Mathematical programming model for heat exchanger design through optimization of partial objectives

Mathematical programming can be used for the optimal design of shell-and-tube heat exchangers (STHEs). This paper proposes a mixed integer non-linear programming (MINLP) model for the design of STHEs, following rigorously the standards of the Tubular Exchanger Manufacturers Association (TEMA). Bell–Delaware Method is used for the shell-side calculations. This approach produces a large and non-convex model that cannot be solved to global optimality with the current state of the art solvers. Notwithstanding, it is proposed to perform a sequential optimization approach of partial objective targets through the division of the problem into sets of related equations that are easier to solve. For each one of these problems a heuristic objective function is selected based on the physical behavior of the problem. The global optimal solution of the original problem cannot be ensured even in the case in which each of the sub-problems is solved to global optimality, but at least a very good solution is always guaranteed. Three cases extracted from the literature were studied. The results showed that in all cases the values obtained using the proposed MINLP model containing multiple objective functions improved the values presented in the literature.

Performance Assessment of a Polymer Electrolyte Membrane Electrochemical Reactor under Alkaline Conditions – A Case Study with the Electrooxidation of Alcohols

A novel polymer electrolyte membrane electrochemical reactor (PEMER) configuration has been employed for the direct electrooxidation of propargyl alcohol (PGA), a model primary alcohol, towards its carboxylic acid derivatives in alkaline medium. The PEMER configuration comprised of an anode and cathode based on nanoparticulate Ni and Pt electrocatalysts, respectively, supported on carbonaceous substrates. The electrooxidation of PGA was performed in 1.0 M NaOH, where a cathode based on a gas diffusion electrode was manufactured for the reduction of oxygen in alkaline conditions. The performance of a novel alkaline anion-exchange membrane based on Chitosan (CS) and Poly(vinyl) alcohol (PVA) in a 50:50 composition ratio doped with a 5 wt.% of poly (4-vinylpyridine) organic ionomer cross-linked, methyl chloride quaternary salt resin (4VP) was assessed as solid polymer electrolyte. The influence of 4VP anionic ionomer loading of 7, 12 and 20 wt.% incorporated into the electrocatalytic layers was examined by SEM and cyclic voltammetry (CV) upon the optimisation of the electroactive area, the mechanical stability and cohesion of the catalytic ink onto the carbonaceous substrate for both electrodes. The performance of the 4VP/CS:PVA membrane was compared with the commercial alkaline anion-exchange membrane FAA −a membrane generally used in direct alcohol alkaline fuel cells- in terms of polarisation plots in alkaline conditions. Furthermore, preparative electrolyses of the electrooxidation of PGA was performed under alkaline conditions of 1 M NaOH at constant current density of 20 mA cm−2 using a PEMER configuration to provide proof of the principle of the feasibility of the electrooxidation of other alcohols in alkaline media. PGA conversion to Z isomers of 3-(2-propynoxy)-2-propenoic acid (Z-PPA) was circa 0.77, with average current efficiency of 0.32. Alkaline stability of the membranes within the PEMER configuration was finally evaluated after the electrooxidation of PGA.

Applying scanning electron microscopy for the ultrastructural and clinical analysis of periprosthetic capsules in implant-based breast reconstruction

La reconstruction en deux étapes par expanseur et implant est la technique la plus répandue pour la reconstruction mammmaire post mastectomie. La formation d’une capsule périprothétique est une réponse physiologique universelle à tout corps étranger présent dans le corps humain; par contre, la formation d’une capsule pathologique mène souvent à des complications et par conséquent à des résultats esthétiques sous-optimaux. Le microscope électronique à balayage (MEB) est un outil puissant qui permet d’effectuer une évaluation sans pareille de la topographie ultrastructurelle de spécimens. Le premier objectif de cette thèse est de comparer le MEB conventionnel (Hi-Vac) à une technologie plus récente, soit le MEB environnemental (ESEM), afin de déterminer si cette dernière mène à une évaluation supérieure des tissus capsulaires du sein. Le deuxième objectif est d‘appliquer la modalité de MEB supérieure et d’étudier les modifications ultrastructurelles des capsules périprothétiques chez les femmes subissant différents protocoles d’expansion de tissus dans le contexte de reconstruction mammaire prothétique. Deux études prospectives ont été réalisées afin de répondre à nos objectifs de recherche. Dix patientes ont été incluses dans la première, et 48 dans la seconde. La modalité Hi-Vac s’est avérée supérieure pour l’analyse compréhensive de tissus capsulaires mammaires. En employant le mode Hi-Vac dans notre protocole de recherche établi, un relief 3-D plus prononcé à été observé autour des expanseurs BIOCELL® dans le groupe d’approche d’intervention retardée (6 semaines). Des changements significatifs n’ont pas été observés au niveau des capsules SILTEX® dans les groupes d’approche d’intervention précoce (2 semaines) ni retardée.

The Challenges of the EU Banking Union - will it succeed in dealing with the next financial crisis? Bruges European Economic Policy Briefings 36/2015

The EU Banking Union combines micro- and macro-prudential regulation. It aims at breaking the “doom loop” between banks and sovereign debt, promoting financial stability and mitigating the next financial shock to the real EU economy, at the lowest possible cost to the financial institutions and to the taxpayers. Success, or failure, is determined by how the banking union copes with the challenges to its two main pillars, the Single Supervisory Mechanism (SSM) and the Single Resolution Mechanism (SRM). Under the SSM, in its new supervisory role, the ECB may be subject to conflicts between the objectives of price and financial stability, and the single-supervisor role may be sub-optimal. Two regulators might have been preferable and more focus on ECB accountability will now be required. The shock-absorbing Single Resolution Fund (SRF), which is part of the SRM, may not have the capacity to deal with a crisis of the size of the one of 2008. Especially as the nature and severity of a future financial crisis cannot be forecasted. The design of the banking union is not the result of theoretical studies, but a political compromise to deal with an acute crisis. The theoretical studies that are included in this paper are not supportive of the banking union in its current form. Nevertheless, there is a good chance that the EU Banking Union may succeed, as ECB supervision of the 123 systemically important banks should contain potential demands on the SRM. In the event of a crisis that is too severe for the banking union to absorb with its current capability, the crucial assumption is that there is political will to rapidly provide new resources. The same applies, if a major financial crisis develops before the banking union is fully operational.

The Challenges of the EU Banking Union - will it succeed in dealing with the next financial crisis? Bruges European Economic Policy (BEEP) Briefings 36/2015

The EU Banking Union combines micro- and macro-prudential regulation. It aims at breaking the “doom loop” between banks and sovereign debt, promoting financial stability and mitigating the next financial shock to the real EU economy, at the lowest possible cost to the financial institutions and to the taxpayers. Success, or failure, is determined by how the banking union copes with the challenges to its two main pillars, the Single Supervisory Mechanism (SSM) and the Single Resolution Mechanism (SRM). Under the SSM, in its new supervisory role, the ECB may be subject to conflicts between the objectives of price and financial stability, and the single-supervisor role may be sub-optimal. Two regulators might have been preferable and more focus on ECB accountability will now be required. The shock-absorbing Single Resolution Fund (SRF), which is part of the SRM, may not have the capacity to deal with a crisis of the size of the one of 2008. Especially as the nature and severity of a future financial crisis cannot be forecasted. The design of the banking union is not the result of theoretical studies, but a political compromise to deal with an acute crisis. The theoretical studies that are included in this paper are not supportive of the banking union in its current form. Nevertheless, there is a good chance that the EU Banking Union may succeed, as ECB supervision of the 123 systemically important banks should contain potential demands on the SRM. In the event of a crisis that is too severe for the banking union to absorb with its current capability, the crucial assumption is that there is political will to rapidly provide new resources. The same applies, if a major financial crisis develops before the banking union is fully operational.