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Development of THW Instruments for fluids

Development of THW Instruments for fluids Development of THW Instruments for fluids Development of THW Instruments for fluids Development of THW Instruments for fluids Development of THW Instruments for fluids

The figure shows some characteristic typical changes that the transient hot wire has undergone since 1971. Design (a) refers to two 7 μm diameter Pt wires, fixed at both ends. These were Wollaston processed wires. Such wires were employed for gases and liquids, but they were soon abandoned as they became slack during heating. Design (b) was a logical improvement step. The gold spring ensured that the wires were always taut. The Wollaston processed wires were also substituted by 10 μm-diameter wires.
 
An alternative arrangement was to introduce a weight. The cells shown in (c) include a weight, and this worked very well for the measurement of the thermal conductivity of liquids. In 1982, in order to measure the thermal conductivity of electrically conducting liquids, Alloush et al. proposed that the wires are made from tantalum. Tantalum upon oxidation, forms a thin layer of tantalum pentoxide which is an electrical insulator. A small correction to the temperature calculated should be applied. The cells shown at (c), the weights and all electrical connections are all made of tantalum and were consequently anodized in situo. This arrangement worked excellently and it is still used today.
 
Designs (d) and (e) are more recent and are based on the tantalum idea. However instead of a weight, the wire supports are also made of tantalum so they expand similarly to the wire when the temperature rises; hence the wire is always kept taut. Also in design (e) the wires are much shorter and are placed one over the other.
 

(a)  J.J. de Groot, J. Kestin, and H. Sookiazian, Physica, 75:454-482 (1974).
    C.A. Nieto de Castro, J.C.G. Calado, W.A. Wakeham, and M. Dix, J. Phys. E: Sci. Instrum., 9:1073-1080 (1976).
(b)  J. Kestin, R. Paul, A.A. Clifford, and W.A. Wakeham, Physica, 100A:349-369 (1980).
  M.J. Assael, M. Dix, A. Lucas, and W.A. Wakeham, J. Chem.Soc.,Faraday Trans. I, 77:439-464 (1981).
  E.N. Haran, and W.A. Wakeham, J. Phys. E: Sci. Instrum.,15:839-842 (1982).
(c)  J. Menashe, and W.A. Wakeham, Ber. Bunsenges. Phys. Chem., 85:340 (1981).
  Y. Nagasaka, and A. Nagashima, J. Phys. E: Sci. Instrum., 14:1435-1440 (1981).
  W.A. Wakeham, and M.Zalaf, Physica, 139:105 (1986).
   E. Charitidou, M. Dix, C.A. Nieto de Castro, and W.A. Wakeham, Int. J. Thermophys., 8:511-519 (1987).
(d)  S.H. Jawad, M.J. Dix, and W.A. Wakeham, Int. J. Thermophys., 20:45-54 (1999).
(e)  M.J. Assael, C-F. Chen, I. Metaxa, and W.A. Wakeham, Int. J. Thermophys. 25:971-985 (2004) .

 

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