# Sealed tank pressure evolution

1. Oct 13, 2016

### hybro

Hi all,
I have some troubles with some basics thermodynamic rules. I have a sealed tank filled with fuel at Patm and at a temperature T. In this tank after filling, is composed of 3/4 liquid and 1/4 gas. I was wondering how the pressure inside the tank will change if we change the boundaries conditions (outside temperature). Will the pressure rise in the tank if the outside temperature goes up? Is it due to the vapor created because of the temperature variation (vapor pressure of the fuel?) or because of the liquid which exerce a pressure on the surface of the tank ?
With the perfect gas law we know that with the temperature the pressure will rise with the temperature but the vapor/liquid ratio will change too. And fuel is like incompressible so the tank expands too ?
Thank you for your help guys !

2. Oct 13, 2016

### Staff: Mentor

If you raise the temperature in the tank (with the tank volume held fixed), the pressure in the tank will increase. The pressure in the tank will be equal to the equilibrium vapor pressure of the substance, which increases with temperature (neglecting hydrostatic pressure variation in the liquid).

3. Oct 14, 2016

### hybro

So that means we will always have liquid and vapor in the tank ? impossible to have only vapor if the temperature rise ?

4. Oct 14, 2016

### Staff: Mentor

No. Under certain starting conditions, of course, after you have raised the temperature enough, all the liquid will have evaporated. But, even here, the pressure rises monotonically with temperature.