Solid Food Thermal Conductivity Determination at High Temperatures

Thermal conductivity of carrots and potatoes was measured using a line heat source probe adapted for measurements to 130°C. Fastest response and rapid attainment of linearity in temperature rise vs In time plots, were obtained with a silicone oil-filled probe with an uninsulated thermocouple junction. Custom designed electronics to amplify thermocouple output, and computer control of measurements, data acquisition and analysis resulted in 0.4% data repeatability (two standard deviations) for calibration standards. Thermal conductivity of carrot and potato vs temperature agreed well with the published volume fraction model for multi-component foods.     

Methodology to Obtain True Thermal Conductivity of Low Porosity Food Powders

ABSTRACT: A technique was developed to measure, at a porosity close to zero, the true thermal conductivity of food powders. Samples of low porosities were prepared by mechanically compressing the food powder using a hydraulic press at pressures up to 3.035 × 10⁵ kPa (abs) in specially designed stainless steel cylinders with a dummy probe in place. Variation in porosity of the samples was less than 5%. Thermal conductivity was measured as a function of porosity (0.086 to 0.7), moisture content (0 to 37%, dry basis), and temperature (30 to 150 °C) by the thermal conductivity probe method. The thermal conductivity values decreased with an increase in porosity and increased with an increase in moisture content and temperature.     

非稳态热线法测定大麦的导热系数

将一根细长的线性热源埋于自然堆积的大麦中 ,通过一套由稳压电源、电位差计、电流表等二次仪表组成的测试装置 ,测定热线的升温速率 ,然后根据非稳态法热线测定的理论模型 ,计算出不同含水率大麦的导热系数。结果显示 ,在常温下 ,含水率在 10 %～ 2 6 .5 3%间的大麦的导热系数在 0 .1344～ 0 .192 1W/m·K之间 ,与其含水率呈现一定的相关性     

热线法测量食品热导率的实验研究

在食品材料的热导率的测量中,热线法是一种比较理想的方法。本文在介绍热线法的同时,运用自行研制的热线法导热系数测量仪对一些食品材料的热导率进行了测量。并将实验得到的数据同一些经验公式进行了对比,重点研究了食品中的水分对食品材料的热导率的影响,并得到了食品材料的热导率和其含水率关系的经验公式。     

Wheat Gluten and Glutenin Thermal Conductivity and Diffusivity at Extruder Temperatures

Thermal properties (thermal conductivity and diffusivity) of gluten and glutenin were measured in the temperature range 60-175°typically used in extrusion processing. Thermal conductivity and diffusivity of gluten decreased with increasing temperature and increased with increasing moisture content. Thermal conductivity and diffusivity of glutenin increased with temperature and moisture content. Thermal conductivity of gluten was 0.06-0.35 W/m-C and glutenin was 0.29-0.49 W/m-C for the temperature range 60-175°and moisture content range of 0-30%.     

Thermal Conductivities of Starch Gels at High Temperatures Influenced by Moisture

Thermal conductivities (k) of gelatinized starch gels and of starch gels with dissolved sucrose were determined at 80 to 120°C and at 39.6 to 75% moisture by a line heat source probe method. A special made sample holder prevented moisture evaporation during determination. Regression equations relating k to temperature and moisture were developed through stepwise regression analysis. Reliability of the developed equations was verified through experiments. The maximum error for regressed k values was 0.0085 W/mK.     

Measurement of Food Thermal Conductivity Using Differential Scanning Calorimetry

To measure thermal conductivity of foods, an attachment to a differential scanning calorimeter was constructed. A needle probe with a 40 gauge type-T thermocouple was used to measure the temperature of a cylindrical food sample. The DSC heating pan temperature was maintained at 40°C, and then raised to 50°C. The average thermal conductivities of rutabagas, radish, parsnip, turnip, potato, green apple, and carrot were 0.447, 0.499, 0.392, 0.480, 0.552, 0.405, and 0.564 W/m°C, respectively, for a temperature range between 40–50°C. The DSC method was reliable, precise, and a relatively rapid technique for determining thermal conductivity of foods.     

Permeability Measurements of Porous Food Materials

Permeability of air through porous pre-gelatinized flour dough was measured as a function of porosity (0.10–0.60), moisture content (15–50%, wet basis), and fat content (0–6%). At free stream velocities <2 cm/sec, flow rate and pressure drop followed Darcy's law for flow through porous media. Permeability values ranged from 0.02 darcies at 0.10 porosity to about 23 darcies at 0.60 porosity. Permeability of dough does not follow the Kozeny model for granular materials, possibly due to differences in tortuosity between dough and granular materials. Moisture content <50% and fat content to 6% did not directly affect permeability.     

玻璃棉纤维纸导热性能的研究

研究了温度、多孔填料及填料的添加比例对6种不同打浆度玻璃棉纤维纸导热系数的影响。结果表明,在-10～20℃之间,随着温度的升高, BM-1和BM-3纤维纸对应的导热系数变化不大,当温度由-10℃升高到0℃时,BM-2纤维纸的导热系数由0.0182 W/m·K增加到0.0287 W/m·K,增加了57.7%,变化非常明显,而BM-4、BM-5、BM-6纤维纸的导热系数也分别增加了30.4%、40.6%、32.4%。添加200～400目膨胀珍珠岩的玻璃棉纤维纸导热系数比蛭石的小,且二者的添加比例为30%时,其成纸的导热系数最低。填料的目数对其成纸的导热系数影响变化不大。     

Intrinsic Thermal Conductivity of Starch: A Model-independent Determination

Effective thermal conductivities of two-phase mixtures of potato or soluble starch granules with pure liquids or aqueous solutions (thermal conductivities in the range 0.169–0.602 W.m^?1.K^?1) were measured at 18.5±2.2°C using the steady state method. Measured values were compared with the thermal conductivities of the liquids and the results indicated a range of 0.38–0.40 W.m^?1K^?l for intrinsic thermal conductivity. Similar measurements, at temperatures up to 50°C for soluble starch (to assess the temperature dependence of the intrinsic thermal conductivity) indicated no significant change over the range of temperature studied for mixtures with pure liquids.     

Measurement of the Thermal Conductivity of Foods at High Pressure

The line heat source probe method, widely used for determining thermal conductivity of food materials, was applied in a pilot scale high-pressure unit and the possibility of extending this technique to pressures up to 400 MPa was investigated. Commercially canned tomato paste and apple pulp were used as test products. Probes were calibrated to 1.5% agar gel. A probe specific pressure- and temperature-dependant calibration factor was applied. The accuracy at high-pressure was similar to published values. Given the simplicity of the method, this approach seems very promising for determining thermal conductivity of foods over a range of pressures and temperatures.     

圆球导热法测定粮食导热系数研究

采用圆球导热法测定了稻谷、小麦、玉米和大豆的导热系数,并对稳态时间、装样均匀性和水分迁移等影响试验准确性的因素进行了分析.结果表明,该方法测定粮食导热系数的稳定时间至少需要8～10h,通过内外球壁多个热电偶的电势差能确保装样均匀,水分含量分别为10.9%、10.1%、11.0%、6.9%的稻谷、小麦、玉米和大豆的导热系数分别为0.105 4、0.141 8、0.136 2、0.127 4 W/(m·℃),水分迁移对低水分粮食导热系数测定结果的影响可以忽略.     

Reference Materials for Calibrating Probes Used for Measuring Thermal Conductivity of Frozen Foods

Reference materials which contained either 8% or 10% bentonite pastes and very fine pure copper powder (300 mesh, 30–.55%), provided thermal conductivities ranging from 0.9 to 1.9 W/mK. These materials were used to calibrate probes for measuring thermal conductivity of frozen food materials. Thermal conductivity values measured by the steady-state (parallel plate) method, the unsteady-state heat transfer (heating curve) method, and the probe method agreed within 5%. Although experimental density and heat capacity data of copper-filled bentonite pastes agreed with a mass average value of component properties, measured thermal conductivity values were much lower than the volume fraction average values.     

Thermal Properties of Restructured Beef Products at Different Isothermal Temperatures

Thermal properties and components of restructured beef products formulated with five binders (0.5–5.0%) were determined after heating to 35, 45, 55, or 65°C. Binders were: isolated soy protein, sodium caseinate, waxy modified corn starch, carrageenan, and oat flour. Water losses were greater when no binders were used until 65°C was attained. Density was influenced by both temperature and binder; specific heat was influenced by temperature; and thermal conductivity and thermal diffusivity were influenced by binder. All thermal properties correlated with water and/or protein contents of restructured beef products.     

Modelling Thermal Conductivity in Heterogeneous Media with the Finite Element Method

Three-dimensional finite element simulations were developed to predict the effective thermal conductivity of theoretical composite materials having complex structures. The models simulated a steady-state thermal conductivity measurement device performing measurements on theoretical materials with varying structures. The structure of a composite was considered to be composed of some simplified basic models. When the geometry, orientation type and number of dispersion are specified, the computer randomly generated the position and orientation for each dispersion and created the geometrical model and finite element mesh. The effective thermal conductivity of the theoretical composite was calculated using this method and compared to the values obtained by simple effective thermal conductivity models methods. The influence of some factors such as the volume fraction and the ratio of the thermal conductivities of the heterogeneities and the surrounding material on the effective thermal conductivity is discussed.     

蛋白基多孔材料的制备及其表征

本文以自组装小麦醇溶蛋白颗粒(GP)稳定的Pickering高内相乳液(HIPEs)为模板制备具有开孔结构的多孔材料并进行相关表征。通过反溶剂法制备GP,混合丙烯酰胺、聚乙二醇为连续相,正十二烷为分散相制备稳定Pickering HIPEs,研究不同蛋白浓度及油相体积对高内相乳液模板及多孔材料相关性质的影响。在p H 4时,GP浓度为1.5%、2.0%和2.5%及油相分数为75%、80%和85%均能以HIPEs为模板制备出稳定的亲水性多孔材料。GP浓度从1.5%增加至2.5%时,HIPEs中乳液粒径减小,材料内部结构孔壁变厚,表观密度增大,压缩模量从15.16 MPa增至18.01 MPa,2.0%GP浓度制备的多孔材料具有较好的持水能力,吸水率可达10.18 g/g;随着油相体积从75%增加至85%,乳液粒径分布更为均匀,材料的孔洞的D3,2由19.94μm增至23.59μm,表观密度下降,压缩模量由22.58 MPa下降到14.67 MPa。通过以GP稳定的HIPEs模板,成功制备出具有开孔和良好力学性质的亲水性多孔材料,对于多孔聚合材料在食品、生物医药上的应用具有重要意义。     

高导电、导热碳纸的制备及性能表征

为了提高碳纸的导电、导热性,采用电阻小且导热系数高的中间相沥青基碳纤维为原料,部分替代聚丙烯腈基碳纤维以制备碳纸;研究了中间相沥青基碳纤维不同添加比例对碳纸的微观形貌、结晶结构及导电、导热性能的影响。结果表明,随着中间相沥青基碳纤维添加比例的提高,碳纸的石墨化度明显提升,导电、导热性能显著增加。当中间相沥青基碳纤维与聚丙烯腈基碳纤维的质量比为3∶7时,经过石墨化的碳纸石墨化度为97.4%,与石墨化后纯聚丙烯腈基碳纸相比,电阻率由6.80 mΩ·cm降低至4.37 mΩ·cm,降低了35.7%;垂直表面的导热系数由0.084 W/(m·K)提高到0.159 W/(m·K),提高了88.8%。     

基于暖体出汗假人的双层保暖内衣热舒适性研究

以男士双层保暖内衣为研究对象,使用暖体出汗假人同时测量了该内衣的热阻与湿阻,并使用三维人体扫描仪对其与暖体假人之间的空气层体积进行了测量,建立了空气层体积与保暖内衣热阻和湿阻之间的多项回归模型。结果显示,在内衣测量范围内,其热阻随着号型的增大先增加后减小,而湿阻则随着号型的增大逐渐增加。进一步研究发现,其透湿指数随着号型的增大逐渐减小,说明其热舒适性随着号型的增大而减弱。     

Dielectric Properties and Thermal Conductivity of Marinated Shrimp and Channel Catfish

Peeled shrimp (Peneaus spp.) and channel catfish (Ictalutus punctatus) fillets were either mixed with commercial lemon pepper marinade and vacuum tumbled at 4°C for 30 min or soaked in 2% tripolyphosphate solution overnight. Dielectric constant and loss factor of marinated seafood and the penetration depth of microwaves were functions of temperature. When cooking temperature increased, the dielectric constant increased, while the loss factor and depth of penetration decreased. Because of the large variation in thermal conductivity measured for individual shrimp, no correlation between thermal conductivity and temperature was found. At constant temperature, thermal conductivity of 2% sodium tripolyphosphate-treated shrimp was higher than that of both marinated and nonmarinated shrimp as a result of higher moisture content. However, no difference in thermal conductivity was found between marinated and nonmarinated shrimp or catfish.     

提高加热不燃烧卷烟专用薄片导热特性的研究

研究了添加纳米石墨烯、碳纳米管、纳米氧化铝、碳化硅4种导热助剂对薄片导热性能的影响.结果表明,添加纳米石墨烯的薄片导热性能最好.与未添加导热助剂的薄片相比,纳米石墨烯添加量为3.2％时,薄片导热系数增幅达95.39％.进一步研究了不同水分条件下,纳米石墨烯用量对薄片导热性能的影响.结果表明,薄片导热系数随纳米石墨烯用量...