Effects of swirl on the heating process of a central gas stream in a tubular flame

•Swirl tubular flame burner yields a wider operation limit than the slit burner without rotation.•Heating rate enhances with swirl number via increase of heat transfer area or turbulence.•Turbulent mixing under cold flow evolves to flow laminarization under combustion condition.•Propose a formula employing swirl number to accurately predict the heating rate.