Effect of mixture composition on heat transfer characteristics of impinging methane-air flame jets of tube burners equipped with twisted tapes

Present study investigates the effect of the mixture equivalence ratio on the heat transfer characteristics of impinging premixed methane-air flame jets of tube burners equipped with twisted tape inserts. The induced swirl flow enhances the mixing process and improves the flame stability limits. The flame jet with mixture Reynolds number of 800 and burner to plate spacing of four times burner diameter is chosen based on the flame stability range. The heat transfer characteristics of non-swirling flame jet are compared with the swirling flame jets for various mixture compositions. Swirl flow is achieved with twisted tape inserts having twist ratios of 2, 3.2, 4.5 and 7.5. Twisted tape inserts resulted asymmetric flame. The flame shape is found to be highly influencing the heat transfer from the flame jet to the target surface. Better heat transfer distribution is achieved with stoichiometric mixture. However, the rich mixture produces more uniform heat flux distribution. Best thermal performance is observed for twisted tape with twist ratio of 7.5. The present study helps in better understanding and optimum design of the flame jet impingement heat transfer equipment.