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High is the default on every device. Low or ?q=low lowers resolution and shadows.
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The science
What an MSF plant does
Seawater is heated to the top brine temperature (TBT) in the brine heater and then flows through a cascade of chambers kept at falling pressure. In each stage a little of the hot brine flashes to vapour; the vapour condenses on a tube bundle that carries the cooler recycle brine and drips into a distillate tray. The condensing heat pre-heats the recycle, so the same heat is used again in every stage. The vapour fraction produced per stage is x = cp ΔTb / λ.
Stage model
For stage j the condensing vapour at Tv heats a tube stream F with effectiveness ε = 1 - exp(-UA/(F cp)). Balancing brine enthalpy release against tube gain gives Tv = [B cp(Tb,in - δ) + ε F cp Tc,in] / [B cp + ε F cp], heat Q = ε F cp (Tv - Tc,in) and distillate D = Q / λ(Tv). The brine leaves at Tb = Tv + δ where δ is the boiling-point elevation (BPE, grows with salinity and temperature) plus a non-equilibrium allowance of 0.6 K. Brine and tube temperatures relax with a 45 s lag per stage, so changes ripple down the cascade.
Mass, salt and energy
Makeup M = Bd + D; salt balance M Sf = Bd SN so the concentration factor is CF = 1 + D/Bd. Heater duty is Q = R cp (TBT - Tc,out,1) and the gained output ratio is GOR = D / msteam. The ideal many-stage limit of the distillate fraction is 1 - exp(-cp ΔT / λ), which the numerical checks compare against.
Scaling, fouling and gas
Alkaline scale (Mg(OH)2, CaCO3) and CaSO4 deposit faster above about 112 C and at high concentration factor; antiscalant slows it. The model lets tube cleanliness decay as exp((TBT - 100)/6) / (1 + 0.9 dose) and lowers UA accordingly. Non-condensable gas (air, CO2) blankets the condensers and reduces UA by up to 35 %; the vent ejector removes it at a steam and power cost.
Honest simplifications
Equal heat capacity for brine and tube streams, one lumped effectiveness per stage, no flashing-orifice hydraulics, no distillate flash-box recovery, constant overall coefficient (2.6 kW/m2/K clean), perfect demisting and instant salinity mixing in the pool. Pumping power is a simple head x flow estimate. Numbers are textbook-scale, not a design for a real plant.