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Division 3.3.2.1 Vapour pressure of water

United Kingdom

Original text. Later amendments are not shown.

The vapour pressure of water p H2O [kPa] for a given saturation temperature condition, T sat [K], shall be calculated by means of equations (7-77) or (7-78):

  1. (a)

    For humidity measurements made at ambient temperatures from 0 to 100 °C or for humidity measurements made over super-cooled water at ambient temperatures from – 50 to 0 °C:

    log 10 p H2O = 10,79574 × 1 − 273,16 T sat − 5,02800 × log 10 T sat 273,16 + 1,50475 × 10 − 4 × 1 − 10 − 8,2969 × T sat 273,16 − 1 + 0,42873 × 10 − 3 × 10 4,76955 × 1 − 273,16 T sat − 1 − 0,2138602 (7-77)

    Where:

    p H2O

  2. vapour pressure of water at saturation temperature condition [kPa]

    3. T sat

  3. saturation temperature of water at measured condition [K]

  • (b)

    For humidity measurements made over ice at ambient temperatures from (– 100 to 0) °C:

    log 10 p H2O = − 9,096853 × 273,16 T sat − 1 − 3,566506 × log 10 273,16 T sat + 0,876812 × 1 − T sat 273,16 − 0,2138602 (7-78)

    Where:

    T sat

  • saturation temperature of water at measured condition [K]