Taking into account the close similarity between pervaporation and vapour permeation techniques, a method for employing pervaporation flux data in the modelling of vapour permeation modules is proposed. It is based on the use of fugacity gradients across the membrane, instead of concentration ones, as the driving force for mass transfer. This procedure is interesting, for instance, in the case of aroma recovery systems, for which there is much more experimental data on pervaporation available in the literature than on vapour permeation. In order to illustrate the application of this method, pervaporation experiments for an isotropic PDMS membrane were conducted with aqueous solutions of ethyl acetate (113-2474 mg/L), and the results obtained were used to enable simulation of different vapour permeation hollow-fibre modules for recovering ethyl acetate from diluted air streams.

Aiming at simulating air-heating systems, two algorithms were developed for the calculation of finned elliptical-tube heat exchangers, whose basic difference lies in the kind of hot fluid employed: saturated steam or hot liquid. In both cases, a crossflow unit, in which the cold fluid is mixed and always flows on the shell side, is considered. The hot fluid may exhibit multiple passes in the tubes and is assumed unmixed, except for the region between the passes. A comparison between calculated results and operating data on industrial exchangers indicated the adequacy of the algorithms developed. The codes were then introduced into the ASPEN Plus shell, enabling simulation of the steady-state operation of the whole drying-air heating system of a powdered milk plant. Moreover, a sensitivity analysis of this system was conducted for one of its operating parameters and the existence of an optimal value for this variable was clearly shown.

Experimental bubble size distributions and bubble mean diameters were obtained by means of a photographic technique for a direct-contact evaporator operating in the quasi-steady-state regime. Four gas superficial velocities and three different spargers were analysed for the air-water system. In order to assure the statistical significance of the determined size distributions, a minimum number of 450 bubbles was analysed for each experimental condition. Some runs were also conducted with an aqueous solution of sucrose to study the solute effect on bubble size distribution. For the lowest gas superficial velocity considered, at which the homogeneous bubbling regime is observed, the size distribution was log-normal and depended on the orifice diameter in the sparger. As the gas superficial velocity was increased, the size distribution progressively acquired a bimodal shape, regardless of the sparger employed. The presence of sucrose in the continuous phase led to coalescence hindrance.