Thermal boundaries of intumescent-type insulations in cone calorimeter testing

Intumescent fire-retardant coatings are often tested using a cone calorimeter. During the tests, these types of specimen demonstrate anisotropic intumescences, mainly toward the spatially stationary heater. The primary movement of the specimens’ exposed bounda-ries generates progressive uncertainties in terms of net heat stored per time increment. Simultaneously, the expansion causes an exposure of the perimeter faces to both the heater and the surroundings. The heat transmitted through the significantly increased pe-rimeter areas aggravates the uncertainties. As an essential part of full clarification on thermal boundaries, this work aims to solve two issues regarding the secondary phenom-enon:
• Irradiance is non-uniformly distributed on the exposed surfaces because of the unique geometric configuration of the test apparatus. Its non-linearity is theoretically exam-ined using the view factor, particularly on the vertical perimeter faces. A mathemati-cal formula is derived utilising the contour integration method.
• The convective heat loss from the sides is different from that from the horizontal top surface which has been conventionally considered in existing literature. A coefficient is derived from correlations for free convective motions over vertical planes.
The defined thermal boundaries are verified by direct measurements and cone calorime-ter tests on plain steel plates. For practical purposes, thermal boundaries of an intumes-cent-type coating are discussed. The contributions of the heats transmitted through its sides are estimated in percentage terms. It is concluded that the contributions account for approximately 18.7 % and 52.8 % of the total heat gain and loss, respectively, and the determined view factor and coefficient can be generalised for engineering applications.