Gas–liquid two-phase flow measurements by full stream batch sampling

This paper presents a gas–liquid two-phase flow measurement method by sampling a very small fraction (5%) of the total flow. Unlike the conventional sample technique, the sample is drawn from the whole cross section instead of a local place. During the sampling, a discrete total two-phase flow sample is extracted by a sampling device and separated into single phase flows with a much small separator, and they are subsequently metered by two single phase flowmeters respectively, after that, these two streams will return to the main stream. The sample is able to represent the total flow and accurately determine the total flowrates. Because the sample is only a very small fraction of the total flow, the separator can be greatly reduced in size, which can be as small as a single phase flowmeter. At the same time, considering the flow has become two single phase streams after the separation, the measurement reliability is significantly improved. Experiments were conducted in an air–water two phase flow test loop. The inner pipe diameter of the test loop was 50 mm, and the superficial gas velocity varied from 1.5 m/s to 22 m/s, the liquid superficial velocity was in the range of 0.02–0.45 m/s. The flow pattern occurring during the experiments included stratified flow, stratified wave, slug flow and annular flow. The experimental results showed that this sampling method was feasible of measuring the two phase flowrates, and independent of flow pattern, the error of flowrates measurements was less than ±5%.