Thermal properties of fruit juices as a function of concentration and temperature determined using the photopyroelectric (PPE) method

The photopyroelectric (PPE) method is proposed as a new technique for therm al characterisation of fruit juices. By combining different geometries and experimental conditions, the PPE method was shown capable of providing temp erature-dependent (between 0 and 70 degrees C) values of thermophysical par ameters (thermal diffusivity, thermal effusivity, thermal conductivity and volume specific heat) for juices having different Brix index. The computer- controlled PPE cell allowed stable temperature variation rates and continuo us signal acquisition. The experimental data were used to develop empirical models and hence prediction equations for all the thermal parameters. (C) 1999 Society of Chemical Industry.