Thermal diffusivity measurements on Single Wall Carbon Nanohorns-based nanolubricants by a temperature controlled photoacoustic device

The accurate and precise measurement of thermal diffusivity of fluids has been a major concern for several years in the past and estimations on different fluids have been reported by authors with larger spreads than reported experimental errors.[1] We built a device based on, as is conventionally called, the photoacoustic effect for the estimation of the thermal diffusivity of fluids at different temperatures. The mathematical basis of photothermal techniques has been developed at the end of the seventies.[2] These techniques, just to cite some [3], have been employed for the characterization of several physical properties of matter, such as absorption spectrum, detection of gas traces, imaging and depth profiling. The proposed technique has been already successfully used to measure diffusivity and thermal effusivity of fluids [4,5] and, more recently, of nanofluids.[6-8] In particular, the photoacustic technique demonstrated a potential for a more accurate estimates of thermal diffusivity of fluids compared to more conventional techniques such as the "Hot Disk" and "Laser Flash" methods that seem more suitable for the characterization of solids and powders. As an example, Zhang et al. [9] reported an errors of 5% for thermal diffusivity estimations of nanonofluids by using the transient short-hot-wire technique. The device presented in this paper is inspired to the works of Balderas-Lopez [5], that we improved by an accurate sample temperature control (from room temperature up to 70 °C), and a fully automation of measurements obtained with a National Instruments Labview® interface in order to limit possible error sources. The capability of this technique to measure very small changes in thermal diffusivity due to addition of small contents of nanoparticles to fluids is demonstrated. In fact, an example of thermal diffusivity measurements of lubricants containing differ amounts of Single Wall Carbon Nanohorns (SWCNHs) is reported, together with an overview of the influence oh these nanoparticles on the tribological properties.