MECHANISMS OF DRYING OF SKIN-FORMING MATERIALS.III. DROPLETS OF NATURAL PRODUCTS.

ABSTRACT

Drying studies were carried out on single droplets suspended from a rotating nozzle in a horizontal wind tunnel. Droplets were of solution of a third type of skin-forming material, namely the natural products skim milk or fructose. Droplet weight and temperature were measured during the drying process. Dried crusts were recovered and examined by Scanning Electron Microscopy.

With this type of material a skin first forms at any drying condition on the surface of the droplet at a cerlain stage of drying. A crust subsequently forms beneath the skin. The final dried panicle retains the structure and properties of the original powder, unless the material is dried at very high temperatures. e.g. >300 °C. which result in burning.

An increase in air temperature resulted in the formation of a smoother skin offering a higher resistance to vapour diffusion. At temperatures over 100 °C droplets exhibited puffing or ballooning phenomena; i.e. they inflated and deflated many times before forming the final dried particles.     

ONE-DIMENSIONAL SIMULATION OF THE BREAKUP OF CAPILLARY JETS OF CONDUCTING LIQUIDS. APPLICATION TO E.H.D. SPRAYING

Nonlinear breakup of charged liquid jets is numerically analyzed in this work in the limit of a very small electrical Strouhal number T_e/T_b≪1 (i.e. negligible charge relaxation effects, applicable to highly conducting liquids), where T_e is the electric relaxation time of charges, and T_b is the breakup time in a Lagrangian framework following the liquid jet at its average axial velocity. The influence of the electrical Bond’s number and viscosity on (i) the capillary Rayleigh’s most probable breakup length, (ii) the breakup time, (iii) the volume of the satellite, and (iv) the charge of both main drop and satellite, are analyzed. The model is related to the microjet break-up phenomena in the electrospraying of liquids in steady cone-jet mode, and its range of applicability to those particular problems discussed. Previous experimental results [Mutoh et al., 1979, Convergence and disintegration of liquid jets induced by an electrostatic field. J. Appl. Phys. 50, 3174–3179; Clopeau and Prunet-Foch, 1989, Electrostatic spraying of liquids in cone-jet mode. J. Electrostatics 22, 135–159.] support our numerical finding that the influence of the electrical Bond’s number on Rayleigh’s length is small within the usual parametrical limits of stability of a steady Taylor cone-jet at atmospheric pressure.     

美国氰胺公司和杜邦公司的腈纶生产技术

介绍了美国氰胺公司Santarosa腈纶厂的湿法生产工艺和杜邦公司Waynesboro腈纶厂及Camden腈纶厂的干法生产工艺,并将两者进行了比较。     

混烧立窑的工艺探讨

主要论述石灰机械立窑从不良运作到平稳高效运行的过程，通过原材料规格选定，调控燃料配比、煅烧带位置、鼓风量等工艺参数，利用尾气成分、顶压顶温的分析实施反馈控制，达到司窑目的。实践证明，相比于国外先进石灰窑，混料式机械立窑具有造价低、经济性好等优点。     

ANIONIC POLYMERIZATION OF LACTAMS IN MICRODISPERSION. I. KINETIC ASPECTS OF THE PROCESS OF CAPROLACTAM POLYMERIZATION

Kinetics of the anionic polymerization of caprolactam (CL) in microdispersion was investigated at temperatures between 90 and 130°C and at stirring rates between 500 and 2000 rpm, respectively. For the investigated range of temperature data analysis showed pseudo-first order kinetics with respect to the monomer concentration. The rate constants are strongly influenced by temperature, increasing with the increase in temperature. For the associated activation energy, a value of 22.51 kJ/mol was obtained. The reaction order is also influenced by the hydrodynamic regime. It seems that below a threshold value of Reynolds Number, the rate of the reaction is independent of the concentration of CL, following pseudo-zero-order kinetics, which is replaced by first-order kinetics above this threshold value of N _Re. However, in the second region of N _Re, the values of rate constant are almost independent of N _Re.     

DRYING OF CARROTS. I. DRYING MODELS.

Three models of different complexity are proposed to describe the falling rate period of the carrot drying process with shrinkage. A moving or fixed boundary problem as well as a constant or local moisture and temperature dependent effective diffusivity are considered. The moving boundary problem is solved by an explicit finite difference method. Heat transfer coefficient and effective diffusivity identification were carried out. The results of the heat transfer coefficient show a good agreement with other sources. Using experimental data and the models. describing the heat and mass transfer three different expressions for the effective diffusivity are established. Two of them are only temperature dependent considering or not particle shrinkage. The third one takes into account temperature and local moisture as well as shrinkage.

Drying of foods is a complicated process involving simultaneous coupled heat and mass transfer phenomena which occur inside the material being dried (Chiang and Petersen, 1987). Several models are found in the literature, representing mass and energy transfer which take place during food drying (King, 1968; Sokhansanj and Gustafson, 1980). Usually, approximate solutions are obtained with these     

焦锑酸钠生产工艺及研究进展

论述了焦锑酸钠的各种生产工艺及研究进展，讨论了各种工艺的优缺点。