Heat Transfer Effects of Sintered Particle Monolayers on Steam Flow Condensation in Mini-Channels With Flow Visualization

In this study, the enhancement of filmwise condensation heat transfer is explored for forced flow steam condensation in mini-channels, where the condensing surface has been modified with the addition of monolayer of sintered spherical particles. Filmwise condensation enhancement is the emphasis of this study as this is the most prevalent condensation mode in heat exchangers. Two copper test coupons were constructed with a monolayer of 100 μm or 200 μm diameter copper particles and compared against a plain coupon with no monolayer. All coupons have a hydraulic diameter of 1.9 mm and heat transfer coefficients were measured for steam mass fluxes of 50 kg/m2s and 125 kg/m2s. For a mass flux of 50 kg/m2s, both monolayer coupons displayed roughly parabolic trends in for heat transfer coefficient enhancement with the greatest enhancements, up to 52.8%, occurring at low (x ∼ 0.2) quality, up to 22.1%, occurring at a high (x ∼ 0.9) quality, but a decrease in heat transfer coefficient mid-range qualities (0.4 < x < 0.8) high as 11.4%. For the steam mass flux of 125 kg/m2s, there was far less quality dependence and the heat transfer coefficients were enhanced for all qualities with the enhancement ranging from 9.9% to 16.2%. Visualization confirmed that the monolayers could disrupt the fluid flow. However, flooding occurred for lower qualities where the film was thickest and for a mass flux of 50 kg/m2s where shear forces at the vapor-liquid interface were weakest.