Question

Water flows through a horizontal coil heated from the outside by high temperature flue gases. as it passes through the coil water changes state from liquid at 200 kpa and 80 c to vapor at 100 kpa and 125
c. its entering velocity is 3 m s-1 and its exit velocity is 200 m s-1. determine the heat transferred through the coil per unit mass of water. enthalpies of the inlet and outlet streams are 334.9 and 2,726.5 kj kg-1, respectively.

Answer 1

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

 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,

 (2726.5 - 334.9) x 1000 + (200^2 - 3^2)/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