Session: 21-02: Wet Steam

Paper Number: 152178

Suppression of Coarse Droplet Formation From Gas-Sheared Liquid Sheets by Controlling the Trailing Edge Shape and Wettability 

To mitigate the erosion issue in steam turbines, it is crucial to suppress the formation of coarse droplets spreading from the trailing edge upstream. The droplet size will be highly dependent on the trailing edge shapes and the wettability, while the quantitative measurement under well-controlled flow conditions is limited, and hence, the theoretical prediction model including the effect of controlled trailing edge has yet established. We have developed a sophisticate experimental setup, in which the shearing gas is fully developed and the liquid sheet on a wall is in uniform thickness along the transversal direction, allowing for the quantitative and general discussion from the wavy liquid sheets to the fragmenting droplet in a consistent manner (as presented by Kamada et al., ASME Turbo Expo 2023, 2024). In the present study, we perform the visualization experiment on an acrylic pipe flow at the trailing edge thickness of 0.5mm, 1.0mm, and 2mm, and the tapered angle of 10deg and 30deg, and at the wettability of hydrophilic and hydrophobic conditions. We successfully quantify the extending ligament from the trailing edge and the following droplet statistics using a high-speed imaging technique. By implementing the hydrophobic tapered wall with 10deg, we clearly find that the circumferential wavelength between two ligaments on the trailing edge becomes short by minimizing the stagnating liquid on the edge stimulated by the Rayleigh-Taylor instability, leading to the formation of small droplet and suppression of coarse droplets. We further find that the ligament extension velocity and the breakup frequency are equivalent with the liquid film velocity and the capillary timescale, respectively. We finally formulate a theoretical model to predict the mean droplet size and distributions with considering the shape of trailing edge and wettability, which is validated by the present experimental results.

Presenting Author: Chihiro Inoue Kyushu University

Presenting Author Biography: Prof. Dr. Chihiro Inoue is an associate professor in Department of Aenonautics and Astronautics, Kyushu University.
His research area is thermo-fluid dynamics of multi-phase flow in prupulsion and energy systems.
His approach is high-speed imaging combined with theoretical modeling.

Authors:

Yoshiaki Kamada Kyushu University
Keito Murakami Kyushu University
Zhenying Wang Kyushu University
Chihiro Inoue Kyushu University
Shigeki Senoo Mitsubishi Heavy industries, Ltd.