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1-Methylcyclopropene (1-MCP) is a synthetic plant growth regulator used commercially to delay ripening of fruits. 1-MCP (SmartFresh) is applied in gaseous form (as a fumigant) in the cool store room. This paper uses a porous medium computational fluid dynamics model to numerically analyze the distribution of 1-MCP in cool store rooms for apple fruit. The effects of air circulation, room shape, and bin material were investigated. Dose calculation based on filling density was explored. The 1-MCP distribution in commercial cool stores, under room cooling condition, was uniform irrespective of room shape. Rooms filled with fruit in wooden bins deplete 25 % more of the active substance than rooms filled with fruit in plastic bins. The calculated dose increases linearly with the amount of fruit in the cool store (filling density). Hence, this study suggests that dose prescription based on filling density is feasible. [ABSTRACT FROM AUTHOR]

In this paper, a direct model based on explicit geometry of stacked products in boxes was developed and used to study the diffusion, convection and adsorption of 1-methylcyclopropene (1-MCP) gas in cool stores for apple fruit. The discrete element method was employed to generate random stacking of spherical products in a box. A three-dimensional finite volume-based computational fluid dynamics model was developed, verified and used to study the distribution and partitioning of the 1-MCP gas inside loaded container. The study addressed the gas distribution in a 500 L container with or without air circulation. For each case, 80 kg Jonagold apples at 1 °C and a 1-MCP dose of 1 μL L was used to collect validation data. In the presence of air circulation, diffusion-convection in air and diffusion adsorption in the product was applied. Simulations were performed with an unstructured tetrahedral mesh using the software ANSYS-CFX, a Reynolds-averaged Navier-Stokes solver. The case without air circulation was modelled as a diffusion problem in air and diffusion coupled with adsorption inside the product. Convection-diffusion-adsorption model parameters that were previously developed and validated were applied. The estimated equilibrium distribution of the 1-MCP gas equals 11, 34 and 55 % as unbounded in fruit, bonded in fruit and remaining in container, respectively. Profiles of free (unbounded) and adsorbed (bounded) 1-MCP concentrations inside fruit were estimated for reduced dosages: 0.5, 0.3, 0.1 and 0.02 μL L. [ABSTRACT FROM AUTHOR]

The paper aims at developing a validated model that can accurately predict the flow of a particulate material. This model will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. Therefore an experimental setup consisting of a vertical glass tube is filled with 500±30 μm spherical glass particles. The experiment is then placed in a vacuum and the particles are released by opening a valve. The velocity of the particles is recorded during their fall at three different heights using a non invasive optical tracking technique with an original implementation. The same experiment is then simulated using the Discrete Element Method and results are compared. A good agreement between the simulation and the experiment was found. The sensitivity of the simulation to a change in the contact stiffness, dynamic Coulomb coefficient of friction and tangential contact force model was investigated. The influence of the initial position of the simulated particles on the packing factor was shown to be very important. Finally the experiment proved to be extremely sensitive to a perturbation of the outflow section of the tube, something that was predicted by the simulations. [ABSTRACT FROM AUTHOR]

For the past few decades there has been a growing concern about the environmental implications associated with the use of soil fertilizers. In Europe, over 90% of fertilizer is distributed using spinning disc spreaders. The popularity of spinning disc spreaders lies with their relative low cost. However, the performance of these machines is highly dependent on the particle properties (e.g. friction coefficients, shape). This results in large differences in spread patterns depending on the fertilizer type as well as the prevailing weather conditions (e.g. air humidity). This dependence requires extensive experimental calibration of the spreader for each type of fertilizer. When a new spreader is designed this calibration work has to be largely repeated. DEM is believed to be the key to increase the understanding of the spreading process, the design of better spreaders and a drastic reduction of experimental calibration. The paper reviews recent results in experimentation and modelling of an international research consortium running several industrial research projects on centrifugal fertilizer projects. [ABSTRACT FROM AUTHOR]

The finite element method is used to investigate the validity of the Hertz model for normal contact under conditions that violate some of the assumptions on which the Hertz model was derived. The conditions investigated are: frictional contact, non-flat contact surface and large strains. The investigations were performed for the case of two elastic spheres in contact as well as that of a sphere in contact with a flat plate. The existence of friction for normal contact does not appear to lead to any erroneous predictions of the force-deflection relationship by the Hertz model. The Hertz model also does not appear to predict significant errors when the contact surface is not flat. However, large strains were found to cause important prediction errors by the Hertz model. Calibration curves for the corrections on the Hertz model are proposed. [ABSTRACT FROM AUTHOR]

The theory of elastic contact between two spherical bodies is used as a basis for an extension to include the contribution of the viscous effects to the total stress for viscoelastic spheres subjected to twisting moments. Expressions relating twisting moment to penetration of slip and penetration of slip to twist angle are derived. Two term power series truncations of the relations are then used to derive approximate expressions for torsional compliance of the bodies. Validation experiments for the extended model were performed by use of a rheometer device. Applications for the model in post-harvest agriculture include extraction of material properties for use in Discrete Element Modelling of mechanical interactions of fruits and other regular shaped produce during machine handling. A specific application is performed involving the use of a rheometer to measure the coefficient of friction for fruit-fruit contact. [ABSTRACT FROM AUTHOR]