Question Set 20

Question No. 1

State all the laws of Thermodynamics?

Answer:

Generally thermodynamics contains four laws;

(A) Zeroth law: deals with thermal equilibrium and establishes a concept of temperature.

(B) First law: throws light on concept of internal energy.

(C) Second law: indicates the limit of converting heat into work and introduces the principle of increase of entropy.

(D) Third law: defines the absolute zero of entropy.

Question No. 2

What is the difference between scavenging and supercharging?

Answer:

Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends. Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

Question No. 3

What are the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes?

Answer:

Isothermal, isobaric, isochoric, free expression, throttling and adiabatic processes respectively.

Question No. 4

Explain Second Law of Thermodynamics?

Answer:

The entropy of the universe increases over time and moves towards a maximum value.

Question No. 5

Compare Brayton Cycle and Otto Cycle?

Answer:

The heat addition and rejection processes in Otto cycle are of constant volume, whereas in Brayton cycle, they are of constant pressure.

Otto cycle is the ideal cycle for spark ignition engines.

Brayton cycle is the ideal cycle for gas power turbines.

Question No. 6

What is the importance of Thermodynamics?

Answer:

All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.

Question No. 7

How to Measure Temperature in Wet Bulb Thermometer?

Answer:

Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.

Question No. 8

In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and condenser pressure same, what will happen to dryness fraction of steam after expansion?

Answer:

It will decrease.

Question No. 9

Why entropy change for a reversible adiabatic process is zero?

Answer:

Because there is no heat transfer in this process.

Question No. 10

What is the purpose of Scrapper Ring?

Answer:

Scraps the excess lube oil from the cylinder walls. There by preventing oil from entering combustion zone.