FEATURES OF USING SOLAR AIR HEATERS OF HOSE TYPE FOR LOW-TEMPERATURE DRYING OF PLANT RAW MATERIALS
Drying is an energy consuming process, therefore, for farmers to reduce energy costs is the relevant task. In the present work the dependence of the thermal efficiency of solar air heaters of hose type on the air flow at all equal conditions was studied. The relevance of research conducted in the North-Caucasian Research Institute of Mountain and Foothill Agriculture (Mikhailovskoye, RNO-Alania) is due to some features in using solar air heaters of hose type related to need for reducing the cost of solar air heaters on the one hand and increase their thermal efficiency on the other. The following parameters were measured; the intensity of solar insolation, ambient air temperature, air flow rate and air temperature at the outflow from the solar air heaters, the wind speed at the surface of solar air heaters. Air flow rate was maintained in four variations: 0,05 m3/s; 0,06 m3/s; 0,07 m3/s and 0,08 m3/s. Measurements were made every 15 minutes during the period of maximum solar insolation - 708 W/m2, ambient air temperature - 24°C, average wind speed - 0,82 m/s. Studies showed that the best indexes (hгн = 0,38) are provided when the air flow rate is 0,06 and 0,07 m3/s. It is established that the most optimal channel shape is a flattened ellipse because above - the area of the absorber aperture and below - the reflectivity of transparent fence that provides the device for high thermal performance.