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Ian Bell (Fed)

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.  A key theme of Dr. Bell's work is to develop new numerical tools to be used in the new version of NIST REFPROP.  This includes:

Entropy Scaling

Isomorph theory forms the basis for the observation that in many cases, there is a monovariate relationship between macroscopically scaled transport properties and the residual (or excess) entropy.  A number of publications have investigated this link, and highlighted how the residual entropy is a very important thermodynamic property that is connected to many other thermophysical properties. Some highlights:


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 addition, a number of recent efforts have focused on refrigerant (pure and mixture) screening.

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 equations of state, etc.  In most cases, the code for these algorithms are provided as supplemental information along with the associated publication.

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:

  • teqp (website) : An open-source library for efficiently carrying out derivatives of an equation of state in C++ with automatic differentiation
  • multicomplex (website) : An open-source C++ and Python library for doing derivatives with multicomplex algebra
  • potter (website) : An open-source C++ library for calculating virial coefficients from pair potentials
  • 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.


2022: Awarded the I&EC Research 2022 Excellence in Review Award

2018: Recognized as Emerging Investigator by the Journal of Chemical and Engineering Data


Non-flammable Low-GWP Refrigerant Blends to Replace HFC-134a

Harrison M. Skye, Piotr A. Domanski, Mark O. McLinden, Valeri I. Babushok, Ian Bell, Tara Fortin, Michael Hegetschweiler, Mark A. Kedzierski, Dennis Kim, Lingnan Lin, Gregory T. Linteris, Stephanie L. Outcalt, Vance (Wm.) Payne, Richard A. Perkins, Aaron Rowane
Non-flammable, lower global-warming-potential (GWP) refrigerants are needed to replace HFC-134a (GWP=1300) in military equipment. We previously used

Towards Global Parameter Estimation Exploiting Reduced Data Sets

Susanne Sass, Angelos Tsoukalas, Ian Bell, Dominik Bongartz, Jaromil Najman, Alexander Mitsos
We focus on deterministic global optimization (DGO) methods for solving nonconvex parameter estimation problems. In estimation problems, realistic and accurate
Created October 9, 2019, Updated February 15, 2023