It is known from recent studies that evaporation induces flow around a droplet at atmospheric conditions. This flow is visible even for slowly evaporating liquids like water. In the present study, we investigate the influence of the ambient gas on the evaporating droplet. We observe from the experiments that the rate of evaporation at atmospheric temperature and pressure decreases in a heavier ambient gas. The evaporation-induced flow in these gases for different liquids is measured using particle image velocimetry and found to be very different from each other. However, the width of the disturbed zone around the droplet is seen to be independent of the evaporating liquid and the size of the needle (for the range of needle diameters studied), and only depends on the ambient gas used. © 2019 Author(s).

T. N. C. Anand

Department of Mechanical Engineering

Shamit Bakshi

Drops

Evaporation

Gases

Liquids

Needles

Velocity measurement

Ambient gas

Atmospheric conditions

Induced flows

Particle image velocimetries

Temperature and pressures

Atmospheric movements

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Evaporation-induced flow around a droplet in different gases

Physics of Fluids

The behavior of droplets of urea-water-solution (UWS) evaporating under the influence of a hot stream of air was investigated experimentally, under temperatures ranging from 100°C to 400°C. The droplets were suspended on a glass microfiber to minimize the influence of heat conduction, through the fiber, on the evaporation rate of the droplet. The flow rate of air, under all experimental conditions, was measured and these data were used to estimate the average velocity of air around the droplet. Experiments were also conducted on droplets of pure water and the results were compared. The initial mass fraction of urea, in the solution, did not appear to have a significant effect on the evaporation constant, but it did affect a few essential aspects of the evaporation behavior. The evaporation of water droplets was in accordance with the d2 law at all temperatures, whereas the evaporation of UWS droplets was ambient-temperature dependent. © 2019 American Institute of Chemical Engineers

AIChE Journal

Experimental investigation of the evaporation behavior of urea-water-solution droplets exposed to a hot air stream

The influence of the suspender on the evaporation of droplets under quiescent atmospheric conditions was studied experimentally using pendant droplets of ethanol (volatile) and water (non-volatile). Conducting and non-conducting suspenders of different materials and configurations (a steel needle, glass needle, steel rod, and glass rod) were evaluated. For both liquids, it is observed that the rate of evaporation is higher with steel suspenders. More importantly, for ethanol droplets, there is a difference in the evaporation rates between the needle and rod configurations of the same material. Thus, it is shown for the ethanol droplet that the configuration (needle versus solid rod) also plays a role in the evaporation process, apart from the material. The water droplet does not show this dependence. Visualization of internal flow and heat transfer calculations explain this observation. The results will be useful in choosing an appropriate suspender while using the pendant droplet method for studying complex interactions in an evaporating droplet. © 2019 Elsevier Masson SAS

International Journal of Thermal Sciences

Influence of the suspender in evaporating pendant droplets

Studies on the evaporation of suspended microlitre droplets under atmospheric conditions have observed faster evaporation rates than the theoretical diffusion-driven rate, especially for rapidly evaporating droplets such as ethanol. Convective flow inside rapidly evaporating droplets has also been reported in the literature. The surrounding gas around the evaporating droplet has, however, been considered to be quiescent in many studies, the validity of which can be questioned. In the present work, we try to answer this question by direct experimental observation of the flow. The possible causes of such a flow are also explored. © 2015 AIP Publishing LLC.

Fulltext

Evaporation-induced flow around a pendant droplet and its influence on evaporation

Evaporation of a single droplet of a pure liquid in a confined chamber under atmospheric ambient condition is expected to be purely controlled by the rate of diffusion of the vapor into the surrounding. But, it is seen from the experimental results presented in this paper that for several liquids the process is faster than a theoretical estimate of the diffusion-driven process. It is seen from the visualization inside the droplet that these liquids exhibit intense internal circulation during evaporation. From a scaling analysis the temperature variations within the droplet due to surface traction and buoyancy-driven convection during evaporation is estimated. Marangoni and Rayleigh numbers are also obtained from these estimates. The values of these numbers indicate that Marangoni convection aided by buoyancy is probably the reason for the internal circulation induced within the droplet. The average velocity of the internal circulation is measured and is found to compare well with the velocity scale for Marangoni convection. © 2012 Elsevier Ltd.

International Journal of Multiphase Flow

Internal circulation in a single droplet evaporating in a closed chamber

Building and Environment

Experimental investigation of near-field stream-wise flow development and spatial structure in triple buoyant plumes

International Journal of Heat and Mass Transfer

Correlation for sessile drop evaporation over a wide range of drop volatilities, ambient gases and pressures

Journal	Data powered by TypesetPhysics of Fluids
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	10706631
Open Access	No