Clover drying process by forced convection
2017
Kic, P., Czech Univ. of Life Sciences, Prague (Czech Republic)
The aim of this paper is to inform about the experimental and theoretical investigations of red clover (Trifolium pratense) drying by forced convection. This research is focused on verification of influence of different air velocities on the drying process of red clover in thin layer in mild temperatures (22 ºC ) and rather high relative humidity of air (70 %). The initial moisture content of clover was determined by gravimetric method using the hot air drying in the electric oven. Special device for convection drying with air flow passing through material from the bottom through supporting trays with a sieve (dimensions of mesh 3x4 mm) by constant temperature was used for drying when the air velocity was 0 m• s E-1, 0.7 m• s E-1, 1 m• s E-1, 1.2 m• s E-1 and 2.0 m• s E-1. Changes of clover samples were determined from the measured values of weight using the gravimetric methods. The evaluation of the measurement results was focused on the curves of the drying rate, changes in the water content and changes of moisture depending on the time and their mutual relations, which are important for description of drying. To achieve humidity of 55 %, which would correspond to a request for storage in the form of red clover haylage (DM 45 %), drying by forced convection for 20 hours is sufficient, in the case of drying by natural convection with zero velocity it would require 40 hours. The experimental data create the back ground for calculation of the main parameters useful for description and modelling of the drying process, e.g., for decision of the optimum drying time.
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