Theoretical Analysis And Experimental Study On Combined Convective And Infrared Radiation Drying

Infrared radiation drying is a novel drying technology, which is an efficient, energy-saving, low-pollution dehydration method. Infrared radiation drying transfers inner energy by the electromagnetic wave. When infrared ray irradiates to the surface of material and radiating frequency is same as material molecular frequency, the radiating energy is strongly absorbed by the material. The absorbed energy results in material molecular motion and makes material temperature rise. Theoretical and experimental studies on combined convective and infrared drying were carried out in this dissertation. The main works in this dissertation were summarized as fallowings:1. Based on analyzing the general property of radiation, convection and material, an experimental equipment was designed and manufactured. This equipment used the electricity as the heating resource and the radiator was manufactured of the SIC material. The structural and technological parameters were variable in order to study the drying characteristic well.2. The theory of infrared radiation was analyzed and the theory of electromagnetic wave was used to discuss the heat transferring mechanism. This dissertation also elaborated and overviewed the researches on the theory of infrared radiation.3. Based on the analysis and experimental studies of infrared spectral character, the selective heating character was put forward besides the heat character of infrared radiation. The thermal region of infrared spectral of agricultural material like paddy is between 2.5 m and 25 m. The infrared absorptivity of paddy is low in the region wave length less than 2.5 m. It is remarkable that FIR radiation is considered as one of the possible alternatives to microwave and high frequency heating technique.4. Radiant penetration effects on paddy and bread were found to be small. Studies show that FIR radiation should be considered as a surface heating process unlike other thermal radiations. It is proved first that penetration effects on paddy is not dependent on the peak wave length of infrared ray and spectral extent. Studies indicate that different initial moisture content result in different penetration effects on bread but it is not observed identical conclusion on paddy.5. In studies exploring the characteristic of FIR radiation, it was verified that radiant intensity has an important effect on convection whose effects are not simple addition between radiation and convection. Some concepts such as radiation strengthening coefficient of heating transferring and mass transferring were put forward and established the relation formula between radiation and convection. The models of paddy moisture diffusion and temperature were solved by finite difference and thermal resistance concept. Simulation results show that there is high relativity between the numerical model curves and experimental curves.6.The influencing factors on drying characteristic of paddy such as radiant intensity, mediatemperature, material initial moisture content, convective velocity, radiation distance and material layer thickness. Studies results indicate that the radiant intensity, material initial moisture content , radiation distance and material layer thickness have strongly effect on the drying characteristic of paddy and convective velocity not only has a certain effect on drying characteristic of paddy but restraining high surface temperature media temperature material initial moisture content has no effect on the drying characteristic of paddy.