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EXPERIMENTAL SIMULATION OF THE FIRE PLUMES: EFFECTS OF AN AIR ENTRAINMENT MODE ON THE SELF-SIMILARITY ZONE

DOI: 10.1615/ICHMT.2009.CONV.480
page 16

A O M Mahmoud
University of Nouakchott

Jamel Bouslimi
National Institute of the Applied Sciences and Technology, BP 676, 1080 Tunis, Tunisia

Rejeb Ben Maad
University Tunis El Manar, Faculty of Sciences of Tunis, Department of Physics, Laboratory of Energizing and Thermal and Mass Transfers, 2092 El Manar II, Tunis, Tunisia

Abstract

This paper presents an experimental simulation of the two heat sources of fire plumes, one placed at ground level, the other at a height above the ground, in order to determine the effects of source air entrainment on the self-similarity zone. The development of a free thermal plume was examined by a plume produced from an electrically heated disk at a constant temperature. We first studied the existence of the self-similarity zone in a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the axial development of the plume showed that the beginning of the self-similarity zone is close to the source. In this zone, the profiles can be deduced one of the other through a simple mathematical transformation and the turbulence is fully developed. We then determined the existence of the self-similarity zone of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume. Analysis of the results noted that the maximal axial velocity is localised at an altitude relatively moved away of the source. The radial profiles become self-similar and almost identical indicating that the turbulence is fully developed. Comparison of the plumes produced from the two configurations showed that the self-similarity zone is strongly influenced by the nature of the source of air entrainment. With the lateral entrainment of air, the self-similarity zone is reached at a level close to the source; whereas with the simultaneous vertical and lateral entrainment mode the maximal axial velocity is reached only at a relatively distant altitude. The lateral entrainment mode entails a faster development of the flow from the location of a more rapid spread of the plume.

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