Evaporation of Ethanol Drops on a Heated Substrate Under Microgravity Conditions

Abstract

We present in this paper results obtained from a parabolic flight campaign regarding ethanol sessile drop evaporation under reduced gravity conditions. Drops are created using a syringe pump by means of injection through a PTFE (polytetrafluoroethylene) substrate. The drops are recorded using a video camera and an infrared camera to observe the thermal motion inside the drop and on the heating substrate. The experimental set-up presented in this paper enables the simultaneous visualization and access to the heat flux density that is transferred to the drop using a heat flux meter placed between the heating block and the PTFE substrate. We evidence original thermal spreading phenomena during the ethanol drop creation on a heated PTFE substrate. The drop exhibits specific behaviour which is discussed here. This work is performed in the frame of a French-Chinese collaboration (project IM-PACHT) for future experiments in a Chinese scientific satellite.

The heat flux near the contact line of the droplets on heated foil

“…The basic element of the test cells is a constantan foil (CuNi) of the thickness of 25 ߤm, size of 80 × 35mm 2 and heat conductivity ߣ of 23W/mK was used as the substrate. This foil is soldered to the two brass electrodes (4).…”

“…This foil is soldered to the two brass electrodes (4). The substrate was heated by Joule heating from power supply (2). The temperature of the bottom foil surface was measured by IR camera Titanium 570M (7) with help of gold mirror (1).…”

“…The wetting (contact) angle is determined by the Young equation, [1]. Analysis of papers where drop is placed on the heated substrate with different level of gravity shows that there is not enough information about the process of evaporation and wetting of a solid substrate for variable levels of gravity [2,3]. The process in a sessile liquid drop on the heated substrates with different wettability are investigated numerically and experimentally in [4,5].…”

Temperature and chemical composition of droplets by optical measurement techniques: a state-of-the-art review

“…The emissivity was adjusted to obtain the best temperature correlations between the measurements. Brutin et al (2010Brutin et al ( , 2011 considered the case of semi-transparent droplets in a study of sessile droplets deposited on a flat heated surface. The authors drew attention to the fact that measurements obtained with different semi-transparent liquids correspond to different depths of penetration.…”

“…In Savino and Fico (2004), drops are attached to the tip of a capillary tube and heated in a hot air stream. The use of IRT was also demonstrated for the investigation of thermocapillary convection within droplets resting on a heated solid surface (Brutin et al 2010(Brutin et al , 2011Ganzevles and Van Der Geld 1998;Sefiane et al 2008). Infrared thermography can be used to measure the occurrence of temperature gradients on the droplet surface (Ganzevles and Van Der Geld 1998) and also makes it possible to visualize cellular patterns driven by internal convection and spontaneous evaporation (Fig.…”