Thermo-acoustic analysis of apples when dehydrated in an ultrasound-assisted convection system

In this work, the finite element method (FEM) is used to perform a thermo-acoustic analysis of apples when dehydrated in an electrical system of convection dehydration assisted by ultrasound signals. First, the heat and wave equations are defined for an electric convection dehydrator assisted by transducers that radiate ultrasound signals considering two case studies. In the first case study, one piezoelectric transducer is installed at the bottom-center of the dehydration chamber; meanwhile in the second case study, three piezoelectric transducers are installed uniformly distributed at the bottom of the dehydration chamber. In both case studies, the electric convection dehydrator is assumed in thermal equilibrium at 60C, the apple samples are 5mm-plate apples, and the dehydration chamber has five drying racks. Then, for the two case studies, the temporal and spectral behaviors of the apple dehydration system are analyzed by estimating the temperature changes in the apple samples as a function of radiation time and frequency of ultrasound signals. From the 2-D spectral analysis, and considering a frequency range of (20 kHz, 1 MHz) for ultrasound signals, the spatial distribution of the sound intensity level (SIL) of the ultrasound signals applied to the apple samples is shown. Thus, the optimum frequency of ultrasound signals for the apple dehydration is determined from the average pressure generated in the dehydration chamber. Using this frequency, the thermal behavior for the apple samples is estimated as a function of the radiation time. Finally, the thermo-acoustic behavior for the two proposed case studies is compared.