Droplet最新文献

Undesired heat transfer during droplet impact on cold surfaces can lead to ice formation and damage to renewable infrastructure, among others. To address this, superhydrophobic surfaces aim to minimize the droplet surface interaction thereby, holding promise to greatly limit heat transfer. However, the droplet impact on such surfaces spans only a few milliseconds making it difficult to quantify the heat exchange at the droplet–solid interface. Here, we employ high-speed infrared thermography and a three-dimensional transient heat conduction COMSOL model to map the dynamic heat flux distribution during droplet impact on a cold superhydrophobic surface. The comprehensive droplet impact experiments for varying surface temperature, droplet size, and impacting height reveal that the heat transfer effectiveness ($�Q^{\prime }$) scales with the dimensionless maximum spreading radius as $��Q^{\prime }�\sim �{�(�R_{\max }�/�R_i�)�}^{1.6}�$, deviating from previous semi-infinite scaling. Interestingly, despite shorter contact times, droplets impacting from higher heights demonstrate increased heat transfer effectiveness due to expanded contact area. The results suggest that reducing droplet spreading time, as opposed to contact time alone, can be a more effective strategy for minimizing heat transfer. The results presented here highlight the importance of both contact area and contact time on the heat exchange between a droplet and a cold superhydrophobic surface.

Liquid surfaces can be depressed by applying acoustic radiation force. The balance between the acoustic radiation force, surface tension force, and buoyant force sustains the stable dimple depression. Beyond a certain threshold, higher acoustic radiation force leads to instability and bubble formation. The bubble size is determined by the acoustic radiation force and the liquid surface tension. Effective management of bubble generation can be achieved by controlling acoustic radiation waves. A novel method for creating depression on liquid surfaces and generating bubbles is described, which requires neither gas supply nor direct contact with equipment.

Magnetic nanofluid possesses the characteristic of interfering with the propagation of the magnetic field, endowing it with the sensing property in motion. However, the residual adhesion of magnetic nanofluid as it flows over solid surfaces remains an open question. Liquid marbles allow for quantities of liquids to be encapsulated by hydrophobic particles, ensuring a unique nonstick property for utilization in different applications. In this study, being capsuled by hydrophobic nano-/microscale powders, a magnetic nanofluid-based liquid marble (MNLM) with well mechanical stability has been fabricated. A magnetic nanofluid posture detector (MNPD), which consists of an MNLM, a magnetic tube, and coils, has been assembled that can convert mechanical energy to electricity as it freely rolls on the solid surface. Gesture recognition can be achieved when combining five MNPDs with fingers. The fabricated MNPD possesses a good signal recognition capability, which can separately distinguish the bending of each finger. Moreover, a variety of language hand gestures with specific meanings (digits, letters, “OK,” and “I Love You”) can be further recognized through corresponding combinations. The potential of MNPD in the realm of gesture recognition will offer a novel avenue for flexible wearables.

Thin-film deposition of fluids is ubiquitous in a wide range of engineering and biological applications, such as surface coating, polymer processing, and biomedical device fabrication. While the thin viscous film deposition in Newtonian fluids has been extensively investigated, the deposition dynamics in frequently encountered non-Newtonian complex fluids remain elusive, with respect to predictive scaling laws for the film thickness. Here, we investigate the deposition of thin films of shear-thinning viscoelastic fluids by the motion of a long bubble translating in a circular capillary tube. Considering the weakly elastic regime with a shear-thinning viscosity, we provide a quantitative measurement of the film thickness with systematic experiments. We further harness the recently developed hydrodynamic lubrication theory to quantitatively rationalize our experimental observations considering the effective capillary number $��C�a_e�$ and the effective Weissenberg number $��W�i_e�$, which describe the shear-thinning and the viscoelastic effects on the film formation, respectively. The obtained scaling law agrees reasonably well with the experimentally measured film thickness for all test fluids. Our work may potentially advance the fundamental understanding of the thin-film deposition in a confined geometry and provide valuable engineering guidance for processes that incorporate thin-film flows and non-Newtonian fluids.

Frontispiece 2: The cover image is based on the Review Article Magnetically responsive manipulation of droplets and bubbles by Jiang et al.

Based on the merits of remote control, exceptional biocompatibility, and no need for complex circuits, magnetically responsive manipulation of droplets/bubbles has a wide range of application potential in biomedical, microchemistry, analytical detection, and so on. This review provides a comprehensive and systematic overview of the current state of the art of the magnetically responsive manipulation of droplets and bubbles. (DOI: 10.1002/dro2.117)

Front Cover: The cover image is based on the Research Article Extraordinary stability of surfactant-free bubbles suspended in ultrasound by Ji et al.

By using ultrasonic levitation, the suspending bubble exhibits extraordinary stability against liquid drainage, thus achieving significantly prolonged bubble life which resembles that aboard the space station. (DOI: 10.1002/dro2.119)

Back Cover: The cover image is based on the Research Article Droplet Laplace valve-enabled glaucoma implant for intraocular pressure management by Wang et al.

This cover image depicts an innovative moving-parts-free microvalve with customizable and consistent threshold valving pressures for the treatment of refractory glaucoma. Operating on the principle of capillarity-driven flow discretization, it showcases a simple design with a droplet-generation nozzle and collecting reservoir. Such technology holds great promise for glaucoma implants and other microsystems that require a passive yet highly reliable microvalve. (DOI: 10.1002/dro2.109)

Inside Back Cover: The cover image is based on the Review Article Jumping droplets by Boreyko.

This cover image depicts dew droplets spontaneously jumping from a wheat leaf upon coalescence. The corresponding review covers the historical development of capillary-inertial jumping droplets, details the enabling mechanisms of droplet inflation (pre-coalescence) and energy conversion via symmetry breaking (during coalescence), and presents 15 variations on a theme of jumping. (DOI: 10.1002/dro2.105)

Inside Front Cover: The cover image is based on the Review Article Exploring anomalous nanofluidic transport at the interfaces by Zhang et al.

Interactions between interfaces are amplified, and many anomalous nanofluidic phenomena appear as the dimension approaches the nanoscale. This review summarizes three crucial interfaces governing nanofluidic transport, namely liquid-gas, liquid-solid, and liquid-liquid interfaces, and discusses related transport behaviors in detail. This review could inspire the manipulation of nanofluidics and provide promising opportunities for practical applications. (DOI: 10.1002/dro2.110)

Frontispiece 1: The cover image is based on the Research Article Controllable self-transport of bouncing droplets on ultraslippery surfaces with wedgeshaped grooves by Yue et al.

Inspired by Nepenthes, liquid-infused porous surfaces (SLIPS) with wedge-shaped grooves are designed for bouncing droplets self-transport control, the energy changing and self-transporting mechanism are revealed, and a new strategy for droplets manipulation is proposed. (DOI: 10.1002/dro2.118)