اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدStability of Respiratory-Like Droplets under Evaporation
97
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Pathogens contained in airborne respiratory droplets have been seen to remain infectious for periods of time that depend on the ambient temperature and humidity. In particular, regarding the humidity, the empirically least favorable conditions for the survival of viral pathogens are found at intermediate humidities. However, the precise physico-chemical mechanisms that generate such least-favorable conditions are not understood yet. In this work, we analyze the evaporation dynamics of respiratory-like droplets in air, semi-levitating them on superhydrophobic substrates with minimal solid-liquid contact area. Our results reveal that, compared to pure water droplets, the salt dissolved in the droplets can significantly change the evaporation behaviour, especially for high humidities close to and above the deliquesence limit. Due to the hygroscopic properties of salt, water evaporation is inhibited once the salt concentration reaches a critical value that depends on the relative humidity. The salt concentration in a stable droplet reaches its maximum at around 75% relative humidity, generating conditions that might shorten the time in which pathogens remain infectious.
قيم البحث
اقرأ أيضاً
The present article experimentally and theoretically probes the evaporation kinetics of sessile saline droplets. Observations reveal that presence of solvated ions leads to modulated evaporation kinetics, which is further a function of surface wettab
ility. On hydrophilic surfaces, increasing salt concentration leads to enhanced evaporation rates, whereas on superhydrophobic surfaces, it first enhances and reduces with concentration. Also, the nature and extents of the evaporation regimes constant contact angle or constant contact radius are dependent on the salt concentration. The reduced evaporation on superhydrophobic surfaces has been explained based on observed via microscopy crystal nucleation behaviour within the droplet. Purely diffusion driven evaporation models are noted to be unable to predict the modulated evaporation rates. Further, the changes in the surface tension and static contact angles due to solvated salts also cannot explain the improved evaporation behaviour. Internal advection is observed using PIV to be generated within the droplet and is dependent on the salt concentration. The advection dynamics has been used to explain and quantify the improved evaporation behaviour by appealing to the concept of interfacial shear modified Stefan flows around the evaporating droplet. The analysis leads to accurate predictions of the evaporation rates. Further, another scaling analysis has been proposed to show that the thermal and solutal Marangoni advection within the system leads to the advection behaviour. The analysis also shows that the dominant mode is the solutal advection and the theory predicts the internal circulation velocities with good accuracy. The findings may be of importance to microfluidic thermal and species transport systems.
The present article discusses the physics and mechanics of evaporation of pendent, aqueous ferrofluid droplets and modulation of the same by external magnetic field. We show experimentally and by mathematical analysis that the presence of magnetic fi
eld improves the evaporation rates of ferrofluid droplets. First we tackle the question of improved evaporation of the colloidal droplets compared to water, and propose physical mechanisms to explain the same. Experiments show that the changes in evaporation rates aided by the magnetic field cannot be explained on the basis of changes in surface tension, or based on classical diffusion driven evaporation models. Probing using particle image velocimetry shows that the internal advection kinetics of such droplets plays a direct role towards the augmented evaporation rates by modulating the associated Stefan flow. Infrared thermography reveal changes in the thermal gradients within the droplet and evaluating the dynamic surface tension reveals presence of solutal gradients within the droplet, both brought about by the external field. Based on the premise, a scaling analysis of the internal magnetothermal and magnetosolutal ferroadvection behavior is presented. The model incorporates the role of the governing Hartmann number, the magnetothermal Prandtl number and the magnetosolutal Schmidt number. The analysis and stability maps reveal that the magneto-solutal ferroadvection is the more dominant mechanism, and the model is able to predict the internal advection velocities with accuracy. Further, another scaling model to predict the modified Stefan flow is proposed, and is found to accurately predict the improved evaporation rates.
For a pendant drop whose contact line is a circle of radius $r_0$, we derive the relation $mgsinalpha={piover2}gamma r_0,(costheta^{rm min}-costheta^{rm max})$ at first order in the Bond number, where $theta^{rm min}$ and $theta^{rm max}$ are the con
tact angles at the back (uphill) and at the front (downhill), $m$ is the mass of the drop and $gamma$ the surface tension of the liquid. The Bond (or Eotvos) number is taken as $Bo=mg/(2r_0gamma)$. The tilt angle $alpha$ may increase from $alpha=0$ (sessile drop) to $alpha=pi/2$ (drop pinned on vertical wall) to $alpha=pi$ (drop pendant from ceiling). The focus will be on pendant drops with $alpha=pi/2$ and $alpha=3pi/4$. The drop profile is computed exactly, in the same approximation. Results are compared with surface evolver simulations, showing good agreement up to about $Bo=1.2$, corresponding for example to hemispherical water droplets of volume up to about $50,mu$L. An explicit formula for each contact angle $theta^{rm min}$ and $theta^{rm max}$ is also given and compared with the almost exact surface evolver values.
The article experimentally reveals and theoretically establishes the influence of electric fields on the evaporation kinetics of pendant droplets. It is shown that the evaporation kinetics of saline pendant droplets can be augmented by the applicatio
n of an external alternating electric field. The evaporation behaviour is modulated by an increase in the field strength and frequency. The classical diffusion driven evaporation model is found insufficient in predicting the improved evaporation rates. The change in surface tension due to field constraint is insufficient for explaining the observed physics. Consequently, the internal hydrodynamics of the droplet is probed employing particle image velocimetry. It is revealed that the electric field induces enhanced internal advection, which improves the evaporation rates. A scaled analytical model is proposed to understand the role of internal electrohydrodynamics, electrothermal and the electrosolutal effects. Stability maps reveal that the advection is caused nearly equally by the electrosolutal and electrothermal effects within the droplet. The model is able to illustrate the influence played by the governing thermal and solutal Marangoni number, the electro Prandtl and electro Schmidt number, and the associated Electrohydrodynamic number. The magnitude of the internal circulation can be well predicted by the proposed model, which validates the proposed mechanism.
A liquid droplet hovering on a hot surface is commonly referred to as a Leidenfrost droplet. In this study, we discover that a Leidenfrost droplet involuntarily performs a series of distinct oscillations as it shrinks during the span of its life. The
oscillation first starts out erratically, followed by a stage with stable frequencies, and finally turns into periodic bouncing with signatures of a parametric oscillation and occasional resonances. The last bouncing stage exhibits nearly perfect collisions. We showed experimentally and theoretically the enabling effects of each oscillation mode and how the droplet switches between such modes. We finally show that these self-regulating oscillation modes and the conditions for transitioning between modes are universal for all tested combinations of liquids and surfaces.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
