Quantifying Thermal Boundary Condition Details Using a Hybrid Heat Flux Gage

Abstract

New methods and experimental techniques were developed in this research to quantify the incident heat flux, absorbed (net) heat flux into a sample, and heat transfer coefficient for samples exposed to mixed mode (radiation and convection) heat transfer typical in fires. Net heat flux into the material was measured at elevated temperatures using a recently developed hybrid heat flux gage, which is both a thermopile type gage as well as a slug calorimeter with an operating temperature >1000 ºC without cooling. The heat transfer coefficient was determined as a function of time using the hybrid gage output only through a reference state approach. The net heat flux and heat transfer coefficient were then used to calculate a cold surface heat flux and the adiabatic surface temperature. Experiments were performed in the cone calorimeter at different heat fluxes to quantify the incident heat flux, net heat flux, heat transfer coefficient, cold surface heat flux, and adiabatic surface temperature as a function of time. Measured heat transfer coefficients were 9-18 % different than values calculated using idealized natural convection correlations. The cold surface heat fluxes determined with the hybrid gage were within 5 % of cold surface heat fluxes measured using a water-cooled Schmidt-Boelter heat flux gage.KEYWORDS: heat flux, heat transfer coefficient, adiabatic surface temperature, cone calorimeter, high temperature heat flux gage, hybrid gage. NOMENCLATURE LISTINGA s area of exposed surface (m 2 ) β thermal expansion coefficient (