1. 2. A fuel is burned with 70 percent theoretical air. This is equivalent to a)

Question

1.

2.      A fuel is burned with 70 percent theoretical air. This is equivalent to

a)      30 % excess air

b)      70 % excess air

c)      30 % deficiency of air

d)     70 % deficiency of air

3.      Gas turbine cycle with generator improves

a)      Thermal efficiency

b)      Work ratio

c)      Avoids pollution

d)     None of these

4.      Which of the following is the correct statement

a)      For a given compression ratio, both Otto and Diesel cycles have the same efficiency

b)      For a given compression ratio, Otto cycle is more efficient than Diesel cycle

c)      For a given compression ratio, Diesel cycle is more efficient than Otto cycle

d)     The efficiency of Otto or Diesel cycle has nothing to do with compression ratio

5.      A point, in a compressible flow where the fluid velocity is zero is called

a)      Critical point

b)      Vena contracta

c)      Stagnation point

d)     None of these

6.      The pressure at the stagnation point is always

a)      High

b)      Low

c)      Constant

d)     None of the above

7.      In vapor compression refrigeration system, a throttle valve is used in place of an expander because

a)      It considerably reduce the mass of the system

b)      It improve the COP as the condenser is small

c)      The positive work in isentropic expansion of liquids is very small

d)     It leads to a significant cost reduction

8.      The undesirable property of a refrigerant is

a)      Non-toxic

b)      Non-flammable

c)      Non-explosive

d)     High boiling point

9.      Consider a simple ideal Rankine cycle with a fixed condenser pressure. If the boiler pressure is raised while the turbine inlet temperature is held constant, (select the correct statement)

a)      the turbine work output will decrease.

b)      the amount of heat rejected will increase.

c)      the moisture content at turbine exit will increase.

d)     the cycle efficiency will decrease.

10. Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures and turbine inlet temperature. If the cycle is modified with ideal regeneration that involves one closed feed water heater, (select the correct statement per unit mass of steam flowing through the boiler)

a)      the turbine work output will increase.

b)      the amount of heat input will decrease.

c)      the amount of heat rejected will increase.

d)     the quality of steam at turbine exit will decrease.

11. The increase in entropy of a system represents

a)      Increase in availability of energy

b)      Increase in temperature

c)      Decrease in pressure

d)     Degradation of energy

12. The entropy %u2026%u2026%u2026%u2026%u2026%u2026 in irreversible cycle process

a)      remains constant

b)      decreases

c)      increases

Explanation / Answer

2) c

3) a

4) b

Efficiency of Otto cycle is given by

=1- Qr/Qs

Where, Qs is the heat supplied in the Otto cycle and is equal to the area under the curve

on the T-s diagram ]. The efficiency of the Diesel cycle is given by,

=1 - Qr/Qs'

Where Q%u2019s is heat supplied in the Diesel cycle and is equal to the area under the curve

' on the T-s diagram [. From the T-s diagram it is clear that

Qs > Q%u2019s i.e., heat supplied in the Otto cycle is more than that of the Diesel cycle. Hence,

it is evident that, the efficiency of the Otto cycle is greater than the efficiency of the

Diesel cycle for a given compression ratio and heat rejection.

5) c

6) a

7) c

8) d

9)

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