An apparatus for precise and absolute measurement of the thermal conductivity of electrically conducting liquids using the transient hot-wire method has been developed. In the present apparatus, a metallic wire coated with a thin electrical insulation layer has been used as a heating element and a resistance thermometer instead of a bare metallic wire. The effects on the thermal conductivity measurement caused by the thin insulation layer have been analysed. In the analysis, it was found that the effects can be negligibly small if the instrument is adequately designed. The usability of the method for electrically conducting liquids has been tested to measure the thermal conductivity of an aqueous NaCl solution in the temperature range 0 to 45 degrees C at atmospheric pressure. The accuracy of the present measurement was estimated to be +or-0.5%.

https://iopscience.iop.org/article/10.1088/0022-3735/14/12/020/pdf

Absolute measurement of the thermal conductivity of electrically conducting liquids by the transient hot-wire method.

A new apparatus for measuring the thermal conductivity of fluids is described. This is an absolute method utilizing a transient hot wire. Measurements are made with a 12.7 p,m diameter platinum wire at real times of up to 1 second. The data acquisition system includes a minicomputer and a digital voltmeter. The experimental core of the system incorporates a compensating hot wire in a Wheatstone bridge circuit. The cell containing the core of the apparatus is designed to accommodate pressures from 0 to 70 MPa and temperatures from 70 to 320 K. Oxygel1 was measured over a wide range of physical states including the dilute gas, the moderately dense gas, the near critical region, the compressed liquid states, and the vapor ai temperatures below the critical temper· ature. Performance checks of the apparatus were conducted with nitrogen, helium and argon. Measurement of rare gases allows a direct comparison to the kinetic theory of gases through the viscosity. A second check looks at the variation of the measured thermal conductivity as a function of the applied power. The precision (2 a) of the new system is between 0.5 and 0.8 percent for wire temperature transients of 4 to 5 K, while the accuracy is estitnated at around 1.5 percent.

/pdf/a-transient-hot-wire-thermal-conductivity-apparatus-for-58gocv9m51.pdf

A Transient Hot Wire Thermal Conductivity Apparatus for Fluids.

There are many thermoanalytical techniques but only several of them such as thermogravimetric analysis (TG), high resolution thermogravimetric analysis (Hi-Res™ TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), calorimetry, differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), evolved gas analysis (EGA), transient thermal analysis (TTA) and thermal conductivity (k) have selected to be discussed in this paper. Simultaneous thermal analysis (STA) is ideal for investigating issues such as the glass transition of modified glasses, binder burnout, dehydration of ceramic materials or decomposition behaviour of inorganic building materials, also with gas analysis. Selected applications of various thermoanalytical techniques from medicine to construction have also been discussed in this paper.

Selected thermoanalytical methods and their applications from medicine to construction

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50051

Thermal conductivity correlations for minor constituent fluids in natural gas: n-octane, n-nonane and n-decane

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.

John Frank Townsend Pittman

Papers

Fluid thermal conductivity determination by the transient, line source method