An experimental study on the dynamic frosting characteristics on the edge zone of a horizontal copper plate under forced convection

Abstract

<p>To retard the negative effects of frosting, it is necessary to better understand the frosting mechanism on cold surfaces. In this study, a systematical study on the dynamic frosting characteristics on the edge zone of a horizontal copper plate under forced convection was conducted. The results showed that the air velocity effect and edge effect on droplet condensation, frozen and frost layer growth characteristics were significant. The duration of droplet condensation stage decreased from 365 to 113 s with a decrease of 69.0% when air velocity increased from 0.5 to 2.5 m/s. Besides, the average freezing wave propagation velocity for Region I (an area where a row of water droplets closest to plate edge) was significantly larger than that for Region II (the remained area). As a result, the duration of droplet frozen stage for Region I was much shorter than that for Region II. Accordingly, frost layer amount for Region I was notably larger than that for Region II. Besides, the frost surface roughness for Region I increased as air velocity increased at the early frosting stage, but decreased as air velocity increased at the later frosting stage. The general turning point for frost surface roughness at 1.5 m/s surpassed the value at 0.5 m/s was around 21.4 × 10−6 m at 390 s, and that between 2.5 m/s and 1.5 m/s was around 30.3 × 10−6 m at 450 s. This study can help to establish a better relationship among different frosting stages, and better understand the plate edge effect on frosting.</p>