浮法玻璃厂保护气体设计问题(续)

(四)保护气体干燥1、概述保护气体的干燥主要是除去气体中的水分.另外通过分子筛除二氧化碳.脱水方法有二:一是冷冻冷凝;一是深度脱水,即采用干燥剂.前者用于气体中水分较大或者常温下处于饱和状态,通过冷凝将大部分水分除去,以便提高深度干燥效果.我国南方气体含水量大;冷却水温又高,应在深度干燥前加冷凝措施.对原料气中水分不大,如KFS-860型的氮气,露点只有-33～-37℃,因为除氧加入部分饱和水分的氢气,混     

节能的干燥设备

在工业生产中,所谓干燥,是指用蒸发的办法除去物料中的水分。为提高蒸发效率,通常采用加热或减压的方法。因此,如何以少量的热能除去物料中的水分,是选择干燥设备的关键问题。如在干燥前,先用机械脱水的办法最大限度地减少物料中的水分,则干燥设备即可缩小。这样不仅节省设备费用,而且运转     

列管式真空蒸发器的快速取样装置

<正> 浓缩工序是明胶生产中的一个重要工序,其主要作用是利用减压蒸发器将水分从过滤后的稀明胶溶液中蒸发除去,提高明胶溶液的浓度,为明胶冷冻干燥创造有利条件,缩短干燥过程中的时间,达到节     

食品渗透脱水研究进展

将具有细胞组织结构、含有多种可溶性成分的食品原料浸渍于渗透液中，会引起多组分物质迁移和原料渗透脱水。探讨了渗透脱水的物质迁移机制，综述了影响渗透脱水物质迁移的因素和加速物质迁移的方法，讨论了渗透脱水在果蔬预处理和功能性食品、中等水分食品加工方面的应用。     

水果蔬菜热力干燥的研究

介绍了水果蔬菜在热力脱水过程的降解反应动力学，讨论了几种果蔬的热力脱水工艺。由于水果蔬菜在热力脱水时其营养成分会发生降解作用，所以对干燥操作的评价产品质量是第一位的，其次为环境保护、能源消耗及投资。为了获得质量上乘的果蔬干品，应根据物料的特性选择适当的干燥方法，使物料在干燥过程中的受热温度尽量低，受热时间尽量短。     

膜分离过程及其在染料工业中的应用

一、概述膜分离过程是六十年代初发展起来的新兴分离技术,主要包括反渗透、超滤、微滤、电渗析以及气体的渗透分离等。它的原理是利用膜的选择透过性而使不同的物质得到分离。反渗透是通过外压克服溶液的渗透压而使溶液中的溶剂从高浓度溶液透过膜流向低浓度溶液,溶液则被膜截留。自从1960年Loeb和Souirajan发明了第一张具有高选择性和高透水率的不对称醋酸纤维素膜后才使反渗透过程进入实用阶段。反渗透主要用于苦咸水和海水淡化,因     

NaA分子筛膜的合成及在渗透蒸发中的应用

介绍了近几年来国内外在NaA分子筛膜的合成及应用方面的研究进展,重点介绍了NaA分子筛膜渗透蒸发的机理和在有机物脱水中的应用.提供了分子筛膜渗透蒸发与蒸馏过程在有机物脱水中的经济比较,发现渗透蒸发过程能降低一半成本.最后对NaA分子筛膜的制备和渗透蒸发进行了展望.     

渗透脱水传质过程的国内外研究进展

组织细胞在高渗透性溶液中浸透,在细胞内外将会发生物质的传递现象。一部分水分和少量天然溶质从细胞内渗出,同时,高渗透溶液的溶质会渗入细胞中。在物质迁移的过程中,影响渗透传质的因素主要有:样品的组织特性,渗透溶液的组成与浓度,温度,渗透比,搅拌程度。而一些高新科技技术,如高静水压,高压脉冲电场,微波等通过改变组织细胞的某些特性可以加快渗透脱水的传质过程。简要介绍了渗透脱水过程影响水分和固体传递的作用因素和增强处理方法的内在机理与研究成果。综述了渗透脱水传质过程的动力学模型的发展。     

渗透膜蒸馏过程的试验研究及计算

利用纯水-氯化钠溶液(0.5～4.0 mol·L-1)为试验体系,对渗透膜蒸馏过程中氯化钠溶液流量,温度和浓度对渗透通量的影响进行了试验研究,在不同试验条件下考察了料液浓度和水分渗透总量随操作时间的变化.在试验研究的基础上,建立了用于描述渗透蒸馏过程中水分渗透总量和料液浓度变化的关系,并利用试验测定结果,对不同操作条件下的水分渗透总量和料液浓度进行了计算,计算结果与试验结果一致性较好.     

你知道吗?——反渗透技术的几个第一

第一次发现渗透现象是法国阿布尔·诺莱特(Abble Nellet)于1748年通过水自盐扩散进入到猪膀胱里的酒精中的试验而获得;第一个渗析装置是由都伯朗福特(Dubrunfaut)于1863年究制成功,并首次在糖业生产上以羊皮纸作为渗透膜来除去糖蜜中的盐;第一张具有选择性的半透膜是由特劳勃(Traube)于1864年采用亚铁氰化铜首次制得;第一次测定溶液渗透压是由     

声空强化渗透脱水过程质扩散研究

An experimental study on intensifying osmotic dehydration was carried out in a state of nature and with acoustic cavitation of different cavitating intensity (0.5A, 0.7A and 0.9A) respectively, in which the material is apple slice of 5mm thickness. The result showed that acoustic cavitation remarkably enhanced the osmotic dehydration, and the water loss was accelerated with the increase of cavitating intensity. The water diffusivity coefficients ranged from 1.8×10-10m2·s-1 at 0.5A to 2.6×10-10m2·s-1 at 0.9A, and solute diffusivity coefficients ranged from 3.5×10-11m2·s-1 at 0.5A to 4.6×10-11 m2·s-1 at 0.9A. On the basis of experiments, a mathematical model was established about mass transfer during osmotic dehydration, and the numerical simulation was carried out. The calculated results agree well with experimental data, and represent the rule of mass transfer during osmotic dehydration intensified by acoustic cavitation.     

果蔬渗透脱水过程动力学研究

结合植物组织结构与流体传输过程机理建立了渗透脱水过程的一维质量传递数学模型。模型以植物细胞为传输过程的基本单元，考虑了各组分在细胞内、细胞外、通过细胞膜及胞间连丝的质量扩散，和由于体积收缩而导致的集流传输。以土豆为实验物料，在40℃恒温条件下，采用40％（质量百分比）的蔗糖溶液作为渗透液，进行渗透脱水实验，得到的实验结果与模拟结果十分接近，验证了模型的有效性。通过数值模拟可详细描述渗透脱水过程中土豆细胞内外水和蔗糖的质量浓度分布。并就能源与生产效率方面对“渗透-干燥”与“无预处理干燥”过程作了比较。     

DRYING CHARACTERISTICS OF OSMOTICALLY DEHYDRATED FRUITS COATED WITH SEMIPERMEABLE EDIBLE FILMS

This paper deals with key issues of the coating technology applied to plant materials prior to osmotic dehydration and convective drying. Coatings created with solutions of starch products and pectin were examined. It was shown that coating of foods to be dehydrated influences mass transfer in a plant tissue during osmotic pre-treatment as well as during convective drying. Each coating should be individually examined. The properties of coatings depend on their composition and the method used for the fabrication of a coating. Coating of foods with an artificial barrier on the surface may efficiently hinder the penetration of solute inside the food, not affecting much the rate of water removal. The coated plant materials had a greater water loss/solids gain ratio then the uncoated ones. Osmotic dehydration seems to be one of possible pre-treatment methods before drying. The conditions of convective drying are changed upon osmotic dehydration of plant materials. It was shown that changes in drying rate depend on the kind of coating substance. Bigger differences were observed at higher water content and these differences narrowed as water content in dried material decreased. The positive effect of coatings on the physical properties of dried fruits was found.     

DRYING CHARACTERISTICS OF OSMOTICALLY DEHYDRATED FRUITS COATED WITH SEMIPERMEABLE EDIBLE FILMS

This paper deals with key issues of the coating technology applied to plant materials prior to osmotic dehydration and convective drying. Coatings created with solutions of starch products and pectin were examined. It was shown that coating of foods to be dehydrated influences mass transfer in a plant tissue during osmotic pre-treatment as well as during convective drying. Each coating should be individually examined. The properties of coatings depend on their composition and the method used for the fabrication of a coating. Coating of foods with an artificial barrier on the surface may efficiently hinder the penetration of solute inside the food, not affecting much the rate of water removal. The coated plant materials had a greater water loss/solids gain ratio then the uncoated ones. Osmotic dehydration seems to be one of possible pre-treatment methods before drying. The conditions of convective drying are changed upon osmotic dehydration of plant materials. It was shown that changes in drying rate depend on the kind of coating substance. Bigger differences were observed at higher water content and these differences narrowed as water content in dried material decreased. The positive effect of coatings on the physical properties of dried fruits was found.     

Osmotic dehydration of lemon (Citrus limon L.) slices: Modeling mass transfer kinetics correlated with dry matter holding capacity and juice sac losses

Osmotic dehydration of lemon slices was performed using hypertonic NaCl solution. Due to low dry matter holding capacity (DHC) of lemon, the moisture loss, salt gain, and solid loss kinetics during osmotic dehydration were studied by considering the loss of juice sacs from lemon. The slices were immersed in the osmotic solutions maintained with four concentrations of NaCl (5–20%, w/v) and three temperatures (30, 40, and 50°C) for predetermined time intervals (10–180?min). The sample to solution ratio was maintained at 1:10. Azuara model based on Peleg model was used to determine the equilibrium moisture loss and salt gain. Apart from the moisture loss and salt gain, it was found that the loss of solid constituents and juice sacs from the fruit into the osmotic solution was significant. Therefore, the DHC was determined to correlate the rate of solid loss. The DHC was found to be greatly affected by temperature as lemon was less capable to withhold its cell integrity at higher temperature. A combined correlation model was used to determine the effect of osmosis time, solution concentration, and temperature on moisture loss, salt gain, and solid loss. High temperature is not preferable for osmotic dehydration of lemon as it increases losses. The optimal condition was found to be 20% salt concentration and 30°C osmotic solution for 180?min to attain high moisture loss, less solid loss, and required salt uptake within allowable limits.     

Optimization of Osmotic Dehydration of Kiwifruit

Mass transfer rates were quantitatively investigated during osmotic dehydration of kiwifruit slices using response surface methodology with the sucrose concentration (20-80%, w/w), temperature of sucrose solution (15-75°C), osmotic time (60-420 min), and slice thickness (2-10 mm) as the independent process variables. Quadratic regression equations are obtained to describe the effects of independent process variables on the water loss (WL), sucrose gain (SG), and ascorbic acid loss (AAL). It was found that all factors had significant effect on the WL during osmotic dehydration of kiwifruit. Effects of temperature, time, and slice thickness were more pronounced on SG than the effect of concentration of sucrose solution. The osmotic solution temperature was the most significant factor affecting the AAL, followed by slice thickness and duration of treatment. The optimal conditions for osmotic dehydration were: 60% sucrose concentration, 30-40°C osmotic temperature, 150 min osmotic time, and 8 mm slice thickness.     

EFFECT OF OSMOTIC AGENT ON OSMOTIC DEHYDRATION OF FRUITS

Mass transfer phenomena were investigated during osmotic dehydration of apple, banana and kiwi in glucose and sucrose osmotic solution. A complete set of experiments was performed for a wide range of temperature, sample size, speed of agitation, osmotic agent concentration and immersion time. An empirical model, based on a first order kinetic equation, was fitted satisfactorily to experimental data. Furthermore, the effect of solute molecular weight on mass transfer phenomena during the osmotic treatment was evaluated. The results showed that low molecular weight solute (glucose) leads to higher water loss and solids uptake than high molecular weight solute (sucrose), of osmodehydrated fruits under the same solution concentration.     

Osmotic Dehydration Pretreatment in Drying of Fruits and Vegetables

Several vegetables and fruits, apple, ginger, carrot, and pumpkin were dehydrated under various osmotic conditions using sucrose and salt as the permeating agents. The dehydrated materials were then dried. The influence of solute concentration, process temperature and the type of solute on osmotic dehydration and further thermal drying were investigated. The nutrition loss during the osmotic process was measured using carotene as the nutrition index. The effect of calcium chloride present in osmotic solution on the product quality was also studied. A first order kinetic model was chosen to describe the mass transfer phenomena of the osmotic process. The equilibrium value of water loss, solute gained, kinetic constants K_WL and K_SG under various conditions are successfully predicted by the model. The relationship between the equilibrium value and four major factors that influence osmotic process of carrot was obtained based on the experimental data. The relations between the loss constant of carotene and the solute concentration in carrot and pumpkin were obtained based on the experimental data. The qualities of dried products are better for the osmotic dehydration pretreated samples than those dried directly.     

EFFECT OF OSMOTIC AGENT ON OSMOTIC DEHYDRATION OF FRUITS

ABSTRACT

Mass transfer phenomena were investigated during osmotic dehydration of apple, banana and kiwi in glucose and sucrose osmotic solution. A complete set of experiments was performed for a wide range of temperature, sample size, speed of agitation, osmotic agent concentration and immersion time. An empirical model, based on a first order kinetic equation, was fitted satisfactorily to experimental data. Furthermore, the effect of solute molecular weight on mass transfer phenomena during the osmotic treatment was evaluated. The results showed that low molecular weight solute (glucose) leads to higher water loss and solids uptake than high molecular weight solute (sucrose), of osmodehydrated fruits under the same solution concentration.     

Osmotic dehydration of blueberries pretreated with pulsed electric fields: Effects on dehydration kinetics,and microbiological and nutritional qualities

Fresh blueberries were treated by pulsed electric fields (PEF) at 2?kV/cm before osmotic dehydration in 70% cane sugar syrup. The changes in water loss, solids gain, populations of native microorganisms, antioxidant activity, contents of anthocyanins, predominant phenolic acids and flavonols, and total phenolics in blueberries were investigated after PEF pretreatment and during osmotic dehydration at 40°C. Compared with non-PEF-pretreated blueberry samples, PEF pretreatment reduced the osmotic dehydration time of blueberry samples from 120 to 48?h at target moisture content (3.0?g/g initial dry matter). No significant differences (p?>?0.05) in total phenolics, antioxidant activity, anthocyanins, and predominant phenolic acids and flavonols were observed between the PEF-pretreated and non-PEF-pretreated blueberry samples. The PEF-pretreated blueberry samples had lower microbial populations than those which were not subjected to PEF pretreatment. Regardless of pretreatment, decreases in anthocyanins, predominant phenolic acids and flavonols, total phenolics, and antioxidant activity in blueberries were observed during the osmotic dehydration process. The results demonstrate that PEF pretreatment significantly reduced the dehydration time and enhanced the microbiological quality of blueberries without affecting their nutritional quality.