Natural convection heat transfer from a horizontal cylinder in liquid sodium - Part I. Experimental results

Natural convection heat transfer from horizontal 7.6 and 10.7 mm diameter test cylinders to liquid sodium were measured for the heat fluxes ranging from 8 x 10(3) to 2.64 x 10(6) W/m(2). The average Nusselt numbers for 7.6- and 10.7 mm diameter test cylinders are in good agreement with each other in the overlapping range of 1.5 less than or equal to GrPr(2)/(1 + Pr) less than or equal to 35 on the graph of log Nu versus log GrPr(2)/(1 + Pr). The average Nusselt numbers were obtained for GrPr(2)/(1 + Pr) from 0.2 to 120 (41 less than or equal to Ra less than or equal to 25 650) as a single curve on the graph by using these two different diameter cylinders. The average Nusselt numbers become higher than the values predicted by the correlation of Kutateladze et al, from 36 to 100% with decreasing Rayleigh numbers. It was assumed that this is because the boundary layer approximation by which the correlation was derived becomes inappropriate as the thermal boundary layer becomes thicker compared with the cylinder diameter with decreasing Rayleigh numbers. The natural convection heat transfer correlation of Churchill and Chu, that of Hyman et al. and that of Sugiyama ct al. underpredicted the experimental results about 20%, from 43 to 66%, and from 8 to 14%, respectively. (C) 1999 Elsevier Science S.A. All rights reserved.