Abstract: This paper presents a computational study of steady
state three dimensional very high turbulent flow and heat transfer
characteristics in a constant temperature-surfaced circular duct fitted
with 900 hemispherical inline baffles. The computations are based on
realizable k-ɛ model with standard wall function considering the
finite volume method, and the SIMPLE algorithm has been
implemented. Computational Study are carried out for Reynolds
number, Re ranging from 80000 to 120000, Prandtl Number, Pr of
0.73, Pitch Ratios, PR of 1,2,3,4,5 based on the hydraulic diameter of
the channel, hydrodynamic entry length, thermal entry length and the
test section. Ansys Fluent 15.0 software has been used to solve the
flow field. Study reveals that circular pipe having baffles has a higher
Nusselt number and friction factor compared to the smooth circular
pipe without baffles. Maximum Nusselt number and friction factor
are obtained for the PR=5 and PR=1 respectively. Nusselt number
increases while pitch ratio increases in the range of study; however,
friction factor also decreases up to PR 3 and after which it becomes
almost constant up to PR 5. Thermal enhancement factor increases
with increasing pitch ratio but with slightly decreasing Reynolds
number in the range of study and becomes almost constant at higher
Reynolds number. The computational results reveal that optimum
thermal enhancement factor of 900 inline hemispherical baffle is
about 1.23 for pitch ratio 5 at Reynolds number 120000.It also shows
that the optimum pitch ratio for which the baffles can be installed in
such very high turbulent flows should be 5. Results show that pitch
ratio and Reynolds number play an important role on both fluid flow
and heat transfer characteristics.
Abstract: Flows developed between two parallel disks have
many engineering applications. Two types of non-swirling flows can
be generated in such a domain. One is purely source flow in disc type
domain (outward flow). Other is purely sink flow in disc type domain
(inward flow). This situation often appears in some turbo machinery
components such as air bearings, heat exchanger, radial diffuser,
vortex gyroscope, disc valves, and viscosity meters. The main goal of
this paper is to show the mesh convergence, because mesh
convergence saves time, and economical to run and increase the
efficiency of modeling for both sink and source flow. Then flow field
is resolved using a very fine mesh near-wall, using enhanced wall
treatment. After that we are going to compare this flow using
standard k-epsilon, RNG k-epsilon turbulence models. Lastly
compare some experimental data with numerical solution for sink
flow. The good agreement of numerical solution with the
experimental works validates the current modeling.
Abstract: Due to adverse pressure gradient along the diverging
walls of wide-angled diffusers, the attached flow separates from
one wall and remains attached permanently to the other wall in a
process called stalling. Stalled diffusers render the whole fluid flow
system, in which they are part of, very inefficient. There is then an
engineering need to try to understand the whole process of diffuser
stall if any meaningful attempts to improve on diffuser efficiency
are to be made. In this regard, this paper provides a data bank
contribution for the mean flow-field in wide-angled diffusers where
the complete velocity and static pressure fields, and pressure recovery
data for diffusers in the fully stalled flow regime are experimentally
measured. The measurements were carried out at Reynolds numbers
between 1.07×105 and 2.14×105 based on inlet hydraulic diameter
and centreline velocity for diffusers whose divergence angles were
between 30Ôùª and 50Ôùª. Variation of Reynolds number did not significantly
affect the velocity and static pressure profiles. The wall static
pressure recovery was found to be more sensitive to changes in the
Reynolds number. By increasing the velocity from 10 m/s to 20 m/s,
the wall static pressure recovery increased by 8.31%. However, as the
divergence angle was increased, a similar increase in the Reynolds
number resulted in a higher percentage increase in pressure recovery.
Experimental results showed that regardless of the wall to which
the flow was attached, both the velocity and pressure fields were
replicated with discrepancies below 2%.
Abstract: In recent five decades, textured yarns of polyester fiber produced by false twist method are the most
important and mass-produced manmade fibers. There are
many parameters of cross section which affect the physical and mechanical properties of textured yarns. These parameters
are surface area, perimeter, equivalent diameter, large
diameter, small diameter, convexity, stiffness, eccentricity, and hydraulic diameter. These parameters were evaluated by
digital image processing techniques. To find trends between production criteria and evaluated parameters of cross section, three criteria of production line have been adjusted and different types of yarns were produced. These criteria are
temperature, drafting ratio, and D/Y ratio. Finally the relations between production criteria and cross section parameters were
considered. The results showed that the presented technique can recognize and measure the parameters of fiber cross section in acceptable accuracy. Also, the optimum condition
of adjustments has been estimated from results of image analysis evaluation.
Abstract: In order to investigate a PROX microreactor
performance, two-dimensional modeling of the reacting flow
between two parallel plates is performed through a finite volume
method using an improved SIMPLE algorithm. A three-step surface
kinetics including hydrogen oxidation, carbon monoxide oxidation
and water-gas shift reaction is applied for a Pt-Fe/γ-Al2O3 catalyst
and operating temperatures of about 100ºC. Flow pattern, pressure
field, temperature distribution, and mole fractions of species are
found in the whole domain for all cases. Also, the required reactive
length for removing carbon monoxide from about 2% to less than 10
ppm is found. Furthermore, effects of hydraulic diameter, wall
temperature, and inlet mole fraction of air and water are investigated
by considering carbon monoxide selectivity and conversion. It is
found that air and water addition may improve the performance of
the microreactor in carbon monoxide removal in such operating
conditions; this is in agreement with the pervious published results.