# Very low pressure and Temperature to high P, high T (constant volume, constant heat)

1. Jul 25, 2012

### neutrons

Hi all,

There is a block of ice (say 20 cm^3) sitting inside a box (50cm^3, constant volume) at very low P and low T (say P = 10^(-8) kPa and T = 100 K .... roughly ambient moon P and T).

There is a constant heat flux incident on the box. I want a 'path-way' (explicit phase transition regimes etc) that will take this ice block to high T (~ 500 K) and high P (~ 18 MPa), and quantify energy requirement in each step. The heat source is infinite. Please make any other assumption that may prove helpful.

My approach:

The given P and T is well below the triple point. If I heat the ice, it will increase its T under the same initial P. Once it hits the sublimation line, the energy input will convert it directly to vapor (under constant P, is this assumption valid?) .

Now, after everything is vapor, if I continue heating, I am not sure how to quantify the path-way in the P-T diagram. (Assuming ideal gas under constant V.... P has linear relationship with T but I can't tell anything about the slope). How does the P and T change now (after sublimation) under constant volume and constant heat source?

Many thanks !

(I was looking at XSteam and there is no data at low P and T.)

2. Jul 26, 2012

### etudiant

Re: Very low pressure and Temperature to high P, high T (constant volume, constant he

Not sure your system will be that well behaved.
The ice will shrink as it melts, so there will be an interval where you have liquid water and water vapor in your box. That will put a kink in your P-T diagram between 273 and 277 K, with another one at 373+ K when the water turns to steam.