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Thermal Conductiivity - Fluids PDF Print

   Method employed  


  • The technique employed is the Transient Hot-Wire 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. The technique is applied to gases similarly as in liquids (in that case however, the wires are usually much thinner).

    thw

    In an actual instrument, the cell employs two 25 μm-diameter (14 μm for gases), tantalum-wire heat sources, differing only in length. All electrical connections are also made out of thick tantalum wire. The resistance change of the tantalum wires as a function of time is observed by the use of a fully-automated Wheatstone-type bridge coupled to a micro-computer. This arrangement allows sampling of temperature rise vs time sets in a time scale from 20 microseconds to seconds.

    A full FEM analysis for the exact geometry employed, produces the value of the thermal conductivity of the fluid.

    The precision is 0.1%, while the absolute uncertainty is 0.5 - 1%.

     

     From left to right:
    a) original Ta wires with weight
    b) Ta wires attached to Ta supports
    c) short Ta wires attached to Ta supports.

   Ranges & uncertainties  


  • Liquids - Present instruments cover the following ranges:
    - Pressure: 0.1 to 400 bars
    - Temperature: -70 to +100 'C
    - Uncertainty: 0.5%
  • Gases (or vapours) - Present instruments cover the following ranges:
    - Pressure: 0.1 to 400 bars
    - Temperature: -20 to +200 'C
    - Uncertainty: 0.5 - 1%

Both electrically conducting and non-conducting fluids have been studied

   Systems sudied so far  


  • Hydrocarbons - Selected papers:
    Assael M.J. and Dalaouti N.K., "The Thermal Conductivity of Toluene + Cyclopentane Mixtures: Measurements and Prediction", Int. J.Thermophys. 22:659-678 (2001).
    Vesovic V., Wakeham W.A., Luettmer-Strathmann J., Sengers J.V., Millat J., Vogel E. and Assael M.J. "The Transport Properties of Ethane. II. Thermal Conductivity", Int.J.Thermophys. 15:33-66 (1994).
    Al-Harbi D.K., Assael M.J., Karagiannidis L. and Wakeham W.A., "Thermal Conductivity of Iso-Pentane in the Temperature Range 307-355 K at Pressures up to 0.4 GPa", Int.J.Thermophys. 12:17-25 (1991).
    Assael M.J., Ramirez M.L.V., Nieto de Castro C.A. and Wakeham W.A., "Benzene. A Further Liquid Thermal Conductivity Standard Meterial", J.Phys.Chem.Ref.Data. 19:113-117 (1990).
    Assael M.J., Charitidou E. and Avgoustiniatos S., "The Thermal Conductivity of Xylene Isomers in the Temperature Range 290-360K", Int.J.Thermophys. 9:501-510 (1988).
    Charitidou E., Molidou Ch. and Assael M.J., "The Thermal Conductivity and Viscosity of Benzene", Int.J. Thermophys. 9:37-45 (1988).
    Assael M.J., Charitidou E., Nieto de Castro C.A. and Wakeham W.A., "The Thermal Conductivity of n-Hexane, n-Heptane and n-Decane by the Transient Hot-Wire Method", Int.J.Thermophys. 8:663-670 (1987).

  • Ethers and ketones - Selected papers:
    Assael M.J., Karagiannidis L. and Papadaki M., "The Thermal Conductivity of Ethers and Ketones", Int. J. Thermophys. 12:937-942 (1991).

  • Alcohols, Glycols and their Mictures with Water or other Hydrocarbons - Selected papers:
    Ramires M.L.V., Nieto de Castro C.A., Nagasaka Y., Nagashima A., Assael M.J. and Wakeham W.A., "Standard Reference Data for the Thermal Conductivity of Water ", J.Phys.Chem.Ref.Data 24:1377-1381 (1995).
    Assael M.J., Charitidou E. and Karagiannidis L., "The Thermal Conductivity of n-Hexadecane and Ethanol and n-Decane and Butanol Mixtures", Int.J.Thermophys. 12:491-500 (1991).
    Assael M.J. and Charitidou E., "Measurement of the Thermal Conductivity of Alcohol and n-Hexane Mixtures", Int. J. Thermophys. 11:1001-1009 (1990).
    Assael M.J., Charitidou E., Avgoustiniatos S. and Wakeham W.A., "Absolute Measurements of the Thermal Conductivity of Mixtures of Alkene-Glycols and Water", Int.J.Thermophys. 10:1127-1140 (1989).
    Assael M.J., Charitidou E. and Wakeham W.A., "The Thermal Conductivity of Mixtures of Alcohols and Water", Int.J. Thermophys. 10:793-803 (1989).
    Assael M.J., Charitidou E. and Nieto de Castro C.A., "Absolute Measurements of the Thermal Conductivity of Alcohols by the Transient Hot-Wire Technique", Int.J.Thermophys. 9:813-824 (1988).
 

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