Investigation of the phenomena occurring near the liquid–vapor interface during evaporation of water at low pressures

Three-Dimensional Reconstruction of Evaporation-Induced Instabilities Using Volumetric Scanning Particle Image Velocimetry

“…Note that only half of this vortex is captured in our PIV experiments due to the limitation in the depth of focus of the lenses. It was shown by numerical simulation that the induced vortex observed here is related to the gravitational forces rather than being driven by the surface tension gradient effects [22].…”

“…The symmetry in the flow is tremendously desirable for researchers in this field as it simplifies the temperature measurements and consequently the investigation of the different modes of energy transport to the interface of an evaporating liquid, something similar to what has been carried out in References [24,25]. It is worth noting that the evaporation driven flow studied here was slow enough and occurred at a pseudo-steady state condition [22] so that it enabled the application of scanning PIV.…”

“…Therefore, we conclude that the measured velocity field does not change with concentration within the range of particle concentration that is commonly used in PIV experiments. It has been shown earlier that this concentration of the suspension does not have a noticeable effect on the total evaporation flux at the interface [22]. For the 2 µm diameter polystyrene spheres immersed in water with a solid density of 1050 kg/m 3 , the relaxation time (t 0 = ρ p d p 2 /18µ ≈ 10 −7 s, where ρ p is the density of the particles, d p is the diameter of the particles and µ is the viscosity of water) is 8 orders of magnitude smaller than the characteristic time of the flow (t = l 0 /u 0 ≈ 20 s, where l 0 is half of the channel's width and u 0 is the maximum velocity measured in the liquid) and therefore, it can be assumed that the particles follow the fluid streamlines.…”

“…Studying evaporation driven flows in liquids is important for understanding the complex phenomena involved in evaporation [22] as the bulk motion of the fluids dictates the temperature distribution in the fluids at the interface and therefore determines the rate of mass transfer across the interface [23]. In certain experimental studies on the evaporation of water at low pressures [24][25][26], it was reported that if the convective transport of energy is overlooked in the energy balance at the interface, the conservation of energy is not satisfied.…”

“…This is becoming even more important in this specific field where researchers attribute the interfacial flow of the liquid to thermocapillary effects (see Reference [35] for instance) while the interfacial liquid flow may be affected by the geometrical arrangement of the boundaries and capillary forces (the flow toward the interface to compensate the evaporation loss and maintain the shape of the interface) in addition to the surface tension gradient. Readers may refer to the studies by Kazemi et al [22,23] for further details. Therefore, understanding the whole velocity field is necessary to investigate the main source of these instabilities.…”