A piston-cylinder device contains 12 kg of saturated vapor R-134a at 2.4 bar (St

Question

                    A piston-cylinder device contains 12 kg of saturated vapor R-134a at 2.4 bar (State 1). A 110V electric source supplies current to a resistor within the                     cylinder for 6 minutes and heat transfer of 300kJ occurs to the system. During these energy interactions, the pressure is maintained constat and the                     refrigerant is heated to 70 degrees C (State 2).                 

                    a) Calculate the current (A) supplied to the resistor.                 

                    b) Show the expansion process for R-134a on a P-v diagram. Label states, show property values, and indicate appropriate lines of constant temperature.

Please show all work!

                                     Thanks for any help you can give!

Explanation / Answer

b)

From R-134a properties,

For sat. vapor at 2.4 bar, we get v1 = 0.0839 m^3/kg, h1 = 247 kJ/kg

For P2 = P1 = 2.4 bar and T2 = 70 deg C we get v2 = 0.113 m^3/kg, h2 = 315 kJ/kg

Hence, P-v diagram will look like a straight horizontal line from right to left.

P1 = 2.4 bar

P2 = 2.4 bar

v1 = 0.0839 m3/kg

v2 = 0.113 m3/kg

Q = m*(h2 - h1)

Q = 12*(315-247) = 816 kJ

816 = 300 + V*I*t

816 = 300 + 110*I*(6*60)

I = 13.03 amp

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.