Abstract
The flow, heat transfer and emissions features of a methane–air premixed impinging flame jet on an oval flat tube involving both smooth and concave surfaces are numerically investigated. The effects of important parameters such as Reynolds number (Re = 400, 800, 1200, 1600 and 2000) and nozzle-to-tube distance (H/D = 3, 5 and 8) on streamlines, pressure coefficient temperature field, surface heat flux, energy efficiency and pollutants formation are evaluated. Results reveal that at higher Reynolds number, a larger recirculation zone beyond the concave surface is generated, the flame direction becomes horizontal and maximum temperature is shifted far away from stagnation point. The highest value of pressure coefficient is found at Re = 400 occurring on stagnation point. Under constant Reynolds number, the maximum temperature value belongs to configuration with less H/D in which the thermal boundary layer becomes narrower. Except for Re = 2000, the highest heat flux values are associated with stagnation point, while a considerable off-stagnation heat flux is detected for Re = 2000. More amount of energy releases for less H/D at lower Reynolds number, while an inverse behavior is observed at higher ones. Simulations show that the best energy efficiency is found at Re = 400 and H/D = 3. The production of CO species is of high remarkable value at Re = 400 when the space between nozzle and tube is reduced. The highest value of NOx production is distinguished at the highest H/D and lowest Re (i.e., H/D = 8 and Re = 400), while the concentration of UHC remarkably increases with rising Reynolds number, especially for higher H/D.
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