by CalebBell

CalebBell / thermo

Thermodynamics, phase equilibria, transport properties and chemical database component of Chemical E...

244 Stars 60 Forks Last release: about 3 years ago (2017-08-26) MIT License 422 Commits 28 Releases

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What is thermo?

thermo is open-source software for engineers, scientists, technicians and anyone trying to understand the universe in more detail. It facilitates the retrieval of constants of chemicals, the calculation of temperature and pressure dependent chemical properties (both thermodynamic and transport), the calculation of the same for chemical mixtures (including phase equilibria), and assorted information of a regulatory or legal nature about chemicals.

The thermo library depends on the SciPy library to povide numerical constants, interpolation, integration, differentiation, and numerical solving functionality. thermo all operating systems which support Python, is quick to install, and is free of charge. thermo is designed to be easy to use while still providing powerful functionality. If you need to know something about a chemical, give thermo a try.


Get the latest version of thermo from

If you have an installation of Python with pip, simple install it with:

$ pip install thermo

Alternatively, if you are using

_ as your package management, you can simply install thermo in your environment from
_ channel with:
$ conda install -c conda-forge thermo

To get the git version, run:

$ git clone git://


thermo's documentation is available on the web:

Getting Started

The library is designed around base SI units only for development convenience. All chemicals default to 298.15 K and 101325 Pa on creation, unless specified. All constant-properties are loaded on the creation of a Chemical instance.

.. code-block:: python

>>> from thermo.chemical import Chemical
>>> tol = Chemical('toluene')
>>> tol.Tm, tol.Tb, tol.Tc
(179.2, 383.75, 591.75)
>>> tol.rho, tol.Cp, tol.k,
(862.2380125827527, 1706.0746129119084, 0.13034801424538045, 0.0005521951637285534)

For pure species, the phase is easily identified, allowing for properties to be obtained without needing to specify the phase. However, the properties are also available in the hypothetical gas phase (when under the boiling point) and in the hypothetical liquid phase (when above the boiling point) as these properties are needed to evaluate mixture properties. Specify the phase of a property to be retrieved by appending 'l' or 'g' or 's' to the property.

.. code-block:: python

>>> tol.rhog, tol.Cpg,, tol.mug
(4.032009635018902, 1126.5533755283168, 0.010736843919054837, 6.973325939594919e-06)

Creating a chemical object involves identifying the appropriate chemical by name through a database, and retrieving all constant and temperature and pressure dependent coefficients from Pandas DataFrames - a ~1 ms process. To obtain properties at different conditions quickly, the method calculate has been implemented.

.. code-block:: python

>>> tol.calculate(T=310, P=101325)
>>> tol.rho, tol.Cp, tol.k,
(851.1582219886011, 1743.280497511088, 0.12705495902514785, 0.00048161578053599225)
>>> tol.calculate(310, 2E6)
>>> tol.rho, tol.Cp, tol.k,
(852.7643604407997, 1743.280497511088, 0.12773606382684732, 0.0004894942399156052)

Each property is implemented through an independent object-oriented method, based on the classes TDependentProperty and TPDependentProperty to allow for shared methods of plotting, integrating, differentiating, solving, interpolating, sanity checking, and error handling. For example, to solve for the temperature at which the vapor pressure of toluene is 2 bar. For each property, as many methods of calculating or estimating it are included as possible. All methods can be visualized independently:

.. code-block:: python

>>> Chemical('toluene').VaporPressure.solve_prop(2E5)
>>> Chemical('toluene').SurfaceTension.plot_T_dependent_property()

Mixtures are supported and many mixing rules have been implemented. However, there is no error handling. Inputs as mole fractions (

), mass fractions (
), or volume fractions (
) are supported. Some shortcuts are supported to predefined mixtures.

.. code-block:: python

>>> from thermo.chemical import Mixture
>>> vodka = Mixture(['water', 'ethanol'], Vfls=[.6, .4], T=300, P=1E5)
>>> vodka.Prl,vodka.Prg
(35.13075699606542, 0.9822705235442692)
>>> air = Mixture('air', T=400, P=1e5)
>>> air.Cp


The author's main development item is phase equilibrium, a particularly tricky area.

Latest source code

The latest development version of thermo's sources can be obtained at

Bug reports

To report bugs, please use the thermo's Bug Tracker at:

License information


for information on the terms & conditions for usage of this software, and a DISCLAIMER OF ALL WARRANTIES.

Although not required by the thermo license, if it is convenient for you, please cite thermo if used in your work. Please also consider contributing any changes you make back, and benefit the community.


To cite thermo in publications use::

Caleb Bell and Contributors (2016-2020). thermo: Chemical properties component of Chemical Engineering Design Library (ChEDL)

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