MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT

ABSTRACT

Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels.

In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry salting were studied. Slabs of beef m. trapezius with an infinite plate geometry were salted in a NaCl saturated solution or in a dry salt bed, at two temperatures (10 and 20°C) and different time exposures (120 min and 96 hours). Equilibration studies were extended up to six days.

It was observed that water loss increased with salt uptake, for increasing periods of times. At 20°C the moisture loss was higher than it was at 10°C in both salting processes. On the other hand, the kinetics of salt uptake and moisture loss were of greater importance in the process of dry salting than in that of wet salting.

The salt diffusion coefficient for wet salting was 0.26 × 10^?10m²/s at20°C and 0.25 × 10^?10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^?10 m²/s at 20°C and 17.21 × 10^?10 m²/s at 10°C.     

流化催化精馏过程汽液传质系数的测定

提出了在三相流态化板式塔中进行催化精馏的设想，将球形强酸性离子交换树脂催化剂置于单板装置的筛板上，进行了甲缩醛合成流化催化精馏试验，测定了汽液传质系数，考察了催化剂浓度、操作汽、液速度对传质系数的影响     

传质系数与浓度的关系

在含 6块塔板的板式塔中选择 2个非理想性较大的二元物系进行全回流蒸馏传质实验 ,同时从描述多组分扩散过程的普遍化方程———Maxwell-Stefan(MS)方程出发建立一个求算传质系数的数学模型 .数据处理和计算的结果表明 ,传质系数不仅与该塔板的浓度有关 ,还与相邻塔板的浓度有关 .对于非理想程度大的醇水物系 ,在不同浓度下的传质系数最大值与最小值相差可达约 1个数量级 .因此 ,对于非理想物系 ,在设计计算中将传质系数当作常数的处理将会产生较大误差 .     

DIFFUSION AND MASS TRANSFER IN MICELLAR SYSTEMS

Research on diffusion and mass transfer in micellar systems is reviewed. Models for interfacial transport at liquid/liquid interfaces, solubilization at solid/liquid and at liquid/liquid interfaces, and for detergency are discussed and similarities between these phenomena are elucidated. The literature on diffusion in micellar systems is discussed, especially in the region of the critical micelle concentration where previous investigators have presented results in disagreement with each other. Finally, the mechanism of micellar transport through membranes is also reviewed.     

反渗透过程的浓度极化及其传质系数测定

The relationship between osmotic pressure difference across the membrane and mass transfer coefficient is developed in this paper. On the basis of this relationship, a method for measuring mass transfer coefficient by using experimental data on reverse osmosis is established. Pitzer's equations are used to calculate osmotic pressure differences in order to assure accuracy of results. Under the conditions of constant operating pressure and bulk flow, mass transfer coefficient is scarcely affected by membrane structure, but decreases slightly with increasing feed concentration. The solute concentration in the polarization layer is calculated by using the measured values of mass transfer coefficient. Polarization layer concentration increases with augmentation in bulk concentration. However, their difference increases with increasing bulk concentration until a maximum difference is reached, and then decreases. Mass transfer coefficient increases with higher velocity of bulk flow. If mass transfer coefficient is so large that the ratio(PwΔπσ/k)becomes very small, polarization could be neglected.     

INFLUENCE OF LIQUID PROPERTIES ON THE DETERMINATION OF THE VOLUMETRIC MASS TRANSFER COEFFICIENT WITH THE HYDRAZINE METHOD

The oxidation of hydrazine in aqueous solution by atmospheric oxygen in presence of a homogeneous catalyst (copper tetrasulphophthalocyanine) is well suited for the determination of volumetric mass transfer coefficients. In contrast to other chemical methods the hydrazine oxidation permits to vary coalescence behaviour of the liquid phase by adding electrolytes or organic compounds, because without these solutes the reaction liquid does not inhibit bubble coalescence. With appropriate high molecular additives the hydrazine method can also be used for mass transfer measurements in liquids of high viscosity. Compared to the dynamic method the hydrazine method as a steady state method is far less influenced by systematic errors originating from the evaluation model. For this reason the application of the hydrazine method for testing semi-industrial and industrial gas-liquid contacting devices should be especially attractive.     

多管环流反应器的流动和传质特性

根据动量平衡原理建立了多管气升式环流反应器 (MALR)中液体速度的理论关系式 ,给出了流动阻力系数的计算方法 ;以Higbie的渗透理论为基础提出了计算液体表面微元在相界面暴露时间的方法 ,并建立了预测体积传质系数的模型方程 .测定了空气 -水体系中MALR的体积传质系数和循环液速随两个上升管表观气速的变化规律 ,并分别将体积传质系数、循环液速的预测值与实测值进行了比较     

AN APPLICATION OF SIMULTANEOUS HEAT AND MASS TRANSFER IN A CYLINDER USING THE FINITE-DIFFERENCE METHOD

ABSTRACT

A study of simultaneous heat and mass transfer during drying an infinite cylinder shape material (twigs of ilex paraguayenais saint hilaire) was carried out. The finite-difference method was used to solve the drying model and a simultaneous heat and mass balance in each node was made. Models with different assumptions were tested and the external mass transfer coefficient was used as a parameter to fit the model to experimental data. The thickness of the node and the time step were selected considering the system stability.

Drying temperature, twig diameter and air velocity were selected as study variables. The models results were in good agreement with experimental measurements giving mass coefficient values between 1.97 10^?4and 9.55 10^?4 Kg/m² s.     

三相外环流反应器的液相返混特性和气液传质特性

主要研究了气速与固相对三相外环流反应器液相返混特性和气液传质特性的影响规律,并用“组合模型”分析了反应器各局部区域的返混情况。实验结果表明:液相返混主要由循环返混所致,约占95%以上;固相的存在对液相返混特性和气液传质特性均有显著的影响。研究结果对开发这类反应器具有重要意义。     

ON THE METHODS FOR THE DETERMINATION OF THE OXYGEN TRANSFER COEFFICIENT IN MECHANICALLY AGITATED VESSELS

This paper reports on the determination of the overall oxygen transfer coefficient in mechanically agitated vessels. Many variants of the sulfite oxidation method are compared with the dynamic method. A new variant of the sulfite oxidation method, called the reaction time method, is proposed. Overall oxygen mass transfer coefficients were obtained with two probes having significantly different time constants and for various agitation levels. The advantages and disadvantages of the main methods used for the determination of the oxygen transfer coefficient are reviewed and discussed.     

关于活性炭吸附容积传质系数求解公式的探讨

本文从活性炭表现液膜内的物质传递规律出发,通过适当的假定及变量推导出表征活性炭吸附性能的容积传质系数求解公式。得到的容积传质数闰是ｋｇ／ｓ．ｍ＾３＝ｇ／ｓ．ｄｍ＾３。利用所求得的数据,在传质单元高度及吸附带宽度计算中得到恰当的数量级,为容积传质系数的确定提供新的途径,本文作者通过对厌氧     

LIQUID-PHASE MASS TRANSFER COEFFICIENT IN SLURRY BUBBLE COLUMN REACTORS: THEORY AND EXPERIMENTAL DATA IN SIMULATED FERMENTATION MEDIA

Mass transfer in a slurry bubble column reactor was examined. A theoretical correlation for liquid-phase mass transfer coefficient was developed using a combination of Higbie's penetration theory and the Einstein-Li periodic viscous sublayer model. The proposed correlation predicts that the liquid-phase mass transfer coefficient decreases with an increase of the yield stress of slurries. The measurement of mass transfer rates was conducted in a 40-L bubble column reactor. The slurries containing low-density particles were simulated by aqueous carboxypolmethylene solutions. Satisfactory agreement was found between the proposed correlation and the experimental data.     

A MODEL FOR THE MASS TRANSFER COEFFICIENT IN ROTATING PACKED BED

Abstract

Based on the locus of ink on the well-rotating disc, a model for the mean residence time of liquid in a rotating packed bed, t = ?′ ε (ctg(α₂/2) ? ctg (α₁/2))ωu), is proposed. Model predictions agreed with the reported data with relative error within ±15%. A modified surface renewal model based on Danckwerts, is used. For evaluation of the mass transfer coefficient, prediction of surface renewal frequency 5 is assumed as S =?ω(?is a model parameter), and effective contact time t is determined by the residence time model. Model predictions for k_L agreed well with the experimental data with relative error within ±14%     

氢气和一氧化碳在混二甲苯中的传质系数

在１Ｌ表面进气式高压机械搅拌釜中,采用气体间歇吸收技术,在不同的温度,气体压力下研究了Ｈ２和ＣＯ在混二 的体积传质系数,结果表明,Ｈ２和Ｃ类混二甲苯中的体积传质系数均随温度的升高而升高,随压力增加而增加,而且在桢的温度和压力下,ＣＯ在混二甲苯中的体积传质系数大于Ｈ２的体积传质系数,但数量级是相同的,同时随着搅拌速率的升高,体积传质系数也在增加。     

氢气在松节油中高压平衡溶解度和体积传质系数

引　言松节油的主要组分是α 和 β 蒎烯 ,含量约91%左右[1] .蒎烯在温度 35 3～ 4 33K、压力 2 0～7 0MPa下 ,经催化加氢制得蒎烷 .蒎烷是一种具有温和松针样气息的透明状液体 ,有重要的工业用途[2 ] .蒎烷经氧化、还原及裂解等反应可制备芳樟醇 ,芳樟醇是重要的香料 ,同时也     

DETERMINATION OF MASS DIFFUSIVITY COEFFICIENT OF SWEET POTATO

Abstract

Using Luikov's heat and mass transfer equations and a finite element formulation, the drying process of an anisotropic biological product (sweet potato) was investigated. The model was used to determine the coefficients of heat and mass transfer, the mass diffusivity normal and parallel to the fibers of sweet potato samples. These parameters were estimated by minimizing the deviation of experimental data and numerical predictions.

Laboratory experiments with three different configurations were conducted to measure the temperature and moisture content of sweet potato samples during drying. Numerical simulation showed good agreement with the measured values.     

高压搅拌釜中H_2、CO在不同液体介质中的溶解度和体积传质系数的研究

使用高压搅拌釜，应用气体间歇吸收技术，在温度３７３～５７３Ｋ、压力１．０～４．０ＭＰａ，转速８００ｒ／ｍｉｎ的实验条件下，测定了Ｈ_２、ＣＯ在液体石蜡，正二十八烷烃和ＦＴ３００蜡中的溶解度和体积传质系数。实验结果表明Ｈ_２、ＣＯ在３种液体介质中的溶解度和体积传质系数均随温度和压力的升高而增加，随液体介质分子量增加而减少。同时获得了溶解度随温度变化的关联式和气体在液体中的溶解热数据。     

盘式连续干燥器的传质传热模型

建立了盘式连续干燥器内加热盘面物料的传质模型,给出了干燥器内料环高度、盘面积料量及干燥时间的计算方法.应用颗粒传热理论和扩散理论,导出了每道料环的传热计算公式,由该迭代公式可逐步计算出每道料环的出料温度、出料湿含量及干燥速率.扩散理论中的惟一经验参数——搅拌参数N_mix,在本模型中可由不同进料工况下的多组实验数据加以确定.最后给出了应用该模型进行计算的实例,结果表明,理论计算值与实测值吻合较好,误差一般在20%以内.