# Modeling Assumptions

The cycle designs you construct in CyclePad are only models of real artifacts, and the results that CyclePad produces are therefore only approximations of the actual results one would observe with a physical cycle operating under real-world conditions. Models intentionally simplify reality, in order to make it tractable. What is critical is that you understand how your model simplifies reality.
Good modeling assumptions make life easier and don't adversely affect the results, while bad ones will produce results that diverge wildly from reality. For example, because liquids are incompressible, there is little change in the temperature of a working fluid as it passes through a pump. There is in fact a little, as some of the energy the pump imparts to the fluid is converted into heat, but for the most part an assumption that temperature across the pump remains constant is a sound one. In contrast, compressing an ideal gas generally causes a large increase in its temperature, so assuming that the temperature of the working fluid remains constant across a compressor would be a bad idea.

The advantage that you gain from making modeling assumptions is that you license CyclePad to propagate values. For example, assuming that a pump is isothermal enables CyclePad to derive the outlet temperature from its inlet temperature or vice versa.

Here is a table of the modeling assumptions you may make in CyclePad. Only a subset of these assumptions will apply to any given component.

Isobaric Pressure remains constant. This is a sound assumption to make for components such as heaters and coolers, because in reality the pressure won't change drastically across them.
Isothermal Temperature remains constant.
Isentropic Entropy remains constant.
Polytropic The term pvk remains constant. Polytropic processes approximate actual expansion and compression curves for pressure in the range of hundreds of psi. The specific heats of the working fluid are assumed to remain constant.
Non-polytropic The term pvk is free to vary.
Adiabatic No heat transfer occurs between the process and the environment. Under this assumption, the casing of a turbine radiates no heat from the steam passing through it.
Saturated When applied to splitters, the parameters of the two outlet stuffs are not constrained to be the identical.
Non-saturated When applied to splitters, the two outlet stuffs are assumed to be parametrically identical.