The Mechanism And Experimental Study On Far-infrared Radiation And Convection Method For Grain Drying

In our country, grain production has more than600million tons every year. Drying is animportant part before the grain storage and a higher energy consumption post-harvest handling unit. For long-term storage, high moisture grain after harvest must be dropped to the safemoisture content. Drying grain usually used artificial drying or mechanical drying, grain drying is the highest post-harvest handling unit in the energy consumption. At present, the scaleof drying is around100million tons every year with the high demand of the market.In recent years, new demands for grain drying technology were put forward constantly with the industrial production of new energy, new materials, new technology research promotion. This paper researched and developed high efficiency and energy saving drying machine in order to besuitable for the vast farmers of China. It will provide technical support for the small grain drying machine universal engineering.Starting from the basic theory of infrared radiation, it researched on the infraredspectrum and its mechanism of material, the relation between the radiation characteristicsand infrared wavelength, and grain absorption characteristics of infrared radiation. Based onthe infrared spectra of grain, this paper chose the medium and low temperature infraredradiation coatings (HS-2-1).Calculation showed that this kind of infrared radiation coatingscan emit the suitable infrared for drying rice when the temperature was about289.7K to482.9K, and the optimal temperature was318.8K. It analyzed the moisture migration ofinfrared radiation grain and laid the foundation for follow-up study by the model analysis offar-infrared convection combination grain drying.The comprehensive experimental research and analysis of Far-infrared convectioncombination grain drying transfer effect explored the internal parameters relation andinfluence each other in the process of heat transfer. Based on the theory of matchedabsorption and grain of far-infrared absorption characteristics, it optimized the far-infrared coating material, tube plate material and the structure of far infrared radiation component.Selecting the medium temperature in heat exchange tube, the wall thickness and the airvolume ratio of heat exchange tube as the test factors, the main performance indicators werethe quantity of heat exchange, the efficiency of heat exchange and hot air outlet temperature.The mathematical models on heat transfer performance were established by the quadraticorthogonal rotational regression experiment research for the heat transfer performance of thetest table. Through the analysis of variance of the coefficient of significance test, the order ofvarious factors affecting the heat transfer properties were determined and then optimized forthe mathematical model on the quantity of heat exchange, the efficiency of heat exchangeand hot air outlet temperature. The interaction among various factors effecting on the heatexchange performance were analyzed to find suitable far-infrared convection combinationheat transfer technology for small and medium-sized grain drier. On the basis of analyzingthe influence factors, the key parts of the far-infrared convection combination grain dryingdevice were designed and analyzed, and the main problems in the process of work wereresearched. Through the establishment of the relevant mathematical model and analysis ofimages, the relationships among various factors, the interaction of heat transfer and themovement process of the moving parts were researched and analyzed.Based on the results of the research on virtual prototype technology and theoreticalanalysis, the energy saving and low cost of convection combination far-infrared dryer hasdeveloped with a set of lifting materials, hot air drying period, control discharge speeddevice, far infrared drying, conveying material, heat supply device and driving medium flowdevice. The experimental study confirmed the overall layout and working process of themachine. In the no-load or filled condition, the air volume from dryer export position weremeasured and calculated apparent wind speed. Under the same frequency, the drier apparentwind speed of unload state＞filled with corn state＞full of rice state; when rice were indifferent fan frequency corresponding, the apparent wind speed was the following that theapparent wind speed was0.047m/s when the fan delivery was7200m3/h; the apparent windspeed was0.09m/s when the fan delivery was9600m3/h; the apparent wind speed was0.10m/s when the fan delivery was12000m3/h. By the drying experiment of the whole system performance and operating quality testing, the temperature changes, the moisture changeregularity of rice and the relationship among the drying rate of rice and the moisture contentwere received in the drying process, and the unit heat consumption and detonation waist ratewere calculated. It was shown that the unit heat consumption of far-infrared convectioncombination drying was3011.6kJ/kg, and unit heat consumption of hot air drying alone was4235.3kJ/kg. It was far below the national standard that the unit heat consumption of ricewas less5800kJ/kg by directing heating (JB/T10268-2001).The unit heat consumption offar-infrared convection combination drying reduced28.9%than the unit heat consumption ofhot air drying alone. The increment of rice detonation waist rate was that it was2.8%withhot air drying alone and it was0.3%with far infrared convection combination grain drying.It was less than the increment of the critical waist rate increased which was3%stipulated inthe national standard (JB/T10268-2001).