Heat Transmission by Radiation, Conduction and Convection

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D. Van Nostrand, 1921 - Heat - 238 pages
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Page 112 - The heat carried off by air or any fluid from a surface, apart from the effect of radiation, is proportional to the internal diffusion of the fluid at and near the surface...
Page 111 - Newton appears to have assumed that the rate at which heat is transmitted from a surface to a gas and vice versa is ceteris paribus directly proportional to the difference in temperature between the surface and the gas, whereas Dulong and Petit, followed by Peclet, came to the conclusion from their experiments that it followed altogether a different law.* These philosophers do not seem to have advanced any theoretical reasons for the law which they have taken, but have deduced it entirely from their...
Page 89 - ... bend, R0, is from 5 to 7-5 times the radius r of the pipe, increasing slightly up to the value R0 about 13r. FIG. 26. — Flow of water at sharp bends. Alexander* concludes that the loss of head due to a bend of radius R0=5r is equivalent to that offered by a straight length of pipe equal to 3-38/, where I is the length of the curved portion of the pipe. Experiments made at the Yorkshire Collegef on an easy right-angled bend showed a resistance equivalent to a straight pipe 10 to 15 diameters...
Page 112 - I have to say, and is based on the molecular theory of fluids. Now the rate of this diffusion has been shown from various considerations to depend on two things : — 1. The natural internal diffusion of the fluid when at rest. 2. The eddies caused by visible motion which mixes the fluid up and continually brings fresh particles into contact with the surface.
Page 115 - B for different fluids be determined, we should then be able to determine, as regards length and extent, the best proportion for the tubes and flues of boilers. In further explanation of his theory Professor Reynolds contributed the following demonstration to the paper by Dr. Stanton referred to on p. 117. " The motion of heat from the surface of the pipe follows the same laws as the motion of momentum to the surface...
Page 98 - U•tube with the two limbs widely apart, and the difference of pressure on the surfaces of the water in the two limbs of the tube is measured by tilting the gauge through a very small angle so that there is no displacement of the water along the tube.
Page 112 - The second cause, the effect of eddies, arises entirely from the motion of the fluid, and is proportional both to the density of the fluid, if gas, and the velocity with which it flows past the surface.
Page 74 - Rayleigh has shown, however, that the solution given by equation 11, p. 70, is only a particular case of a general law of resistance of bodies immersed in fluids moving relatively to them, under the assumption that this resistance depends only on the linear dimensions of the body and on the velocity, density, and the ratio of viscosity to density of the fluid.
Page 112 - ... surface, apart from the effect of radiation, is proportional to the internal diffusion of the fluid at and near the surface, ie, is proportional to the rate at which particles or molecules pass backwards and forwards from the surface to any given depth within the fluid, thus, if AB be the surface and ab an ideal line in the fluid parallel to AB then the heat carried off...

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