  Since the liquid flow rate of the annular flow is closely related to the heat
exchange efficiency, it has great significance to measure the liquid flow rate
of the annular flow in vertical tee junction. In order to acquire the liquid
flow rate of the annular flow in vertical tee junction, a measurement method
has been designed, which implements the digital subtraction method to measure
the thickness of the liquid film under the visible light and to apply the image
feature matching algorithm to obtain the liquid velocity field. Moreover, the
accuracy of the liquid film velocity field as well as the spatial and temporal
stability of the mass flow rate is tested by proposed algorithms in this study.
Experimental results show that the measurement error of our method is
approximately 5% in the lower section of the main pipe and the branch pipe, and
lower than 15% in the upper section of the main pipe. Therefore, this method
has a high accuracy in comparison with other measurement approaches. Our method
can be applied to measure and analyse the shape and property of the annular
flow in the vertical tee junction.
