On gaseous free-convection heat transfer with well-defined boundary conditions

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Abstract

The scaling of free convection heat transfer is investigated. The nondimensional groups for Boussinesq and fully compressible variable property free convection, driven by isothermal surfaces, are derived using a previously published novel method of dimensional analysis. Both flows are described by a different set of groups. The applicability of each flow description is experimentally investigated for the case of the isothermal horizontal cylinder in an air-filled isothermal enclosure. The approach taken to the boundary conditions differs from that previous investigations. Here, it is argued that the best definition of the boundary conditions is achieved for heat exchange between the cylinder and the enclosure rather than the cylinder and an arbitrarily chosen fluid region. The enclosure temperature is shown both analytically and experimentally to affect the Nusselt number. The previously published view that the Boussinesq approximation has only a limited range of application is confirmed, and the groups derived for variable property compressible free convection are demonstrated to be correct experimentally. A new correlation for horizontal cylinder Nusselt number prediction is presented.

Original languageEnglish
Pages (from-to)661-668
Number of pages8
JournalJournal of Heat Transfer
Volume122
Issue number4
DOIs
Publication statusPublished - Nov 2000

Keywords

  • Cylinder
  • Heat transfer
  • Laminar
  • Natural convection
  • Scaling

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