Irreversible, anisentropic process
Definition
... a process at defined by an isentropic efficiency below 100 percent, indicated by a curve showing increasing entropy on a Ts diagram.
Where it occurs.
Largely in compressors and turbines, but also nozzles.
Special features
Were the isentropic efficiency set to 100 percent a vertical line would follow. Heat transfer is equal to the area under the curve only for reversible processes.
For these curves we cannot get the heat transfer by integration.
How to draw it
In the appropriate text box, set the isentropic efficiency to between 0 and 1. Locate the POI and press either expansion or compression.
The theory
The state is calculated for a set of end pressures, \( p_2 \). At each of these a tentative estimate of temperature is made according to isentropic expansion.
$$ T_{2,isen} = T_1 (\frac {p_2}{p_1})^{(\gamma-1)/\gamma)} $$
For expansion the irreversible version of T2 is,
$$ T_2 = T_1 + \eta_{isen,t} \times (T_{2,isen}-T_1) $$
For compression the irreversible version of T2 is,
$$ T_2 = T_1 + \frac{ (T_{2,isen}-T_1)}{ \eta_{isen,c} } $$
The calculations of ideal gas internal energy, enthalpy and specific volume are explained in conjunction with
the point of interest.
Exercises
Set an efficiency of 0.85, click on the graph to get a POI and plot an isentropic expansion through it. Click along the curve to set new POIs and note changes in pressure and enthalpy. Repeat with compression.
Repeat with an efficiency of 1.00.
Links
... to follow.