Improving Heat Transfer Models of Air Gaps in Bench Top Tests of Thermal Protective Fabrics

An improved model has been developed to simulate heat transfer in horizontal air spaces between thermal protective fabrics and test sensors in bench top tests, such as the thermal protective performance test. This model calculates the radiation and convection heat transfer from the test specimen to the test sensor. Radiation heat transfer is calculated by treating the bottom boundary of the enclosure as a series of isothermal rectangular pieces. Convection heat transfer is calculated using an empirical correlation and by assuming that convection only occurs over a portion of the cross-section of the enclosure. Predicted times required to exceed the Stoll second degree burn criterion were found to be within 3 % of those measured during actual bench top tests of steel shimstock using air gaps from 6.4 mm (1/4 in.) to 19.1 mm (3/4 in.).