I was just wondering what the reference state for the enthalpy of water in TOUGH2 is? The reason is I would like to define water infiltration (precipitation) with a temperature of 20˚C. Therefore, I ran a single element in TMVOC initialized with only water at atmospheric pressure and a 20˚C, and I got 8.4 J/kg as the enthalpy. Also, I get roughly similar number in NIST chemistry webbook. However, if I use this number, I noticed the temperature in the elements drops and goes below 20˚C. So, I came across a publication where an enthalpy of 9.4e4 J/ kg corresponding to 20˚C was used. Now, when I use that number I get the right temperature of 20˚C. I suppose it might be due to a discrepancy in the reference temperature. Could anybody explain this please? How should I calculate the right enthalpy corresponding to a given temperature (say 20˚C) to be used in TOUGH2?
The best way to inject liquid (or gas) at a fixed temperature is to attach a virtual grid block to the block that you want the fluid injected into. Give this virtual grid block a rock type with an infinite (or very large) density and whatever initial temperature you want your injected fluid to be. Then when you inject your fluid into the virtual block, the fluid will equilibrate with the block temperature and fluid of that fixed temperature will flow into your actual injection grid block.
This approach works for both gases and liquids. The reason this is necessary is that you cannot know a priori the enthalpy of the injected fluid because you don't know a priori what its pressure will be upon injection.