The radiator of a steam system has a volume of 20 l and is filled with superheated water vapor at 200 kpa and 150 oc. at t = 0, both the inlet and outlet valves to the radiator are closed. after a while the temperature of the steam drops to 40 oc as a result of heat transfer to the room air. determine the entropy change of the steam during this process.

Δs = 0.133 KJ/.K

Explanation:

Given that

V= 20 L = 0.02 m³

At P₁= 200KPa and T₁=150 C :

v₁=0.93 m³/kg

s₁=7.2 KJ/kg.K

At  T₂=40 C :

v₁ = v₂

vf= 0.001 m³/kg

vg = 19.51 m³/kg

v₂ = vf + x(vg-vf)

0.93 = 0.001 + x(19.51 - 0.001)

x=0.047

s₂ = sf + x(sg-sf)

s₂ = 0.57 + 0.047(7.638) KJ/kg.K

s₂ = 0.93 KJ/kg.K

Δs= s₁ - s₂

Δs= 7.2 - 0.93 =6.2 KJ/kg.K

m=V/v₁

m=0.02/0.93 = 0.021 kg

Δs = 0.021 x 6.2 = 0.133 KJ/.K

Δs = 0.133 KJ/.K

answer: 500 wph.

explanation:

the warning light flashes for a second or two when the engine starts. if it stays on, there's must be something wrong with the coolant. you should never dare to continue driving when the light is on. pull over as soon as possible and shut the engine off.

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