Bárbara Teruel

Automatized control in greenhouses: climatic variables and fertigation

A aplicacao de tecnicas de automacao e controle em casas de vegetacao teve inicio nos anos 50, com o controle da temperatura atraves de termostatos; desde entao, as mudancas tecnologicas tem abarcado todos os aspectos que compoem o sistema, do projeto estrutural ate aspectos relacionados a sustentabilidade. Dentre os parâmetros que devem ser controlados, a temperatura e umidade relativa do ar, a radiacao solar, a concentracao de CO2, a ventilacao e a fertigacao tem tido uma evolucao significativa, dos quais se apresenta uma panorâmica atraves da revisao do estado da arte de trabalhos publicados nessas tematicas, nos ultimos anos. Na atualidade, temas relacionados com a reducao do impacto ao meio ambiente e a producao eficiente e com qualidade, estao levando as casas de vegetacao ao caminho da Agricultura de Precisao.

Estudo comparativo do resfriamento de laranja valência com ar forçado e com água

This work presents a study to compare the orange Valencia (Citrus sinensis O.) cooling with forced-air cooling and hydrocooling. The forced-air cooling system operated with air flow of 1933m3/h, at 1oC, RH= 88,4 ± 2,0% and air velocity around 1m/s. The experiments with immersion hydrocooling systems with capacity of 0,23m3 of water at 1oC, approximately. The half-cooling time and seven-eighths cooling time, they are determinate with the temperature data, made two repetitions. The results showed that the cooling the bed fruits, with air cooling, is not homogeneous, and obtained cooling time average, between 107min and 170min, depending on the position the fruit in the package. In the hydrocooling system, the cooling of the bed fruits happens uniformly in the bed, with average cooling time of 57min.

ESTUDO TEÓRICO DO RESFRIAMENTO COM AR FORÇADO DE FRUTAS DE GEOMETRIAS DIFERENTES

This paper presents a numerical study for obtaining cooling curves of orange Valencia (Citrus sinensis O.) and banana Prata (Mussa Balbisiana Colla), in different positions along the bed and conditioned in package with 40% of effective opening area. The fruits were pre-cooled in a forced-air system (1.933m3/h), at 1°C and 7°C, RH= 88,4 ± 2,0% and air velocity around 1m/s. A two-dimensional mathematical model was applied, assuming prolate spheroid coordinate, to characterize the transient heat transfer process inside the fruits considering convective profile conditions at the surface of the body. The generated equations were numerically solved by finite-volume method. The convective heat transfer coefficients were obtained using the least square method by comparison between experimental and numerical data. The comparative analysis of the theoretical and experimental curves presented a satisfactory agreement, with error between 5% and 7%. It was noted that the convective heat transfer coefficient changes with the fruits position in the bed and cooling time present a variation of approximately 38% among the different points. The spatial distributions of temperature inside the fruits, for three times, demonstrate the existence of a temperature differential between the center and the surface of 30%, approximately. The model predicts that the cooling rate is in the extremes of the banana. The Bi and Fo numbers obtained represent very well the heat transfer process in the fruits under different relationships of volume/area.

Estudo comparativo do resfriamento de laranja valência, em três sistemas de resfriamento

This work presents a study to compare the cooling of oranges with room cooling, forced-air cooling and hydrocooling systems of the Valencia orange (Citrus Sinensis Osbeck). The forced-air cooling system operated with an air flow of 1933 m3 h-1, at 1oC, relative humidity (RH) of 88.4% ± 2.0 and air velocity around 1 m s-1. In the experiments with cold water an immersion hydrocooling system with a capacity of 0.23 m3 of water was used at a temperature of 1oC, approximately. The half cooling time and seven-eighths cooling time were determined from the temperature data, with two replications. The results showed that the cooling of the bed fruits with forced air is not homogeneous, obtaining a mean between 107 a 170 min, depending on the position of the fruit in the package. In the hydrocooling system, the cooling of the fruits occurs uniformly in the bed, with a mean cooling time of 57 min. In room cooling, the time of cooling was 362 and 460 min, eight times that of hydrocooling system and more than three times that of the forced air cooling time.

Cooling parameters for fruits and vegetables of different sizes in a hydrocooling system

The cooling of fruits and vegetables in hydrocooling system can be a suitable technique. This work aimed to define cooling time for fruits and vegetables of different sizes, presenting practical indexes that could be used to estimate cooling time for produce with similar characteristics. Fruits (orange melon-Cucumis melo, mango-Mangifera indica, guava-Psidium guajava, orange-Citrus sinensis Osbeck, plum-Prunus domestica, lime-Citrus limon, and acerola-Prunus cerasus) and vegetables (cucumber-Cucumis sativus, carrot-Daucus carota, and green bean-Phaseolus vulgaris), were cooled in a hydrocooling system at 1°C. The volume of fruits and vegetables ranged between 8.18 cm3 and 1,150.35 cm3, and between 13.06 cm3 and 438.4 cm3, respectively. Cooling time varied proportionally to produce volume (from 8.5 to 124 min for fruits, and from 1.5 to 55 min, for vegetables). The relationship between volume and time needed to cool fruits (from 1.03 min cm-3 to 0.107 min cm-3) and vegetables (from 0.06 min cm-3 to 0.12 min cm-3) is an index that could be used to estimate cooling time for fruits and vegetables with similar dimensions as those presented in this work.

Resfriamento de banana-prata com ar forçado

This work presents the cooling curves for bananas Prata, (Musa balbisiana Colla), and determinates half-cooling and seven-eight cooling times and the cooling rate. Bananas were kept in a cold room with a forced-air system at 7oC and RH = 87.6±3.8%. The experiment was conducted in a 2x2 factorial design, to test the effects of two flow rates (factors) of air passing through the product, and two types of boxes (levels). The statistical analysis was performed at p<0.10. The air flow rates were 1933 and 1160 m3/h and the boxes differed from each other by the area of openings, allowing more or less contact of the cooling media with the product (boxes with 40% or 3,5% of opening area). Significant differences were observed between cooling times of the product. The shortest cooling time was reached when the product was packed in a box with 40% of opening area and with the largest air flow rate of 1933 m3/h. The longest cooling time was obtained using a box with 3,2% of opening area and with the smallest air flow of 1160 m3/h. The results demonstrated the influence of the package opening area and the air flow on the cooling rate of bananas. The average time cooling was 117 min at 555 min in the different treatments. There is no statistical difference on weight loss.

Avaliação preliminar dos custos de resfriamento de laranja in natura

This paper presents study of the cooling cost of Valencia orange in a forced-air system and room cooling (Ta=1oC and RH = 88,4±2,0%).The fruits was conditioned in two package with 3,5% and 40% of opening effective area. The annual total cost was determined with the fixed and variable costs of the installation and the cooling total costs with the quantity of cooling products in the each system for the same period. The cooling total cost is the 40 to 20% smaller, if compared with the cost when the fruits cooling in the conventional room.

Interface homem-máquina para controle de processos de resfriamento com ar forçado visando à economia de energia

Apresenta-se o desenvolvimento de um equipamento microprocessado, com saida de corrente, para controle da velocidade de rotacao do motor do ventilador de sistemas de ar forcado, usando inversor de frequencia. Atraves de programacao (software IHM.EXE), o usuario pode definir a massa a ser resfriada em quilogramas de produto. O equipamento calcula, atraves de um polinomio previamente estabelecido e programavel, a frequencia de operacao do inversor, que corresponde a uma vazao de ar especifica, dentro dos limites estabelecidos no projeto. O equipamento foi instalado num sistema de resfriamento com ar forcado, estimando-se, pelo calculo da variacao da potencia util mecânica, uma economia de energia da ordem de 82%, com uma rotacao equivalente a 56% da nominal do ventilador, proporcionando, desta forma, uma economia significativa no custo de operacao do sistema.

Transmisión de Calor y Materia con Reducción de Volumen Durante el Secado de Ladrillos de Cerámica

Se presenta un modelo matematico tridimensional transitorio aplicado al fenomeno de difusion de calor y materia con reduccion de volumen en el interior de solidos paralelepipedos. El modelo se ha aplicado al proceso de secado de ladrillos ceramicos. Se uso el metodo de los volumenes finitos considerando propiedades termicas y mecanicas constantes y una condicion de contorno convectiva en la superficie del material. El modelo fue utilizado para estudiar el proceso de secado de un ladrillo de ceramica a temperaturas de 60 y 80oC y en con humedades relativas del aire de 10,07 y 4,66%. Los resultados numericos de contenido de humedad, temperatura y reduccion de volumen, fueron comparados con datos experimentales para determinar los coeficientes de transporte. Se pudo concluir que: el fenomeno de reduccion de volumen tiene dos periodos y afecta considerablemente la velocidad de secado del solido, asi como la distribucion del contenido de humedad en el interior del mismo.

Experimental evaluation of the performance of a wireless sensor network in agricultural environments

Um estudo experimental, visando a avaliar a distância de operacao adequada entre os nos de uma rede de sensores sem fio disponivel no mercado, foi realizado para diferentes cultivos agricolas (milho, pinhao-paraguaio e eucalipto), buscando oferecer aos agricultores e pesquisadores dados experimentais do desempenho da rede, que possa good yield are environmental factors, which include high temperatures and high humidity within the facilities, causing stress to the animal and consequent decreased production (SOUSA, 2005).am ser uteis para ser considerados no dimensionamento e no projeto de redes de sensores sem fio em situacoes semelhantes as estudadas. A avaliacao mostrou que a distância de separacao dos nos depende do tipo de cultura e e um fator critico para garantir a viabilidade do uso da RSSF. Na configuracao usada, com envio de pacotes a cada 2 segundos, a autonomia da bateria foi de cerca de quatro dias. Portanto, a autonomia pode ser aumentada com um intervalo maior de tempo entre o envio de pacotes.