MEASUREMENTS OF HEAT-TRANSFER AND FRICTION COEFFICIENTS FOR AIR FLOWING IN A TUBE OF LENGTH-DIAMETER RATIO OF 15 AT HIGH SURFACE TEMPERATURES

摘要

The results indicate that in the turbulent range of Reynolds numbers based on tube diameter, good correlations of the average heattransfer and friction coefficients are obtained when the physical properties and density of the air are evaluated at a reference film temperature midway between the surface and fluid bulk temperature. The average heat-transfer coefficients correlated with those obtained previously from the same test equipment with longer tubes (length-to-diameter ratios of 30, 60, and 120) at high surface temperatures and heat fluxes on the basis that the average heat-transfer coefficient varies as the -0.1 power of the length-to-diameter ratio. The average friction coefficients were the same as the values obtained with longer tubes for Reynolds numbers above approximately 30,000.