Abstract: The study explores the hybrid combination of Hydrodynamic Cavitation (HC) and Subcritical Wet Air Oxidation-based pretreatment of complex industrial effluent to enhance the biodegradability selectively (without major COD destruction) to facilitate subsequent enhanced downstream processing via anaerobic or aerobic biological treatment. Advanced oxidation based techniques can be less efficient as standalone options and a hybrid approach by combining Hydrodynamic Cavitation (HC), and Wet Air Oxidation (WAO) can lead to a synergistic effect since both the options are based on common free radical mechanism. The HC can be used for initial turbulence and generation of hotspots which can begin the free radical attack and this agitating mixture then can be subjected to less intense WAO since initial heat (to raise the activation energy) can be taken care by HC alone. Lab-scale venturi-based hydrodynamic cavitation and wet air oxidation reactor with biomethanated distillery wastewater (BMDWW) as a model effluent was examined for establishing the proof-of-concept. The results indicated that for a desirable biodegradability index (BOD: COD - BI) enhancement (up to 0.4), the Cavitation (standalone) pretreatment condition was: 5 bar and 88 min reaction time with a COD reduction of 36 % and BI enhancement of up to 0.27 (initial BI - 0.17). The optimum WAO condition (standalone) was: 150oC, 6 bar and 30 minutes with 31% COD reduction and 0.33 BI. The hybrid pretreatment (combined Cavitation + WAO) worked out to be 23.18 min HC (at 5 bar) followed by 30 min WAO at 150oC, 6 bar, at which around 50% COD was retained yielding a BI of 0.55. FTIR & NMR analysis of pretreated effluent indicated dissociation and/or reorientation of complex organic compounds in untreated effluent to simpler organic compounds post-pretreatment.
Abstract: This article presents a numerical analysis of a turbulent flow past DTMB 4119 marine propeller by the means of RANS approach; the propeller designed at David Taylor Model Basin in USA. The purpose of this study is to predict the hydrodynamic performance of the marine propeller, it aims also to compare the results obtained with the experiment carried out in open water tests; a periodical computational domain was created to reduce the unstructured mesh size generated. The standard kw turbulence model for the simulation is selected; the results were in a good agreement. Therefore, the errors were estimated respectively to 1.3% and 5.9% for KT and KQ.
Abstract: Liquid storage tanks have become widespread during the recent decades due to their extensive usage. Analysis of liquid containing tanks is known to be complex due to hydrodynamic force exerted on tank which makes the analysis a complex one. The objective of this research is to carry out analysis of liquid domain along with structural interaction for various geometries of circular tanks considering seismic effects. An attempt has been made to determine hydrodynamic pressure distribution on the tank wall considering impulsive and convective components of liquid mass. To get a better picture, a comparative study of Draft IS 1893 Part 2, ACI 350.3 and Eurocode 8 for Circular Shaped Tank has been performed. Further, the differences in the magnitude of shear and moment at base as obtained from static (IS 3370 IV) and dynamic (Draft IS 1892 Part 2) analysis of ground supported circular tank highlight the need for us to mature from the old code to a newer code, which is more accurate and reliable.
Abstract: The effectiveness of microchannels in enhancing heat
transfer has been demonstrated in the semiconductor industry. In
order to tap the microscale heat transfer effects into macro
geometries, overcoming the cost and technological constraints,
microscale passages were created in macro geometries machined
using conventional fabrication methods. A cylindrical insert was
placed within a pipe, and geometrical profiles were created on the
outer surface of the insert to enhance heat transfer under steady-state
single-phase liquid flow conditions. However, while heat transfer
coefficient values of above 10 kW/m2·K were achieved, the heat
transfer enhancement was accompanied by undesirable pressure drop
increment. Therefore, this study aims to address the high pressure
drop issue using Constructal theory, a universal design law for both
animate and inanimate systems. Two designs based on Constructal theory were developed to study
the effectiveness of Constructal features in reducing the pressure drop
increment as compared to parallel channels, which are commonly
found in microchannel fabrication. The hydrodynamic and heat
transfer performance for the Tree insert and Constructal fin (Cfin)
insert were studied using experimental methods, and the underlying
mechanisms were substantiated by numerical results. In technical
terms, the objective is to achieve at least comparable increment in
both heat transfer coefficient and pressure drop, if not higher
increment in the former parameter. Results show that the Tree insert improved the heat transfer
performance by more than 16 percent at low flow rates, as compared
to the Tree-parallel insert. However, the heat transfer enhancement
reduced to less than 5 percent at high Reynolds numbers. On the
other hand, the pressure drop increment stayed almost constant at 20
percent. This suggests that the Tree insert has better heat transfer
performance in the low Reynolds number region. More importantly,
the Cfin insert displayed improved heat transfer performance along
with favourable hydrodynamic performance, as compared to Cfinparallel
insert, at all flow rates in this study. At 2 L/min, the
enhancement of heat transfer was more than 30 percent, with 20
percent pressure drop increment, as compared to Cfin-parallel insert.
Furthermore, comparable increment in both heat transfer coefficient
and pressure drop was observed at 8 L/min. In other words, the Cfin
insert successfully achieved the objective of this study. Analysis of the results suggests that bifurcation of flows is
effective in reducing the increment in pressure drop relative to heat
transfer enhancement. Optimising the geometries of the Constructal
fins is therefore the potential future study in achieving a bigger stride
in energy efficiency at much lower costs.
Abstract: The exploitation of flow pulsation in micro- and
mini-channels is a potentially useful technique for enhancing cooling
of high-end photonics and electronics systems. It is thought that
pulsation alters the thickness of the hydrodynamic and thermal
boundary layers, and hence affects the overall thermal resistance
of the heat sink. Although the fluid mechanics and heat transfer
are inextricably linked, it can be useful to decouple the parameters
to better understand the mechanisms underlying any heat transfer
enhancement. Using two-dimensional, two-component particle image
velocimetry, the current work intends to characterize the heat transfer
mechanisms in pulsating flow with a mean Reynolds number of
48 by experimentally quantifying the hydrodynamics of a generic
liquid-cooled channel geometry. Flows circulated through the test
section by a gear pump are modulated using a controller to achieve
sinusoidal flow pulsations with Womersley numbers of 7.45 and
2.36 and an amplitude ratio of 0.75. It is found that the transient
characteristics of the measured velocity profiles are dependent on the
speed of oscillation, in accordance with the analytical solution for
flow in a rectangular channel. A large velocity overshoot is observed
close to the wall at high frequencies, resulting from the interaction
of near-wall viscous stresses and inertial effects of the main fluid
body. The steep velocity gradients at the wall are indicative of
augmented heat transfer, although the local flow reversal may reduce
the upstream temperature difference in heat transfer applications.
While unsteady effects remain evident at the lower frequency, the
annular effect subsides and retreats from the wall. The shear rate at
the wall is increased during the accelerating half-cycle and decreased
during deceleration compared to steady flow, suggesting that the flow
may experience both enhanced and diminished heat transfer during
a single period. Hence, the thickness of the hydrodynamic boundary
layer is reduced for positively moving flow during one half of the
pulsation cycle at the investigated frequencies. It is expected that the
size of the thermal boundary layer is similarly reduced during the
cycle, leading to intervals of heat transfer enhancement.
Abstract: Interaction between mixing and crystallization is often
ignored despite the fact that it affects almost every aspect of the
operation including nucleation, growth, and maintenance of the
crystal slurry. This is especially pronounced in multiple impeller
systems where flow complexity is increased. By choosing proper
mixing parameters, what closely depends on the knowledge of the
hydrodynamics in a mixing vessel, the process of batch cooling
crystallization may considerably be improved. The values that render
useful information when making this choice are mixing time and
power consumption. The predominant motivation for this work was
to investigate the extent to which radial dual impeller configuration
influences mixing time, power consumption and consequently the
values of metastable zone width and nucleation rate. In this research,
crystallization of borax was conducted in a 15 dm3 baffled batch
cooling crystallizer with an aspect ratio (H/T) of 1.3. Mixing was
performed using two straight blade turbines (4-SBT) mounted on the
same shaft that generated radial fluid flow. Experiments were
conducted at different values of N/NJS ratio (impeller speed/
minimum impeller speed for complete suspension), D/T ratio
(impeller diameter/crystallizer diameter), c/D ratio (lower impeller
off-bottom clearance/impeller diameter), and s/D ratio (spacing
between impellers/impeller diameter). Mother liquor was saturated at
30°C and was cooled at the rate of 6°C/h. Its concentration was
monitored in line by Na-ion selective electrode. From the values of
supersaturation that was monitored continuously over process time, it
was possible to determine the metastable zone width and
subsequently the nucleation rate using the Mersmann’s nucleation
criterion. For all applied dual impeller configurations, the mixing
time was determined by potentiometric method using a pulse
technique, while the power consumption was determined using a
torque meter produced by Himmelstein & Co. Results obtained in
this investigation show that dual impeller configuration significantly
influences the values of mixing time, power consumption as well as
the metastable zone width and nucleation rate. A special attention
should be addressed to the impeller spacing considering the flow
interaction that could be more or less pronounced depending on the
spacing value.
Abstract: Motion response of floating structures is of great
concern in marine engineering. Nonlinearity is an inherent property
of any floating bodies subjected to irregular waves. These floating
structures are continuously subjected to environmental loadings from
wave, current, wind etc. This can result in undesirable motions of the
vessel which may challenge the operability. For a floating body to
remain in its position, it should be able to induce a restoring force
when displaced. Mooring is provided to enable this restoring force.
This paper discusses the hydrodynamic performance and motion
characteristics of an 8 point spread mooring system applied to a pipe
laying barge operating in the West African sea. The modelling of the
barge is done using a computer aided-design (CAD) software
RHINOCEROS. Irregular waves are generated using a suitable wave
spectrum. Both frequency domain and time domain analysis is done.
Numerical simulations based on potential theory are carried out to
find the responses and hydrodynamic performance of the barge in
both free floating as well as moored conditions. Initially, potential
flow frequency domain analysis is done to obtain the Response
Amplitude Operator (RAO) which gives an idea about the structural
motion in free floating state. RAOs for different wave headings are
analyzed. In the following step, a time domain analysis is carried out
to obtain the responses of the structure in the moored condition. In
this study, wave induced motions are only taken into consideration.
Wind and current loads are ruled out and shall be included in further
studies. For the current study, 2000 seconds simulation is taken. The
results represent wave induced motion responses, mooring line
tensions and identify critical mooring lines.
Abstract: Journal bearings used in IC engines are prone to premature
failures and are likely to fail earlier than the rated life due to
highly impulsive and unstable operating conditions and frequent
starts/stops. Vibration signature extraction and wear debris analysis
techniques are prevalent in industry for condition monitoring of
rotary machinery. However, both techniques involve a great deal of
technical expertise, time, and cost. Limited literature is available on
the application of these techniques for fault detection in reciprocating
machinery, due to the complex nature of impact forces that
confounds the extraction of fault signals for vibration-based analysis
and wear prediction. In present study, a simulation model was developed to investigate
the bearing wear behaviour, resulting because of different operating
conditions, to complement the vibration analysis. In current
simulation, the dynamics of the engine was established first, based on
which the hydrodynamic journal bearing forces were evaluated by
numerical solution of the Reynold’s equation. In addition, the
essential outputs of interest in this study, critical to determine wear
rates are the tangential velocity and oil film thickness between the
journals and bearing sleeve, which if not maintained appropriately,
have a detrimental effect on the bearing performance. Archard’s wear prediction model was used in the simulation to
calculate the wear rate of bearings with specific location information
as all determinative parameters were obtained with reference to crank
rotation. Oil film thickness obtained from the model was used as a
criterion to determine if the lubrication is sufficient to prevent contact
between the journal and bearing thus causing accelerated wear. A
limiting value of 1 μm was used as the minimum oil film thickness
needed to prevent contact. The increased wear rate with growing
severity of operating conditions is analogous and comparable to the
rise in amplitude of the squared envelope of the referenced vibration
signals. Thus on one hand, the developed model demonstrated its
capability to explain wear behaviour and on the other hand it also
helps to establish a co-relation between wear based and vibration
based analysis. Therefore, the model provides a cost effective and
quick approach to predict the impending wear in IC engine bearings
under various operating conditions.
Abstract: The main purpose of this study is to assess the
sediment quality and potential ecological risk in marine sediments in
Gymea Bay located in south Sydney, Australia. A total of 32 surface
sediment samples were collected from the bay. Current track
trajectories and velocities have also been measured in the bay. The
resultant trace elements were compared with the adverse biological
effect values Effect Range Low (ERL) and Effect Range Median
(ERM) classifications. The results indicate that the average values of
chromium, arsenic, copper, zinc, and lead in surface sediments all
reveal low pollution levels and are below ERL and ERM values. The
highest concentrations of trace elements were found close to
discharge points and in the inner bay, and were linked with high
percentages of clay minerals, pyrite and organic matter, which can
play a significant role in trapping and accumulating these elements.
The lowest concentrations of trace elements were found to be on the
shoreline of the bay, which contained high percentages of sand
fractions. It is postulated that the fine particles and trace elements are
disturbed by currents and tides, then transported and deposited in
deeper areas. The current track velocities recorded in Gymea Bay had
the capability to transport fine particles and trace element pollution
within the bay. As a result, hydrodynamic measurements were able to
provide useful information and to help explain the distribution of
sedimentary particles and geochemical properties. This may lead to
knowledge transfer to other bay systems, including those in remote
areas. These activities can be conducted at a low cost, and are
therefore also transferrable to developing countries. The advent of
portable instruments to measure trace elements in the field has also
contributed to the development of these lower cost and easily applied
methodologies available for use in remote locations and low-cost
economies.
Abstract: A three-dimensional numerical simulation of flow
through mini and microchannels with designed roughness is
conducted here. The effect of the roughness height (surface
roughness), geometry, Reynolds number on the friction factor, and
Nusselt number is investigated. The study is carried out by
employing CFD software, CFX. Our work focuses on a water flow
inside a circular mini-channel of 1 mm and microchannels of 500 and
100 m in diameter. The speed entry varies from 0.1 m/s to 20 m/s.
The general trend can be observed that bigger sizes of roughness
element lead to higher flow resistance. It is found that the friction
factor increases in a nonlinear fashion with the increase in obstruction
height. Particularly, the effect of roughness can no longer be ignored
at relative roughness height higher than 3%. A significant increase in
Poiseuille number is detected for all configurations considered. The
same observation can be done for Nusselt number. The transition
zone between laminar and turbulent flow depends on the channel
diameter.
Abstract: In the present study, analysis of heat transfer is carried
out in the slip flow region for the fluid flowing between two parallel
plates by employing the asymmetric heat fluxes at surface of the
plates. The flow is assumed to be hydrodynamically and thermally
fully developed for the analysis. The second order velocity slip and
viscous dissipation effects are considered for the analysis. Closed
form expressions are obtained for the Nusselt number as a function of
Knudsen number and modified Brinkman number. The limiting
condition of the present prediction for Kn = 0, Kn2 = 0, and Brq1 = 0
is considered and found to agree well with other analytical results.
Abstract: The present study focused on the investigation of the
effects of roughness elements on heat transfer during natural
convection in a rectangular cavity using numerical technique.
Roughness elements were introduced on the bottom hot wall with a
normalized amplitude (A*/H) of 0.1. Thermal and hydrodynamic
behaviors were studied using computational method based on Lattice
Boltzmann method (LBM). Numerical studies were performed for a
laminar flow in the range of Rayleigh number (Ra) from 103 to 106
for a rectangular cavity of aspect ratio (L/H) 2.0 with a fluid of
Prandtl number (Pr) 1.0. The presence of the sinusoidal roughness
elements caused a minimum to maximum decrease in the heat
transfer as 7% to 17% respectively compared to smooth enclosure.
The results are presented for mean Nusselt number (Nu), isotherms
and streamlines.
Abstract: The hydrodynamic and thermal behaviors of fluid
flow in wavy microchannel are investigated numerically. Effects of
Reynolds number on the hydrodynamics and thermal behaviors are
investigated. Three cases of Reynolds number (580, 1244, and 1910)
are adopted in this study. It is found that the separation zone begin
appears when Reynolds number is greater than 1910 at the endsection
of the wave. Also it is found that dimensionless maximum
velocity at the mid-section of the wave decreases and becomes as a
turbulent behavior as Reynolds numbers increases. The maximum
temperature at the center line at the mid-section of the wave increases
as Reynolds number increases until it reaches the turbulent behavior
when Reynolds number is equal or greater than 1244, while this
behavior will be achieved at very high velocities at the end section of
the wave.
Abstract: This paper describes a sliding mode controller for
autonomous underwater vehicles (AUVs). The dynamic of AUV
model is highly nonlinear because of many factors, such as
hydrodynamic drag, damping, and lift forces, Coriolis and centripetal
forces, gravity and buoyancy forces, as well as forces from thruster.
To address these difficulties, a nonlinear sliding mode controller is
designed to approximate the nonlinear dynamics of AUV and
improve trajectory tracking. Moreover, the proposed controller can
profoundly attenuate the effects of uncertainties and external
disturbances in the closed-loop system. Using the Lyapunov theory
the boundedness of AUV tracking errors and the stability of the
proposed control system are also guaranteed. Numerical simulation
studies of an AUV are included to illustrate the effectiveness of the
presented approach.
Abstract: This paper presents a fully Lagrangian coupled
Fluid-Structure Interaction (FSI) solver for simulations of
fluid-structure interactions, which is based on the Moving Particle
Semi-implicit (MPS) method to solve the governing equations
corresponding to incompressible flows as well as elastic structures.
The developed solver is verified by reproducing the high velocity
impact loads of deformable thin wedges with three different materials
such as mild steel, aluminium and tin during water entry. The present
simulation results for aluminium are compared with analytical solution
derived from the hydrodynamic Wagner model and linear Wan’s
theory. And also, the impact pressure and strain on the water entry
wedge with three different materials, such as mild steel, aluminium
and tin, are simulated and the effects of hydro-elasticity are discussed.
Abstract: Method of combined teaching laws of classical
mechanics and hydrostatics in non-inertial reference frames for
undergraduate students is proposed. Pressure distribution in a liquid
(or gas) moving with acceleration is considered. Combined effect of
hydrostatic force and force of inertia on a body immersed in a liquid
can lead to paradoxical results, in a motion of pendulum in particular.
The body motion under Stokes force influence and forces in rotating
reference frames are investigated as well. Problems and difficulties in
student perceptions are analyzed.
Abstract: This paper presents modeling and simulation of
flexible robot in an underwater environment. The underwater
environment completely contrasts with ground or space environment.
The robot in an underwater situation is subjected to various dynamic
forces like buoyancy forces, hydrostatic and hydrodynamic forces.
The underwater robot is modeled as Rayleigh beam. The developed
model further allows estimating the deflection of tip in two
directions. The complete dynamics of the underwater robot is
analyzed, which is the main focus of this investigation. The control of
robot trajectory is not discussed in this paper. Simulation is
performed using Symbol Shakti software.
Abstract: Intermittent behavior near the boundary of phase
synchronization in the presence of noise is studied. In certain range of
the coupling parameter and noise intensity the intermittency of eyelet
and ring intermittencies is shown to take place. Main results are
illustrated using the example of two unidirectional coupled Rössler
systems. Similar behavior is shown to take place in two
hydrodynamical models of Pierce diode coupled unidirectional.
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: Using the quantum hydrodynamic (QHD) model the
nonlinear properties of ion-acoustic waves in are lativistically
degenerate quantum plasma is investigated by deriving a nonlinear
Spherical Kadomtsev–Petviashvili (SKP) equation using the
standard reductive perturbation method equation. It was found that
the electron degeneracy parameter significantly affects the linear
and nonlinear properties of ion-acoustic waves in quantum plasma.