Experimental investigation of the condensation phenomenon in micro-grooved plates

Abstract

The addition of micro-grooves to a condensing surface has been proposed with the aim of reducing the film thickness so that the condensation heat transfer coefficient is increased. Micro-grooves promote the removal of condensate via the capillary pressure induced by the difference in curvature of the meniscus formed in the groove. Triangular micro-grooves of different apex angles (45° and 60°), and hydraulic diameters (0.14 mm, 0.20 mm, 0.21 mm, 0.32 mm, and 0.33 mm) were machined on a copper plate 140 mm long by 25.4 mm wide. A test apparatus was designed and fabricated. Film condensation at macroscopic scale was observed on the plate. Results from the experimental testing demonstrated the beneficial presence of the grooves in achieving enhancement factors of 2.28 in the overall Nusselt number. This enhancement factor was obtained due to a combination of gravitational body force, steam stream velocity and micro-groove dimensions. Visual observation of the phenomenon demonstrates that micro-grooves have an active length. However, its effect is easily obscured by the macroscopic phenomenon that produces a thick condensate film over a relatively large plate length (roughly 11 times larger than the grooves' active length). Conclusions from the current research indicate that micro-grooves are able to improve the heat transfer process even in a macro scale environment since they add a path to remove condensate. When conditions similar to micro-scale condensation were obtained, the effect of the grooves was isolated and found to be very satisfactory. To evaluate the real effect of micro-grooves in a micro-scale environment, several changes to the experimental apparatus are suggested based on the results obtained in this investigation.