Rapid, non-destructive and non-contact inspection of solid foods by means of photothermal radiometry; thermal effusivity and initial heating coefficient

Abstract

CO 2-laser photothermal radiometry (PTR) was demonstrated to be suitable for the non-destructive and non-contact characterization (both optical and thermal) of solid phase agricultural commodities (fresh vegetables, fruits) and confectionery products (candy). Proper interpretation of PTR signals enable one to calculate two parameters, i.e. the well known thermal effusivity e ( e= λρc p , where λ and ρc p are the thermal conductivity and the volume specific heat, respectively) and a newly introduced physical quantity termed ‘initial heating coefficient’ chi ( χ= β/( ρc p ), β is the absorption coefficient). Obtained values for e are in a good agreement with data reported in the literature. PTR enables one to rapidly determine e via a single measurement. As opposed to this, the knowledge of two out of three thermophysical parameters (thermal diffusivity, thermal conductivity and volume specific heat) is a condition sine qua non for determining effusivity in the conventional manner.