Natural Convection Adjacent to Horizontal Surface of Various Planforms

[+] Author and Article Information
J. R. Lloyd, W. R. Moran

University of Notre Dame, Notre Dame, Ind.

J. Heat Transfer 96(4), 443-447 (Nov 01, 1974) (5 pages) doi:10.1115/1.3450224 History: Received April 08, 1974; Online August 11, 2010


Natural convection adjacent to horizontal surfaces of circular, square, rectangular, and right triangular planforms has been studied experimentally. Electrochemical techniques were employed involving a fluid with a Schmidt number of about 2200. The results encompass a wide range of Rayleigh numbers thus providing information on both the laminar and the turbulent regimes. The data for all planforms are reduced to a single correlation in the laminar and turbulent regimes using the characteristic length, as recommended by Goldstein, Sparrow, and Jones. L* = A/p, where A is the surface area and p is the surface perimeter. The laminar data for all planforms are correlated by the expression

Sh = 0.54 Ra1/4
  (2.2 × 104 ≤ Ra ≤ 8 × 106)
and the data for the turbulent regime are correlated by the expression
Sh = 0.15 Ra1/3
  (8 × 106 ≤ 1.6 × 109)
Transition is found to occur at about Ra = 8 × 106 . The present work thus significantly extends the Rayleigh number range of validity for the use of L* through the 1/4 power laminar regime into the turbulent 1/3 power regime. It also demonstrates the validity of the use of L* to correlate natural convection transfer coefficients for highly unsymmetrical planforms, which heretofore had not been demonstrated. Comparisons to analytical solutions and other experimental heat and mass transfer data are presented.

Copyright © 1974 by ASME
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