Feasibility of identifying two-phase flow quality by Shadowgraphy

Two-phase process conditions are applied across numerous applications due to their effectiveness in energy transfer, production and storage. Two-phase is important for heat transfer in cryogenics, dense expansion in power production, and storage in liquid-cooled batteries. Shadowgraphy capture offers a non-invasive technique that allows a real-time measurement of characteristics, such as steam wetness. If phase conditions could be determined during operation, optimum fluid wetness could be maintained, resulting in a more efficient energy system. This paper employs the optical technique of shadowgraphy, utilising a Photron SA4 camera for image capture, coupled to the developed algorithm in the imaging software tool, ImageJ, to develop a method for the process of estimating steam quality and void fraction captured in a horizontal orientation. Void fraction was achieved using chordal widths of 20 pixels, both horizontal and vertical across a 30 mm tubular sight glass, estimating the chordal liquid content with a time-averaged quantitative comparison, using processed greyscale images. Techniques for further optimisation of accuracy are detailed with respect to image visulisation, image processing, and importantly, results from a gravitational condensate trap are presented for validation. Results for a flow velocity of 50 m/s and at a pressure of 1.3 bar were calculated as near 0.98 gaseous content. This work demonstrates the feasibility of shadowgraphy for wet steam process conditions, and offers a new measurement technique for estimating the two-phase fraction in flows of high vapour content, thus complementing the advancement in parallel techniques such as vortex and orifice flow measurements.