International Journal of Thermophysics, Vol. 9, No. 3, 1988 Thermal Diffusivity Measurement by the Transient Hot-Wire Technique: A Reappraisal C. A. Nieto de Castro, 1 B. Taxis, 2 H. M. Roder, 3 and W. A. Wakeham 2 Received October 30, 1987 The theory of the transient hot-wire technique for thermal conductivity measurements is reassessed in the special context of thermal diffusivity measurements. A careful examination of the working equation and an error analysis are employed to identify the principal sources of error. Notwithstanding earlier claims to the contrary, the best precision that can be attained in thermal diffusivity measurements is of the order of +3%, while the accuracy is inevitably poorer. Experimental evidence is adduced from two different instruments that supports the analysis given here. Although the technique can- not yield values of the thermal diffusivity, K, as accurate as can be achieved by the use of the best possible individual values of 2, p, and Cp in the relation K = ~/pCp, the simplicity of the technique makes it attractive for many purposes. It is even possible to derive values of the isobaric heat capacity Cp for many fluids not available from other methods. KEY WORDS: argon; thermal conductivity; thermal diffusivity; toluene; transient hot-wire technique; m-xylene. 1. INTRODUCTION The transient hot-wire technique for thermal conductivity measurements has now become established as the primary method for accurate deter- minations over a wide variety of thermodynamic states [1-3]. Since the very first application of the technique [4] it has been recognized that it is possible, in principle, to obtain both the thermal conductivity and the ther- 1Departamento de Quimica, FCUL and Centro de Quimica Estrutural, Complexo I, 1096 Lisboa Codex, Portugal. 2 Department of Chemical Engineering and Chemical Technology, Imperial College, Prince Consort Road, London SW7 2BY, United Kingdom. 3 Thermophysics Division, National Bureau of Standards, Boulder, Colorado 80303, U.S.A. 293 0195-928X/88/0500~0293506.00/0 ~ 1988 Plenum Publishing Corporation