On the Effect of Marangoni Flow on Evaporation Rates of Heated Water Drops

Abstract

In this letter we show that the Marangoni flow contribution to the evaporation rate of small heated water droplets resting on hot substrates is negligible. We compare data of evaporating droplet experiments with numerical results and assess the effect of Marangoni flow and its contribution to the evaporation process. We demonstrate that heat conduction inside these water droplets is sufficient to give an accurate estimate of evaporation rates. Although convection in evaporating water droplets remains an open problem, our aim in this study is to demonstrate that these effects can be neglected in the investigation of evaporation rate evaluation. It is worth noting that the presented results apply to volatile heated drops which might differ from spontaneously evaporating cases.

Instantaneous distribution of fluxes in the course of evaporation of sessile liquid droplets: Computer simulations

“…The measurements of evaporation rate of droplets on different solid surfaces can be used for production of materials providing optimal regime of work in air conditioners, dryers and cooling systems [3]. On the other hand the investigation of evaporating droplets can reveal the influence of Derjaguin pressure in a vicinity of the apparent three-phase contact line [4] as well as the effect of latent heat of vaporization and Marangoni convection [5] on evaporation process.…”

“…Theoretical and computer simulation studies [5,[11][12][13][14][15] give the following equation for the evaporation rate of a sessile droplet:…”

“…Larson [16][17][18]. The former investigated the influence of substrate heating [14][15], air humidity [14] and Marangoni convection [5]. They concluded that the contribution of Marangoni convection to the total vapour flux is negligible, whereas heating the substrate is significant.…”

Evaporation of Sessile Water Droplets in Presence of Contact Angle Hysteresis

“…Different studies [19][20][21][22][23]35] give similar equation for the evaporation rate of a sessile droplet:…”

“…(1.1) ignores the temperature distribution along the droplet-air interface. Evaporation of droplets with contact angles θ < 120 • was studied by Girard et al [19][20][21][22][23] and Hu and Larson [25][26][27]. The former investigated the influence of substrate heating [22,23], air humidity [22] and Marangoni convection [19].…”