Influence of Channel Orientation on Heat Transfer in a Two-Pass Smooth and Ribbed Rectangular Channel (AR=2:1) Under Large Rotation Numbers

Abstract

Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 (Dh=16.9 mm). Results for two surface conditions are presented: smooth and one ribbed configurations. For the ribbed channel, the leading and trailing walls are roughened with ribs (P/e=10, e/Dh=0.094) and are placed at an angle (α=45 deg) to the mainstream flow. For each surface condition, two angles of rotation (β=90 deg,135 deg) were studied. For each angle of rotation, five Reynolds numbers (Re=10–40 K) were considered. At each Reynolds number, five rotational speeds (Ω=0–400 rpm) were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data (±10%). Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap Nu/Nus ratio observed was 2.8.

Rotating Heat Transfer Measurements on a Multi-Pass Internal Cooling Channel: II — Experimental Tests

“…6). As expected, an overall enhancement with respect to the smooth channel case is observed on the whole channel surface thanks to the turbulent mixing produced by the ribs [6,11]. The same enhancement (about 1.5) is also found in the first 180° turn, at least in the measured area (the outer portion of the curve was not optically accessible).…”

“…In the experiments of [10] it is shown how the heat transfer inside a two-pass smooth square channel can vary with the channel orientation angle, the latter being defined as the angle between the channel outer wall in chord-wise direction and the channel rotation direction. The heat transfer inside a rectangular two-pass channel with 2:1 aspect ratio was studied by [11] for two channel orientations (90° and 45°) and smooth or ribbed walls. Again, it was reported how the channel orientation is important to heat transfer development and, in their particular case, it is beneficial to heat transfer augmentation on the leading surface of the first passage.…”

Formation of vertex flow in the rotating channel and influence of geometric factors on its intensity

“…Хух [4] провел экспериментальное исследова-ние влияние положения двухходового канала отно-сительно оси вращения на теплопередачу. Опыт осу-ществлялся при повороте канала на 90 и 135° отно-сительно оси вращения для гладкого канала и канала с оребрением.…”

“…Лей провел исследование влия-ния расстояния между ребрами в двухходовом вра-щающемся канале на интенсивность теплопередачи. Эксперимент выполняли на той же установке, что и в [4], для различных отношений расстояния между ребрами к высоте ребра (5; 7,5; 10). Угол располо-жения ребер к потоку составлял 45°.…”

Rotating Heat Transfer Measurements on a Multi-Pass Internal Cooling Channel: I — Rig Development

“…Probably the simplest way to do it is to make use of thermocouples installed on the measurement surface. Examples of the application of this method can be found in the contributions by [1][2]. The main drawback of this method is the spatial resolution achieved, which is usually not sufficient to investigate local heat transfer distributions generated by passage features (i.e.…”