Undercooling in Steam Nozzles

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Abstract
This paper deals primarily with the effect of wall roughness on the flow of steam in nozzles; and secondarily with drop growth and the occurrence of initial condensation. It was found that roughness of the nozzle walls caused a retardation of steam flow and resulted in the Wilson line’s occurring at the 3.2 per cent moisture line on the Mollier diagram instead of at the 3.7 per cent moisture line as was found for a nozzle with smooth walls. In a specially designed nozzle drop growth was accomplished as evidenced by the complete visible spectrum which resulted from the scattering of light by the expanding steam in this nozzle. Photographs of the condensation region show that condensation is not occurring at any point previous to where the eye sees it. These researches indicate that the location of the Wilson line on the Mollier diagram depends entirely upon the rate of change of velocity of the steam, and, therefore, cannot be fixed for all conditions. In accordance with this fact it is suggested that the term “Wilson line” is a misnomer and should be replaced by the more appropriate one of “Wilson zone.”

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