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
110 V electric source supplies current to a resistor within the cylinder for 6 minutes and
heat transfer of 300 kJ occurs to the system. During these energy interactions, the
pressure is maintained constant and the refrigerant is heated to 70?C (State 2).

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

Answers: (a) 13.5 A; (b) Not attached

Explanation / Answer

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.