A steady-state hot-wire method for thermal conductivity measurements of fluids

Abstract A steady-state hot wire technique based on the wire thermal resistance dependence upon the natural convection heat transfer coefficient is developed and tested for thermal conductivity measurement of several fluids. A Pt90/Rh10 alloy microwire which serves both as a heater and as an electrical resistance thermometer is mounted in a 4-wire setup in order to reduce the experimental errors. The natural convection heat transfer coefficient is deduced from the fit of the slope of the wire temperature rise as a function of the electrical power dissipated. Once the heat convection coefficient is known, the thermal conductivity is calculated from an appropriate Nusselt number correlation for V shape microprobe with tip opening angles 30°, 90° and 180° and compared with the reference values for eight fluids. The results indicated that the 30° tip was working the best with the Nusselt number correlation used from literature. The method can be used also for finding directly the thermal conductivity of a fluid, if the probe calibration curve is built, with good precision, using a series of known thermal properties fluids.