Non-intrusive detection of gas–water interface in circular pipes inclined at various angles

A new method for detecting a gas–water interface in a circular pipe is proposed. In the method, ultrasonic signals are used for non-intrusive measurement and three types of signal analyses are conducted: time-of-flight (TOF), local amplitude, and global amplitude analyses. Horizontal, 45° inclined, and vertical pipe configurations were used to verify the applicability of the proposed detection method. In the case of a horizontal pipe with an acoustic beam directed perpendicular to the water surface, TOF and amplitude analyses detect the water level. In the cases of a horizontal pipe with an acoustic beam directed parallel to the water surface, a 45° inclined pipe, and a vertical pipe, when the pipes were filled with water, TOF analysis was not applicable and amplitude analysis detects the water level. In conclusion, the gas–liquid interface in circular pipes could be analyzed qualitatively and quantitatively through the proposed non-intrusive acoustic method.