According to the Transient Hot-Wire (THW) technique, ideally, the thermal conductivity of the fluid is determined by observing the rate at which the temperature of a very thin metallic wire increases with time after a step change in voltage has been applied to it, thus creating in the fluid a line source of essentially constant heat flux per unit length.

Approximate analysis (Healy 1976)

ΔΤid  q  ln( 4kt )
4πλ a2C


However today, It is much better, and much more accurate, to solve the full heat transfer equations for the wire and the fluid by FEM.

No approximations!


In this section, we will walk through history to see the evolution and development of the THW technique…

Not a thorough list of dates, numbers and equations but through designs and drawings of instruments. The section will include a typical selection of instruments in order to demonstrate its evolution and will certainly not include all investigators. The whole presentation is published in literature (Assael et al. 2009, 2010).


J.J. Healy, J.J. de Groot, and J. Kestin, Physica C, 82:392 (1976).
M.J. Assael, K.E. Antoniadis, W.A. Wakeham,  Int. J. Thermophys. 31:1051-1072  (2010).
M.J. Assael, K.E. Antoniadis, Proc. 30th Int. Therm. Conduct. Conf. & 18th Int. Therm. Expansion Symp. 28 Aug. - 3 Sept. Pittsburg (2009).