I work at a hospital and I noticed that the oxygen cylinders are labelled as containing 630 litres of oxygen. (Yes yes, suuuper busy day at work) Similarly the flow rate out of the cylinder is set in L/min. This piqued my interest as I know a litre is a set volume, yet clearly the cylinder was not that large. So what is a litre in this case? …and why is it this way?
In: Physics
You are correct that the more accurate measurement would be by mass. However it can be hard to measure the mass of something. For example the regulator on the gas flask would be much more complex if it had to measure the flow rate by mass and not by volume. The easiest way would have been to measure the flow rate in volume and then use a convertion factor. This is how they are able to list the volume of air in the cylinder. They know the weight of the gas in the cylinder and then use a convertion factor to a standard volume of oxygen (volume in standard atmospheric pressure and temperature). But of course as the gas is pressurized it does not take up as much volume as if it had been at standard atmospheric pressure. Another way to measure gas is by pressure. Of course this does not give you how much gas there is as this depends on the volume of the tank but it is often much easier to measure then the weight of the tank itself.
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