Interfacial Wave Dynamics and Liquid Holdup During Slug-to-Annular Transition in Horizontal Air–Water Two-Phase Flow Using Conductivity-Based Measurements

Suryadi Suryadi (Mechanical Engineering Study Program, Universitas Malikussaleh, Aceh Utara, 24351)
Muhammad Sayuthi (Mechanical Engineering Study Program, Universitas Malikussaleh, Aceh Utara, 24351)
M. Iqbal Adhya Putra (Mechanical Engineering Study Program, Universitas Malikussaleh, Aceh Utara, 24351)
Muhammad Habibi (Mechanical Engineering Study Program, Universitas Malikussaleh, Aceh Utara, 24351)
Aljufri Aljufri (Mechanical Engineering Study Program, Universitas Malikussaleh, Aceh Utara, 24351)

Electronic Journal of Education, Social Economics and Technology
Vol 7, No 1 (2026)

Two-phase water–air flow in a horizontal pipe exhibits complex characteristics due to the interaction of superficial velocity, gravity, surface tension and interface dynamics. This study aims to analyse the wave characteristics and liquid hold-up during the slug–annular transition in co-current water–air flow. Experiments were conducted using a horizontal acrylic pipe with an internal diameter of 26 mm and a development length of 9.5 m. Flow patterns were observed using a high-speed camera at 400 frames per second, whilst liquid hold-up was measured using three Constant Electric Current Method (CECM) sensors spaced 215 mm apart. Signals were recorded at a sampling rate of 500 Hz for 20 s and analysed using statistical methods and Power Spectral Density (PSD). The results show that an increase in the superficial velocity of both the gas and liquid influences wave development and the formation of the liquid film towards an annular pattern. The wave velocity increases as the superficial velocity of both the gas and liquid rises. Under annular conditions, ripple waves and disturbance waves were identified, indicating fluctuations in the liquid film. The average liquid hold-up increased with increasing liquid superficial velocity at a constant gas velocity. The combination of visualisation and CECM is effective for characterising interface dynamics and liquid hold-up distribution during the slug–annular transition.