1) A rigid tank contains 2 kg of 134a refrigerant at 800 kPa and 120°C. Determine tank volume and total internal energy.

V = 0.07525 [m³]

U  = 655.74 [kJ]

Explanation:

To solve this problem we must use the superheated refrigerant table for refrigerant 134a. The attached image shows the specific volume and specific internal energy values for a pressure of 800 [kPa] and a temperature of 120 [°C].

m = mass =2 [kg]

the specific volume = v = 0.037625 [m³/kg]

The volume of the tank can be found using the following expression:

V = v*m

V = 0.037625*2 = 0.07525 [m³]

The Specific internal energy = u = 327.87 [kJ/kg]

U = u*m

U = 327.87*2 = 655.74 [kJ]

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form