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

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 degrees, 90 degrees and 180 degrees and compared with the reference values for eight fluids. The results indicated that the 30 degrees 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. (C) 2019 Elsevier Ltd. All rights reserved.