Comparison of Isothermal Heat Transfer. A s s tated prev ious ly, the

free convection heat transfer from an isothermal horizontal cylinder was first solved by Hermann [1], It is therefore advisable to compare the present heat transfer results with those of [1], Since Hermann's results are valid for Pr = 0.74, it is necessary to modify his results so that the comparison may be made based on the same Prandtl number (i.e., Pr = 0.7). Using (23), it is found that the correction factor is 0.976, i.e., / Nu \ / Nu \ Using equation (25), the heat transfer results as given by Her-mann and those of the present calculations for Pr = 0.7 are listed as follows: method. The wall surface temperature is assumed to be varied in the manner of a,(x/R)2 + a2(x/R)4. A special transformation is used so that the solutions are independent of the parameters ai and a2, and hence results are applicable for all reasonable values of tfi and (i2. It is found that the functional relationship between heat transfer and the Prandtl number for a cylinder is essentially the same as that for a vertical plate. Furthermore, the wall tem-perature variation has a significant effect on heat transfer and the heat transfer from a nonisothermal wall may not be computed from solutions corresponding to an isothermal wall. Acknowledgment The authors wish to express their appreciation to Mr. N. Carver for preparing the figures in this paper