Influence of Entrance Geometry on Heat Transfer in Rotating Rectangular Cooling Channels (AR=4:1) With Angled Ribs

Abstract

The effect of entrance geometry on the heat transfer in rotating, narrow rectangular cooling channels is investigated in this study. Both smooth channels and channels with angled ribs are considered with three different entrance conditions: fully developed, sudden contraction, and partial sudden contraction. The rectangular channel has as aspect ratio of 4:1, and it is oriented at 135° with respect to the plane of rotation. In the test section with angled ribs, the ribs are angled at 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio e/Dh is 0.078, and the rib pitch-to-height ratio P/e is 10. The range of flow parameters includes Reynolds number (Re=5000–40,000), rotation number (Ro=0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ=0.12). The heat transfer at the entrance of the heated portion of the smooth channel is significantly enhanced with the sudden contraction and partial sudden contraction entrances. In the smooth rotating channels, the effect of the entrance geometry is also present; however, as the rotation number increases, the effect of the entrance geometry decreases. It was also found in this study that the sudden and partial sudden contraction entrances provide higher heat transfer enhancement than the fully developed entrance through the first three to four hydraulic diameters of the channels with angled ribs. Again, the effect of the entrance geometry is greater in the stationary channels with angled ribs than the rotating channels with ribs. In both stationary and rotating channels, the influence of the entrance geometry on the heat transfer is more apparent in the smooth channels than in the ribbed channels.

Effects of inlet velocity profile on flow and heat transfer in the entrance region of a ribbed channel

“…Huh et al [12,13] compared four different entrance shapes of a 4:1 stationary channel and showed that the change in the entrance shape could result in three times higher heat transfer performance. Wright et al [14] studied three different entrance shapes of s-shape, 90°bend entrance, and twisted entrance cases, and confirmed that the entrance shape affected the distribution of local velocity and heat transfer performance.…”

Effect of rib height on heat transfer in a two pass rectangular channel (AR=1:4) with a sharp entrance at high rotation numbers

“…The heat transfer enhancement differs from that of fully developed flow when entrance effects are present. Wright et al [16] conducted a survey of rectangular channels with aspect ratios of 4:1 and 8:1. They studied three different entrance geometries and concluded that the entrance effects will greatly enhance the heat transfer.…”

Heat transfer study in a rotating ribbed two-pass channel with engine-similar cross section at high rotation number

“…Wright et al [20] performed experiments in channels with three different entrance geometries. They concluded that the entrance condition enhanced the heat transfer.…”