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posted by  TheodoreNg on 11/5/2009 11:29:47 PM  |  status: Closed  |  Earned Karma: 220

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Course Textbook Chapter Problem Needs by
Thermodynamics Fundamentals of Thermodynamics (7th) by Sonntag, Borgnakke 9 109P 11/6/2009 at 7:00:00 AM
Question Details:
A one meter cubed rigid tank contains 100 kg of R-410a at ambient temperature, 15 degrees C.  A valve on top of the tank is opened, and saturated vapor is throttled to ambient pressure, 100 kPa an flows to a collector system.  During the process, the temperature in the tank remains at 15 degrees C.  The valve is closed when no more liquid remains inside.  Calculate the heat transfer to the tank and the total entropy generation in the process.

I realize how to calculate Sgen but i need help starting the calculation for Q (heat transfer).  What equations do we need?  Please help.  I rate high.  Thank you for your time and expertise. 

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posted by harry9(MNK) on 11/6/2009 7:39:25 AM  |  status: Live
Asker's Rating: Lifesaver   
Response Details:
Continuity Equation: m2 - m1 = − me

Energy Equation: m2u2 - m1u1 = Q − mehe

Entropy Equation: m2s2 - m1s1 = Q/TSUR − mese + Sgen

 v1 = V1/m1 => 1/100 = 0.000812 + x1* 0.02918

=>x1 = 0.3149,

u1 = 61.88 + 0.3149 × 169.47 = 115.25 kJ/kg

s1 = 0.2382 + 0.3149 × 0.668 = 0.44855

 he = hg = 255.0 kJ/kg

 v2 = vg = 0.02999,

 u2 = ug = 231.35,

 s2 = 0.9062 kJ/kg K

 he = 255.0,

 Pe = 100 kPa

 Te = -4.7°C, se = 1.0917

m2 = 1/0.02999 = 33.34 kg;

me = 100 - 33.34 = 66.66 kg

Q = m2u2 - m1u1 + mehe

=>Q= 33.34×231.35 - 100×115.25 + 66.66×255

=>Q = 13,186 kJ

ΔScv = m2s2 - m1s1 = 33.34(0.9062) - 100(0.44855) = -14.6

ΔSSUR = − Q/TSUR + mese = -13186/288.2 + 66.66(1.0917) = 27

Sgen =  -14.6 + 27

Sgen = 12.4 kJ/K
harry
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