Visualisation_of_Temperature_Fields_at_Heat_Loading_of_Wood

3.4.1 Visualisation of Temperature Fields at Heat Loading of Wood

Wood is one of the oldest building materials and neither presently it loses its importance. However, natural wood as well as wood-based materials have also certain disadvantages, the most important being: low resistance to the attack by biodegradable agents (possible attack by rot and wood deteriorating insects), unfavourable influence of humidity changes rebounding in the changes of physical and mechanical properties of wood, its easy inflammability and combustibility. The reason of its failures is the fact that wood by its nature is an organic substance composed mainly of carbon, oxygen and hydrogen. From the viewpoint of the applied usage of wood in constructions it means that out of the three basic conditions for burning and fire origin (presence of combustible material, oxygen and sufficient temperature) in the case of wood structures at least the first two fulfilled (Osvald, 1997).

This fact brings about the necessity of detailed knowledge of fire-technical properties of wood, processes of its inflammation, burning and thermal decomposition. Description of the chemical and physical processes of burning of solid materials (Krakovský, 1992) is a serious research problem. This problem also involves the visualisation of temperature fields on the marginal layer of the wood – surrounding interface. It is a serious problem because it deals with a non-stationary phenomenon.

The heat transmission in the space is generally described by the partial differential equation (Božek, Halama, 1999). To investigate the arrangement of the temperature field by classical methods is possible, however, it is a slow and arduous process (Plášek, 1999). Therefore, the optical imaging method of holographic interferometry was applied to visualise the temperature fields. It helps reveal the physical essence of the investigated events, specify and expand the possibilities to display the physical fields without disturbing the observed area by sensors or sensing heads that are usually applied to detect local temperatures.