Precoat filtration with body-feed and variable pressure. Part I: Mathematical modelling

The precoat filtration with body-feed is an unit operation of agricultural and food engineering. Mostly it is implemented by using centrifugal pump, which pump curve has a partial horizontal trend. Classically, in filtration theory, this prerogative of the centrifugal pumps leads to the simplifying assumption that filtration occurs with constant pressure. Because of this, it is easy to integrate the Darcy\u2019s differential equation [1, 2 and 3] for the precoat filtration with body-feed, obtaining the well known Carman equation [4]. This is the equation which relates the filtration time with the filtrate volume, the operating pressure, the filter area, and the solid-liquid suspension characteristics. The Carman equation is the start point for the subsequent optimization of the filtration cycles, e.g. by establishing the relationship between the filtration time and the filter cleaning time [5]. A better optimization of the precoat filtration with body-feed could be obtain, with some economic benefits, if an integration of the Darcy ODE was developed starting from actual trend of the pressure produced by the centrifugal pump, that is if a variable pressure was considered, as expected from the pump curve. In this sense a proposal was done by Tiller and Crump [6] many years ago in accordance with a graphic method of integration of the Darcy ODE. However the graphic procedure is tedious since it is iterative and not computerizable. For this reason the aim of this work was to find an analytical solution to the Darcy ODE for the filtration with variable pressure in order to obtain a quick and easy-to-use equation for the subsequent optimization calculations of filtration cycles, even if more complex of the Carman equation

Water sensitive papers simulation to assess deposits on targets

Aim of the study is to assess the possibility to use water sensitive papers to estimate, beside the superficial coverage, also the amount of deposit on the target at varying the spray features. To point out the main quantities influencing the deposit, the behaviour of the water sensitive papers was simulated by assuming some simplifying hypotheses: log-normal distribution of the diameter population of the drops and circular spots. Several images (630) of water sensitive papers, sprayed with drops of different mean diameter (from 100 up to 500 μm), constant coefficient of variation (0.50), and theoretical percentage of covered surface ranging from 10 up to 100%, were produced by means of simulation. These images were considered as effective water sensitive paper images and then analysed by means of an image processing software. The correlations between measured and effective values were studied and they allowed for an estimate of deposit and spray features from the image data. This implies that the analysis of the water sensitive paper images allows the determination of more complex parameters such as the unitary deposit and the impact density, all data strictly related to the efficacy of a phytosanitary treatment

Vibration risk evaluation in hand-held harvesters for olives

This research aims to evaluate the vibration transmitted to the hand-arm system by two electric portable harvesters, different for size and teeth features of the harvesting head. Moreover, being the bars of the two machines telescopic, they were operated at minimum and maximum length. The acceleration was measured, at different times, in two points, 1 m apart, next to the hand positions. Finally, measurements were carried out both at no load, in standard controlled conditions, and in field, under ordinary working conditions. To smooth the influence of external factors, the machines were operated by the same operator. The results showed that the greater and heavier harvesting head produced significantly higher acceleration at no load (10.7 m/s2 vs. 5.5 m/s2), and comparable acceleration at load (13.9 vs. 14.2 m/s2). On average, the vibration was significantly higher at load (14.0 vs. 8.1 m/s2). The difference between the two bar lengths was not statistically significant: 9.4 m/s2 when using the minimum length and 9.8 m/s2 when using the maximum one. Finally, the difference between the two measuring points was affected by the bar length: it was statistically significant when using the bar at its minimum length only. As far as the components are concerned, at no load the highest acceleration was measured along the bar axis for both harvesting heads (9.2 m/s2 for the greater head and 4.2 m/s2 for the smaller one). At load all the three components were comparable in the greater head (about 7.8 m/s2) whereas the x component was predominant in the other one (11.4 vs. 4.8 (y) and 6.6 m/s2 (z))

An innovative pneumatic electrostatic sprayer useful for tendone vineyards

The aim of this note is to analyse the features of the ESS “150 RB14” electrostatic sprayer, an innovative model compared to the standard air-assisted sprayers traditionally used by Apulian growers (Southern Italy) in “tendone” vineyards. The experimental tests showed that the activation of the electrostatic system produced a significant increase in the mean deposit, but it was located only on the foliar layer of the canopy closer to the sprayer. However this result should also imply an increase in the deposits on the bunches when the electrostatic system is activated, even if further tests are necessary to verify this expectation. If this will be substantiated, the electrostatic sprayer ESS “150 RB14” would be suitable for the targeted applications usually performed in “tendone” table grape vineyards

Special Issue on Pesticide Applications in Agricultural Systems

The European Directive 2009/128/EC on the Sustainable Use of Pesticides recognizes the use of Plant Protection Products (PPP) as having great impact on human health and the environment [...

Operator Dermal Exposure to Pesticides in Tomato and Strawberry Greenhouses from Hand-Held Sprayers

Protection of greenhouse crops in southern Italy usually requires 15–20 phytosanitary treatments per year, with volume rates in the range of 1000–2000 L ha1, depending on the plant growth stage. The most widespread sprayers are hand-held, high-pressure devices, which may expose operators to high levels of pesticides. This paper, also with the aim to lead toward a more sustainable use of greenhouses in agricultural productions, including some aspects of workers’ safety, reports the results of experimental tests aimed at measuring the amount of the mixture deposited on the worker’s body (potential dermal exposure, PDE) during pesticide applications to tomato and strawberry plants in a protected environment. Experimental tests on tomatoes were carried out taking into account two plant growth stages (flowering and senescence), two types of spray lance, two working pressures (1 and 2 MPa), and two walking directions (forwards and backwards). Those on the strawberries were carried out at the maturity of the fruit growth stage, comparing two hand-held sprayers (a standard spray gun and a short hand-held spray boom equipped with two nozzles) and working according to the common practice: forwards movement of the operator and high pressure (2 MPa). The results showed that with the tomato plants, the most important factor in reducing the deposit on the operator was the walking direction: on average, the PDE was 718 mL per 1000 L of the sprayed mixture (0.72h) while walking forwards and 133 mL (0.13h) while walking backwards. The reduction factor ranged from 3.0 at the flowering growth stage to 7.2 at the senescence growth stage. With respect to the strawberry plants, the PDE was significantly higher when the operator used the short hand-held spray boom (887 mL per 1000 L of the sprayed mixture, equivalent to 0.89h), rather than the spray gun (344 mL, 0.34h). In both cases, the most exposed body parts were the lower limbs, which accounted for 89–94% of the total PDE

Simulation of Water Sensitive Papers for Spray Analysis

Aim of this study was to simulate the water sensitive paper (WSP) behaviour for estimate the unitary spray deposition on the target at varying spray features and target coverage.  WSP images were produced assuming some simplifying hypotheses: spherical drops and circular stains randomly placed on the images. Sprays were described in terms of probability distribution function (PDF) of drop size (log-normal and Rosin-Rammler), coefficient of variation of diameters (CV), arithmetic mean diameter (AMD), and volume median diameter (VMD).  The results from the simulations showed that the overlap between stains was independent of spray features: when the percentage of covered surface of WSP images ranged from 4.7 up to 61.6%, the overlap between stains ranged from 0.3 up to 33.4%.   On the contrary, unitary deposit (volume per square centimetre, mL cm-2) and particle density (number of distinct particles per square centimetre, cm-2) could be obtained from the percentage of covered surface if CV, AMD, VMD and PDF were known.  However, assuming as spray parameter the VMD, the drop size distribution had almost no effect on the unitary deposit: with the same percentage of covered surface, the Rosin-Rammler PDF provided an estimate of the unitary deposit higher than log-normal distribution between 5 and 7% only

Modelling Spray Pressure Effects on Droplet Size Distribution from Agricultural Nozzles

For spray applications, drop size is the most important feature as it affects all aspects of a phytosanitary treatment: biological efficacy, environmental pollution, and operator safety. In turn, drop size distribution depends on nozzle type, liquid properties, and working pressure. In this research, three nozzles were studied under ordinary working conditions and the effect of pressure on drop size distribution was assessed. The nozzles under test, all from Albuz (France), were an orange hollow cone nozzle ATR 80 (European color code), an air induction flat spray nozzle AVI 11003, and an air induction hollow cone nozzle TVI 8002. The ATR 80 and the TVI 8002 nozzles were tested at four pressure values: 0.3, 0.5, 1.0, and 1.5 MPa; the AVI 11003 nozzle was tested at 0.3 and 0.5 MPa. The drop size measurement technique was based on the liquid immersion method by using a custom-made test bench; spray quality parameters were computed by means of suitable functions written in R language. Results showed that an increase in working pressure caused an increase in drop pulverization regardless of the type of nozzle, and drop pulverization was higher for the turbulence nozzle than for the two air induction nozzles. Based on skewness and kurtosis values, the theoretical gamma distribution was the most adapt to fit the experimental data. The scale parameter showed a decreasing trend with the increase in the pressure, a clear index of higher drop pulverization

Vibration produced by hand-held olive electrical harvesters

The paper reports the results of some laboratory and field tests aimed at assessing the acceleration levels transmitted to the hand-arm system by electric portable harvesters for olive. Four harvesting heads, different for shape and kinematic system, and five bars, different for diameter, length and material (aluminium and carbon fibre), were used in assembling eleven harvesters. The vibrations were measured in two points, next to the handgrips. The laboratory tests allowed the evaluation of the acceleration levels in standard controlled conditions, while the field tests allowed the assessing of the effects of the tree canopy with respect to the no load running. The laboratory tests showed that in reducing the vibration level plays a major role the kinematic system of the harvesting head and then the bar material. The classical flap-type harvester produced accelerations of around 20 m/s2, while by using a harvesting head with two parts in opposite movement, the accelerations were lowered to about 6 m/s2. The use of carbon fibres for the bars, besides the reduction in weight, produced also a reduction in acceleration (from 21 to 16 m/s2). The field tests proved that the tree canopy had a negative effect on the vibrations transmitted to the hand-arm system, especially when the aluminium bar of small diameter was used

FEM Analysis of Effects of Mechanical Impact Parameters on Fruit Characteristics

Mechanical impact on fresh agriculture commodities may be a criterial issue during mechanical processes such as grading, sorting, conveying, packing or transport. The applications of electronic measuring devices in form of artificial fruits like ‘Instrumented Spheres’ (IS) are an aid to quantify influences of mechanical impact on the value of fruit, vegetable and potato. Additionally, modelling and simulation of impact on fruits helps to identify those influencing parameters. In this study, modelling and simulation runs were performed based on the Finite Element Method (FEM). For dropping tests an ‘Acceleration Measuring Unit’ (AMU) was used which can be implemented into real or artificial fruits to measure the accelerations upon impact. The test stand was equipped with a force sensor. The relevant parameters Young moduli, density, mass, fruit dimensions, and dropping test heights were varied for the tests. FEM simulation results were compared with measured acceleration values of the AMU and force values of the test stand. On dropping potato tubers with mass of 100‑120 g from 25 cm height onto steel plates, the impact force ranged from 190 to 220 N. Simulations showed that the impact force in similar conditions (mass of 102‑113 g and Young moduli of 2.5‑3.5 MPa) ranged from 198 to 242 N, which is in good agreement with the experimental results. When the tuber mass was 190‑210 g, the measured impact force varied from 310 to 325 N. Simulations for masses of 199–221 g resulted in impact forces of 306‑325 N, again in good agreement with the experimental results. However, AMU acceleration values ranged from 922‑932 m s-2, for masses of 100‑200 g, to 765‑824 m s-2 for masses of 190‑210 g. Simulations, in similar conditions, provided acceleration values of 1934‑2314 m s-2 for masses of 102‑221 g (Young moduli 2.5‑3.5 MPa) and ranging from 1497 to 1843 m s-2 for masses of 199‑221 g, which are about twice as high than measured, probably due to effects from imperfect fit when implanted the AMU into the test fruit