Saturated liquid R-134a at 120 psia enters a throttling valve. The R-134a exits the throttling valve at a pressure of 30 psia. Assume that there is no change in velocity.

Question

(a) Determine the exit quality of the R-134a.
(b) Using your model of a throttling device, determine the exit quality of the R-134a for exit pressures ranging from 20 psia to 100 psia.

Given: P1 = 120 psia; x1 = 0 (saturated liquid); P2 = 30 psia
R-134a (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 ?KE = ?PE = 0

What will be an ideal response?

Answer 1

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

h1=h2

For R-134a: h1 = 40.91 Btu/lbm

Therefore, h2 = 40.91 Btu/lbm

At 30 psia, hf = 16.31 Btu/lbm, hg = 103.96 Btu/lbm

So, x2=h2?h1/hg?hf = 0.281

(b) For the pressure range given:



range given:

The lower the exit pressure, the higher the quality (more R-134a is vaporized with the larger pressure drop).