Construction of a liquid droplet flowmeter for low-permeable gas separation membranes

A column-based liquid flowmeter was fabricated to correct the errors arising from the diffusion of gases through the soap film in soap bubble flowmeters (back diffusion). The soap film was replaced with a liquid droplet (soap or paraffin), without introducing any noticeable error caused by the weight of the droplet. To the best of our knowledge, this was the first time that liquid paraffin was used as an indicating medium in a gas flowmeter. The flow rates were measured in five segments on the flowmeter. The results showed that the liquid droplet flowmeter was a suitable instrument to measure the permeability of the low-permeable membranes with flow rate in the range of mu L/min. Based on the results obtained from the evaluation of the flows of different gases (N-2, O-2 and CO2), unlike a soap bubble flowmeter, type of the gas had no effect on the accuracy of the measurements in the new flowmeter. It was also observed that the liquid droplet flowmeter solved the back diffusion problem, which is a major concern in the soap bubble flowmeters.