Abstract
An unnoticeable and sizeable error in the throughput measurement is detected in a liquid displacement gas flowmeter, constructed based on Stevenson's design. It is observed that as soon as the flow measurement is started, the pressure inside the burette reduces rapidly for first few seconds and afterwards it becomes constant. The reason for this pressure drop and its contribution to the magnitude of error in the measured throughput value is discussed. The root cause of this pressure change is found to be due to an initial delay in falling of the oil in the burette from the reservoir. To find out the magnitude of pressure drop, an experimental study is carried out using the 1000 and 500 cm 3 burettes incorporated in the present flowmeter. As a result of this study it is found that the magnitude of pressure is ranging from 4 to 6 mbar, which to some extent depends on the initially trapped volume of the gas. Therefore, due to this sizeable pressure change all the advantages associated with this unique design of the apparatus are being lost. Hence, the measured throughput values with this apparatus require correction, the magnitude of which depends on the combined contribution of pressure change and the ratio of the trapped volume to the displaced volume. In the present case this correction is found to lie between 2% to 6% for the two burettes, though in general the magnitude of this correction depends on several factors as are being discussed in detail.
Published Version
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