Optical device and method for sensing multiphase flow

An apparatus for measuring the velocity of a multiphase fluid flowing in a pipe having transparent portions, the multiphase fluid comprising a liquid phase and a gaseous or solid phase, the apparatus comprising:

• an illuminator for generating a pair of collimated beams of light and directing said beams through the multiphase fluid by said transparent portions of the pipe, said pair of collimated beams spaced apart in a direction of flow of the multiphase fluid by a predetermined distance;
• a pair of photodetectors positioned across the pipe from said illuminator, each of said pair of photodetectors optically associated with one of said pair of collimated beams for detecting scattered, deflected and attenuated light from the associated beam and generating a signal;
• and
• a signal processing apparatus for processing the signals from said pair of photodetectors and calculating cross-correlation functions between the signals to determine a time delay, and for calculating the velocity of the multiphase fluid by taking a ratio of the predetermined distance to the time delay, said signal processing apparatus comprising a plurality of band-pass filters for isolating a plurality of frequency components of each of the pair of signals.

A method for measuring the velocity of a multiphase fluid flowing in a pipe having transparent portions, the multiphase fluid comprising a liquid phase and a gaseous or solid phase, the method comprising the steps of:

• directing a pair of light sheets from an illuminator through the multiphase fluid by said transparent portions of the pipe, said pair of light sheets oriented perpendicular to a direction of flow of multiphase fluid and spaced apart in the direction of flow by a predetermined distance;
• detecting scattered and deflected light with a pair of photodetectors to produce a pair of signals, each of said pair of photodetectors being associated with one of said pair of light sheets;
• calculating a cross-correlation function between said pair of signals to determine a time delay between the signals;
• calculating the average velocity of the multiphase fluid by taking the ratio of the predetermined distance to the time delay;
• and
• calculating an amount of liquid fraction in the multiphase fluid based on dispersion of signals from said photodetectors.

An apparatus for measuring the velocity of a multiphase fluid flowing in a pipe having transparent portions, the multiphase fluid comprising a liquid phase and a gaseous or solid phase, the apparatus comprising:

• an illuminator for generating a pair of light sheets and directing said light sheets through the multiphase fluid by said transparent portions of the pipe, said pair of light sheets oriented perpendicular to a direction of flow of multiphase fluid and spaced apart in the direction of flow by a predetermined distance;
• a pair of photodetectors positioned across the pipe from said illuminator, each of said pair of photodetectors optically associated with one of said light sheets for detecting scattered light from the associated light sheet and for generating a signal;
• and
• a signal processing apparatus for processing the signals from said pair of photodetectors, for calculating cross-correlation functions between the signals to determine a time delay, for calculating the velocity of the multiphase fluid by taking a ratio of the predetermined distance to the time delay, and for calculating an amount of liquid fraction in the multiphase fluid based on dispersion of signals from said photodetectors.