Open-Cycle OTEC Flash Evaporator

Ocean Water Temperatures

Warm surface intake T_warm 28 °C

Cold deep-water intake T_cold 6 °C

Flash Chamber

Vacuum set-point T_sat 20 °C

Warm-water flow rate ṁ_w 200 kg/s

Lower T_sat = deeper vacuum → more flashes to steam, but a bigger pressure drop costs more pump power to hold. Find the sweet spot.

Live Output

Flash fraction x—

Net power P_net—

Fresh water yield—

How it works

Unlike closed-cycle OTEC (which boils a separate working fluid like ammonia), open-cycle OTEC flash-evaporates the warm seawater itself. Pumped into a chamber held below atmospheric pressure, a small fraction of the water instantly boils because its saturation temperature there is lower than its actual temperature — no external heat input needed, just the vacuum.

Flash fraction:  x = c_p(T_warm − T_sat) / h_fg(T_sat)
Turbine work:    w_t = η_t · h_fg(T_sat) · (T_sat − T_cond) / T_sat[K]
Turbine power:   P_turbine = x·ṁ_w · w_t
Net power:       P_net = P_turbine − P_pump(ṁ_w, T_warm−T_sat)

The low-pressure steam spins a turbine, then a surface condenser cools it with the cold deep-water stream — recovering it as salt-free desalinated fresh water, a real byproduct of open-cycle plants (this is exactly how NELHA's Hawaii demonstration plant produced both electricity and drinking water).

x is small on purpose — with only a ~20 °C surface-to-deep gradient, real OTEC flash fractions sit around 0.5–1.5%; the rising bubbles in the chamber are animated at an exaggerated rate purely so the mechanism is visible, but the flash-fraction readout itself is the exact computed value.
Vacuum set-point (T_sat) — a deeper vacuum (lower T_sat) flashes more water but shrinks (T_sat − T_cond), the turbine's driving temperature drop, while pump power keeps rising — the two effects trade off, so net power peaks at an intermediate vacuum, not the deepest one.
Turbine efficiency is fixed at η_t = 0.75 and the condenser approach temperature at T_cold + 2 °C, both typical engineering values, so the sliders isolate the thermodynamic trade-off rather than turbine hardware quality.

Warm intake water Flashed steam Condensed fresh water

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