The drying of ryegrass seeds in deep layers

Abstract

Preservation of quality is the primary consideration in the drying of grass seed. Quality may be lost through destruction of seed viability and contamination by mould. Both result from the establishment, within the drying bed, of undesirable temperature and moisture conditions generated by the interaction of the seed and drying air. The work was based on the assumption that such moisture and temperature changes could be calculated from a knowledge of the heat and mass transfer properties of the seed and air, and that it would be possible to proceed from this physical framework to the calculation and imposition of biological restraints upon the selection of drying conditions. Experimental work was carried out with a large and a small seeded strain of ryegrass of similar shape and structure. For each strain, potential germination was expressed as a function of moisture content at threshing. Apparatus was developed for determining exposed layer drying curves at a wide range of air conditions and numerical procedures were developed for fitting the data to alternative diffusion equations. The fitted constants were expressed as functions of drying air temperature, humidity and seed initial moisture content. Effects on germination were expressed as functions of drying air temperature, exposure time and potential germination. A mathematical model of the drying process was programmed in FORTRAN and used the exposed layer constants to predict moisture and temperature changes in deep beds subjected to fluctuating inlet air conditions. The model was stable, economical in computing time and gave reasonable overall agreement with experimental deep bed results. Consistent over-cptimism of the. drying time predictions was identified with cumulative error in temperature changes. Possible revisions of the basic equations pose problems of integration beyond the scope of the present work.