Solution of population balances with growth and nucleation by high order moment-conserving method of classes

The high order method of classes, developed in our earlier work [Alopaeus, V., Laakkonen, M., Aittamaa J., 2006a. Solution of population balances with breakage and agglomeration by high order moment-conserving method of classes. Chemical Engineering Science 61, 6732-6752] for solution of population balances (PBs), is extended to problems with growth and primary nucleation. The growth problem leads to a hyperbolic partial differential equation with fundamentally different numerical characteristics than the PB with breakage and agglomeration only. However, we show that the principle of moment conservation in the numerical solution can also be applied to this advection-type problem, leading to extremely accurate numerical solutions. The method is tested for two numerical cases. The first one is mass transfer induced particle growth, and the second one is primary nucleation with constant growth (similar to the Riemann advection problem). For mass transfer induced growth, we first analyze functional form of the growth rate from mass transfer correlation viewpoint, and derive a general analytical solution for the power-law growth. The numerical results from the moment conserving method are also compared to one well established high resolution numerical method for advection problems, namely the Lax-Wendroff method with van Leer flux limiter. It was shown that the present method is far superior by predicting the distribution moments with several order of magnitudes lower numerical error. For the Riemann problem with constant growth rate, the present method predicts the shock front location exactly without any numerical diffusion.     

Newness,Tradition and Identity: Existential Content and Meaning in Architecture

At a time when novelty and aesthetic invention have become the established norm for contemporary architecture, the esteemed Finnish author and architect Juhani Pallasmaa speaks out in defence of tradition. He explains how nuance, expressive subtlety and an ambition for an experiential and existential quality in a work require a sense of historical continuum: ‘An embodiment of the essence of tradition’ as a precursor for ‘meaningful creativity’.     

Temperature optimisation of a diesel engine using exhaust gas heat recovery and thermal energy storage (diesel engine with thermal energy storage)

Modern automotive diesel engines are so energy efficient that they are heating up slowly and tend to run rather cold at subzero temperatures. The problem is especially severe in mail delivery operations where the average speed is low and the drive cycle includes plenty of idling. The problem is typically solved by adding a diesel fuelled additional engine heater which is used for the preheating of the engine during cold start and additional heating of the engine if the coolant temperature falls below a thermostat set point during the drive cycle. However, this additional heater may drastically increase the total fuel consumption and exhaust gas emissions of the vehicle. In this study the additional heater was replaced by a combination of exhaust gas heat recovery system and latent heat accumulator for thermal energy storage. The system was evaluated on a laboratory dynamometer using a simulated drive cycle and in field testing in the city of Oulu (65°N), Finland in February 2009.     

The Ehrenfeucht conjecture: a compactness claim for finitely generated free monoids

We survey recent results on the so-called Ehrenfeucht Conjecture which states: For each language L over a finite alphabet Σ there exists a finite subset F of L such that for each pair (g, h) of morphisms on Σ¹ the equation g(x)=h(x) holds for all x in L if and only if holds for all x in F.We point out that the conjecture is closely related to the theory of equations in free monoids. We also state a suprising consequence of the conjecture: If it holds (even noneffectively) for all DOL languages, then the HDOL sequence equivalence problem is decidable. Furthermore, we give examples of when the conjecture is known to hold. In particular, we establish it for all binary languages, as well as for all languages when attention is restricted to bounded delay morphisms of some fixed delay.     

Synchronizable deterministic pushdown automata and the decidability of their equivalence

Summary The notion of synchronized and synchronizable deterministic pushdown automata (DPDA's) is introduced. It is shown that the equivalence of two synchronized and even of synchronizable DPDA's can be tested. It is conjectured that every two equivalent DPDA's are synchronizable. It is also shown that the equivalence of two deterministic pushdown transducers whose underlying DPDA's are synchronized can be tested.This work was supported by the Natural Sciences and Engineering Research Council of Canada under Grant A-7403.This work has been done during the second author's visit at the University of Waterloo     

High temperature erosion of Ti(Mo)C–Ni cermets

The resistance of Ti(Mo)C–Ni cermets of different binder content to solid particle erosion was evaluated at 25, 350 and 650 °C. The elevated temperature erosion of cermets containing 40, 50, 60, 70 and 80 wt.% of titanium carbides and produced from the powder of initially different ratios of Ni to Mo were tested with the help of specially designed centrifugal particle accelerator using silica as the abrasive. Erosion rate was related to both microstructure developed during sintering and materials removal mechanisms operating at the test conditions (impact angle of particles jet was 30° and 90° and velocity was 50 ms⁻¹). The erosion rate decreases with the increase of TiC and Mo contents in the composite. At 650 °C the process of tribo-oxidation affected the material performance to a great extent. The morphology of the worn surface was analyzed with SEM to determine the erosion mechanisms.     

The problem of verification with reference to the Girkmann problem

This paper is concerned with the problem of verification of the numerical accuracy of computed information with particular reference to a model problem in solid mechanics. The basic concepts and procedures are outlined and illustrated by examples.     

Modelling of a side reactor configuration combining reaction and distillation

A new software tool to simulate and optimise processes that combine distillation column with a reactor sequence has been developed. This kind of combination is particularly interesting when new intensified and integrated processes are developed. The unit block contains both the distillation column model and the models for the coupled reactors. The model equations are solved simultaneously in one block and not sequentially as it is done when the reactor/distillation systems are solved by present flowsheet programs. This software module has been implemented into a flowsheet simulator environment that contains all required physical and chemical data banks and enables large-scale process optimisation. The applicability of the new module is demonstrated by solving two presently interesting processes: production of MTBE and isooctene. The model has shown good convergence properties.     

Perspectives on the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during municipal solid waste (MSW) incineration and other combustion processes

The pathways by which polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are formed and the interactions between their aromatic precursors, in particular chlorophenols (ClPhs), and transition metal catalysts are discussed. A literature survey and data from pilot-scale combustion experiments allow conclusions to be drawn on the relations between ClPhs and PCDD/Fs in municipal waste incineration and other combustion processes. The results suggest that the ClPh pathway is among the most important for the formation of PCDD/Fs.