Influence of geometrical and thermal parameters on the thermal component of a pin-on-disk system

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Strong temperature gradients are often the cause of malfunctions taking place in mechanical systems which associate two rubbing solids. This work presents the thermal behaviour of a system consisting on a rotating disk in rubbing contact with a pin. Immersed in an environment characterized by a surface conductance h ͚. and a temperature T ͚ ,the disk is subjected to localised beat flux generated by the friction with the pin, eccentric with respect to the rotating axis of the disk. Several parameters intervene decisively on the local heat transfer and therefore on the temperature of the contact surface between the two solids in friction. In addition to the conductance, other parameters as the angular velocity of the disk, the frictional heat flux or the pin diameter and its off­-center with respect to the disk rotation axis, play a major role in the thermal exchange. The present work examines the influence of such parameters on the thermal solution. An analytical expression is proposed for the calculation of the 3D disk's temperature. The presented thermal cartographies make possible to locate the zones of the system undergoing the greatest temperature gradients and thus the associated spots of mechanical rupture. Results are compared with other analytical solutions found in the specialized literature.ej201

Carob pulp as raw material for production of the biocontrol agent P. agglomerans PBC-1

Large-scale production has been the major obstacle to the success of many biopesticides. The spreading of microbial biocontrol agents against postharvest disease, as a safe and environmentally friendly alternative to synthetic fungicides, is quite dependent on their industrial mass production from low-cost raw materials. Considerable interest has been shown in using agricultural waste products and by-products from food industry as nitrogen and carbon sources. In this work, carob pulp aqueous extracts were used as carbon source in the production of the biocontrol agent Pantoea agglomerans PBC-1. Optimal sugar extraction was achieved at a solid/liquid ratio of 1:10 (w/v), at 25°C, for 1 h. Batch experiments were performed in shake flasks, at different concentrations and in stirred reactors at two initial inoculums concentrations, 106 and 107 cfu ml−1. The initial sugar concentration of 5 g l−1 allowed rapid growth (0.16 h−1) and high biomass productivity (0.28 g l−1 h−1) and was chosen as the value for use in stirred reactor experiments. After 22 and 32 h of fermentation the viable population reached was 3.2 × 109 and 6.2 × 109 cfu ml−1 in the fermenter inoculated at 106 cfu ml−1 and 2.7 × 109 and 6.7 × 109 cfu ml−1 in the bioreactor inoculated at 107 cfu ml−1. A 78% reduction of the pathogen incidence was achieved with PBC-1 at 1 × 108 cfu ml−1, grown in medium with carob extracts, on artificially wounded apples stored after 7 days at 25°C against P. expansum

Transport and Utilization of Hexoses and Pentoses in the Halotolerant Yeast Debaryomyces hansenii

Debaryomyces hansenii is a yeast species that is known for its halotolerance. This organism has seldom been mentioned as a pentose consumer. In the present work, a strain of this species was investigated with respect to the utilization of pentoses and hexoses in mixtures and as single carbon sources. Growth parameters were calculated for batch aerobic cultures containing pentoses, hexoses, and mixtures of both types of sugars. Growth on pentoses was slower than growth on hexoses, but the values obtained for biomass yields were very similar with the two types of sugars. Furthermore, when mixtures of two sugars were used, a preference for one carbon source did not inhibit consumption of the other. Glucose and xylose were transported by cells grown on glucose via a specific low-affinity facilitated diffusion system. Cells derepressed by growth on xylose had two distinct high-affinity transport systems for glucose and xylose. The sensitivity of labeled glucose and xylose transport to dissipation of the transmembrane proton gradient by the protonophore carbonyl cyanide m-chlorophenylhydrazone allowed us to consider these transport systems as proton symports, although the cells displayed sugar-associated proton uptake exclusively in the presence of NaCl or KCl. When the V(max) values of transport systems for glucose and xylose were compared with glucose- and xylose-specific consumption rates during growth on either sugar, it appeared that transport did not limit the growth rate