Volume and rate measurement of slowly generated gas bubbles. (April 2020) - Abid, Hassan Ali
Abstract: The use of an inverted burette arrangement that allowed volume and time-course tracking of bubble movement via camera imaging is shown here to improve on the classical inverted jar (or beaker) method for measuring gases generated in small volumes and at slow rates (below 1 mL/s). In tests involving discrete gas volume measurements delivered at 0.57 mL/s, comparison with pre-set air volume delivered by a syringe pump showed high correspondence, linearity, and repeatability. Tests with continuous gas flows at 0.2, 0.32 and 0.57 mL/s revealed average bubble count versus volume trends that displayed high linearity to indicate that the bubble volumes (at any flowrate) were constant. The average bubble count versus time also showed linear trends and repeatability indicating that the time intervals between the appearance of any two bubbles (at a particular flowrate) were uniform. The analytical and simulated results helped to explain why bubble size determination by high speed camera recording for measuring gas volume and flowrate is fraught with inherent problems. An analysis using light ray tracing showed that flowrate determination using such an approach would necessitate complicated image correction when two cameras are used for simultaneous recording due to distortion effects resulting from refraction. A virtual gate approach involving the binarization of images recorded with a standard camera is shown to be more feasible in establishing the flowrate using bubble counting or finding the time interval between bubbles. Graphical abstract: Image 1 Highlights: The inverted burette arrangement here improves on the classical inverted jar in volume and rate gas measurement. Good measurement correspondence, linearity and repeatability of volume was confirmed with absolute syringe pump. Bubbles formed have constant volumes and regular periods between their creation to aid flowrate measurement. Optical analytical and simulations reveal problems with flowrate determination using bubble size measurement. A virtual gate approach that involves the binarization of images allows use of standard cameras.