A. Baars

High pressure rheology and the impact on process homogeneity

The impact of different viscous substances on homogeneous thermal treatment during high pressure processes is exemplified for a cylinder piston system. Therefore, the relevant equations of thermofluid dynamics have been examined and conditions for homogeneous thermal processing have been set up. Furthermore, the analysis of an n-order inactivation kinetic delivers criteria for insensitivity of reactions to spatial temperature heterogeneities. The findings have been applied to a short time high pressure process and compared with results of numerical simulations. Good agreement could be achieved.

Towards system theory based adaptive strategies for high pressure bioprocesses

High pressure has been shown to offer unique possibilities for designing novel bioprocesses and generating new structures. However, high pressure processes have to be considered also as instantaneous but not homogeneous. As a consequence of this, thermofluiddynamical processes influence molecular and cellular mechanisms and kinetics. Thus, the urgent requirement for creating an adaptive process management, missing in the literature, is obvious. In this paper, a first attempt towards the development of adaptive process strategies is presented. It is shown that adaptive strategies have to include considerations regarding the interactions of all the components of the high-pressure system, variances due to the biological origin of the substances, and, particularly, methods for managing different data and knowledge sources. Furthermore, suggestions for the suitable design of adaptive process management strategies are presented and discussed. By means of a few examples it is elucidated that hybrid methods can contribute significantly in achieving the adaptability required. This paper is conceived as a brief composition to a plenary lecture presented at the XLIV EHPRG Meeting 2006 in Prague.

Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions

A visualization of pressure-shift freezing of 0.7 w/w sucrose solutions was carried out at three temperatures 268, 253 and 235 K by release of pressure from 200 MPa to atmospheric value. Furthermore, pressure-shift freezing at 268 K and additionally pressure-shift thawing was carried out for a solution of 0.2 sucrose mass fraction. The solid phase observed at 268 K in the case of solution with 0.2 w/w sucrose fraction was ice I. The phase changes of 0.7 w/w sucrose solutions at 253 K and 235 K resulted in formation of spherical solids which are hypothesized to be eutectics, i.e. crystals with structure containing sucrose hydrates and water. The visual evaluation revealed differences in size and distribution of spherical crystals. The solids formed at 235 K were more numerous, more homogenously distributed and finally smaller than those observed at 253 K. It is explained by the higher supercooling of the solution in the former case, which provided higher driving force for nucleation and crystal growth.