The obtained results present different process parameters for drying in air fluidized beds and also a significant contribution of an immersed heat exchanger element. In this process, the drying time at lower temperatures is shorter, the product quality is higher and the rehydratation time is shorter as well.
This paper comprises research work on celeriae and peas dried in a fluidized bed. The goal has been to obtain dry vegetables with 6% to 10% water content and of good rehydration quality. Experimental data (bed height, gas temperature and velocity, pressure drop over the bed, drying time and the total humidity of drying) have been measured and relevant values have been calculated.
First the aerodynamic properties of a fluidizing bed in motion were experimentally investigated and then the particles were dried at given temperatures in different time intervals and at an air flow rate ranging from 0.30 m/s to 4.93 m/s.
Two columns of different dimensions were used: a cylindrical column (d = 0.10 m and h = 1.0 m) and a square column (a = 0.09 m, b = 0.18 m and h = 0.83 m). Working parameters were:
1. particle dimensions (blanched): 5×5×5 mm and 5×5×10 mm for celeriae and 8 mm (first class) and 9 mm (second class) diameter for peas
2. particle mass: 0.200 kg, 0.300 kg and 0.400 kg
3. drying temperature 40°C, 50°C and 60°C
The results have shown that drying of vegetables in a fluidized bed produces dry vegetable pieces of excellent quality in a much shorter time than in continuous belt-dryers which are generally used.
The best results of celeriae drying were obtained with the following dimensions of celeriae: 5×5×5 mm, 200 g, in a cylindrical column at 60°C and at the maximum air flow rate of 4.3 m/s. The best results of peas drying were achieved with the first class peas, 400 g, in a square column at 60°C and at the maximum air flow rate of 2.46 m/s.