Numerical simulations and experimental measurements on the distribution of air and drying of round hay bales

The artificial drying of round bales offers the possibility to consistently produce quality hay by reducing field curing time and leaf shattering. Air distribution in the bale must be appropriate in order to achieve a uniform and efficient drying process. The air distribution and drying of four designs of round bale dryer were simulated using computational fluid dynamics. A round bale was modelled as a cylindrical porous media having a soft core. Bales were modelled both as being perfectly formed and as having a lower density close to their circular faces. Simulations showed that the simplest dryer design in which air enters the bale through one end, provides a deficient air distribution and inadequate drying, even when the bale is perfectly formed. Other designs studied showed, to varying degrees, an improved air distribution and drying uniformity. Simulations of a design in which an axial void is created in the bale centre, produced an optimal situation where the air and the drying front moves radially from the centre outwards. Conveying of air through both bale ends also contributed significantly to flow and drying uniformity. However, simulations for bales with a deficient density profile, as often found in practice, showed important distortions in the air distribution negatively affected drying. Therefore the uniformity of bale dry matter density is a determinant for the successful operation of any dryer. Additional efforts must be invested in the field to produce more uniform bales, particularly during raking and baling.