Experimental Study of Laminar Film Condensation on Bank of Horizontal Tubes with Stefan Number Greater Than Unity PDF Download
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Author: R. K. Sharma
Publisher:
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Category :
Languages : en
Pages :
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Author: R. K. Sharma
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 724
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Author: John William Rauscher
Publisher:
ISBN:
Category : Steam
Languages : en
Pages : 296
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Author:
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Category : Dissertations, Academic
Languages : en
Pages : 790
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 124
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Analytical studies have been made of laminar film condensation on a horizontal elliptical cylinder in a pure saturated vapor under conditions of free and forced convection. Estimation of interfacial shear stress was made in two ways: the first involving an asymptotic value of the shear stress under conditions of infinite condensation rate and the second based on simultaneously solving the two-phase vapor boundary layer and condensate equations. The latter approach enables the determination of the vapor boundary layer separation point. For the assumption of asymptotic shear stress, effects of surface tension and pressure gradient in the condensate film have been included. At the extremes of eccentricity, corresponding to a circular tube and a vertical plate, the results are compared with theoretical and experimental work of others. Improvement in the condensation heat transfer coefficient was found for elliptical tubes under both free and forced convection conditions when compared to circular tubes of the same surface area. In the latter case, this improvement was due mainly to the reduced drag of the elliptical tube providing a higher vapor velocity for the same pressure drop as that across a circular tube ... Laminar film condensation, Horizontal elliptical tube, Free and forced convection.
Author: Tetsu Fujii
Publisher: Springer Science & Business Media
ISBN: 1461231523
Category : Science
Languages : en
Pages : 225
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Since the petroleum crisis in the 1970s, a lot of effort to save energy was made in industry, and remarkable achievements have been made. In the research and development concerning thermal energy, however, it was clar ified that one of the most important problems was manufacturing con densing systems with smaller size and higher performance. To solve this problem we need a method which synthesizes selections_ of the type of con denser, cooling tube and its arrangement, assessment of fouling on the cooling surfaces, consideration of transient characteristics of a condenser, etc. The majority of effort, however, has been to devise a surface element which enhances the heat transfer coefficient in condensation of a single or multicomponent vapor. Condensation phenomena are complexly affected by a lot of physical property values, and accordingly the results of theo retical research are expressed with several dimensionless parameters. On the other hand, the experimental research is limited to those with some specified cooling surfaces and some specified working fluids. Hence, the basic research of condensation is necessary for criticizing the enhancement effect as well as for an academic interest.
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Languages : en
Pages :
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The problem of condensation of steam on a vertical tier of horizontal tubes is investigated by both analytical and experimental methods in this study. A computer program is written to perform the analysis of laminar film condensation on the horizontal tubes. The program is capable to calculate condensate film thickness and velocity distribution, as well as the heat transfer coefficient within the condensate. An experimental setup was also manufactured to observe the condensation phenomenon. Effects of tube diameter and temperature difference between steam and the tube wall on condensation heat transfer have been analytically investigated with the computer program. Experiments were carried out at different inclinations of the tier of horizontal tubes. Effects of the steam velocity and the distance between the horizontal tubes are also experimentally investigated. Results of the experiments are compared to those of the studies of Abdullah et al., Kumar et al. and Nusselt as well as to the analytical results of the present study.
Author: Vance Hiro Adams
Publisher:
ISBN:
Category :
Languages : en
Pages : 111
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Author: Esam Saleh
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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A complete two-phase numerical model of film condensation from a mixture of a vapour and a non-condensing gas that is based on the two-dimensional elliptic governing equations with variable physical properties is presented. The model predicts the full viscous flow and heat and mass transfer for the mixture around the tube and in the entire liquid film from the top of the tube to the falling film below the tube. A finite volume method is used with a segregated solution approach and a dynamically moving computational grid that tracks the phase interface sharply. Fundamental balances of mass, energy, and force are enforced accurately at the phase interface. The model was developed in steps and validated against various experimental and theoretical works in the literature for different two-phase flows. The validation tests included stratified flow of liquid and gas in a horizontal channel, falling liquid film over a vertical wall, and condensation of steam from a steam-air mixture in a vertical channel. The model was used to simulate laminar film condensation from a downward flowing steam-air mixture over an isothermal horizontal tube. The validity of this new model is demonstrated by comparisons with previous theoretical and experimental studies. New results are presented on the effects of free-stream-to-tube temperature difference, upstream Reynolds number, free-stream gas mass fraction, and free-stream pressure on the condensate film development, the local and average heat transfer coefficients, and the total condensate mass flow rate. It was found that the temperature difference had the greatest effect on the condensation rate and film thickness. The presence of non-condensing gas in the vapour has a strong negative impact on the condensation process. For the pure steam case, moderate changes in the upstream Reynolds number showed slight increases in condensate mass flow rate with increased Reynolds number. For the mixture case, however, moderate increase in upstream Reynolds number increases significantly the condensate mass flow rate and film thickness. This trend becomes more noticeable as the free-steam gas mass fraction increases. Changing the free-stream pressure demonstrated that property variation had a relatively smaller effect than temperature difference and gas mass fraction changes.
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Category :
Languages : en
Pages : 0
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Heat transfer and hydrodynamic performance of eight different geometrically enhanced tubes of different metals was determined. Results were compared to a 25.4 mm (1.0 in.) OD, smooth stainless steel tube. Steam at about 21 kPa (3 psia) was condensed on the outside surface of each enhanced tube, horizontally mounted in the center of a dummy tube Bank. Each tube was cooled on the inside by water. The overall heat transfer coefficient was determined directly from experimental data. The inside and outside heat transfer coefficients were determined using the Wilson plot technique. The cooling water pressure drop was measured inside the tube and converted to the friction factor in the enhanced section. The overall heat transfer coefficients of the enhanced tubes were increased as much as 1.9 times, and the corrected pressure drops of the enhanced tubes were as large as 4 times the corresponding smooth tube value for the same cooling water velocity. The helix angle should be 45 deg to 60 deg on the inside surface and 90 deg on the outside surface of the tube to obtain maximum inside and outside heat transfer coefficients. (Author).
