Sorry to deep res this thread -- found it on a search
I just did this on paper for my own use...
You can follow the same steps. You're interested in the following measurements:
I assume Beer Smith calculates thermal mass in calories -- I don't have the program installed at work to check.
1. Weight of water (in grams) (Mw)
2. Initial Temperature of Mash Tun (Tt) (temp. units don't matter - they'll cancel)
3. Initial Temperature of Water (Tw)
4. Final Temperature of Water (Tf)
The equation for thermal energy (see Beer Smith documentation)
MwTw + MtCtTt = (Mw + MtCt)Tf
All values are known except MtCt, which is the thermal mass of the tun.
Solving for MtCt:
MtCt = Mw (Tf - Tw) / (Tt - Tf)
All values on the right side of the equation are known.
If Beer Smith requires the tun's weight, you can weigh it and find out the specific heat -- or just use a dummy value. This will work, but it's not actually correct.
This has been my problem with this value all along (and is part of why I've gone and figured it out -- also, I'm learning Android programming )... a cooler is an inner wall and an outer wall with insulation between. The thermal mass really consists of only the inner wall and some of the insulation -- insulation likely has low thermal mass, but the rate of heat transfer is decreased. This emulates a closed system for a period of time.