0.94 lbm of water fills a container whose volume is 1.94 ft3. The pressure in the container is 100 psia. Calculate the total internal energy and enthalpy in the container. Use data from the steam tables. The total internal energy in the container is 280.29 Btu. The enthalpy in the container is 280.59 Btu.

The total internal energy is 280.17 Btu.

The enthalpy is 280.54 Btu

Explanation:

P = 100 psia = 100/14.5 = 6.897 bar

Using the steam table, the internal energy at 6 and 7 bar are 669 and 696 kJ/kg respectively.

The internal energy at 6.897 bar is obtained by interpolation

P. U

6. 669

6.897. y

7. 696

6.897-6/7-6 = y-669/696-669

0.897×27 = y-669

y = 669+24.219 = 693.219 kJ/kg

Mass of container = 0.94 lbm = 0.94×0.45359 = 0.4263746 kg

Total internal energy = 693.219 kJ/kg × 0.4263746 kg = 295.6kJ = 295.6/1.05506 = 280.17 Btu

Enthalpy at 6.897 bar = 694.219 kJ/kg × 0.4263746 kg = 295.99 kJ = 295.99/1.05506 = 280.54 Btu

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