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.

Isochoric        Volume remains constant.  This assumption is most commonly made for heating and cooling processes in closed-cycle systems.  As a gas is heated or cooled, it will expand or contract.  In an isochoric heating process, the gas will attempt to expand, but the constant volume of the process will result in an increase in the pressure of the gas.  Therefore, isobaric and isochoric are in general mutually exclusive assumptions.

Isothermal        Temperature remains constant.

Isentropic        Entropy remains constant.

Polytropic        For ideal gases, the term pv^k 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 pv^k is free to vary.

Adiabatic        The process allows no heat transfer to occur between the working fluid and the environment.  Under this assumption, for example, the casing of a turbine radiates no heat from the steam passing through it, which is a very reasonable assumption for many turbines, where the heat lost to the environment is quite tiny compared to the heat converted to work.

Non-isoparametric        When applied to splitters and saturated working fluids, the parameters of the two outlet stuffs are not constrained to be the identical.  That is, for a saturated working fluid entering the splitter, one outlet leg could contain fluid of a different quality than the other and, thereby, different specific volumes, et cetera.

Isoparametric        When applied to splitters, the two outlet stuffs are assumed to be parametrically identical and will have the same quality and other intensive values.


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