The Determination of Working Process Indicators in a Steam Screw-Type Machine

The authors propose a method of determining the working process indicators of a steam screw-type machine (SSM).  The method takes into account heat exchange with the SSM walls for superheated and wet vapour, as well as losses of the working medium due to throttling through the gaps between the SSM working parts and incomplete expansion of the steam between the screw rotors.  The article describes a method of determining the parameters at the expansion endpoint, which is located in the wet vapour area. The similarity criteria based on the SSM design and operating parameters are introduced. For non-stationary volume expansion in the screw groove, it is important that the Strouhal number is considered. This criterion is obtained by comparing the time of supercritical drain of the working cavity through the gaps between the screws, with the typical time of the working cycle. Criterion dependencies connecting the experimentally obtained relative indicated and discharge efficiency with the Strouhal number are presented in the article. It is shown that the experimental results are consistent with the obtained criterion dependency.

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