This paper reports on the development of an approximate empirical-CFD modelling procedure combining experimental correlations for the heat and mass transfer coefficient determination and specific user-defined functions (UDF) implemented in the commercial CFD code Fluent to simulate the interrelationships at play between airflow and transfers of unwrapped food products bathing in air. Transfer modelling required specific calculation to account for water evaporation from the product surface. Mean transfer coefficients at the air-product interface were determined empirically from validated experimental correlations, where the CFD mean air velocity that is calculated in a small user-defined volume surrounding the product was incorporated. Internal water diffusion was taken into account by considering the product as a motionless fluid composed of dry matter and water. The procedure developed allows, in a single CFD calculation using a single mesh, temperature and water concentration fields to be computed and the water loss kinetics of the products to be determined together with the temperature and relative humidity fields of the air flowing around them. Although the established procedure was set up with the aim of assessing heat and water exchanges occurring in large stacks of unwrapped food products subjected to airflow, this last was validated for modelling, first, one-dimensional drying of a meat cylinder and second, three-dimensional drying of five cylindrical plaster casts placed in a row. Its application to the ripening of a row of six cheeses is also discussed.

The young larvae of insects living on dry food produce large amounts of water by the metabolic combustion of dietary lipids. The metabolic production of water needed for larval growth, previously known as hypermetabolic responses to juvenile hormone (JH), is associated with a 10 to 20-fold increase in the rate of O2 consumption (10,000 microL O2/g/h in contrast to the usual rate of 500 microL O2/g/h). Growing and moulting larvae are naturally hypermetabolic due to the endogenous release of JH from the corpora allata. At the last, larval-pupal or larval-adult moult there is no JH and as a consequence the metabolic rate is much lower and the dietary lipid is not metabolized to produce water but stored in the fat body. At this developmental stage, however, a hypermetabolic response can be induced by the exogenous treatment of the last larval instars with a synthetic JH analogue. In D. vulpinus, the JH-treated hypermetabolic larvae survive for several weeks without moulting or pupating. In T. castaneum and G. mellonella, the JH-treated hypermetabolic larvae moult several times but do not pupate. All these larvae consume dry food and the hypermetabolic response to JH is considered to be a secondary feature of a hormone, which is produced by some subordinated endocrine organ. The organ is most probably the controversial prothoracic gland (PG), which is a typical larval endocrine gland that only functions when JH is present. According to our hypothesis, PG activated by JH releases an adipokinetic superhormone, which initiates the conversion of dietary lipid into metabolic water. This type of metabolic combustion of dietary lipid produces large quantities of endothermic energy, which is dissipated by the larvae in the form of heat. Thermovision imaging revealed that the body of hypermetabolic larvae of G. mellonella can be as hot as 43 deg C or more. In contrast, the temperature of "cold" normal last instar larvae did not differ significantly from that of their environment. It is highly likely that thermovision will facilitate the elucidation of the currently poorly understood hormonal mechanisms that initiate the production of metabolic water essential for the survival of insects that live in absolutely dry conditions.

L'herbe fraîche est un aliment de bonne valeur alimentaire pour les ruminants mais son ingestion par les vaches laitières reste limitée au regard de sa digestibilité. La forte teneur en eau de l'herbe fraîche pourrait limiter la quantité ingérée de MS d'herbe. L'effet de l'eau externe à la plante sur l'ingestion, le comportement alimentaire et l'encombrement ruminal a été étudié sur des vaches laitières nourries à l'auge avec du ray-grass anglais distribué ad libitum. Trois traitements ont été comparés : herbe verte témoin, fauchée une fois par jour (C)C plus de l'eau ajoutée sur l'herbe (SW) et C plus perfusion d'eau dans le rumen après chaque distribution (PW). La distribution d'herbe a été faite à 14:00 h, 19:00 h et 07:00 h le lendemain matin. L'eau de boisson était en accès libre. Dans le traitement SW, la teneur en MS de l'herbe offerte a été réduite de 161 à 117 g / kg brut ( P 0,02) sans changer la composition chimique de l'herbe. Par rapport à C et PW, la quantité brute ingérée d'herbe et la vitesse d'ingestion en brut ont fortement augmenté (respectivement + 36 et 39 pour cent), mais la quantité de MS d'herbe ingérée (16,4 kg MS/ j), la vitesse d'ingestion de MS (35,3 g MS/min) et les durées journalières d'ingestion (468 min) et de rumination (515 min) n'ont pas été modifiées. Perfuser l'eau dans le rumen n'a affecté ni l'ingestion ni le comportement alimentaire. Le poids total du contenu du rumen (150 kg), la teneur en MS du contenu (115 g/kg ), l'osmolarité du liquide ruminal, la proportion d'eau libre et d'eau liée ainsi que le taux de renouvellement des liquides n'ont pas été modifiés par les traitements. En conclusion, pour des vaches en production nourries à l'herbe, un apport même important d'eau externe ne constitue pas de limite à la prise alimentaire, ni à l'encombrement dans le rumen, et n'affecte pas la quantité de MS d'herbe ingérée