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ISSN Online: 2377-424X

ISBN Print: 0-89116-299-2

International Heat Transfer Conference 7
September, 6-10, 1982, Munich, Germany

MINIMUM FLOW-RATES AND REWETTING-RATES OF FALLING FILMS

Get access (open in a dialog) DOI: 10.1615/IHTC7.420
pages 83-88

摘要

In order to precalculate the minimum flow-rates of isothermally falling films Hartley/Murgatroyd and Hobler in 1964 proposed two models known as the force criterion and the energy criterion. The results indicate an extremely strong influence of the contact angle. Own measurements especially directed to the water contact angle on industrial surfaces and a thermodynamic analysis of the wetting behaviour of heterogeneous surfaces reveal that the contact angle hysteresis on these surfaces can be very large.
This means that to predict minimum flow-rates and rewetting-rates for falling films it has to be distinguished between the advancing and the receding contact angle. The receding contact angle has to be considered if a minimum flow-rate to prevent film rupture is to be calculated. The flow-rate however that rewets a dry surface is determined by the advancing contact angle.