Thermal diffusivity measurement of Au nanofluids of very low concentration by using photoflash technique Sepideh Soltaninejad a,⇑ , M.S. Husin a , Amir R. Sadrolhosseini b , R. Zamiri a , A. Zakaria a , M.M. Moksin a,⇑ , E. Gharibshahi a a Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia b Wireless and Photonics Networks Research Center (WiPNet), Faculty of Engineering Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia article info Article history: Received 18 March 2013 Received in revised form 22 May 2013 Accepted 30 July 2013 Available online 12 August 2013 Keywords: Thermal diffusivity Photoflash technique Gold nanofluids Laser ablation abstract In this paper, the application of photoflash technique to measuring the thermal diffusivity of gold nanofluids of very low concentration at room temperature was presented. The nanofluid samples were prepared from the pulse laser ablation procedure. The thermal dif- fusivity was obtained by fitting the theoretical temperature signal to the experimental data, and it was found to increase linearly from 1.47  10 3 cm 2 s 1 to 1.68  10 3 cm 2 s 1 as the concentration increased from 1.11 mg/L to 3.18 mg/L. The increase in thermal diffu- sivity in these multidispersed nanofluids was attributed to the higher nanoparticle concen- tration as well as to the increasing presence of the smaller size nanoparticles. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Metal nanofluids are known to have important desired qualities. Higher thermal diffusivity of nanofluid than its base fluid have made Cu nanofluids better tribological per- formance at higher lubricant temperature [1] and im- proved heating and cooling rates of phase change materials [2] for examples. On the other hand Au nanofl- uids were found suitable for applications in medical thera- pies and drug delivery [3] besides having preferable tribological properties and thermal conductivity [4]. Usage of very low and effective concentration and quantity of precious metals nanofluids is also an important consider- ation to mitigate cost. Thermal lens and hot wire tech- niques [5,6] had been used in measuring thermal diffusivity of nanofluids which also work well for low con- centration fluids. Those techniques however require a sig- nificant amount of fluid since the probing light beam of the technique had to pass through a sufficient distance in the fluid to be able to record an appreciable beam deviation. A simpler photoacoustic method [7], in spite of the advan- tage of requiring a small amount of sample of 0.5 mL on thermal diffusivity measurement of Au nanofluids of con- centration as low as 0.2 mg/mL, the sample concentration is still much higher than that reported by using thermal lens technique [6]. In this work the reasonably small amount of slightly less than 0.5 mL of low concentration samples were used in measuring thermal diffusivity of Au nanofluids by using a much simpler photoflash method. Photoflash method which conventionally is being used to measuring thermal diffusivity of solids was also found applicable to liquids [8,9]. In the method a laser pulse of sufficiently short duration is irradiated on to the surface of a test sample to locally inducing heat subsequent to the radiation absorption and the temperature history of the sample which is detected at the opposite surface is analyzed to retrieve its thermal diffusivity. In the present work the application of the photoflash method was 0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.07.043 ⇑ Corresponding authors. Tel.: +60 172010937. E-mail addresses: sepidehsoltaninejad2012@gmail.com (S. Soltaninejad), Maarofmoksin@gmail.com (M.M. Moksin). Measurement 46 (2013) 4321–4327 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement