高湿稻谷多段逆流干燥缓苏解析模型研究

为了获得高湿稻谷逆流干燥层内的水分分布,实现干燥过程动态跟踪和调控,基于干燥水分扩散模型和深层干燥质量平衡方程,在线解析稻谷逆流干燥水分变化,给出了稻谷多段逆流干燥、缓苏复杂工艺条件下,层内含水率分布及干燥速率解析式,验证了风量谷物比为4,温度50℃的热风流过0.5 m厚的逆流层后,仍具有较强的干燥能力,解析结果与实测的干燥机出粮口水分偏差在±0.5%范围内,证实了解析模型的可靠性。     

稻谷平床式深层干燥的均匀性研究

在一台平床干燥机上，进行稻谷深层干燥试验，研究各种层厚下，热风风量、稻谷温度和稻谷含水率沿平床表面的分布规律以及稻谷温度和稻谷含水率沿层厚方向的分布状况，结果表明：沿平床表面，风量、稻谷温度和含水率的分布明显不均。增加稻谷层厚，保持层厚均匀可以显著改革这种不均匀性。沿层厚方向，稻谷温度和含水率明显分层。当谷层过厚，底层稻谷过度干燥而表层稻谷却得不到有效干燥。     

稻谷干燥风量与谷物质量比的优化研究

研究了风量与谷物质量比对干燥速率的影响。当风量与谷物质量比增大时,干燥速率大幅度上升;但是当风量与谷物质量比增大到一定程度,干燥速率增大率明显减小。干燥初期稻谷的含水率较大时,加大风量可以大大提高干燥速率,而干燥后期风量对干燥速率的影响不明显。以风量与谷物质量比为基准,研究了饱和相对湿度线的移行规律,给出了不同热风温度和稻谷含水率下合理的风量与谷物质量比以及拟合方程。     

基于玻璃化转变的稻谷变温热风干燥工艺研究

为保证稻谷干燥后品质、提高干燥效率,基于不同含水率稻谷的玻璃化转变温度,提出变温热风干燥工艺。采用三因素五水平中心组合试验方法,以稻谷温度、初始含水率和热风风速为影响因素,以稻谷爆腰指数、整精米率和干燥时间为评价指标,研究稻谷玻璃化转变温度、恒温和变温干燥特性,模拟解析稻谷干燥过程中传热传质规律,以5、10、15℃的变温幅度进行变温干燥试验。结果表明,稻谷玻璃化转变温度与其含水率呈负相关,恒温干燥最佳工艺参数为稻谷温度47℃、初始含水率22.0%、热风风速0.50 m/s,干燥后稻谷爆腰指数70、整精米率57.67%、干燥时间195 min;与恒温干燥相比,以5℃和10℃为变温幅度的变温干燥工艺,干燥后稻谷爆腰指数分别降低了20和10,整精米率提高12.6、7.7个百分点,干燥时间缩短30 min和60 min。研究表明,基于玻璃化转变的稻谷变温热风干燥工艺明显改善了稻谷干燥后品质,提高了干燥效率。     

稻谷固定床式深层干燥试验研究

以木反和通风板构建一台面积22．3m^2的固定床干燥机，采用燃油直接燃烧加热的方式对谷物进行干燥。在不同的热风温度、稻谷初始含水率及总厚度条件下，测定了稻谷干燥的均匀性、各层稻谷的温升曲线和干燥曲线，分析了干燥参数对干燥床性能的影响。研究表明：沿层厚方向存在显著的温度梯度，干燥逐层进行。热风温度越高、总厚度越大，分层干燥现象越明显。在定风量的条件下，热风温度要对干燥的热量消耗无明显影响；总厚度增加、稻谷初含水率降低，干燥的热量消耗呈降低趋势。     

稻谷籽粒内部热湿传递三维适体数学模型研究

针对稻谷热风干燥过程中出现爆腰,而其机理又尚未明确的问题,以图像法构建稻谷籽粒三维适体网格,TPS法测定导热系数,逆推法计算水分有效扩散系数,利用COMSOL Multiphysics软件模拟计算热风干燥过程中稻谷籽粒内部的温度和水分分布,并与实验结果对比。结果表明:三维适体数学模型具有较高的精度,干燥过程中稻谷籽粒干基含水率模拟数据与实验数据最大误差低于8%;稻谷籽粒内部温度和水分分布梯度沿径向(短轴)比沿轴向(长轴)大,且水分梯度维持时间远大于温度梯度;沿籽粒径向由外表面至中心1/3长度内的水分梯度较径向其它部分的水分梯度大,与实验观察的爆腰由籽粒表面向内扩展相吻合。研究结果为准确预测籽粒内部的干燥应力,揭示稻谷爆腰机理提供了基础。     

稻谷干燥含水率在线检测装置设计与试验

为了解决稻谷的形状、厚度、密度、温度波动以及内部水分分布不均等因素影响含水率测量的问题,实现单粒稻谷水分在线精确测量,研究了稻谷干燥水分在线检测技术及装置.利用多路复选测量方案与解析计算相结合的方法,解决了稻谷含水率测量非线性问题.将动态过程中的转换电压时序曲线图峰高作为含水率在23.5%以下时的测量属性;当含水率在23.5%以上时,测量属性采用时序曲线峰面积.分别在夏季高温、高湿、大水分域和冬季低温、高粉尘作业条件下现场在线应用,验证了检测技术和装置的可靠性和实用性,在线检测误差在±0.5%范围内.     

稻谷籽粒内部热湿传递三维适体数学模型

针对稻谷热风干燥过程中的爆腰现象,而其机理又尚未明确的问题,以图像法构建稻谷籽粒三维适体网格,TPS法测定导热系数,逆推法计算水分有效扩散系数,利用COMSOL Multiphysics软件模拟计算热风干燥过程中稻谷籽粒内部的温度和水分分布,并与实验结果对比。结果表明:三维适体数学模型具有较高的精度,干燥过程中稻谷籽粒干基含水率模拟数据与实验数据最大误差低于8%;稻谷籽粒内部温度和水分分布梯度沿径向(短轴)比沿轴向(长轴)大,且水分梯度维持时间远大于温度梯度;沿籽粒径向由外表面至中心1/3长度内的水分梯度较径向其它部分的水分梯度大,与实验观察的爆腰由籽粒表面向内扩展相吻合。研究结果为准确预测籽粒内部的干燥应力,揭示稻谷爆腰机理提供了基础。     

稻谷水分测定方法的探讨

水分是构成稻谷及其制品的基本物质,是食物中不可缺少的成分。稻谷经粉碎后测定的结果与稻谷真实水分存在较大的偏差,这主要是样品在粉碎过程中筛下物不均匀。本研究采用谷糙分离烘干法与130℃、40min稻谷粉碎烘干法进行比较,前者的测定结果更接近由130℃、9h稻谷籽粒烘干法测得的真实值,而且偏差小、准确度高。谷糙分离烘干法与稻谷籽粒烘干法相比:结果一致,节省时间,准确性高。     

稻谷内部水分汽化潜热的推算

稻谷内部水分的汽化潜热是谷物干燥研究的基础参数。以南方稻谷的动平衡含水率模型为基础，推算出稻谷内部水分的汽化潜热值。     

水稻颗粒玻璃化转变的试验研究

通过水稻颗粒玻璃化转变的试验，测量了不同干燥条件下水稻颗粒的玻璃化转变温度，探讨了干燥条件对水稻颗粒玻璃化转变的影响，研究了水稻颗粒含水率和玻璃化转变温度的关系，建立了水稻颗粒玻璃化转变温度与颗粒含水率的数学模型。     

稻谷吸湿过程中内部应力峰值分析

使用空间轴对称有限元方法,将稻谷颗粒视为由３种材料组成的３层旋转椭球体,在不同初始湿度Ｍ０、温度Ｔ和相对湿度ＲＨ条件下,对内部的湿度Ｍ、温度Ｔ进行了数值模拟,应用所得结果对吸湿应力场进行了数值计算,分析了胚乳中截面的应力分布随时间的变化。计算结果表明,接伸应力峰值出现在谷粒中心,垂直于中截面,由于此峰值应力对裂纹的产生有直接的影响。西方着重研究了Ｍ０、ＲＨ和颗粒吸湿量对中心轴向应力峰值及其出现时间     

Stochastic Modelling of Grain Drying: Part 3. Analysis of Crossflow Drying

In Part 3 of the papers on stochastic dryer model- ling of grain drying, the MSU stochastic drying model is used to investigate the distribution of the kernel moisture content during the crossflow drying of maize. It is shown that the standard deviation of the moisture content gradually increases during the drying process, and becomes larger when the drying temperature is increased or the airflow rate is decreased. A grain-inverter placed in a crossflow dryer is demonstrated to have a beneficial effect on the grain quality by decreasing the value of the standard deviation of the moisture content of the grain leaving the dryer.     

Modelling the Drying Kinetics of Maize in a Microwave Environment

Microwave drying of grains is fundamentally different from either convection or conduction drying. Drying of cereal grains appears to proceed mainly in the period when the drying rate is decreasing (in the falling rate period), a characteristic of internally controlled diffusion. However, the analytical solution to Fick's second law of diffusion for a homogeneous, isotropic sphere with constant initial and boundary conditions does not adequately describe the drying behaviour. In an attempt to overcome this problem, the moisture ratio was written in terms of the surface moisture content rather than the equilibrium value. The associated surface drying coefficient, as determined by an iterative technique, was found to be expressible as a linear function of the initial free moisture content of the grain. The resulting empirical model better described the observed drying kinetics. This approach also resulted in good fits to independent data from experiments on convective drying of rough rice, microwave drying of wheat and combined microwave-fluidized bed drying of wheat.     

稻谷热风、微波干燥品质与玻璃化转变研究

以函数拟合、近红外检测及发芽率测定,研究稻谷热风、微波干燥的去水性能及其蛋白质、直链淀粉含量与出芽品质;结合TG/DSC测试,探讨2种热源干燥稻谷的玻璃化转变对其干燥后品质的影响。结果表明:以对数函数拟合稻谷热风、微波干燥去水性能的准确度高;经2种热源干燥稻谷的蛋白质、淀粉含量过程差异不显著;但热风干燥稻谷初期蛋白质含量差异明显。鲜稻谷发芽率显著低于其经热风、微波干燥后的发芽率,三者分别为0.65±0.19、0.93±0.03、0.77±0.02。随含水率降低,经热风、微波干燥稻谷的热重损失与热流则呈不同趋势变化,二者中点温度均减小,综合影响干谷品质。     

Mechanical Behaviour of Macadamia Nut under Compression Loading

The operation of cracking Macadamia nuts is the most critical and delicate step for achieving high-quality kernels. The nuts, usually at high moisture content, are dried to a recommended moisture, before cracking, in a process that takes from 3 to 4 weeks at the expense of large energy consumption. The present paper examines the basis of shell rupture which is needed for the development of new methodologies or techniques to reduce the drying period and to obtain a more efficient kernel extraction process. Requirements in terms of force, specific deformation and energy for initial rupturing of the macadamia nut shell under compression were experimentally investigated as a function of moisture content, nut size, and compression load position. The experiments have shown that there is a compression position for which force, specific deformation and energy values are minimal, independent of nut size and shell moisture. A damage evaluation of compressed nuts showed a trend for the void between kernel and shell to be the greatest at this position with the force acting longitudinally through the hilum.     

Stochastic Modelling of Grain Drying: Part 1. Experimental Investigation

Previous research has shown that the variance in the moisture content of individual maize kernels is significant at harvest. In this series of three papers, the stochastic nature of the moisture content of maize before and after drying is explored. Part 1 presents experimental data of the distribution of moisture content of maize kernels in samples taken at harvest time, after thin-layer drying, and after crossflow drying. The moisture content in recently harvested and in thin-layer dried maize appears to be normally distributed and in crossflow-dried maize to be skewed. In Part 2, stochastic models are developed of the distribution of moisture content of maize kernels dried in concurrent-flow, counter-flow and crossflow dryers, and in Part 3 one of the models is used to analyse the process of grain drying in a crossflow dryer.     

Stochastic Modelling of Grain Drying: Part 2. Model Development

In Part 1 of this series of three papers, it was shown that the moisture content in maize reaching a dryer is approximatelynormallydistributed. In Part 2, stochastic drying models are developed for grain with an initial normal distribution in moisture content. It is shown that the moisture content is still normally distributed after one-dimensional drying (i.e. concurrent- or counter-flow drying), but is skewed after two-dimensional drying (i.e. crossflow drying). The models predict, for dried grain, both the average moisture content and its standard deviation to an acceptable accuracy.