F.L. Moreno

Multi-plate freeze concentration: Recovery of solutes occluded in the ice and determination of thawing time

The retention of solutes in the ice formed in a falling-film freeze concentrator (multi-plate freeze-concentrator) was analysed. Solutions of fructose, glucose and sucrose and a simulated juice with initial concentrations of 5, 10, 15 and 20 °Brix were freeze concentrated. The ice produced in the four steps of the process retains solutes at levels of 1.0–8.8 °Brix (expressed as solute mass fraction in the ice). The recovery of these solutes during thawing can increase overall system efficiency. All thawing steps were carried out dividing the sample in 10 fractions at 20 ℃. The first thawed fractions showed solute concentrations that were 1.9–3.3 times higher than the mean solute mass fraction in the ice, while the last fractions of ice showed very low levels of retained solutes, less than 0.2 times the mean solute mass fraction in the ice. It was found that fractionated thawing can recover most of the solute content in the ice. The procedure presented in the present study allows the determination of the solute concentration achieved in the various thawing fractions and predicts the thawing time required for a given form factor, melting temperature and initial solute mass fraction in the ice.

Effect of process parameters on progressive freeze concentration of sucrose solutions

The progressive freeze concentration of sucrose solutions was tested. The effect of the initial concentration of the solution (C0), the temperature of the refrigerant (T), and the stirring speed (ω) on the final concentration of the solution (Cf) was determined. The effects were significant on the freeze concentration, for both individual and combined effects. The maximum concentration achieved in the progressive freeze concentration was 53°Brix, when the initial concentration was 35°Brix, at a speed of 800 rpm and a temperature of refrigerant of −20°C. The best values of the concentration index (CI) are obtained at low concentrations, high ω, and low temperature. The average distribution coefficient increased with C0. The average yield parameter (WY) at different initial concentrations is around 0.6 kg ice · kg sol−1 · h−1.

Mathematical simulation parameters for drying of cassava starch pellets

Based on experimental tests, it was obtained the equations for drying, equilibrium moisture content, latent heat of vaporization of water contained in the product and the equation of specific heat of cassava starch pellets, essential parameters for realizing modeling and mathematical simulation of mechanical drying of cassava starch for a new technique proposed, consisting of preformed by pelleting and subsequent artificial drying of starch pellets. Drying tests were conducted in an experimental chamber by varying the air temperature, relative humidity, air velocity and product load. The specific heat of starch was determined by differential scanning calorimetry. The generated equations were validated through regression analysis, finding an appropriate correlation of the data, which indicates that by using these equations, can accurately model and simulate the drying process of cassava starch pellets.