Improved 3-omega measurement of thermal conductivity in liquid, gases, and powders using a metal-coated optical fiber

<p>A novel 3<em>ω</em>thermal conductivitymeasurement technique called metal-coated 3<em>ω</em> is introduced for use with liquids, gases, powders, and aerogels. This technique employs a micron-scale metal-coated glass fiber as a heater/thermometer that is suspended within the sample. Metal-coated 3<em>ω</em> exceeds alternate 3<em>ω</em> based fluid sensing techniques in a number of key metrics enabling rapid measurements of small samples of materials with very low thermal effusivity (gases), using smaller temperature oscillations with lower parasitic conduction losses. Its advantages relative to existing fluid measurement techniques, including transient hot-wire, steady-state methods, and solid-wire 3<em>ω</em> are discussed. A generalized <em>n</em>-layer concentric cylindrical periodic heating solution that accounts for thermal boundary resistance is presented. Improved sensitivity to boundary conductance is recognized through this model. Metal-coated 3<em>ω</em> was successfully validated through a benchmark study of gases and liquids spanning two-orders of magnitude in thermal conductivity.</p>