Work from Steam Expanded to Low Quality Levels

摘要

To improve the efficiency of steam engines, designers resorted to larger temperature differences between the heat source and the heat sink. A high temperature of approximately 1100 F, limited by the materials of construction, was soon reached. The heat sink is limited by the environment and mechanically to a large extent by the moisture level to which the work-fluid is expanded. Because of the close dimensional tolerances together with the inability to simultaneously remove the condensate, modern steam turbines are restricted to expansion cycles from super-heat to steam qualities of approximately 95%. Large losses of efficiency are experienced when expanding to lower steam qualities. Thus the development of modern reheat cycles which use multiple super-heats and turbines which result in cycle efficiencies of approximately 38%, and in more expensive installations. True reaction turbines overcome these limitations. This paper presents the effect of extending the expansion of super-heated steam beyond the saturated vapor line down to steam qualities of approximately 70% using true reaction turbines to obtain more economical cycles as efficient as reheat cycles.