TRANSIENT HOT-WIRE TECHNIQUE - A NUMERICAL APPROACH

The measurement of the thermal conductivity of a fluid by means of the transient hot-wire technique so far has made use of an analytical sol ution of the energy conservation equation for an ideal model, coupled with a set of approximate analytical corrections to account for small departures from the model. For this solution to be valid, constraints were always imposed on the experimental conditions and the constructio n of the apparatus, resulting in an inability to measure the thermal c onductivity of high-thermal diffusivity fluids. In this paper, the set of energy conservation equations describing the transient hot-wire ap paratus is solved using the numerical finite-element method. Because n o approximate solutions are involved, this provides a much more genera l treatment of the heat transfer processes taking part in the real exp eriment, removing all the aforementioned constraints. In the case of t he measurement of the thermal conductivity of liquids (fluids with low thermal-diffusivity values), the numerical solution fully agrees with the existing analytical solution. In the case of the measurement of t he thermal conductivity of gases, the present solution allows the exte nsion of the application of the transient hot-wire technique to experi mental conditions where the value of the thermal diffusivity of the fl uid is high.