STP1239

    Time of Wetness and Dew Formation: A Model of Atmospheric Heat Transfer

    Published: Jan 1995


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    Abstract

    Time of wetness is a critical factor in atmospheric corrosion. Dew is a major contributor to time of wetness. In normal atmospheric exposures, dew formation is a result of radiative cooling of exposed surfaces below the dew point of surrounding air. The extent of radiational cooling of an object is affected by the effective sky temperature, the presence of clouds, the view of other surfaces at different temperatures, and air movement by wind or natural convection adjacent to the cooling surfaces. This paper models the temperature of a boldly exposed panel as a function of humidity and air current velocity. The model predicts a maximum panel temperature depression of approximately 16°C below ambient air temperature in still air. For wind velocities of 4.5 m/s (10 mph) radiational cooling lowers the panel temperature 3°C below ambient air temperature.

    Keywords:

    atmospheric corrosion, time of wetness, radiational cooling, dew formation, wind velocity


    Author Information:

    Dean, SW
    Air Products Fellow and lead materials engineer, Air Products and Chemicals, Inc., Allentown, PA

    Reiser, DB
    Air Products Fellow and lead materials engineer, Air Products and Chemicals, Inc., Allentown, PA


    Paper ID: STP14909S

    Committee/Subcommittee: G01.04

    DOI: 10.1520/STP14909S


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