HEAT AND MASS TRANSFER RELATIONSHIPS IN THE DRYING OF GRASS

Abstract

Experimental apparatus was constructed and used to determine the drying characteristics of grass. Thin layer samples of Italian and Perennial Ryegrasses were dried by through-flow of air under controlled conditions. Samples of grass were also split into leaves and stems, and these were dried separately. The temperature, humidity and velocity of the air, and the maturity, length of chop and species of grass were varied. A computer program was written to process the recorded experimental data. It was found that the form of the drying equation varied with the air temperature. Above 200°C, drying took place entirely within the constant rate period. Below this temperature, the drying rate was proportional to the moisture content. At temperatures below 80°C, up to three such linear periods were observed. The constants in the different equations were correlated with the experimental variables. The results have been interpreted in the light of the physiology of the grass. The melting of the cuticular waxes is shown to be responsible for the increase in drying rate at high temperatures. Mathematical models of two types, of drier were developed as an aid to design. The models were tested by programming them on a digital computer. The static deep-bed drier model was validated by simulating laboratory experiments on hay, barley and wheat. The rotary drier model was validated by simulating a farm grass drier.