增湿加热稻谷干燥工艺的试验研究

研究了增湿加热的稻谷干燥工艺减少爆腰产生的机理。采用增湿的热空气干燥稻谷时,可以减少稻谷内部水分梯度,降低了内部应力。通过试验分析了稻谷干燥爆腰率增值与空气温、湿度关系,提出了合理的增湿加热干燥工艺参数。     

增湿加热稻保干燥工艺的试验研究

研究了增湿加热的稻谷干燥工艺减少爆腰产生的机理，采用增湿的热空气干燥稻谷时，可以减少稻谷内部水分梯度，降低了内部应力。通过试验分析了稻谷干燥爆腰率增值与空气温、湿度关系，提出了合理的增湿加热干燥工艺参数。     

磁场对稻谷干燥特性的影响

针对稻谷的传统干燥过程存在能量消耗大，发芽率低和爆腰率高等缺点，把磁场引入稻谷干燥过程中，能快速而经济地降低稻谷的水分并保持其良好品质。采用永磁场强化稻谷的干燥过程，比较干燥时间、发芽率和爆腰率的变化。结果表明：在相同功率下稻谷在磁场中干燥时间比无磁场时缩短5％，平均失水速率加大，稻谷的发芽率有所升高、爆腰率下降；随着干燥功率的增加，磁场对稻谷的发芽率和爆腰率的影响加大。在试验基础上探讨了磁场对稻谷干燥过程的影响机理。     

稻谷热风干燥缓苏工艺参数优化与试验

为提高稻谷干燥特性与营养品质,该研究探究了缓苏温度、缓苏起始时刻、缓苏时长、缓苏循环次数等缓苏工艺参数对稻谷爆腰增率、整精米率、蛋白质质量分数与脂肪酸值等干燥品质指标的影响。首先,通过单因素试验分析了稻谷干燥品质随缓苏工艺参数的变化趋势,得出爆腰增率、整精米率、蛋白质质量分数与脂肪酸值的权重均大于20%,为稻谷缓苏干燥的关键性指标;其次,通过隶属函数模型确定影响稻谷干燥品质的主要因素为：缓苏温度、缓苏起始含水率与缓苏时长;最后,以缓苏温度、缓苏起始含水率、缓苏时长为试验因子,采用Central-Composite试验,通过建立回归模型分析了各试验因素与品质指标之间的相互关系并阐释结果产生的原因。结果表明：优化参数组合为缓苏温度45 ℃、缓苏起始含水率21%、缓苏时长1.61 h,此参数组合下稻谷干燥后的爆腰增率6.63%、蛋白质质量分数5.39%、脂肪酸值11.68%,验证试验结果与优化结果间相对误差为2.97%。研究表明,优化后的缓苏干燥工艺明显改善了稻谷干燥品质,该结果可为生产实践及深入探究稻谷品质变化机理提供理论基础。     

稻谷颗粒内部传质及其应用

本文推导了用于分析稻谷颗粒内部水分扩散的三层体模型。并编制了用于分析干燥和缓苏过程中颗粒内部水分扩散和颗粒降水速度的模拟软件。经验证模拟结果与实验结果能很好的逼近。并利用该软件分析了颗粒内部水分的扩散过程及间歇干燥过程中间歇比和循环周期对降水速度的影响。     

中国稻谷干燥现状和稻谷干燥设备的开发

介绍了我国稻谷干燥技术和干燥设备的现状,重点探讨了稻谷干燥的特点,如低温、大风量和干燥后必须缓苏等。对稻谷干燥中的爆腰问题作了深入的分析,对影响稻谷品质的主要因素如干燥速率、缓苏时间和爆腰率的测定时间和方法进行了讨论。对进一步发展我国的稻谷干燥技术提出了建议。     

水稻间歇干燥工艺的模拟分析

在稻谷颗粒内部水分扩散模拟和应力计算的基础上,编制了水稻间歇干燥工艺的模拟程序,并对模拟结果作了实验验证,然后利用模拟程序对水稻间歇干燥工艺的特点进行了分析,得出了间歇参数对水稻降水速度,内部水分梯度和内部应力的影响规律,为间歇干燥工艺的设计和参数选择提供了理论依据。     

稻谷烘干过程中的水分扩散特性与品质特性

为深入研究稻谷高效均匀化烘干过程中的水分扩散与质量转变耦合特性,该文测定了玉香油粘稻谷经50、65、80℃分别烘干时的水分有效扩散系数;检测了以上3种温度分别烘干稻谷的色差、籽粒颖壳断面孔隙率与分形维数及玻璃化转变温度,考察了已烘干稻谷的含水率、硬度、爆腰率、发芽率等过程品质差异。结果表明:玉香油粘稻谷烘干过程的有效水分扩散系数为3.576×10-8e15 684/Tm2/s;随烘干温度增加,籽粒颖壳断面的孔隙率由鲜谷的0.39±0.06依次降为0.22±0.09、0.17±0.04、0.13±0.05,但烘干稻谷的分形维数、色差、玻璃化转变温度则较其鲜谷波动增加;已烘干稻谷的含水率、硬度、爆腰率、发芽率组间差异显著(P0.05)。50℃烘干稻谷的爆腰率、发芽率性能优,宜选为稻谷烘干常用工艺温度,研究结果为稻谷高效均化烘干提供了理论与基础数据参考。     

高湿稻谷逐步升温干燥工艺试验研究

针对南方双季稻区高湿稻谷,对薄层谷粒的水分迁移过程进行动态跟踪,发现降速干燥过程具有明显的二段性。通过测定深层干燥中气流状态的变化过程,由热质衡算得出深层干燥特性曲线,研究了高湿稻谷深层干燥中的热质运动规律,结合稻谷爆腰率的变化规律,给出了合理的干燥工艺     

仓内稻谷干燥的多尺度多层结构热质传递模拟及试验

为研究仓内稻谷干燥的热质传递机理,确定稻谷颗粒内部不同组织结构特性对干燥过程的影响,以仓内稻谷堆为研究对象,针对谷粒的多层结构问题,运用多尺度理论、热质传递原理和孔道网络方法等知识,建立了仓内稻谷热风干燥的多尺度多层结构热质传递模型,并进行了稻谷堆热风干燥试验,模拟分析了仓内稻谷的干基含水率、温度分布以及孔隙汽相的温度分布等情况。结果表明:建立的热质传递模型可有效模拟仓内稻谷干燥过程,干燥器尺度下仓内稻谷的平均干基含水率的模拟值与试验值的最大相对误差为7.6%,颗粒尺度下单颗粒稻谷干基含水率的模拟值与试验值的最大相对误差约为6.8%;稻谷颗粒内部传热比传质速率快,颗粒内存在较大的水分梯度。稻谷胚扩散系数对干燥的影响较大,其次是稻谷壳扩散系数,稻谷衣扩散系数影响最小。研究结果为稻谷就仓干燥的品质及工艺分析提供了理论基础。     

Preservation of Head Rice Yield Under High‐Temperature Tempering as Explained by the Glass Transition of Rice Kernels

Tempering has been shown in literature to preserve head rice yield after heated air drying. Most reported tempering work was done adiabatically at a temperature below that for rice drying. In this study, the effect of a tempering temperature above that for rice drying on the whole kernel percentage was investigated. High‐temperature tempering is an effective way to preserve the whole kernel percentage for rice dried at a raised temperature (e.g., 60°C) at which head rice yield would otherwise incur a pronounced reduction without tempering. Tempering helped relax the strains inside a rice kernel induced by internal stresses developed during the drying process. The strains had two components (elastic component and viscous component) due to the viscoelasticity of rice kernels. The reduction of moisture content gradients inside a rice kernel during tempering helped eliminate the elastic component of the strains due to the elasticity of the rice kernel. Results showed that to effectively eliminate the viscous component of the strains due to the viscosity of the rice kernel, tempering temperatures must be kept well above the glass transition temperature of the rice kernel. A tempering temperature below the glass transition temperature failed to preserve the whole kernel percentage. For example, with a tempering temperature of 80°C and a tempering duration of 80 min, the whole kernel percentage for the rice with an initial moisture content of 20.4% wb dried at 60°C and 17% rh for 120 min down to 10.2% wb (10.2 percentage points of moisture content removal in one drying pass) was preserved to a level close to that of the control sample.     

水稻顺流干燥工艺缓苏过程的研究

系统地分析了水稻顺流干燥工艺中,谷物温度、降水幅度、初始水分对缓苏过程的影响,通过计算机求解扩散模型,揭示出缓苏与提高干燥能力之间的关系。该文求解出的谷物内部传热传质模型的模拟值与实验结果相符。     

Relationship of Kernel Moisture Content Gradients and Glass Transition Temperatures to Head Rice Yield

The relationship of glass transition temperature T_g and moisture content (MC) gradient of rice kernels to head rice yield (HRY) variation was investigated. Mathematical models describing heat and moisture transfer inside rice kernels during drying were developed and solved using the finite element method. Moisture distributions inside a kernel were simulated and verified using thin-layer drying experiments, and the intra-kernel MC gradients during drying were accordingly determined and analysed. Results showed that in the glassy region, rice did not incur measurable HRY reduction after drying. However, when rice was dried in the rubbery region and then cooled down immediately without being tempered following drying, HRY decreased markedly after MC gradients exceeded certain levels. It was found in this study that the time when the percentage point of moisture removal reached a maximally allowable level before HRY decreased dramatically coincided with the time at which the curve of kernel MC gradients versus drying duration reached its peak. Such a relation was verified with the HRY data of two varieties (Cypress and M202) as measured in this study and cited from literature. The HRY trends for these two varieties were well explained through the behaviour of glass transition and MC gradients of rice.     

稻谷种子安全干燥温度模型研究

以稻谷干燥时的活力退化动力学方程为基础，结合稻谷玻璃化转变理论建立了稻谷种子安全干燥温度模型。并通过稻谷种子的发芽率试验确定了种子安全干燥温度模型方程的系数。数学模拟结果表明，稻谷干燥过程中随着水分的降低，种子安全干燥温度曲线存在一个最低点；依据稻谷初始含水率由高到低，其最低安全干燥温度由低到高，而且种子通过最低安全干燥温度曲线最低点以后所能承受的温度则有所提高；当稻谷初始含水率低于13%(w.b.)时，种子安全干燥温度曲线后半段近似为一直线，不再有拐点（最低点）。论文最后提出了稻谷种子安全干燥温度和操作工艺，以及选择种子安全干燥温度时应注意的问题。     

Glassy State Transition and Rice Drying: Development of a Brown Rice State Diagram

The effect of moisture content (MC) on the glass transition temperature (T_g) of individual brown rice kernels of Bengal, a medium‐grain cultivar, and Cypress, a long‐grain cultivar, was studied. Three methods were investigated for measuring T_g: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Among these methods, TMA was chosen, because it can also measure changes in the thermal volumetric coefficient (β) of the kernel during glass transition. TMA‐measured T_g at similar MC levels for both cultivars were not significantly different and were combined to generate a brown rice state diagram. Individual kernel T_g for both cultivars increased from 22 to 58°C as MC decreased from 27 to 3% wb. Linear and sigmoid models were derived to relate T_g to MC. The linear model was sufficient to describe the property changes in the MC range encountered during rice drying. Mean β values across both cultivars in the rubbery state was 4.62 × 10^‐4/°C and was higher than the mean β value of 0.87 × 10^‐4/°C in the glassy state. A hypothetical rice drying process was mapped onto the combined state diagram generated for Bengal and Cypress.     

热风干燥联合真空降温缓苏提升黄秋葵干制品品质

为提升黄秋葵热风干燥产品品质,试验将真空降温缓苏技术应用于黄秋葵热风干燥过程中。研究了不同缓苏时长下黄秋葵干燥特性和品质指标的变化规律;利用Weibull分布函数分析缓苏处理对黄秋葵热风干燥过程中水分扩散机制的影响;采用一元非线性回归分析构建适用于黄秋葵真空降温缓苏-热风联合干燥过程中干燥特性和品质指标随缓苏时长变化的学数模型;以总干燥耗时、总干燥能耗、复水比、色相角以及总营养物质保存率为指标,对不同缓苏时长下的黄秋葵热风干燥进行加权综合评价。结果表明：缓苏处理能够提升黄秋葵热风干燥速率,且随着缓苏时长的延长其促进作用会增强;Weibull分布函数能够准确描述（R2>0.99且离差平方和χ2处于10-4数量级）黄秋葵真空降温缓苏-热风联合干燥过程中水分比随干燥时间的变化规律;常用函数一元非线性回归分析能够构建出黄秋葵真空降温缓苏-热风联合干燥过程中各干燥特性和品质指标随缓苏时长的变化规律的动力学模型;联合干燥过程中,缓苏60 min处理的综合评分值最高为0.55,在干燥温度和风速分别为60℃、1.5 m/s条件下,该缓苏时长较适合应用于黄秋葵热风干燥。研究表明,真空降温缓苏处理能够提升黄秋葵热风干燥的干燥速率和干燥品质,该文可为真空降温缓苏技术在高品质黄秋葵干制品工业生产上的应用提供理论依据。     

切片土豆间歇干燥过程传热传质模拟研究

在土豆干燥中,常采用间歇干燥工艺以缩短净干燥时间、降低有效能耗和提高干后品质。干燥过程中土豆的物理化学性质和营养成分变化都与温度、水分和时间有关。如果能够准确地预测间歇干燥过程中土豆内部的水分分布、温度、水分变化,就能为合理选择间歇干燥较佳工艺提供依据。该文提出了间歇干燥缓苏过程模型,可随时定量求得缓苏段土豆片内部水分重新分布情况以及土豆片内部水分分布时所需缓苏时间,为制定间歇干燥工艺提供依据。