IMPROVEMENT OF THE BASIC CORRELATING EQUATIONS AND TRANSITION CRITERIA OF NATURAL CONVECTION HEAT TRANSFER

In this paper, improvements in the basic physical laws of natural convection heat transfer were implemented in two major respects through incorporating recent research findings in this field. A preferred transition criterion was adopted to correlate all the experimental data in this paper. Since the transition of correlation are primarily flow stability problems, the Grashof number, instead of the Rayleigh number, was found to be the preferred criterion. Furthermore, in the case of natural convection heat transfer from horizontal cylinder, a series of experimental data in the high Rayleigh number regions were available recently. These data made it possible to establish new reliable correlation and also to test the validity of previous correlation. It is concluded that the previous correlation for horizontal cylinder in high Rayleigh number regions was based on unreliable experimental results. The transition of laminar correlation for horizontal cylinder occurred at much higher values of Rayleigh number than the previous recommendation. In the case of natural convection teat transfer from vertical plate, more accurate property values for air under pressurized conditions are now available. This made it possible to re-plot the reliable data of Saunders. From this result and experimental result of Warner and Arpaci, a new set of basic correlation in natural convection heat transfer for laminar, transitional and turbulent regimes are recommended. These recommendations reflect a better understanding of the basic physical laws in the field of heat convection.