The working substance is a phase-change
fluid. That is, it can exist as a subcooled liquid,
superheated
vapor or as a mixture of saturated liquid and vapor. Example:
H2O executing the Rankine cycle.
PC/PC Model
Combined cycles using a different phase-change fluid for each cycle can be analyzed with this model. Two choices for selecting the working fluid model make it necessary to individually specify the working fluid for each state. Example: A Rankine cycle with steam is executed on top of a Rankine cycle with R-134a as the working fluid.
Gases:
PG Model
Obeys the ideal gas equation (pv=RT). Moreover, the specific heats are assumed constant. A perfect gas (PG) , thus, is a simplified ideal gas. Example:
The air standard Brayton cycle.
IG Model
Obeys the ideal
gas equation
(pv=RT). Specific heats are temperature dependent; therefore, the IG model is
more
accurate than the PG model. Example:
The air standard Brayton cycle with variable specific heats.
n-IG Model
The working fluid can be a general mixture of ideal gases. Form the mixture just once with up to sixty gases and use it as the working fluid for the entire cycle Example: Brayton cycle with a working fluid that must be modeled as a mixture of gases.
PC/IG Model
Combined cycles using a phase-change (PC) fluid
for one cycle and an ideal gas (IG) for another
can be analyzed
with this model. Two choices for selecting the working fluid model make
it necessary to individually specify the working fluid
for each state. Example:
A Rankine cycle with steam is executed below a Brayton cycle with air
as the working fluid.
Gas
Power
Cycle
Vapor
Power
Cycle
An open cycle is a cyclic sequence of devices connected back-to-back forming a loop. Brayton and Rankine cycles shown here are examples of gas and vapor power cycle. For more examples of open power cycles, visit VT.Chapters-8,9 pages.
