Investigating thermal properties of biodiesel/diesel mixtures using photopyroelectric technique

Abstract

In this work we explored the photopyroelectric technique (PPE) for the thermal characterization of biodiesel/diesel and other binary liquid mixtures, such as ethanol and ethylene glycol in water. We have used the back configuration (BPPE), in the thickness scan approach, and the front one (FPPE), in the frequency scan approach, for getting the thermal diffusivity and effusivity values, respectively. For all the measured systems, we got good data fittings when using the model proposed by Matvienko and Mandelis for thermal diffusivity of liquid mixtures. In addition, we could evidence the different strength in the molecular interaction related to the several mixtures, based on the normalized excess values for thermal diffusivity, as proposed by Dadarlat et al. For biodiesel/diesel mixtures, which present weak cohesive interactions among the saturated/aromatic hydrocarbons of diesel and the alkyl esters of biodiesel, we proposed a semi empirical model for the thermal diffusivity, based on the logarithm mixing model for the thermal conductivity and a simple addictive law for the heat capacity per unit volume.