John H. Lienhard IV, John H. Lienhard V. A Heat Transfer Textbook (776116), страница 86
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Compare the result to eqn. (10.31).Does specular reflection reduce the heat transfer?10.48Some values of the monochromatic absorption coefficient forliquid water, as ρκλ (cm−1 ), are listed below [10.4]. For eachwavelength, find the thickness of a layer of water for whichthe transmittance is 10%. On this basis, discuss the colors onemight see underwater and water’s infrared emittance.λ (µm)0.30.40.50.60.81.02.02.6–10.0ρκλ (cm−1 )0.00670.000580.000250.00230.01960.36369.1> 100.ColorvioletgreenorangeChapter 10: Radiative heat transfer59210.49The sun has a diameter of 1.391 × 106 km. The earth has adiameter of 12,740 km and lies at a mean distance of 1.496 ×108 km from the center of the sun. (a) If the earth is treated as aflat disk normal to the radius from sun to earth, determine theview factor Fsun–earth .
(b) Use this view factor and the measuredsolar irradiation of 1367 W/m2 to show that the effective blackbody temperature of the sun is 5777 K.References[10.1] E. M. Sparrow and R. D. Cess. Radiation Heat Transfer. Hemisphere Publishing Corp./McGraw-Hill Book Company, Washington, D.C., 1978.[10.2] M. F. Modest. Radiative Heat Transfer. McGraw-Hill, New York,1993.[10.3] D. K.
Edwards. Radiation Heat Transfer Notes. Hemisphere Publishing Corp., Washington, D.C., 1981.[10.4] R. Siegel and J. R. Howell. Thermal Radiation Heat Transfer. Taylor and Francis-Hemisphere, Washington, D.C., 4th edition, 2001.[10.5] J. R.
Howell. A Catalog of Radiation Heat Transfer ConfigurationFactors. University of Texas, Austin, 2nd edition, 2001. Availableonline at http://www.me.utexas.edu/∼howell/.[10.6] A. K. Oppenheim. Radiation analysis by the network method.Trans. ASME, 78:725–735, 1956.[10.7] W.-J. Yang, H. Taniguchi, and K. Kudo. Radiative heat transfer bythe Monte Carlo method. In T.F. Irvine, Jr., J.
P. Hartnett, Y. I. Cho,and G. A. Greene, editors, Advances in Heat Transfer, volume 27.Academic Press, Inc., San Diego, 1995.[10.8] H. C. van de Hulst. Light Scattering by Small Particles. DoverPublications Inc., New York, 1981.[10.9] P. W. Atkins. Physical Chemistry. W. H. Freeman and Co., NewYork, 3rd edition, 1986.[10.10] G.
Herzberg. Molecular Spectra and Molecular Structure. KreigerPublishing, Malabar, Florida, 1989. In three volumes.References[10.11] D. K. Edwards. Molecular gas band radiation. In T. F. Irvine, Jr.and J. P. Hartnett, editors, Advances in Heat Transfer, volume 12,pages 119–193. Academic Press, Inc., New York, 1976.[10.12] H. C. Hottel and A. F. Sarofim.
Radiative Transfer. McGraw-HillBook Company, New York, 1967.[10.13] D. K. Edwards and R. Matavosian. Scaling rules for total absorptivity and emissivity of gases. J. Heat Transfer, 106(4):684–689,1984.[10.14] M. Iqbal. An Introduction to Solar Radiation.
Academic Press, Inc.,New York, 1983.[10.15] J. A. Duffie and W. A. Beckman. Solar Engineering of ThermalProcesses. John Wiley & Sons, Inc., New York, 2nd edition, 1991.[10.16] H. G. Houghton. Physical Meteorology. MIT Press, Cambridge, MA,1985.[10.17] P. Berdahl and R. Fromberg. The thermal radiance of clear skies.Solar Energy, 29:299–314, 1982.[10.18] A. Skartveit, J. A. Olseth, G. Czeplak, and M.
Rommel. On theestimation of atmospheric radiation from surface meteorologicaldata. Solar Energy, 56:349–359, 1996.[10.19] P. Berdahl and M. Martin. The emissivity of clear skies. SolarEnergy, 32:663–664, 1984.[10.20] J. A. Fay and D. S. Gollub. Energy and Environment. Oxford University Press, New York, 2002.[10.21] J.
Hansen, R. Ruedy, M. Sato, M. Imhoff, W. Lawrence, D. Easterling, T. Peterson, and T. Karl. A closer look at United States andglobal surface temperature change. J. Geophysical Research, 106:23947, 2001.[10.22] R. T. Watson, editor. Climate Change 2001: Synthesis Report.Third assessment report of the Intergovernmental Panel on Climate Change.
Cambridge University Press, New York, 2002. Alsoavailable at http://www.ipcc.ch.593594Chapter 10: Radiative heat transfer[10.23] P. A. Stott, S. F. B. Tett, G. S. Jones, M. R. Allen, J. F. B. Mitchell,and G. J. Jenkins. External control of 20th century temperatureby natural and anthropogenic forcings. Science, 290:2133–2137,2000.[10.24] F.
Kreith and J. F. Kreider. Principles of Solar Engineering. Hemisphere Publishing Corp./McGraw-Hill Book Company, Washington, D.C., 1978.[10.25] U.S. Department of Commerce. Solar Heating and Cooling of Residential Buildings, volume 1 and 2.
Washington, D.C., October1977.Part VMass Transfer59511. An introduction to mass transferThe edge of a colossal jungle, so dark-green as to be almost black, fringedwith white surf, ran straight, like a ruled line, far, far away along a bluesea whose glitter was blurred by a creeping mist. The sun was fierce, theland seemed to glisten and drip with steam.Heart of Darkness, Joseph Conrad, 190211.1IntroductionWe have, so far, dealt with heat transfer by convection, radiation, anddiffusion (which we have been calling conduction). We have dealt onlywith situations in which heat passes through, or is carried by, a singlemedium.
Many heat transfer processes, however, occur in mixtures ofmore than one substance. A wall exposed to a hot air stream may becooled evaporatively by bleeding water through its surface. Water vapormay condense out of damp air onto cool surfaces. Heat will flow throughan air-water mixture in these situations, but water vapor will diffuse orconvect through air as well.This sort of transport of one substance relative to another is calledmass transfer ; it did not occur in the single-component processes of thepreceding chapters. In this chapter, we study mass transfer phenomenawith an eye toward predicting heat and mass transfer rates in situationslike those just mentioned.During mass transfer processes, an individual chemical species travels from regions where it has a high concentration to regions where it hasa low concentration. When liquid water is exposed to a dry air stream, itsvapor pressure may produce a comparatively high concentration of water vapor in the air near the water surface.
The concentration differencebetween the water vapor near the surface and that in the air stream willdrive the diffusion of vapor into the air stream. We call this evaporation.597598An introduction to mass transfer§11.1Figure 11.1 Schematic diagram of a natural-draft coolingtower at the Rancho Seco nuclear power plant.
(From [11.1],courtesy of W. C. Reynolds.)In this and other respects, mass transfer is analogous to heat transfer. Just as thermal energy diffuses from regions of high temperatureto regions of low temperature (following the temperature gradient), themass of one species diffuses from regions high concentration to regionsof low concentration (following its concentration gradient.) Just as thediffusional (or conductive) heat flux is directly proportional to a temperature gradient, so the diffusional mass flux of a species is often directlyproportional to its concentration gradient; this is called Fick’s law of diffusion. Just as conservation of energy and Fourier’s law lead to equationsfor the convection and diffusion of heat, conservation of mass and Fick’slaw lead to equations for the convection and diffusion of species in amixture.The great similarity of the equations of heat convection and diffusionto those of mass convection and diffusion extends to the use of convective mass transfer coefficients, which, like heat transfer coefficients,relate convective fluxes to concentration differences.
In fact, with simple modifications, the heat transfer coefficients of previous chapters mayoften be applied to mass transfer calculations.§11.1IntroductionFigure 11.2 A mechanical-draft cooling tower. The fans arelocated within the cylindrical housings at the top. Air is drawnin through the louvres on the side.Mass transfer, by its very nature, is intimately concerned with mixtures of chemical species. We begin this chapter by learning how to quantify the concentration of chemical species and by defining rates of movement of species. We make frequent reference to an arbitrary “species i,”the ith component of a mixture of N different species. These definitionsmay remind you of your first course in chemistry. We also spend sometime, in Section 11.4, discussing how to calculate the transport propertiesof mixtures, such as diffusion coefficients and viscosities.Consider a typical technology that is dominated by mass transfer processes.
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