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Corresponding Author

Mosaad, Mohamed

Subject Area

Mechanical Power Engineering

Article Type

Original Study

Abstract

The heat transfer in laminar film condensation of pure saturated stagnant vapour outside an inclined tube is analyzed by applying the principles of the laminar-boundary-layer theory. The analysis results in a partial differential equation for the local film thickness, which in the vertical case, yields the result found by Nusselt. However, for the horizontal case, this equation reduces to an ordinary differential equation which verifies that the film thickness at the top point of a horizontal tube is not zero as assumed by Nusselt, and certain value has been determined. This value is of order of the critical thickness of the stable film; defined by another author studied the characteristic of transient, and steady condensate film. Consequently, a modified Nusselt formula has been determined for calculating the average heat transfer coefficient, in which the constant coefficient is 0.65 instead of O. 728 in the Nusselt solution. This modification may be in the right direction in view of some authors proposed such a modification for better agreement with measured data. Then, the main partial differential equation has numerically been solved for the inclined tube, and results obtained for inclination angles with the horizontal; from 0 to 90. The exact solution of the vertical, and that of the horizontal tube are used to test the numerical solution. The results indicate that small inclination angle with the horizontalis is) results in an increase in the heat transfer coefficient over the horizontal value. While for a vertical tube, small inclinations from the vertical position, (SS) results in a significant increase in the heat transfer coefficient above the vertical value. Comparison of present results with available correlations has been made.

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