Abstract: The flow pattern inside rectangular intake air duct of 300 MW lignite coal-fired power plant is investigated in order to analyze and reduce overall inlet system pressure drop. The system consists of the 45-degree inlet elbow, the flow instrument, the 90-degree mitered elbow and fans, respectively. The energy loss in each section can be determined by Bernoulli’s equation and ASHRAE standard table. Hence, computational fluid dynamics (CFD) is used in this study based on Navier-Stroke equation and the standard k-epsilon turbulence modeling. Input boundary condition is 175 kg/s mass flow rate inside the 11-m2 cross sectional duct. According to the inlet air flow rate, the Reynolds number of airstream is 2.7x106 (based on the hydraulic duct diameter), thus the flow behavior is turbulence. The numerical results are validated with the real operation data. It is found that the numerical result agrees well with the operating data, and dominant loss occurs at the flow rate measurement device. Normally, the air flow rate is measured by the airfoil and it gets high pressure drop inside the duct. To overcome this problem, the airfoil is planned to be replaced with the other type measuring instrument, such as the average pitot tube which generates low pressure drop of airstream. The numerical result in case of average pitot tube shows that the pressure drop inside the inlet airstream duct is decreased significantly. It should be noted that the energy consumption of inlet air system is reduced too.
Abstract: This numerical study investigates the travelling wave’s appearance and the behavior of Poiseuille-Rayleigh-Benard (PRB) flow induced in 3D thermosolutale mixed convection (TSMC) in horizontal rectangular channels. The governing equations are discretized by using a control volume method with third order Quick scheme in approximating the advection terms. Simpler algorithm is used to handle coupling between the momentum and continuity equations. To avoid the excessively high computer time, full approximation storage (FAS) with full multigrid (FMG) method is used to solve the problem. For a broad range of dimensionless controlling parameters, the contribution of this work is to analyzing the flow regimes of the steady longitudinal thermoconvective rolls (noted R//) for both thermal and mass transfer (TSMC). The transition from the opposed volume forces to cooperating ones, considerably affects the birth and the development of the longitudinal rolls. The heat and mass transfers distribution are also examined.
Abstract: The end panels of a large rectangular industrial duct,
which experience significant internal pressures, also experience
considerable transverse shear due to transfer of gravity loads to the
supports. The current design practice of such thin plate panels for
shear load is based on methods used for the design of plate girder
webs. The structural arrangements, the loadings and the resulting
behavior associated with the industrial duct end panels are, however,
significantly different from those of the web of a plate girder. The
large aspect ratio of the end panels gives rise to multiple bands of
tension fields, whereas the plate girder web design is based on one
tension field. In addition to shear, the industrial end panels are
subjected to internal pressure which in turn produces significant
membrane action. This paper reports a study which was undertaken
to review the current industrial analysis and design methods and to
propose a comprehensive method of designing industrial duct end
panels for shear resistance. In this investigation, a nonlinear finite element model was
developed to simulate the behavior of industrial duct end panel, along
with the associated edge stiffeners, subjected to transverse shear and
internal pressures. The model considered the geometric imperfections
and constitutive relations for steels. Six scale independent
dimensionless parameters that govern the behavior of such end panel
were identified and were then used in a parametric study. It was
concluded that the plate slenderness dominates the shear strength of
stockier end panels, and whereas, both the plate slenderness and the
aspect ratio influence the shear strength of slender end panels. Based
on these studies, this paper proposes design aids for estimating the
shear strength of rectangular duct end panels.
Abstract: In the present study, mixed convection in a horizontal
rectangular duct using Al2O3 is numerically investigated. The effects
of different Rayleigh number, Reynolds number and radiation on
flow and heat transfer characteristics are studied in detail. This study
covers Rayleigh number in the range of 2 × 10^6 ≤ Ra ≤ 2 × 10^7 and
Reynolds number in the range of 100 ≤ Re ≤ 1100. Results reveal that
the Nusselt number increases as Reynolds and Rayleigh numbers
increase. It is also found that the dimensionless temperature
distribution increases as Rayleigh number increases.
Abstract: This study comprehensively simulate the use of k-ε
model for predicting flow and heat transfer with measured flow field
data in a stationary duct with elucidates on the detailed physics
encountered in the fully developed flow region, and the sharp 180°
bend region. Among the major flow features predicted with accuracy
are flow transition at the entrance of the duct, the distribution of
mean and turbulent quantities in the developing, fully developed, and
sharp 180° bend, the development of secondary flows in the duct
cross-section and the sharp 180° bend, and heat transfer
augmentation. Turbulence intensities in the sharp 180° bend are
found to reach high values and local heat transfer comparisons show
that the heat transfer augmentation shifts towards the wall and along
the duct. Therefore, understanding of the unsteady heat transfer in
sharp 180° bends is important. The design and simulation are related
to concept of fluid mechanics, heat transfer and thermodynamics.
Simulation study has been conducted on the response of turbulent
flow in a rectangular duct in order to evaluate the heat transfer rate
along the small scale multiple rectangular duct