RESEARCH PROJECTS
B-EXPRESS: a new bounded extremum PREserving strategy for convective schemes The indiscriminate application of the Convective Boundedness
Criterion (CBC) in all flow regions results in a new and subtle error that
leads to a significant reduction in accuracy at locations where extrema
(maxima or minima) with steep profiles are present. In this paper, a new
Bounded Extremum PREserving Strategy (B-EXPRESS) that addresses this issue
is presented. The new strategy is applied to the SMART and BSEVENTH schemes
to yield two new schemes denoted by B-EXPRESS-3 and B-EXPRESS-7, respectively.
These schemes are tested by solving four problems. Results obtained reveal
the B-EXPRESS-3 to greatly reduce the rate of attenuation in the levels
of the profiles and to be as accurate as the BSEVENTH scheme which, on
average, requires 540% more CPU time than the B-EXPRESS-3 scheme. Moreover,
the B-EXPRESS-7 scheme completely eliminated the attenuation in the levels
of the profiles while marginally increasing the CPU effort (3.43% on average)
over the BSEVENTH scheme. M. Darwish and F. Moukalled.
Numerical study of heat transfer augmentation of flow in corrugated channels The heat transport characteristics of supercritical flows
and modulated subcritical flows in periodic corrugated channels are investigated
numerically using the spectral element method. Computations are performed
in the Reynolds number range of 50-800, for corrugation angles of ¡
= 20° and ¡ = 30°, and for wall
spacing to periodicity length ratio of b/L = 0.15 and 0.23. Results on
the steady and time-dependent flow and temperature fields are presented.
The critical Reynolds number for onset of time-periodic, self-sustained
oscillatory state decreases with increasing corrugation angle and with
decreasing b/L ratio. The transport of heat and momentum due to the oscillatory
states in the channel are investigated. The heat transfer of the corrugated
channel increases as much as 120% when compared to straight parallel channel
at the same Reynolds number. An optimal geometrical ratio of b/L is also
found where a distinct maximum heat removal rate is obtained. At the low
mean Reynolds number flows, flow pulsation at frequencies close to the
natural frequency resulted in heat transfer augmentation by a factor of
2 over the non-pulsated flow. N. Ghaddar. (Supported by AUB URB.)
Numerical study of unsteady free convective heat transfer in an enclosure with varying heat fluxes Unsteady natural convection flow in a square enclosure with
one of the vertical walls heated and with the opposite vertical wall cooled
to a uniform temperature, the remaining walls being adiabatic, is being
numerically studied. The heat flux at the heated wall is spatially uniform
but will be, in general, varying periodically in a stepwise manner in time
or sinusoidally. The flow is laminar and two-dimensional. The numerical
method that will be used is the spectral element method. The spectral element
solver which will be adapted to implement time dependent boundary conditions.
The study will be performed for Prandtl number of 1 to a wide range of
dimensionless amplitudes and periods of heat flux variations. The work
will extend to investigate possibilities of resonance in natural. N.
Ghaddar. (Supported by AUB URB.)
Experimental study of a novel thermosyphonic magnetohydrodynamic generator A direct energy conversion from thermal to electrical will
be experimentally verified in using a thermosyphonic hydromagnetic closed
loop flow as an electrical generator. Magnetohydrodynamic (MHD) generators
are typically based on pressure driven electrically conducting liquid flow
in a channel passing between poles of a magnet. The generator in this work
differs in using thermosyphon driven motion in a bottom-heated closed loop,
thus eliminating the use of a pump while permitting operation at high temperatures.
A workable model of the generator is designed and built using liquid metal
mercury. Experimental work will also consider other fluids such as sea
water. The design calculations of the MHD generator and the range of parameters
involved are based on the analytical results obtained from previous work,
which allowed prediction of the optimal range of the magnetic field strength
as related to the driving temperature difference. N. Ghaddar, F. Chaaban,
and A. Nahle*. (Supported by AUB URB.)
Characterization of the breaking force of latex particle aggregates by micromanipulation The breaking force of single polyslatex aggregates has been
measured by micromanipulation. Aggregates were made by mixing primary particles
at their isoelectric point using a vortex mixer and Brownian motion respectively.
The aggregates made by the former method had a mean breaking force of 51
±
3 m N, whilst those by the latter had a mean
breaking force of 5.3 ± 0.5 m
N for samples taken at aggregation times of 20 min to 6 h. This clearly
demonstrates that the micromanipulation technique is suitable for characterizing
the breaking force of particle aggregates made under different aggregation
conditions, and that the way collisions of primary particles were created
had a significant impact on the breaking force of the formed aggregates.
Z.
Zhang*, M.L. Sisk*, H. Mashmoushy, and C.R. Thomas*.
Prediction of yeast cell-disruption efficiency during high-pressure homogenization High-pressure homogenization is widely used to achieve process-scale
cell-disruption. However, modeling and optimization of this unit operation
has been restricted by the lack of fundamental information available regarding
cell mechanical properties and their interaction with the homogenizer flow
field. In this study, the ultimate cell-wall tensions of two cultures of
a bakers’ yeast are determined from micromanipulation experiments combined
with a theoretical analysis. These ultimate cell-wall tensions are then
combined with previous calculations of the maximum dell-wall tensions produced
as a cell passes through a homogenizer valve. This results in the first
truly a priori predictions of homogenate cell size distributions,
and cell-disruption efficiency, following homogenization. Further work
is required to extrapolate the results obtained here (single pass, yeast
cells, valve-inlet region) to multiple passes, different microorganisms,
and different valve designs, and to improve the accuracy of the predictions.
A.R.
Kleinig*, H. Mashmoushy, A.P.J. Middelberg*, C.R. Thomas*,
and Z.
Zhang*.
Calibration characteristics of a three point probe and static tube in wet steam Total pressure tubes, yawmeters and static probes can be used
for measurements in droplet laden flows, e.g. mist and wet steam. But to
be successful it is important that when calibrating the instruments the
characteristics of the droplets be satisfactorily matched. Water droplets
formed by nucleation in the wet stages of steam turbines are very small
and difficult to reproduce under steady flow conditions. To produce wet
steam with realistic droplet sizes requires a supply of supercooled steam
that can be created under blow-down conditions by the equipment employed.
The calibration characteristics of a three point probe and static tube
in superheated and in wet steam are presented. F. Bakhtar*, andH.
Mashmoushy.
Micromanipulation studies of the mechanical properties of single corneocyte envelopes Mechanical strengths of single corneocyte envelopes taken
from six samples of human stratum corneum were measured by micromanipulation.
These samples were of corneocytes taken from superficial and deep skin
layers of two people (denoted SL and SB), and were further divided into
“fragile” (immature) and “resilient” (mature) types. The strength of each
corneocyte envelope was characterized by the stress required to cause the
maximum deformation of its envelope. The envelopes in the sample “SL-superficial
fragile” seemed to be significantly stronger than those in “SL-deep fragile”,
but both of them were much weaker than those in the corresponding “SL-resilient”
samples. However, envelopes in the sample “SB-superficial resilient” and
“SB-deep resilient” showed no significant differences in their strengths.
These results demonstrate that micromanipulation can be used to quantify
the mechanical properties of single corneocyte envelopes which should be
useful for the Industry. H. Mashmoushy, C. R. Thomas*, and
Z. Zhang*
Mechanical properties of latex aggregates Micromanipulation is a technique that has been developed to
directly measure the bursting strength and size of single animal and yeast
cells. Such measurements could be used to predict cell damage in bioreactors
and processing equipment. This novel method involves the use of an optical
fiber probe attached to a force transducer which measures the resistance
of a particle as it is being squeezed on a slide until it bursts. The resistance
to deformation is converted to a voltage readout and from this the probe
displacement in relation to particle deformation to bursting and bursting
force of the particle can be calculated. For latex particles aggregated
with 1M phosphate-citrate buffer at pH 3.8 the mean bursting force was
found to be 51 m N and the mean displacement
was 1.89 m m. M. L. Sisk*, H. Mashmoushy,
C.
M. MacFarlane*, Z. Zhang*, and C. R. Thomas*.
Natural convection in trapezoidal cavities with baffles mounted to their upper inclined planes A numerical investigation to study the effects of mounting
baffles to the upper inclined planes of trapezoidal cavities has been undertaken.
Two thermal boundary conditions are considered: (a) the vertical and upper
surfaces are heated while the lower surface is cooled (summer-like conditions);
(b) the lower surface is heated while the other surfaces are cooled (winter-like
conditions). For both boundary conditions, results obtained with air as
the working fluid, reveal a decrease in heat transfer in the presence of
baffles. In Winter-like conditions, convection starts to dominate at a
Rayleigh number much lower than that in summer-like conditions. Whereas
the rate of decrease in heat transfer increases as the baffle get closer
to the heated vertical wall for the bottom-cooled situation, it increases
as the baffle get closer to the symmetry-line for the bottom-heated case.
In general, this rate of decrease in heat transfer is higher with taller
baffles. F. Moukalled, and S. Acharya*.
A pressure-based high-resolution algorithm for fluid flow at all speeds A new finite volume-based solution procedure for predicting
viscous compressible and incompressible flows is presented. The technique
is equally applicable in the subsonic, transonic, and supersonic regimes.
Arbitrary geometry is easily and efficiently handled by formulating the
method on a non-orthogonal coordinate system with collocated variable using
Cartesian velocity components. Pressure is selected as a dependent variable
in preference to density because changes in pressure are significant at
all speeds as opposed to variations in density which become very small
at low Mach numbers. Furthermore, a high-resolution scheme is used in interpolating
density and convective fluxes to enhance the shock capturing property of
the algorithm. F. Moukalled and M. Darwish.
A unified formulation of the segregated class of algorithms for fluid flow at all speeds In this paper, the segregated SIMPLE algorithm and its variants
are reformulated, using a collocated variable approach, to predict fluid
flow at all speeds. In the formulation, a unified, compact, and easy to
understand notation is employed. The SIMPLE, SIMPLER, SIMPLEST, SIMPLEM,
SIMPLEC, SIMPLEX, PRIME, and PISO algorithms that are scattered in the
literature and appear to a non-versed CFD user as being unrelated, are
shown to share the same essence in their derivations and to be equally
applicable for the simulation of incompressible and compressible flows.
Moreover, the philosophies behind these algorithms in addition to their
similarities and differences are explained. F. Moukalled and M. Darwish.
Mixed convection heat transfer in concave and convex channels A numerical investigation of laminar mixed convection heat
transfer of air in concave and convex channels is presented. Six different
channel aspects ratios (R/L = 1.04, 1.25, 2.5, 5, 10, and ¥
) and five different values of Gr/Re2 (Gr/Re2=0,
0.1, 1, 3, 5) are considered. Results are displayed in terms of streamline
and isotherm plots, velocity and temperature profiles, and local and average
Nusselt number estimates. Numerical predictions reveal that compared to
straight channels of equal height, concave channels of low aspect ratio
have lower heat at relatively low values of Gr/Re2 and higher
heat transfer at high values of Gr/Re2. When compared to straight
channels of equal heated length, concave channels are always found to have
lower heat transfer and for all values of Gr/Re2. On the other
hand, predictions for convex channels revealed enhancement in heat transfer
compared to straight channels of equal height and/or equal heated length
for all values of Gr/Re2. F. Moukalled, A. Doughan,
and S. Acharya*.
A parametric study of mixed convection heat transfer in concave and convex channels Mixed convection heat transfer in channels with a heated curved
surface bounded by a vertical adiabatic wall has been studied numerically.
Two cases are considered: in the first case, the flow experiences a convex
curvature and an increasing cross-sectional flow area, while in the second
case, the flow experiences a concave curvature with a decreasing flow cross-section.
Results are obtained for various curvature ratios (R/L) of the concave/convex
wall, and compared with straight channels of equal heated lengths and equal
heights. For channels with a convex heated surface, separation is observed
near the heated surface at low values of Gr/Re2 and on the opposite
vertical wall at high values of Gr/Re2. For channels with concave
walls, separation is not observed, and considerably greater heat transfer
rates are obtained. The overall heat transfer on the concave surface is
always greater than a straight channel of equal height. F. Moukalled,
A. Doughan, and S. Acharya*.
Computer aided analysis of hydraulic pumps This paper describes PUMPS, a microcomputer-based, interactive,
and menu-driven software package for use as an educational tool by mechanical
engineering students in investigating and understanding hydraulic pumps.
The package is written in the Pascal computer language and runs on any
IBM PC, or compatible. The program can handle problems related to radial,
mixed, or axial flow hydraulic pumps by solving for any unknown variable
through a complete set of equations covering all pump installation. Furthermore,
the graphical utilities of the package allow the user to display diagrammatic
sketches of the pump, to employ some recommended charts, to draw velocity
triangles, and to plot pump and pipeline characteristic curves. The most
important feature of the program however, is its ability to plot the variation
of any variable versus any other one. Through this option, the package
guides the student in understanding the effects of varying design parameters
on the overall performance of the machine. F. Moukalled and A. Honein.
Entropy generation in heat engines The objective is to study the critical performance of the
class of power producing devices falling under the heat engine classification.
Particular attention is given to direct energy conversion devices such
as thermoelectric and thermionic systems. The physical and practical limits
on performance will be scrutinized. Entropy generation minimization will
guide the work. R.Y. Nuwayhid, and F. Moukalled. (Supported by URB.)
On entropy generation in thermoelectric devices In this paper, a comparison between the Entropy Generation
Minimization method and the Power Maximization technique is presented.
The assessment is performed by analyzing, as a typical example of direct
conversion heat engines, the thermoelectric generator. The effects of heat
leak and finite rate heat transfer on the performance of the generator,
which is modeled as a Carnot-like engine with internal irreversibilities,
are studied. Even though both methods lead to the same conclusions, the
entropy generation minimization method, when applied for such an inherently
irreversible device, is shown to be less straightforward then the power
maximization technique requiring careful accounting of the different sources
of irreversibilities. Moreover, the entropy generation versus efficiency
behavior of the generator reveals that efficiency at minimum entropy generation
and maximum efficiency are distinct. R.Y. Nuwayhid, F. Moukalled, N.
Noueihed.
Bakhtar, F.*, Mashmoushy, H., and Buckley, J. R.*, On the performance of a cascade of turbine rotor tip section blading in wet steam, Part 1: Generation of wet steam of prescribed droplet sizes. Proceedings Institution of Mechanical Engineers, 211 Part C (C7), 519-529, 1997. Bakhtar, F.*, Mashmoushy, H., and Jadayel, O.*, On the performance of a cascade of turbine rotor tip section blading in wet steam, Part 2: Surface pressure distributions. Proceedings Institution of Mechanical Engineers, 211 Part C (C7), 531-540, 1997. ———, On the performance of a cascade of turbine rotor tip section blading in wet steam, Part 3: wake traverses. Proceedings Institution of Mechanical Engineers, 211 Part C (C8), 639-648, 1997. Darwish, M., Diab, H., and Moukalled, F., An educational two-dimensional interactive dynamic grid generator. International Journal of Mechanical Engineering Education, 24 (4), 279-290, 1997 Darwish, M., and Moukalled, F., An efficient very high resolution scheme based on an adaptive-scheme strategy, Numerical Heat Transfer, Part B, 34, 191-213, 1998. Ghaddar, N., Numerical simulation of side-heated thermosyphonic loop placed in transverse magnetic field; the induced electric current. The International Journal for Numerical Methods in heat and Fluid Flow, 8 (7), 814-840, 1998. ———, Analytical model of thermal energy conversion to electrical energy via a thermosyphonic magnetohydrodynamic generator. International Journal of Engineering Sciences, 36 (7,8), 783-800, 1998. ———, Analytical model of a side-heated free convection loop placed in a transverse magnetic field. ASME Journal of Fluid Engineering, 120, 62-69, 1998. ———, Analytical model of induced electric current from a free-convection loop placed in a transverse magnetic field. International Journal of Heat and Mass transfer, 41 (8-9), 1075-1086, 1998. ———, Numerical simulation of a vertical thermosyphonic loop in a transverse magnetic field. Numerical Heat Transfer, 32 (2), 231-246, 1997. Ghaddar, N., and Bdeir, F., Performance of solar absorption systems for space cooling in Beirut. Renewable Energy Journal, 10 (4), 535-558, 1997. Ghaddar, N., and Bsat, A., Energy conservation of residential buildings in Beirut. International Journal of Energy Research, 32 (2), 523-546, 1998. Ghaddar, N., and Nasr, Y., Experimental study of refrigerant-charged heat pipe solar water heater. International Journal of Energy Research, 22 (7), 625-638, 1998. Mashmoushy, H., Kleinig*, A. R., Middelberg*, A. P. J., Zhang*, Z., and Thomas, C. R.*, Can we predict the breakage of yeast cells? CHEMECA 1996, 4, 117-121, 1996. Mashmoushy, H., Zhang*, Z., and Thomas*, C. R., Micromanipulation measurement of the mechanical properties of baker’s yeast cells. Biotechnology Techniques and Bioengineering Journal, 12 (12), 925-929, December 1998. Moukalled, F., and Acharya, S*., Buoyancy-induced heat transfer in partially divided trapezoidal cavities. Numerical Heat Transfer, Part A, 32, 787-810, 1997. Moukalled, F., and Darwish, M., A new bounded skew central difference scheme, Part I. Formulation and testing. Numerical Heat Transfer, Part B, 31 (1), 91-110, 1997. ———, A new bounded skew central difference, Part II. Application to natural convection in an eccentric cavity. Numerical Heat Transfer, Part B, 31 (1) 111-133, 1997. ———, A new family streamline-based very high resolution schemes. Numerical Heat Transfer, 32 (3), 299-320, 1997. ———, New family of adaptive very high resolution schemes. Numerical Heat Transfer, Part B, 34, 215-239, 1998. Moukalled, F., and Honein, A., Computer aided analysis of hydraulic reaction turbines. International Journal of Mechanical Engineering Education, 25 (2), 73-91, 1997. Najm, H.N.*, Azoury, P.H., Piasecki, M.*, Hydraulic ram analysis: a new look at an old problem. Proceedings Institution of Mechanical Engineers, 213 (Part A [A2]), 127-141, 1999. Nuwayhid, R.Y, and Moukalled, F., On the power and efficiency
of thermoelectric devices. In Recent Advances in Finite-Time Thermodynamics,
ed. Chih, N. et. al., Chap24. New York: Nova Science Publishing, 1999.
ABSTRACTS,
PRESENTATIONS AND PROCEEDINGS
Bakhtar, F.*, Mashmoushy, H. and Jadayel, O.*, Modeling of two-phase flows of steam in turbines. Published by Institute of Mechanical Engineering, following the 11th International Heat Transfer Conference, Kyongju, Korea, 23-28 August 1998. Blewett, J. M.*, Mashmoushy, H., Zhang, Z.*, and Thomas, C. R.*, Measurements of plant cells mechanical properties. Proceedings II, International Conference for Plant Biomechanics, Centre for Biomimetics, The University of Reading, U.K., 22-24, September 1997. ———, Measurement of plant cell mechanical properties using micromanipulation. In Plant Biomechanics: Conference Proceedings II Posters, ed. G. Jeronimidis and J. F. V. Vincent, Centre for Biomimetics: The University of Reading, 23-24, September 1997. Darwish, M., and Moukalled, F., An adaptive stencil very high resolution scheme. In the Proceedings of the Second LAAS International Conference on Computer Simulation, 560-567, 1997. ———, A strategy for preserving extrema in convective schemes. Accepted for presentation and publication at the IASTED International Conference on Modeling and Simulation to be held in Pittsburgh-USA, May 13-17, 439-443, 1998. Ghaddar, N., Analytical model of a novel turbulent thermosyphonic MHD electrical generator. Proceedings of the International Conference on Energy Research and Development (ICERD), 1174-1184, Kuwait, 1998. ———, A novel MHD electrical generator using turbulent hydromagnetic flow in a side-heated thermosyphonic loop. Proceedings of the 33rd Intersociety Energy Conversion Engineering Conference (IECED), 51, Colorado Springs CO, USA, August 2-6, 1998. ———, Numerical study of free convection loop placed in transverse magnetic field. Proceedings of the Second International Conference on Computer Simulation, 421-428, September, Beirut-Lebanon, 1997. ———, Numerical study of side-heated convection loop placed in transverse magnetic field. Proceedings of the Tenth International Conference on Numerical Methods in thermal problems, 115-126, University of Wales Swansea, Swansea, UK, July 1997. ———, Energy conservation measures of residential buildings in Beirut. UNDP and EDL Two-day Workshop on Reforms for the Efficient Use of Energy in Arab States, Beirut, Lebanon, September 16 & 17, 1998. ———, Inventory of greenhouse gas emissions from industrial sources in Lebanon. One-day Workshop Organized by the Ministry of Environment and UNDP on Climate Change and The First National Inventory of Greenhouse Gas Emissions, Beirut, Lebanon, May, 1998. ———, Solar energy applications and energy code of practice in residential buildings. The First International Symposium on Renewable Energy, LNCSR, Beirut, Lebanon, September 18, 1997. Ghaddar, N., and El-Hajj, A., Numerical study of heat transfer augmentation of supercritical flows and pulsating flows in corrugated channel. International Conference on Scientific Computations ICSC99, Beirut, Lebanon, 1999. Ghaddar, N., Nasr, Y., Refrigerant-charged heat pipe operated solar water heater. The First Conference and Exhibition on Industrial Research and Development in Lebanon, Beirut-Lebanon, October 9-12, 1997. Kleinig, A. R.*, Mashmoushy, H., Middelberg, A.P. J.*, Thomas, C. R.* and Zhang, Z.*, Predicting the breakage of yeast cells during high-pressure homogenization. The 10th International Biotechnology Symposium, Sydney, Australia, p134 (poster), 26-30 August 1996. Mashmoushy, H., Tang, S.*, MacFarlane, C. M.*, Zhang, Z.*, and Thomas, C. R.*, Fractal related mechanical properties of latex aggregates. Fluid Particles Interactions V., New Mexico, U.S.A., Program 4.3., May 1999. Moukalled, F., Doughan, A., and Acharya, S*, Mixed convection heat transfer in concave and convex channels. ASME-National Heat Transfer Conference, Baltimore, ASME-HTD, Vol. 346., Volume 8, edited by P.H. Oosthuizen, T.S. Chen, S. Acharya, B.F. Armly, and D.W. Pepper, August 1997. ———, Mixed convection in channels with concave and convex surfaces. (Paper # AJTE99/6192). 5th ASME/JSME Joint Thermal Engineering Conference, San Diego, California, March 15-19, 1999. Shiu, C.*, Mashmoushy, H., Zhang, Z.*, and Thomas, C. R.*,
Micromanipulation studies of bacterial cell strengths. Proceedings of
the 1998, IChemE Research Event in CM-ROM Records, U.K., 1348-1388,
1998.
El-Hajj, A., Numerical study of heat transfer augmentation of flow in corrugated channels, (1998). N. Ghaddar. Itani, A., A high resolution pressure-based algorithm for fluid flow at all speeds, (1998). F. Moukalled. Nasr, Y., Experimental study of refrigerant-charged heat pipe
solar collector, (1997). N. Ghaddar
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