Numerical validation of a population balance model describing cement paste rheology

Rheology control is essential during the period in which cement and concrete pastes are encountered in the fresh state, due to the fact that it directly affects workability, initial placement and the structural performance of the hardened material. Optimizations of clinker formulations and reductions in cement-to-water ratios induced by economic and environmental considerations have a significant effect in rheology, which invokes the need for mechanistic models capable of describing the effect of multiple relevant phenomena on the observed paste flow. In this work, the population balance framework was implemented to develop a model able to relate the transient microstructural evolution of cement pastes under typical experimental conditions with its macroscopic rheological responses. Numerical details and performance are assessed and discussed. It was found that the model is capable of reproducing experimentally observed flow curves by using measured cluster size distribution information. It is also able to predict the complex rheological characteristics typically found in cement pastes. Furthermore, a spatially resolved scheme was proposed to investigate the nature of flow inside a parallel-plates rheometer geometry with the objective of assessing the ability of the model of qualitatively predicting experimentally observed behavior and to gain insight into the effect of possible secondary flows

Beyond Russia’s ‘Versailles syndrome’. Egmont Security Policy Brief No. 58, November 2014

Russia alleges that at the end of the Cold War it underwent a soft version of a Versailles Treaty, pushing it into the periphery of global politics and cutting it out of European decision-making. The crisis in Ukraine is about the survival of Putin’s regime and the dismantling of the post-Cold War settlement. We should not accept the fallacious narrative of victimhood propagated by the Kremlin’s Versailles syndrome. Even so, it is time to explore practical ways of coexisting with Russia. The Helsinki Process and the disarmament and arms control agreements of the Cold War could serve as a model for a mutually acceptable security architecture

A compartmental model of anaerobic digester for improved description of the process performance

Understanding anaerobic digester (AD) performance relates to the complex interplay between hydrodynamics and kinetics. The latter is not straightforward and has been tackled by means of models. However, the computational burden to run such a model in a dynamic way is still too large. Here, a simplified compartmental model (CM) is derived from a CFD model (hydrodynamics). Compatibility of the CM and CFD model was tested by comparing the RTD curve of a virtual pulse tracer test. Subsequently, the CM was integrated with ADM1 in each compartment and the steady state performance was compared with that of a CSTR model with ADM1

A dynamic model for reverse osmosis as part of decision support tool for water fit-for-use

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