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Research Papers: Forced Convection

Effect of Pin Tip Clearance on Flow and Heat Transfer at Low Reynolds Numbers

[+] Author and Article Information
Ali Rozati

Mechanical Engineering Department, Virginia Polytechnic Institute and State University, 114-I Randolph Hall, Mail Code 0238, Blacksburg, VA 24061

Danesh K. Tafti1

Mechanical Engineering Department, Virginia Polytechnic Institute and State University, 114-I Randolph Hall, Mail Code 0238, Blacksburg, VA 24061dtafti@vt.edu

Neal E. Blackwell

 U.S. Army RDECOM CERDEC, Fort Belvoir, VA 22060-5816

1

Corresponding author.

J. Heat Transfer 130(7), 071704 (May 20, 2008) (10 pages) doi:10.1115/1.2909184 History: Received April 20, 2007; Revised October 08, 2007; Published May 20, 2008

Cylindrical pin fins with tip clearances are investigated in the low Reynolds number range 5<ReD<400 in a plane minichannel. Five tip gaps are investigated ranging from a full pin fin (t*=0.0) to a clearance of t*=0.4D*, where D* is the pin diameter. It is established that unlike high Reynolds number flows, the flow and heat transfer are quite sensitive to tip clearance. A number of unique flow effects, which increase the heat transfer performance, are identified. The tip gap affects the heat transfer coefficient by eliminating viscosity dominated end wall effects on the pin, by eliminating the pin wake shadow on the end walls, by inducing accelerated flow in the clearance, by reducing or impeding the development of recirculating wakes, and by redistributing the flow along the height of the channel. In addition, tip gaps also reduce form losses and friction factor. A clearance of t*=0.3D* was found to provide the best performance at ReD<100; however, for ReD>100, both t*=0.2D* and 0.3D* were comparable in performance.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Definition of pin fin channel geometry and computational domain

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Figure 2

Comparison of f for numerical results and experiments of Kosar (15)

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Figure 6

Temperature (θ−θref) on the (a) bottom end wall (t=0.0), (b) top wall (t=0.3), and (c) pin-top surface (t=0.3) at ReD≈10

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Figure 8

Wake time-averaged streamlines at ReD≈325; (a) t=0.0 and (b) t=0.3

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Figure 9

Time-averaged temperature (θ−θref) on the pin surface at ReD≈325; (a) t=0.0 and (b) t=0.3

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Figure 10

Time-averaged temperature (θ−θref) on the (a) top wall, and (b) pin-top surface (t=0.3) at ReD≈325

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Figure 15

Increase in thermal conductance compared to a plane channel at the same pumping power

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Figure 3

Wake streamlines at ReD≈10; (a) t=0.0 and (b) t=0.3

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Figure 4

Velocity gradient (∂u∕∂n) on the bottom end wall at ReD≈10 (normalized by umax)

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Figure 5

Temperature (θ−θref) on the pin surface at ReD≈10; (a) t=0.0 and (b) t=0.3

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Figure 7

Surface temperature (θ−θref) of Domain II (t=0.1) at ReD≈10

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Figure 11

Time-averaged temperature (θ−θref) (top) and velocity gradient (∂u∕∂n, bottom) on the bottom end wall at ReD≈325 for (a) t=0.0 and (b) t=0.3

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Figure 12

(a) Friction factor and (b) friction factor ratio in pin finned channels

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Figure 13

Pin, end walls, and total Nusselt number versus ReD at all clearances

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Figure 14

(a) Heat transfer coefficient and (b) thermal conductance augmentation

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