In-situ visualization of spatiotemporal non-uniform frosting dynamics on refrigerator evaporators under intermittent thermal-moisture shocks

Intermittent door opening introduces significant thermal and moisture shocks to household refrigerators, severely exacerbating evaporator frosting. However, the dynamic evolution of localized non-uniform frosting under these complex operating conditions remains insufficiently characterized. This study develops a non-invasive in-situ visualization system equipped with anti-condensation technology to quantitatively investigate the spatiotemporal non-uniform frosting characteristics on a fin-and-tube evaporator under periodic door openings. Experimental results reveal that periodic moisture load surges significantly enhance frost accumulation, resulting in a distinct S-shaped frost thickness distribution along the airflow direction. While transverse uniformity within fin rows remains relatively stable, the global longitudinal frost uniformity coefficient (FUC) heavily degrades to 70%–77% under prolonged door opening and high humidity conditions. Furthermore, despite exhibiting thinner individual frost layers, the downstream region with the smallest fin spacing experiences the most severe localized flow-passage constriction, reaching a blockage ratio of 43%–50%. This localized blockage is accompanied by a marked deterioration in system performance, with the air-side pressure drop increasing from less than 7 Pa under the closed-door condition to over 16 Pa under the most severe frosting condition, while the average system power increases by nearly 30%, from 106.32 W to 137.47 W. These findings establish a direct link between spatial frost distribution, geometry-dependent blockage, and refrigerator performance, providing an experimental basis for identifying critical frosting regions and developing zonal and on-demand defrosting strategies.