Deicing of Sessile Droplets Using Surface Acoustic Waves.

Deicing has significant relevance in various applications such as transportation, energy production, and telecommunication. The use of surface acoustic waves (SAWs) is an attractive option for deicing as it offers several advantages such as localized heating, in situ control, low power, and system integration for highly efficient deicing. Here, we report an understanding of the dynamics of deicing of microlitre volume water droplets (1 to 30 µL) exposed to low power (0.3 W) SAW actuation using an interdigitated electrode on a piezoelectric (LiNbO3) substrate. We study the time variation of the volume of liquid water from the onset of SAW actuation to complete deicing, which takes 2.5 to 35 s depending on the droplet volume. The deicing phenomenon is attributed to acoustothermal heating which is found to be greatly influenced by the loss of ice adhesion with the substrate and the acoustic streaming within the liquid water. Acoustothermal heating inside the droplet is characterized by the temperature distribution inside the droplet using infrared thermography, and acoustic streaming is observed using dye-based optical microscopy. A rapid enhancement in deicing is observed upon the detachment of ice from the substrate and the onset of acoustic streaming, marked by a sudden increase in the liquid water volume, droplet temperature, and heat transfer coefficient. The deicing time is found to increase linearly with droplet volume as observed from experiments and further verified using a theoretical model. Our study provides an improved understanding of the recently introduced SAW-based deicing technique that may open up the avenue for a suitable alternative to standard deicing protocols.

Effects of surface acoustic waves on droplet impact dynamics.

HYPOTHESIS: Surface acoustic waves (SAW) propagating along a solid surface can significantly affect the dynamics of droplet impact. Although droplet impact in presence of SAW has been attempted recently, here, we investigate the effects of surface wettability, droplet size, impact velocity, and SAW power on the impact and spreading dynamics along with post-impact oscillation dynamics of a drop. EXPERIMENTS: Here, we study droplet impact on a surface exposed to traveling SAW produced using an interdigitated electrode patterned on a piezoelectric substrate. The effects of Weber number (We), surface wettability, and SAW power on the impact and spreading dynamics and post-impact oscillation dynamics are studied. FINDINGS: Our study unravels that the interplay between capillary and viscous forces, and inertia forces arising due to pre-impact kinetic energy and SAW-induced bulk acoustic streaming underpins the phenomena. Remarkably, we find that the effect of SAW on droplet impact dynamics is predominant in the case of a hydrophilic (HPL) substrate at a higher SAW power and smaller We and hydrophobic (HPB) substrate irrespective of SAW power. Our study reveals that the maximum droplet spreading diameter increases with SAW power at smaller We for an HPL surface whereas it is independent of SAW power at higher We. Post-impact oscillation of a droplet over an HPL surface is found to be overdamped with a smaller amplitude compared to an HPB substrate, and a faster decay in oscillation amplitude is observed in the case of an HPB surface and higher We. Our study provides an improved understanding of droplet impact on a surface exposed to SAW that may find relevance in various practical applications.

Multifocal Tuberculous osteomyelitis: possible inherited interferon gamma axis defect.

Multifocal Tuberculous (TB) osteomyelitis is an extremely rare entity in immunocompetent individuals. The authors report a 19-mo-old girl with multifocal TB osteomyelitis which resolved completely following institution of four drug antituberculous treatment for 1 y and detailed immunological evaluation was found to be normal but as the response of interferon gamma (IFN γ) in terms of production of IL12p40 was severely impaired, she is suggested to have a possible defect in the interferon gamma axis even though the exact defect in the pathway could not be delineated. This case report reiterates the need for detailed immunological evaluation in children presenting with multifocal TB osteomyelitis.