Fluid properties#

The basic fluid properties are handled by CoolProp. All available fluids can be found on their homepage. Also see [4].

CoolProp back ends#

CoolProp provides multiple back ends for fluid property calculation. The back ends vary in calculation speed and calculation accuracy. It is possible to choose from the following back ends:

  • HEOS: Helmhotz Equation Of State with highest accuracy and lowest calculation speed. This is the default back end!

  • BICUBIC: Tabular back end with high accuracy and very high calculation speed.

  • TTSE: Tabular back end with lowest accuracy and very high calculation speed.

  • INCOMP: Back end for incompressible fluids.

  • IF97: Back end for the IAPWS-IF97 of water, very accurate and much higher calculation speed than HEOS. Due to a bug in the CoolProp back end this option is available with a fix (not the original implementation), for more information see the CoolProp issue #1918.

For more information on the Back ends please visit the CoolProp online documentation.

Pure and pseudo-pure fluids#

If you use pure fluids, TESPy directly uses CoolProp functions to gather all fluid properties. CoolProp covers the most important fluids such as water, air as a pseudo-pure fluid as well as its components, several fuels and refrigerants etc.. Look for the aliases in the list of fluids. All fluids provided in this list cover liquid and gaseous state and the two-phase region.

Incompressible fluids#

If you are looking for heat transfer fluids, the list of incompressible fluids might be interesting for you. In contrast to the pure fluids, the properties cover liquid state only.

Fluid mixtures#

CoolProp provides fluid properties for two component mixtures. BUT: These are NOT integrated in TESPy! Nevertheless, you can use fluid mixtures for gases.

Ideal mixtures of gaseous fluids#

TESPy can handle mixtures of gaseous fluids, by using the single fluid properties from CoolProp together with corresponding equations for mixtures. The equations can be found in the fluid_properties module and are applied automatically to the fluid vector.

Other mixtures#

Apart from partially liquid water in flue gases it is not possible to use mixtures of liquids and other liquids or gaseous fluids at the moment! If you try to use a mixture of two liquid or gaseous fluids and liquid fluids, e.g. water and methanol, the equations will still be applied, but obviously return wrong values. If you have ideas for the implementation of new kinds of mixtures we appreciate you contacting us.

Creating Fluid Property Diagrams#

logph diagram of NH3 with a simple heat pump cycle

Figure: logph diagram of NH3 with a simple heat pump cycle#

Ts diagram of NH3 with a simple heat pump cycle

Figure: Ts diagram of NH3 with a simple heat pump cycle#

CoolProp has an inbuilt feature for creating fluid property diagrams. Unfortunately, the handling is not very easy at the moment. We recommend using fluprodia (Fluid Property Diagram) instead. You can create and customize different types of diagrams for all pure and pseudo-pure fluids available in CoolProp. In order to plot your process data into a diagram, you can use the get_plotting_data method of each component. The method returns a dictionary, that can be passed as **kwargs to the calc_individual_isoline method of a fluprodia FluidPropertyDiagram object. The fluprodia documentation provides examples of how to plot a process into different diagrams, too. For more information on fluprodia have a look at the online documentation. You can install the package with pip.

pip install fluprodia

Note

The plotting data a returned from the get_plotting_data as a nested dictionary. The first level key contains the connection id of the state change (change state from incoming connection to outgoing connection). The table below shows the state change and the respective id.

State change and respective ids of dictionary#

component

state from

state to

id

components with one inlet and one outlet only

in1

out1

1

class HeatExchanger and subclasses

in1

out1

1

in2

out2

2

class ORCEvaporator

in1

out1

1

in2

out2

2

in3

out3

3

class Merge

in1

out1

1

in2

out1

2

class Drum

out1

out2

1

All other components do not return any information as either there is no change in state or the state change is accompanied by a change in fluid composition.