Question

Refrigerant-134a enters the expansion valve of a refrigeration system at 130 psia as a saturated liquid and leaves at 20 psia. Determine the temperature and internal energy changes across the valve. Use data from the steam tables.

Answer 1

Answer:

The answer is "$\bold{-98.079 ^{\circ} F \ \ and \ -2.6686 \frac{Btu}{lbm}}$"

Explanation:

Calculating the value from the property tables of R-134a,

At 130 psia:

$T_1= 95.64^{\circ} \ F$

Internal energy:

$u_1= 43.258 \ \frac{Btu}{lbm}$

At 20 psia:

$T_2= -2.43^{\circ} \ F$

Internal energy

$u_2= 40.5894 \ \frac{Btu}{lbm}$

 Calculating temperature:

$\to \Delta T= T_2-T_1$

          $= -2.43-95.64\\\\= -98.079^{\circ} \ F$

  Calculating  internal energy:

$\to \Delta u= u_2-u_1$

          $= 40.5894 -43.258 \\\\=-2.6686 \ \frac{Btu}{lbm}$