The effect of natural convection on viscous-flow heat transfer in horizontal tubes

Abstract

Experimental work dealing with the laminar flow of relatively non-viscous Newtonian liquids through a horizontal jacketed tube is described. The extent of the heat transfer by natural convection differs from that previously predicted [7, 8] and data from the literature are used in order to further examine the effect. It is shown that when the group ( Gr m Pr m D/L) is taken as the factor controlling natural convection, the information obtained in tubes of different dimensions is inconsistent. Better agreement is obtained when the ratio D/L is omitted from the group and further improvement results from the incorporation of the ratio L/D, all the data being adequately represented by the equation ▪ This equation becomes inaccurate when Gz m < π Nu am and it should be mentioned that the power of L/D is only provisional. Finally, the equations for heat transfer to fluids in both vertical and horizontal tubes are discussed with reference to the probable flow patterns obtained, and possible means of improving the form of the equations briefly described.