Numerical Analysis on Thermohydraulic Performance of the Tube Inserted with Rectangular Winglet Vortex Generators

The aim of this design was to improve the heat transfer performance significantly due to larger turbulent region and much vortices formed by tube inserted. In this article, the BSL k-ω model was chosen as turbulence model to simulate the thermohydraulic performance of the proposed tubes inserted with rectangular winglet vortex generators (RWVGs) when the Re was set as 5000 to 15,000. The reliability of the simulation results was obtained by comparing with the empirical formulas and experimental results. By means of numerical simulation, the influence mechanism of geometric parameters of RWVGs on thermal-hydraulic performance in tubes was analyzed. And the impact of three configurational parameters on the thermal performance was studied, namely the angle α, the height H and the number N of the RWVGs, respectively. The results revealed that the capacity of heat transfer in tubes with RWVG inserts was obviously larger than that in ordinary circular tube. In addition, it could be seen from the results that both Nu and f increased with the increase of H and N. At the same time, the case of α = 135° showed the greatest enhancement of thermal performance than the case of α = 45° and α = 90°.The PEC achieved the highest value of 1.23 when the height H of RWVG was 0.7 mm, the number N was 20, and angle α was 135°.

Slow axisymmetric rotation of a sphere in a circular tube with slip surfaces

The steady rotation of a slip spherical particle about a diameter lying along the longitudinal axis of a slip circular tube filled with an incompressible Newtonian fluid at low Reynolds numbers is analyzed. To solve the Stokes equations for the fluid flow, the solution is constituted by the summation of general solutions in both cylindrical and spherical coordinates. The boundary conditions are implemented first along the tube wall via the Fourier cosine transform and then over the particle surface through a collocation method. Results of the resisting torque acting on the particle are obtained for various values of the relevant dimensionless parameters. The effect of the confining tube on the axisymmetric rotation of the particle with slip surfaces is interesting. The torque increases monotonically with an increase in the stickiness of the tube wall, keeping the other parameters unchanged. When the stickiness of the tube wall is greater than a critical value, the torque is greater than that on the particle in an unbounded identical fluid and increases with increases in the stickiness of the particle surface and particle-to-tube radius ratio. When the stickiness of the tube wall is less than the critical value, conversely, the torque is smaller than that on the unconfined particle and decreases with increases in the particle stickiness and radius ratio.