Newsletter  2023.3  Index

Theme : "The Conference of Fluid Engineering Division (March issue)" Preface （T. Hashimoto，S. Matsuda，H.J. Park） Ejection stability of high-viscosity liquid painting equipment Hiroya WATANABE (Tokyo University of Agriculture and Technology), Kyota KAMAMOTO(Tokyo University of Agriculture and Technology), Jingzu YEE (Tokyo University of Agriculture and Technology)，Kazuya U. KOBAYASHI (Nippon Institute of Technology) and Yoshiyuki TAGAWA (Tokyo University of Agriculture and Technology) Breakage mechanism of a glass tube and development of crack-free system with generation of laser-induced microjets Shoto SEKIGUCHI (Tokyo University of Agriculture and Technology), Kazuya U. KOBAYASHI (Nippon Institute of Technology), Yoshiyuki TAGAWA (Tokyo University of Agriculture and Technology) Optimization of a Francis Turbine Runner by Means of Inverse Design and CFD Calculation Shunsuke Nagata (Waseda University), Nak-Joong LEE (Waseda University), Tatsuya IRIE (Waseda University), Kazuyoshi MIYAGAWA (Waseda University) Gas removal from a closed-end hole by irradiating acoustic wave Yuta MATSUMOTO (Shizuoka University), Yuki MIZUSHIMA (Shizuoka University), Toshiyuki SANADA (Shizuoka University)

 

Ejection stability of high-viscosity liquid painting equipment

Hiroya WATANABE Tokyo University of Agriculture and Technolog	Kyota KAMAMOTO Tokyo University of Agriculture and Technolog	Jingzu YEE Tokyo University of Agriculture and Technolog	Kazuya U. KOBAYASHI Nippon Institute of Technology	Yoshiyuki TAGAWA Tokyo University of Agriculture and Technolog

Contents

In industry, a variety of high-viscosity liquids are applied on substrates. We have developed a device to eject a highly viscous liquid as a focused jet using an impulsive force (Kamamoto et al. Flow 2021). Based on this device, a high-viscosity liquid ejection system was developed (Figure 1). In this system, an air cylinder is used to move the ejector up and down, and a jet is generated by accelerating the liquid in the ejector with the impulsive force generated when the ejector struck against a stopper. However, variations in shape and area of the coated droplets were observed during the periodic ejection of jets. Therefore, this study aims to elucidate the factors of the instability during the periodic jetting and to improve the quality of coating. For that, we experimentally observed the jet behavior during the periodic jetting (Figure 1). It is observed that the meniscus position and the shape of the meniscus changes with each ejection (Figure 2). Since the rise of the meniscus position can change the gradient of pressure impulse, which causes the acceleration of the fluid, and the meniscus shape can affect flow-focusing effect, these changes were found to cause variations in jet behavior at each ejection. It was also observed that changes in jet behavior induced variations in coating results. It was anticipated that the delay in supply due to the high viscosity of the liquid was a contributing factor to the elevated position of the meniscus during periodic ejection. To control liquid replenishment by setting a high pressure and actively circulating the liquid, a circulating supply system was introduced instead of the conventional tank type supply system (Figure 3). Remarkably, reproducible ejection was achieved for more than 10 minutes (Figure 4). Also, the coating quality are considerably improved than that with the tank system. These results will facilitate the practical use of three-dimensional coating technology of high viscosity-liquids.

Key words

Drop impact, Viscous jets, Coating

Figures

Figure 1　Experimental setup of high-viscosity liquid ejection system.

Figure 2　Meniscus position during repetitive ejection (top) and coating result (bottom) using the tank-type supply system.

Figure 3　Schematics of (a) the tank-type supply system and (b) the circulating supply system.

Figure 4　 Meniscus position (top) and coating results (bottom) at t = 0, 5, 10 min during repetitive ejections using the recirculating supply system.