Minichannel condensation in downward, upward and horizontal configuration

Abstract

An experimental investigation of condensation of R134a inside a single square cross section minichannel when varying the channel orientation is presented. Local heat transfer coefficients are measured in horizontal, vertical downflow and vertical upflow configurations. In the literature the number of local heat transfer coefficient values measured during condensation inside non-circular minichannels is rather limited and the effect of channel orientation during condensation is not much investigated. Some studies have been performed in inclined smooth tubes of larger diameters, where it was shown that the heat transfer coefficient is strongly affected by the liquid and vapour distributions. But minichannels may display a different behaviour because of the relative importance of shear stress, gravity and surface tension. The action of these forces may depend on operating conditions and orientation. In the present study, the channel is obtained from a copper rod and has a square cross section with 1.18 mm side length. Each corner has a curvature radius equal to 0.15 mm, which leads to a hydraulic diameter equal to 1.23 mm. Tests have been performed with R134a at 40°C saturation temperature, at mass velocity ranging between 100 and 790 kg m−2 s−1. From the experimental results, the effect of the channel inclination when varying mass velocity and vapour quality is investigated.