I know that scuba tanks are pressurized to 3000 psi. This is then released by the regulator to a pressure close to the water pressure for breathing. Now refrigeration works by pressurizing a gas, letting it cool down to ambient temperature, and then decompressing it. In the decompression it gets colder. How come the 3000 psi air inside the scuba tank, the pressure used to cool the atmosphere into liquid nitrogen, is not too cold to breathe on decompression?
When you take a breathe from your tank, the high pressure air is converted to medium pressure by the first stage of your regulator (the bit that fits on the tank). The mouth piece transfers this air to your mouth at ambient pressure. If the high pressure air came straight into your mouth, it’d blow your ‘ead off(ish). If you open the valve on a tank (check with the staff that you can waste a tank) fully and leave it to empty a 3000psi tank, once it’s near empty, feel the valve, you’ll find it’s pretty bloody cold, so you’re kinda right that when gases go from high pressure to low pressure (according to Charles’ law:at a constant pressure, the volume occupied by a given quantity of gas decreases as the temperature of the gas decreases (p1v1/t1=p2v2/t2) but the volume of the tank remains unchanged, the temp decreases.
With scuba tanks, the only thing in the tank is the same air you’re breathing right now. Refrigeration (on the other hand) uses gases such ammonia or freon to create this cooling reaction.
In other words, with refrigeration, it’s engineered to get cooler. With scuba diving, we don’t need that extra engineering. In fact, it’s very dangerous to divers if anything BUT regular air ends up in the tank.
If you want to know a whole lot more about how scuba compressors work, check out the link below.
References :
http://www.neptunoworld.com/articles/compressors.html
When you take a breathe from your tank, the high pressure air is converted to medium pressure by the first stage of your regulator (the bit that fits on the tank). The mouth piece transfers this air to your mouth at ambient pressure. If the high pressure air came straight into your mouth, it’d blow your ‘ead off(ish). If you open the valve on a tank (check with the staff that you can waste a tank) fully and leave it to empty a 3000psi tank, once it’s near empty, feel the valve, you’ll find it’s pretty bloody cold, so you’re kinda right that when gases go from high pressure to low pressure (according to Charles’ law:at a constant pressure, the volume occupied by a given quantity of gas decreases as the temperature of the gas decreases (p1v1/t1=p2v2/t2) but the volume of the tank remains unchanged, the temp decreases.
References :