Measurement of mean gas and liquid phase velocities in two phase flows using hot-film anemometry

A relatively simple technique has been developed to estimate the mean liquid and gas phase velocities in vertically-upward two-phase flows. The large difference in heat transfer coefficient between a hot-film sensor and the liquid and gas phases enables the accurate discrimination of the anemometer output signal between the two phases. The discrimination of the signal between the two phases is based on an amplitude and slope threshold detection technique. The discretized signal is time averaged to obtain the local gas and liquid time fractions, defined as the ratio of time the sensor is in each phase to the total time at the measurement location. The probe is traversed across the pipe diameter to obtain the radial distribution of the local time fractions. By assuming radial symmetry, the local time fraction distribution is integrated over the cross section of the pipe to obtain an average time fraction, which can be interpreted as the void fraction. As part of the flow loop instrumentation, the individual volume flow rates of the two phases are measured using turbine flow meters before they mix. The phase velocities are estimated from the individual volume flow rates and the void fraction. Measurements performed in a three-inch flow loop for the case of slug and churn flows are in good agreement with visual observations of the flow.