Basic Of Thermodynamics | Interview Question and Answers

Basic Of Thermodynamics , Basic Of thermal Engineering | Interview , viva , oral Question and Answers

1. Define thermodynamic system.

A thermodynamic system is defined as a quantity of matter or a region in space, on which the analysis of the problem is concentrated.

2. Name the different types of system.

1. Closed system (only energy transfer and no mass transfer)
2. Open system (Both energy and mass transfer)
3. Isolated system (No mass and energy transfer)

3. Should the automobile radiator be analyzed as a closed system or as an open system? Explain.

Automobile radiator system is analyzed as closed system. In this no mass (water) cross the boundary.

4. Define thermodynamic equilibrium.

If a system is in Mechanical, Thermal and Chemical Equilibrium then the system is in Thermodynamically equilibrium.

(or)
If the system is isolated from its surrounding there will be no change in the macroscopic property, then the system is said to exist in a state of thermodynamic equilibrium.

5. What do you mean by quasi-static process?

Infinite slowness is the characteristic feature of a quasi-static process. A quasi-static process is that a succession of equilibrium states. A quasi-static process is also called as reversible process.

6. Differentiate between point function and path function.

7. Name and explain the two types of properties.

The two types of properties are intensive property and extensive property.

Intensive Property: It is independent of the mass of the system. Example: pressure, temperature, specific volume, specific energy, density.

Extensive Property: It is dependent on the mass of the system. Example: Volume, energy. If the mass is increased the values of the extensive properties also Increase.

8. Explain homogeneous and heterogeneous system.

The system consist of single phase is called homogeneous system and the system consist of more than one phase is called heterogeneous system.

9. What is a steady flow process?

Steady flow means that the rates of flow of mass and energy across the control surface are constant.

10. Prove that for an isolated system, there is no change in internal energy.

In isolated system there is no interaction between the system and the surroundings. There is no mass transfer and energy transfer.

According to first law of thermodynamics as dQ = dU + dW; dU = dQ –dW; dQ = 0, dW = 0,
Therefore dU = 0 by integrating the above equation U = constant, therefore the internal energy is constant for isolated system.

11. Indicate the practical application of steady flow energy equation.

1. Turbine, 2. Nozzle, 3. Condenser, 4. Compressor.

12. Define system.

It is defined as the quantity of the matter or a region in space upon which we focus attention to study its property.

13. Define cycle.

It is defined as a series of state changes such that the final state is identical with the initial state.

14. Explain Mechanical equilibrium.

If the forces are balanced between the system and surroundings are called Mechanical equilibrium

15. Explain Chemical equilibrium.

If there is no chemical reaction or transfer of matter form one part of the system to another is called Chemical equilibrium.

16. Explain Thermal equilibrium.

If the temperature difference between the system and surroundings is zero then it is in Thermal Equilibrium.

17. Define Zeroth law of Thermodynamics.

When two systems are separately in thermal equilibrium with a third system then they themselves is in thermal equilibrium with each other.

18. What are the limitations of first law of thermodynamics?

1. According to first law of thermodynamics heat and work are mutually convertible during any cycle of a closed system. But this law does not specify the possible conditions under which the heat is converted into work.
2. According to the first law of thermodynamics it is impossible to transfer heat from lower temperature to higher temperature.
3. It does not give any information regarding change of state or whether the process is possible or not.
4. The law does not specify the direction of heat and work.

19. What is perpetual motion machine of first kind?

It is defined as a machine, which produces work energy without consuming an equivalent of energy from other source. It is impossible to obtain in actual practice, because no machine can produce energy of its own without consuming any other form of energy.

20. Define: Specific heat capacity at constant pressure.

It is defined as the amount of heat energy required to raise or lower the temperature of unit mass of the substance through one degree when the pressure kept constant. It is denoted by Cp.

21. Define: Specific heat capacity at constant volume.

It is defined as the amount of heat energy required to raise or lower the temperature of unit mass of the substance through one degree when volume kept constant.

22. Define the term enthalpy?

The Combination of internal energy and flow energy is known as enthalpy of the system. It may also be defined as the total heat of the substance.

Mathematically, enthalpy (H) = U + pv KJ)
Where, U – internal energy
p – Pressure
v – Volume
In terms of Cp& T → H = mCp (T2-T1) KJ

23. Define the term internal energy

Internal energy of a gas is the energy stored in a gas due to its molecular interactions. It is also defined as the energy possessed by a gas at a given temperature.

24. What is meant by thermodynamic work?

It is the work done by the system when the energy transferred across the boundary of the system. It is mainly due to intensive property difference between the system and surroundings.

25. What is meant by reversible and irreversible process?

A process is said to be reversible, it should trace the same path in the reverse direction when the process is reversed. It is possible only when the system passes through a continuous series of equilibrium state.

27. Why does free expansion have zero work transfer?

In free expansion there is no external force acting on the gas so that the energy given to the gas can be utilized to produce heat and to overcome the repulsions between the gases which does not happen in free expansion therefore there is no work transfer.

28. Distinguish between ‘Macroscopic energy’ and ‘Microscopic energy’.

Statistical Thermodynamics is microscopic approach in which, the matter is assumed to be made of numerous individual molecules. Hence, it can be regarded as a branch of statistical mechanics dealing with the average behaviour of a large number of molecules.

Classical thermodynamics is macroscopic approach. Here, the matter is considered to be a continuum without any concern to its atomic structure.

29. Show that the energy of an isolated system remains constant.

A system which does not exchange energy with its surroundings through work and heat interactions is called an isolated system. That is for an isolated system dW = 0 and dQ=0.

The first law of thermodynamics gives dE = dQ – dW

Hence, for an isolated system, the first law of thermodynamics reduces to dE = 0 or E2 = E1. In other words, the energy of an isolated thermodynamic system remains constant.

30. What are the conditions for steady flow process?

No properties within the control volume change with time.
That is mcv = constant Ecv = constant
No properties change at the boundaries with time. Thus, the fluid properties at an inlet or exit will remain the same during the whole process. They can be different at different opens.
The heat and work interactions between a steady-flow system and its surroundings do not change with time.