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Authors
Abstract(s)
Atualmente existe uma necessidade crescente de prolongar a vida útil dos produtos
alimentares perecíveis, quer para garantir a qualidade e segurança alimentar, quer para
reduzir o desperdício alimentar, que no caso dos produtos hortícolas atinge
aproximadamente 50%. Para produtos hortícolas, tais como frutas, legumes e flores
cortadas, a temperatura é um parâmetro extrínseco muito importante que afeta a taxa de
deterioração do produto e a vida pós-colheita. A rápida remoção de calor do campo após
a colheita por arrefecimento e manutenção da temperatura ideal do produto em
abastecimento logístico são, portanto, de extrema relevância. A presente dissertação tem
como objetivo desenvolver estudos paramétricos por Dinâmica de Fluidos
Computacional de acomodação e estrutura de embalagens envolvendo simultaneamente
parâmetros estruturais, geométricos e térmicos para a previsão do escoamento do ar e
transferência de calor que permitam avaliar o desempenho de embalagens de produtos
alimentares. Um modelo tridimensional transitório de CFD de uma câmara fria com
caixas de embalagem cheias de frutos é apresentado para prever o escoamento de ar
transitório e a transferência de calor por convecção e condução no interior dos frutos. Na
construção dos modelos CFD, foi definido um modelo físico-matemático baseado nas
equações da continuidade, da quantidade de movimento e da energia. A turbulência foi
considerada através do modelo de turbulência SST- k - ?. O estudo paramétrico
considera o desenvolvimento de modelos de CFD com diferentes disposições:
empilhamento lateral, empilhamento vertical e o modelo de orientação das caixas, para
analisar o escoamento de ar e a transferência de calor durante o período de arrefecimento
para extrair o calor do campo após a colheita dos frutos.
Ao final das 8 horas de arrefecimento, a variação da temperatura média prevista nas
esferas de ágar para o (1) modelo com três embalagens de frutas (modelo padrão), indica
que na embalagem do topo, em contacto com ar refrigerado, os simuladores dos produtos
apresentam a temperatura mais baixa. A diferença de temperatura nas esferas
localizadas nas embalagens a diferentes alturas atinge o máximo de 1,3ºC; (2) caso de
estudo do empilhamento lateral, que a temperatura média nos produtos localizados nas
embalagens que não ficam na direção do ar refrigerado da câmara, seja cerca 0,5ºC mais
elevada. Neste modelo, a discrepância em altura dos valores de temperatura dos
produtos é superior que no modelo padrão, atingindo mais de 2ºC; (3) o modelo de
empilhamento vertical, é previsto que a temperatura média nos produtos aumenta à medida que a altura decresce, sendo a variação média entre o valor máximo e mínimo de
temperatura dos produtos de cerca 4ºC; (4) o modelo orientado a 90º relativamente ao
escoamento de ar refrigerado, a temperatura média dos produtos é mais elevada
aproximadamente 1ºC do que no modelo padrão (orientado a 0º).
Assim, os resultados permitem avaliar o tempo e/ou a temperatura e velocidade do ar de
descarga necessária para que todas as frutas dentro das caixas de embalagem atinjam a
temperatura de conservação que garanta a sua qualidade e segurança das frutas antes de
entrarem na cadeia de distribuição. Com base nestes resultados, os operadores podem
tomar decisões acerca do armazenamento das embalagens de forma a promover uma
temperatura mais baixa dos produtos, com ganhos a nível energético, de segurança e
qualidade alimentar.
Currently, there is an increasing need to extend the shelf life of perishable food products, both to ensure food quality and safety and to reduce food waste, which in the case of vegetables reaches approximately 50%. For vegetables, such as fruits, vegetables and cut flowers, temperature is a very important extrinsic parameter that affects the rate of product spoilage and post-harvest life. Rapid removal of heat from the field after harvest by cooling and maintenance of optimum product temperature in logistical supply are therefore of utmost relevance. The present dissertation aims to develop parametric studies by Computational Fluid Dynamics of packaging accommodation and structure involving simultaneously structural, geometric and thermal parameters for the prediction of air flow and heat transfer that allow to evaluate the performance of food product packaging. A three-dimensional transient CFD model of a cold room with packaging cases filled with fruits is presented to predict the transient airflow and heat transfer by convection and conduction inside the fruits. In the construction of the CFD models, a physicomathematical model based on the equations of continuity, quantity of motion and energy was defined. Turbulence was considered through the turbulence model SST- k - ?. The parametric study considers the development of CFD models with different layouts: lateral stacking, vertical stacking and the box orientation model, to analyze the airflow and heat transfer during the cooling period to extract heat from the field after fruit harvest. After 8 hours cooling, the variation of the average temperature predicted on the agar spheres for the (1) model with three fruit packaging (standard model), indicates that in the top packaging, in contact with the cold air, the product simulators have the lowest temperature. The temperature difference in the spheres located in packagaging at different heights reaches a maximum of 1.3°C; (2) case study of lateral stacking, that the average temperature in the products located in the packaging that are not in the direction of the cold air, is about 0.5ºC higher. In this model, the discrepancy of the products’ temperature values due to height location is higher than in the standard model, reaching more than 2ºC; (3) vertical stacking model, it is predicted that the products’ average temperature increases as the height decreases, with a variation between the maximum and minimum products’ temperature around 4°C; (4) 90° oriented model in relation to the cold air flow, the products’ average temperature is approximately 1°C higher than in the standard model (0° oriented). Thus, the results allow us to evaluate the time and/or temperature and velocity of the discharge air required for all the fruit inside the packaging boxes to reach the preservation temperature that guarantees their quality and fruit safety before entering the distribution chain. Based on these results, operators can make decisions about the packaging cold storage to promote a lower temperature of the products, with gains in terms of energy, safety and food quality.
Currently, there is an increasing need to extend the shelf life of perishable food products, both to ensure food quality and safety and to reduce food waste, which in the case of vegetables reaches approximately 50%. For vegetables, such as fruits, vegetables and cut flowers, temperature is a very important extrinsic parameter that affects the rate of product spoilage and post-harvest life. Rapid removal of heat from the field after harvest by cooling and maintenance of optimum product temperature in logistical supply are therefore of utmost relevance. The present dissertation aims to develop parametric studies by Computational Fluid Dynamics of packaging accommodation and structure involving simultaneously structural, geometric and thermal parameters for the prediction of air flow and heat transfer that allow to evaluate the performance of food product packaging. A three-dimensional transient CFD model of a cold room with packaging cases filled with fruits is presented to predict the transient airflow and heat transfer by convection and conduction inside the fruits. In the construction of the CFD models, a physicomathematical model based on the equations of continuity, quantity of motion and energy was defined. Turbulence was considered through the turbulence model SST- k - ?. The parametric study considers the development of CFD models with different layouts: lateral stacking, vertical stacking and the box orientation model, to analyze the airflow and heat transfer during the cooling period to extract heat from the field after fruit harvest. After 8 hours cooling, the variation of the average temperature predicted on the agar spheres for the (1) model with three fruit packaging (standard model), indicates that in the top packaging, in contact with the cold air, the product simulators have the lowest temperature. The temperature difference in the spheres located in packagaging at different heights reaches a maximum of 1.3°C; (2) case study of lateral stacking, that the average temperature in the products located in the packaging that are not in the direction of the cold air, is about 0.5ºC higher. In this model, the discrepancy of the products’ temperature values due to height location is higher than in the standard model, reaching more than 2ºC; (3) vertical stacking model, it is predicted that the products’ average temperature increases as the height decreases, with a variation between the maximum and minimum products’ temperature around 4°C; (4) 90° oriented model in relation to the cold air flow, the products’ average temperature is approximately 1°C higher than in the standard model (0° oriented). Thus, the results allow us to evaluate the time and/or temperature and velocity of the discharge air required for all the fruit inside the packaging boxes to reach the preservation temperature that guarantees their quality and fruit safety before entering the distribution chain. Based on these results, operators can make decisions about the packaging cold storage to promote a lower temperature of the products, with gains in terms of energy, safety and food quality.
Description
Keywords
Arranjos de Caixas Cfd Desempenho Térmico Embalagem Refrigeração das Frutas