The Effect of Adsorbed Volatile Organic Compounds on an Ultrathin Water Film Measurement

Abstract

Using surface plasmon resonance imaging (SPRi), we have recently shown for the first time the existence of a monolayer water film between droplets during dropwise condensation. This study examines the effect of adsorbed volatile organic compounds (VOCs) on the ultrathin film measurement using SPRi. Further, the work presents the proper surface-treatment process that enables measurements of the ultrathin water layer during high-speed imaging of dropwise condensation at 3000 frame per second. In this study, two methods were applied for cleaning the surface (gold-coated glass)—(1) standard cleaning procedure (SCP) using acetone, isopropyl alcohol, and deionized water and (2) SCP followed by air plasma cleaning. This work discusses the effect of the cleaning procedures on surface roughness, contact angle, and surface chemistry using atomic force microscopy, optical microscopy, and an X-ray photoelectron spectroscope meter. The results showed that SCP before the SPRi is a proper surface-treatment method. The effect of adsorbed VOCs during dropwise condensation on a surface treated with SCP was measured to be 0.0025 (reflectivity unit), which was 70% smaller than the reflectance associated with a monolayer water film. The results of this work confirm a monolayer water film observation during the dropwise condensation, which has been reported before.

Dropwise Condensation Mechanism on Smooth Hydrophilic Surfaces

“…It is worth noting that the adsorbed molecules on the surface mostly consist of water molecules and not volatile organic compounds (VOCs). In our previous work [15], we showed that the rate of adsorption of VOCs on the gold surface is much slower than the rate of adsorption of the molecularly adsorbed water layer on the surface. In a different set of experiments, the water bridge on the surface was slightly relocated on the surface by moving the ITO coated glass that is on the top of the water bridge (see Figure 1a).…”

“…It is worth noting that the adsorbed molecules on the surface mostly consist of water molecules and not volatile organic compounds (VOCs). In our previous work [15], we showed that the rate of adsorption of VOCs on the gold surface is much slower than the rate of adsorption of the molecularly adsorbed water layer on the surface.…”

“…Due to the need for visualization of interfacial phenomena with high-frequency features, such as ultrathin film instabilities, we developed an automated SPRi instrument, the first-ever reported instrument capable of imaging a sub-nanometer film at high-speed (up to 10,000 FPS) in ambient conditions [14]. This newly developed near-field imaging system was applied [14][15][16][17] to understand the physics of dropwise condensation, which have been under debate for the past nine decades [4]. We interpret the static dropwise condensation in Umar and Griffith's work [6] as stable dropwise condensation (SDC) occurring at a very low condensation rate, or dropwise condensation that can be sustained on the surface for a long-time.…”

Film cooling modeling of a gas turbine blade by considering different injection holes with and without opening angles through CFD

“…The effect of film cooling on the performance of blades is becoming significantly important when the temperature of the gas turbine is raised to enhance its performance [3][4][5]. Computational Fluid Dynamics (CFD) has now found its place among experimental and analytical methods for analyzing fluid flow, heat transfer [6][7][8][9][10][11][12][13], and diverse problems [14][15][16], and the use of this method for engineering analysis has become more common [17][18][19][20].…”

Dropwise Condensation Mechanism on Smooth Hydrophilic Surfaces

“…Due to the need for visualization of interfacial phenomena with high-frequency features, such as ultrathin film instabilities, we developed an automated SPRi instrument, the first-ever reported instrument capable of imaging a sub-nanometer film at high-speed (up to 10,000 FPS) in ambient conditions [12]. This newly developed near-field imaging system was applied [12][13][14][15] to understand the physics of dropwise condensation, which have been under debate for the past nine decades [4]. We interpret the static dropwise condensation in Umar and Griffith's work [6] as stable dropwise condensation (SDC) occurring at a very low condensation rate, or dropwise condensation that can be sustained on the surface for a long-time.…”