Research Papers

Rib Turbulator Heat Transfer Enhancements at Very High Reynolds Numbers

[+] Author and Article Information
Mingyang Zhang

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061
e-mail: mingyz1@vt.edu

Prashant Singh

Department of Mechanical and Aerospace Engineering,
North Carolina State University,
911 Oval Dr., Engineering Building 3, Room 3002,
Raleigh, NC 27695
e-mail: psingh23@ncsu.edu

Srinath V. Ekkad

Department of Mechanical and Aerospace Engineering,
North Carolina State University,
911 Oval Dr., Engineering Building 3, Room 3002,
Raleigh, NC 27695
e-mail: sekkad@ncsu.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Thermal Science and Engineering Applications. Manuscript received June 27, 2018; final manuscript received April 2, 2019; published online May 20, 2019. Assoc. Editor: T.S. Ravigururajan.

J. Thermal Sci. Eng. Appl 11(6), 061014 (May 20, 2019) (9 pages) Paper No: TSEA-18-1329; doi: 10.1115/1.4043465 History: Received June 27, 2018; Accepted April 03, 2019

High-pressure stage gas turbine blades feature serpentine passages where rib turbulators are installed to enhance heat transfer between the relatively colder air bled off from the compressor and the hot internal walls. Most of the prior studies have been restricted to Reynolds number of 90,000 and several studies have been carried out to determine geometrically optimized parameters for achieving high levels of heat transfer in this range of Reynolds number. However, for land-based power generation gas turbines, the Reynolds numbers are significantly high and vary between 105 and 106. The present study is targeted toward these high Reynolds numbers where traditional rib turbulator shapes and prescribed optimum geometrical parameters have been investigated experimentally. A steady-state liquid crystal thermography technique is employed for measurement of detailed heat transfer coefficient. Five different rib configurations, viz., 45 deg, V-shaped, inverse V-shaped, W-shaped, and M-shaped have been investigated for Reynolds numbers ranging from 150,000 to 400,000. The ribs were installed on two opposite walls of a straight duct with an aspect ratio of unity. For very high Reynolds numbers, the heat transfer enhancement levels for different rib shapes varied between 1.4 and 1.7 and the thermal hydraulic performance was found to be less than unity.

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Fig. 1

Schematic of experimental setup

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Fig. 2

Liquid crystal assembly (not drawn to scale), isometric view of the ribbed channel (blue color indicating thermochromic liquid crystal sheet)

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Fig. 3

Test configurations

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Fig. 4

Wall temperature variation with normalized hue

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Fig. 5

Nusselt number ratio (Nu/Nu0) for 45-deg inclined ribs at the selected region 3.75 < x/dh < 4.75: (a) Re = 179,457, (b) Re = 264,199, (c) Re = 307,218, (d) Re = 348,941, and (e) Re = 390,986

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Fig. 6

Nusselt number ratio (Nu/Nu0) for V-shaped ribs at the selected region 3.75 < x/dh < 4.75: (a) Re = 168,013, (b) Re = 252,900, (c) Re = 292,468, (d) Re = 334,912, and (e) Re = 376,534

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Fig. 7

Nusselt number ratio (Nu/Nu0) for Inverted V-shaped ribs at the selected region 3.75 < x/dh < 4.75: (a) Re = 167,782, (b) Re = 249,689, (c) Re = 291,258, (d) Re = 331,596, and (e) Re = 372,244

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Fig. 8

Nusselt number ratio (Nu/Nu0) for W-shaped ribs at the selected region 3.75 < x/dh < 4.75: (a) Re = 169,454, (b) Re = 250,197, (c) Re = 291,584, (d) Re = 331,955, and (e) Re = 372,617

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Fig. 9

Nusselt number ratio (Nu/Nu0) for M-shaped ribs at the selected region 3.75 < x/dh < 4.75: (a) Re = 169,390, (b) Re = 250,580, (c) Re = 291,744, (d) Re = 332,839, and (e) Re = 373,668

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Fig. 10

Regionally averaged Nusselt number ratio variation with Reynolds number

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Fig. 11

Normalized friction factor variation with Reynolds number

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Fig. 12

Thermal hydraulic performance variation with Reynolds number

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Fig. 13

Friction roughness function (R) variation with roughness Reynolds number (e+)

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Fig. 14

Heat transfer roughness function (G) variation with roughness Reynolds number (e+)



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