Fluid Properties in pandapipes

The pipelines in the pandapipes network are run with a certain fluid. This can be chosen individually for the net from the fluid library or by own creation. The fluids are defined by certain properties.

The following fluids currently exist in the library:

hgas and lgas (high and low calorific natural gas),
hydrogen,
methane,
water,
biomethane_pure and biomathane_treated (compositions below)
air.

Note

Biomethane(s): A particularity of injecting biomethane in the gas grid in Germany is the addition of LPG to enhance the Wobbe-Index and the heating value of the gas and thus make it equivalent to the (high-calorific) natural gas transported in the grid. This addition is done in a gas treatment unit (Biogaseinspeiseanlage) upstream of the biomethane feed-in junction. The properties of the biomethane(s) were computed based on the package CoolProp.

	Biomethane pure	Biomethane treated
methane	96.15%	90.94%
nitrogen	0.75 %	0.69 %
carbon dioxide	2.9 %	2.68 %
oxygen	0.2 %	0.19 %
propane	0 %	5 %
butane	0 %	0.5 %
Wobbe-Index (normal conditions) \([\frac{KWh}{m^3}]\)	13.9	14.9
HHV (normal conditions) \([\frac{KWh}{m^3}]\)	10.6	11.6

The Fluid Class

Inside this class, different properties with their values are implemented. These properties can be called by different functions. There exists a general function, which returns the values of the requested property. Furthermore, there are different specified functions to return directly the value of the density, viscosity and heat capacity.

In addition to the already existing properties there is a function, which allows to add new properties. It also warns if there is already a property with the same name and can overwrite an existing property with a new value.

class Fluid(name, fluid_type, **kwargs)

add_property(property_name, prop, overwrite=True, warn_on_duplicates=True)

This function adds a new property.

Parameters:

property_name (str) – Name of the new property
prop (pandapipes.FluidProperty) – Values for the property, for example a curve or just a constant value
overwrite (bool) – True if existing property with the same name shall be overwritten
warn_on_duplicates (bool) – True, if a warning of properties with the same name should be returned

Example:

>>> fluid.add_property('water_density', pandapipes.FluidPropertyConstant(998.2061),                                   overwrite=True, warn_on_duplicates=False)

get_compressibility(p_bar)

This function returns the compressibility at a certain pressure.

Parameters:: p_bar (float or array of floats) – pressure at which the compressibility is queried
Returns:: compressibility at the required pressure

get_density(temperature)

This function returns the density at a certain temperature.

Parameters:: temperature (float) – Temperature at which the density is queried
Returns:: Density at the required temperature

get_der_compressibility()

This function returns the derivative of the compressibility with respect to pressure.

Returns:: derivative of the compressibility

get_heat_capacity(temperature)

This function returns the heat capacity at a certain temperature.

Parameters:: temperature (float) – Temperature at which the heat capacity is queried
Returns:: Heat capacity at the required temperature

get_molar_mass()

This function returns the molar mass.

Returns:: molar mass

get_property(property_name, *at_values)

This function returns the value of the requested property.

Parameters:

property_name (str) – Name of the searched property
at_values – Value for which the property should be returned

Returns:

Returns property at the certain value

Return type:

pandapipes.FluidProperty

get_viscosity(temperature)

This function returns the viscosity at a certain temperature.

Parameters:: temperature (float) – Temperature at which the viscosity is queried
Returns:: Viscosity at the required temperature

Properties

The idea behind the properties is a functional correlation between physical quantities, e. g. a linear correlation between pressure and temperature based on the ideal gas law. This way the pandapipes components can ask for a specific fluid property, such as the density, at a given operation point. Some classes for different functional correlations have already been implemented. All properties have to inherit from the Property base class in order to be used in a fluid. These classes shall be introduced in the following. They all inherit from the pandapower JSONSerializableClass, as they shall also be saved and reloaded savely (see also the chapter Save and Load Networks).

Property Base Class

class FluidProperty: Property Base Class

Property With Constant Value

class FluidPropertyConstant(value, warn_dependent_variables=False)

Creates Property with a constant value.

classmethod from_path(path)

Reads a text file with temperature values in the first column and property values in second column.

Parameters:: path
Returns:
Return type:

get_at_integral_value(upper_limit_arg, lower_limit_arg)

Parameters:

upper_limit_arg (float or list-like objects) – one or more values of upper limit values for which the function of the property should calculate the integral for
lower_limit_arg (float or list-like objects) – one or more values of lower limit values for which the function of the property should calculate the integral for

Returns:

integral between the limits

Return type:

float, array

Example:

>>> comp_fact = get_fluid(net).all_properties["heat_capacity"].get_at_integral_value(                    t_upper_k, t_lower_k)

get_at_value(*args)

Parameters:

args (str) – Name of the property

Returns:

Value of the property

Return type:

float

Example:

>>> heat_capacity = get_fluid(net).all_properties["heat_capacity"].get_at_value(293.15)

Property With Linear Correlation

class FluidPropertyLinear(slope, offset)

Creates Property with a linear course.

classmethod from_path(path)

Reads a text file with temperature values in the first column and property values in second column.

Parameters:: path
Returns:
Return type:

get_at_integral_value(upper_limit_arg, lower_limit_arg)

Parameters:

upper_limit_arg (float or list-like objects) – one or more values of upper limit values for which the function of the property should calculate the integral for
lower_limit_arg (float or list-like objects) – one or more values of lower limit values for which the function of the property should calculate the integral for

Returns:

integral between the limits

Return type:

float, array

Example:

>>> comp_fact = get_fluid(net).all_properties["heat_capacity"].get_at_integral_value(                    t_upper_k, t_lower_k)

get_at_value(arg)

Parameters:

arg (str, float or array) – Name of the property and one or more values (x-values) for which the function of the property should be calculated

Returns:

y-value or function values

Return type:

float, array

Example:

>>> comp_fact = get_fluid(net).all_properties["compressibility"].get_at_value(p_bar)

Property With Interpolated Measure Points

class FluidPropertyInterExtra(x_values, y_values, method='interpolate_extrapolate')

Creates Property with interpolated or extrapolated values.

classmethod from_path(path, method='interpolate_extrapolate')

Reads a text file with temperature values in the first column and property values in second column.

Parameters:

path (str) – Target path of the txt file
method (str) – Method with which the values are to be interpolated

Returns:

interpolated values

Return type:

pandapipes.FluidProperty

get_at_integral_value(upper_limit_arg, lower_limit_arg)

Parameters:

upper_limit_arg (float or list-like objects) – one or more values of upper limit values for which the function of the property should calculate the integral for
lower_limit_arg (float or list-like objects) – one or more values of lower limit values for which the function of the property should calculate the integral for

Returns:

integral between the limits

Return type:

float, array

Example:

>>> comp_fact = get_fluid(net).all_properties["heat_capacity"].get_at_integral_value(                    t_upper_k, t_lower_k)

get_at_value(arg)

Parameters:: arg (str, float or array) – Name of the property and one or more values (x-values) for which the y-values of the property are to be displayed
Returns:: y-value/s
Return type:: float, array