In the present work a systematic investigation on several mechanisms affecting the thermal conductivity of Alumina based nanofluid, such as layering, Brownian motion, clustering, ballistic phonon motion, thermal boundary resistance and mass difference scattering, is presented. The effect of mass difference scattering is for the first time suggested and studied in the present work. Both theoretical and experimental approaches have been carried out in order to analyze the competition of these phenomena and to identify the most relevant. This was obtained by comparing micrometric and nanometric particles suspended in liquid water (293 K), frozen water (253 K) and diathermic oil (293 K). Each of the above-mentioned conditions was selected to make dominant only one of the mechanisms that affect nanofluid thermal conductivity. The main results of this investigation concern the mass difference scattering, which has …