INFLUENCE OF HUMIDITY ON HOT-WIRE MEASUREMENTS

When applying hot-wire anemometry to velocity measurements in air, it is standard practice to neglect the effect of humidity. In this paper the influence of the thermodynamic and transport properties of humid a ir on hot-wire measurements is examined on the basis of the correlatio ns for Nusselt number proposed previously by other researchers. Experi mental results at controlled levels of relative humidity between 30% a nd 90% at 30 degrees C, 50 degrees C and 70 degrees C are reproduced s atisfactorily by the theoretical approaches of two of these equations. A corrective term is defined to expand formulae designed for dry air to work in a humid environment. The error in velocity by omitting the influence of humidity is estimated in terms of temperature and relativ e humidity.