Why and how to control the escape speed of bubbles?

The bubble escape rate will affect the bubble size, and then affect the pressure difference, so it is necessary to ensure that the bubble escape rate is constant during the determination. In the experiment, we can know the approximate speed of gas flow rate by observing the speed of bubbles. Too fast will slow down the ventilation speed, too slow will speed up the ventilation speed.

Bubbles are required to escape from the capillary slowly, one by one, and the escaping bubbles are about 10 per minute. Adjust by controlling the discharging speed of the dropping funnel.

Reduce the pressure and the flow will come down. If it is an open system, just reduce the potential difference. Gas cylinders are generally used. If you want to observe, you should add a liquid whose gas is insoluble in liquid to the cylinder. For example, ammonia is insoluble in carbon tetrachloride, so carbon tetrachloride is used as a liquid in gas cylinders. Then observe the bubble occurrence rate to judge the gas flow.