Thermal conductivity measurement of TBAB hydrate by the transient hot-wire using parylene-coated probe

Semiclathrate hydrate consists of cage structures composed of water molecules and ionic large guest molecules, which distinguish semiclathrate hydrate from normal clathrate hydrate. Semiclathrate hydrate is stable under atmospheric pressure condition and at near room temperature. This is the reason semiclathrate hydrate is expected to be used in various novel technologies, for example use as a cool-energy storage agent and gas separator. However, there is little knowledge about thermophysical properties of semiclathrate hydrate. Up to the present, few experimental data on its thermal conductivity have been reported. Thermal conductivity is necessary for the evaluation of industrial formation process of semiclathrate hydrate and heat transfer performance of semiclathrate hydrate used as cool-energy storage agent. The present paper reports measurements of the thermal conductivity of Tetra Butyl Ammonium Bromide (TBAB) hydrate by the transient hot-wire technique using a newly developed Parylene-coated probe, in which a metallic wire is coated with a thin electrical insulation layer formed by a chemical vapor deposition of poly-para-xylyene polymer. In order to confirm the reliability of the probe, we have performed check measurements on the thermal conductivity of toluene and water. We have measured the thermal conductivity of TBAB hydrate in the temperature range from 193 to 282 K with the uncertainty of ±2 %. It is found that the thermal conductivity of TBAB hydrate is less than 17 % of that of ice with almost no temperature dependence and its absolute value is lower than that of normal clathrate hydrate such as methane hydrate.