Performance analysis of a novel W-type radiant tube

Highlights: • A novel W-type radiant tube with a flue gas circulation structure was developed. • The effects of nozzle diameter on the N-WRT performance were analyzed and discussed. • The effects of nozzle location on the N-WRT performance were analyzed and discussed. • The effects of circulating tube diameter on the N-WRT performance were discussed. • The gas flow, temperature distribution, and NOx emission of the N-WRT were analyzed. -- Abstract: In this study, based on the structural characteristics of the traditional W-type radiation tube, a novel W-type radiant tube (N-WRT) with a flue gas circulation structure was developed to improve the heating uniformity of the radiator tube and the heating efficiency of the workpiece. New three-dimensional computational fluid dynamics modeling of the N-WRT was conducted to assess the heat transfer and combustion phenomena. In addition, the effects of nozzle diameter, nozzle location, and circulating tube diameter (all of which affect the main performance of the N-WRT) on the gas flow, temperature distribution, and nitrogen oxide (NOx) emission were analyzed and discussed in detail. Moreover, the amount of heat transfer, ratio of circulating flue gas, surface temperature distribution, thermal efficiency, and NOx concentration of the N-WRT based on different nozzle characteristics were compared. The results showed that the circulation ratio of flue gas increased from 0.47 at D60 mm to 2.2 at D28 mm. The NOx emission decreased most significantly from 100 ppm at D60 mm to 40 ppm at D50 mm. When the circulating tube diameter changed from 180 to 120 mm, the gas velocity at the junction decreased by 12%.