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Tinus T.,HAS Den Bosch University of Applied Sciences | Damour M.,Institute National Dhorticulture Et Of Paysage | Van Riel V.,HAS Den Bosch University of Applied Sciences | Sopade P.A.,University of Queensland
Journal of Food Engineering | Year: 2012

The kinetics of starch and protein digestion in hammer- and cryo-milled cowpea (70-370 μm) were investigated. The pH during the protein digestion reduced with time, and both the starch and protein digestion exhibited monophasic digestograms, which were suitably (r 2 > 0.97, p < 0.001) described by a modified first-order kinetic model. The in vitro protein digestibility of the cowpea (>80%) was independent of the milling conditions. The hammer-milled cowpea digested more, but the reciprocal of its rate of protein digestion was independent of the square of the particle size. The rate of protein digestion in the cryo-milled cowpea inversely depended (p < 0.05) on the square of the particle size, with 67 × 10 -7 cm 2 s -1 as the diffusion coefficient. For the starch digestion, diffusion coefficients (cm 2 s -1) were 0.6 × 10 -7 (hammer-milled) and 0.3 × 10 -7 (cryo-milled). The protein digestion proceeded at a much faster (100×) rate than the starch digestion. © 2012 Elsevier Ltd. All rights reserved. Source


Bournet P.-E.,Institute National Dhorticulture Et Of Paysage | Kichah A.,Institute National Dhorticulture Et Of Paysage | Chasseriaux G.,Institute National Dhorticulture Et Of Paysage
Acta Horticulturae | Year: 2011

The crop activity strongly interacts with the climate inside a greenhouse. The crop exerts a mechanical strain onto the flow and exchanges heat and water vapour with the surrounding environment. Conversely, the outside climate conditions (wind, air temperature and radiation) also affect the metabolism of plants. Up to now, the mechanisms involved in the transpiration process have been largely investigated, at least experimentally. However, few numerical studies of the distributed climate including the transfers at crop level exist. In order to better control the crop behaviour and growth, it remains relevant to assess the heterogeneity of the climatic parameters (radiation, temperature, humidity) inside the canopy. A commercially available computational fluid dynamics (CFD) software was used for simulations. The modelling approach is based on the resolution of the 2D Navier-Stokes equations taking account of turbulence (standard k-ε model). A submodel based on the resolution of the Radiative Transfer Equation and distinguishing short and long wavelength was implemented. The radiation reaching the plants decreased inside the canopy according to the Beer's law. The crop (Impatiens cultivar) was considered as a porous medium exchanging latent and sensible heat with the ambient environment. The latent heat flux was deduced from an energy balance over the leaves. Simulations were conducted for a 2500 m 2 glasshouse equipped with continuous roof vents. The analysis focuses on two scales: the building and the canopy. The heterogeneity of the velocity, temperature and humidity distributions is first investigated. But the main point deals with the heterogeneity of the radiation reaching the canopy. This heterogeneity affects the photosynthesis process and results in complex latent and sensible heat flux distributions inside the crop. Source


Cable A.,Institute National Dhorticulture Et Of Paysage | Bournet P.E.,Institute National Dhorticulture Et Of Paysage | Morille B.,Institute National Dhorticulture Et Of Paysage | Chasseriaux G.,Institute National Dhorticulture Et Of Paysage
Acta Horticulturae | Year: 2012

In order to improve crop quality and reduce consumption of water, energy and fertilizer in greenhouses, it is crucial to have a precise knowledge of the internal distributed climate. During the day, because of the path of the sun, there are important variations in the amount of solar radiation reaching the crop, which strongly impacts climate and therefore crop activity. Up to now, this mechanism was scarcely considered in CFD studies. In this work, a 2D pseudo-unsteady CFD approach is implemented to compute the radiation, temperature and humidity variations at plant and greenhouse levels during a solar day in summer. The studied greenhouse is a Venlo glasshouse containing an Impatiens crop under oceanic temperate conditions. The Navier-Stokes equations were solved using the standard k-e turbulence model and a bi-band radiative submodel distinguishing short and long wavelength radiations was employed. A user-defined crop submodel including the aerodynamic drag of the crop considered as a porous medium as well as the sensible and latent heat exchanges occurring at plant level were included. Boundary conditions were set each hour, with varying radiation intensity, diffuse fraction and direction, soil heat flux and inlet temperature. The model makes it possible to assess the climate evolutions of the air and leaf temperature distributions inside the greenhouse. Source


Kichah A.,Institute National Dhorticulture Et Of Paysage | Bournet P.-E.,Institute National Dhorticulture Et Of Paysage | Migeon C.,Institute National Dhorticulture Et Of Paysage | Chasseriaux G.,Institute National Dhorticulture Et Of Paysage
Acta Horticulturae | Year: 2011

Over the past two decades, the modelling of greenhouse climate with CFD techniques mainly focussed on the understanding of the physical behaviour of greenhouses (ventilation, light transmission). Only few numerical CFD studies however, properly describe the interaction of the crop with the local climate and most authors have to cope with a lack of data for validation. The impact of the crop on the climate may be significant as it is known to slow the flow and to exchange heat and mass (water vapour) with the inside ambient air. The present study aims at validating numerical simulations on the basis of both latent and sensible heat transfers occurring at plant level and considering the major climatic/physical components which govern these exchange processes (such as the leaf temperature, or the stomatal and aerodynamic resistances). Experiments were conducted in a 100-m 2 greenhouse compartment. Potted impatiens plants growing on shelves were considered. A set of sensors including a sonic anemometer, thermocouples, airhumidity/ temperature probes, pyranometers, pyrradiometers and balances was used to assess the greenhouse micrometeorology and to estimate the heat and mass transfers from the canopy. Two-dimensional simulations were carried out with a computational fluid dynamics software. The calculation domain reduced to a parallelepipedic shape including the plants. The Navier-Stokes equations were solved using the standard k-ε turbulence model and a radiative submodel was activated. A porous medium model (Darcy Forchheimer) was adopted for the crop and a specific routine was developed to take account of latent and sensible heat transfers. Comparison with experimental data provided reasonable agreement for the air and leaf temperatures in particular. Even if some discrepancies remain, the modelling approach appears to be a useful tool to predict the impact of the canopy on the local climate inside the greenhouse. Source

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