Knowing the rate of flow of various gases is useful for designing and developing new gaseous systems. The rate of flow of a gas is measured in units of pressure-equivalent flow.
The most common units for flow rates are the inch-pound per square inch (psi) scale, which is used on air, liquid, and foam products; and the furlong-kilogram per square meter (kgal) scale, which is used in engineering designations such as fire and safety ratings.
This article focuses on knowing the rate of flow of gases. There are several articles dedicated to specific rates for different gases, so read those first if you need more information.
Determine the mass of oxygen
When we measure the amount of oxygen in an air sample, we find the proportion of O 2 to N 2 is about 1:1.
This means that for every N 2 molecule in one atom of oxygen, there is an atom of nitrogen molecule.
This makes sense because O 2 is a relatively small molecule, and N 2 is a larger one. Even though it looks like a neutral gas, O 2 has a positive charge, which makes it stick to certain things in the atmosphere. This makes sense when you think about it- if you wanted to purify O 2 , you would have to remove its positive charge!
The other gas we are looking for has a slightly different mass ratio. When we measure the unknown gas’s rate of effusion (how fast it expands and contracts), we find that it has a mass ratio of 0.935. This means that when it enters our lungs, its oxygen content is 0.
Calculate the mole fraction of the other gas
If we know the mass of oxygen, we can calculate its effusion rate. We would say that 200 mmoles of oxygen will effuse 0.935 mmoles of oxygen during one minute.
However, we do not know the mass of oxygen. We can only calculate it from other gases present in the mixture.
This is true for all gas mixtures. If there is another gas in an oxidizer/fuel mixture, then there must be a known amount of Oxygen to give to the mixture to maintain sufficient effusion.
If there are no known gases in an oxidizer/fuel mixture, then an assumed average amount of 2 kg per person per month is necessary.
Determine the mass of the other gas
In order to determine the other gas, you must find its mass. The unknown gas is the spring constant of a voltage change on a meter, or in other words, the other gas’s mass.
How do you find the other gas? You use a powerful vacuum tube and attach it to a source of energy such as electricity or fuel. With this tool, you can determine the amount of energy in a flow of air or another unknown gas.
You can also use high-tech equipment that uses lasers and spectroscopy to analyze an unknown gas. These tools are more advanced, but they are possible!
Either way, you need to know what they are measuring in order to determine the unknown gas’s mass.
Combine all steps to determine the identity of the other gas
In order to find out the identity of the unknown gas, you must first determine the rate of oxygen to other gases.
The amount of oxygen in an unknown gas is its rate of effusion. An unknown gas has a low effusion rate, which means more oxygen needs to be added to it.
The formula for effusion is O+-2X, where O is an unknown gas and X is another gas. The number in the parentheses depends on which other gas it is.
X can be zero, one, or two atoms of another substance. In this case, we want to know the ratio of one atom to two atoms of that other substance.
If you are thinking of a familiar scent, think smell-proofed door hardware or carpet padding.
Check your results
When you’re done, your device should show a number between 1 and 5, representing the rate of effusion for that gas. A number lower than 1 indicates less oxygen to the liquid, which may be problematic if the gas is something important.
If your test shows an amount higher than 5, this does not mean that there is too much oxygen to the liquid- it could be a function of a different gas. Most commonly, this is argon, which has a high ratio of inert nitrogen to oxygen.
However, there are some devices that measure only an amount lower than 5- in those cases, you can check your results by adding more distilled water! It may take some time to see an improvement in your machine, but eventually you will.
