Tube Entrance Heat Transfer with Deposit Formation
TL;DR: In this article, a kerosene-type gas turbine fuel through a direct-resistance heated tube, a condition was found which resulted in a tube wall temperature profile with two peaks near the tube entrance.
Abstract: While flowing a kerosene-type gas turbine fuel through a direct-resistance heated tube, a condition was found which resulted in a tube wall temperature profile with two peaks near the tube entrance. The downstream peak gradually diminished as deposits formed inside the tube and only one peak remained after seven hours. On the basis of existing analytical studies and experimental data pertaining to heat transfer in the entrance region of tubes, it was concluded that the temperature profile can be divided into five regions: development of the thermal boundary layer, appearance of secondary flows, fully developed thermal boundary layer, transition to turbulent flow and turbulent flow. Deposits increased the tube roughness and reduced the length required for laminar-turbulent transition.
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TL;DR: Synthese des travaux publies et bibliographie mondiale sur le transfert de chaleur pour l'annee 1983 as discussed by the authors.
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01 Jan 1955
TL;DR: The flow laws of the actual flows at high Reynolds numbers differ considerably from those of the laminar flows treated in the preceding part, denoted as turbulence as discussed by the authors, and the actual flow is very different from that of the Poiseuille flow.
Abstract: The flow laws of the actual flows at high Reynolds numbers differ considerably from those of the laminar flows treated in the preceding part. These actual flows show a special characteristic, denoted as turbulence. The character of a turbulent flow is most easily understood the case of the pipe flow. Consider the flow through a straight pipe of circular cross section and with a smooth wall. For laminar flow each fluid particle moves with uniform velocity along a rectilinear path. Because of viscosity, the velocity of the particles near the wall is smaller than that of the particles at the center. i% order to maintain the motion, a pressure decrease is required which, for laminar flow, is proportional to the first power of the mean flow velocity. Actually, however, one ob~erves that, for larger Reynolds numbers, the pressure drop increases almost with the square of the velocity and is very much larger then that given by the Hagen Poiseuille law. One may conclude that the actual flow is very different from that of the Poiseuille flow.
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253 citations
TL;DR: In this paper, an analysis was performed to determine the heat transfer characteristics for a laminar forced convection flow in a circular tube with prescribed wall heat flux, and the solution contained a series expansion whose form was similar to that obtained by Graetz for the uniform wall temperature problem.
Abstract: An analysis is performed to determine the heat transfer characteristics for a laminar forced convection flow in a circular tube with prescribed wall heat flux. Results are first obtained for the case of uniform heat flux, and these are then generalized to apply to the situation of arbitrary longitudinal variation of wall heat flux. The solution contains a series expansion whose form is similar to that obtained by Graetz for the uniform wall temperature problem.
173 citations
TL;DR: In this article, a thermal entry length is defined as the heated length required to bring the local Nusselt number to within 5 percent of the fully developed value of the fluid.
Abstract: An analysis has been performed using a method similar to Graetz’s formulation for the laminar thermal entry region. The fluid is assumed to have a fully developed turbulent velocity profile throughout the length of the pipe. Local and fully developed Nusselt numbers are presented for fluids with Prandtl numbers ranging from 0.7 to 100 for Reynolds numbers between 50000 and 500000. A thermal entrance length is defined as the heated length required to bring the local Nusselt number to within 5 percent of the fully developed value. This length is found to decrease with increasing Prandtl number, dropping from about 10 diameters for a Prandtl number of 0.7 to less than one diameter for a Prandtl number of 100. Comparison is made with the results of Deissler, who used an integral method-boundary layer approach, and also with available experimental data. The effect of the thermal boundary conditions was studied by comparing the present uniform heat flux results with those of previous investigators who considered uniform wall temperature.
114 citations
TL;DR: In this paper, the effect of buoyancy on forced convective heat transfer in a horizontal straight tube has been investigated by means of accurate experiments on the fully developed flow of air in a uniformly heated horizontal tube.
94 citations