基于水势的稻谷真空干燥过程中水分迁移的试验研究

基于水势的理论分析,建立了稻谷真空干燥过程中水分迁移的速率模型.该模型反映了干燥速率与干燥温度、环境的相对湿度及真空度的关系.与热风干燥比较,真空干燥在低温下能有效地提高稻谷颗粒相对环境的水势,有利于提高干燥效率和降低能源损耗.     

胡萝卜片渗透脱水与真空油炸联合干燥动力学研究

为降低真空油炸果蔬脆片的脂肪含量,提高产品品质,本文研究了胡萝卜片渗透脱水与真空油炸联合干燥动力学,结果表明:随着渗透时间的延长,胡萝卜片的初始水分含量和平衡水分含量逐渐降低,脂肪含量、平衡脂肪含量以及脂肪的吸收速率也逐渐减少,皮尔逊积差相关分析显示:脂肪含量与其初始水分含量具有极显著的相关性(P<0.001);将渗透脱水Fick水分扩散规律和真空油炸一级反应动力学规律相结合,获得了胡萝卜片联合干燥过程中水分与脂肪含量变化的动力学方程,采用非线性回归法确定了方程系数,结果表明方程具有较高的决定系数,能够较好地预测渗透脱水与真空油炸联合干燥胡萝卜片水分和脂肪含量的变化。     

谷物平衡水分研究概况

控制吸湿是谷物安全贮藏的基本原则之一,平衡水分测定可用来判断谷物水分变化的趋向.概述了谷物平衡水分测定的原理及数学模型分析,并归纳,发生纳滞后效应的可能理论、影响谷物吸着(包括吸附与解吸)等温线测定的因子,还重点介绍了近年发展起来的、利用平衡水分吸附/解吸数据分析谷物及食品的热动力学函数--水分吸着等热.这些研究进展对完善我国储粮生态区域划分、谷物主产区低温干燥、设计干燥程序和设备、谷物及加工产品的包装及货架期皆有意义.     

谷物湿热平衡新模型及热力学特性的研究

建立谷物平衡水分与相对湿度在不同温度下的关系模型,并利用小麦、玉米、水稻、大米的静态平衡试验数据进行拟合。结果表明,该方程适合描述小麦、玉米、水稻、大米的等温线,可直接求解出谷物的平衡水分。另外,根据所建立的模型,预测了不同温度条件下的安全储藏水分,并对谷物的热力学性能进行了分析:吸着等热值随着平衡水分值的减小而增加,解吸等热值增加更为显著;解吸和吸附过程中吸着等热值均高于水汽化潜热;平衡水分大于25%后,吸着等热值趋于稳定,与汽化潜热值接近;根据分析所得数据,拟合了小麦、稻谷、玉米解吸与吸附过程的吸着等热曲线回归方程,为以能量化的观念实施粮仓作业管理,实现高效、合理、节能储粮提供了有利依据。     

小米挤压膨化产品的吸湿动力学研究

挤压膨化食品极易从周围环境中吸收水分,导致脆性丧失;对吸湿动力学过程的了解有助于选定合适的包装材料和存储环境。将4种形态的小米挤压膨化产品在不同温度、相对湿度下吸湿,并对吸湿过程进行模拟分析。与扩散模型、Peleg模型相比,Weibull模型最能预测小米挤压膨化产品的吸湿行为。根据Weibull模型,同一温度下,初始吸湿速率随相对湿度增大而近似线性增大。同一相对湿度下,总体吸湿速率随温度升高呈近似线性增大。温度越低、相对湿度越高,平衡水分越高。不同样品间的平衡水分差异较小,而吸湿速度差异明显,尤其在低温—低相对湿度条件时。外层气孔结构的差异可能是样品间初始吸湿速率差异的主要原因。     

肉苁蓉超声真空干燥的动力学研究

以新鲜肉苁蓉为原料,研究了20、30、40℃条件下肉苁蓉的超声真空干燥特性。选取了6种经典薄层干燥模型并进行非线性拟合。结果表明,肉苁蓉的超声真空干燥过程一直处于降速干燥阶段,无明显恒速干燥阶段。在20℃~40℃内,温度升高可提高肉苁蓉的超声真空干燥速率,提高内部有效水分扩散系数,水分有效扩散系数在2.66×10-10 m2/s~3.65×10-10m2/s;Midilli et al.模型(R20.999)能较好地描述肉苁蓉超声真空干燥过程水分的变化规律,该模型为肉苁蓉超声真空干燥工艺的优化提供了理论基础。     

热辐射下织物内水分干燥实验及其动力学研究

为研究低热流辐射环境下织物内的水分传递特征,借助红外成像仪及干燥理论方法分析了织物内部水分蒸发过程以及水分蒸发对织物隔热性能的影响。结果表明干燥过程可分为3个阶段：在加热阶段,织物干燥速率和温度快速提高,水分含量缓慢降低;在中间阶段,织物干燥速率保持稳定,温度缓慢升高,水分含量快速下降;在最后阶段,织物干燥速率降低,水分含量缓慢减少。含水率较高的织物其隔热性能较好,但含水率低于20% 时,其隔热性能快速下降,致使织物表面温度快速上升。通过拟合水分干燥速率等数据,采用Page、Niwton 及Henderson 3种经典干燥动力学模型,分析了织物水分扩散机制。结果显示,Page 模型比较适合于描述低辐射热下织物内水分的动态干燥过程。     

菠菜低温真空干燥实验研究

实验以菠菜为研究对象,设置干燥温度为0、5、10℃,研究了低温真空干燥的动力学特征,包括其含水量、水分比、干燥速率。并与冷冻真空干燥、热风干燥对比研究了干燥菠菜的复水特性、维生素C含量和叶绿素含量。结果表明:菠菜低温真空干燥过程只有加速和减速阶段,不存在恒速阶段。低温真空干燥复水比为8.0,大于热风干燥但小于冷冻真空干燥。和冷冻真空干燥和热风干燥相比较,低温真空干燥的维生素C保有量最高,低温真空干燥和冷冻真空干燥对于叶绿素的保存效果相同。     

稻谷低温低湿干燥特性与水分迁移分析

对初始含水率18.9%~29.6%的稻谷进行低温低湿薄层干燥,基于模型拟合、干燥时间和有效水分扩散系数的计算,研究稻谷初始含水率和温湿度因素对其表观水分扩散特性的影响,通过核磁共振技术探究前者内在水分动态。结果表明:在低温低湿条件下干燥温度越低,除湿对缩短稻谷干燥时间的效果越显著。Page模型拟合效果理想,参数k和n能较好地用实验变量所建立的回归方程描述。稻谷的有效水分扩散系数Deff在3.0697×10-10m2/s到5.0369×10-10m2/s范围内,MC0、T和RH对其有极显著的影响(p0.01)。同时,核磁数据反映出干燥过程中,稻谷内表征"结合水"的A21峰面积和束缚水的A22峰面积降低显著,自由水的A23峰面积变化较小,含水率降至14.5%~16.5%范围时束缚水的信号峰消失。连续称重法结合LF-NMR技术能够有效分析稻谷低温低湿干燥过程中水分扩散和状态转化的规律。     

稻谷的微波干燥特性及质热模型

微波干燥时谷物的失水、温度变化过程均可分二个阶段。干燥功率０．２Ｗ／ｇ或０．２Ｗ／ｇ以下，发芽率高，爆腰率低。干燥贮藏后脂肪酸含量比热风的低。建立了谷物微波干燥的水分和热量传递模型，确定了水分扩散系数。     

玉米红外低温真空干燥试验

以玉米为试验物料进行红外低温真空干燥工艺基础性研究,分析红外加热温度、真空度对玉米水分变化规律和干燥速率的影响。结果表明,干燥过程没有明显的恒速干燥阶段;与干燥室内真空度相比,干燥温度对玉米干燥的影响程度较大。红外低温真空干燥方法是粮食干燥可选的方法。     

Fixed and Incremental Levels of Microwave Power Application on Drying Grapes under Vacuum

ABSTRACT: Microwave vacuum drying has been investigated as promising potential for high-quality dried fruits. In this study, a batch microwave vacuum dryer was used to understand the effect of levels of microwave power on the drying characteristics and moisture content of grapes. Thompson seedless grapes were treated 1st for 30, 60, and 90 min at fixed levels of 500, 750,1000,1250, and 1500 W at a reduced pressure of 2.7 kPa and then treated by 3 staged microwave power levels: a higher level of power during the initial stages of dehydration and 2 subsequently lower levels of power applied as the moisture content decreased. A typical temperature profile was found during the drying process, linearly increasing at the start of drying, followed by a nearly constant value during the drying period while water was evaporating. The total specific energy estimated by the energy balance model was 0.97 to 1.01 W-h/g of fresh grapes and agreed well with the experimental specific energy of 0.85 to 0.90 W-h/g for the fixed power tests. The multiple regression results showed that the specific energy was the most influential parameter on the final moisture content of grapes both in fixed and incremental power levels. Further research is needed to further improve the process with high efficiency and good product quality using product temperature as a control measure. Keywords: microwave vacuum dehydration, specific energy, fruits, grapes     

不同干燥方法对栀子黄色素品质的影响

选择喷雾干燥、冷冻干燥和低温真空干燥三种方法对天然栀子黄色素进行干燥研究。通过粉末产品的品质(含水量、色价和色差)以及微观形态等性能指标的分析,发现喷雾、冷冻及低温真空干燥处理下的栀子黄色素产品含水量、色价及色差分别为2.89%、5.13%、5.94%,82.3、88.5、87.9,81.79、73.63和73.88;SEM表明喷雾干燥产品粉末微观形态均一,多呈凹球形;而低温真空干燥和冷冻干燥的粉末产品形状多样且不规则。3种干燥方式的能耗进行比较得知,喷雾干燥能耗最低,低温真空干燥次之,冷冻干燥能耗最大。综合产品品质和经济效益考虑,低温真空干燥适合于天然栀子黄色素的制粉加工。     

基于多尺度的稻谷干燥热湿耦合传递的数值研究

为保证稻谷在储藏时的品质,收获后的稻谷通常需要干燥到一定水分后储藏,研究稻谷干燥过程的热湿传递规律具有重要意义。目前稻谷干燥过程中热湿传递的分析大多基于连续介质假说和局部热湿平衡原理而进行的,这种方法的局限性在于很难获得粮堆干燥过程中粮粒内部的热湿迁移规律。本文基于稻谷粮堆孔隙尺度和粮粒尺度,采用局部非平衡热湿传递模型,模拟分析了在对流干燥条件下稻谷单颗粒以及颗粒群的热湿传递规律。研究结果表明,本研究模拟值与文献中干燥实验数据相对误差(RE)小于6.50 %,平均相对偏差(MRD)小于4.00 %,得出该模型具有一定的准确性;与基于局部热湿平衡多孔介质热湿耦合研究方法所得的稻谷颗粒群温度和水分传递结果进行对比,本研究所建立的模型更能准确体现出谷物颗粒在通风干燥时内部的热湿迁移规律。本研究所开发的模型能预测不同尺度下稻谷颗粒的温度和水分分布。     

Heat and Moisture Transfer in Composite Food—Theoretical Analysis of Influence of Surface Conductance and Component Arrangement

Heat and moisture transfer in composite bodies undergoing drying was simulated using a previously developed mathematical model which included the chemical potential of moisture as a mass transfer potential. Composite bodies included layered cylinders and concentric spheres consisting of a starch granule hydrate (H) and a hydrate of starch granules-sucrose 3:l mixture (S). The influence of the following factors on heat and moisture transfer was examined: convective surface mass transfer conductance, initial moisture, and component arrangement. The three factors significantly influenced moisture transfer white they had slight influence on heat transfer. Overall drying rate of each composite body was infhrenced interactively by moisture fluxes, which were caused by a surrounding drying medium and by a mass transfer potential difference across the interface of H and S.     

真空冷冻干燥南美白对虾干燥模型及品质研究

目的:以南美白对虾为研究对象,探究真空冷冻干燥南美白对虾的干燥特性,并建立干燥模型。方法:通过干基含水率和干燥速率探究干燥温度和装载量对干燥特性的影响并进行干燥模型拟合,同时基于收缩率、复水率、质构、感官评定对比分析真空冷冻干燥和热风干燥对对虾品质的影响。结果:干燥温度和装载量是影响干燥速率的关键因素,随着干燥温度的增加和装载量的减少,干燥时间缩短;而干燥速率随着干基含水率的下降呈现下降趋势。优化三种干燥模型,发现Page模型能更好的拟合真空冷冻干燥对虾的干燥特性。此外,与传统热风干燥相比,真空冷冻干燥对虾干制品具有低收缩率和高复水率特性(分别达到30.11%±0.04%、74.98%±0.01%),硬度、粘性和咀嚼性更低,并且色泽和感官上均优于热风干燥对虾干制品。结论:通过真空冷冻干燥技术可以获得品质更佳的南美白对虾干制品。     

Zur Feuchtebewegung im Holz während der konvektiven Vakuumtrocknung

This research was conducted to better understand moisture transport in wood during convective vacuum drying. Boards of beech, oak, spruce and scots pine with initial moisture contents of 66%, 92%, 28% and 33%, respectively, were dried under similar conditions in vacuum and at atmospheric pressure. We determined drying times and moisture content distributions, pressures and temperatures in the boards during the whole process. The boards of beech, spruce and scots pine dried approximately three times faster in vacuum than at atmospheric pressure, while the drying times for oak are hardly different. Above 45% moisture content beech and oak dried similarily, thus vacuum only accelerated hygroscopical drying. Pressures measured in beech and oak were always higher than saturation pressures corresponding to simultaneously measured temperatures, although during drying of beech we had boiling conditions in the vessel. We conclude that during vacuum drying air contained in the lumina keeps the pressure up, and water cannot boil as is often supposed. Diffusions coefficients calculated from moisture content gradients in the boards increased significantly at low moisture contents at vacuum drying but not at drying with normal pressures.     

黄淮流域高水分玉米就仓干燥技术优化研究

以现行的国家储粮技术规范为基础,结合黄淮流域储粮生态和粮情,采用精准检测水分、合理布置风网、机械通风降水、倒仓平衡水分的方法,通过优化试验,解决了在具体的干燥实践过程中出现的粮食过度干燥,通风降水过程存在"瓶颈现象"造成干燥效果下降,以及粮堆各部位水分梯度较大等问题。     

燃气催化式红外干燥稻谷的平均干燥速率对爆腰率的影响

采用自制的燃气催化式红外干燥实验装置研究稻米的红外干燥特性。本研究在单因素实验的基础上,采用响应曲面设计的试验方法研究了稻米的红外干燥工艺参数(初始含水率、辐射距离、干燥温度、处理量)对稻谷平均干燥速率及其爆腰率的影响规律。用SAS 9.1软件对试验数据进行处理并建立数学模型,并运用SPSS21.0分析软件对所得数据进行分析,获得平均干燥速率与爆腰率之间的相关性。结果表明：催化式红外干燥工艺参数对稻谷平均干燥速率的影响程度依次为：干燥温度、辐射距离、处理量、物料初始含水率。催化式红外干燥工艺参数对稻谷爆腰率的影响程度依次为：辐射距离、干燥温度、初始含水率、处理量。稻谷平均干燥速率与爆腰率之间存在正相关关系,平均干燥速率越快,水分从内部向外部的迁移速度越快,导致爆腰率增加。     

Einflu? von Ethanol auf den Trocknungsverlauf und die Makrostruktur eines Einzel-Zellmaterials aus Apfelparenchym (Sorte Granny Smith)

Ethanol pre-treated apple parenchyma cells are dried in a laboratory vacuum dryer. Various ethanol contents (75 to 95% m/m) and moisture contents (2 to 15 g ethanol-water-mixture per g dry mass) of the cells were adjusted before drying and the influence of these factors on drying behaviour as well as the related structural changes are studied. The initial ethanol content was found to have a significant influence on both, drying behaviour and macrostructure of the dried material. In the case of a low initial value, the ethanol content during drying already drops at moisture contents of about 0.5–1.5 g/g. As a consequence the residual particle moisture consists mainly of water at the end of drying. In contrast to high initial ethanol contents, cells at a low initial ethanol content become strongly deformed on drying. The porosity of the dried material also decreases in the latter case, relatively large and stable aggregates are formed and the water binding capacity of the dried product has diminished on a large scale. The initial moisture content influences the drying behaviour especially on applying low initial ethanol contents. If the initial moisture content is reduced the drop of the ethanol content is shifted towards the end of the drying process. The influence of initial moisture content on macrostructure, however, was found to be small compared with the effect of the initial ethanol content.