Abstract: The present work is a numerical simulation of
nanofluids flow in a double pipe heat exchanger provided with
porous baffles. The hot nanofluid flows in the inner cylinder, whereas
the cold nanofluid circulates in the annular gap. The Darcy-
Brinkman-Forchheimer model is adopted to describe the flow in the
porous regions, and the governing equations with the appropriate
boundary conditions are solved by the finite volume method. The
results reveal that the addition of metallic nanoparticles enhances the
rate of heat transfer in comparison to conventional fluids but this
augmentation is accompanied by an increase in pressure drop. The
highest heat exchanger performances are obtained when
nanoparticles are added only to the cold fluid.
Abstract: the intension in this work is to investigate the effect of
different bending manifold pipes on engine performance for different
engine speed. Power, Torque, and BSFC were calculated and
presented to show the effect of varying bending pipes angles on them
for all cases considered. A special program used to carry out the
calculations. A simulation model for 4-cylinders spark ignition
engine with turbocharger has been built and calculated. The analysis
of the results shows that for 120o angle the torque increases about
40% at 3000 rpm and 25% at 4000 rpm without changing in fuel
consumption. For 90o angle the increment in torque is about 10 %.
For the same bending angle the increment in brake power is around
40% at 3000 rpm and 25% at 4000 rpm. The increment in fuel
consumption is about 12% for 60o and 30% for 90o between (6000-
7000) rpm.
Abstract: In this paper, a bond graph dynamic model for a valvecontrolled
hydraulic cylinder has been developed. A simplified bond
graph model of the inter-actuator interactions in a multi-cylinder
hydraulic system has also been presented. The overall bond graph
model of a valve-controlled hydraulic cylinder was developed by
combining the bond graph sub-models of the pump, spool valve and
the actuator using junction structures. Causality was then assigned
in order to obtain a computational model which could be simulated.
The causal bond graph model of the hydraulic cylinder was verified
by comparing the open loop state responses to those of an ODE
model which had been developed in literature based on the same
assumptions. The results were found to correlate very well both
in the shape of the curves, magnitude and the response times,
thus indicating that the developed model represents the hydraulic
dynamics of a valve-controlled cylinder. A simplified model for interactuator
interaction was presented by connecting an effort source with
constant pump pressure to the zero-junction from which the cylinders
in a multi-cylinder system are supplied with a constant pressure from
the pump. On simulating the state responses of the developed model
under different situations of cylinder operations, indicated that such
a simple model can be used to predict the inter-actuator interactions.
Abstract: Laminar natural-convective heat transfer from a
horizontal cylinder is studied by solving the Navier-Stokes and
energy equations using higher order compact scheme in cylindrical
polar coordinates. Results are obtained for Rayleigh numbers of 1,
10, 100 and 1000 for a Prandtl number of 0.7. The local Nusselt
number and mean Nusselt number are calculated and compared with
available experimental and theoretical results. Streamlines, vorticity -
lines and isotherms are plotted.
Abstract: Natural convection heat transfer from a heated
horizontal semi-circular cylinder (flat surface upward) has been
investigated for the following ranges of conditions; Grashof number,
and Prandtl number. The governing partial differential equations
(continuity, Navier-Stokes and energy equations) have been solved
numerically using a finite volume formulation. In addition, the role of
the type of the thermal boundary condition imposed at cylinder
surface, namely, constant wall temperature (CWT) and constant heat
flux (CHF) are explored. Natural convection heat transfer from a
heated horizontal semi-circular cylinder (flat surface upward) has
been investigated for the following ranges of conditions; Grashof
number, and Prandtl number, . The governing partial differential
equations (continuity, Navier-Stokes and energy equations) have
been solved numerically using a finite volume formulation. In
addition, the role of the type of the thermal boundary condition
imposed at cylinder surface, namely, constant wall temperature
(CWT) and constant heat flux (CHF) are explored. The resulting flow
and temperature fields are visualized in terms of the streamline and
isotherm patterns in the proximity of the cylinder. The flow remains
attached to the cylinder surface over the range of conditions spanned
here except that for and ; at these conditions, a separated flow
region is observed when the condition of the constant wall
temperature is prescribed on the surface of the cylinder. The heat
transfer characteristics are analyzed in terms of the local and average
Nusselt numbers. The maximum value of the local Nusselt number
always occurs at the corner points whereas it is found to be minimum
at the rear stagnation point on the flat surface. Overall, the average
Nusselt number increases with Grashof number and/ or Prandtl
number in accordance with the scaling considerations. The numerical
results are used to develop simple correlations as functions of
Grashof and Prandtl number thereby enabling the interpolation of the
present numerical results for the intermediate values of the Prandtl or
Grashof numbers for both thermal boundary conditions.
Abstract: A two-dimensional numerical simulation of crossflow
around four cylinders in an in-line rectangular configuration is
studied by using the lattice Boltzmann method (LBM). Special
attention is paid to the effect of the spacing between the cylinders.
The Reynolds number ( Re ) is chosen to be e 100 R = and the
spacing ratio L / D is set at 0.5, 1.5, 2.5, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0
and 10.0. Results show that, as in the case of four cylinders in an inline
rectangular configuration , flow fields show four different
features depending on the spacing (single square cylinder, stable
shielding flow, wiggling shielding flow and a vortex shedding flow)
are observed in this study. The effects of spacing ratio on physical
quantities such as mean drag coefficient, Strouhal number and rootmean-
square value of the drag and lift coefficients are also presented.
There is more than one shedding frequency at small spacing ratios.
The mean drag coefficients for downstream cylinders are less than
that of the single cylinder for all spacing ratios. The present results
using the LBM are compared with some existing experimental data
and numerical studies. The comparison shows that the LBM can
capture the characteristics of the bluff body flow reasonably well and
is a good tool for bluff body flow studies.
Abstract: One of the major disadvantages of the minimally
invasive surgery (MIS) is the lack of tactile feedback to the surgeon.
In order to identify and avoid any damage to the grasped complex
tissue by endoscopic graspers, it is important to measure the local
softness of tissue during MIS. One way to display the measured
softness to the surgeon is a graphical method. In this paper, a new
tactile sensor has been reported. The tactile sensor consists of an
array of four softness sensors, which are integrated into the jaws of a
modified commercial endoscopic grasper. Each individual softness
sensor consists of two piezoelectric polymer Polyvinylidene Fluoride
(PVDF) films, which are positioned below a rigid and a compliant
cylinder. The compliant cylinder is fabricated using a micro molding
technique. The combination of output voltages from PVDF films is
used to determine the softness of the grasped object. The theoretical
analysis of the sensor is also presented.
A method has been developed with the aim of reproducing the
tactile softness to the surgeon by using a graphical method. In this
approach, the proposed system, including the interfacing and the data
acquisition card, receives signals from the array of softness sensors.
After the signals are processed, the tactile information is displayed
by means of a color coding method. It is shown that the degrees of
softness of the grasped objects/tissues can be visually differentiated
and displayed on a monitor.
Abstract: Swedish truck industry is investigating the possibility
for implementing the use of Compacted Graphite Iron (CGI) in their
heavy duty diesel engines. Compared to the alloyed gray iron used
today, CGI has superior mechanical properties but not as good
machinability. Another issue that needs to be addressed when
implementing CGI is the inhomogeneous microstructure when the
cast component has different section thicknesses, as in cylinder
blocks. Thinner sections results in finer pearlite, in the material, with
higher strength. Therefore an investigation on its influence on
machinability was needed. This paper focuses on the effect that
interlamellar distance in pearlite has on CGI machinability and
material physical properties. The effect of pearlite content and
nodularity is also examined. The results showed that interlamellar
distance in pearlite did not have as large effect on the material
physical properties or machinability as pearlite content. The paper
also shows the difficulties of obtaining a homogeneous
microstructure in inhomogeneous workpieces.
Abstract: The fundamental aim of extended expansion concept is
to achieve higher work done which in turn leads to higher thermal
efficiency. This concept is compatible with the application of
turbocharger and LHR engine. The Low Heat Rejection engine was
developed by coating the piston crown, cylinder head inside with
valves and cylinder liner with partially stabilized zirconia coating of
0.5 mm thickness. Extended expansion in diesel engines is termed as
Miller cycle in which the expansion ratio is increased by reducing the
compression ratio by modifying the inlet cam for late inlet valve
closing. The specific fuel consumption reduces to an appreciable level
and the thermal efficiency of the extended expansion turbocharged
LHR engine is improved.
In this work, a thermodynamic model was formulated and
developed to simulate the LHR based extended expansion
turbocharged direct injection diesel engine. It includes a gas flow
model, a heat transfer model, and a two zone combustion model. Gas
exchange model is modified by incorporating the Miller cycle, by
delaying inlet valve closing timing which had resulted in considerable
improvement in thermal efficiency of turbocharged LHR engines. The
heat transfer model, calculates the convective and radiative heat
transfer between the gas and wall by taking into account of the
combustion chamber surface temperature swings. Using the two-zone
combustion model, the combustion parameters and the chemical
equilibrium compositions were determined. The chemical equilibrium
compositions were used to calculate the Nitric oxide formation rate by
assuming a modified Zeldovich mechanism. The accuracy of this
model is scrutinized against actual test results from the engine. The
factors which affect thermal efficiency and exhaust emissions were
deduced and their influences were discussed. In the final analysis it is
seen that there is an excellent agreement in all of these evaluations.
Abstract: The performance of Advection Upstream Splitting
Method AUSM schemes are evaluated against experimental flow
fields at different Mach numbers and results are compared with
experimental data of subsonic, supersonic and hypersonic flow fields.
The turbulent model used here is SST model by Menter. The
numerical predictions include lift coefficient, drag coefficient and
pitching moment coefficient at different mach numbers and angle of
attacks. This work describes a computational study undertaken to
compute the Aerodynamic characteristics of different air vehicles
configurations using a structured Navier-Stokes computational
technique. The CFD code bases on the idea of upwind scheme for the
convective (convective-moving) fluxes. CFD results for GLC305
airfoil and cone cylinder tail fined missile calculated on above
mentioned turbulence model are compared with the available data.
Wide ranges of Mach number from subsonic to hypersonic speeds are
simulated and results are compared. When the computation is done
by using viscous turbulence model the above mentioned coefficients
have a very good agreement with the experimental values. AUSM
scheme is very efficient in the regions of very high pressure gradients
like shock waves and discontinuities. The AUSM versions simulate
the all types of flows from lower subsonic to hypersonic flow without
oscillations.
Abstract: An accurate optimal design of laminated composite
structures may present considerable difficulties due to the complexity
and multi-modality of the functional design space. The Big Bang
– Big Crunch (BB-BC) optimization method is a relatively new
technique and has already proved to be a valuable tool for structural
optimization. In the present study the exceptional efficiency of the
method is demonstrated by an example of the lay-up optimization
of multilayered anisotropic cylinders based on a three-dimensional
elasticity solution. It is shown that, due to its simplicity and speed,
the BB-BC is much more efficient for this class of problems when
compared to the genetic algorithms.
Abstract: A numerical study is made of laminar, unsteady flow
behind a rotationally oscillating circular cylinder using a recently
developed higher order compact (HOC) scheme. The stream function
vorticity formulation of Navier-Stokes (N-S) equations in cylindrical
polar coordinates are considered as the governing equations. The
temporal behaviour of vortex formation and relevant streamline
patterns of the flow are scrutinized over broad ranges of two
externally specified parameters namely dimensionless forced
oscillating frequency Sf and dimensionless peak rotation rate αm for
the Reynolds-s number Re = 200. Excellent agreements are found
both qualitatively and quantitatively with the existing experimental
and standard numerical results.
Abstract: Fluid flow in cylinders of elliptic cross-section was investigated. Fluid used is Liquefied petroleum gas (LPG). LPG found in Nigeria contains majorly butane with percentages of propane. Commercial available code FLUENT which uses finite volume method was used to solve fluid flow governing equations. There has been little attention paid to fluid flow in cylindrical elliptic pipes. The present work aims to predict the LPG gas flow in cylindrical pipes of elliptic cross-section. Results of flow parameters of velocity and pressure distributions are presented. Results show that the pressure drop in elliptic pipes is higher than circular pipe of the same cross-sectional area. This is an important result as the pressure drop is related to the pump power needed to drive the flow. Results show that the velocity increases towards centre of the pipe as the flow moves downstream, and also increases towards the outlet of the pipe.
Abstract: The lecture represents significant advances in
understanding of the transfer processes mechanism in turbulent
separated flows. Based upon experimental data suggesting the
governing role of generated local pressure gradient that takes place in
the immediate vicinity of the wall in separated flow as a result of
intense instantaneous accelerations induced by large-scale vortex
flow structures similarity laws for mean velocity and temperature and
spectral characteristics and heat and mass transfer law for turbulent
separated flows have been developed. These laws are confirmed by
available experimental data. The results obtained were employed for
analysis of heat and mass transfer in some very complex processes
occurring in technological applications such as impinging jets, heat
transfer of cylinders in cross flow and in tube banks, packed beds
where processes manifest distinct properties which allow them to be
classified under turbulent separated flows. Many facts have got an
explanation for the first time.
Abstract: Axisymmetric vibration of an infinite Pyrocomposite
circular hollow cylinder made of inner and outer pyroelectric layer of
6mm-class bonded together by a Linear Elastic Material with Voids
(LEMV) layer is studied. The exact frequency equation is obtained
for the traction free surfaces with continuity condition at the
interfaces. Numerical results in the form of data and dispersion
curves for the first and second mode of the axisymmetric vibration of
the cylinder BaTio3 / Adhesive / BaTio3 by taking the Adhesive layer
as an existing Carbon Fibre Reinforced Polymer (CFRP) are
compared with a hypothetical LEMV layer with and without voids
and as well with a pyroelectric hollow cylinder. The damping is
analyzed through the imaginary parts of the complex frequencies.
Abstract: The concerns about clean environment and high oil
prices driving forces for the research on alternative fuels. The
research efforts directed towards improving the performance of C.I
engines using vegetable oil as fuel. The paper deals results of
performance of a four stroke, single cylinder C.I. engine by preheated
neat Karanja oil is done from 30
o
C to 100
o
C. The performance of the
engine was studied for a speed range between 1500 to 4000 rpm, with
the engine operated under full load conditions. The performance
parameters considered for comparing are brake specific fuel
consumption, thermal efficiency, brake power, Nox emission of the
engine. The engine offers lower thermal efficiency when it is
powered by preheated neat Karanja oil at higher speed. The power
developed and Nox emission increase with the increase in the fuel
inlet temperature and the specific fuel consumption is higher than
diesel fuel operation at all elevated fuel inlet temperature.
Abstract: The interaction between wakes of bluff body and
airfoil have profound influences on system performance in many
industrial applications, e.g., turbo-machinery and cooling fan. The
present work investigates the effect of configuration include; airfoil-s
angle of attack, transverse and inline spacing of the models, on
frequency behavior of the cylinder-s near-wake. The experiments
carried on under subcritical flow regime, using the hot-wire
anemometry (HWA). The relationship between the Strouhal numbers
and arrangements provide an insight into the global physical
processes of wake interaction and vortex shedding.
Abstract: This paper is concerned with propagation of thermoelastic longitudinal vibrations of an infinite circular cylinder, in the context of the linear theory of generalized thermoelasticity with two relaxation time parameters (Green and Lindsay theory). Three displacement potential functions are introduced to uncouple the equations of motion. The frequency equation, by using the traction free boundary conditions, is given in the form of a determinant involving Bessel functions. The roots of the frequency equation give the value of the characteristic circular frequency as function of the wave number. These roots, which correspond to various modes, are numerically computed and presented graphically for different values of the thermal relaxation times. It is found that the influences of the thermal relaxation times on the amplitudes of the elastic and thermal waves are remarkable. Also, it is shown in this study that the propagation of thermoelastic longitudinal vibrations based on the generalized thermoelasticity can differ significantly compared with the results under the classical formulation. A comparison of the results for the case with no thermal effects shows well agreement with some of the corresponding earlier results.
Abstract: Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann method at Reynolds number 150. The effects of upstream locations, downstream locations and blockage are investigated systematically. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The results had shown that the upstream, downstream and height of the computational domain are at least 7.5, 37.5 and 12 diameters of the cylinder, respectively.
Abstract: In this study, a semi-cylinder obstacle placed in a
channel is handled to determine the effect of flow and heat transfer
around the obstacle. Both faces of the semi-cylinder are used in the
numerical analysis. First, the front face of the semi-cylinder is stated
perpendicular to flow, than the rear face is placed. The study is
carried out numerically, by using commercial software ANSYS 11.0.
The well-known κ-ε model is applied as the turbulence model.
Reynolds number is in the range of 104 to 105 and air is assumed as
the flowing fluid. The results showed that, heat transfer increased
approximately 15 % in the front faze case, while it enhanced up to 28
% in the rear face case.