Basic Thermodynamics

A: A lines up with the evaporation process. As water flashes to steam, mass leaves but most impurities stay, so without a bleed the system walks toward higher chemical potential and fouling. B sounds right if you're thinking control theory, but pressure oscillations are handled by drum geometry and controls, not mandated blowdown. C mixes up thermal effectiveness with water chemistry; residence time doesn’t drift just because blowdown changes. D borrows a real concern from metallurgy, yet the heat carried out in blowdown is tiny compared to furnace duty and doesn’t set metal temperature.

A: A addresses the physics directly: at 25 bar, Z and cp deviate enough that ideal assumptions overstate enthalpy change. B feels safe from a project-risk angle, but it hides a modeling error instead of fixing it and can cascade into oversizing. C jumps domains; isothermal compression is a limit case, not a sizing basis for a finite exchanger. D confuses thermodynamic non-ideality with frictional losses, which live in a different part of the model.

A: A comes from the math: 1 MW / 5 kg/s is 200 kJ/kg. Saturated vapor to 10 kPa has a latent heat on the order of 2,000 kJ/kg, so only a slice of that is used, leaving most vapor intact. B sounds intuitive if you focus only on pressure, but ignores the actual energy extracted. C forgets that any real work output must come from reducing vapor enthalpy, so some condensation is unavoidable. D overweights pressure ratio without tying it back to specific work.

A: A matches the symptom pattern. Non-condensables kill condensation coefficients without changing ΔP much, and the slow drift fits gas accumulation. B would usually show a gradual ΔP increase as well. C affects both heat transfer and pressure drop more abruptly once the valve position changes. D explains bad numbers, but not the real loss of duty observed in downstream equipment.