A heat exchanger is used to reduce the temperature of sea water from 25 C to -15C at a rate of 20kg/s. The heat that is removed from the sea water is discarded to the atmosphere at 30C. If the efficiency is 0.27, what is the power requirement for the heat exchanger? Assume Cp for sea water is 3.5kJ/kgCI was thinking this is probably an open energy balance, Wdot=m*deltaH-Qdot, but how do we find Q?
Umm, first, if you reduce the temperature of seawater to -15C, you have ice. Yes, seawater freezes at a lower temperature than fresh water but nothing like -15C. Unless you are talking maybe about the Dead Sea. Q = 20 kg/sec * 3.5 kJ/kgC * 40C = 2800 kJ/sec = 2800 kW I don't know what is intended by the comment If the efficiency is 0.27 in terms of the heat exchanger.
