Abstract: In this study, the three-dimensional cavitating
turbulent flow in a complete Francis turbine is simulated using
mixture model for cavity/liquid two-phase flows. Numerical analysis
is carried out using ANSYS CFX software release 12, and standard k-ε
turbulence model is adopted for this analysis. The computational
fluid domain consist of spiral casing, stay vanes, guide vanes, runner
and draft tube. The computational domain is discretized with a threedimensional
mesh system of unstructured tetrahedron mesh. The
finite volume method (FVM) is used to solve the governing equations
of the mixture model. Results of cavitation on the runner’s blades
under three different boundary conditions are presented and
discussed. From the numerical results it has been found that the
numerical method was successfully applied to simulate the cavitating
two-phase turbulent flow through a Francis turbine, and also
cavitation is clearly predicted in the form of water vapor formation
inside the turbine. By comparison the numerical prediction results
with a real runner; it’s shown that the region of higher volume
fraction obtained by simulation is consistent with the region of runner
cavitation damage.
Abstract: Natural fibers are used in polymer composites to
improve mechanical properties to replace inorganic reinforcing
agents produced by non-renewable resources. The present study
investigates the tensile and flexural behaviors of palm fibers-high
density polyethylene (HDPE) composite as a function of volume
fraction. The surface of the fibers was treated by mercerization
treatments to improve the wetting behavior of the apolar HDPE. The
treatment characterization was obtained by scanning electron
microscopy, X-Ray diffraction and infrared spectroscopy. Results
evidences that a good adhesion interfacial between fibers-matrix
caused an increase strength and modulus flexural as well as tensile
strength in the modified fibers/HDPE composites when compared to
the pure HDPE and untreated fibers reinforced composites.
Abstract: Boiling process is characterized by the rapid
formation of vapour bubbles at the solid–liquid interface (nucleate
boiling) with pre-existing vapour or gas pockets. Computational fluid
dynamics (CFD) is an important tool to study bubble dynamics. In
the present study, CFD simulation has been carried out to determine
the bubble detachment diameter and its terminal velocity. Volume of
fluid method is used to model the bubble and the surrounding by
solving single set of momentum equations and tracking the volume
fraction of each of the fluids throughout the domain. In the
simulation, bubble is generated by allowing water-vapour to enter a
cylinder filled with liquid water through an inlet at the bottom. After
the bubble is fully formed, the bubble detaches from the surface and
rises up during which the bubble accelerates due to the net balance
between buoyancy force and viscous drag. Finally when these forces
exactly balance each other, it attains a constant terminal velocity. The
bubble detachment diameter and the terminal velocity of the bubble
are captured by the monitor function provided in FLUENT. The
detachment diameter and the terminal velocity obtained are compared
with the established results based on the shape of the bubble. A good
agreement is obtained between the results obtained from simulation
and the equations in comparison with the established results.
Abstract: Today, the pollution due to non-degradable material
such as plastics, has led to studies about the development of
environmental-friendly material. Because of biodegradability
obtained from natural sources, polylactid acid (PLA) and ijuk fiber
are interesting to modify into a composite. This material is also
expected to reduce the impact of environmental pollution. Surface
modification of ijuk fiber through alkalinization with 0.25 M NaOH
solution for 30 minutes was aimed to enhance its compatibility to
PLA, in order to improve properties of the composite such as the
mechanical properties. Alkalinization of the ijuk fibers annihilates
some surface components such as lignin, wax and hemicelloluse, so
the pore on the surface clearly appeared, decreasing of the density
and diameter of the ijuk fibers. The change of the ijuk fiber properties
leads to increase the mechanical properties of PLA composites
reinforced the ijuk fibers through strengthening of the mechanical
interlocking with the PLA matrix. An addition to enhance the
distribution of the fibers in the PLA matrix, the stirring during DCM
solvent evaporation from the mixture of the ijuk fibers and the
dissolved-PLA can reduce amount of the trapped-voids and fibers
pull-out phenomena, which can decrease the mechanical properties of
the composite.
Abstract: Combustion, emission and performance
characterization of a single cylinder diesel engine using methanol
diesel blends was carried out. The blends were 5% (v/v) methanol in
diesel (MD05) and 10% (v/v) methanol in diesel (MD10). The
problem of solubility of methanol and diesel was addressed by an
agitator placed inside the fuel tank to prevent phase separation. The
results indicated that total combustion duration was reduced by15.8%
for MD05 and 31.27% for MD10compared to the baseline data.
Ignition delay was increased with increasing methanol volume
fraction in the test fuel. Total cyclic heat release was reduced by
1.5% for MD05 and 6.7% for MD10 as compared to diesel baseline.
Emissions of carbon monoxide, hydrocarbons along with smoke were
reduced and that of nitrogen oxides were increased with rising
methanol contents in the test fuel. Full load brake thermal efficiency
was marginally reduced with increased methanol composition in the
blend.
Abstract: In this study, the thermal and mechanical properties of
basalt fibre reinforced concrete were investigated. The volume
fractions of basalt fibre of (0.1, 0.2, 0.3, and 0.5% by total mix
volume) were used. Properties such as heat transfer, compressive and
splitting tensile strengths were examined. Results indicated that the
strength increases with increase the fibre content till 0.3% then there
is a slight reduction when 0.5% fibre used. Lower amount of heat
conducted through the thickness of concrete specimens than the
conventional concrete was also recorded.