RESUMO

Air flow is of great importance in pneumatic sprayers as it is related to droplets sprayed size. Currently, there is a deficiency in regulating air flow in these sprayers. This work aimed to develop a system to control air flow of a pneumatic sprayer (Berthoud), and evaluate, in relation to air flow, power demanded by PTO and technical parameters of spraying (VMD, coefficient of homogeneity, percent coverage and droplets density), related to air flow. The diaphragm valve was projected using the software CAD, which was later made in galvanized steel and fixed to the fan air inlet. Air flow and power demanded on PTO was evaluated in eight diaphragm aperture positions (100, 90, 80, 70, 60, 50, 40 and 30%), and also using water sensitive papers, parameters of spraying were evaluated through a range of 30 meters in five diaphragm apertures (100, 90, 80, 70 and 60%). At the end it was found that between aperture of 100 and 70%, the closing of diaphragm caused a decrease of 4.56% in air flow. From aperture of 60%, reduction of air flow was more evident, resulting in reductions in air flow of 14.08, 24.00, 35.37 and 47.09% for opening levels 60, 50 , 40 and 30% of diaphragm, respectively. The power demand decreased linearly as diaphragm was closed. The system proved to be efficient to control spraying parameters with reduction of air flow, it has also increased droplet size (VMD), therefore resulted in reducing droplets density. Coverage percentage was influenced only by distance, reducing it as distance from the spray nozzle increased. The coefficient of homogeneity decreased as increased air flow and distanced from the spray nozzle.

Nos pulverizadores pneumáticos, a vazão de ar é de grande importância uma vez que está relacionado ao tamanho das gotas pulverizadas. Atualmente, verifica-se que existe a deficiência na regulagem da vazão de ar, nestes equipamentos. Sendo assim objetivou-se com este trabalho desenvolver um sistema de controle de vazão de ar em um pulverizador pneumático (Berthoud) e avaliar quanto à vazão de ar, potência exigida na TDP, e os parâmetros técnicos da pulverização (DMV, coeficiente de homogeneidade, porcentagem de cobertura e densidade de gotas). Projetou-se o diafragma com o auxilio do programa computacional CAD e que posteriormente foi confeccionado em aço galvanizado e fixado na entrada de ar do ventilador. Avaliaram-se as vazões de ar e a potência exigida pela TDP em oito posições de abertura do diafragma (100; 90; 80; 70; 60; 50; 40 e 30%), e também, com o auxílio de etiquetas hidrosenssíveis, avaliou os parâmetros da pulverização, ao longo de uma faixa de 30 metros em cinco aberturas do diafragma (100; 90; 80; 70 e 60%). Ao final verificou-se que entre as aberturas de 100 e 70%, o fechamento do diafragma promoveu um decréscimo de 4,56% na vazão de ar. A partir da abertura de 60%, a redução da vazão de ar foi mais evidente, obtendo-se reduções na vazão de ar de 14,08; 24,00; 35,37 e 47,09% para as aberturas de 60, 50, 40 e 30% do diafragma, respectivamente. Quanto à exigência de potência, este reduziu linearmente à medida que se fechou o diafragma. O sistema demonstrou ser eficiente no controle dos parâmetros da pulverização, com a redução da vazão de ar, aumentou o tamanho das gotas pulverizadas (DMV), consequentemente acarretou na redução da densidade de gotas. A porcentagem de cobertura foi influenciada somente pela distância, reduzindo-o conforme se distanciou do bocal do pulverizador. O coeficiente de homogeneidade reduziu à medida que aumentou a vazão de ar e se distanciou do bocal do pulverizador.

Assuntos

RESUMO

Fractal scaling of the exponential type is used to establish the cumulative volume (V) distribution applied through agricultural spray nozzles in size x droplets, smaller than the characteristic size X. From exponent d, we deduced the fractal dimension (Df) which measures the degree of irregularity of the medium. This property is known as 'self-similarity'. Assuming that the droplet set from a spray nozzle is self-similar, the objectives of this study were to develop a methodology for calculating a Df factor associated with a given nozzle and to determine regression coefficients in order to predict droplet spectra factors from a nozzle, taking into account its own Df and pressure operating. Based on the iterated function system, we developed an algorithm to relate nozzle types to a particular value of Df. Four nozzles and five operating pressure droplet size characteristics were measured using a Phase Doppler Particle Analyser (PDPA). The data input consisted of droplet size spectra factors derived from these measurements. Estimated Df values showed dependence on nozzle type and independence of operating pressure. We developed an exponential model based on the Df to enable us to predict droplet size spectra factors. Significant coefficients of determination were found for the fitted model. This model could prove useful as a means of comparing the behavior of nozzles which only differ in not measurable geometric parameters and it can predict droplet spectra factors of a nozzle operating under different pressures from data measured only in extreme work pressures.

RESUMO

Fractal scaling of the exponential type is used to establish the cumulative volume (V) distribution applied through agricultural spray nozzles in size x droplets, smaller than the characteristic size X. From exponent d, we deduced the fractal dimension (Df) which measures the degree of irregularity of the medium. This property is known as 'self-similarity'. Assuming that the droplet set from a spray nozzle is self-similar, the objectives of this study were to develop a methodology for calculating a Df factor associated with a given nozzle and to determine regression coefficients in order to predict droplet spectra factors from a nozzle, taking into account its own Df and pressure operating. Based on the iterated function system, we developed an algorithm to relate nozzle types to a particular value of Df. Four nozzles and five operating pressure droplet size characteristics were measured using a Phase Doppler Particle Analyser (PDPA). The data input consisted of droplet size spectra factors derived from these measurements. Estimated Df values showed dependence on nozzle type and independence of operating pressure. We developed an exponential model based on the Df to enable us to predict droplet size spectra factors. Significant coefficients of determination were found for the fitted model. This model could prove useful as a means of comparing the behavior of nozzles which only differ in not measurable geometric parameters and it can predict droplet spectra factors of a nozzle operating under different pressures from data measured only in extreme work pressures.