Research Papers: Heat Transfer Enhancement

Protuberances in a Turbulent Thermal Boundary Layer

[+] Author and Article Information
Steven R. Mart, Stephen T. McClain

 Mechanical Engineering Department, Baylor University, Waco, TX 76798-7356Stephen_McClain@baylor.edu

J. Heat Transfer 134(1), 011902 (Nov 21, 2011) (12 pages) doi:10.1115/1.4004716 History: Received February 23, 2011; Revised July 15, 2011; Published November 21, 2011; Online November 21, 2011

Recent efforts to evaluate the effects of isolated protuberances within velocity and thermal boundary layers have been performed using transient heat transfer approaches. While these approaches provide accurate and highly resolved measurements of surface flux, measuring the state of the thermal boundary layer during transient tests with high spatial resolution presents several challenges. As such, the heat transfer enhancement evaluated during transient tests is presently correlated to a Reynolds number based either on the distance from the leading edge or on the momentum thickness. Heat flux and temperature variations along the surface of a turbine blade may cause significant differences between the shapes and sizes of the velocity and thermal boundary layer profiles. Therefore, correlations are needed which relate the states of both the velocity and thermal boundary layers to protuberance and roughness distribution heat transfer. In this study, a series of three experiments are performed for various freestream velocities to investigate the local temperature details of protuberances interacting with thermal boundary layers. The experimental measurements are performed using isolated protuberances of varying thermal conductivity on a steadily heated, constant flux flat plate. In the first experiment, detailed surface temperature maps are recorded using infrared thermography. In the second experiment, the unperturbed velocity profile over the plate without heating is measured using hot-wire anemometry. Finally, the thermal boundary layer over the steadily heated plate is measured using a thermocouple probe. Because of the constant flux experimental configuration, the protuberances provide negligible heat flux augmentation. Consequently, the variation in protuberance temperature is investigated using the velocity boundary layer parameters, the thermal boundary layer parameters, and the local fluid temperature at the protuberance apices. A comparison of results using plastic and steel protuberances illuminates the importance of the shape of the thermal and velocity boundary layers in determining the minimum protuberance temperatures.

Copyright © 2012 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Figure 1

Protuberances on an isothermal plate and on a plate with an unheated starting length (not to scale)

Grahic Jump Location
Figure 2

Turbulent viscous and thermal boundary layer profiles for situation

Grahic Jump Location
Figure 3

Side view of wind tunnel test section (all dimensions in meters)

Grahic Jump Location
Figure 4

Dimensionless surface temperatures for the 15 m/s case

Grahic Jump Location
Figure 5

Frossling number comparison of the unperturbed sections of the test plate

Grahic Jump Location
Figure 6

Measured skin friction coefficients versus Reynolds number

Grahic Jump Location
Figure 7

Measured velocity profiles cast in inner region coordinates

Grahic Jump Location
Figure 8

Measured temperature profiles cast in inner region coordinates

Grahic Jump Location
Figure 9

Measured integral boundary layer quantities and their variation versus local Reynolds number

Grahic Jump Location
Figure 10

Maximum apparent enhancement versus Reynolds number

Grahic Jump Location
Figure 11

Dimensionless temperature values along the centerline of the (a) large plastic element (b) steel element (c) small plastic element

Grahic Jump Location
Figure 12

The maximum protuberance dimensionless temperatures versus the local freestream Reynolds number

Grahic Jump Location
Figure 13

The maximum protuberance θ values versus the temperature thickness scaled by the protuberance height

Grahic Jump Location
Figure 14

The variation in the protuberance θmax values relative to the scaled temperature thickness adjusted for changes in local convection coefficients



Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In