Stress analysis of internally finned bayonet tube in a high temperature heat exchanger

In this paper, the thermal stress and deformation of the internally finned bayonet tube used for high temperature heat exchangers are presented. The internally finned bayonet tube is developed from the traditional bayonet tube, where the longitudinal plain fins are proposed to be welded on the inner surface of outer tube to enhance the heat transfer performance. However, significant temperature gradient is observed along both the axial and radial directions. The large stress is still generated in the joint of inner fin and inner tube, and the joint of inner fin and outer tube due to the discontinuous change of the structure, although the bayonet structure has a great potential to reduce the stress. Therefore, the inner fin and inner tube are proposed to not be welded together so that they can expand or contract freely and the expansion does not affect each other. The effect of gap between inner tube and inner fin on the stress and heat transfer performances is compared. The result indicates that the gap between them should be less than 1 mm for considered bayonet tube with 6 mm annulus height according to the coupled consideration of heat transfer and stress performances.