturbulent velocity profile for various Reynolds and Prandtl numbers. Difference methods are used tosolve the energy equation. The velocity and eddy diffusivities are described by semi-empirical relationships.The geometrical picture is simple: flow between parallel plates, one of which is thermally insulated, theother transmits a known heat flux. Certain comparisons with calculations on laminar flow are made as acheck on the reliability of the numerical method. This also provides an estimate of the influence of turbulencein the various cases and gives a possibility of judging the validity of approximations. Finally a comparisonwith available empirical expressions for fully developed heat transfer is shown
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| 2. |
- Leckner, Bo G, 1936
(författare)
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Radiation from flames and gases in a cold wall combustion chamber
- 1970
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 13:1, s. 185-197
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of heat transfer in furnaces is usually based on coarse approximations of temperatureand emissivity in the combustion chamber. This paper suggests a method suitable for machinecomputation of the heat transfer from flames and gases to the walls of a furnace. A theoretical derivationof the basic equation is made and the simplifications necessary for execution of the calculation in acceptabletime are discussed The patterns of temperature and flame. emissivity are described by means of simplefunctions, a mathematical model. Experiments were carried out in an experimental furnace of simplegeometry using one oil-burner in order to check the accuracy of the theoretical assumptions. Mcasurementsof flame and gas temperature, flame emissivity, wall heat flux and exterior measurements necessaryfor the heat balance of the furnace were done. The measurements of temperature and emissivity define themathematical model.The heat transfer from flame and gases (including the contribution due to reflexion, non-cold surfacesand convection) was calculated at four different loads of the furnace and compared with the heat fluxmeasurements. The difference between measured and calculated heat flux, due to errors of measurementsand calculations, was less than about 15 per cent of the total heat flux.
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| 3. |
- Leckner, Bo G, 1936
(författare)
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Radiative heat transfer calculations in real gases
- 1974
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Ingår i: Waerme-Stoffuebertrag Thermo-Fluid Dyn. - 0042-9929 .- 1432-1181. ; 70:4, s. 236-247
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Tidskriftsartikel (refereegranskat)abstract
- A general formulation for radiative heat transfercalculations is presented, based on integrated quantities such as total emissivities and absorptivities. The procedure is intended particularly for combustion chamber applications of varEing degree of complexity, the radiative active medium consisting of gases such as H20 and CO2 and of soot. First, some preliminary calculations are given for the often treated radiative equilibrium cases of plane parallel plates and infinite concentric cylinders. Then an example of a combustion chamber calculation is studied where the radiative heat transfer calculation is included in a system of partial differential equations describing momentum, hear and mass transfer with combustion.
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| 4. |
- Leckner, Bo G, 1936
(författare)
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Some elements of radiative heat transfer calculations in flames and gases
- 1973
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Ingår i: Archiwum Procesów Spalania. ; 4:4, s. 377-398
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Tidskriftsartikel (refereegranskat)abstract
- The validity of approximations in methods to be used in radiative heat flux calculations in flames and combustion gases is discussed. The principal problem is whether quantities such as emissivity and abrorptivity of gases and soot, defined for homogeneous media, may be employed alsoin media where temperature and concentration vary. Some examples are studied where the approximative methods are compared with resulrs from more refined calculations for carbon dioxide, water vapour and soot-gas mixtures.
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| 5. |
- Leckner, Bo G, 1936
(författare)
-
Spectral and total emissivity of water vapor and carbon dioxide
- 1972
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Ingår i: Combustion and Flame. - 1556-2921 .- 0010-2180. ; 19:1, s. 33-48
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Tidskriftsartikel (refereegranskat)abstract
- Data on the infrared radiation characteristics of carbon dioxide and water vapor in the form of absorption coefficients and line spacings averaged over narrow spectral intervals have been compiled from various sources. These data are to be used in heat transfer calculations from hot gases. In order to investigate the accuracy of the data, the simplest case possible is chosen: a comparison with the total emissivity charts of water vapor and carbon dioxide. It appears however that the charts are not entirely reliable as standards for comparison: it seems probable that Hottel's chart for water vapor gives too low values at temperatures above 900°C and that the partial pressure correction is temperature dependent. With the exception of some regions where judgment is difficult, the calculations using spectral data seem to represent total emissivities with a maximum error which is estimated to around 10%. Sources of error in the spectral data and in Hottel's total emissivity charts are discussed. Total emissivity charts, pressure and overlap corrections based on calculations with spectral data are presented.
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| 6. |
- Leckner, Bo G, 1936
(författare)
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The spectral and total emissivity of carbon dioxide
- 1971
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Ingår i: Combustion and Flame. - 1556-2921 .- 0010-2180. ; 17:1, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of radiative heat transfer from flames and combustion gases requires, in the general case of non-homogeneous gases, a knowledge of the spectral characteristics of the gases. In this paper an analysis is made of available spectral data on carbon dioxide, extended with an approximative description of the 15-μm, 10-μm, and 2-μm bands, in the form of a comparison with measured total emissivities. The contribution of the bands to the total emissivity is shown at various temperatures and path lengths. The spectral emissivity is expressed as mean-values over wave-number intervals by means of the statistical band model. The agreement between Hottel's diagrams of total emissivities and the total emissivities calculated on the basis of spectral data is good for optical path lengths greater than 1.0 cm atm. If Hottel's values are corrected in the small-path length region for the possible influence of carbon dioxide in the air layer between the measuring instrument and the gas container, there remains a discrepancy of less than 15% around path lengths of 0.1 cm atm.
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| 7. |
- Leckner, Bo G, 1936
(författare)
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The spectral distribution of solar radiation at the earth's surface—elements of a model
- 1978
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Ingår i: Solar Energy. - 0038-092X. ; 20:2, s. 143-150
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Tidskriftsartikel (refereegranskat)abstract
- The attenuating properties of the atmosphere are presented in a form that permits the calculation of direct, diffuse and global spectral solar irradiance at ground level, using the extraterrestrial irradiance values of Thekaekara. Input data describing the state of the atmosphere are obtained from standard meteorological information or from tabulated average values. Clear sky diffuse spectral irradiance on a horizontal surface is estimated from the direct beam by means of an empirical simplification. Examples of the agreement between calculated and measured values are shown.
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