The working range and instrumentation of an air conditioning and thin layer drying apparatus are described. Particular attention is paid to the measurement of air humidity through the use of a differential psychrometer. The effect of drying depth is examined in relation to the drying of large samples for subsequent work on quality. The bed depth and boundary layer resistance errors are examined theoretically and experimentally. The bed depth error predominates even for layers one seed deep. For a 4 mm bed depth of barley, theory predicts a bed depth error of less than 5% at air velocities greater than 0·08 m/s. The theoretical prediction for the boundary layer effect indicates an error of less than 1% at velocities above 0·01 m/s. A method of continuously monitoring the aerodynamic force on a sample by means of a pressure differential is also described and shown to be effective in determining true sample weight. © 1993 Silsoe Research Institute.
