Evaporation-induced flow around a droplet in different gases
TL;DR: In this article, the influence of the ambient gas on the evaporation induced flow around a droplet at atmospheric conditions was investigated, and it was shown that the evapse-induced flow in these gases for different liquids was measured using particle image velocimetry.
Abstract: 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.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.
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TL;DR: In this paper, a nanocapillary membrane containing both nanopores and nanochannels based on an assembly of holey graphene oxide (HGO) nanosheets was constructed to enable water molecules to permeate and simultaneously evaporate from the nanostructure.
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TL;DR: In this article , a nanocapillary membrane containing both nanopores and nanochannels based on an assembly of holey graphene oxide (HGO) nanosheets was proposed to enable water molecules to permeate and simultaneously evaporate from the nanostructure.
19 citations
TL;DR: In this article , a highly flexible and efficient evaporation-induced electricity generator (EIEG) that dexterously exploits the directional water capillary flow inside the silicon nanowires (SiNWs) mesh nanopores is developed.
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TL;DR: Advective effects are found to boost the global evaporation rate by a factor of 4 as compared to the diffusion-limited theory and a new boundary-layer theory accounting for a buoyancy-induced convection in the gas and the influence upon it of a thermal Marangoni flow.
Abstract: The local evaporation rate and interfacial temperature are two quintessential characteristics for the study of evaporating droplets. Here, it is shown how one can extract these quantities by measuring the vapor concentration field around the droplet with digital holographic interferometry. As a concrete example, an evaporating freely receding pending droplet of 3M Novec HFE-7000 is analyzed at ambient conditions. The measured vapor cloud is shown to deviate significantly from a pure-diffusion regime calculation, but it compares favorably to a new boundary-layer theory accounting for a buoyancy-induced convection in the gas and the influence upon it of a thermal Marangoni flow. By integration of the measured local evaporation rate over the interface, the global evaporation rate is obtained and validated by a side-view measurement of the droplet shape. Advective effects are found to boost the global evaporation rate by a factor of 4 as compared to the diffusion-limited theory.
90 citations
TL;DR: In this article, a complete set of easily programmable computer algorithms, and a set of numerical tables, for the thermal conductivities of the nine gases: N2, O2, NO, CO, CO2, N2O, CH4, CF4, and SF6.
Abstract: We present a complete set of easily programmable computer algorithms, and a set of numerical tables, for the thermal conductivities of the nine gases: N2, O2, NO, CO, CO2, N2O, CH4, CF4, and SF6. This complements our earlier corresponding‐states work on the equilibrium and transport properties of these gases [J. Phys. Chem. Ref. Data 16, 445 (1987); 17, 255 (1988)]. The results embrace the temperature range from T*=kT/e=1 up to a nominal upper limit of 3000 K. The accuracy achieved is specified, and the correlation can be used in a predictive mode.
88 citations
TL;DR: In this article, a combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets, where the experiments were performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons.
Abstract: A combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets. The experiments are performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons. The temperature of the disk sustaining the drop is rapidly increased or decreased in order to study transient heating or cooling processes. The velocity field in the droplet is evaluated monitoring the motion of tracers in the meridian plane, using a laser sheet illumination system and a video camera. Surface temperature distributions of the drops are detected by infrared thermocamera. The numerical model is based on axisymmetric Navier–Stokes equations, taking into account the presence of Marangoni shear stresses and evaporative cooling at the liquid-air interface. Marangoni flows cause a larger, more uniform surface temperature, increasing heat transfer from disk to droplet, as well as evaporation rate. When Marangoni effects are negligible, larger surface temperature differences occur along the drop surface and heat transfer is relatively small. The role of Marangoni and buoyancy flows in silicone oils with different viscosities and hydrocarbons is discussed and correlations are presented between experimental and numerical results.
82 citations
TL;DR: In this paper, a convection-diffusion model was developed to analyze the effect of buoyant convection in the surrounding air on heat and mass transfer phenomena during the evaporation of a pinned water drop deposited on a horizontal substrate of large dimensions.
Abstract: A convection-diffusion model is developed to analyze the effect of buoyant convection in the surrounding air on the heat and mass transfer phenomena during the evaporation of a pinned water drop deposited on a horizontal substrate of large dimensions. The substrate is maintained at constant temperature which can be equal or higher than the temperature of the ambient air. The mathematical model accounts for the motion of the gas phase surrounding the drop due to thermal and solutal buoyancy effects, while only thermal diffusion is considered in the liquid phase. A quasisteady state regime is adopted because of the slow motion of the liquid-gas interface as well as the induced heat and mass transfer phenomena in both phases. The numerical results obtained with the diffusion model or the convection-diffusion model show that heat and mass transfer rates are important toward the contact line. The heat required for evaporation process is taken from the environment, both the liquid and the gas phase, and results in a small cold zone on both sides of the interface. The influence of the buoyancy in air is of greater importance in the lower part of the interface and beyond a distance of a contact radius above the droplet. A weak variation of the evaporation rate is observed on a wider range of contact angle for high wall temperatures. The diffusion model underestimates the overall evaporation rate by 8.5% for a wall temperature equal to an ambient temperature of 25 ° C and by 27.3% for a wall temperature of 70 ° C . Numerical calculations show that the length of the heated wall has very little effect on the evaporation process when it exceeds 25 times the contact radius.
81 citations