Coanda flames for development of flat burners

Abstract

The Coanda effect is the tendency of a fluid to stay attached to a nearby surface. Since its discovery, several applications have been developed in aerodynamics, heat transfer and medical fields using this concept. A potential, and currently unexplored, application of the Coanda effect is its use in heating equipment. However, few research has been conducted on the behavior of flames under a Coanda flow pattern regime. Thus, the present study uses a generic swirl burner to analyze influence of the flow rate and fuel mixture on the flame stability. The objective is to identify differences in the behavior of a flame under an Open jet flow pattern and Coanda jet flow pattern that will lead to further development of novel flat burners. Changes in the burner configuration were made to induce one of the two flow patterns. Methane was used as a fuel and air as an oxidizer. Both gases were supplied to the burner at ~20°C and almost atmospheric pressure. Flow rates were regulated using variable area flowmeter. Gas flow was increased from 3 L/min to a maximum of 12 L/min with incremental steps of 1 L/min. For each gas flow rate, the oxidizer flow rate was increased, and the flame behavior recorded. It was found that a stable Coanda flame could only be induced when an Open jet flame existed. It is theorized that this behavior is due to a coherent structure that breaks down when a stable Open jet flame changes to Coanda flame. The concept is now presented as a novel option for development of novel, large industrial devices capable of stabilizing the flame while reducing size for their use in high temperature processes.