171. For a single stage impulse turbine with rotor diameter of 2 m and a speed of 3000 rpm when the nozzle angle is 20°, the optimum velocity of steam in m/s is

1. 1. 334

   
   
   

   2. 356

   
   
   

   3. 668

   
   
   

   4. 711

   
   
   

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1. View Hint View Answer Discuss in Forum

   u	=	cosα
   v1		2

   
   

   v1 =	2v
   	cosα

   
   

   =	2 × (πDN/60)	=	π × 3000
   	cosα		30 × cos20

   
   [v₁ = 668.6 m/s]

   Correct Option: C

   u	=	cosα
   v1		2

   
   

   v1 =	2v
   	cosα

   
   

   =	2 × (πDN/60)	=	π × 3000
   	cosα		30 × cos20

   
   [v₁ = 668.6 m/s]

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172. A steam turbine operating with less moisture is _____(more/less) efficiency and _____ (less/ more) prone to blade damage.

1. 1. more more, less

   
   
   

   2. less , more more,

   
   
   

   3. Less,

   
   
   

   4. Less, more more, less

   
   
   

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1. View Hint View Answer Discuss in Forum

   Less, more more, less

   Correct Option: D

   Less, more more, less

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173. Velocity compounded steam turbine known as _____ (curtis/rateau) turbine uses the principle of converting entire _______(pressure/velocity) energy before entering the first stage runner itself.
     

1. 1. Curtis

   
   
   

   2. Curtis Pressure

   
   
   

   3. Pressure

   
   
   

   4. Pressure Curtis

   
   
   

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1. View Hint View Answer Discuss in Forum

   Curtis Pressure

   Correct Option: B

   Curtis Pressure

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174. An economizer in a steam generator performs the function of

1. 1. Preheating the combustion air

   
   
   

   2. Preheating the feed water

   
   
   

   3. Preheating the input fuel

   
   
   

   4. Raising the temperature of steam

   
   
   

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1. View Hint View Answer Discuss in Forum

   Economiser is used for preheating the feed water heater using exhaust fuel gasses.

   Correct Option: B

   Economiser is used for preheating the feed water heater using exhaust fuel gasses.

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175. A gas turbine with air as the working fluid has an isentropic efficiency of 0.70 when operating at a pressure ratio of 3. Now, the pressure ratio of t he t ur bi ne i s i ncr eased t o 5, whi l e maintaining the same inlet conditions. Assume air as a perfect gas with specific heat ratio γ = 1.4. I f the specific work output remains the same for both the cases, the isentropic efficiency of t he t ur bi ne at t he pr essur e r at i o of 5 is___(round off to two decimal places).

1. 1. 5

   
   
   

   2. 7

   
   
   

   3. 0.51

   
   
   

   4. 1

   
   
   

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1. View Hint View Answer Discuss in Forum

   η = 0.7, (r_ρ)₁ = 3
   η₂ =? (r_ρ)₂ = 5
   r = 1.4
   (W_T)₁ = (W_T)₂
   As Inlet condition same,
   
   Here,
   

   η1 =	h1 - h2	=	h1 - h2
   	T1 - T2s

   
   

   =	h1 - h2
   	T1 - T2s	T1 - T2s/x

   
   

   η1		T1 -	T1		=	η2		T1 -	T2
   			x						y

   
   

   0.7		1 -	1		=	η2		1 -	1
   			(3)2/7						(5)2/4

   
   η₂ = 0.51
   Hence, Isentropic efficiency of turbine is 0.51.

   Correct Option: C

   η = 0.7, (r_ρ)₁ = 3
   η₂ =? (r_ρ)₂ = 5
   r = 1.4
   (W_T)₁ = (W_T)₂
   As Inlet condition same,
   
   Here,
   

   η1 =	h1 - h2	=	h1 - h2
   	T1 - T2s

   
   

   =	h1 - h2
   	T1 - T2s	T1 - T2s/x

   
   

   η1		T1 -	T1		=	η2		T1 -	T2
   			x						y

   
   

   0.7		1 -	1		=	η2		1 -	1
   			(3)2/7						(5)2/4

   
   η₂ = 0.51
   Hence, Isentropic efficiency of turbine is 0.51.

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