Mini-channel flow condensation enhancement through hydrophobicity in the presence of noncondensable gas

Abstract

Steam condensation is important for a broad range of industrial applications, including power generation and nuclear containment systems. The presence of noncondensable gases in these systems significantly reduces heat transfer, prompting the need for condensation heat transfer enhancement. Steam was condensed in the presence of nitrogen in hydrophilic and hydrophobic 1.82-mm rectangular mini-channels for a range of experimental conditions: steam mass flux (i.e., 35–75kg/m2s), steam quality (i.e., 0.3<x<0.9), and nitrogen mass fraction (i.e., 0–30%). In the hydrophilic channel, nitrogen mass fractions of 10–30% reduced condensation heat transfer coefficients by 24–55%. Experimental results were well predicted by the Caruso et al. (2013) correlation. Dropwise condensation was observed in the hydrophobic channel, although the addition of nitrogen suppressed nucleation. In the hydrophobic channel, heat transfer was enhanced by 34–205% over the hydrophilic channel in presence of 10–30% nitrogen, particularly at low vapor mass fractions. Heat transfer coefficients in the hydrophobic channel with 30% nitrogen were identical or higher than those of pure steam in the hydrophilic channel at the same mass flux and quality. Heat transfer coefficients strongly depended on vapor mass fraction, defined as the vapor mass flow rate divided by the three-phase (vapor, liquid and nitrogen) mass flow rate.