Production of large crystals by continuous ripening in a stirrer tank

\u3cp\u3eA new bulk crystallisation process is described in which the supersaturation in the crystalliser is maintained by feeding very small subcritical crystals. Supercritical crystals that are present in the crystalliser grow at the expense of the dissolving subcritical crystals. The process is described by means of a mathematical model. With this model the influences of crystal concentration, production rate, and size of the feed crystals upon the average product crystal size are calculated. The model predicts an increase of the mean size of the product crystals with a decrease of feed crystal size for small feed crystals. The size of the product crystals also increases with an increase in crystal concentration in the crystalliser. The process has been studied experimentally for the growth of ice crystals from aqueous sucrose solutions. The theoretically predicted effects of crystal concentration and feed crystal size on product crystal size are confirmed by the experiments.\u3c/p\u3

Numerical solution of diffusion equations with strongly variable diffusion coefficients. Calculation of flavor loss in drying food liquids

The loss of volatile org. components in drying food liqs. is to some extent governed by the simultaneous flux of water and is stronly influenced by the different ways in which the diffusion coeffs. of the volatile components and of water depend on the water concn. The strong water concn. dependence of the diffusion coeffs. makes an anal. soln. of the diffusion equations describing the mass transfer in the drying product impossible. However, if the drying system does not have too complex a geometry the diffusion equations can be solved numerically. Because of the very steep concn. gradient near the evapg. surface, the implicit (as well as explicit) standard numerical calcn. procedures require a lot of computer time. A new numerical method is discussed in this paper. With this method the drying rate curve and volatile component retention were calcd. for a slab composed of water and maltodextrin to which acetone was added as a model org. volatile. The calcd. retentions of water and acetone fit the exptl. data within the accuracy of the observations. [on SciFinder (R)

Short-cut calculation for non-isothermal drying of shrinking and non-shrinking particles and of hollow spheres containing an expanding central gas core

\u3cp\u3eA procedure is presented for the calculation of non-isothermal drying rates of shrinking and non-shrinking particles of different geometries including rectangular bodies, cylinders, spheres and hollow cylinders and spheres. The implication on drying rate of changes in volume of the gas bubble in hollow spheres is taken into account. Starting point are the experimentally observed isothermal drying rates versus fraction water removed of a slab of the material of interest at two temperature levels. With the aid of a short cut calculation method based on the exact numerical computer solutions of the diffusion equation valid for concentration dependent diffusion coefficients and complex boundary conditions the information obtained from the isothermal slab drying experiments is transformed to other geometries and non-isothermal conditions.\u3c/p\u3

Nucleation and growth kinetics for the crystallization of ice from dextrose solutions in a continuous stirred tank crystallizer with supercooled feed

\u3cp\u3eThe crystallization of ice in aqueous dextrose solutions is studied in an adiabatic continuous stirred tank crystallizer with a supercooled feed stream. The effective diameter of the ice crystals was determined for various values of mean crystal residence time, feed supercooling, magma density, stirring rate, and dextrose concentration. For all process conditions the supercooling was measured at 9‐12 different locations in the crystallizer. These local supercoolings were averaged algebraically to yield the bulksupercooling. From the experimental results growth and nucleation rates have been calculated. By comparing the experimental growth rates to growth rates calculated by means of a mathematical model kinetics for the inbuilding of water molecules into the ice lattice have been determined. The growth rate appears to be directly proportional to the interface supercooling. The rate constant decreases exponentially with increasing weight percentage of dextrose in the solution. The nucleation rate was found to be directly proportional to total crystal surface per unit volume of suspension and proportional to the bulksupercooling to the power 2.1. Nucleation is believed to occur by breakage of dendrites from the surface of parent crystals.\u3c/p\u3

Aroma recovery and retention in concentration and drying of foods

\u3cp\u3eIt is primarily food aroma that distinguishes the flavor of one food from that of another, and aroma quality often determines the acceptability of a food. When water is removed from a food, the loss or retention of the food aroma is one of the major considerations in the design of the food processing operation. This chapter reviews the research work that examines the behavior of food aroma when water is removed by the various techniques used in food processing. Water is removed from foods to provide microbiological stability, and to reduce storage and transportation costs. This chapter distinguishes between concentration and dehydration processes; the former includes those processes that increase solids content to about 60 % and the latter those that reduce water content to less than 10%. This chapter discusses the various aroma recovery processes. It then takes a look at the concentration processes where aromas are retained in the concentrate and drying processes where aroma is retained. This chapter ends with a discussion of the economics of concentration and drying processes.\u3c/p\u3