the ammonia, determine the work and heat transfer, each in kJ/kg. A rigid, well-

Question

the ammonia, determine the work and heat transfer, each in kJ/kg. A rigid, well-insulated container with a volume of 2 ft3 holds 0.12 lb of ammonia initially at a pressure of 20 lbf/in.2 The ammonia is stirred by a paddle wheel, resulting in an energy transfer to the ammonia with a magnitude of 1 Btu. For the ammonia, determine the initial and final temperatures, each in degree R, and the final pressure, in lbf/in.2 Neglect kinetic and potential energy effects. Water contained in a piston-cylinder assembly, initially at

Explanation / Answer

This problem is all about interpolation off of a chart for superheated ammonia vapor. Below is basically all the interpolation work pulled from table A-15E from Fundamentals of Engineering Thermodynamics 6th edition.

Initial state:

P1 = 20 lbf/in2

V = 2/.12 = 16.667 ft3/lb (this remains constant because the container is fixed)

Interpolate for u1 and T1 via known specific volume:

T1 = (80 – 70)*(16.667 – 16.436)/(16.765 – 16.436) + 70 + 460 = 536.69oR
U1 = (595.26 – 591.23)*(16.667 – 16.436)/(16.765 – 16.436) + 594.06 Btu/lb

Now we add 1 Btu to .12 lb ammonia:

u2 = u1 + ?E/m = 594.06 + 1/.12 = 602.39 Btu/lb

Now we can interpolate for the final temperature and pressure via known specific energy:

T2 = (110 – 90)*(602.393 – 599.30)/(606.28 – 599.30) + 90 + 460 = 558.86oR
P2 = (30 – 20)*(602.393 – 599.30)/(606.28 – 599.30) + 20 = 24.43 lbf/in2

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