Transient hot wire method explained

The transient hot wire method (THW) is a very popular, accurate and precise technique to measure the thermal conductivity of gases, liquids,^[1] solids,^[2] nanofluids^[3] and refrigerants^[4] in a wide temperature and pressure range. The technique is based on recording the transient temperature rise of a thin vertical metal wire with infinite length when a step voltage is applied to it. The wire is immersed in a fluid and can act both as an electrical heating element and a resistance thermometer. The transient hot wire method has advantage over the other thermal conductivity methods, since there is a fully developed theory and there is no calibration or single-point calibration. Furthermore, because of the very small measuring time (1 s) there is no convection present in the measurements and only the thermal conductivity of the fluid is measured with very high accuracy.

Most of the transient hot wire sensors used in academia consist of two identical very thin wires with only difference in the length. Sensors using a single wire^{[5] [6]} are used both in academia and industry with the advantage over the two-wire sensors in the ease of handling of the sensor and change of the wire.

An ASTM standard is published for the measurements of engine coolants using a single-transient hot wire method.^[7]

History

200 years ago scientists were using a crude version of this method to make the first ever thermal conductivity measurements on gases.

• 1781 - Joseph Priestley attempts to measure the ability of different gases to conduct heat using the heated wire experiment.
• 1931 - Sven Pyk and Bertil Stalhane proposed the first “transient” hot wire method for the measurement of thermal conductivity of solids and powders. Unlike previous methods, the one devised by Pyk and Stalhane used shorter measurement times due to the transient nature of the measurement.
• 1971 - Davis et al. proposed introduced a modified design with thinner and shorter wires, enabling measuring times between 1 and 10 seconds using a digital voltmeter.^[8] J. W. Haarman who introduced the electronic Wheatstone bridge that is a common feature of other modern transient methods.^{[9] [10]}
• 1976 - Healy et al. published a journal article detailing the theory of the transient hot wire, described by an ideal solution with appropriate corrections to address effects like convection, among others.^{[11] [12]}

Notes and References

1. Book: Wakeham. W.A. . Nagashima. A. . Sengers. J.V. . Measurement of the Transport Properties of Fluids. Experimental Thermodynamics . 1st . 3 . Oxford . Blackwell Scientific Publications. 1991.
2. Assael. M.J. . Antoniadis. K.D.. Metaxa. I.N. . Mylona. S.K. . Assael. J.-A.M. . Wu. J.. Hu. M. . A Novel Portable Absolute Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids. International Journal of Thermophysics. 36 . 10–11 . 3083–3105 . 10.1007/s10765-015-1964-6. 2015 . 2015IJT....36.3083A . 118547999 .
3. Assael. M.J. . Chen. C.F.. Metaxa. I. . Wakeham. W.A. . Thermal conductivity of suspensions of carbon nanotubes in water . International Journal of Thermophysics. 25 . 4 . 971–985 . 10.1023/B:IJOT.0000038494.22494.04. 2004 . 2004IJT....25..971A . 97459543 .
4. Mylona . Sofia K. . Hughes . Thomas J. . Saeed . Amina A. . Rowland . Darren . Park . Juwoon . Tsuji . Tomoya . Tanaka . Yukio . Seiki . Yoshio . May . Eric F. . Thermal conductivity data for refrigerant mixtures containing R1234yf and R1234ze(E) . The Journal of Chemical Thermodynamics. 133 . 135–142 . 10.1016/j.jct.2019.01.028. 2019 . 104413076 .
5. Nagasaka . N. . Nagashima . A. . Simultaneous measurement of the thermal conductivity and the thermal diffusivity of liquids by the transient hot‐wire method. Review of Scientific Instruments. 52 . 2 . 229–232 . 10.1063/1.1136577. 1981 . 1981RScI...52..229N .
6. Fujii . M. . Zhang . X. . Imaishi . N. . Fujiwara . S. . Sakamoto . T. . Simultaneous measurements of thermal conductivity and thermal diffusivity of liquids under microgravity conditions . International Journal of Thermophysics. 18 . 2 . 327–339 . 10.1007/BF02575164. 1997 . 1997IJT....18..327F . 122155913 .
7. 10.1520/D7896-14. Test Method for Thermal Conductivity, Thermal Diffusivity and Volumetric Heat Capacity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method.
8. Web site: Transient Hot Wire Method . 2024-07-04.
9. Book: Vesovic . Velisa . Assael . Marc J. . Goodwin . Anthony R. H. . Wakeham . William A. . Experimental Thermodynamics Volume IX: Advances in Transport Properties of Fluids . 2014 . Royal Society of Chemistry . 978-1-78262-525-4 . 135 . en.
10. PhD thesis University of Eindhoven 1971
11. Book: Sattler . Klaus D. . Handbook of Nanophysics: Nanoparticles and Quantum Dots . 2016 . CRC Press . 978-1-4200-7545-8 . 32–4 . en.
12. 1976 . The Theory of the Transient Hot-Wire Method for Measuring Thermal Conductivity . Physica C. 82. 2 . 392–408. 10.1016/0378-4363(76)90203-5. 1976PhyBC..82..392H . Healy . J.J. . De Groot . J.J. . Kestin . J. .