Abstract
IT has become of late years increasingly obvious that the equilibrium state of saturation, assumed as the basis of the theory of the steam-engine, does not apply accurately to the case of rapid expansion, especially in turbines. Steam in rapid expansion does not even begin to condense until its temperature has fallen far below the saturation limit. This fact has been familiar for many years as a general property of vapours called supersaturation, but it was not realised until recently that it might produce effects which could not be ignored in practice. Many authorities (e.g. Prof. Rateau, “Flow of Steam,”1905) held that there was no appreciable retard in the condensation even in a steam-nozzle where the expansion reaches the limit of rapidity. On the other hand, Callendar and Nicolson (Proc. Inst. C.E., 1897) found experimental evidence of supersaturation in the cylinder of a reciprocating engine at comparatively low speeds. Assuming that the adiabatic of supersaturated steam was simply a continuation of that of superheated steam, they calculated that a loss of 20 per cent. of available heat-drop would result at low pressures if there were no condensation; but as there was known to be a limit to the state of supersaturation they estimated that the actual loss due to this cause would not exceed 5 per cent, to 10 per cent, in practice, depending on the range and rapidity of expansion.
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CALLENDAR, H. Supersaturation and Turbine Theory 1 . Nature 102, 367–368 (1919). https://doi.org/10.1038/102367a0
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DOI: https://doi.org/10.1038/102367a0