2019 年 4 巻 p. 49-54
Experimental investigations have been carried out on the fluid flow and heat transfer of natural convection induced in a horizontal circular slot. The circular slot confined with two circular disks of equal diameter, where the lower disk is heated with uniform temperature and the upper disk is insulated. Water was adopted as a working fluid. The diameter D and the gap between two disks H were varied systematically as, D = 50-250 mm, and H = 10-50 mm, ∞ (without upper disk). The flow fields were first visualized with dye. The results depicted that the following flows appear in the circular slots. A laminar boundary layer develops over the lower disk near the outer periphery of the slot. Then, the boundary layer separates threedimensionally from the surface of the lower disk, and the streaky flow appears downstream the separation, and a turbulent flow is attained near the center of the slot. It was found that the onset of the separation over the lower disk shifts to the outer periphery of the slot, and that the radial-pitches of the separation are decreased significantly with decreasing the gap H. The overall Nusselt numbers of the heated lower disk were subsequently measured. The results showed that the Nusselt numbers remain identical as those without the upper disk when the gap H is large enough. However, the numbers decrease significantly with decreasing H, in particular, when the diameter of the disk D is large.
