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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Effects of non-condensable gases on mini-channel flow condensation




Abstract

The presence of air reduces condensation heat transfer coefficients in the dephlegmator of an air-cooled condenser. Air and other non-condensable gases (NCG) gather at the liquid-vapor interface in condensing flows, thereby impeding condensation. Simultaneous flow visualization and heat transfer experiments were conducted in open-loop steam apparatus with hydrophilic (contact angle of 70°) and hydrophobic (contact angle of 110°) mini-gaps of 1.82 mm hydraulic diameter at steam mass flux from 35 to 75 kg/m2s, steam quality from 0.2 to 0.8. Nitrogen is introduced as non-condensable gas with mass fraction from 0 to 25% of steam. In both hydrophilic and hydrophobic gaps, at each fixed steam mass flux (35, 50 and 75 kg/m2) and quality (0.4 0.5 and 0.6) heat transfer coefficient, flow pattern are compared for different NCG mass fractions. Pressure drops and heat transfer coefficients in hydrophilic gap with 0% NCG are compared to the Kim and Mudawar (2013) correlation. Heat transfer coefficients in hydrophilic gap with different NCG contents are compared with the Caruso (2013) and the Wen (2016) correlations. In hydrophobic gap, droplet departure diameter are analyzed for different steam mass flux, quality and NCG mass fraction.

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