Question

1) What is the thermodynamic definition of state and how many properties are needed to fix a state in simple compressible system? Comment on independent properties on system consisting of single phase and two phase mixture cases.

2)Explain the problem associated with evaluation of an expansion or compression work for processes where quasi-equilibrium assumption is not valid

3)Explain possible energy storage mechanism and give examples to them

4)Define ideal gas model and assumptions used in this model

5)Explain enthalpy and its difference with internal energy

6)What is the definition of a reversible process?

7)What are the requirements for a process to be isentropic?

Answer 1

Thermodynamic state is a set of measurable property sufficient to determine all other properties. Two properties are required to fix a state in simple compressible system. For single phase system temperature, pressure, volume, specific entropy or specific enthalpy can be used as independent variable while in two phase system dryness fraction is used to fix the state point.

2. If the quasi equilibrium process is not valid, the process will be irreversible and we cannot locate the intermediate state point undergone by the system and since work done is a path function and hence to calculate the work done we need to know the path undergone by the process to achieve the final state.

3. Gravitational potential energy storage like in dam

b. Sensible heat thermal energy storage like solar heater

c. kinetic energy storage like flywheel

4. In ideal gas model,

  

where P - pressure (N/m2)

V - volume (m3)

m - mass (kg)

R characteristic gas constant (J/kg K)

T - temperature (K)

Assumption

a. Intermolecular interactions are neglected

b. particle that form gas have no volume

c. kinetic energy and potential energy loss are neglected

5. Enthalpy is the maximum energy carrying capacity of flowing fluid and is the sum of internal energy and flow energy while internal energy indicate the energy carrying capacity of stationary fluid

6. A process is said to be reversible if it returns to its original state without leaving any trace or simply we can say without effecting surrounding.

7. A process is said to be isentropic if change in entropy during the process is zero. Hence all reversible adiabatic process are isentropic but reverse is not true.