Estimation of pyrolysis-related properties using repulsive particle swarm optimization

Abstract

The pyrolysis-related properties of the specimen are obtained by optimizing the repulsive particle swarm optimization technique. Eight pyrolysis-related properties were obtained: virgin thermal conductivity, char thermal conductivity, virgin specific heat, char specific heat, char density, heat of pyrolysis, pre-exponential factor, and activation energy. The surface temperature and the mass loss rate obtained using the optimized properties were consistent with the measured values. In assuming that the properties obtained are physically valid, and that the surface temperature and mass loss rate measured in the experiment are correct, a valid fire phenomenon may be considered for replication if fire analysis is conducted using the properties obtained from the procedures proposed in this study. The modeling technique can be used to provide the evi- dence required during the product development stage or by the building code or other regulations. This technique can also reduce the time required for the test as an effective alternative to very expensive full-scale tests. However, techniques in computational fluid dynamics (CFD) can also be used for the precise prediction of fire growth in case fire in the laboratory is not easy to reproduce. The absence of solid fuel properties, as required by the numerical pyrolysis model of CFD, is one of the biggest interference factors restricting the use of fire growth modeling based on CFD. Recently, pyrolysis-related material properties have been obtained using the Genetic Al- gorithm (GA) optimization technique (1) and its variation (2). Park et al. (3) compared the performance of repulsive particle swarm optimization (RPSO) and GA by obtaining the pyroly- sis-related properties for virtual materials. In the present study, RPSO was used to obtain the eight pyrolysis-related properties using the measured surface temperatures and the pyrolysis mass loss rate of the wood specimen that was subjected to a certain heat flux. 2. Tests The cone calorimeter was used to estimate the pyrolysis- related properties. The cone calorimeter test was standardized in ISO 5660 (4). The mass loss rate and surface temperatures of the specimen were measured as the combustibility of the specimen. Heat must be applied evenly on all parts of the sur- face of the specimen to cancel out the spatial effects; conduc- tive heat transfer on the specimen is expressed in one- dimension in the cone calorimeter. Common specimen holders are made of steel, thus, "edge effects" occur in three dimen- sions (5). Accordingly, the shortcomings of the existing steel holder were dealt with in the present work by utilizing ceramic fiberboards (12.5 mm thick) and ceramic blankets. The speci- men was enclosed sufficiently within five layers of ceramic fiberboards wherein the middle parts were cut out into 100 mm x 100 mm squares. Nonflammable materials, such as steel wire or pin, were applied to the four corners to prevent the ceramic holders in the layers from shaking. Flexible ce- ramic blankets, such as textiles, were inserted into the cutout area of the fiberboards up to the height required to have the specimen positioned horizontally in an even line with the sur- face of the topmost ceramic fiberboard. After placing the specimen holder on the load cell, the k-type thermocouple was fixed on the center of the specimen to measure surface tem- perature. Since the specimen is wood (charring material), the thermocouple must be fixed, considering that the subject of *