Answer to Question #128455 in Mechanical Engineering for Afra Syab

Question #128455
Freon 12 is contained in a sealed glass container at 50°C. As it is cooled, vapor droplets arc noted condensing on the sidewalls at 20°C. Find the original pressure in the container. Arts. 650 kPa
Expert's answer

At state 1

Temperature = T1 = 500C

Pressure = P1 = ?kpa

Specific volume = V1 = ? m3/kg

At state 2

Temperature = T2 = 200C

Pressure = P2 = ?kpa

Specific volume = V2 = ? m3/kg


Control volume = fixed volume (v) and fixed mass (m) at 500C

Process- cooling 200C at constant volume we assume saturated process

At state 2

v2 at 200C

So, v2 = 0.0308m3/kg

At state 1

v1 = v2 = 0.0308m3/kg

From super heated table of R-12

at pressure of 625 kpa volume is 0.0305 m3/kg

at pressure of 600kpa volume is 0.0489 m3/kg

so interpolating between those two points we will get pressure at state 1

i.e P1

p1 = 625 + {0.0489/0.0305 -0.0308/0.0305} (625-600)

P1 = 649.789Kpa = 650kpa

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