Free convective heat transfer across inclined air layers

This paper presents new experimental measurements on free convective heat transfer rates through inclined air layers of high aspect ratio, heated from below. The Rayleigh number range covered is from subcritical to 10 to the 5; the range of the angle of inclination, theta measured from the horizontal is: between 0 and 70 degrees. Although it was anticipated that the results might be identical to the results for the horizontal layer if one replaced Ra by Ra cos theta, significant departures from this behavior were observed, particularly in the range Ra cos theta between 1708 and 10 to the 4, theta is between 30 and 60 degrees. A recommended relationship giving the Nusselt number as a function of Ra cos theta and theta is reported.