Heat transfer from a swirling hydrocarbon flame

In this study the concept of using an external tangential flow to control the heat transfer rates from a premixed hydrocarbon flame to the walls of a small combustion chamber over a wide range of burner Reynolds numbers, burner fuel/air equivalence ratios, and swirl intensities was examined experimentally and numerically. A vertical constant-flow cylindrical calorimeter located over a long glass tube burner with the swirl generators was used to measure the heat transfer rate to the chamber walls. The total heat transfer rate to the calorimeter walls was obtained from the measured rate of flow of the cooling water and its increase in temperature between the inlet and the outlet of the calorimeter.; Experimental observations were made to visualize the general structure of the exhaust gas flow-field and to provide a physical explanation for the trends observed in the heat transfer measurements. The visualization showed that the flame shape was significantly distorted due to the tangential velocity from a cone shape to a pyramid shape with a square cross section at weak swirl intensity and low burner Reynolds number. The flame shape then again changes from a pyramid shape to a cylindrical shape at moderate and high swirl intensity.; The experimental and numerical data indicate that applying tangential jets of air to the axial reactants before exiting the burner increases the heat transfer rate as much as 80 percent, and applying tangential jets of air around the burner premixed flame, close to the chamber walls, increases the heat transfer rate to the chamber walls as much as 60 percent. The heat transfer rate changes significantly at weak swirl intensities and low burner Reynolds numbers. This increase in the heat transfer rate is due to the dramatic change in the flame shape. The heat transfer rate increases steadily in the case of moderate and high swirl intensity. This increase in heat transfer rate is due to the centrifugal force applied to the gas and high velocity close to the chamber walls. The heat transfer from the swirling reactants indicates that the geometrical swirl numbers have the most significant effect, burner Reynolds numbers have less effect, and the burner fuel/air equivalence ratios have the least effect on the heat transfer rate to the calorimeter walls. In the swirling products, the injection mass ratios have the most significant effect, the burner fuel/air equivalence ratios have a lesser effect, and the burner Reynolds numbers have the least effect on the heat transfer rates to the calorimeter walls.; FLUENT software was used to model some of the experimental results. The experimental and numerical data indicate that the introduction of external tangential air increases the heat transfer rate to the calorimeter walls regardless of the method of application, and that the introduction of an external axial air jet decreases the heat transfer rate to the calorimeter walls.