How Much Water Boils Off?

Hi Guest,

You are probably not too wide of the mark in absolute terms ;but as the incoming stream of water is above boiling point why not either a) reduce the temperature to below 100C before turning it loose to atmosphere and recover some useful energy or b) take the pipe down to the bottom of the tank and therefore ensure that the whole tank is at 100C. This latter suggestion will not save you any energy but may reduce the amount of flash steam to be dealt with.

Heat recovery should be the primary objective if this is a continuous process.

Regards,

Massey.

I would say around 965 because the flash off of heat will release after only a few inches above the tank.

Your answer is correct.

Carry out a combined energy and mass balance using Steam Tables. All will become clear.

thank you for your reply. Could you explain a bit further what you mean.

thank you very much

mike

One fluid enters the flash boiling location. Two fluids leave it. So:

• Conserve matter at the flash boiling location: q₁ = q₂ + q₃, where q is a mass flowrate, ₁ is the incoming stream, ₂ is the outgoing liquid stream and ₃ is the outgoing vapour stream.
• Conserve energy at the flash boiling location: q₁h_f1=q₂h_f2 +q₃h_g3, where h is the enthalpy of the fluid ₁, ₂ and ₃ at each one's temperature and pressure, the figures for which can be had from Steam Tables; _f represents the liquid state and _g the vapour state.

Two equations in two unknowns? The rest is arithmetic.

thank you very much for your reply and the clear way you put it.

thank you

mike

thank you all for your replies.

mike