Conversion of Water to Steam

Water flows through a horizontal coil heated from outside. During its passage, it changes state from liquid at 200 kPa and 80oC to vapor at 100 kPa and 125oC. The entering and exit velocities are 3 m/s and 200 m/s respectively. Determine the heat transferred through the coil per unit mass of water. Hinlet = 334.9 kJ/kg; Houtlet = 2726 kJ/kg.

Calculations:

For the steady flow process, the first law is written as

DH + Du2/2 + gDz = Q + Ws

since there is no shaft work, Ws = 0

and flow is horizontal, Dz = 0

Therefore,

DH + Du2/2 = Q

substituting for the quantities,

(2726 - 334.9) x 1000 + (2002 - 32)/2 = Q (in terms of J/kg)

Q = 2411.1 kJ/kg

Heat transferred through the coil per unit mass of water = 2411.1 kJ