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RESEARCH PAPERS: Heat and Mass Transfer

# Heat (Mass) Transfer Distribution in a Two-Pass Trapezoidal Channel With a $180deg$ Turn

[+] Author and Article Information
S. W. Lee, H. S. Ahn

Convective Heat and Mass Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

S. C. Lau1

Convective Heat and Mass Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

1

Corresponding author.

J. Heat Transfer 129(11), 1529-1537 (Mar 08, 2007) (9 pages) doi:10.1115/1.2764084 History: Received August 03, 2006; Revised March 08, 2007

## Abstract

The heat transfer characteristics of airflows in serpentine cooling channels in stator vanes of gas turbines were studied. The cooling channels were modeled as a two-pass trapezoidal channel with a $180deg$ turn. Naphthalene sublimation experiments were conducted and the heat and mass transfer analogy was applied to study the local heat (mass) transfer distributions on one of the two primary walls of the channel. Results were obtained for turbulent airflow through the channel with smooth walls, and with transverse ribs on one wall and on two opposite walls, over a range of Reynolds numbers between about 10,000 and 60,000. The results showed that there was a very large variation of the local heat (mass) transfer distribution in the turn and downstream of the turn. In all of the cases studied, the regional average heat (mass) transfer was higher on the downstream half of the turn than on the upstream half of the turn and was higher in the turn with the flow entering the channel through the smaller straight section than when the flow was reversed. The shape of the local heat (mass) transfer distribution at the turn was not significantly affected by varying the air mass flow rate. In the smooth wall case, the local heat (mass) transfer was high near the end wall and the downstream outer wall in the turn and was relatively low in two regions near the upstream outer wall and the downstream edge at the tip of the divider wall in the turn. With ribs on two opposite walls, the variation of the local heat (mass) transfer was larger, especially in the turn and downstream of the turn, than in the smooth wall case. The pressure drop across the turn was higher in the case of the flow entering the channel through the larger straight section than when the flow was reversed. As expected, the ribs increased the pressure drop across the turn.

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## Figures

Figure 1

Schematic of test apparatus for this study

Figure 2

Schematics of walls of trapezoidal test channel

Figure 3

Local mass transfer distributions at sharp turn in square channel with smooth walls

Figure 4

Segmental mass transfer distributions along square channel with smooth walls

Figure 5

Local mass transfer distributions at sharp turn in trapezoidal channel with smooth walls and a smaller inlet straight section

Figure 6

Local mass transfer distributions at sharp turn in trapezoidal channel with smooth walls and a larger inlet straight section

Figure 7

Segmental mass transfer distributions along trapezoidal channel: (a) with smooth walls, (b) with ribs on one wall, and (c) with ribs on two opposite walls

Figure 8

Local mass transfer distributions at sharp turn in trapezoidal channel with ribs on two opposite walls and a smaller inlet straight section

Figure 9

Local mass transfer distributions at sharp turn in trapezoidal channel with ribs on two opposite walls and a larger inlet straight section

Figure 10

Overall pressure drops across sharp turns in square and trapezoidal channels

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