Laser-based investigation into injection, formation and flow processes of ethanol films on metal surface

Abstract

Dynamic liquid films exist widely in various industrial processes, and the investigations into these films with high temporal and spatial resolution are of great significances to understand the formation mechanisms and flow characteristics of liquid films, as well as to optimize relevant processes. Since ethanol is often used as a diluent for the film-forming substance in the coating process, it was chosen as research object here. In the work, the absorption spectrum of ethanol in the near-infrared region (6000 cm−1–8000 cm−1) was firstly analyzed. And liquid films on horizontal metal surface were investigated based on diode laser absorption spectroscopy (DLAS) by manual injection of ethanol with a needle (injection mode 1) and automatic injection of ethanol with a peristaltic pump (injection mode 2), respectively. Meanwhile, ultrasonic pulse-echo method (UPEM) was employed to verify the measurement accuracy of DLAS method. It revealed that the variations of liquid film thicknesses during the injection and formation processes obtained by these two methods were in good agreement. Furthermore, the formation and falling processes of ethanol films on vertical metal surface by injection mode 2 at different outlet flow rates were also investigated by DLAS method. It revealed that if the flow rates increased by 100 ml/min, the time increased by ∼0.14 s on average for dynamic liquid film to get a steady state. And the film kept stable for 7.31/31.20/50.73/52.43 s at flow rates of 100/200/300/400 ml/min, and the corresponding film thickness was 246.3/243.5/202.7/200.1 μm, respectively. Keywords: Measurement, Diode laser absorption spectroscopy, Film thickness, Injection, Falling