Expander - Constant Isentropic Efficiency Model

Model description

The constant isentropic efficiency model is a simple model based on the assumption that the isentropic efficiency stays constant.

\[\varepsilon_{is} = \frac{h_{ex} - h_{su}}{h_{ex, is} - h_{su}}\]

where \(\varepsilon_{is}\) is the isentropic efficiency, \(h_{su}\) is the supply specific enthalpy, \(h_{ex, is}\) is the exhaust specific isentropic enthalpy and \(h_{ex}\) is the exhaust specific enthalpy.

Based on the isentropic efficiency definition, the specific enthalpy at the exhaust outlet can be calculated and thus also the exhaust temperature.

Class description

class component.expander.expander_csteff.ExpanderCstEff[source]

Component: Expander

Model: Constant isentropic efficiency model

Reference: /

Description:

This component models an expander using a constant isentropic efficiency. Given the suction conditions (pressure, temperature, fluid) and the exhaust pressure, it calculates the exhaust specific enthalpy and exhaust temperature. This simple model can be used for on-design models of systems.

Assumptions:

  • Steady-state operation.

  • Isentropic efficiency stays constant for all the conditions.

  • Negligible heat losses and mechanical losses except those accounted for by efficiency.

Connectors:

su (MassConnector): Mass connector for the suction side.

ex (MassConnector): Mass connector for the exhaust side.

W (WorkConnector): Work connector.

Parameters:

eta_is: Isentropic efficiency of the expander (0 < eta_is ≤ 1) [-]

Inputs:

P_su: Suction side pressure. [Pa]

T_su: Suction side temperature. [K]

m_dot: Mass flow flow rate. [kg/s]

P_ex: Exhaust side pressure. [Pa]

fluid: fluid. [-]

Ouputs:

h_ex: Exhaust side specific enthalpy. [J/kg]

T_ex: Exhaust side temperature. [K]

W_dot_exp (float): Mechanical power of the expander [W]

Example of use

from labothappy.component.expander.expander_csteff import ExpanderCstEff

# Example usage
EXP = ExpanderCstEff()
EXP.print_setup()

# "If the inputs are not set directly BUT throught the connectors"
EXP.su.set_properties(P=955214.9, T=374.18, fluid='R134a', m_dot = 0.1)
EXP.ex.set_properties(P=293940.1)
EXP.set_parameters(eta_is=0.8)
EXP.print_setup()

EXP.solve()
EXP.print_results()

fig = EXP.plot_Ts()
fig.show()

References

/