## Abstract

Experimental over-all average heat-transfer coefficients for spheres in a subsonic air stream are presented for the slip-flow region in the range of Mach number M, and Reynolds number Re (based on diameter), 0.1 ⩽ M1 ⩽ 0.69 and 1.75 ⩽ Re1 ⩽ 124. A simplified analysis is presented which yields the convective heat-transfer coefficient for a rarefied gas by means of a correction to the continuum coefficient at the same Reynolds number. Comparison of this analysis is made with an existing theory for cylinders. An expression for the nondimensional over-all average heat-transfer coefficient for spheres in a rarefied subsonic flow is given as
$Nuavg=Nu°avg1+3.42M1Re1PrNu°avg$
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