Optimal Design Of Far-infrared Convection Dryer

Usually paddy was dehydrated by using hot-air drying. It was rarely studied thatfar-infrared drying combined with hot-air drying was applied with paddy drying. Thedevelopment of its corresponding equipment is relatively behind. Through the contrastof hot-air drying, far-infrared drying and combination drying of rice, paddy thin-layerdrying model was established, and the optimum drying processes of three kinds ofdrying methods were mastered and the effect of tempering on quality of dried paddywas drawn. And then optimal design of far-infrared convection grain dryer wasfinished. The main conclusions are as follows:1. The multi-functional far-infrared convection dryer was designed, well adaptedto hot-air drying, far-infrared drying and far-infrared convection drying.2. Thin-layer drying characteristics and model of paddy was achieved on the basisof single factor experiments. The results have shown that thin-layer drying of paddyhad two drying periods: acceleration drying stage and falling rate drying periods; ricethin-layer drying process was fitted well by Page equation.3. The drying process of hot-air drying, far-infrared drying and combinationdrying of paddy was optimized. Results have shown that optimal parameters of hot-airdrying were initial moisture content18.3%, drying temperature40℃and load0.2kg,in which the increase of crack percentage was47%; optimal parameters of far-infrareddrying were radiation power675W radiation distance10-18cm and dryingtemperature40℃in which the increase of crack percentage was approximately45%and radiation power had significant effects on rice cracking percentage; optimalparameters of combination drying were radiation power675W, radiation distance18cm and apparent wind speed0.8m/s in which the increase of crack percentage was0%and apparent wind speed had significant effects on rice cracking percentage.4. Effects of radiation power, initial moisture content, drying temperature,tempering temperature and tempering duration on crack percentage of rice wereexamined. And paddy was dried by using constant temperature drying and heating-up variable temperature drying. Experimental results have shown that cracking additionalpercentage of paddy decreased with the increase of radiation power; initial moisturecontent of rice had insignificant effect on rice cracking percentage; tempering durationhad significant effect on rice cracking percentage, which drastically decreased in therange of0-120minutes tempering duration and tended to be stable over120minutestempering duration; drying temperature should be controlled between50to60℃andtempering temperature should be controlled between60℃to70℃, at that moment theincrease of cracking percentage failed to the minimum; Compared with constanttemperature drying, heating-up variable temperature drying can greatly decrease ricecracking percentage.5. Design of far-infrared convection grain dryer was optimized: increasing theonline weighing device and installing the corresponding sensor; changing tunnels intouniform air plate; installing anemometer and corresponding sensor; setting up moreradiation distance gradient.