Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Flexibility Analysis in the Case of Incomplete Information about Uncertain Parameters

In recent years the flexibility analysis of chemical processes has attracted a significant amount of attention among researchers in the chemical engineering community. Flexibility analysis permits to identify/create chemical processes, which can satisfy all design specifications in spite of process and parametric uncertainty (from several sources) at the operation stage. All formulations of the flexibility problem are based on the supposition that during the operation stage there is enough experimental data from which exact values of the uncertain parameters can be obtained. However, in practice this assumption is often not met. Here in this paper, we consider the case when the uncertain parameters can be divided into two sets, namely a set that can be estimated with sufficient accuracy (at the operation stage) and a set that cannot be. Based on this view, we have developed extensions of the feasibility test and two-stage optimization problem to handle the two sets of uncertainty. We have developed the relevant split and bound algorithm for solving the new two-step optimization problem.     

Linear models for prediction of ibuprofen crystal morphology based on hydrogen bonding propensities

Solvents have a significant impact on the final crystal form of organic solids during solution crystallization. The use of polarity scales such as Hildebrand solubility parameter and dielectric constant for solvent selection often proves too generalized and do not provide enough insights into the solvent–solute intermolecular interactions directly affecting crystal growth and morphology. This paper addresses the challenging task of selecting an appropriate single component solvent property index that most accurately and sufficiently characterizes crystal morphology. Cooling crystallization experiments were carried out in a wide range of solvents using ibuprofen as a model pharmaceutical compound. Subsequently, optical microscope images were used for quantitative characterization of morphology. Linear models that correlate ibuprofen crystal morphology with pure solvent properties were developed. Our results show that, in general, there is a negative linear correlation between crystal aspect ratio (morphology) and a given solvent index. Some correlations revealed significant deviations which were explained with the help of infrared spectroscopic measurements. The “acceptance number” was identified as an index that significantly captures the ibuprofen–solvent hydrogen bonding intermolecular interactions. Predictions, using model based on acceptance number, were found to compare very well with experimentally determined aspect ratio data from the open literature. Finally, based on insights gained from this work, a flowchart which serves as a useful solvent selection guideline for crystallization of ibuprofen is proposed.     

A Kinetic Study of the Dehydration of VOPO4.2H2O by Thermal Methods

The dehydration of VOPO₄.2H₂O hasbeen studied by thermogravimetric analysis (TGA),differential thermal analysis (DTA) and differentialscanning calorimetry (DSC). From the shift of the DTA,DTG, and DSC peaks, activation energies of thedehydration processes have been calculated based onKissinger's method. The most suitable kinetic modelsfor two-step dehydration have been found.