Filmwise condensation of steam on sinusoidal pin fin arrays: Effects of fin height and fin pitch

Abstract

An experimental investigation on the use of sinusoidal pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with pin fin arrays were fabricated by Selective Laser Melting (SLM) and tested in a condensation chamber. The pin fin arrays have the same fin base diameter (db) but are of different fin heights (l) and fin pitches (p). At the same fin pitch (p = 1.25 mm and 1.67 mm), the heat flux (q″) and condensation heat transfer coefficient (h) increase as l increases from 1.25 mm to 1.66 mm. However, with further increment in l from 1.66 mm to 2.49 mm, reductions in q″ and h were observed. At the same fin heights of l = 1.25 mm and 1.66 mm, an increase in p from 1.25 mm to 1.67 mm has negligible effects on q″ and h. However, with further increment in p from 1.67 mm to 2.50 mm, significant reductions in q″ and h were observed. Visualization studies of the static condensate retention height (Have) show that two distinct flooding regions can be identified for sinusoidal pin fin surfaces. The static condensate retention height of both regions decreases with increasing p but remains unchanged with varying l. A fin analysis was performed to determine the average heat transfer coefficients (ht) which considers the total heat transfer areas (At) of the enhanced surfaces. Our results show that the highest thermal enhancement factor (η) of 1.86 is achieved with Specimens S4 and S5 whereas Specimens S3 has the highest average heat transfer coefficient (ht). In comparison with cylindrical pin fin surfaces, the sinusoidal pin fin surfaces show better heat transfer performances at the same p/l ratio.