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Ian Bell

Mechanical Engineer


Dr.Bell’s research interests include computational routines and tools used for the development and application of thermodynamic mixture models.  These mixture models are used in software tools like NIST REFPROP, a modeling tool widely used in industry. 

Google Scholar Citation Page

NIST REFPROP – The industry standard in thermophysical properties

Dr. Bell is part of the team involved in the development of NIST REFPROP.  This software tool is the industry standard for thermophysical properties of pure fluids and mixtures, and is one of NIST’s flagship products.  His interest is especially focused on development of interfaces to facilitate the interfacing of REFPROP with other high-level environments like python, C++, Microsoft Excel, etc.

Aside from his activities in interfacing REFPROP with other programming environments, he is also involved in developing the mixture models and mixture estimation schemes implemented in NIST REFPROP.

Development of mixture models

Dr. Bell developed a number of open-source tools based in C++ and python for carrying out parameter optimization for a wide range of mixtures.  In a publication in 2016, interaction parameters for more than 1000 mixtures were fit, and efforts are continuing to develop mixture models for mixtures that employ binary mixture specific departure functions.

Bell, I.H., Lemmon, E.W., 2016, Automatic Fitting of Binary Interaction Parameters for Multi-fluid Helmholtz-Energy-Explicit Mixture Models, J. Chem. Eng. Data, 61 (11), 3752-3760

Algorithms for thermodynamic calculations of mixtures

Dr. Bell is actively involved the development of algorithms for mixture calculations.  In this category are algorithms for the calculation of all the critical points for mixtures, phase envelope cross-sections, robust and efficient algorithms for calculating density values from multi-parameter nist-equations of state, etc.  In most cases, the code for these algorithms are provided as supplemental information along with the associated publication.

Bell, I.H., Jager, A., Calculation of critical points from Helmholtz-energy-explicit mixture models, Fluid Phase Equilib., 2017

Development of open-source software tools:

In the last few years Dr. Bell has been involved in a number of open-source software projects;  open-source software forms the cornerstone of replicable science.

Those projects are publicly available on NIST’s github page:

  • envy (website ) : A javascript-based visualization tool for phase envelopes of mixtures, running entirely in the browser.
  • NISTfit (website) : A C++11-threading framework used to computationally efficiently develop correlations.
  • ChebTools (website ) : C++ tools for constructing and working with Chebyshev expansions of functions in one dimension.  Can also be used to obtain roots of nonlinear functions in one dimension over fixed interval.


Created October 9, 2019