NDLI: Polytropic Change of State Calculations With Condensation or Evaporation and its Use for Thermal Power Cycles

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Hans, E. Wettstein
Copyright Year	2015
Abstract	In the paper [1] three polytropic change of state calculation methods for air gases and CO2 are compared. The conclusions are that the most used formulas can produce with the same input data deviations in terms of polytropic efficiency up to 1.5% points even for nearly ideal gases like nitrogen. The paper suggests therefore a recursive algorithm, which is based directly on the classic definition of a polytropic change of state. This definition assumes a constant dissipation rate during an adiabatic change of state. The proposed algorithm can be applied for any gas with an equation of state, which is an unambiguous function of the two variables pressure p and temperature T. The latter condition is not fulfilled by steam in the wetness range because the specific volume v depends not only from p and T but also from the vapor fraction x. The aim of this paper is the development of an analogous recursive “constant dissipation rate algorithm” for a two phase mixture assuming equilibrium conditions between the vapor and the liquid fractions. The method shall be demonstrated with expanding wet steam. The result of the algorithm will be the discharge enthalpy, temperature and the discharge vapor fraction for given initial pressure and temperature, discharge pressure and polytropic efficiency. Based on the developed formulas some well-known but nevertheless paradoxically perceived results and comparisons with expanding dry air can be shown.
Sponsorship	International Gas Turbine Institute
File Format	PDF
ISBN	9780791856796
DOI	10.1115/GT2015-42075
Volume Number	Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines
Conference Proceedings	ASME Turbo Expo 2015: Turbine Technical Conference and Exposition
Language	English
Publisher Date	2015-06-15
Publisher Place	Montreal, Quebec, Canada
Access Restriction	Subscribed
Subject Keyword	Cycles Computational methods Temperature Enthalpy Equilibrium (physics) Carbon dioxide Vapors Evaporation Nitrogen Condensation Pressure Thermal energy Gases Algorithms Equations of state Energy dissipation Steam
Content Type	Text
Resource Type	Article

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