Drying process by forced convection of clover

Abstract

Abstract. 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 -1 , 0.7 m·s -1 , 1 m·s -1 , 1.2 m·s -1 and 2.0 m·s -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 background for calculation of the main parameters useful for description and modelling of the drying process, e.g., for decision of the optimum drying time.Keywords: air, drying time, forced drying, natural drying, moisture. IntroductionRed clover (Trifolium pratense) is widely grown as a fodder crop, valued for its high protein and minerals content, therefore it is sown for feeding cattle. It is also very useful in the system of crop rotation. It is because its nitrogen fixation, which increases soil fertility. The big advantage of clover is that in the Czech Republic it is growing in almost all altitudes. Red clover is most often harvested and conserved as hay, but can also be made into haylage or silage. The differences are according to the moisture or dry matter (DM) content.Red clover, if properly harvested and stored, provides high-quality forage. Red clover is most often stored as haylage since it is difficult to store it as dry hay. Small particles of dry leaves in hay create dust and increase losses of feed material. DM is one of the fundamental characteristics in conservation of red clover [1; 2]. The DM content in fresh plants varies depending on the weather and on phenophases (age) in a wide range from 11 to 25 %. At the younger vegetation the DM content of red clover is lower, which requires long drying, but there is also a lower fibre content and improved digestibility of forage. During conservation it is necessary to increase the amount of dry matter at least to 35 % (preferably 40 %) for the production of silage (suitable technological process using horizontal or tower silos). The economic ...