Milk yield and composition of crossbred Sahelian × Anglo-Nubian goats in the semi-intensive system in Mali during the preweaning period

The aim of this study was to evaluate milk yield and its composition during the preweaning period for Sahelian goats (SG) and Anglo-Nubian (AN) crossbred depending on some factors. The experiments were conducted from January to December 2008 for 44 suckled and hand-milked does, randomized, and divided into two equal groups: SG (n022) and F1 Anglo-Nubian × Sahelian goats (1/2AN; n0 22). The does and their offsprings were kept in a pen where they stayed indoors for 45 days before they were allowed outdoors when the weather was suitable. Each category received supplemental feeds depending on the season (rainy season, dry cold season, and dry hot season). The average daily milk yield was recorded weekly from parturition to 100 days of age. Individual milk samples were taken for chemical analysis in connection with the yield measurements twice per month from the fourth week of lactation throughout the different seasons (rainy, cold dry, and hot dry). The daily milk yield differed between breed types (P0 0.001) during the preweaning, while the effect of kids' sex on daily milk production was not significant. Litter size affected milk yield up to day 60 (P00.032) where does with twins producing more milk than those with single kid. However, at day 100, both groups had similar (P00.001) milk production. Total milk yield at weaning increased by 103 % in 1/2AN over SG. The highest concentration of total solids of milk was (12.76 %) recorded in the hot dry season. The results of this study indicate that crossbreeding native Sahelian goats with high potential Anglo-Nubian buck improved milk production and its composition

A numerical analysis of pollutant dispersion in street canyon: influence of the turbulent Schmidt number

Realizing the growing importance and availability of motor vehicles, we observe that the main source of pollution in the street canyons comes from the dispersion of automobile engine exhaust gas. It represents a substantial effect on the micro-climate conditions in urban areas. Seven idealized-2D building configurations are investigated by numerical simulations. The turbulent Schmidt number is introduced in the pollutant transport equation in order the take into account the proportion between the rate of momentum turbulent transport and the mass turbulent transport by diffusion. In the present paper, we attempt to approach the experimental test results by adjusting the values of turbulent Schmidt number to its corresponding application. It was with interest that we established this link for achieving our objectives, since the numerical results agree well with the experimental ones. The CFD code ANSYS CFX, the k, e and the RNGk-e models of turbulence have been adopted for the resolutions. From the simulation results, the turbulent Schmidt number is a range of 0.1 to 1.3 that has some effect on the prediction of pollutant dispersion in the street canyons. In the case of a flat roof canyon configuration (case: runa000), appropriate turbulent Schmidt number of 0.6 is estimated using the k-epsilon model and of 0.5 using the RNG k-e model

Performance investigation of a volute porous tongue of a turbocharger turbine

The design for better performance of the spiral housing volute used commonly in radial and mixed inflow gas turbines is of prime importance as it affects the machine stage at both design and off design conditions. The tongue of the scroll divides the flow into two streams, and represents a severe source of disturbances, in terms of thermodynamic parameter uniformity, maximum kinetic energy, the right angle of attack to the rotor and minimum losses. Besides, the volute suffers an undesirable effect due to the recirculating mass flow rate in near bottom vicinity of the tongue. The present project is an attempt to design a tongue fitted with cylindrical holes traversing normal to the stream wise direction, where on account of the large pressure difference between the top and the bottom sides of the tongue will force the recirculating flow to go through the rotor inlet. This possibility with its limitations has not yet been explored. A numerical simulation is performed which might provide our suitable objectives. To achieve this goal the ANSYS code is used to build the geometry, generate the mesh, and to simulate the flow by solving numerically the averaged Navier Stokes equations. Apparently, the numerical results show evidence of favorable impact in using porous tongue. The realization of a contact between the main and recirculation flow by drilled holes on the tongue surface leads to a flow field uniformity, a reduction in the magnitude of the loss coefficient, and a 20 % reduction in the recirculating mass flow rate

The separation wall effect of a volute twin entry cross section area on the mixed inflow turbine performance

The pulse turbocharging system is used in many diesel engines and it is fortunate that nozzleless mixed turbines allow unsteady flow with less performance losses. It operates with a double or sometimes triple-entry casing creating different flow regimes in each sector. A nozzleless casing is used. The division of the cross section area takes the form of a solid wall in the radial plane. When the flow rate through one or the other volute inlet drops to zero, some reverse flow is observed from the other inlet. This situation suffers undesirable effects, diminishing the benefits of the divided volute casing types. A numerical investigation on the effect of the length of the dividing wall in the radial plane is performed using the ANSYS code. This possibility is explored and the results show that extending the wall to a limiting length enhances the flow behavior with better performance

The number of blade effects on the performance of a mixed turbine rotor

Turbochargers have become widely applied to diesel vehicle engines. The mixed flow turbine type is suitable for systems where compact power sources are required with higher boost pressure. The sensitivity of the rotor to incidence effects and tendency of the flow to separate have given rise to considerations of the optimum number of blades. This paper investigates the performance of a mixed inflow turbine under steady conditions with the effect of the blade number. This study deals with the determination of the performance characteristics of a mixed flow turbine by solving numerically the 3D Reynolds averaged Navier-Stokes equations. The ANSYSICEM software is used to build the geometry and generate the unstructured meshes while the ANSYS-CFX code is used to simulate the flow in the mixed flow turbine. The numerical method is also used to determine optimum geometrical characteristics such as the optimum number of blades. It has been found that the rotor with 14 blades exhibits better performance

Computational aerodynamic performance of mixed-flow turbine blade design

The performance of two mixed flow turbocharger turbine rotors is numerically investigated. Significantly, the two rotors differ mainly in their inlet angle geometry, one has a constant blade angle (rotor A) and the other has a nominal constant incidence angle (rotor B). Since experimental data alone are not sufficient for understanding the detailed flow field within the turbocharger turbine stage, a complete 3-D Computational Fluid Dynamics model is developed using commercial software Ansys CFX. The model is validated against experimental data for all steady conditions. This study presents a numerical performance prediction of two mixed flow turbine rotors for a wide range of rotational speeds and pressure ratios. The influence of inlet blade angle on the turbine performances is also investigated