The peer-reviewed journal article “Measuring Two-Dimensional Heat Flux Using a Plate Sensor and Infrared Thermography” has been published in MethodsX. This manuscript highlights the methodological advances and procedural details that support the Heat Flux using Infrared Thermography over Surfaces (HFITS) research program, led by the Fire Safety Research Institute (FSRI), part of UL Research Institutes. This paper was authored by FSRI research engineers Matt DiDomizio and Parham Dehghani.
Developing New and Improved Methods to Measure Heat Flux
HFITS is a methodology for measuring the thermal exposure from a heat source, such as a fire or hot object, to a planar surface. HFITS builds upon the thin-skin calorimeter (ASTM E459) and other temperature-based instruments, which have been employed for single-location heat flux measurements in fire applications for decades, by expanding the measurement field to a two-dimensional plane. The spatially- and temporally-resolved measurements that are produced with the HFITS method are of particular value when it is desired to measure the thermal exposure over large areas, such as to the walls of a structure or the surroundings of a fire source, with minimal instrumentation overhead.
The HFITS methodology involves positioning a plate sensor (consisting of a thin metallic surface that is optically and thermally characterized) near a heat source at the location where field heat flux measurements are desired. An infrared camera measures the plate sensor's temperature over time. Thermogram sequences are translated to a rectilinear grid, and a two-dimensional inverse heat transfer model is used to derive the net heat flux over the plate sensor. Convective heat flux is estimated, and incident radiative heat flux (the parameter of interest in typical fire applications) is then calculated. The analysis procedure is as follows:
- The sensor area is discretized into finite elements at locations corresponding to the thermogram pixels
- The temperature of each element is given by the thermographic measurement
- Convective and radiative boundary conditions are established on the exposed and unexposed sides of each element
- Lateral conduction heat transfer between adjoining elements is accounted for
- Convection heat transfer accounts for the variation in film temperature over the surface of the sensor
- Numerical approximations of temporal and spatial derivatives are used to calculate the incident radiative heat flux to the exposed side of each element.
Utilizing HFITS
The HFITS method involves three analysis steps: thermogram processing, heat transfer analysis, and post-processing. While the procedures are presented in a general form in the paper, FSRI research engineers Matt DiDomizio and Parham Dehghani also developed an open-source software to automate this analysis. A validation experiment was performed using a propane-fired radiant panel burner, and the HFITS method was shown to produce measurements consistent with Schmidt-Boelter heat flux gauges. Additionally, exemplar plate sensor designs, thermophysical and optical property data for the recommended sensing surface, and infrared camera considerations are provided to support method application. Limitations of the methodology are also provided, including response time, sensor survivability, sensor orientation, numerical approximations and noise, and measurement uncertainty.
The focus of this article was to present the methodological advances in this measurement technique; recent and future studies address the application of this technique to fire research. The HFITS method was recently employed to measure heat flux over the surface of walls exposed to fires from gas burners, liquid pools, wood cribs, and upholstered furniture. It is also currently being employed to characterize the thermal hazards from burning electric vehicles.
To learn more about this study, visit the full article here.
“The HFITS method may be used to obtain spatially-resolved measurements of heat flux over a fire-exposed surface. This method is an advancement of techniques previously explored by our team, and other research groups, in one-off studies.. With this open-access paper, we have provided a technical reference both for the instrument design and the data analysis procedures required for the community to employ this method in research and fire testing applications.”
—Matt DiDomizio, Lead Research Engineer, FSRI
About MethodsX
MethodsX is a multidisciplinary, open-access, peer-reviewed journal, which publishes detailed but digestible articles that describe methodological advances. It contributes to open science and improves reproducibility by making methods, protocols, reviews and the associated research more discoverable; opening doors for collaboration; and sparking new lines of inquiry to enhance the research cycle.
