Numerical investigation on cooling heat transfer and flow characteristic of supercritical CO2 in spirally fluted tubes

Abstract

To study the heat transfer and flow characteristic of supercritical CO2 cooling in the spirally fluted tubes, this paper presents numerically investigation of heat transfer performance of various cases within different geometric parameters (the radius of the groove r1, the radius of the fillet r2, the depth of the groove e1, the distance between the main tube and the outer sleeve e2 and the helix angle w). Based on the verified turbulent model at an inlet temperature of 323.15 K, an operating pressure of 8.0 MPa, an inlet Reynolds number of 35,000 and a total heat of 4200 W, the optimal structure is obtained (r1 = 6.5 mm, r2 = 2.0 mm, e1 = 5.5 mm, e2 = 1.0 mm, w = 0.70 rad) according to the evaluation factors proposed in the paper. The representative parameters (e1 and w) are employed to investigate the variation of the local heat transfer coefficient and turbulent kinetic energy, and mechanisms underlying the effect of parameters on heat transfer are revealed. Furthermore, the buoyancy effect is also discussed. Results show that the buoyancy force has an improvement effect on the heat transfer performance. However, as w increases, the influence of buoyancy will be weakened.