Modeling Heat Transfer in Thin Fire Blanket Materials under High External Heat Fluxes

Abstract

To investigate the performance of thin fire blanket materials for house protection from wildland fires, a one-dimensional numerical model, which combines conductive and radiative heat transfer, has been developed, solved and compared with bench-scale experiments. Two types of incident heat sources are studied: convective heating from a burner flame and radiative heating from a cone heater. Radiative heat exchange between the blanket and the environment is critical in the performance of the blankets at high temperatures. The treatment of radiation includes the solution of the radiative transfer equation by the discrete ordinate method since in-depth absorbing, emitting and scattering are believed to be important in these thin blanket materials. A number of material combinations were tested and analyzed, including single and double layers of fiberglass fabric with and without aluminum foil on the front and back surfaces. It is found that high heat-blocking efficiencies can be obtained using thin blankets. Interestingly, it is also found that protecting a house from convective heating is a more difficult challenge than protecting it from radiant heating.

Thermal response characteristics of fire blanket materials

“…In this manner, it is possible to analyze the heat‐blocking effectiveness of each fire blanket material to each form of heating as well as their synergistic effects. In a previous paper , we have developed a numerical model, which includes in‐depth radiation and conductive heat transfer of several layers of materials, and computed time histories of temperature and heat flux with reasonable agreement with measurement. This paper reports the experimental results for single‐layer fabric materials from four different fiber groups (aramid, fiberglass, amorphous silica, and pre‐oxidized carbon) and their composites with or without coatings.…”

“…Note that the mechanisms of preventing heat from transmitting through the blanket in steady state are radiation reflection and radiation re‐emission .…”

Whole-House Fire Blanket Protection From Wildland-Urban Interface Fires

“…In previous papers (Hsu et al, 2011;Takahashi et al, 2014), thermal response characteristics of more than 50 relatively thin fire blanket materials have been investigated experimentally and selected cases have been analyzed computationally. Each specimen was exposed to a convective or radiant heat flux.…”

“…Among the materials tested, relatively thin (∼1 mm) fiberglass or amorphous silica fabric laminated with aluminum foil performed reasonably well for a wide range of conditions. The numerical modeling was performed (1) to simulate the heat transfer phenomena in the laboratory experiment (Hsu et al, 2011) and 2to optimize the performance of fire blanket materials (Brent, 2012). The former is the physics-based modeling using the one-dimensional transient heat-transfer equation, which includes radiation as well as conduction in the interior of layered fire blanket materials.…”

“…This observation was consistent with video observations showing more fire attack on Panels #3/#4 compared to #1/#2 (see Figure 6C and Supplementary Video 1). Figure 8B shows the numerical results based on the method previously used (Hsu et al, 2011) for Panel #3 as well (dashed). Note that the applied heat source as a function of time is prescribed according to the measured incident heat flux, and the simulated through-the-blanket heat flux and T back are respectively obtained at x = L f and x = L s in the model.…”