Thin-Layer Drying of Flax Fiber: III. Influence of Layer Thickness on Drying Parameters

Wet flax fiber was dried after rinsing at four layer thicknesses of 5, 10, 15, and 20 mm using four drying air temperatures of 30, 50, 70, and 100°C. The coefficients of diffusion of flax fiber at different drying conditions were estimated using a three-term series solution of Fick's second law of diffusion. The Page model was used to model the drying characteristic curves. The estimated coefficient of diffusion of the flax fiber and the drying constant of the Page model were both linearly proportional to drying air temperature and increased exponentially with the thickness of the drying layer.     

Thin-Layer Drying of Flax Fiber: I. Analysis of Modeling Using Fick's Second Law of Diffusion

Thin-layer drying of moist flax fiber was performed at four temperatures of 30, 50, 70, and 100°C with a constant absolute humidity of 0.0065 kg water per kg dry air. The coefficients of diffusion of the fiber at different drying conditions were estimated by modeling the drying process using the one- to five-term solutions of the second Fick's law of diffusion. The models underestimated the drying process during the initial stages of drying and overestimated this process during the final stages. The estimated coefficient of diffusions ranged from 5.11 × 10^-9 to 1.92 × 10^-8 m²/s and linearly increased with the drying air temperature.     

Thin-Layer Drying of Flax Fiber: I. Analysis of Modeling Using Fick's Second Law of Diffusion

Thin-layer drying of moist flax fiber was performed at four temperatures of 30, 50, 70, and 100°C with a constant absolute humidity of 0.0065 kg water per kg dry air. The coefficients of diffusion of the fiber at different drying conditions were estimated by modeling the drying process using the one- to five-term solutions of the second Fick's law of diffusion. The models underestimated the drying process during the initial stages of drying and overestimated this process during the final stages. The estimated coefficient of diffusions ranged from 5.11 × 10^?9 to 1.92 × 10^?8 m²/s and linearly increased with the drying air temperature.     

Thin-Layer Drying of Flax Fiber: II. Modeling Drying Process Using Semi-Theoretical and Empirical Models

Thin-layer drying experiments were performed for drying flax fiber under four different drying conditions. In all drying treatments the absolute humidity of drying air was 0.0065 kg of water per kg of dry air, but the drying temperature were 30, 50, 70, and 100°C. The drying process was modeled using the drying data and five semi?theoretical and empirical models cited in different literatures. From the five tested models, the Page model gave the best fitting for experimental data with R ² equal to 0.99, for all treatments. The estimated drying constants at different drying temperatures were highly correlated with drying air temperature. The drying constants were also highly correlated with the calculated coefficient of diffusions.     

Thin-Layer Drying of Flax Fiber: II. Modeling Drying Process Using Semi-Theoretical and Empirical Models

Thin-layer drying experiments were performed for drying flax fiber under four different drying conditions. In all drying treatments the absolute humidity of drying air was 0.0065 kg of water per kg of dry air, but the drying temperature were 30, 50, 70, and 100°C. The drying process was modeled using the drying data and five semi-theoretical and empirical models cited in different literatures. From the five tested models, the Page model gave the best fitting for experimental data with R² equal to 0.99, for all treatments. The estimated drying constants at different drying temperatures were highly correlated with drying air temperature. The drying constants were also highly correlated with the calculated coefficient of diffusions.     

Evaluation of Thin-Layer Models for Mushroom (Agaricus bisporus) Drying

In the present research, seven well-known mathematical thin-layer drying models were fitted to mushroom (Agaricus bisporus) drying experimental data, implementing nonlinear regression analysis techniques. The experiments were conducted in two laboratory-scale dryers. A range of temperatures 50–65°C and air velocities 1.0–5.0 m/s were tested. The statistical analysis concluded that the best model in terms of fitting performance was the logarithmic model. Correlations expressing this model parameter dependence with the drying air coefficients are also reported.     

Evaluation of Thin-Layer Models for Mushroom (Agaricus bisporus) Drying

In the present research, seven well-known mathematical thin-layer drying models were fitted to mushroom (Agaricus bisporus) drying experimental data, implementing nonlinear regression analysis techniques. The experiments were conducted in two laboratory-scale dryers. A range of temperatures 50-65°C and air velocities 1.0-5.0 m/s were tested. The statistical analysis concluded that the best model in terms of fitting performance was the logarithmic model. Correlations expressing this model parameter dependence with the drying air coefficients are also reported.     

Prediction of Microwave Drying Behavior of Pharmaceutical Powders Using Thin-Layer Models

Common pharmaceutical excipients and active ingredients, wetted with specific solvents, were dried under selected continuous power microwave and pulsed power microwave-vacuum conditions in an experimental system. Irrespective of the drying technique, a typical drying profile, with a constant drying rate stage followed by two falling rate periods, was exhibited. The experimental moisture loss data were fitted to semi-theoretical and empirical thin-layer drying equations and the models compared on the basis of three statistical parameters. The drying characteristics were satisfactorily described by the Lewis, Page, Logarithmic, Chavez-Mendez et al., and Midilli et al. models, with the latter providing the best representation of the data.     

Prediction of Microwave Drying Behavior of Pharmaceutical Powders Using Thin-Layer Models

Common pharmaceutical excipients and active ingredients, wetted with specific solvents, were dried under selected continuous power microwave and pulsed power microwave-vacuum conditions in an experimental system. Irrespective of the drying technique, a typical drying profile, with a constant drying rate stage followed by two falling rate periods, was exhibited. The experimental moisture loss data were fitted to semi-theoretical and empirical thin-layer drying equations and the models compared on the basis of three statistical parameters. The drying characteristics were satisfactorily described by the Lewis, Page, Logarithmic, Chavez-Mendez et al., and Midilli et al. models, with the latter providing the best representation of the data.     

制备工艺对亚麻增强热塑性复合材料拉伸力学性能的影响

将增强体亚麻纱线和基体丙纶复丝制成pp/亚麻包覆纱后,进行织造,织物用层合热压法制成复合材料.制备工艺中,包覆纱法对复合材料的拉伸强度最好;麻含量50%的复合材料的拉伸强度达到最佳;当纬纱密度相同时,随着经纱密度的增大经向的拉伸强力和拉伸弹性模量也随之增大,而纬向的却随之减小,当经纱密度相同时,随着纬纱密度的增大,经向的拉伸强力和拉伸弹性模量随之减小,纬向的随之增大.     

短亚麻纤维/聚乳酸复合材料制备与性能研究

采用双螺杆挤出机制备出一系列短亚麻纤维/聚乳酸复合材料,通过力学性能测试、SEM和DSC等方法研究了短亚麻纤维用量、偶联剂种类对短亚麻纤维/聚乳酸复合材料力学性能、结晶性能、流变性能和耐热性能的影响。结果表明:短亚麻纤维用量达到4.62%时,亚麻纤维/聚乳酸复合材料力学性能达到最佳;随短亚麻纤维用量的增加亚,麻纤维/聚乳酸复合材料流动性降低而,结晶度和耐热性有所提高。     

Na+阻燃改性亚麻纤维及其对纤维性能的影响

首先用马来酸酐(MA)对亚麻纤维(FF)进行化学接枝,得到MA-FF,然后用Na_2CO_3溶液处理MA-FF,得到Na~+阻燃改性的FF,用Na_2CO_3-MA-FF表示。FTIR中羰基峰的出现证明了MA接枝到FF上;用酸碱滴定法测定了MA在FF上的接枝率(Gd);用极限氧指数(LOI)和垂直燃烧评价了Na~+对FF的阻燃效果,用XRD分析了FF结晶度的变化。结果表明:105℃下,m(MA)∶m(FF)=48∶60的原料在DMF溶液中反应2.4 h,MA在FF上的接枝率达到71%～75%;Na_2CO_3-MA-FF的阻燃性随着Na~+含量增加而提高,20 g/L Na_2CO_3溶液处理的MA-FF(记为20-Na_2CO_3-MA-FF)的LOI值由20%提高到28.9%,续燃时间由43 s降低到0 s,损毁长度由30 cm降低到8.3 cm;MA接枝后,FF结晶度由66.7%提高到75.0%,20-Na_2CO_3-MA-FF结晶度稍降到71.8%,但是XRD中2q角没有变化,均为14.8°、16.7°和22.8°。     

Energy and Exergy Analyses of Thin-Layer Drying of Potato Slices in a Semi-Industrial Continuous Band Dryer

This article is concerned with the energy and exergy analyses of the continuous-convection drying of potato slices. The first and second laws of thermodynamics were used to calculate the energy and exergy. A semi-industrial continuous-band dryer has been designed and used for drying experiments. The equipment has a drying chamber of 2 m length and the inlet air used for drying is heated by gas power. The experiments were conducted on potato slices with thickness of 5 mm at three different air temperatures of 50, 60 and 70°C, drying air mass flow rates of 0.61, 1.22, and 1.83 kg/s and feeding rates of 2.31 × 10^?4, 2.78 × 10^?4, and 3.48 × 10^?4 kg/s. The energy utilization and energy utilization ratio were found to vary between 3.75 and 24.04 kJ/s and 0.1513 and 0.3700, respectively. These values show that only a small proportion of the supplied energy by the heater was used for drying. The exergy loss and exergy efficiency were found to be in the range of 0.5987 to 13.71 kJ/s and 0.5713 to 0.9405, respectively, indicating that the drying process was thermodynamically inefficient and much energy was vented in the exhaust air. In addition, the results showed that the feeding rate and the temperature and flow rate of the drying air had an important effect on energy and exergy use. This knowledge will provide insights into the optimization of a continuous dryer and the operating parameters that causes reduction of energy consumption and losses in continuous drying.     

Heat Pump Drying of Green Sweet Pepper

Thin-layer drying experiments under controlled conditions were conducted for green sweet pepper in heat pump dryer at 30, 35, and 40°C and hot air dryer at 45°C with relative humidities ranging from 19 to 55%. The moisture content of sweet pepper slices reduced exponentially with drying time. As the temperature increased, the drying curve exhibited a steeper slope, thus exhibiting an increase in drying rate. Drying of green sweet pepper took place mainly under the falling-rate period. The Page equation was found to be better than the Lewis equation to describe the thin-layer drying of green sweet pepper with higher coefficient of determination and lower root mean square error. Drying in heat pump dryer at 40°C took less time with higher drying rate and specific moisture extraction rate as compared to hot air drying at 45°C due to lower relative humidity of the drying air in a heat pump dryer though the drying air temperature was less. The retention of total chlorophyll content and ascorbic acid content was observed to be more in heat pump–dried samples with higher rehydration ratios and sensory scores. The quality parameters showed a declining trend with increase in drying air temperature from 30 to 45°C. Keeping in view the energy consumption and quality attributes of dehydrated products, it is proposed to dry green sweet pepper at 35°C in heat pump dryer.     

The Thin-Layer Drying Characterstics of White Onion Slices

ABSTRACT

A batch–type experimental dryer with a computer–aided data acquisition system was designed and built for the thin layer drying studies of onion (Allium cew L., cv. Southport White Globe) slices. Twenty seven single–layer drying curves were established for a temperature range of 42.5–90⁰C, an air velocity range of 0.6–1.4 m/s, an air humidity range of 0.0093–0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002–0.005 m. The single–term exponential model adequately described the single–layer drying behaviour of the onion slices. l'he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius–type relationship. The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.     

玻璃纤维纺织型浸润剂烘干工艺研究

研究了玻璃纤维纺织型浸润剂的烘干工艺。试验了原丝不同自然存放条件、热风烘干的温度与时间等烘干工艺对玻璃纤维原丝含水率、可燃物含量、强度、浸润剂成膜效果与迁移分布,以及退并合股纱的纺织工艺情况和强度与耐磨性能等理化指标的影响。     

Influence of Drying Conditions on the Hazelnut Quality. III. Browning

The influence of drying conditions on browning in hazelnut (Corylus avellana L.) has been studied by means of color measurement. Samples of unshelled and shelled hazelnuts were dried under six air temperatures (30. 40, 50, 60, 70 and 80°C). The drying experiments were done with forced air circulation, and two varieties of hazelnut were investigated, Negret and Pauetet. CiELab system was used to evaluate changes in total color (δE^*), lightness (L^*), chroma (C^*) and hue angle (H^*) on dried hazelnuts. Browning of hazelnut was observed to occur a1 all temperatures studied. The rate of pigment formation was determined from the δE' values with zero-order kinetic model, and temperature dependence was described by the Arrhenius equation with an activation energy (E_a) varying from 28 to 39 kJlmol. Negret variety showed the highest rate of browning.     

Influence of Drying Conditions on the Hazelnut Quality. III. Browning

ABSTRACT

The influence of drying conditions on browning in hazelnut (Corylus avellana L.) has been studied by means of color measurement. Samples of unshelled and shelled hazelnuts were dried under six air temperatures (30. 40, 50, 60, 70 and 80°C). The drying experiments were done with forced air circulation, and two varieties of hazelnut were investigated, Negret and Pauetet. CiELab system was used to evaluate changes in total color (δE^?), lightness (L^?), chroma (C^?) and hue angle (H^?) on dried hazelnuts. Browning of hazelnut was observed to occur a1 all temperatures studied. The rate of pigment formation was determined from the δE' values with zero-order kinetic model, and temperature dependence was described by the Arrhenius equation with an activation energy (E_a) varying from 28 to 39 kJlmol. Negret variety showed the highest rate of browning.     

碱式氯化镁纳米棒干燥动力学方程及参数的确定

在不同床层厚度和不同干燥介质温度下，对碱式氯化镁纳米棒进行干燥动力学实验，得到其干燥曲线和干燥速率曲线。采用薄层干燥模型对所得干燥动力学实验数据进行数学处理，得到碱式氯化镁纳米棒的干燥方程为MR=exp[-（kτ）^n]，干燥速率方程为-dMR／dτ=knMR（-lnMR）^（n-1）/n，干燥速率常数k=Aexp[-Ev（1＋CLL）／RT]，干燥时间指数n=1．821，界面蒸发活化能Ev=11．228kJ／mol，指前因子A=4．237min^-1，经验常数CL=55．556m^-1。     

无机纤维板干燥过程的数学模拟研究

本文通过对无机纤维板干燥过程的分析,建立了干燥过程中热量传递和质量传递的数学模型,模拟结果与实测结果有较好的一致性.