Saturated liquid water at 2000 kPa enters a throttling valve at 5 m/s. The stream exits the throttling valve at 400 kPa, at a velocity of 25 m/s.

Question

(a) Determine the quality of the exiting saturated mixture.
(b) Using your model of a throttling device, plot the exit quality for the same inlet conditions and same outlet pressure, but for exit vel°Cities ranging from 1 m/s to 100 m/s.

(a) Given: P1 = 2000 kPa; x1 = 0 (saturated liquid); V1 = 5 m/s; P2 = 400 kPa; V2 = 25 m/s
Water (Take State 1 as the inlet, State 2 as the outlet.)
Assume: Q?=W?=0. For a throttling valve, assume steady-state, steady-flow, single-inlet, single-outlet flow, with ?PE = 0 (we are considering the impact of changes in kinetic energy)

What will be an ideal response?

Answer 1

With these assumptions, the First Law for open systems reduces to



For water, h1 = 908.62 kJ/kg

Solving for h2 = 908.32 kJ/kg

This corresponds, at P2 to x2 = 0.142

(b) For the range of exit velocities, the exit quality is



Note: There is very little impact on the exit quality of the exit velocity (and so changes in kinetic energy can usually be ignored for throttling valves).