Surface temperature measurements in the cone calorimeter using phosphorescence

The Cone Calorimeter is the most complete reaction-to fire test apparatus available presently. It measures heat release rates and mass loss rate, ignitability properties and smoke and toxic gas production rate. One of the main advantages remains in its wide spread and use. There are, however, some drawbacks in the cone calorimeter that should be noticed and maybe corrected for. The sample size is relatively small which means that the edge effects will be fairly substantial for some types of products, e.g. products with protective surfaces suffer from this. The constant external radiation throughout the test is significantly increased after ignition when the flame radiation is added to the electrical cone radiation. This is not a significant problem for classification tests, ranking or evaluation of products as the flames are “self-produced” thus including a factor also relevant to fire safety, but for modelling purposes the added flame radiation need to be accounted for. Another important parameter to have good knowledge of, is the surface temperature since that determines the heat balance between the wall and the gas phase. Thermocouples are traditionally used for surface temperature measurements but newer, non-intrusive techniques are proposed in order to give better values. In the investigation presented here surface temperature measurements have been made on the cone calorimeter samples using both thermocouples and the phosphorescence technique for comparison purposes. In this investigation the temperature was measured from the time the sample was inserted in the cone calorimeter, up to ignition. The intention is to develop the method so that it can also be used for burning samples in the near future. Surface temperature is often hard to measure. A major problem is that the probes normally used, such as thermocouples, will affect the surface and will not measure the true surface temperature but instead the probe temperature. If infrared thermometry is used, one should take in consideration the uncertainty of the target emissivity, background reflection from the target and the surrounding, and the attenuation of radiation between the target and the detector. These uncertainties could lead to poor measurement accuracy