Water vapor and mechanical work: A comparison of Carnot and steam cycles

Research output: Contribution to journalArticlepeer-review


The impact of water vapor on the production of kinetic energy in the atmosphere is discussed here by comparing two idealized heat engines: the Carnot cycle and the steam cycle. A steam cycle transports water from a warm moist source to a colder dryer sink. It acts as a heat engine in which the energy source is the latent heat of evaporation. It is shown here that the amount of work produced by a steam cycle depends on relative humidity and is always less than that produced by the corresponding Carnot cycle. The Carnot and steam cycles can be combined into a mixed cycle that is forced by both sensible and latent heating at the warm source. The work performed depends on four parameters: the total energy transport; the temperature difference between the energy source and sink; the Bowen ratio, which measures the partitioning between the sensible and latent heat transports; and the relative humidity of the atmosphere. The role of relative humidity on the work produced by a steam cycle is discussed in terms of the Gibbs free energy and in terms of the internal entropy production.

Original languageEnglish (US)
Pages (from-to)91-102
Number of pages12
JournalJournal of the Atmospheric Sciences
Issue number1
StatePublished - Jan 2011


  • Energy transport
  • Hydrologic cycle
  • Kinetic energy
  • Latent heating/cooling
  • Thermodynamics
  • Water vapor

ASJC Scopus subject areas

  • Atmospheric Science


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