EXPERIMENTAL STUDIES OF THE DRYING PROCESS OF WALNUTS IN A CONVECTIVE BUNKER DRYER

Walnuts are a high-calorie source of micro- and macronutrients, which makes them a valuable bio-concentrate for nutrition. However, to preserve their quality during storage and transportation, it is important to consider the botanical variety and growing conditions, as they affect resistance to oxidation. To ensure long-term storage and high quality of walnuts, it is necessary to improve drying methods that allow to reduce humidity to a safe level, minimize energy consumption and reduce the risks of spoilage and oxidative deterioration of product quality. The purpose of the study is to establish the functional dependencies of the process of drying walnuts and justify the optimal design, operating and technological parameters of the convective bunker dryer. An experimental sample of the CGK-4 «Tiras» walnut dryer was made to check the theoretical dependencies and justify the design and technological parameters of the dryer. Experimental studies were conducted on freshly picked walnuts of the Chandler variety with an initial moisture content of 22–28%. The effect of such factors as screw rotation frequency, air supply and drying duration on drying quality, energy consumption and productivity was studied. Modern methods of measuring humidity and energy consumption were used for the research, which made it possible to determine the average moisture of nuts, homogeneity of moisture, productivity of the dryer and efficiency of energy consumption. On the basis of the conducted studies, the functional dependence of the process of drying walnuts was determined, namely changes in the average moisture content of nuts wμ (%), homogeneity of moisture content of nuts in the hopper Θw (%) and specific energy consumption for the drying process Eq (MJ/kg) on the screw rotation frequency n (rpm), air supply Q (m3/h) and drying time t (h). These dependencies make it possible to justify the optimal parameters of the convective hopper dryer to ensure efficient and uniform drying: n = 30.6 rpm, Q = 1690.5 m3/h, t = 10.7 h. With these values wμ = 8%, Θw = 95% and Eq = 0.558 MJ/kg.