The dependence of hot-wire calibration on gas temperature at low Reynolds numbers

Calibration curves of a constant-temperature hot-wire anemometer in air flow were determined at different gas temperatures in the range 283-353 K, and the results are compared with other investigations and are interpreted on the basis of a Nu-Re relationship. Gas parameters were measured at the gas temperature and not at the film temperature, as is usually done. The results could be fitted by the relationship Nu = a + b times Re to the exponent m. The parameter a was practically constant, provided that the gas thermal conductivity is taken at the gas temperature and not the film temperature. The values of the parameter b vary slightly with temperature, while their deviation from the average value could be reduced by using a proper loading factor.