Thermodynamics_16 Marks.... 2nd Question

Question 2:

0.2m³ of air at 4 bar and 130^oC is contained in a system. A reversible adiabatic expansion takes place till the pressure falls to 1.02bar. The gas is then heated at constant pressure till enthalpy increases by 72.5KJ. Calculate work done and index of expansion if the above process is Polytrophic. Take C_p=1KJ/KgK     C _v=0.714KJ/Kg K..

Thermodyanamics_Important 2 Marks

1. Differentiate between open & closed system?

2.  Define zeroth law of thermodynamics ?

Zeroth law of thermodynamics states that when two systems are separately in thermal equilibrium with a third system, then they themselves are in thermal equilibrium with each other

3. Define quasi static process?

 The process is said to be quasi – static, it should proceed infinitesimally slow and follows continuous series of equilibrium states. Therefore, the quasi static, it should proceed infinitesimally slow and follows continuous series of equilibrium states. Therefore, the quasi static process may be an reversible process.

4. Define first law of thermodynamics?

First of thermodynamics states that when system undergoes a cyclic process the net heat transfer is equal to work transfer.

5. Define thermal Energy reservoir?

A thermal reservoir, a short-form of thermal energy reservoir, orthermal bath is a thermodynamic system with a heat capacity that is large enough that when it is in thermal contact with another system of interest or its environment, its temperature remains effectively constant.

6.Write down differences between refrigerator & heat pump?

Heat pump is a device which operating in cyclic process, maintains the temperature of a hot body at a temperature higher than the temperature of surroundings. A refrigerator is a device which operating in a cyclic process, maintains the temperature of a cold body at a temperature lower than the temperature of the surroundings.

7. Define Daltons law of  Partial Pressure?

The pressure of a mixture of gases is equal to the sum of the partial pressures exerted by individual gases if each one of them occupied separately in the total volume of the mixture at mixture temperature. p = p1 +p2+p3+….pk

8. Define latent heat of evaporation.

The amount of heat added during heating of water boiling point to dry saturated stage is called as latent heat of vaporization or enthalpy of vaporization or latent heat of steam.

9.Define dryness fraction of steam. (or) What is quality of steam?

It is defined as the ratio of the mass of the total steam actually present to the mass of the total steam.

Dryness fraction


10. Explain Joule Thompson effect?

a change in temperature of a thermally insulated gas when it is forced through a small hole or a porous material. For each gas there is a temperature of inversion above which the change is positive and below which it is negative. Also called: Joule-Kelvin effect.

11. Differentiate Control volume and Control mass?

The control mass system may be defined as a system having some mass and surrounded by a fixed boundary i.e. transfer of mass is not allowed but energy transfer may takes place. 

In case of control volume system energy and mass both can interact with system and surrounding. When mass of a system is fixed then there is only one difference between these two type of system i.e. identity.

12.Draw the Pv and Ts diagram of Carnot cycle with process?

13. Define Entropy and Entropy Principle?

Entropy is an index of unavailability or degradation of energy.

Entropy Principle:
Form the Clausius inequality, ∫ δQ / T ≤ 0
As the entropy is a property of the system, therefore the cyclic integral of a property is zero and the above equation can also be written as:
∫ δQ / T ≤ ∫ dS
SQ / T ≤ dS
dS ≥ δQ / T
for isolated system, SQ = 0

therefore
(dS)_iso ≥ 0
For a reversible process: (dS) _iso = 0
Or
S = constant
For an irreversible process: dS) _iso > 0 or entropy increases.

Thus it may be concluded that entropy of an isolated system can never decrease. It always increases with every irreversible process and remains constant when the process is reversible. This is known as principle of entropy increase or in other words the entropy of principle.

14. Define Carnot's theorem and its Corollaries?

Carnot's theorem is a formal statement of this fact: No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs.

This maximum efficiency  is defined to be:

where

 is the work done by the system (energy exiting the system as work),

 is the heat put into the system (heat energy entering the system),

 is the absolute temperature of the cold reservoir, and

 is the absolute temperature of the hot reservoir.

A corollary to Carnot's theorem states that: All reversible engines operating between the same heat reservoirs are equally efficient.

16. Methods to find the dryness fraction of the steam mixture?

17. Define super heated and sub cooled liquid?


sub cooling is the condition of liquid refrigerant in colder than minimum temperature ( saturation temperature) required to keep it from boiling and hence change from liquid to a gas state while

Super heat is the temperature of vapor above the boiling  point at particular pressure.

18. Define point function and path function?

The quantity which is independent on the process or path followed by the system is known as point functions. 

Example: Pressure, volume, temperature, etc., 

The quantities which are dependent on the process or path followed by the system are known as path functions. 

Example: Heat transfer, work transfer. 

19. Define Extensive and Intensive property?

The properties which are independent on the mass of the system is called intensive properties.

E.g., Pressure, Temperature, Specific Volume etc., 

The properties which are dependent on the mass of the system is called extensive properties.


E.g., Total energy, Total volume, weight etc.