Saturated water with a quality of 0.25 and a temperature of 300°F enters an uninsulated diffuser at a velocity of 510 ft/s. The mass flow rate is 5.2 lbm/s.

Question

(a) If the water is to exit as saturated water vapor at a temperature of 300°F, with a velocity of 25 ft/s, determine the necessary heat transfer rate.
(b) Using your model of a diffuser, determine the necessary heat transfer rates for the flow to exit as a saturated substance with qualities ranging from 0.40 to 1.0.
(c) Using your model of a diffuser, determine the necessary heat transfer rates for the flow to exit as a saturated vapor at 300°F, with exit velocities ranging from 0 ft/s to 300 ft/s.

Given: Water: x1 =0.25; T1 = 300°F; V1 = 510 ft/s; x2 = 1.0; T2 = 300oF; V2 = 25 ft/s;m?=5.2 lbm/s
What will be an ideal response?

Answer 1

For a diffuser, assume steady –state, steady-flow single-inlet, single-outlet flow, and assume that W?=?pe=0

These assumptions result in the first law being (State 1 is inlet, State 2 is outlet)



Finding steam properties: h1 = 497.31 Btu/lbm; h2 = 1179.96 Btu/lbm



(Substantial heat transfer is necessary to complete boiling the water)

(b)



(c)



Note the scale on the y-axis – the problem is dominated by the change in quality rather than the exit velocity.