arXiv subjects

Sivanandan Kavuri

Publications and source records attributed to Sivanandan Kavuri.

4 recordsLinked to original sources

arXiv2026

Asymmetric freezing of a sliding droplet on an inclined surface

We investigate the asymmetric freezing of a liquid droplet sliding on an inclined cold surface using numerical simulations based on the lubrication approximation. The combined effects of gravity, capillarity, and solidification kinetics on droplet motion, interfacial deformation, and the resulting frozen morphology are examined through systematic variations in substrate inclination, wettability, effective Bond number, and Stefan number. Our results show that sliding prior to and during the early stages of freezing plays a dominant role in governing the asymmetry of the frozen droplet. A tilted ice cusp forms at the droplet tip due to the competition between gravitational forces and capillary resistance, with its orientation and magnitude strongly dependent on substrate wettability and inclination. Greater inclination and increased wettability enhance asymmetry in droplet morphology. Further, highly wetting substrates favor capillary-driven retraction and induce transient liquid motion opposite to gravity during freezing. The evolution of contact-angle hysteresis at both the solid surface and the liquid-ice interface underscores the importance of early-time dynamics, when the unfrozen liquid remains mobile and gravitational effects are most pronounced. Decomposition of the liquid motion into capillary and gravity-driven contributions provides physical insight into contact-line pinning, receding-edge thinning, and the development of asymmetric liquid-ice contact angles. Increasing the Stefan number accelerates freezing, limits sliding-induced deformation, and reduces both the cusp angle and the post-freezing contact-angle contrast. Overall, this study establishes a physical framework for understanding the morphology of frozen droplets on inclined substrates.

physics.flu-dyn↗

arXiv2025

Evaporation of sessile drops on a heated superhydrophobic substrate

We experimentally investigate the evaporation dynamics of sessile water droplets on a micro-nano textured superhydrophobic aluminum substrate at various temperatures using shadowgraphy imaging. By comparing the evaporation behavior of two droplets placed side-by-side with that of an isolated droplet, we find that droplets in the two-drop system evaporate more slowly due to the vapor shielding effect, which increases vapor concentration between the droplets. This leads to asymmetric evaporation and longer lifetimes, particularly at room temperature compared to higher temperatures. At room temperature, the isolated droplet primarily follows a constant contact angle (CCA) mode, with occasional stick-slip events. The two-drop system predominantly exhibits CCA mode for most of its lifetime, with mixed-mode evaporation and some stick-slip behavior. At elevated temperatures, the isolated droplet maintains a nearly constant contact angle for the first half of its lifetime, transitioning to a mixed evaporation mode with occasional stick-slip events. In contrast, the two-drop system follows a mixed evaporation mode throughout, with occasional stick-slip behavior. Furthermore, a comprehensive theoretical model that accounts for diffusion, evaporative cooling, and convection accurately captures the evaporation dynamics of sessile droplets on a superhydrophobic substrate in both isolated and paired configurations at elevated substrate temperatures. In contrast, a diffusion-based model alone adequately describes the evaporation behaviour at room temperature.

physics.flu-dyn↗

arXiv2024

Evaporation-driven coalescence of two droplets undergoing freezing

We examine the evaporation-induced coalescence of two droplets undergoing freezing by conducting numerical simulations employing the lubrication approximation. When two sessile drops undergo freezing in close vicinity over a substrate, they interact with each other through the gaseous phase and the simultaneous presence of evaporation/condensation. In an unsaturated environment, the evaporation flux over the two volatile sessile drops is asymmetric, with lower evaporation in the region between the two drops. This asymmetry in the evaporation flux generates an asymmetric curvature in each drop, which results in a capillary flow that drives the drops closer to each other, eventually leading to their coalescence. This capillary flow, driven by evaporation, competes with the upward movement of the freezing front, depending on the relative humidity in the surrounding environment. We found that higher relative humidity reduces the evaporative flux, delaying capillary flow and impeding coalescence by restricting contact line motion. For a constant relative humidity, the substrate temperature governs the coalescence phenomenon, and resulting condensation can accelerate this process. Interestingly, lower substrate temperatures are observed to facilitate faster propagation of the freezing front, which, in turn, restricts coalescence.

physics.flu-dyn↗

arXiv2023

Freezing of sessile droplet and frost halo formation

The freezing of a sessile droplet unveils fascinating physics, characterised by the emergence of a frost halo on the underlying substrate, the progression of the liquid-ice interface, and the formation of a cusp-like morphology at the tip of the droplet. We investigate the freezing of a volatile sessile droplet, focusing on the frost halo formation, which has not been theoretically explored. The formation of the frost halo is associated with the inherent evaporation process in the early freezing stages. We observe a negative evaporation flux enveloping the droplet in the initial stages, which indicates that vapour produced during freezing condenses on the substrate close to the contact line, forming a frost halo. The condensate accumulation triggers re-evaporation, resulting in a temporal shift of the frost halo region away from the contact line. Eventually, it disappears due to the diffusive nature of the water vapour far away from the droplet. We found that increasing the relative humidity increases the lifetime of the frost halo due to a substantial reduction in evaporation that prolonged the presence of net condensate on the substrate. Increasing liquid volatility increases the evaporation flux, and condensation occurs closer to the droplet, as a higher amount of vapour is in the periphery of the droplet. We also found that decreasing the thermal conductivity of the substrate increases the total freezing time. The slower freezing process is accompanied by increased vaporized liquid, resulting in condensation with its concentration reaching supersaturation.

physics.flu-dyn↗