Experimental Study of Slug Flow for Condensation in a Square Cross-Section Micro-Channel at Low Mass Velocities

Abstract

In this paper, condensation flows in a cross-flow air-cooled micro-condenser were investigated for mass velocities (representing the mass flow rates over the micro-condenser cross-section area) lower than 12 kg.m (−2).s(−1), with n-pentane used as the working fluid. This micro-condenser consisted of a transparent square cross-section micro-channel placed horizontally, having inner and outer edges of 553 and 675 μm, respectively, and a real length exposed to the coolant of 196 mm. One of the specificities of the experimental bench was the choice of the air as a coolant so that the external heat transfer is limiting. Three main flow zones were identified: annular zone, intermittent (i.e. elongated bubbles or slug) zone and spherical bubbles zone. A specific experimental procedure based on bubbles tracking was developed in order to determine the hydraulic and thermal parameters in the intermittent zone. The mean displacement and condensation velocities of the elongated bubbles were determined according to their mean length for different mass velocities of the n-pentane. Besides, the mean latent heat flux density released by the condensation of the elongated bubbles was determined according to their mean surface for different mass velocities of the n-pentane, and compared to the imposed heat flux density.