【作者】 汪喜波；

【导师】 刘相东；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2003， 博士

【摘要】 红外辐射干燥是一种高效、节能、低污染的新型干燥技术。红外辐射是辐射物体以电磁波的方式传播内能的过程，当红外线照射到某一物体时，如果入射的红外线频率和物体分子固有频率相一致，则物质分子就会表现出对红外线的强烈吸收，吸收的那一部分能量就转化为分子的热运动，使物体温度升高，达到加热干燥的目的。为了揭示红外辐射与对流联合干燥机理，找出红外辐射与对流联合干燥的影响因素，本文较为系统地进行了红外辐射与对流联合干燥的机理与试验研究。论文的主要研究内容如下： 1．在对辐射、对流以及物料特征全面分析的基础上，设计制作了红外辐射与对流联合干燥试验装置。试验装置是直热式、以电加热为热源，以SiC为辐射材料的板式辐射器。辐射与对流的结构参数可调。提出了试验装置的设计依据和选型原则。 2．对红外辐射理论进行了分析，从电磁波动和粒子说理论出发，分析了红外辐射换热的机理，详尽地归纳、综述了红外辐射的研究理论。 3．通过对水稻等农产物料进行了光谱特性分析和试验研究，提出红外辐射除了热特性之外，还有选择性加热特性的重要结论。对水稻等农产物料，红外光谱热效应区域一般在2.5μm～25μm，对低于2.5μm的辐射，吸收率较低。在2.5μm～3.5μm波段，光谱吸收率逐渐增大。对不同的波谱范围，吸收的能量也不一样。这一重要发现使得红外辐射代替微波、高频等电磁辐射成为可能。 4．通过对水稻和面包团的穿透性试验研究，证明了红外辐射对农产物料的穿透性非常小，辐射加热主要是作用在物料表面的。试验证明了红外辐射对水稻等物料的穿透性能依赖于峰值波长和辐射频谱范围的关系不明显。同时，得出了不同初始含水率对辐射穿透性的影响，因不同物料而不同的结论。 5．进行了红外辐射与对流联合干燥水稻的传热传质的研究与分析，证明了辐射强度对对流参数的影响并不是对流系数与辐射系数简单的迭加，提出了辐射强化系数的概念。在水稻的辐射对流干燥试验中，还测得了水稻的辐射强化换热系数、辐射强化质量扩散系数计算出辐射强化对流传质系数、导热系数、平衡含水率等物性参数。并建立对流换热系数和扩散系数受辐射强度影响的准数关联式。采用有限差分法和热平衡原理，求解了水稻的水分扩散模型和温度变化模型。并用计算值模拟了水稻的脱水过程和温度变化过程。模拟曲线与试验曲线吻合良好。 6．本文在所研制的红外辐射和对流干燥试验台上，对水稻进行干燥试验研究。分析了辐射强度、对流介质温度、物料的初始含水率、对流速度、辐照距离、物料的装载厚度等参数对干燥性能的影响；证明了辐射强度、初始水分、辐照距离、物料的装载厚度对水稻的干燥性能有显著的影响，对流速度对水稻的脱水抑制表面温度过高有一定作用，对流介质温度对水稻的干燥性能没有显著影响影响。更多还原

【Abstract】 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.更多还原