Quantitative X-ray computed tomography: Prospects for detailed in-situ imaging in bench-scale fire measurements

This paper examines how X-ray Computed Tomography (XCT) can provide detailed and quantitative in-situ measurements in bench-scale fire experiments. The method is illustrated by employing a tabletop X-ray system to image the combustion of different biomass samples heated by convection and radiation. The XCT measurements are utilized to evaluate the gas temperature and quantify the burning rates. In particular, quantitative measurements of the pyrolysis and char oxidation rates are obtained for different types of biomass. Simultaneous 3D gas temperature measurements are enabled by doping the flow with Kr, an inert X-ray contrast gas. To assess the capabilities of XCT as a quantitative and non-intrusive measurement technique, the accuracy of the method is evaluated through repeatability studies, whereas the invasive impact of the XCT method on the combustion is characterized experimentally and theoretically. Finally, the adsorption of Kr on the char during cooling is evidenced, and its impact on the measurements is discussed. This analysis highlights that the XCT solid measurements are entirely non-intrusive and are repeatable within 5% uncertainties, while using Kr for gas temperature measurements results in only a 15% lower heat transfer by natural convection.