レーザフォーカス変位計による鉛直流下液膜の測定 : 第1報, 測定原理と液膜厚さ  [in Japanese] Measuring a Film Flowing Down a Vertical Wall Using Laser Focus Displacement Meters : 1st Report, Measuring Principle and Film Thickness  [in Japanese]

A film flowing down a vertical wall exhibit as many distinct wave features. The produced interfacial waves show fascinating non-linear phenomena, including solitary waves and complex disordered patterns. Abundant measurements have been made of these phenomena using electrical resistance, electrical capacitance, optical, and laser beam methods. In this paper, we present a new way of measuring the thickness of a film flowing down a vertical wall in an entry region using two laser focus displacement meters. With this method, we achieved accurate measurements of film thickness in real time with a sensitivity of 0.2 micron and 1 kilohertz. We also clarified errors caused by the refraction of laser beam passing through the wall and liquid. In the entry region, the wave amplitude decreased as the flow rate increased, which was contrary to results obtained in the past in a fully development region. The average measured film thickness agreed with that calculated using Nusselt's Law, indicating the flow to be laminar in the entry region even at a high flow rate.