Experimental Investigation of Combined Forced and Free Laminar Convection in Horizontal Tubes

The present study considers the effects of property variations on fully developed laminar flow heat transfer and pressure drop in horizontal tubes. A facility was developed to test electrically heated glass and stainless steel tubes, with distilled water and ethylene glycol as working fluids. The Nusselt number for fully developed flow depends primarily on Rayleigh number; however, the Prandtl number and a dimensionless tube wall parameter are also required to correlate the four sets of heat transfer data. This correlation agrees well with data of most previous investigations. The friction factor increases with increasing Rayleigh number; data are within the bounds of limiting analytical predictions.