Lec31 - Refrigerant 22 From CV around Expansion valve...

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ME 200: Thermodynamics I Lecture 31: Applications of rate balance to open systems Sections 6.10.2 Problems: SP31; 6.99, 6.103, 6.109 Professor Hukam Mongia Office Hours: MWF 2:30 to 3:30 pm in ME 83 (Other times email for appointment) Email: [email protected] Phone: 765-494-5640 Course Website: https://engineering.purdue.edu/ME200 Course Secretaries: Diana Akers (ME 84) and Marilyn Morrison (ME 100) See Kul Inn (ME 189) about grading Homework Assignments 1
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2 Applications of rate balance to open systems Example 6.6: Steam Turbine Specific change in entropy: s 2 -s 1 ? h1=3230.9 kJ/kg s1 = 6.9212 kJ/kg.K h2=2676.1 kJ/kg s1 = 6.9212 kJ/kg.K KE and q can’t be neglected? 1 st Law
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4 Example 6.7: Verify the invention; Claims: W cv = 0, Q cv =0 0.6 lb 1.0 lb 0.4 lb Air: Ideal gas w/ c p = 0.24 Btu/lb. o R Is the 1 st Law of Thermo satisfied? c p [(T1-Tref)-0.4(T2-Tref)-0.6(T3-Tref)] =c p (70-0.4x175-0)=c p (70-70)=0 Yes.
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5 What is s 3 -s 1 ? Inventor’s claims are verified by the 1 st and 2 nd laws of thermodynamics.
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6 Example 6.8 Entropy Production in Heat Pump Components
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Unformatted text preview: Refrigerant 22 From CV around Expansion valve Refrigerant 22 Tables A-7 thru A-9 Liquid Condition 1 Condition 2 Condition 3 Condition 4 T, o C p, bar T, o C p, bar T, o C p, bar T, o C p, bar x?-5 3.5 75 14 28 14-10.39 3.5 0.216 249.75 0.9572 294.175 0.98225 79.05 0.2936 79.079 0.3078 h, kJ/kg s, kJ/kg K h, kJ/kg s, kJ/kg K h, kJ/kg s, kJ/kg K h, kJ/kg s, kJ/kg K Approximations made at #3 for h & s-Ignored effect of pressure on h & s h 3 =h 4 Adiabatic 7 Entropy production, kW/K for compressor, condenser and expansion valve? Recommend performance improvements to reduce energy consumption. Apply 1 st law steady-state to condenser to calculate the refrigerant flow rate: Assume ideal gas for air to calculate air flow rate. Calculate : s 6-s 5 : 8 Apply 2 nd Law to compressor: Apply 2 nd Law to expansion valve: Which components we should improve from thermal point of view? Any other considerations?...
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Lec31 - Refrigerant 22 From CV around Expansion valve...

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