Engine nozzle an Exergy

Question 1

Ideal Gas law is applicable to relate pressure, temperature and density

Answer 1

Question 2

Energy Equation

Answer 2

One dimensional isentropic flow (Relationship between pressure, temperature and density (specific volume) ratios – may involve stagnation pressure, temperature and ensity values)

Question 3

Irreversibility

Answer 3

An expression for the ‘irreversibility’, is derived in terms of work loss (Wloss) in a work transfer process, unaccounted heat dissipation (Qloss) in a heat transfer process and loss of net Carnot work (CWnet) opportunity resulting from spontaneous heat transfer across a finite temperature difference during the process.
The thermal irreversibility is attributed to not exploiting the opportunity for extracting work by interposing a combination of Carnot engine(s) and/or Carnot heat pump(s) that exchanges heat with the surrounding and operates across the finite temperature difference.

Question 4

Entropy

Answer 4

The entropy of mass is described as the net emperature-standardised heat transfer to mass understand ideal conditions measured from a datum value
The heat transferred under ideal conditions assumes the heat transfer to have occurred extremely slowly under quasi-equilibrium conditions

Question 5

s = the entropy of mass (kJ/kg K)
s0 = the entropy of surrounding (kJ/kg K)
T0 = temperature of surrounding in K. It is assumed that it remains constant
Heat transfer to mass under ideal conditions with reference to surroundings

Answer 5

The energy of mass that can be transferred to the surrounding environment spontaneously is the difference between the energy of mass and the surrounding energy per kg of mass.

Question 6

Energy of mass that can be transferred to surroundings

Answer 6

Work potential of energy (exergy) = Energy of mass - Heat transfer from mass to surrounding under ideal conditions

Question 7

exergy for closed system

Answer 7

Question 8

reversible process

Answer 8

All three components of irreversibility must be zero.
In addition to zero Wloss and Qloss terms, the CWnet opportunity is either zero or is successfully realised.
An internally reversible process can not have temperature gradients within the control volume (so that the CWnet opportunity remains at zero).

Question 9

internally reversible

Answer 9

The work transfer irreversibility term, W_loss, and unaccounted heat dissipation term, Q_loss , is zero and the non-zerothermal irreversibility component CW_net is ignored.
A reversible process can not have temperature gradients anywhere (within and outside of the control volume)

Question 10

Every reversible adiabatic process is isentropic but the every isentropic process is NOT reversible adiabatic

Answer 10

– It is possible to have an isentropic process that is NOT adiabatic.
– An isentropic and adiabatic process is reversible adiabatic.
– An isentropic and reversible process is reversible adiabatic.
– Internally reversible adiabatic process is reversible adiabatic.