Does swirl number affect the radiative and convective heat transfer from diffusion hydrogen-methane blended flames?

• The author investigated the heat transfer properties of hydrogen-methane blended flames. • The study included both the radiative and convective heat transfer measurements. • The investigation evaluated the effect of swirl number on a flame’s heat transfer. • Methane flames were found to have greater radiative heat transfer than hydrogen. • The study indicated a trend between local temperature and convective heat transfer. Industries are exploring hydrogen fuel switching to achieve net-zero targets. Pure hydrogen combustion eliminates carbon dioxide emissions, but this could adversely affect the heating performance since much of the radiative heat transfer from hydrocarbon flames originates from hot carbon dioxide molecules and soot particles, absent from hydrogen combustion. To investigate the effect of swirl number on a flame’s heat transfer, a generic swirl burner was operated at 25 kW thermal input, with three geometric swirl numbers, a fixed equivalence ratio of 1.0 and methane-hydrogen blends of 0–100 % by volume. Hydrogen and methane exhibited different radiative and convective heat transfer properties. Results showed that increasing geometric swirl number produced shorter flames with lower radiative heat transfer. The maximum radiative heat flux of a flame occurred between ∼50–70 % along the flame’s length. Increasing hydrogen blending resulted in an increased flame temperature. 25–50 % hydrogen blending enhanced methane flame’s radiative heat transfer, while further blending reduced it. Local convective heat flux correlated well with local gas temperature, regardless of fuel. The ratio of radiation to convection was greatest early in the flame, with convection increasing along the flame’s length. Both heat transfer modes decreased at similar rates with radial distance from the burner centreline. This study examined the temperature of a steel slab using a thermocouple array to analyse heat transfer. While the hypothesis was not confirmed, results showed process temperatures are influenced by multiple factors. Steel temperatures were setup specific. Heat flux, flame, and product temperature measurements provided a strong heat transfer assessment.