Air Expansion in a Sealed Tank

Thank you all for your comments and time.

I'm trying to understand physically the process. The point I'm not able to understand is, the equation I used is not having the compressibility parameter (But equation is for Gas) but how its effect is seen in the calculation result. Please give some light on the physical process to understand better.

Thank you

<...Please give some light on the physical process to understand better....>

There's three "good answers" above that do just that.

Come out of the equations and think about the principle of what is happening inside the vessel.

Consider the following:

A 10 liter tank contains 9 liters of water and 1 liter of gas.

If you remove a liter of water, it will contain 8 liters of water and 2 liters of gas. The volume of the gas will have doubled the pressure will be 50% of original.

If the tank starts with 5 liters of water and 5 liters of gas, when you remove a liter of water it will contain 4 liters of water and 6 liters of gas. The volume of gas only increased by 20%. The pressure will have decreased to 83.3% of original.

The pressure in the available volume is constant, regardless of the volume. So it is like trying to fill an automobile tire with a 1/2 liter tank or a 10 liter tank. The 1/2 liter tank will be exhausted much sooner than the 10 liter tank, so you see the pressure drop much faster on the 1/2 liter tank...

Thank you all for the explanations. I could understand now better and also the effect compressibility.

Thank you

Uncompressed air in a water heater (when it's first installed let's say) starts at 14 lbs. Or so, as the tank is filled with water,(with 50 psi. Or so) the air pressure above the water begins to increase. As the level of the water nears the top, the air pressure is increased to sometimes well above the test pressure of the tank (300 psi). This is why water heaters used to be tested with pressurized air (150 psi.) Under water. Also this is why when the tank is filling with (uncompressable) water, the plumber opens a hot water tap, or else (there is massive damage when the tank splits). Of course a tank designed to withstand very high pressure, would be o.k. But household water heaters........never. It is one of the first things you learn in the plumbing trade, because the maths become apparent with out numbers. The "uncompressabllity" of water of course is a different subject, but it can also be understood by the fact that sea mammals can hear each other hundreds and hundreds of miles apart, because sea water can't be compressed any more than it all ready is. There is enough math to fill a small book on these subjects, but I hope this post helps.

This might be considered an off topic math questions about a sealed tank at normal atmospheric pressure.. How many square inches are in the inside of a 50 gallon water tank? If the tank is filled with air to a pressure of 30 psi. What is the total pressure exerted on the inside of the tank? If the tank is filled with 50 gallons of water at 30 psi, what is the total pressure exerted on the inside of the tank? Does a tank half full of water and half full of pressurized air react differently top and bottom? Curiosity.

<...If the tank is filled with air to a pressure of 30 psi. What is the total pressure exerted on the inside of the tank?...> 30psi, as stated in the question.

<...If the tank is filled with 50 gallons of water at 30 psi, what is the total pressure exerted on the inside of the tank?...> 30psi as stated in the question.

<...Does a tank half full of water and half full of pressurized air react differently top and bottom?...> One must make due allowance for the additional head on the bottom of the <...tank...> caused by the column of water below the <...pressurized air...> inside it.

<...the air pressure is increased to sometimes well above the test pressure of the tank...>

That sounds like a recipe for catastrophic and spectacular destructive testing! Please make sure that all other CR4 readers are standing well away when this event is caused to take place.