Simulation and optimisation of the ventilation in a chimney-dependent solar crop dryer

Abstract

As published earlier on the performance of a chimney-dependent solar crop dryer (CDSCD) designed by the authors, the solar chimney can be combined with an appropriately inclined roof of drying chamber for ventilation improvement in the dryer. Mathematical models and a computer code are now developed to simulate the ventilation in relation to the design of the CDSCD. This is done for situations without any crop (no-load) in the dryer, to relate the ventilation to the external dimensions. The pressure-loss and bulk-fluid-temperature coefficients are deduced empirically from trials on the physical model. The simulation code predicts the ventilation to within 5% and the temperatures to within 1.5% of observed data, confirming the validity of the code as an effective design tool for the CDSCD. Results of parametric studies performed with the code indicate that, maximum airflow can be achieved when the inlet-exit area ratio is around 4:1, above which the system then approaches saturation without any real variation. The drying-chamber roof inclination and the chimney height are critical for the design in the geographical regions far from the equator, whereas the decisive parameters in the regions close to the equator are the drying chamber height and the area ratio of the dryer floor to chimney cross section. A high drying chamber with a short solar chimney is generally favoured at locations close to the equator, whereas a short drying chamber with a high solar chimney is suitable for regions far away from the equator.