Answer to Question #128455 in Mechanical Engineering for Afra Syab

Question

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

Answer 1

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

Solution

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