6. Steam enters a well insulated turbine and expands isentropically throughout. At an intermediate pressure, 20 percent of the mass is extracted for process heating and the remaining steam expands isentropically to 9 kPa.
   Inlet to turbine: P = 14 MPa, T = 560°C,
   h = 3486 kJ/kg, s = 6.6 kJ/(kgK)
   Intermediate stage: h = 276 kJ/kg
   Exit of turbine: P = 9 kP_a, h_f = 174 kJ/kg,
   h_g = 2574 kJ/kg, s_f = 0.6 kJ/(kgK), s_g = 8.1 kJ/(kgK)
   If the flow rate of steam entering the turbine is 100 kg/s, then the work output (in MW) is____.

1. 1. 125MW

   
   
   

   2. 125.56 MW

   
   
   

   3. 129.56 MW

   
   
   

   4. 525.56 MW

   
   
   

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1. View Hint View Answer Discuss in Forum

   h₁ = 3486 kJ/kg
   h₂ = 2776 kJ/kg
   s₁ = s₃ = 6.6
   6.6 = .6 + x(0.1 – .6)
   x = 0.8
   
   = 2094 kJ/kg
   w = (3486 – 2776) + .8 (2776 – 2094)
   = 1255.6 kJ/kg = 125.56 MW

   Correct Option: B

   h₁ = 3486 kJ/kg
   h₂ = 2776 kJ/kg
   s₁ = s₃ = 6.6
   6.6 = .6 + x(0.1 – .6)
   x = 0.8
   
   = 2094 kJ/kg
   w = (3486 – 2776) + .8 (2776 – 2094)
   = 1255.6 kJ/kg = 125.56 MW

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7. For reversible adiabatic compression in a steady flow process, the work transfer per unit mass is

1. 1. ∫ pdv

   
   
   

   2. ∫ vdp

   
   
   

   3. ∫ Tds

   
   
   

   4. ∫ sdT

   
   
   

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1. View Hint View Answer Discuss in Forum

   	W	∫vdp		for flow process
   	m

   Correct Option: B

   	W	∫vdp		for flow process
   	m

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8. A mass m of a perfect gas at pressure p₁ and volume V₁ undergoes an isothermal process. The final pressure is p₂ and volume is V₂. The work done on the system is considered positive. If R is the gas constant and T is the temperature, then the work done in the process is

1. 1. p₁V₁ In V₂/V₁

   
   
   

   2. –p₁V₁ In ρ/ρ₂

   
   
   

   3. –mRT In V₂/V₁

   
   
   

   4. –mRT In ρ/ρ₂

   
   
   

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1. View Hint View Answer Discuss in Forum

   Wiso = p1V1 in =	V2	= mRT In	V2	= mRT In	p1	= p1v1 In	p1
   	V1		V1		p2		p2

   Correct Option: B

   Wiso = p1V1 in =	V2	= mRT In	V2	= mRT In	p1	= p1v1 In	p1
   	V1		V1		p2		p2

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9. Air is held inside a non-insulated cylinder using a piston (mass M = 25 kg and area A = 100 cm²) and stoppers (of negligible area), as shown in the figure. The initial pressure P₁ and temperature T₁ of air inside the cylinder are 200 kPa and 400° C₁ respectively, The ambient pressure P_∞ and temperature T_∞ are 100 kPa and 27° C respectively. The temperature of the air inside the cylinder (°C) at which the piston will begin to move is ________(correct to two deeimal places).
   

1. 1. T² = 520.03 °C

   
   
   

   2. T² = 150.03 °C

   
   
   

   3. T² = 146.03 °C

   
   
   

   4. T² = 6.03 °C

   
   
   

   5. T² = 14.03 °C

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   

   Pin = Pamb +	mg	= 100 +	25 × 4.81	× 10-3
   	A		100 × 10-4

   
   P₂ = 124.525
   

   P1	=	P2
   T1		T2

   
   

   Correct Option: C

   
   

   Pin = Pamb +	mg	= 100 +	25 × 4.81	× 10-3
   	A		100 × 10-4

   
   P₂ = 124.525
   

   P1	=	P2
   T1		T2

   
   

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10. Steam enters a turbine at 30 bar, 300°C (u = 2750 kJ/kg, h = 2993 kJ/kg) and exits the turbine as saturated liquid at 15 kPa (u = 225 kJ/kg, h = 226 kJ/kg). Heat loss to the surrounding is 50 kJ/kg of steam flowing through the turbine. Neglecting changes in kinetic energy and potential energy, the work output of the turbine (in kJ/kg of steam) is______.

1. 1. 1417 kJ/kg

   
   
   

   2. 2717 kJ/kg

   
   
   

   3. 2728 kJ/kg

   
   
   

   4. 2564 kJ/kg

   
   
   

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1. View Hint View Answer Discuss in Forum

   Work output = (2993 – 226.50) kJ/kg = 2717 kJ/kg

   Correct Option: B

   Work output = (2993 – 226.50) kJ/kg = 2717 kJ/kg

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