Investigating the impact of modeling assumptions and closure models on the steady-state prediction of solar-driven methane steam reforming in a porous reactor

Publisher Copyright: © 2023 The Author(s)In this work, the effect of different modeling assumptions and closure models — frequently considered in the literature of solar thermochemical reactors and closely-related areas — is investigated. The application of different modeling assumptions and closure models may strongly affect the results accuracy and compromise a meaningful comparison across literature works. The following is herein investigated: (i) the role of upstream and downstream fluid regions to the two-phase reactor region; (ii) relevance of species and gas-phase thermal diffusion mechanisms; (iii) reaction heat accounted for in gas- or solid-phase energy balance equations; (iv) local thermal equilibrium (LTE) vs. local thermal non-equilibrium (LTNE) models; (v) model dimension (one-dimensional vs. two-dimensional axisymmetric models); (vi) local volumetric convection heat transfer correlations; and (vii) effective solid thermal conductivity correlations. The relevance of this work extends well beyond the current application (methane steam reforming in a volumetric solar reactor), since similar models and assumptions have also been widely applied for predicting the performance of volumetric solar absorbers and dry reforming solar reactors. The results show that an upstream fluid region should be considered while applying inlet first-type boundary conditions and diffusion transport in the corresponding governing equations to ensure full-conservation and simultaneously to account for developing profiles upstream the reactor inlet section. For the operating conditions considered, species diffusion and gas-phase heat conduction are particularly relevant at the reactor centerline but with a negligible integral effect. A significant difference in the reactor performance is observed while accounting for the reaction heat from surface reactions in the solid- or gas-phase energy balances — for the lowest inlet gas velocity herein considered, the thermochemical efficiency (methane conversion) is approximately equal to 70.8% (76.3%) and 77.3% (84.7%) assigning the reaction heat to the gas- and solid-phase energy balances, respectively. LTE model results are strikingly different from the results obtained with the LTNE model considering the reaction heat accounted for in the gas-phase energy balance but not significantly different from the results computed with the LTNE model with the reaction heat assigned to the solid-phase energy balance. One-dimensional reactor modeling provided with an average concentrated solar heat flux value results in a similar average performance as that given by a two-dimensional model but fails to predict the high temperatures observed at reactor centerline — for the lowest inlet gas velocity, the difference between the maximum solid temperatures predicted by one- and two-dimensional models is about 340K.publishersversionpublishe

Numerical investigation of an inertization system for a radiative coil coating oven

Funding Information: This research was funded by the European Community's Framework Programme for Research and Innovation Horizon 2020 under grant agreement no. 768692 (ECCO). This work was also supported by Fundação para a Ciência e a Tecnologia, Portugal, through IDMEC, under LAETA, project UIDB/50022/2020. Funding Information: This research was funded by the European Community’s Framework Programme for Research and Innovation Horizon 2020 under grant agreement no. 768692 (ECCO) . This work was also supported by Fundação para a Ciência e a Tecnologia, Portugal , through IDMEC, under LAETA, project UIDB/50022/2020. Publisher Copyright: © 2023 The Author(s)In this work the inertization of a radiative curing oven for coil coating is numerically investigated. Inertization chambers (IC) — comprised by a confined impinging slot jet and an exhaust slot — are applied at the curing oven openings to prevent external air from entering and toxic solvents from exiting the oven, avoiding simultaneously the contamination of the external surroundings and the development of explosive conditions within the oven. The influence of the main IC operating parameters — extracted-to-injected mass flow rate ratio (Ψ), coil plate-to-jet velocity ratio, injection Reynolds number, and oven pressure — on the safety of the sealing process is investigated considering the validated k-kl-ω transition RANS model. To guarantee safety conditions regarding the IC placed at the metal strip entrance, the corresponding range for Ψ was found to be between 0.8 and 1.6 considering oven pressures ranging from −20 to 20 Pa. For the IC placed at the metal strip exit and considering high coil velocities, safety conditions can only be observed with negative oven pressures. Overall, this procedure found a Ψ range between 0.8 and 1.2 that complies with the restrictive safety criteria for a realistic oven operation with typical coil velocities and oven pressures ranging from −20 to 10 Pa.publishersversionpublishe

Numerical simulation of galvanized rebars pullout

The usage of rebars in construction is the most common method for reinforcing plain concrete and thus bridging the tensile stresses along the concrete crack surfaces. Usually design codes for modelling the bond behaviour of rebars and concrete suggest a local bond stress – slip relationship that comprises distinct reinforcement mechanisms, such as adhesion, friction and mechanical anchorage. In this work, numerical simulations of pullout tests were performed using the finite element method framework. The interaction between rebar and concrete was modelled using cohesive elements. Distinct local bond laws were used and compared with ones proposed by the Model Code 2010. Finally an attempt was made to model the geometry of the rebar ribs in conjunction with a material damaged plasticity model for concrete

Ocular drug delivery from contact lenses: mimetizing the hydrodynamic conditions of the eye

Poster presented at the 4th Congress on Innovation in Drug Delivery Site-Specific Drug Delivery (IDD2016). Antibes-Juan-les-Pins, France, 25-28 September 2016N/

Dynamics of a hyperbolic system that applies at the onset of the oscillatory instability

A real hyperbolic system is considered that applies near the onset of the oscillatory instability in large spatial domains. The validity of that system requires that some intermediate scales (large compared with the basic wavelength of the unstable modes but small compared with the size of the system) remain inhibited; that condition is analysed in some detail. The dynamics associated with the hyperbolic system is fully analysed to conclude that it is very simple if the coefficient of the cross-nonlinearity is such that , while the system exhibits increasing complexity (including period-doubling sequences, quasiperiodic transitions, crises) as the bifurcation parameter grows if ; if then the system behaves subcritically. Our results are seen to compare well, both qualitatively and quantitatively, with the experimentally obtained ones for the oscillatory instability of straight rolls in pure Rayleigh - Bénard convection

Influência do efeito de exposições ambientais no comportamento pós-fissurado de um BAC reforçado com fibras de aço

Neste trabalho apresentam-se os principais resultados do estudo da influência de certo tipo de exposições ambientais no comportamento pós-fissurado de betão auto-compactável reforçado com fibras de aço, BACRFA. Para o devido efeito foram produzidos diversos provetes prismáticos de BACRFA. Inicialmente os provetes foram sujeitos a ensaios cíclicos de flexão em três pontos, com o objetivo de se induzir dois níveis de pré-fissuração distintos, respetivamente, com uma abertura de fenda de 0.3 e 1.0 mm. Posteriormente, os provetes pré-fissurados foram submetidos a três tipos de exposição ambiental durante um período de dezoito meses. Por fim caracterizou-se o desempenho mecânico dos provetes após exposição ambiental

Influence of different restraint protocols for the electrocardiogram values of feline night monkeys (Aotus azarae infulatus

Universidade do Estado do Pará. Centro de Ciências Biológicas e da Saúde. Laboratório de Cirurgia Experimental. Belém, PA, Brasil.Universidade Federal Rural da Amazônia. Instituto de Saúde e Produção Animal. Belém, PA, Brasil.Ministério da Saúde. Secretaria de Vigilância em Saúde. Instituto Evandro Chagas. Centro Nacional de Primatas. Ananindeua, PA, Brasil.Ministério da Saúde. Secretaria de Vigilância em Saúde. Instituto Evandro Chagas. Centro Nacional de Primatas. Ananindeua, PA, Brasil.Universidade Federal Rural da Amazônia. Instituto de Saúde e Produção Animal. Belém, PA, Brasil.Universidade do Estado do Pará. Centro de Ciências Biológicas e da Saúde. Laboratório de Cirurgia Experimental. Belém, PA, Brasil.Macacos-da-noite são muito susceptíveis ao estresse e por isso a contenção química ou física deve ser cuidadosamente avaliada antes de qualquer procedimento. Protocolos anestésicos podem alterar alguns parâmetros fisiológicos, sendo o eletrocardiograma (ECG) um exame muito utilizado para avaliação do ritmo e da frequência cardíaca. O objetivo deste estudo foi avaliar a influência de quatro diferentes protocolos de contenção sobre o ECG realizado em Aotus azarae infulatus. Para isso foram utilizados 10 animais, machos, adultos, submetidos à contenção com a associação tiletamina/zolazepam (TZ), isoflurano (ISO), associação cetamina e midazolam (CET) e contenção física (CF). Não foram observadas diferenças nos parâmetros de ondas e complexos obtidos no ECG em todos os grupos testados, no entanto, durante a avaliação do traçado os animais do grupo CF apresentaram uma quantidade maior de alterações. Concluiu-se que os protocolos de contenção utilizados não alteraram os valores do ECG e que não foi possível considerar o grupo CF como controle devido causar mais alterações do que todos os protocolos testados

Determinação da condutividade térmica efectiva através da modelação tridimensional de um queimador poroso

A simulação tridimensional de queimadores porosos é, muitas vezes, necessária devido às características tridimensionais dos fenómenos que ocorrem no seu interior. Contudo, o esforço computacional envolvido nessas simulações é elevado. Para se utilizar modelos de dimensão inferior é necessário dispor de modelos de fecho e propriedades efectivas que reflictam as características tridimensionais. Para o caso do queimador modelado, não existem na literatura valores para a condutividade térmica efectiva da placa perfurada. Essa condutividade foi obtida através da minimização do erro entre resultados obtidos unidimensional e tridimensionalmente. Verificou-se que Ks=34,566*ks*Pe^(-1,3631) se ajusta à condutividade térmica efectiva da placa perfurada

Towards a cooperative traffic network editor

In this paper we explore the potential benefits of concepts such as visual interactive modelling and simulation to devise and implement a cooperative network editor embedded in a collaborative environment for transport analysis. Traditional approaches lack adequate means to foster integrated analyses of transport systems either because they are strict in terms of purpose or because they do not allow multiple users to dynamically interact on the same description of a model. The use of a common geographical data model of the application domain promotes the means for different experts to interact seamlessly in a collaborative environment