Development of a fully automated soap flowmeter for micro flow measurements

A soap flowmeter is commonly used for measuring of low flow rates of gases. In order to have accurate measurements using this instrument, the diameter and the length of the flowmeter tube should be selected on the basis of the expected flow rate [Levy A. The accuracy of the bubble meter method for gas flow measurements. J Sci Instrum 1964;41:449–53]. However, there are restrictions when reducing the diameter of the tube or increasing its length. The objective of this study is to find alternative ways to improve the accuracy of existing flowmeters in the range of micro flow rates. To accomplish this objective a fully automated system for making soap bubbles was developed, and implemented with different commercial soap flowmeters. In addition, a computerized data acquisition was developed to improve the accuracy of the time measurement. The final product is capable of performing hands-free measurements even in isolated areas. Gas flow rates ranging from 5 to 100 μL/min were successfully measured and suggestions for more improvements in the accuracy of flow measurements are proposed. Since the automated bubble maker allows controlling the size of the soap bubbles, the modified soap flowmeter is also suitable for the investigation of free foam films in vertical tubes.