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AIChE Journal 06/2004; 10(4):466 - 470. · 2.26 Impact Factor
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ABSTRACT: A boundary-layer analysis of laminar film condensation on a vertical plate has been carried out to study the effects of superheated vapor and noncondensable gases. For a pure, superheated vapor the effects of superheating on the surface heat transfer are accounted for by a simple modification of previously available results for saturated vapors. For a given temperature difference between the plate surface and the liquid-vapor interface, superheating increases the heat transfer to the surface, but only to a modest extent for most practical situations. Although free convection was not included in the analysis, its role has been estimated to be small. For noncondensable gases the analysis shows that the presence of a few per cent of noncondensable in the bulk of the vapor causes a great reduction in the surface heat transfer. The fact that the predicted reduction is substantially larger than that found experimentally indicates that free convection, which is not included in the analysis, plays an important role when noncondensables are present.
AIChE Journal 06/2004; 7(3):473 - 477. · 2.26 Impact Factor
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ABSTRACT: The effects of fluid injection on the structure of an initially fully developed, low Reynolds number, turbulent pipe flow have been studied by means of a hot-film anemometer. Measurements were made of the axial turbulence intensity field and of the time-mean streamwise velocity distribution, both in the porous-walled pipe and in the solid-walled hydrodynamic development section. Oscilloscope traces showing the timewise pattern of the local velocity fluctuations were also monitored. The Reynolds number of the air flow at the inlet of the porous pipe was varied from 3090 to 6350, and the Reynolds number of the injected air ranged from 60 to 160.
Journal of Fluid Mechanics 04/1972; 52(03):451 - 464. · 2.46 Impact Factor
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ABSTRACT: An analysis is made of the fluid flow and heat transfer processes in a circular cylindrical enclosure rotating about its own axis. A coolant is passed through the enclosure, entering and leaving through centrally located apertures in the end walls. This configuration is intended as a model of rotating enclosures in devices such as gas turbines and air compressors. The Navier-Stokes and energy equations were solved by a finite-difference formulation which can accommodate either steady or transient conditions. Buoyancy forces associated with the rotational body forces were included in some cases. All solutions were performed for laminar flow. For the parameter ranges investigated it was found that rotation inhibited the recirculating motion within the enclosure and thereby decreased the heat transfer relative to that for the stationary enclosure. Buoyancy further reduced the heat transfer owing to the break up of residual circulatory motions in the outer portion of the enclosure. Still stronger buoyancy brought about a slight increase in the heat transfer. The coolant flow was confined to a corridor adjacent to the axis of the enclosure, and there was no mixing between the coolant and the fluid in the enclosure proper.Strmung und ' Wrmebertragung in einem geschlossenen zylindrischen Hohlraum, der um seine Achse rotiert, werden in dieser Arbeit untersucht. Das Khlmittel tritt ein und aus durch zentrale ffnungen in den Abschluwnden. Mit dieser Anordnung kann man rotierende Hohlrume in Gasturbinen und Luftverdichtern nachahmen. Die Navier-Stokes- und Energiegleichungen werden durch eine Differenzenmethode gelst, die sich an stationre und nichtstationre Bedingungen anpassen lt. In einigen Fllen wurden auch Auftriebskrfte bercksichtigt, die mit den Fliehkrften verknpft sind. Alle Lsungen gelten fr laminare Strmung. Im untersuchten Bereich unterdrckt die Rotation die Zirkulationsstrmung und verringert den Wrmebergang im Vergleich zum ruhenden System. Auch der Auftrieb reduziert den Wrmebergang durch den Zerfall der Zirkulationsstrmung in den ueren Teilen des Behlters. Erst ein starker Auftrieb erhht leicht den Wrmebergang. Der Khlstrom war in einem Kanal nahe der Zylinderachse eingeschnrt mit nur geringer Vermischung mit dem brigen Behlterinhalt.
Heat and Mass Transfer 11/1971; 4(4):222-235. · 0.90 Impact Factor
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Journal of Heat Transfer (U.S.). 04/1965; Vol: 87.
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ABSTRACT: An analysis has been made to determine the reduction in stagnation point heat transfer when blowing and a magnetic field act An analysis has been made to determine the reduction in stagnation point heat transfer when blowing and a magnetic field act
simultaneously. It is found that in the presence of blowing, the magnetic field may be considerably more effective in reducing simultaneously. It is found that in the presence of blowing, the magnetic field may be considerably more effective in reducing
heat transfer than in the no-blowing case. The results show that the heat transfer reduction due to the simultaneous action heat transfer than in the no-blowing case. The results show that the heat transfer reduction due to the simultaneous action
of blowing and magnetic field is greater than that attained by multiplying together the separate reductions due to blowing of blowing and magnetic field is greater than that attained by multiplying together the separate reductions due to blowing
alone and magnetic field alone. This favourable interaction diminishes as the Prandtl number diminishes and thus may be of alone and magnetic field alone. This favourable interaction diminishes as the Prandtl number diminishes and thus may be of
lesser importance for highly ionized gases for which the Prandtl number is low. The analysis is carried through for both two- lesser importance for highly ionized gases for which the Prandtl number is low. The analysis is carried through for both two-
and three-dimensional stagnation points, and results are reported for Prandtl numbers of 0.01, 0.1, 0.7, 1, and 10. and three-dimensional stagnation points, and results are reported for Prandtl numbers of 0.01, 0.1, 0.7, 1, and 10.
Applied Scientific Research 04/1963; 11(1):125-147.
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ABSTRACT: An analysis is presented for a two-component laminar boundary layer on a surface with zero pressure gradient and with mass release. The system of partial differential equations describing the velocity, temperature, and concentration field is converted by a similarity transformation into a system of integral equations. Numerical solutions are obtained on electronic digital computers for air flow with hydrogen injection, for Mach numbers 0 to 12, for free-stream temperatures 123 to 2000 R, and for wall-to-free-stream temperature ratios from 1/2 to 6. Solutions for the condition of zero temperature gradient in the boundary layer at and normal to the wall surface lead to temperature recovery factors. The results are utilized to investigate the validity and accuracy of engineering correlations. The proposed correlations describe the reduction in heat flux into the wall surface and in skin friction reasonably well. No simple correlations have been found for the dependence of hydrogen mass fraction at the surface on the mass release rate and for the temperature recovery factor. (Author)
01/1961;
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ABSTRACT: Local heat transfer results were deduced from measurements on turbulent flow of air in a porous-walled tube. Hydrodynamically developed, room temperature air was ducted to the entrance cross section of the tube, and heated air was injected through the tube wall. The experiments were performed for inlet Reynolds numbers of the main flow ranging from 4000 to about 65 000 and for injection Reynolds numbers (based on the tube diameter and injection velocity) of approximately 25, 50, 100 and 200. The local Nusselt numbers in the presence of injection were generally lower than those for a solid-walled tube, with the reductions being most marked at low values of the local main flow Reynolds number. It was found that the local Nusselt numbers in the downstream region of the tube could be correlated by local parameters, the local main flow Reynolds number and the injection Reynolds number, without separate dependence on the inlet Reynolds number and the axial position. At small values of the inlet Reynolds number and high rates of injection, a partial laminarization of the flow was evidenced by very low values of Nusselt number in the initial portion of the tube.RésuméDes résultats de transfert thermique local sont déduits de mesures pratiquées sur un écoulement turbulent d'air dans un tube à paroi poreuse. Développé hydrodynamiquement, de l'air à la température ambiante est conduit jusqu'à la section droite d'entrée du tube, et de l'air chauffé est injecté à travers la paroi du tube. Les expériences ont été conduites pour des nombres de Reynolds de l'écoulement principal à l'entrée compris entre 4000 et 65 000 et pour des nombres de Reynolds à l'injection (basés sur le diamètre du tube et la vitesse d'injection) approximativement égaux à 25, 50, 100 et 200. Les nombres de Nusselt locaux en présence d'injection sont généralement inférieurs à ceux relatifs au tube à paroi imperméable, les réductions étant d'autant plus marquées que le nombre de Reynolds local de l'écoulement principal est faible. On a trouvé que les nombres de Nusselt locaux peuvent être reliés aux paramètres locaux, le nombre de Reynolds local pour l'écoulement principal et le nombre de Reynolds à l'injection, sans dépendance distincte vis à vis du nombre de Reynolds à l'entrée et de la position axiale.Pour des faibles valeurs du nombre de Reynolds à l'entrée et des débits d'injection élevés, une laminarisation partielle de l'écoulement est mise en évidence par de très faibles valeurs du nombre de Nusselt dans la première partie du tube.ZusammenfassungIn prösen Rohren und turbulenter Luftströmung wurde der örtliche Wärmeübergang aus Messungen bestimmt. Luft mit Raumtemperatur im hydrodynamisch eingelaufenen Zustand wurde an die Eintrittsöffnung des Rohres herangeführt, während erhitzte Luft durch die Rohrwand eingeblasen wurde. Die Untersuchungen wurden im Reynolds-Zahlbereich von 4000 bis 65 000 der Hauptströmung durchgeführt. Die Reynolds-Zahlen der durch die Rohrwand eingeblasenen Luft (bezogen auf den Rohrdurchmesser und die Einblasgeschwindigkeit) betrugen etwa 25, 50, 100 und 200. Die örtlichen Nusselt-Zahlen bei Einblasung waren im allgemeinen niedriger als die für das dichte Rohr. Die gröβten Verringerungen traten bei kleinen Reynolds-Zahlen des örtlichen Hauptstromes auf. Die örtliche Nusselt-Zahl in Gebieten stromabwärts konnte mit Hilfe lokaler Parameter, sowie der örtlichen Reynolds-Zahl des Hauptstromes und der des eingeblasenen Stroms, ohne getrennte Abhängigkeit von der Reynolds-Zahl am Eintritt und der axialen Position wiedergegeben werden. Bei kleinen Reynolds-Zahlen am Eintritt und hohen Einblasraten wird an Hand der sehr niedrigen Nusselt-Zahlen eine teilweise Laminarisierung der Strömung im vorderen Teil des Rohres bewiesen.РефератПoлyчenы peзyльтaты пo лoкaльnoмy тeплooбмeny na ocnoвe измepenий в тypбyлenтnoм пoтoкe вoздyчa в тpyбe c пopиcтыми cтenкaми. Гидpoдиnaмичecки paзвитый пoтoк вoздyчa кoмnaтnoй тeмпepaтypь. пocтyпaл вo вчoдnoй yчacтoк тpyбы, a naгpeтый вoздyч вдyвaлcя чepeз cтenкy. Экcпepимenты пpoвoдилиcь для зnaчenий чиceл peйnoльдca ocnoвnoгo пoтoкa oт 400 дo 65 000 и для чиceл peйnoльдca лля вдyвa oкoлo 25, 50, 100 и 200, oтnecennыч к диaмeтpy тpyбы и cкopocти вдyвa. Лoкaльnыe чиcлa nycceльтa пpи вдyвe были, в oбщeм, мenьшe чиceл nycceльтa для тpyбы co cплoшnыми cтenкaми, пpичeм этo yмenьшenиe былo naибoлee зaмeтпым пpи мaлыч зnaчenияч лoкaльnoгo чиcлa peйnoльдca ocnoвnoгo пoтoкa. naйдeno, чтo лoкaльnыe чиcлa nycceльтa в oблacти вnиз пo пoтoкy мoжno oбoбщить c пoмoщью лoкaльnыч пapaмeтpoв, a имenno, лoкaльnoгo чиcлa peйnoльдca ocnoвnoгo пoтoкa и чиcлa peonoльдca вдyвa, бeз yчeтa зaвиcимocти oт чиcлa peйnoльдca na вчoдe и пoлoжenия вдoль тpyбы. Пpи мaлыч чиcлaч peйnoльдca na вчoдe и выcoкич cкopocтяч вдyвa oчenь мaлыe зnaчenия чиcлa nycceльтa в naчaльnoм yчacткe тpyбы cвидeтeльcтвyют o чacтичnoй лaмипapизaции пoтoкa.
International Journal of Heat and Mass Transfer 17(3):429-437. · 2.41 Impact Factor
