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Research interests
Two phase flow and heat transfer. Flow boiling
phenomena, two-phase flow in evaporator, condenser and capillary tube
expansion devices, heat driven pump and pulsating heat pipe for electronic cooling.
Micro-scale heat transfer and fluid flow. Two-fluid electroosmotic
pump for non-conducting fluid, electroosmotic
control of the interface between two fluids in microchannels
and flow switching in microfluidic devices.
Patent/Invention
- Ooi K.T., Yang Chun,
Charles, Wong T.N., Huang X.Y., Marcos, Kang Yue Jun,
2004, Electrokinetic Actuator, US provisional
patent 60/520, 643 (full patent pending)
- Wong
T.N., Nguyen N.T., Yang Chun, Charles,
Chai, J. C., Ooi K.T., Wang Cheng, Gao Yandong, 2004, Multi-sample electrokinetic
flow switch, US provisional patent 60/618, 603 (full patent pending)
Current Research (1)
Active
Control of Hydrodynamic Spreading in Microchannels
We propose a novel concept to
control the interface location of a pressure driven multi-phase flow in a microchannel by using electroosmotic
effects as shown in Fig 1. For the two-liquids, one liquid is a conducting
liquid with high EO mobility and another is nonconducting
with a low EO mobility liquid. When an externally electric field is applied
across the conducting liquid, electroosmotic forces
will be generated and the velocity of the conducting liquid can be regulated
depending on the direction and strength of the applied electric field.
Fig. 1: Schematic representation of
the H-shape microchannel.
By adjusting the applied electric
field, the interface position can be precisely controlled. Analytical
formulas for the interface position as a function of the ratio of the input
flow rates, the ratio of the shear viscosities, the aspect ratio of the
channel, the applied electric field and concentration of the conducting
liquid are determined.
Numerical Simulation
In
numerical work, we simulate two immiscible liquids or two immiscible liquids
with low diffusivity: a high EO mobility liquid at the bottom section and a
low EO liquid at the upper section of the channel as shown in Fig.2. When an
electric flied is applied across the channel, two liquids are driven both by
the pressure and the electroosmosis effects. The
flow of the two-liquid depends on the viscosity ratio, external electric
field, electroosmotic characters of the high EO
mobility liquid and the interfacial curvature between them. A finite volume
method is used to solve the coupled electric potential equation and Navier-Stokes equation together. The level set method is
used to capture the two liquids interface.
Figs. 3 and 4 show the evolutions of the interface and
velocity profiles at the outlet for the three different applied electric
fields when the viscosity ratio m2/m1 = 10. Since liquid 2 is more
viscous, to achieve the same volumetric flowrates,
the more viscous fluid has to spread to a large portion as compare to the
case when m2/m1 = 1. The results further indicate
that by adjusting the magnitude and direction of electric field, electroosmosis effect can be used to control the
interface location of a pressure driven flow in microfluidics
channels.
The velocities of two liquids can be considered as a linear
combination of the electroosmotic flow and a
pressure driven flow. In the cases of adversely applied electric field, the electroosmotic flow works against the pressure driven
flow. Depending on the magnitude of the electric fields, reverse flow occurs
when the electroosmotic force is strong enough as
shown.
The simulations are performed for a specified inlet flowrate conditions and the electroosmotic
forces are applied locally. The simulation results demonstrate the interface
locations of a pressure-driven two-liquid flow in a microchannel
can be controlled by using the electroosmotic flow
effects. This concept has potential application for switching and cell
sorting in bioanalytical systems.
References
(1)
Wong T.N., Nguyen N.T., Yang Chun, Charles, Chai, J. C., Ooi K.T., Wang
Cheng, Gao Yandong, 2004, Multi-sample
electrokinetic flow switch, US provisional
patent 60/618, 603 (full patent
pending)
(2)
Yandong Gao, Wong T.N., Chai, J. C., C.
Yang, Ooi K.T., 2005, Numerical Simulation of Two-Fluid Electroosmotic
Flow in Microchannels, International Journal of
Heat and Mass Transfer, 48, pp 5103-5111
Figure 2: Schematic of two-liquid electroosmotic between parallel plates
Figure 3: The interface profiles
along x/H for m2/m1 = 10
Figure 4: The velocity profiles at
outlet for m2/m1 = 10
Current Research
(2)
Two-Liquid Electroosmotic Pump For Low EO
Mobility Liquid
To induce electroosmosis, the working liquid is required to be a
polar liquid with significant electrical conductivity which is called high EO
mobility liquid. Low EO mobility liquid such as oil cannot be pumped using
the electroosmotic effects due to the low
electrical conductivity. On the other hand, in some biochemical analysis, the
electroosmotic flow (EOF) pumps may not be suitable
to be used directly with the water solutions. This is because that the
voltage applied to the solutions can lead to undesirable problems such as the
electrochemical decomposition of the solute, the fluctuation of the pH of the
buffer solution and the generation of gases. In order to drive low EO
mobility liquids and avoid the above mentioned problems, we developed
theoretical and numerical models to for the two fluids electroosmotic
pump.
This electroosmotic pump consists of two immiscible liquids or
two miscible liquids with low diffusivity: a high EO mobility liquid at the
bottom section and a low EO liquid at the upper section of the channel as
shown in Fig.1. When an electric field is applied across the high EO mobility
liquid, the liquid will be driven by electroosmosis,
which drags the low EO mobility liquid by the hydrodynamic shear force. The
flow of the two liquids depends on the viscosity ratio, the strength of the
external electric field, electroosmotic
characteristics of the high EO mobility liquid and the interfacial curvature
between them. Through this way, the low EO mobility liquid is delivered by electroosmosis. The flow due to this pumping technique is
termed as two-liquid electroosmotic flow.
An obvious
difference between the liquid-liquid interfaces from those of the liquid-wall
is that the interfaces between the two liquids are not stationary. The
external electric intensity interacts with the free charges at the interface
to generate a surface force. Because the solid wall remains stationary, this
force is ignored in the analysis of single fluid electroosmotic
flow. For the two-liquid electroosmotic system,
however, this surface force is significant and has to be taken into account.
In this work, the transient aspects of two-liquid electroosmotic
flow considering the free charges at the interface are analytically studied
to investigate the characteristics of such two-liquid flow system.
The
interface between the two liquids is described as a dividing surface, which
has the ‘excess’ surface charge density. An analytical solution of the
Poisson-Boltzmann equation under the Debye-Hückel linear approximate is presented. Using Laplace transform, the exact
solutions of the velocities and flow rates are obtained for Navier-Stokes equation governing this two-liquid flow.
Fig. 2
shows the 3-D time evolution of the velocity profiles for the two-liquid electroosmotic flow due to the combined effects of the
driving forces within the EDL regions of the high EO mobility liquid and the
force exerted on the interface. The kinematic
viscosity ratio is α=1.5 and
the dynamic viscosity ratio is β=1.
It can be seen that upon the application of the electric field, the flow is
activated in regions close to the channel walls and the interface. The
velocity of the high EO mobility liquid increases from zero in the same
direction within the EDL regions close to the walls and the interface. But
the effects of the force from the free charges of the interface cause the
interface velocity to increase rapidly in the opposite direction. This is
because the interface charges are equal to the total net charges within the
EDL regions, close to the interface. The velocity at the interface region is
significantly influenced by the surface force during the initial transient
state. As time elapses, the liquid inside the EDLs
exerts a hydrodynamic shear stress on its adjacent liquid; the liquid outside
the EDL regions may be considered as 'passive' flow caused by shear viscous
forces.
The surface
free charge density at the interface is directly related to the interface
zeta potential, ζ3. The free charges at the interface
influences the local net charge distribution in the region close to the
interface, hence the driving force within the EDL regions. On other hand, the
interaction between this surface free charge density and the externally
applied electric field generates a force at the interface. Because of the
opposite sign, this surface force at the interface act in the opposite
direction to the electroosmotic body force in the
EDL.
References
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(1) Gao Yandong, Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, Transient
two-liquid electroosmotic flow with electric
charges at the interface, Colloids and Surfaces A: Physicochemical and
Engineering Aspects, 266, pp 117-128
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(2) Gao Yandong, Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, Two-fluid electoosmotic flow in microchannel
, Journal of Colloid and Interfacial Science, Vol 284, pp306-314
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Figure 1: Schematic of
the two-liquid electroosmotic flow
Figure 2: Developing
process for two-liquid electroosmotic flow.
(a)  , (b)  , (c)  , (d) 
( ,  ,  ,  )
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JOURNALS PAPER
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1.
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Yali Zhang, Wong T.N.,
Yang Chun, Charles, Ooi K.T., 2006, Dynamic aspects of electroosmotic flow, Microfluidics
and Nanofluidics, 2, p205-214)
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2.
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Wang Cheng, Nguyen
N.T., Wong T.N., Wu Zhigang,
Yang Chun, Charles, Ooi K.T., 2006, Investigation of Active Interface
Control of Pressure Driven Two-Fluid Flow In Microchannels
, Sensors and Actuators A: Physical (Netherlands). (Accepted for
publication.)
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3.
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Wang Cheng, Nguyen
N.T., Wong T.N., 2006, Optical Measurement of Flow Field and
Concentration Field inside A Moving Nanoliter
Droplet, Sensors and Actuators A: Physical (Netherlands). (Accepted
for publication.)
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4.
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Wang Cheng, Nguyen
N.T., Wong T.N., Low Lee Ngo, Ho Soon Seng, 2006, A
Silicon/glass-based microfluidic device for invetigation of Lagrangian
velocity field in microdroplets, Journal of
Physics: Conference Series (United Kingdom), Vol. 34,
pp 130 - 135.
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5.
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Gao Y, Wong T.N., Yang Chun, Charles, Nguyen N.T.,
Ooi K.T., Wang Cheng, 2006, Theoretical investigation of two-fluid electroosmotic flow in microchannels,
Journal of Physics: Conference Series (United Kingdom), Vol. 34,
pp 470 - 474.
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6.
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Y.F. Yap, Chai, J.
C.,, Wong T.N., Toh K.C., 2006, The Effects of Surface Tension on
Two-Dimensional Two-Phase Stratified Flows, AIAA Journal of Thermophysics and Heat Transfer (United States).
(Accepted for publication.)
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7.
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Xu J.L., Wong
T.N., Huang X.Y., 2006, Two-fluid modeling for low pressure subcooled flow boiling, International Journal of
Heat and Mass Transfer (United
Kingdom), Vol
49, p377-386.
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8.
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Wang Cheng, Gao Yandong, Nguyen N.T., Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, An
experimental study of pressure-driven two-fluid flow in microchannel with electroosmosis
effect, Journal of Micromechanics and Microengineering
(United Kingdom).
Vol 15, No.12, p2289-2297
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9.
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Yandong Gao, Wong T.N.,
Chai, J. C., C. Yang, Ooi K.T., 2005, Numerical Simulation of Two-Fluid Electroosmotic Flow in Microchannels,
International Journal of Heat and Mass Transfer (United Kingdom). Vol 48, p5103-5111
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10.
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Xu J.L., Li Y.X., Wong
T.N., 2005, High speed flow visualization of a closed loop pulsating heat
pipe, International Journal of Heat and Mass Transfer (United Kingdom).
Vol 48, p3338-3351
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11.
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Y. F. Yap, Chai, J.C.,
Toh K.C., Wong T.N., Lam Y.C., 2005, Numerical Modeling of Unidirectional
Stratified Flow with and without Phase Change, International Journal of
Heat and Mass Transfer (United Kingdom) Vol
48, pp 477-486
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12.
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Gao Yandong, Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, Transient
two-liquid electroosmotic flow with electric
charges at the interface, Colloids and Surfaces A: Physicochemical and
Engineering Aspects (Netherlands). 266, p117-128
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13.
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Gao Yandong, Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, Two-fluid electoosmotic flow in microchannel
, Journal of Colloid and Interfacial Science, Vol 284, pp306-314
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14.
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Marcos, Y J Kang, Ooi
K.T., Yang Chun, Charles, Wong
T.N., 2005, Frequency dependent velocity and vorticity
fields ofelectroosmotic flow in a closed-end
cylindrical microchannel, Journal of
Micromechanics and Microengineering (United
Kingdom). Vol. 284, pp 306 – 314
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15.
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Zhang Yali, Wong T.N., Yang Chun, Charles, Ooi K.T., 2005, Elecroosmotic flow in irregular shape microchannels , International Journal of
Engineering Science (United
Kingdom), 43, p1450-1463)
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16.
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Marcos, Ooi K.T., Yang Chun, Charles, Chai, J. C.,, Wong T.N.,
2005, Developing electroosmotic flow in
closed-end microchannels, International Journal
of Engineering Science (United Kingdom), 43, p1349-1362)
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17.
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Y.F. Yap, Chai, J. C.,,
Toh K.C., Wong T.N., 2005, Modeling the Flows of Two Immiscible Fluids in
a Three-Dimensional Square Channel using the Level-Set Method, Numerical
Heat Transfer, Part A (United States), 48, p477-486
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18.
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Zhang H.Y., D.
Pinjala, Y.K. Joshi, Wong T.N., Toh K.C., 2005, Fluid Flow and heat
transfer in liquid cooled form heat sink for electronic packages, IEEE
Transactions on Components and Packaging Technology (United States),
Vol. 26, No. 2, pp 272 – 280
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19.
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Zhang H.Y., D. Pinjala,
Wong T.N., Y.K. Joshi, 2005, Development of liquid cooling techniques for
flip chip ball grid array packages with high flux heat dissipation, IEEE
Transactions on Components and Packaging Technology (United States) Vol 28,
No.1, p127-135
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20.
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Ma tingquan,
Ooi K.T., Wong T.N., 2005, Geometrical Optimization of Miniature Bare
Tube Heat Exchangers for process industries, Journal of Process
Mechanical Engineering (United Kingdom), Vol. 219, No. Imech Part E, pp 139 – 147
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21.
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H.Y. Zhang, D. Pinjala, Wong
T.N., Toh K.C., Y.K. Joshi, 2005, Single-phase liquid cooled microchannel heat sink for electronic packages, Applied
Thermal Engineering (United Kingdom), Vol. 25, pp 1472 – 1487.
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22.
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B.K. Tan, Wong T.N., Ooi K.T., 2005, Analytical
effective length study of a flat plate heat pipe using point source
approach, Applied Thermal Engineering (United Kingdom), Vol. 25,
No. 14-15, pp 2272 – 2284
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23.
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Marcos, Yang Chun,
Charles, Ooi K.T., Wong T.N., J.H. Masliyah,
2004, Frequency Dependent Laminar Electroosmotic
Flow in a Closed-End Rectangular Microchannel ,
Journal of Colloid and Interfacial Science, Vol. 275, pp 679 –
698.
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24.
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Xu J.L., Huang X.Y., Wong T.N., 2003, Study on
heat driven pump part 1: Experimental measurements, International
Journal of Heat and Mass Transfer (United Kingdom), Vol. 46,
pp 3329 – 3335.
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25.
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Xu J.L., Wong T.N., Huang X.Y., 2003, Study on
heat driven pump part 2: Mathematical modeling, International Journal
of Heat and Mass Transfer (United Kingdom), Vol. 46, pp 3337 – 3347.
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26.
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Marcos, Yang Chun,
Charles, Wong T.N., Ooi K.T., 2004, Dynamic Aspects of Electroosmotic Flow in Rectangular Microchannels, International Journal of
Engineering Science (United
Kingdom). Vol
42, pp 1459-1481
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27.
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Yang Chun, Charles, Wong T.N., Leu Yen
Ling, Ooi K.T., Chai, J. C.,, 2003, Characterization of Electroosmotic Flow in Microchannels,
International Journal of Computational Engineering Science (United
Kingdom) Vol
4, No.2, pp 273-276
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28.
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Ooi K.T., Yang Chun,
Charles, Chai, J. C.,, Wong T.N., Ang Pau Hwee, 2003, Effects of Electric Double Layer and
Viscous Dissipation on LiquidFlow in a Microcapillary, International Journal of
Computational Engineering Science (United Kingdom) Vol 4,
No.2, pp 243-247
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29.
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Chong Sh Hua, Ooi
K.T., Wong T.N., 2002, Optimisation of singale and double layer counter flow microchannel heat sinks, Applied Thermal
Engineering (United Kingdom), Vol. 22, No. (2002), pp 1569 - 1585.
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30.
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Tong B Y, Wong T.N., Ooi K.T., 2001, Closed loop
pulsating heat pipe, Applied Thermal Engineering (United Kingdom),
Vol. 21, pp 1845 – 1862
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31.
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Liang S.Y. ,
Wong T.N., Nathan G.K., 2001, Numerical and experimental studies of
refrigerant circuitry of evaporator coils, International Journal of
Refrigeration (United
Kingdom), Vol. 24, pp 823 - 833.
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32.
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Liang S M, Wong T.N., 2001, Numerical modeling
of two-phase refrigerant flow through adiabatic capillary tubes, Applied
Thermal Engineering (United
Kingdom), Vol. 21, pp 1035 - 1048.
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33.
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Tan B.K., Huang X.Y., Wong T.N., Ooi K.T., 2000,
A study of multiple heat sources on a flat plate heat pipe using point
source approach, International Journal of Heat and Mass Transfer
(United Kingdom), Vol. 43, No. 20, pp 3755 - 3764.
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34.
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Xu B, Ooi K.T., Wong T.N., Liu C.Y., 2000, Study
on the viscosity of the liquid flowing im microgeometry, Journal of Micromechanics and Microengineering (United Kingdom), Vol. 9,
pp 377 - 384.
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35.
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Liang S Y, Wong T.N., Nathan G.K., 2000,
Comparison of one-dimensonal and
two-dimensional models for wet-surface fin efficiency of a plate-fin-tube
heat exchanger , Applied Thermal Engineering (United Kingdom),
Vol. 20, pp 941 - 962.
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36.
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Liang S.Y, Wong T.N., Nathan G K, 2000, Study of
refrigerant circuitry of condenser coils with exergy
destruction analysis, Applied Thermal Engineering (United Kingdom),
Vol. 20, pp 559 - 577.
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37.
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Xu B, Ooi K.T., Wong T.N., Choi
W K, 2000, Experimental investigation of flow friction for liquid flow in
microchannels, International Communications
in Heat and Mass Transfer (United Kingdom). Vol. 9, pp 377 - 384
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38.
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Liang S.Y., Wong T.N., Nathan G K, 1999,
Analytical study of evaporator coil in humid environment, Applied
Thermal Engineering (United
Kingdom), Vol. 19, pp 1129 - 1145.
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39.
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Wong T.N., Yau Yeow
Kheng, 1997, Flow patterns in two-phase air-water flow, International
Communications in Heat and Mass Transfer (United Kingdom), Vol. 24,
No. 1, pp 111 - 117.
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40.
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Ooi K.T., Wong T.N., 1997, A computer simulation
of a rotary compressor for house-hold refrigerators, Applied Thermal
Engineering (United
Kingdom), Vol. 17, No. 1, pp 65 -
78.
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41.
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Wong T.N., Ooi K.T., Zhu SP, 1996, A
calibration technique for a parallel-wire depth probe with conductivity
compensation, Experiments in Fluids (United States), Vol. 20,
pp 429 - 432
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42.
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Wong T.N., Ooi K.T., 1996, Adiabatic
capillary tube expansion device: A comparison of the homogeneous flow and
separated flow models, Applied Thermal Engineering (United Kingdom),
Vol. 16, No. 17, pp 625 - 634.
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43.
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Wong T.N., Ooi K.T., 1996, Evaluation of
capillary tube performance for CFC-12 and HFC-134a, International
Communications in Heat and Mass Transfer (United Kingdom), Vol. 23,
No. 7, pp 993 - 1001.
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44.
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Wong T.N., Ooi K.T., 1996, Performance of
a parallel-wire Depth probe, International Communications in Heat and
Mass Transfer (United
Kingdom), Vol. 23, No. 7, pp 1003
- 1009.
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45.
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Wong T.N., Ooi K.T., 1996, Capillary tube flow:
Theoretical modeling and flow assessment for CFC and non-CFC, AIRAH
Journal Australian Refrigeration, Air conditioning and Heating Journal
(Australia), Vol. 50, No. 9, pp 14 - 22.
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46.
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Wong T.N., Ooi K.T., 1995, Refrigerant flow in
capillary tube: An assessment of two-phase viscosity correlation on model
prediction, International Communications in Heat and Mass Transfer (United Kingdom),
Vol. 22, No. 4, pp 595 - 604.
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