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This paper discusses various low density effects on convective heat transfer, and presents useful design information on the individual effects. These low density effects include the merged viscous layer, slip, viscous interaction, transverse curvature, entropy gradient, non-equilibrium, transition and free molecule effects. Hoshizaki's merged viscous layer analysis is discussed and compared to a similar analysis by Probstein and Kemp. Both found that the merged viscous layer effect increases the heat transfer over continuum values. The effect of shock layer entropy gradients on the surface heat transfer is also presented. It is shown that entropy gradients increase the heat transfer, particularly for those portions of the body whose impinging streamlines have passed through the highly oblique regions of the shock. A simplified, approximate engineering method has recently been developed by the author, in order to predict the surface heat transfer on a flat plate with pressure gradient, caused by nose bluntness and viscous interaction effects. This method is discussed, including the attempts of this method to allow for the effect of sweep and angle of attack on the heat transfer. It is also shown that the effects of slip are small compared to other low density effects. (Author)