Economical and environmental contributions of installing a solar heating system in an industrial process: Contribuições econômicas e ambientais da instalação de um sistema de aquecimento solar em um processo industrial

Aware of the harmful consequences of climate change, several industrial sectors search for alternatives to minimize the environmental impact of their production processes. The use of thermal solar collectors is a promising alternative for the heat supply in industrial processes, contributing to the reduction of fossil fuel consumption for this purpose and, consequently, mitigating the environmental impact caused by greenhouse gas emissions. The present research analyzes the contribution of a Solar Heating for Industrial Processes (SHIP) system in an industry’s environmental and economic spheres on the outskirts of Porto Alegre, south Brazil. A solar field of Linear Fresnel concentrating collectors is simulated in SAM software. The field has an aperture area of 352 m² and operates in the supply of saturated steam for a given industrial process. The results indicate that the SHIP system would be able to supply 729 GJth to the industrial process annually. It means a reduction of greenhouse gas emissions in the magnitude of tens of tons of CO2-equivalent each year, whose value increases as the operation of the conventional steam-generating boiler moves away from ideal (theoretical efficiency of 100%). Two methodologies are used to calculate LCOH, resulting in 52 and 54 U$D/MWhth values for the analyzed SHIP system. Compared with the heat supply through burning natural gas and mineral coal, a solar thermal heating system can be evaluated as an environmentally responsible and economically advantageous alternative for the industrial sector that decides on this investment

Experimental and numerical study for the effect of horizontal openings on the external plume and potential fire spread in informal settlements

According to recent UN reports, it is estimated that more than one billion people live in informal settlements globally, exposing them to a large potential fire risk. In previous research, it was found that the main fire spread mechanism between dwellings is the external flaming (plume) and radiative heat fluxes from the vertical openings at the dwelling of origin to the surroundings. In this paper, an experimental and numerical study was conducted to quantify the effect of adding horizontal roof openings to the design of informal settlement dwellings to reduce the fire spread risk by decreasing the length of flames and radiation from the external plumes at the vertical openings. In total, 19 quarter scale ISO-9705 compartment fire experiments were conducted using an identical fuel load (80 MJ/m2 ) of polypropylene and were used to validate a physical computational fluid dynamics model for future studies. Five different total horizontal openings areas (0.0025, 0.01, 0.04, 0.09, and 0.16 m2 ) were investigated using two horizontal openings designs: (1) four square openings at the four corners of the compartment and (2) one slot cut at the middle of the compartment. It was found that adding horizontal openings decreased the average heat flux measured at the door by up to 65% and 69% for corner and slot cases, respectively. Heat flux reductions were achieved at opening areas as low as 0.01 m2 for slot cases, whereas reductions were only achieved at areas of at least 0.09 m2 for corner cases. The Computational Fluid Dynamics (CFD) model was validated using the experimental results. It successfully captured the main fire dynamics within the compartment in addition to the values of the external radiative heat flux. Further, a new empirical ventilation factor was generated to describe the flow field through both openings configurations which showed strong coupling with the inlet mass of fresh air to the compartment

Experimental and Numerical Study for the Effect of Horizontal Openings on the External Plume and Potential Fire Spread in Informal Settlements

According to recent UN reports, it is estimated that more than one billion people live in informal settlements globally, exposing them to a large potential fire risk. In previous research, it was found that the main fire spread mechanism between dwellings is the external flaming (plume) and radiative heat fluxes from the vertical openings at the dwelling of origin to the surroundings. In this paper, an experimental and numerical study was conducted to quantify the effect of adding horizontal roof openings to the design of informal settlement dwellings to reduce the fire spread risk by decreasing the length of flames and radiation from the external plumes at the vertical openings. In total, 19 quarter scale ISO-9705 compartment fire experiments were conducted using an identical fuel load (80 MJ/m2 ) of polypropylene and were used to validate a physical computational fluid dynamics model for future studies. Five different total horizontal openings areas (0.0025, 0.01, 0.04, 0.09, and 0.16 m2 ) were investigated using two horizontal openings designs: (1) four square openings at the four corners of the compartment and (2) one slot cut at the middle of the compartment. It was found that adding horizontal openings decreased the average heat flux measured at the door by up to 65% and 69% for corner and slot cases, respectively. Heat flux reductions were achieved at opening areas as low as 0.01 m2 for slot cases, whereas reductions were only achieved at areas of at least 0.09 m2 for corner cases. The Computational Fluid Dynamics (CFD) model was validated using the experimental results. It successfully captured the main fire dynamics within the compartment in addition to the values of the external radiative heat flux. Further, a new empirical ventilation factor was generated to describe the flow field through both openings configurations which showed strong coupling with the inlet mass of fresh air to the compartment

Estudo numérico de uma aleta elíptica inserida em uma cavidade quadrada com a superfície superior deslizante submetida à convecção mista

This paper aims to evaluate the heat transfer in a square cavity with an elliptical fin located in different positions on the cavity bottom and with different aspect ratios. The optimal geometry was analised using the Constructal Design principle. A two-dimensional, laminar, steady state and incompressible flow was considered. The thermophysics properties were defined for Pr = 0.71 and they are considered constant, except for the specific mass that was determined by the Boussinesq approximation. A Rayleigh number (RaH) of 104 was adopted to define the natural convection, while a Reynolds number (ReH) of 102 was adopted to define the forced convection. The fin position and its dimensions were varied, keeping the ratio of the fin area to cavity area constant (Φ = 0.05). The optimal geometry that maximizes the heat transfer rate was obtained through the Constructal Law. A mesh was created to solve the problem and it was adequately refined to ensure the accuracy of the results. The governing equations of the problem were solved numerically using the software ANSYS/Fluent®. This study shows that the position of the fin which maximizes the average Nusselt number in these conditions is at the point X1 ≈ 0.3 of the lower surface. For the aspect ratio (r) of the fin, it was observed that the minimization of the average Nusselt number occurs for r between 15 and 25. Considering all studied geometries, the optimized one can reach a performance around 50% superior if compared with the worst one, proving the importance of geometric evaluation in this kind of engineering problem, as well as the effectiveness of the Constructal approach.Este trabalho pretende avaliar a transferência de calor em uma cavidade quadrada com uma aleta elíptica localizada em diferentes posições no fundo da cavidade e com diferentes razões de aspecto. A geometria ideal foi analisada usando o princípio do Design Constructal. Foi considerado um escoamento bidimensional, laminar, estacionário e incompressível. As propriedades termo físicas foram definidas para Pr = 0.71 e são consideradas constantes, exceto para a massa específica que foi determinada pela aproximação de Boussinesq. Um número Rayleigh (RaH) de 104 foi adotado para definir a convecção natural, enquanto um número de Reynolds (ReH) de 102 foi adotado para definir a convecção forçada. A posição da aleta e suas dimensões foram variadas, mantendo constante a relação entre a área da aleta e a área da cavidade (Φ = 0,05). A geometria ideal que maximiza a taxa de transferência de calor foi obtida através da Lei Construtal. Uma malha foi criada para resolver o problema e foi adequadamente refinada para garantir a precisão dos resultados. As equações governantes do problema foram resolvidas numericamente usando o software ANSYS / Fluent®. Este estudo mostra que a posição da aleta que maximiza o número de Nusselt médio, nessas condições, está no ponto X1 ≈ 0,3 da superfície inferior. Para a razão de aspecto (r) da aleta, observou-se que a minimização do número médio de Nusselt médio ocorre para r entre 15 e 25. Considerando todas as geometrias estudadas, a otimizada pode atingir um desempenho em torno de 50% superior se comparado com o pior caso, comprovando a importância da avaliação geométrica neste tipo de problema de engenhaaria, bem como a eficácia da abordagem Construtal

WSGG Model Correlations to Compute Nongray Radiation From Carbon Monoxide in Combustion Applications

This paper presents correlations for the weighted-sum-of-gray-gases (WSGG) model for carbon monoxide based on HITEMP2010. The correlations are valid for pressure path lengths from 0.0001 atmÁm up to 10 atmÁm, total pressure in the order of 1.0 atm, and for temperatures ranging from 400 K up to 2500 K. Some test cases embodying nonhomogeneous, nonisothermal conditions are presented, and the results for the WSGG model are compared with the line-by-line (LBL) solutions for CO

Modelagem da radiação térmica em chamas turbulentas da combustão de metano em ar

Este trabalho analisa numericamente a transferência de calor radiativa em uma chama turbulenta de metano-ar. São resolvidas equações de conservação de massa, quantidade de movimento, energia, espécies químicas gasosas e fuligem, e variância da flutuação de temperatura em coordenadas cilíndricas axissimétricas. O modelo de combustão é o Eddy Break-Up – Arrhenius, com reação de combustão em duas etapas. O modelo de turbulência é o k −e padrão. A modelagem das interações turbulência-radiação (TRI - do inglês: Turbulence-Radiation Interactions) considera a “correlação combinada entre coeficiente de absorção e temperatura” e a “autocorrelação de temperatura”. O termo fonte de calor radiativo é calculado com o método de ordenadas discretas, considerando os modelos de gás cinza (GC) e da soma-ponderada-de-gases-cinza (WSGG – do inglês: weighted-sum-of-gray-gases) com correlações clássicas e recentes. O modelo linha-por-linha, considerado benchmark, também é empregado no cálculo daquele termo fonte, porém em cálculos desacoplados entre radiação e dinâmica de fluidos computacional (CFD - do inglês: Computational Fluid Dynamics), com o objetivo de avaliar os modelos WSGG e GC. Primeiramente, estudou-se o efeito da radiação térmica dos gases H2O e CO2 através dos modelos GC e WSGG, em cálculos acoplados radiação-CFD. Os resultados mostraram que os campos de temperatura e do termo fonte de calor radiativo, a transferência de calor para a parede da câmara e a fração radiativa, foram sensíveis aos diferentes modelos, enquanto o efeito sobre as concentrações das espécies foi de menor relevância para o modelo de combustão considerado. Os resultados obtidos com o modelo WSGG mais recente ficaram mais próximos dos dados experimentais da literatura, enquanto que a consideração das interações TRI melhorou esta concordância. As principais contribuições das interações TRI foram sobre a temperatura máxima e a fração radiativa, concordando com resultados da literatura. Os efeitos radiativos da fuligem juntamente com os gases também foram estudados, sendo importantes sobre o termo fonte de calor radiativo somente na região onde a fuligem estava presente (aumento de 30%). O fluxo de calor radiativo sobre a parede radial da câmara aumentou 25% na região de maior concentração de fuligem. A contribuição dos gases para a transferência radiativa foi de 92% e a da fuligem foi de 8%. Ao comparar os resultados dos modelos WSGG e GC com a solução benchmark, considerando o meio composto por gases, o modelo WSGG mais recente foi o que apresentou os melhores resultados (erro máximo 22,49%, médio 4,72%), enquanto ao considerar o meio composto por gases e fuligem, os erros foram menores (máximo 11,07%, médio 2,95%).This work analyses numerically the thermal radiation heat transfer on a methane-air turbulent non-premixed flame. Conservation equations for mass, momentum, gaseous chemical species and soot, energy, and temperature variance, are solved in axisymmetric coordinates. The combustion model is Eddy Break-Up – Arrhenius, with two steps for the combustion reaction. Turbulence is modeled by standard k −e model. Consideration of TRI (Turbulence-Radiation Interactions) effects is made through a methodology that considers both cross-correlation between absorption coefficient and temperature and temperature self-correlation. The radiative heat source term is calculated with the discrete ordinates method, considering the gray gas model (GG) and the weighted-sum-of-gray-gases model (WSGG) based on classical and recent correlations. The benchmark solution obtained by the line-by-line model is also employed to calculate that source term, but in decoupled radiation-CFD (Computational Fluid Dynamics) calculations, with the objective of evaluating WSGG and GG models. Firstly, it was studied the effects of thermal radiation from the gases H2O and CO2 employing GG and WSGG models, and then the influence of TRI was also studied, both in coupled radiation- CFD calculations. Results pointed that temperature and radiative heat source fields, as well as wall heat transfer rates and radiative fraction, were significantly affected by thermal radiation, as well as by the different models and by TRI, while the influence on species concentrations was minor, for the combustion model employed. Numerical results obtained considering the recent WSGG model correlations were closer to experimental data from literature, and consideration of TRI into calculations improved that agreement. The main TRI contributions were the decrease on flame peak temperature and the increase on radiative fraction, in agreement with literature data. Radiative effects of the mixture of soot and gases were also studied, showing to be important for the radiative heat source only in the region with presence of soot (increase of 30%). Radiative heat flux on chamber wall increased 25% locally in the region with the highest soot concentration. Contribution of gases and soot for the net radiative transfer was 92% and 8%. Comparing the results obtained with WSGG and GG models with the benchmark solution in decoupled radiation-CFD calculations, considering the media composed by CO2 and H2O, the recent WSGG reached the best results (maximum error of 22.49%, average error of 4.72%), while considering the media composed by gases and soot, errors were reduced (maximum of 11.07% and average of 2.95%)

Inverse analisys of heat transfer in friction stir welding using the generalized extremal optimization method

A estimativa de parâmetros térmicos relacionados à Soldagem por Fricção Linear (também conhecida como Soldagem por Fricção e Mistura Mecânica) de uma placa de alumínio AA 2195- T8 é estudada nesta dissertação. A determinação dos parâmetros é tratada como um problema de otimização, no qual a função objetivo corresponde a uma função erro entre temperaturas medidas numericamente e temperaturas calculadas, para certos valores da taxa de calor gerada pela fricção, do coeficiente de transferência calor por convecção natural e do coeficiente de transferência de calor entre a placa e a base de suporte. A distribuição transiente de temperaturas sobre a placa é determinada pela solução da equação da condução de calor tridimensional transiente, a qual é resolvida pelo método dos volumes finitos. A minimização da função objetivo é realizada com o auxílio do algoritmo Otimização Extrema Generalizada (GEO), um método evolucionário que pode lidar com diversos tipos de problemas de otimização. A avaliação da sensibilidade da leitura de temperatura é feita com relação ao posicionamento dos sensores, com o objetivo de descobrir as melhores posições para aquisição de dados, e também a determinação do parâmetro t (parâmetro utilizado no método GEO que deve ser ajustado para cada tipo de problema) que melhor se adapta para cada um dos conjuntos de medição de temperatura. Além disso, realiza-se um estudo no qual é analisado um caso em que a fonte de calor possui forma de distribuição desconhecida, sem a utilização de equações para a sua descrição, desta maneira mais parâmetros devem ser estimados pela análise inversa, assim o processo de otimização é mais complexo (cinco valores de taxa de calor e dois coeficientes de transferência de calor, ao invés de uma taxa de calor e dois coeficientes). Ainda, para simular medições de dados reais, os valores de temperatura obtidos a partir da solução numérica para valores específicos da taxa de calor e dos coeficientes de transferência de calor são perturbados com ruídos de acordo com desvios-padrão típicos dessa forma de medição. Este trabalho demonstra que a aproximação inversa proposta pode ser um modo muito efetivo para avaliar e predizer os parâmetros que governam o processo de transferência de calor na Soldagem por Fricção Linear, um importante passo para o seu controle em tempo real.The estimation of thermal parameters related to Friction Stir Welding of a AA 2195-T8 plate is studied in this dissertation. The determination of the parameters is carried out by means of an optimization problem, in which the objective function corresponds to an error function between the numerically measured temperature and the temperature computed for each estimated values of the heat rate input, the heat transfer coefficient on the bottom surface, and the natural convection heat transfer coefficient. The time-dependent temperature distribution on the plate is determined by the solution of the three-dimensional transient state conduction equation, which is solved by the control-volum method. The minimization of the objective function is accomplished with the aid of the Generalized Extremal Optimization (GEO) method, an evolutionary method that can deal with several types of optimization problems. The evaluation of the temperature reading sensitivity is carried out, in relation to the readers locations on the plate, in order to determine the best positions that can be used to acquire datas, and the determination of the t parameter (this parameter is used in the GEO method and it must be adjusted for each type of problem) that best fits with each one of the temperature readers assembly, allowing the determination of the best temperature readers assembly. In addition, it is executed a study that considers a case where the heat rate input has unknown profile distribution, without using equations for its description, in this manner more parameters have to be estimated by the inverse analysis, so the optimization process is more complicated (five heat rate inputs and two heat transfer coefficients, instead of one heat rate input and two heat transfer coefficients). Furthermore, to simulate real-data measurements, the temperature inputs, obtained from a numerical solution for specific values of the heat rate input and the heat transfer coefficients, were perturbed with noises according to the standard deviation of the measurement procedure. This work demonstrates that the proposed inverse approach can be a very effective way to evaluate and predict the parameters that govern the heat transfer process in Friction Stir Welding, an important step to real-time control of this process

Modelagem da radiação térmica em chamas turbulentas da combustão de metano em ar

Este trabalho analisa numericamente a transferência de calor radiativa em uma chama turbulenta de metano-ar. São resolvidas equações de conservação de massa, quantidade de movimento, energia, espécies químicas gasosas e fuligem, e variância da flutuação de temperatura em coordenadas cilíndricas axissimétricas. O modelo de combustão é o Eddy Break-Up – Arrhenius, com reação de combustão em duas etapas. O modelo de turbulência é o k −e padrão. A modelagem das interações turbulência-radiação (TRI - do inglês: Turbulence-Radiation Interactions) considera a “correlação combinada entre coeficiente de absorção e temperatura” e a “autocorrelação de temperatura”. O termo fonte de calor radiativo é calculado com o método de ordenadas discretas, considerando os modelos de gás cinza (GC) e da soma-ponderada-de-gases-cinza (WSGG – do inglês: weighted-sum-of-gray-gases) com correlações clássicas e recentes. O modelo linha-por-linha, considerado benchmark, também é empregado no cálculo daquele termo fonte, porém em cálculos desacoplados entre radiação e dinâmica de fluidos computacional (CFD - do inglês: Computational Fluid Dynamics), com o objetivo de avaliar os modelos WSGG e GC. Primeiramente, estudou-se o efeito da radiação térmica dos gases H2O e CO2 através dos modelos GC e WSGG, em cálculos acoplados radiação-CFD. Os resultados mostraram que os campos de temperatura e do termo fonte de calor radiativo, a transferência de calor para a parede da câmara e a fração radiativa, foram sensíveis aos diferentes modelos, enquanto o efeito sobre as concentrações das espécies foi de menor relevância para o modelo de combustão considerado. Os resultados obtidos com o modelo WSGG mais recente ficaram mais próximos dos dados experimentais da literatura, enquanto que a consideração das interações TRI melhorou esta concordância. As principais contribuições das interações TRI foram sobre a temperatura máxima e a fração radiativa, concordando com resultados da literatura. Os efeitos radiativos da fuligem juntamente com os gases também foram estudados, sendo importantes sobre o termo fonte de calor radiativo somente na região onde a fuligem estava presente (aumento de 30%). O fluxo de calor radiativo sobre a parede radial da câmara aumentou 25% na região de maior concentração de fuligem. A contribuição dos gases para a transferência radiativa foi de 92% e a da fuligem foi de 8%. Ao comparar os resultados dos modelos WSGG e GC com a solução benchmark, considerando o meio composto por gases, o modelo WSGG mais recente foi o que apresentou os melhores resultados (erro máximo 22,49%, médio 4,72%), enquanto ao considerar o meio composto por gases e fuligem, os erros foram menores (máximo 11,07%, médio 2,95%).This work analyses numerically the thermal radiation heat transfer on a methane-air turbulent non-premixed flame. Conservation equations for mass, momentum, gaseous chemical species and soot, energy, and temperature variance, are solved in axisymmetric coordinates. The combustion model is Eddy Break-Up – Arrhenius, with two steps for the combustion reaction. Turbulence is modeled by standard k −e model. Consideration of TRI (Turbulence-Radiation Interactions) effects is made through a methodology that considers both cross-correlation between absorption coefficient and temperature and temperature self-correlation. The radiative heat source term is calculated with the discrete ordinates method, considering the gray gas model (GG) and the weighted-sum-of-gray-gases model (WSGG) based on classical and recent correlations. The benchmark solution obtained by the line-by-line model is also employed to calculate that source term, but in decoupled radiation-CFD (Computational Fluid Dynamics) calculations, with the objective of evaluating WSGG and GG models. Firstly, it was studied the effects of thermal radiation from the gases H2O and CO2 employing GG and WSGG models, and then the influence of TRI was also studied, both in coupled radiation- CFD calculations. Results pointed that temperature and radiative heat source fields, as well as wall heat transfer rates and radiative fraction, were significantly affected by thermal radiation, as well as by the different models and by TRI, while the influence on species concentrations was minor, for the combustion model employed. Numerical results obtained considering the recent WSGG model correlations were closer to experimental data from literature, and consideration of TRI into calculations improved that agreement. The main TRI contributions were the decrease on flame peak temperature and the increase on radiative fraction, in agreement with literature data. Radiative effects of the mixture of soot and gases were also studied, showing to be important for the radiative heat source only in the region with presence of soot (increase of 30%). Radiative heat flux on chamber wall increased 25% locally in the region with the highest soot concentration. Contribution of gases and soot for the net radiative transfer was 92% and 8%. Comparing the results obtained with WSGG and GG models with the benchmark solution in decoupled radiation-CFD calculations, considering the media composed by CO2 and H2O, the recent WSGG reached the best results (maximum error of 22.49%, average error of 4.72%), while considering the media composed by gases and soot, errors were reduced (maximum of 11.07% and average of 2.95%)