  A Wankel steam expander has numerous advantages over other positive
displacement machines as an expansion device. This is due to its high power to
weight ratio, compactness, lower noise, vibration, and potentially lower
specific cost making them a favourable choice over reciprocating expanders.
Admission in the expander chamber occurs through rotary valves fed with steam
supply from a boiler. The present study aims to investigate the magnitude of
pressure losses of the steam during intake and its effect on the net power
output of the expander over a range of rotational speed varying from 1200 to
3000 RPM. The thermodynamic analysis is carried out for the theoretical
pressure-volume cycle of the expander using Python, which is then used for CFD
analysis in Ansys Fluent 19.2. Three dimensional models are developed for the
flow domain stretching from the exit of the intake valve port to the port in
the rotor housing at different rotor angles ranging from admission to cutoff.
Computations are performed to investigate the associated pressure drop of steam
during admission. The boundary conditions at different rotor angles are
obtained from the thermodynamic model of the expander's theoretical
pressure-volume plot, and the state point values were obtained from the REFPROP
database. Validation of the CFD models are carried out by comparing pressure
drop values obtained through an analytical approach using correlations and
expressions reported in literature. A thorough performance analysis of this
expansion device is made and the loss in power output due to the intake
pressure loss is calculated. These losses during admission change the pressure
ratio across the actual expander designed for a given pressure ratio, leading
to a reduced power output by a reasonable margin of 20 to 30%. It is observed
that the percentage loss in power output increases with an increase in shaft
speed.
