Experimental investigation of the heat transfer characteristics and thermal performance inside a ribbed serpentine channel during rotational effects

Abstract

The effect of the speed of rotation on heat transfer characteristics inside a ribbed serpentine channel was studied experimentally. In this study, ribs with square cross sections were located on the leading side (LS) and trailing side (TS) of the serpentine channel wall. The serpentine channel had an aspect ratio (AR) of 1.0 and a hydraulic diameter (Dh) of 50 mm. The rib pitch-to-height ratio (p/e), the rib height-to-hydraulic diameter ratio (e/Dh), the channel length-to-hydraulic diameter ratio (L/Dh), and radius ratio of the channel (r/Dh) were fixed at 10, 0.1, 8, and 5, respectively. There were four different types of geometries for the present study, viz. a smooth wall, a 90° ribbed wall, a 60° V-ribbed wall, and a 60° V-broken ribbed wall. The Reynolds number (Re) based on the hydraulic diameter of the channel was constant at 10,000, and the rotation numbers (Ro) were varied in the range from 0.0 to 0.30. The heat transfer coefficients in a serpentine channel were measured experimentally using the steady thermochromic liquid crystals (TLC) technique. In addition, the friction factor and the thermal-hydraulic performance were measured for each case. The results showed that the ribbed wall attained better regional heat transfer performances than the smooth wall for both stationary and rotating conditions at almost all locations. The heat transfer in the first pass was the highest on the TS wall, followed by the LS wall. A similar trend also occurred in the turn region. However, in the second pass, the heat transfer was the highest for the LS wall, followed by the TS wall. Due to the rotation, the Coriolis force acted on the TS wall in the first pass and on the LS wall in the second pass, while the direction of the centrifugal force was aligned with the radius of the rotation. As a result, the average heat transfer in the first pass was larger than it was in the second pass. The maximum average heat transfer and thermal performance inside a serpentine channel occurred in the case when there was a broken V-60° rib, i.e., it was increased up to about 2.1–2.4 in the range of Ro = 0.0–0.15. The thermal performance factor for the broken V-60° rib at Ro = 0.2–0.3 gained about 2.4–2.6, which was near the case of the V-60° ribs.