Instability of horizontal oil-water flows based on the signal-dependent complex admittance representations

Abstract

Horizontal oil-water two-phase flows are characterized by unstable motions of interfacial wave and entrained droplets. An experiment of horizontal oil-water flow was made in an acrylic pipe with an inner diameter of 20 mm. A measurement system of concave capacitance sensor is designed to detect the real and imaginary parts of flow complex admittance. An Adaptive Optimal Kernel Time-Frequency Representation (AOK TFR) of the complex admittance angle is used to characterize the flow instability in terms of total energy. A detrended cross-correlation analysis (DCCA) of the oil-water complex admittance is conducted to investigate the instability multi-scale flow structures. The cross-correlation coefficients at large and small scales enable to characterize the instability of the oil-water interface and the entrained droplets in continuous phases, respectively. The result suggests that the DCCA cross-correlation coefficients and the total energy extracted from AOK TFR are accordant in uncovering the instability of horizontal oil-water flows.