利用瞬态平面热源法检测烟丝热物性的方法

利用瞬态平面热源法建立了测试堆积烟丝热物性(导热系数、热物性参数、体积热容)的实验装置、计算了仪器工作参数并测量了烟丝在不同含水率、堆积密度下的热物性数据;考察了不同水平下检测热物性数据的重复性.结果表明:实验数据的重复性较好.导热系数测试结果精密度范围为:0.00030～0.00471 W/m·K;热扩散系数测试结果精密度范围为0.00371～0.02424 mm2/s;体积热容测试结果精密度范围为0.00921～0.06537 MJ/m3.K.烟丝导热系数、体积热容与烟丝含水率、堆积密度正相关,热扩散系数与烟丝含水率、堆积密度负相关.     

不同温度条件下烟丝—发烟剂体系热物性研究

采用瞬态平面热源法对加热非燃烧烟草制品的烟丝-发烟剂(丙三醇与丙二醇质量比51)体系的热物性进行研究,分析含水率和发烟剂含量对再造烟叶丝和烤烟丝热物性的影响。结果表明,随温度(22~75℃)的升高,烟草物料导热系数增大[再造烟叶丝0.06~0.12 W/(m·K)、烤烟丝0.06~0.16 W/(m·K)],热扩散系数减小(再造烟叶丝0.33~0.05mm2/s、烤烟丝0.40~0.09mm2/s),体积热容增大[再造烟叶丝0.17~2.70 MJ/(m3·K)、烤烟丝0.15~1.45 MJ/(m3·K)];随含水率(湿基含水率0%~13%)的增大,烟草物料导热系数增大、热扩散系数减小、体积热容增大;随发烟剂含量(0%~25%)的增大,烟草物料导热系数呈增大趋势,但变化很小[再造烟叶丝增大0.005 W/(m·K),烤烟丝增大0.006 W/(m·K)],热扩散系数减小(再造烟叶丝减小0.069mm~2/s,烤烟丝减小0.069 mm2/s),体积热容增大[再造烟叶丝增大0.106 MJ/(m3·K),烤烟丝增大0.138 MJ/(m3·K)]。     

烟草形态对烟草热物性的影响

为了研究烟草形态(片状、丝状、粉状)对烟草热物性参数的影响,采用瞬态平面热源法测量了不同形态烟草堆积体的导热系数、热扩散系数和质量热容,分析了烟草形态对测量重复性、导热系数、质量热容以及热物性对温度敏感程度的影响。结果表明:(1)热物性参数测量重复性为导热系数热扩散系数质量热容;对于同一个热物性参数,烟草尺寸越小,测量重复性越好,即烟粉烟丝烟片。(2)随着堆积密度增大,烟草样品的导热系数逐渐增大,质量热容呈稍微减小的趋势。(3)烟草的特征尺寸越小,导热系数越小;烟片的导热系数对温度的敏感程度大于烟丝的导热系数对温度的敏感程度。     

米粉、绿豆粉及黄豆粉的导热系数的实验研究

农产品热物性是影响其深加工工艺的关键因素,其中导热系数最为重要。通过对现有导热系数测量方法的分析,采用球法测量法测量大米粉、绿豆粉、黄豆粉的导热系数。通过对实验数据的分析,回归了导热系数与温度、含水率、总糖和蛋白质之间的关系。实验结果表明,大米及绿豆的导热系数随着温度升高而降低,黄豆导热系数随温升高而增大,并都随各种营养成分的增加而增大。     

基于实验室批式滚筒干燥装置的热加工强度表征及其对烟丝物理特性的影响

为研究烟丝滚筒干燥过程加工强度的归一化定量表征方法,以实验室批式滚筒干燥装置为平台分析了烟丝在滚筒干燥过程中自身热状态的变化,提供了一种新的烟丝滚筒干燥过程热加工强度表征方法。考察了不同加工条件(筒壁温度和热风温度)对热加工强度的影响,利用图像法和筛分法研究了不同加工条件对烘后烟丝主要物理特性(卷曲度、填充值、耐加工性)的影响规律。结果表明:①以烟丝干燥过程Ts-X特征曲线表征烟丝干燥过程热加工状态变化特征,采用该特征曲线积分平均值表征滚筒干燥过程热加工强度,该参数具有明确的物理意义,即物料在滚筒干燥过程中单位脱水量对应的温度变化率。②实验条件下的滚筒干燥热加工强度范围为4.26～5.10℃/%,筒壁温度和热风温度的升高均会导致热加工强度增大,但筒壁温度和热风温度升高相同温度时,筒壁温度对热加工强度的贡献比热风温度高30%～70%。③在不同的干燥条件下,随着热加工强度增大,烟丝卷曲度和填充值也相应增大,烟丝耐加工性减小。     

工业中试装置中烟丝的滚筒传输特性

在一工业中试装置中对烟丝的滚筒传输特性进行了研究,考察了冷态稳定传输过程中烟丝流量、筒内风速、滚筒转速以及烟丝含水率对烟丝滚筒滞留量、滞留时间和轴向传输速度的影响,分析了不同条件下烟丝在滚筒内升举—抛洒单元运动时间、运动次数及运动步长的变化规律.结果表明:①筒内风速、滚筒转速和烟丝含水率对烟丝滚筒滞留时间影响显著,随筒内风速、滚筒转速的增大,烟丝滚筒滞留时间减小、轴向传输速度增加,烟丝含水率增大则使得烟丝滚筒滞留时间增加、轴向传输速度减小;②随滚筒转速、烟丝流量、烟丝含水率增大,烟丝在滚筒传输过程中经历的升举—抛洒单元运动次数增加、运动步长减小,筒内风速对烟丝在滚筒内的升举—抛洒单元运动次数和运动步长的影响与之相反.     

豆粕热物理特性的试验研究

为研究豆粕热物理特性的测定方法及不同湿基含水率、温度下的相关规律,以5种湿基含水率(分别为4.85%、8.94%、12.81%、16.72%、20.87%)的豆粕为试验材料,在5种温度梯度下(分别为30、45、60、75、90℃),对其比热、热导率、热扩散系数等热物理特性进行了测定。结果表明:豆粕的比热在2.073~5.170 J/(g·K)之间,其热导率在0.066~0.097 W/(m·K)之间,其热扩散系数在0.416×10~(-7)~0.787×10~(-7)m~2/s之间;含水量和温度对其热物理特性影响显著;其比热、热导率均随湿基含水量和温度的升高而增大;热扩散系数随温度的升高而增大,随湿基含水量的增加而减小。根据试验结果,分别拟合出比热、热导率、热扩散系数与湿基含水量、温度的回归方程。     

烟丝热物性测试方法的研究

本文对适用于烟丝的导热系数、比热容和热扩散系数等重要热物性的测试方法进行了研究,并对测试中的一些技术问题进行了讨论。实验表明,准稳态平板法可以快速地测定烟丝的各项主要热物性。     

不同干燥方式下配方烟丝的保润性能

为探索不同干燥方式对同一配方烟丝物理保润性能的影响,采用动态水分检测方法,分析了气流干燥配方烟丝与滚筒干燥配方烟丝在不同相对湿度条件下的吸湿-解湿性能。结果表明:(1)气流干燥烟丝在吸湿-解湿过程中质量变化率(dm)均高于滚筒干燥烟丝,气流干燥烟丝与空气中水蒸气的交换容量更大。(2)吸湿-解湿过程中,气流干燥烟丝平衡含水率变化量高于滚筒干燥烟丝,且两种烟丝平衡含水率变化量的差值随相对湿度增加而增大。(3)两种烟丝吸湿-解湿过程水分比(MR)曲线变化趋势一致。(4)初始条件(40%RH)下,气流干燥烟丝的保润性能较优。(5)吸湿-解湿过程中,高相对湿度(RH60%)条件下,滚筒干燥烟丝保润性能稍优于气流干燥烟丝;低相对湿度(RH≤60%)条件下,气流干燥烟丝保润性能稍优于滚筒干燥烟丝。     

干燥参数对烘箱法烟丝含水率的影响分析

为规范烘箱法干燥参数并提高烘箱法测烟丝含水率的检测结果的一致性,采用烘箱法对不同的样品量、干燥温度、干燥时间以及烘盒个数对烟丝含水率检测结果的影响进行测定。结果表明,在试验范围内,随着样品量的增加,烟丝含水率检测结果标准偏差逐减小;烟丝含水率检测结果随着干燥温度的增加而增大,且干燥平衡所需的时间也越长;在试验范围内,随着烘盒个数的增多,烟丝含水率的检测结果变化不大,但检测结果的相对标准偏差值随烘盒个数的增多而增大。     

烟草颗粒热解与释烟特性影响因素研究

[目的]为探索加热状态下烟草颗粒热解和烟气释放规律.[方法]采用导热系数测试仪、热分析仪(TGA)和锥形量热仪(CONE)表征分析了甘油添加量、水分含量以及粒径对烟草颗粒导热特性、热解过程和烟气释放特性的影响.[结果](1)样品导热系数随水分和甘油含量的增加以及粒径减小整体上呈现不同程度的上升趋势,不同水分与甘油含量样...     

烤烟叶丝微波干燥特性研究

分析了烤烟叶丝含水率和温度随微波作用时间的变化规律并绘制出叶丝微波干燥曲线,研究了不同工艺条件(微波功率、叶丝初始含水率、真空压力)对叶丝微波干燥曲线的影响,在此基础上,建立了烤烟叶丝微波干燥的数学模型。结果表明,烤烟叶丝的微波干燥大致分为3个阶段:第1阶段,干燥速率和温度上升迅速,含水率降低缓慢;第2阶段,干燥速率基本保持不变,温度上升缓慢,含水率下降迅速;第3阶段,干燥速率下降,温度上升缓慢,含水率下降缓慢。微波功率和叶丝初始含水率对叶丝微波干燥曲线的影响显著,而真空压力影响不显著。烤烟叶丝微波干燥的动力学过程可以用薄层干燥的数学模型Page方程描述。     

基于收缩特性分析的叶丝快速对流干燥动力学模型

为准确表征叶丝脱水过程中的干燥动力学特性,分析了烤烟和白肋烟两种叶丝在下行床快速对流干燥中的孔隙结构变化特征,对叶丝干燥收缩过程进行了数学模型拟合,建立了考虑收缩形变的叶丝干燥过程水分扩散模型,并对模型进行了验证。结果表明:①随着干燥过程中两种叶丝内孔容积的减小,叶丝中孔径大于0.5μm的孔容比例呈降低趋势,而孔径小于0.05μm的孔容比例呈升高趋势;在不同干燥阶段两种叶丝孔径分布的分形维数介于2.45~2.71之间,表明其孔隙结构具有分形特征;②线性叠加式收缩模型能够较好地描述叶丝干燥过程中的收缩现象,烤烟叶丝和白肋烟叶丝体积比V/V₀和含水率比X/X₀的线性相关系数均大于0.99,采用该收缩模型对基于Fick第二定律的水分扩散模型进行修正,实验数据的拟合精度从修正前的0.9069提升到修正后的0.9580;③采用修正的水分扩散模型描述叶丝快速干燥动力学发现,考虑了干燥过程中的叶丝收缩现象后,得到的叶丝水分有效扩散系数降低,表明叶丝干燥过程中的体积收缩不利于传质过程。      

叶丝气流干燥过程中水分和丙三醇迁移特性

为了在叶丝气流干燥过程中有效调控物料的水分和丙三醇含量,考察丙三醇含量和干燥温度对叶丝中丙三醇和水分迁移的影响,利用固定床气流干燥装置,在100～145℃下对丙三醇含量为0～6.6%的叶丝进行干燥试验,得到了叶丝中丙三醇和水分释放规律。结果表明：(1)添加丙三醇后叶丝水分迁移规律基本一致,叶丝的干燥速率受丙三醇初始含量的影响较小。干燥过程分为两个阶段,第一阶段（0～100 s）和第二阶段（100～600 s）。(2)叶丝表面温度与干燥温度正相关,与丙三醇的初始含量无关。(3)丙三醇初始含量对其脱除无显著影响。第一阶段丙三醇的损失量基本相同,约占总损失量的50%以上;第二阶段不同丙三醇初始含量的损失速率无明显差异,且随着干燥时间的增加不断减小。(4)干燥温度对丙三醇脱除有显著影响。第一阶段不同干燥温度下丙三醇损失量均为0.6百分点左右,损失速率随干燥时间线性降低,损失速率的变化率与干燥温度呈负相关关系;第二阶段丙三醇损失量随干燥温度的升高而增大,损失速率基本保持稳定。     

Thermophysical Properties of Okara During Drying

The simulation of heat transfer during thermal treatments of foods requires the knowledge of thermophysical properties of the material. In this study some thermophysical properties of okara, such as density, specific heat, thermal conductivity, thermal diffusivity, heat transfer coefficient, and mass transfer coefficient, were obtained during a drying process. Okara was extruded in the shape of spherical pellets and then dried in a fixed bed dryer from 78% of moisture content (w.b.) until 3%. During the drying process, the water content and the temperature of the samples were periodically measured. The thermal properties were obtained from empirical correlations found in the literature, which use the okara centesimal composition, analyzed in a laboratory, and the relative humidity and velocity of the drying air, measured during the process. The results in this study showed that it is possible to estimate the thermal properties cited using the experimental moisture content history and the centesimal composition of the food.     

Influence of Moisture Content and Temperature on Thermal Conductivity and Thermal Diffusivity of Rice Flours

The thermal conductivity and thermal diffusivity for four types of rice flours and one type of rice protein were determined at temperatures ranging from 4.8 to 36.8?°C, bulk densities 535 to 875.8 kg m^?3, and moisture contents 2.6 to 16.7% (w.b.), using a KD2 Thermal Properties Analyzer. The thermal conductivity of rice flours and rice protein increased with the increase in temperature, moisture content as well as with increase in bulk density. Thermal diffusivity decreased with increase in moisture content, increase in temperature and bulk density. The thermal conductivities values obtained were within the range of 0.045 to 0.124 W m^?1 K^?1 whereas the thermal diffusivity values were in the range of 0.094 to 0.138 mm² s^?1.     

PHYSICAL and THERMAL PROPERTIES of GORGON NUT

Bulk density, true density, angle of repose, coefficient of friction on metal surfaces, specific heat, thermal diffusivity and conductivity of gorgon nut were determined using standard techniques for different sizes of nuts at moisture contents and temperatures ranging from 15 to 60% (dry basis) and 25 to 55C, respectively. the physical properties varied quadratically with moisture content. Specific heat increased with moisture and temperature but decreased with the size of the nut; whereas, the thermal diffusivity showed a reverse trend. Thermal conductivity increased with moisture content but did not follow any trend with temperature within the range of the study. the physical and thermal properties data at various moisture contents and temperatures were used to develop equations for different sizes of gorgon nuts.     

滚筒内烟丝干燥过程的数值模拟

为了解析滚筒干燥条件对烟丝干燥过程中筒内的温湿度场和流场的影响规律,采用数值模拟开展烟丝滚筒干燥的筒内温湿度场的研究。通过干燥实验测量滚筒内部空气湿度来验证模拟结果的准确性,探究进口热风温度、进口热风速度、筒壁温度和滚筒转速等因素对滚筒干燥过程中内部水分分布的影响规律。结果表明：(1)增加进口热风温度会使蒸发过程加快;(2)提高进口热风速度能加强滚筒前段部分的水分蒸发,但进口热风速度过大会造成滚筒内整体水分浓度下降;(3)改变筒壁温度直接影响烟丝温度与筒内的平衡含水量,筒内平衡含水量随着筒壁温度的升高而增加;(4)增加滚筒转速会减少烟丝在筒内的停留时间,不利于烟丝的干燥。     

THERMAL PROPERTIES OF CHEDDAR CHEESE: EXPERIMENTAL AND MODELING

Thermal properties (thermal conductivity, thermal diffusivity and heat capacity) of Cheddar cheese were measured as a function of cheese age and composition. The composition ranged from 30–60% moisture, 8–37% fat, and 22–36% protein (wet basis). The thermal conductivity and heat capacity ranged from 0.354–0.481 W/m °C and from 2.444–3.096 kJ/kg °C. Both thermal conductivity and heat capacity increased with moisture and protein content and decreased with fat content. The thermal diffusivity ranged from 1.07×10^?7 ? 1.53 × 10^?7 m²/s. There was no significant relationship between thermal diffusivity and moisture, fat and protein content of cheese. No statistically significant effect (at the 10% level) of age (0 to 28 wk) on thermal properties was observed. Models predicting thermal properties as a function of cheese composition were developed and their predictive ability was compared with that of empirical models available in the literature. In addition, several theoretical thermal conductivity models were evaluated for their usefulness with Cheddar cheese. Published thermal conductivity models cannot accurately predict (mean error was from 3.4 to 42%) the thermal conductivity of Cheddar cheese.     

Thermal properties of tapioca starch

Thermal properties of native tapioca starch, including thermal conductivity, specific heat, and thermal diffusivity at 4, 15, and 30% moisture contents, and 25, 50, and 75°C temperature levels were studied. Thermal conductivity was measured using a line‐heat source thermal probe equipped with a computerized data acquisition system; specific heat was measured using Differential Scanning Calorimetry (DSC) and thermal diffusivity was calculated from the thermal conductivity, density, and specific heat. Thermal conductivity, specific heat, and thermal diffusivity increased with the increase of temperature and/or moisture content. Prediction models for the thermal properties of tapioca starch were developed for practical applications.