# Pressure-Tuned Optima — operating pressure as a design axis

Two-phase systems tune the boiling window via system pressure. The repo's Tb gate assumes 1 atm; sub-atmospheric operation pulls high-Tb fluids into the cold-plate band (facility water ~27-45 C, ASHRAE 5th-Ed). **Report-only.**

| Lead | Tb source | 0.5 atm | 0.7 atm | 1.0 atm | 1.5 atm | 2.0 atm |
|---|---|---|---|---|---|---|
| Pentane+DMC (fuel pentane) | CoolProp | 17.2 | 26.0 | 36.1 | 48.5 | 58.0 |
| MeOH+TriEG (fuel MeOH) | CoolProp | 47.8 | 55.7 | 64.5 | 75.1 | 83.2 |
| HFO+VC (fuel HFO-1336mzz-Z) | Clausius-Clapeyron(Trouton) | 14.6 | 23.4 | 33.4 | 45.6 | 54.9 |
| FK+VC (fuel FK-5-1-12) | Clausius-Clapeyron(Trouton) | 29.2 | 38.5 | 49.0 | 61.8 | 71.6 |
| HCFO+VC (fuel 1233zd-E) | Clausius-Clapeyron(Trouton) | 1.0 | 9.5 | 19.0 | 30.6 | 39.5 |
| siloxane (hexamethyldisiloxane) | Clausius-Clapeyron(Trouton) | 77.6 | 88.4 | 100.6 | 115.5 | 126.8 |
| siloxane lead (small cyclo) | Clausius-Clapeyron(Trouton) | 45.2 | 54.9 | 66.0 | 79.5 | 89.8 |
| DMC (carbonate fuel) | Clausius-Clapeyron(Trouton) | 67.7 | 78.2 | 90.0 | 104.5 | 115.4 |

## Pressure-tuned gains (enter a use-case Tb band only off-1-atm)

- **direct_to_chip** (Tb 45-75 C): Pentane+DMC (fuel pentane), HFO+VC (fuel HFO-1336mzz-Z), DMC (carbonate fuel)
- **immersion_tank** (Tb 55-95 C): Pentane+DMC (fuel pentane), FK+VC (fuel FK-5-1-12), siloxane (hexamethyldisiloxane)
- **two_phase_cold_plate** (Tb 35-70 C): HFO+VC (fuel HFO-1336mzz-Z), HCFO+VC (fuel 1233zd-E), DMC (carbonate fuel)

> Tb(P) via CoolProp where the fluid is in its DB, else Clausius-Clapeyron from Tb(1 atm) + Trouton Hvap (labeled per lead). Report-only design axis; 'pressure-tuned gains' = leads that enter a use case's Tb band at a non-1-atm pressure. Estimates, not measured.