Experimental and numerical investigations on water behaviour in a solar tunnel drier

Solar drying, an energy-saving process, is an efficient food conservation solution for countries that often have only sun as an energy source. Decreased energy requirements for a drying and improved dewatering process result from lower moisture fraction. This investigation focuses on the study of water behaviour inside the product to be dewatered in the particular case of a tunnel drier, and on the evolution of water content during the whole process starting from evaporation and ending with evacuation of the humid air. The mass transfer of water was respectively studied, analysed and simulated as to apprehend better the mechanisms governing drying and to build a real simulation tool to help in the design and automation of tunnel industrial driers. Space and time profiles of water content led to the assessment of drying velocity during the different phases and consequently to the comprehension of quantitative analysis. The kinetics obtained with the model under different working parameters (temperature, pressure, reactor time residence) and within various initial and boundary conditions show good agreement with those obtained experimentally.

The results of this simulation first allowed us to display the different drying phases, then to follow the water behaviour inside the product and outside it (in the tunnel box). The distortion of the drying global kinetics and the analysis of the dewatering curves when the initial and boundary conditions are variable in time and space show the importance of the phenomena and the possibilities of this simulation.