| A fresh analysis of transient hot wire technique measure the thermal conductivity and thermal diffusivity of fluids is made. The influence of wire thermophysical properties, thermal radiation, Knudsen effect, wire coating and variation of energy input are analyzed. A more rigorous mathematical model dealing with the transient heat transfer process is obtained. Additionally a new method is put forward to eliminate systematic errors in the temperature rise of the wire in order to obtain accurate results for the thermal diffusivity.; A measurement facility and measurement method were developed and the system verified by measurements on argon, n-pentane and toluene over the temperature range from 293 K to 423 K at pressures from 3.5 MPa to 65 MPa and the measurement results are reported.; The reproducibility of the thermal conductivity data obtained is within 0.2% and the reproducibility is 2% for the thermal diffusivity. The absolute accuracy of the obtained data is thought to be within 1% for thermal conductivity and 4% for thermal diffusivity.; New corrections to the theory of the transient hot wire instrument for Knudsen effect, fluid thermal radiation, wire coating, and thermophysical properties of the hot wire are presented. |
