  Thermodynamic models are often vital when characterising complex systems,
particularly natural gas, electrolyte, polymer, pharmaceutical and biological
systems. However, their implementations have historically been abstruse and
cumbersome, and as such, the only options available were black-box commercial
tools. In this article, we present Clapeyron.jl: a pioneering attempt at an
open-source fluid-thermodynamics toolkit to build and make use of thermodynamic
models. This toolkit is built in Julia, a modern language for scientific
computing known for its ease of use, extensibility, and first-class support for
differentiable programming. We currently support more models than any package
available, including standard cubic (SRK, PR, PSRK, etc.), activity-coefficient
(NRTL, UNIFAC, etc.), COSMO-based, and the venerable SAFT equations. The
property-estimation methods supported are extensive, including bulk, VLE, LLE,
VLLE and critical properties. With Clapeyron.jl, researchers and enthusiasts
alike will be able to focus on the application and worry less about the
implementation.
