valid.” Again this is conjecture. Linearity of the gas temperature profile may be related to flame radiation, but is not solely controlled by it. I t is interesting to note that in Figure 2 of the paper, the predicted gas temperature is linear even with the assumption of no flame radiation. 3. The comments concerning the uncertainties in some of my assumed heat transfer coefficients are true, and I clearly admit this in my paper. However, I think some of their comments are in error. You notice they state “the ‘correction factor,f’ is introduced to account for ‘the radiant energy that is absorbed by the gas.’ ” If that is truly its purpose, a corresponding factor should also appear in the gas-to-inner kiln wall heat transfer calculation.” Although the gas temperature is higher than the wall temperature, the wall will still radiate to
the colder solid. This radiation will definitely he “filtered” by the absorbing gas species in the combustion products. I n the radiation of the gas to the wall, this filtering is not present. 4. The comment that my comparison of the simulation results to those predicted by the handbook correlations is meaningless is true in one sense. The correlations are not really valid for the cases studied. However, the comparison was made to emphasize strongly the danger of using these correlations in the absence of better information. Allan Sass
U. S. Steel ,4pplied Research Laboratory Monroeville, Pa. 75746
Correction
CRYSTALLIZATION OF CALCIUM SULFATE FROM PHOSPHORIC ACID I n this article by A. B. Amin and M. A. Larson [IND.ENG. CHEM.PROCESS DESIGNDEVELOP.7, 133 (1968)], the following error has been discovered. The conversion factor from base 10 logarithms to natural logarithms was misapplied. All growth rates reported should be divided by 5.3, the square of the conversion factor, and the slope given in Figure 2 should be multiplied by 5.3. The slopes in Figures 5 and 6 are unaffected by this correction, but they should be shifted to the left a distance equal to log 5.3. This error does not alter the nucleation kinetic expression obtained nor the conclusions drawn.
SIMULATION OF HEAT-TRANSFER PHENOMENA IN A ROTARY KILN In this article by Allan Sass [IND.ENG. CHEM.PROCESS DESIGNDEVELOP.6 , 532 (1967)], Equation 3 is incorrect and should read
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I & E C PROCESS D E S I G N A N D DEVELOPMENT
