Question Set 61

1. Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon ?

Ans: Liquid hydrogen has higher burning velocity.

2. Why axial flow compressor is preferred for gas turbines for aeroplanes ?

Ans: Because it has low frontal area.

3. What is the effect of inter cooling in gas turbines ?

Ans: It decreases thermal efficiency but increases net output.

4. Why iso-octane is chosen as reference fuel for S.I. engines and allotted 100 value for its octane number ?

Ans: Iso-octane permits highest compression without causing knocking.

5. Why thermal efficiency of I.C. engines is more than that of gas turbine plant ?

Ans: In I.C. engine maximum temperature attained is higher than in gas turbine.

6. Which are the reference fuels for knock rating of S.I. engines ?

Ans: n-heptane and ISO-octane.

7. When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle ?

Ans: Temperature increases and pressure decreases.

8. Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called ?

Ans: Intensive properties.           

9. The amount of radiation emitted per scm per sec is called .... ?

Ans: Emissive power.

10. In convection heat transfer, if heat flux intensity is doubled then temperature

difference between solid surface and fluid will ?

Ans: Get doubled.