CFD thermal analysis of a three-layer chimney used in residential buildings

Abstract

The two most important parameters to affect the performance and fire safety of a chimney are its insulation properties and the temperature distribution across its layers. When designing a chimney, one needs to consider both the normal conditions of its everyday exploitation as well as such emergencies as soot fire. Soot fire may cause the temperature inside a chimney flue to reach 1000 °C. This is why it is important that a chimney is designed and built in a way that prevents ignition of the remaining structural elements of a building in case of soot fire. Other important issues to consider include temperatures of the chimney's individual layers, which regulate the draft and thermal radiation during its exploitation. It is also worth considering a number of flammable (wooden) structural elements often located in the vicinity of a chimney. For the purpose of this work, in order to determine the temperature distribution and heat radiation of a three-layer steel chimney with an air layer, the author conducted Computational Fluid Dynamics (CFD) analysis. The numerical analysis was carried out for flue gas temperatures ranging 100–400 °C in individual layers of a chimney with special consideration of the cladding. The analysis also involved soot fire conditions, i.e. a temperature of 1000 °C, taking into consideration temperatures of the chimney cladding and a wooden structure that was heated through thermal radiation. The results of the analyses were compared with the findings of an experimental measurement. The conclusions of the numerical analysis are significant for chimney designers. The obtained data and the generated model may be used to conduct fire safety assessments of other chimneys of this type that are already in use.