Effect of Helical Vane Swirler Geometry on Heat Transfer Characteristics for Compressed Natural Gas/Air Swirling Flame Impinging on a Flat Surface

Abstract

An experimental study has been conducted to investigate the effect of helical vane swirler geometry on heat transfer characteristics for compressed natural gas (CNG)/air swirling flame impinging on a flat surface. Effects of helical vane swirler geometric parameters like, length of helical insert (25 mm, 45 mm and 65 mm), depth of groove on the helical insert (2.5 mm, 3.5 mm and 4.5 mm) and number of helical vanes (8, 10 and 12), on heat transfer characteristics have been studied. All the inserts were having fixed helical vane angle of 45°. Also, the burner exit diameter was kept constant (d = 20 mm). Experiments were conducted at different dimensionless separation distances (6, 4, 3 and 2) for fixed values of Reynolds number (6000) and equivalence ratio (1.3). Significant variation in the heat flux profiles has been observed for different swirler inserts till the radial hump in heat flux. After the radial hump, almost in all cases, the heat flux lines merged together. These variations in the heat flux profiles were due to different level of swirling intensities produced by different swirlers at fixed value of the helical vane swirler angle. It was observed that the heating was comparatively more uniform at larger separation distances (H/d = 6). It has been concluded that defining swirl intensity only with the helical vane swirler angle would be incorrect for such type of swirlers. Other geometric parameters of the swirler like, number of vanes, length of the swirler and the depth of the groove should also be included in swirl intensity definition.