Computation of Free Convective Nusselt Number from Horizontal Cylinders Using Semi-Empirical Relationships

Natural convective heat transfer from a horizontal cylinder in gases is theoretically studied. A test cylinder of length 20cm is used. A thin wire runs coaxially in the cylinders of varied diameter of 0.01 to 0.03mm and is maintained at a constant temperature of 540C by an electric current. The wire is exposed progressively to air, argon, carbon dioxide, nitrogen and oxygen at atmospheric pressure and at 230C. On a logarithmic scale, the Nusselt number is plotted against the Raleigh number using five traditional correlations, Morgan, Kyte et al, Chu and Churchill, Kuehn and Goldstein, and Raithby and Holland. A new correlation relation is developed which agrees well with the basis Kyte et al experimental.