Measurement of thermal conductivity of nanofluids and thermal interface materials using the laser-based transient thermoreflectance method

The transient thermoreflectance (TTR) method was used to measure the thermal properties of two types of non-solid substances. First, the method was used to measure the thermal conductivity of several fluids including deionized water, 3M Fluorinert F-770 and a nanofluid composed of a colloidal suspension of 1.33 nm diameter single-wall carbon nanotube in water. The results show a slight increase in the thermal conductivity of the nanofluid (0.664 W/m-K) as compared to the properties of pure water (0.58 W/m-K). The second part presents the results of measuring the thermal properties of several thermal greases used in the electronics industry. Both the intrinsic thermal conductivity and the interface thermal resistance were measured concurrently. The thermal conductivity values of three out of four thermal greases measured were found to be much lower that the values reported by the manufacturer. Since the TTR method is an optical, pump-and-probe approach that relies on reflecting light from a mirror-like surface, measuring the thermal properties of transparent materials or non-solid substances requires the use of a reflective layer between the optics and the non-reflective material of interest. For the present investigation, a layer of gold was deposited on a microscope slide that was then placed upside down on top of the fluids and greases that were tested.