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OpenSC – an Open-source Calculation Tool for Combustion Mixture Emissivity/Absorptivity



Wai Cheong Tam, Walter W. Yuen


A web-based radiation code, OpenSC, is developed to provide an ease-of-use calculation tool to evaluate total emissivity and total absorptivity of a typical combustion mixture consisted of H2O, CO2, N2, O2, and/or soot particulates. The web-based calculation tool utilizes the mathematical formulation of a neural network-based correlation (RAD-NNET) and it accounts for the realistic emission/absorption effect of non-gray gases and soot particulates. A set of examples are provided to illustrate the use of OpenSC to determine the total emissivity and total absorptivity for H2O/CO2/N2/soot mixture in various conditions. Commonly accepted approximate approaches used in fire safety/protection design calculations for the evaluation of non-gray effect for radiation heat transfer, as recommended by engineering handbooks, are assessed. In comparison to results generated by OpenSC, error associated with the predictions obtained from using the approximate approaches is substantial. Quantitative comparison also demonstrates that the gray assumption with the total emissivity equal to the total absorptivity is generally invalid. The emissivity chart method, an approach which has been accepted by many practicing engineers in the fire safety community, can lead to substantial error.
Technical Note (NIST TN) - 2064
Report Number


Neural network, radiative properties, non-gray, total emissivity chart


Tam, W. and Yuen, W. (2019), OpenSC – an Open-source Calculation Tool for Combustion Mixture Emissivity/Absorptivity, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed April 20, 2024)
Created September 12, 2019, Updated February 7, 2023