Search

Artificially drying lucerne immediately after cutting eliminates quality losses during field drying and minimizes the number of field operations. The average potential saving, calculated over a 20-year period for southeast Queensland, is about $40 (Australian)/t of hay, minus drying costs. The optimum technique of hay drying (immediately after cutting) in a solar-supplemented, step-flow dryer was investigated. A computer model was developed to minimize the cost of drying and to define the optimum drying parameters. Sensitivity analyses were carried out for drying air temperatures in tiie range of 30 to 70° C. The results show that there is an optimum number of hours of operation per day (8 h/d) for any combination of the other variables. The most critical factors affecting annual savings are the temperature of drying air, the length of the drying season, the cost of fuel, and the specific cost of the collector. An economic analysis showed that an average annual increase in profit of about $16/t of dried hay (at 12% w.b.) could be attained under optimum sets of operating conditions.

The optimum method of using a solar air collector combined with a grain drying system was investigated. Two types of solar collectors, integrated into a roof are considered; one uncovered (flow under absorber) and one covered (flow over absorber). A computer model was developed to minimize the cost of drying and in doing so optimize the geometry of the collector and the specific rate of air flow through the collector. The ratio of the cost of drying in a solar-supplemented system to the cost of drying in a conventional system was minimized. This ratio represents the maximum possible savings for the given drying conditions. Sensitivity analyses were carried out for drying air temperatures in the range 40 to 90°C and for grain initial moisture contents of 16 to 35% d.b.(dry basis). The effect of daily drying times, the length of the drying season and the specific cost of collector and fuel was also investigated. Two types of farm management systems were considered for various drying conditions: use of the dryer to operate for a fixed number of hours per day and, alternatively, drying a given quantity of grain per day. The results show that there is an optimum number of hours of operation per day, optimum drying temperature and optimum initial moisture content for any combination of the other variables. The most critical factors affecting annual savings are the length of the drying season and the specific cost of the collector. The optimum geometry of the collector and the specific flow rate are also functions of these factors.