An experimental and theoretical analysis of vapor-to-liquid phase change on microstructured surfaces

In this work, an experimental and a theoretical study was carried out on condensation heat transfer on vertically aligned bare unstructured, micro V-grooved and square-grooved copper substrates. During the experiments, dropwise condensation and drop-film-wise condensation modes were achieved. The surface wettability was recorded by using a high-speed camera, while the overall thermal performance has been evaluated through determining heat flux and heat transfer coefficients. Experimental results show that although the condensation surface area increased by 50% utilizing micro-grooves, the thermal performance is approximately 30% lower than the unstructured surface. Additionally, experimentally measured data has been compared with two correlations for filmwise condensation and one correlation proposed for dropwise condensation as classical benchmarks found in open literature. The comparison for the unstructured surface on which dropwise condensation has been visually monitored reveals that the benchmark for dropwise condensation agrees well for the subcooling ranging between 7.5-10 K and 35-40 K. Beyond this range, the correlation either overestimates or underpredicts the heat flux values. Two other correlations show similar trend but exhibit weak agreement with the experimental data. In case of microstructured surfaces, predictions of correlations for filmwise condensation are found to be the best for square-grooved surface than for V-grooved surface. Furthermore, new correlations have been proposed for all three surfaces based on the experimental data obtained in the present study. The proposed correlations show rather a good agreement for the unstructured surface over the full range of sub-cooling, while for those developed for microstructured surfaces, accordance up to 93-95% has been reached.