Ian H. Bell

Uncertainty assessment of equations of state with application to an organic Rankine cycle

ABSTRACT Evaluations of equations of state (EoS) should include uncertainty. This study presents a generic method to analyse EoS from a detailed uncertainty analysis of the mathematical form and the data used to obtain EoS parameter values. The method is illustrated by comparison of Soave–Redlich–Kwong (SRK) cubic EoS with perturbed-chain statistical associating fluid theory (PC-SAFT) EoS for an organic Rankine cycle (ORC) for heat recovery to power from the exhaust gas of a marine diesel engine using cyclopentane as working fluid. Uncertainties of the EoS input parameters including their corresponding correlation structure, are quantified from experimental measurements using a bootstrap method. Variance-based sensitivity analysis is used to compare the uncertainties from the departure function and the ideal-gas contribution. A Monte Carlo procedure propagates fluid parameter input uncertainty onto the model outputs. Uncertainties in the departure function (SRK or PC-SAFT EoS) dominate the total uncertainties of the ORC model output. For this application and working fluid, SRK EoS has less predictive uncertainty in the process model output than does PC-SAFT EoS, though it cannot be determined if this is due to differences in the data for parameter estimation or in the mathematical form of the EoS or both.

ChebTools: C++11 (and Python) tools for working with Chebyshev expansions

Chebyshev-basis expansions, and more broadly, orthogonal polynomial expansions, are commonly used as numerical approximations of continuous functions on closed domains (Boyd 2013,Mason and Handscomb (2003),Battles and Trefethen (2004)). One of the most successful projects that makes use of the Chebyshev expansions is the chebfun library (Driscoll, Hale, and Trefethen 2014) for MATLAB. Other similar libraries are pychebfun1, chebpy2, and Approxfun3. Our library ChebTools fills a similar niche as that of chebfun – working with Chebyshev expansions.