Influence of inclined circular-ring turbulators on thermohydraulic characteristics

Abstract

The present research reports the numerical results of heat transfer enhancement, friction factor and thermal performance characteristics of the tubes inserted with inclined circular-rings (i-CRs) and transverse circular-rings. The inclined circular-rings with different inclination angles of 45^o, 60^o and 75^o and the transverse circular-rings 90^o), were numerically tested under uniform heat flux condition. The figure shows the secondary flow patterns in transverse planes in tubes equipped with the circular-rings, vortex/secondary flow exist in front of the inserts while recirculation zones appear behind the inserts. As inclination angle decreases, the sizes of the vortex/secondary flow and recirculation-zone signifcantly become larger. However, in case of the transverse circular-rings ( = 90^o) only recirculation zones appear together with dead zones which significantly suppress fluid mixing. The contour plots of temperature fields along the transverse plane of tube equipped with the inclined circular-rings and the transverse circular-rings at Re = 5000 are shown in the figure. Evidently, all inclined circular-rings ( = 45^o, 60^o and 75^o) cause more significant change of temperature field than the transverse ones ( = 90^o), attributed to the presence of vortex/secondary flows or high turbulent zones. This indicates that the inclined circular-rings give better fluid mixing and thus, high convection heat transfer than the transverse ones.