单液滴干燥过程中阿拉伯胶乳液的干燥特性

喷雾干燥塔是一个完全封闭的设施,难以对干燥过程中的液滴取样分析。本试验以阿拉伯胶包埋油脂的水包油(O/W)型乳液为样液,采用单液滴干燥技术(SDD)模拟喷雾干燥条件,通过分析乳液液滴在干燥过程中的形态收缩和干燥动力学参数的变化,探究干燥气流速度和乳液中固形物含量对颗粒的表面形成机制的影响。结果表明,在0.70,0.90,1.10 m/s 3种干燥气流速度下乳液液滴的干燥行为差异很大。在1.10 m/s的干燥气流速度下,液滴水分蒸发最快,表壳形成最早,最终所得颗粒收缩率最小。乳液总固形物含量对液滴干燥行为的影响也较为明显。随着总固形物含量的增高,乳液液滴水分蒸发越慢,表壳形成越早,最终所得干燥颗粒形态越大。本试验对于干燥动力学模型的研究和喷雾干燥产品品质的改善具有指导性意义。     

Influence of emulsion composition and inlet air temperature on the microencapsulation of flaxseed oil by spray drying

The objective of this work was to study the influence of some process conditions on the microencapsulation of flaxseed oil by spray drying. The process was carried out on a mini spray dryer and gum Arabic was used as wall material. Seventeen tests were made, according to a central composite design. Independent variables were: inlet air temperature (138-202 °C), total solid content (10-30% w/w) and oil concentration with respect to total solids (10-30% w/w). Encapsulation efficiency, lipid oxidation and powder bulk density were analyzed as responses. Powder morphology and particle size distribution were also analyzed. The feed emulsions were characterized with respect to droplet size and viscosity. Higher solid content and lower oil concentration led to higher encapsulation efficiency and lower lipid oxidation, which was related to the higher emulsion viscosity and lower droplets size. Increasing drying temperature resulted in higher lipid oxidation. Bulk density increased when higher solid content and lower inlet air temperature were used. The particles were rounded and shriveled, and their mean diameter was mainly affected by total solid content.     

Experimental study of heat transfer and air flow in a refrigerated display cabinet

The heat transfer and air flow in a vertical open refrigerated display cabinet loaded with packages of test product was studied in order to analyse unsteady state phenomena. The product and air temperatures in the curtain were measured using tiny thermocouples, air velocity using a hot wire anemometer and PIV (Particle Image Velocimetry). A comparison between the air velocities measured by these two methods shows a good agreement at the internal side of the air curtain. However, these two methods give quite different result at the external side of the air curtain which can be explained by the complex air flow in this region. The temporal variation of the air temperature inside the air curtain is due partly to the “on/off” compressor cycle and partly to the introduction of ambient air via vortices. The latter phenomena contribute to the rapid velocity fluctuations which are greatest in the mixing layer of the air curtain. The product position in the cabinet is a determining factor of its temperature.     

喷气织机辅助喷嘴流场特性与耗气量分析

为研究辅助喷嘴几何结构对喷嘴喷射效果及耗气量的影响,采用CFD软件Fluent对喷气织机辅助喷嘴流场进行数值模拟,获得了辅助喷嘴在不同供气压力、出口截面积、出口形状及喷射角下的纬纱飞行轴线气流速度分布。结果表明:随压力增大,射流速度的提升逐渐变弱,耗气量随压力呈正相关变化;喷嘴出口截面积影响射流速度和持续性,随截面积增加耗气量不断增大;截面积一定时,出口形状变化对筘槽内流场影响较小;纬纱飞行方向上气流速度及峰值位置随喷射角而变化,在实验范围内,喷射角越大耗气量越小,选择合适的辅助喷嘴和引纬工艺,是实现喷气织机高质低耗目标的关键。     

织物喷雾上浆雾化质量评价

为衡量织物喷雾上浆工艺参数配置的合理性,对织物喷雾上浆雾化质量进行了量化。首先介绍了织物上浆液的特性,给出浆液雾化流场图像的获取方法和预处理过程;然后计算了雾化流场喷雾角和喷雾图像相似度,评价浆液雾化流场的稳定性;最后,以相对喷嘴同一位置处的局部喷雾图像为计算区域,计算雾化粒径并统计雾化粒子数量,分析了液滴颗粒的分布,评价了浆液雾化流场的均匀性。结果表明:浆液雾化流场的稳定性评价和均匀性评价,从不同尺度量化了织物喷雾上浆雾化质量,揭示了高黏度浆液的稳定运动状态;通过探究入射在织物表面的浆液小液滴的大小及其分布,为织物喷浆工艺参数的微量调整、织物喷浆质量的在线评价提供参考。     

Adsorption and transport of gas-phase naphthalene on micron-size fog droplets in air

Aromatic hydrocarbon vapors adsorb to the air/water interface and are transported by wet deposition processes via fog, mist, and rain. A falling droplet apparatus was used to study the adsorption and uptake of naphthalene vapor on water droplets with diameters ranging from 14 to 200 microm. Uptake of naphthalene vapor greater than that predicted by bulk (air-water) phase equilibrium was noted for diameters less than 50 microm and was attributed to surface adsorption. The experimental values of the droplet-vapor partition constants were used to obtain the mass accommodation coefficient for naphthalene at the interface. The effect of temperature on the mass accommodation coefficientwas measured. The effects of a synthetic surfactant and a natural organic carbon surrogate (Suwanee Fulvic acid) on the uptake of naphthalene vapors on water droplets were also examined. Small droplet diameter, decreased temperature, and the presence of dissolved surface-active material in water enhanced the uptake of naphthalene into fog droplets.     

Hole and vacuole formation during drying of sessile whey protein droplets

Morphological development from droplet to particle during drying has strong influence on powder structure and functionality. We study the evolving morphological properties of whey protein droplets during single sessile droplet drying experiments as a well-defined model for spray drying. Sessile drying droplets were visualised with a camera and subjected to varying drying conditions such as temperature, initial protein concentration, presence of airflow and droplet rotation. The final particles were imaged by SEM and X-ray tomography. Under all conditions used, the droplets initially shrink steadily while at a specific point a hole nucleates. Subsequently, a vacuole develops until a rigid hollow particle is obtained. The location of the hole was found strongly dependent on the presence and the direction of the applied air flow. We hypothesise that in the early drying stage a skin forms, which becomes more rigid when the hole nucleates. The hole forms at the position where the local modulus of the skin layer is minimal and/or at the point below the skin where the local pressure is minimal, and that after the hole has nucleated, the vacuole develops mainly by evaporation of water through the hole.     

阿拉伯胶/乳清蛋白乳液的干燥行为特性的研究

为了研究液滴/颗粒在喷雾干燥过程中的干燥机理,本实验制备以阿拉伯胶和乳清蛋白为壁材的乳液,采用单液滴干燥技术(single droplet drying,SDD)模拟喷雾干燥环境,对单个液滴/颗粒的干燥过程进行分析,探究气流温度和壁材种类对液滴/颗粒干燥行为和所得颗粒性质的影响。结果表明:气流温度为130 ℃时所得颗粒形态最大,110 ℃次之,90 ℃下所得颗粒最小,气流温度高会促进表壳快速形成,进而抑制颗粒收缩,故所得颗粒较大。此外,增大气流温度有利于提高液滴/颗粒的干燥速率。与阿拉伯胶乳液相比,乳清蛋白乳液液滴降速干燥阶段出现早,所得颗粒收缩程度较小。研究结果表明干燥气流温度和壁材种类对表壳形成过程和颗粒形态有显著的影响。     

鱼油微粉的制备及其稳定性分析

为优化鱼油微粉的制备工艺以及初探其稳定性,本文以鱼粉加工副产物富集所得鱼油为原料,筛选复合壁材,研究喷雾干燥法制备鱼油微粉的工艺条件,考察芯壁比、固形物浓度、乳化温度、进风温度、喷雾压力、进料流量等因素对鱼油微胶囊效果的影响,并测定鱼油微粉的微观结构、溶解性及稳定性。结果表明,壁材选择阿拉伯胶/β-环糊精/玉米糖浆（质量比2:1:6）效果较好,微粉制备的最适工艺参数为:芯壁比32%、固形物浓度25%、乳化温度52 ℃、进风温度206 ℃、喷雾压力35 MPa、进料流量300 mL/h,此条件下制得的鱼油微粉包埋率达92.66%。微粉颗粒表面光滑,无破裂或孔洞,且水溶性好。鱼油微粉的贮藏稳定性显著高于未微胶囊化的鱼油（P<0.05）,且添加抗氧化剂的微胶囊鱼油具有更好的抗氧化能力。     

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。     

Mimicking Spray Drying by Drying of Single Droplets Deposited on a Flat Surface

The inactivation of bioactive ingredients during spray drying is often matrix specific. Therefore, the design of new processes or the optimisation of existing spray drying processes is usually highly product specific and requires numerous experiments. Rapid experimentation methods that facilitate fast data generation are therefore desired. A novel method for drying single droplets to mimic spray drying is proposed. The approach involves droplet deposition on a hydrophobic flat surface followed by controlled drying. A heat and mass transfer model is applied to predict the drying history of the single droplets. The approach is successfully evaluated through studying the inactivation of β-galactosidase during drying. The heat and mass transfer model supplemented with inactivation kinetics provided reasonable prediction of the residual enzyme activity after drying. In addition, the inactivation kinetics could be directly extracted from single droplet experiments rather than using the kinetics from separate heating experiments. Finally, it was demonstrated that the inactivation kinetics found with the single-drop experiments could satisfactorily predict the residual activity of β-galactosidase dried with a laboratory-scale spray dryer.     

Simultaneous desulfurization and denitrification from flue gas by Ferrate(VI)

An innovative semidry process has been developed to simultaneously remove NO and SO? from flue gas. According to the conditions of the flue gas circulating fluidized bed (CFB) system, ferrate(VI) absorbent was prepared and added to humidified water, and the effects of the various influencing factors, such as ferrate(VI) concentration, humidified water pH, inlet flue gas temperature, residence time, molar ratio of Ca/(S+N), and concentrations of SO? and NO on removal efficiencies of SO? and NO were studied experimentally. Removal efficiencies of 96.1% for SO? and 67.2% for NO were obtained, respectively, under the optimal experimental conditions, in which the concentration of ferrate(VI) was 0.03 M, the humidified water pH was 9.32, the inlet flue gas temperature was 130 °C, the residence time was 2.2 s, and the molar ratio of Ca/(S+N) was 1.2. In addition, the reaction mechanism of simultaneous desulfurization and denitrification using ferrate(VI) was proposed.     

Simultaneous Desulfurization and Denitrification of Flue Gas by ·OH Radicals Produced from O(2)(+) and Water Vapor in a Duct

In the present study, simultaneous flue gas desulfurization and denitrification are achieved with ·OH radicals generated from O(2)(+) reacting with water vapor in a duct. The O(2)(+) ions are generated by a strong ionization dielectric barrier discharge and then injected into the duct. Compared with conventional gas discharge treatment, the present method does not need a plasma reaction reactor, additional catalysts, reductants, or oxidants. The main recovered products are the liquids H(2)SO(4) and HNO(3), which can be used in many processes. Removal rates of 97% for NO and 82% for SO(2) are obtained under the following optimal experimental conditions: molar ratio of reactive oxygen species (O(2)(+), O(3)) to SO(2) and NO, 5; inlet flue gas temperature, 65 °C; reaction time, 0.94 s; and H(2)O volume fraction, 8%. Production of O(2)(+) and the plasma reaction mechanisms are discussed, and the recovered acid is characterized. The experimental results show that the present method performs better for denitrification than for desulfurization. Compared with conventional air discharge flue gas treatments, the present method has lower initial investment and operating costs, and the equipment is more compact.     

Reducing the deposition of fat and protein covered particles with low energy surfaces

Deposition behavior of spray dried full cream milk, skim milk and whey particles were observed in a pilot scale dryer. Particle surface dominated with fats exhibit gradual decrease in deposition fluxes when transition from the initial adhesion to the subsequent cohesion mechanism. Whey protein, however, displayed significant differences in the adhesion and cohesion fluxes. Reduction of particle deposition on low energy chamber wall surface is more significant for the hydrophobic whey particles. Further analysis shows that the reduction in droplet–wall contact energy is larger for the more hydrophobic droplet, delineating weaker adhesion interaction. The results suggest that the hydrophobicity of the depositing particles in an important consideration when using lower chamber wall with lower surface energy. This is in addition to the effect of particle rigidity and deposition strength as reported previously.     

双歧杆菌微胶囊喷雾干燥工艺的影响因素研究

选择明胶为壁材,以两歧双歧杆菌(Bifidobacterium bifidus)Bbm为实验菌株,采用喷雾干燥的方法制成徽胶囊。研究了喷雾干燥过程中的固形物浓度、进样流量、进风温度、出口温度对微胶囊产率及菌体存活率的影响,确定最佳操作工艺参数为:固形物浓度为3%,进样流量为360 mL/h,进风温度为105℃,出口温度为54～57℃,微胶囊产率为65.7%,活菌存活率为53.5%,活菌数超过1×10~(10)cfu/g。     

基于CFD-DEM的打叶后烟叶风分运动特性分析与试验

为研究打叶后烟叶在离心风分仓内的运动特性及受力变化，基于CFD-DEM耦合方法分析了不同进风风速下，物料在风分仓内的运动过程及受力变化规律。仿真结果表明:随着进风风速增大，风分仓内压力逐渐增大，片烟间碰撞次数增加，流场均匀性变化较小；当进风风速为11、13、15 m/s时，片烟与仓体壁面产生的最大平均碰撞力分别为0.155、0.164、0.378 N，叶含梗率分别为2.46%、2.37%、3.12%。以叶含梗率作为风分效率评价指标进行试验，结果表明:当进风风速为11、13、15 m/s时，叶含梗率分别为2.27%、1.84%、2.54%，试验结果与仿真结果误差 < 1百分点，验证了仿真模拟的合理性。该研究可为优化风分仓结构和工艺参数提供理论支持。      

The potential of electrospraying for hydrophobic film coating on foods

There is a continuous need for thinner edible coatings with excellent barrier properties, and this requires new application methods. Electrospraying is known to yield fine droplets of size down to 20 μm, giving the potential of very thin and even coatings. A single electrospraying nozzle was used to characterise droplet formation and investigate the formation of thin films on well-defined surfaces. The experimental droplet size was successfully described as a function of operational parameters and liquid properties using scaling relations. The influence of operating parameters as nozzle height and electrostatic potential were evaluated as well.Thin film deposition was experimentally investigated for sunflower oil electro-sprayed on a highly conductive (aluminium) and insulating target surface (Parafilm). For both aluminium foil and Parafilm the droplet deposition was found to be random. For aluminium foil, being a conductive target, this was expected as repellence between droplets on the surface and new droplets is low, due to charge leakage to the ground. For Parafilm, droplet repellence appeared so large that droplets deposited on larger empty spots or were even pushed away from the surface. To evaluate the film formation performance, Monte Carlo simulations were carried out, and it was found that the method is a useful tool to characterise droplet deposition and film formation characteristics.     

Comparisons between membranes for use in cross flow membrane emulsification

Emulsification is an important process, particularly in food production. Membrane emulsification attempts to improve on traditional emulsification methods by producing each droplet singly. Cross flow membrane emulsification uses the flow of the continuous phase to detach droplets from the membrane pores. Different factors were investigated, including the effects of cross flow velocity, trans-membrane pressure, and emulsifier concentration. The effects of using different membrane materials and morphologies were directly compared. The trans-membrane pressure was found to have a large effect on the diameter (D[4,3]) of the droplets, with similar results for all the studied membrane types. Increasing the pressure increases droplet sizes, and can be related to the different mechanisms of droplet detachment from the membrane. An increase in the linear cross flow velocity was shown to cause a decrease in the diameter of the produced droplets. The different membranes each have different characteristics.     

活性墨水流体特性对喷射性能的影响

为了研究活性墨水流体特性、高分子聚合物和表面活性剂对墨滴喷射性能及墨滴参数的影响,配制不同黏度、不同表面张力、不同分子质量聚乙烯吡咯烷酮(PVP)和不同表面活性剂的活性红墨水,利用墨滴观测系统观察墨滴喷射形成过程及飞行轨迹,并对墨滴系带长度、断裂时间、斜喷角度、墨滴速度和体积等参数进行分析。结果表明:随着墨水黏度的增加,墨滴断裂时间明显增加,墨滴速度和体积变小,黏度的增加有利于抑制卫星墨滴的形成,但大于4.56 mPa·s会影响喷射的流畅性;表面张力大于49.1 mN/m不利于墨滴的形成,会出现斜喷现象;与PVP-K15和PVP-K30相比,PVP-K60的加入会引起墨水在喷射过程中回缩而无法形成墨滴。     

肉桂醛微胶囊的制备工艺

研究了以阿拉伯树胶和麦芽糊精为壁材 ,喷雾干燥法制备微胶囊化肉桂醛的工艺条件 .探讨了壁材组成、乳化剂用量、固形物质量分数、芯壁比、进风温度、进料速度、喷射压力等对微胶囊化效果的影响 .经过正交试验 ,确定了最佳工艺条件 .实验结果表明 ,阿拉伯胶和麦芽糊精的最佳质量配比为 1∶1,蒸馏单甘酯的用量为 0 .4 g/dL ,固形物质量分数为 4 0 % ,芯材与壁材的配比为 1mL∶10 g ,肉桂醛微胶囊化的最佳喷雾干燥条件为进风温度 2 2 5℃ ,进料流量 2 10mL/h ,喷射压力0 .18MPa .实验还表明 ,肉桂醛微胶囊产品有一定的缓释抑菌效果 .