Abstract

An experimental study of the laminar free convective average heat transfer in air from isothermal vertical slender cylinder having circular cross-section was performed using a transient technique. These results obtained for Prandtl number Pr = 0.71 in the range of Rayleigh number 1.5 × 10 8 < Ra H < 1.1 × 10 9 and dimensionless height of 0 < H/ D < 60 are correlated with the equation Nu H = ARa H n where A = 0.519 + 0.03454( H/ D) + 0.0008772( H/ D) 2 + 8.855 × 10 −6( H/ D) 3 and n = 0.25–0.00253 ( H/ D) + 1.152 × 10 −5 ( H/ D) 2 agree well with the known numerical data which are approximated with the equation Nu H /Nu H− FP = f( Gr H , H/ D) valid in laminar boundary layer region ( Gr H-crit ⩽ 4 × 10 9) for fluids of Prandtl number within 0.01 < Pr < 100 and for the transverse curvature parameter ξ = 32 Gr H 0.25 H D < 5 . Besides the slenderness criterion determining situation when the vertical isothermal cylinder of circular cross-section cannot be treated as a flat plate is presented in the form Gr H 0.25 D H ⩽ f ( Pr ) .

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