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Room 3 Tuesday, 9 February 2010
RCMeAe
SESSION 1Energy System10.30 - 12.00
Paper Code :111Title :State of the Art on Sorption Refrigeration: a Challenge and Prospect
Author :I Made Astina
Paper Code :219Title :
Author :
Thermal and Flow Characteristics of Water Based Mixture of Coconut Oil and Rich Mixture to be used as Secondary Refrigerant in Air Conditioning System
Y.S. Indartono, H. Usui, H. Suzuki, Y. Komoda, D. Mujahidin
FAME
Paper Code :110Title :Design and Non-Isentropic Performance Simulation of an Ejector Refrigeration
System Powered by Engine Coolant Water
Author :C. Meng, I M. Astina, P. S. Darmanto, H. Sato
Paper Code :122Title :Analytical Study Of The Transport Properties In Different Refrigerants That
Influence The Performance Of An Organic Rankine CycleAuthor :Prabowo, Mika Patayang, Meshack Otedo O.
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Room 3 Tuesday, 9 February 2010
RCMeAe
SESSION 2Energy System14.10 - 15.30
Paper Code :201Title :A Study Of Performance Of Engine Running On Bio Ethanol Fuel And It's
Effect On A Four Stroke Engine ComponentsAuthor :Yusuf Siahaya, Yustinus Edward K.M.
Paper Code :211Title :Influence of Injection Timing on Performance and Combustion of an IDI
engine fuelled with DME
Author :Kanit Wattanavichien
Paper Code :112Title :CFD Assessment of a Combined Ejector Performance Analysis Method
Applied with HCs Working Fluid
Author :S. Chan, A. Suwono, I M. Astina, P. S. Darmanto, H. Sato
Paper Code :215Title :Thermal Engineering Performance Evaluation of a Polymer Electrolyte
Membrane Fuel Cell Stack at Partial LoadAuthor :W.A.Najmi W.M., Rahim A. , M. Fairuz. R
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Room 3 Wednesday, 10 February 2010
About RC-MeAe 2010
Table of Contents
Schedule
Keynote Lectures
Paper List
Author List
RCMeAe
SESSION 1Energy System10.00 - 12.00
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Paper Code :220Title :Experimental Study on the Natural Convection Characteristic of AP1000 Passive
Containment Cooling SystemAuthor :Ari Darmawan Pasek, Yerri N. Kartiko, Daddy Setyawan, Efrison Umar, Aryadi Suwono
Paper Code :139Title :Optimization of Liquid Cooling System of Desktop Computer Through
Computational Fluid Dynamic Simulation
Author :M. Hamdi, W.J Loh, N. Farhanah
Paper Code :136Title :Investigation of higher cooling capacity PC processor heat sink Author :Abdurrachim H., Sutrisno
Paper Code :137Title :Study Of Heat Transfer In A Multihole Plate. Application For Cooling Combustor
Walls And Turbine Blades Of TurbomachineryAuthor :Nguyen Phu Hung, Eva Dorignac
Paper Code :114Title :Numerical Study of Natural Convection Air Cooling of a PEFC: Single Cell and
StackAuthor :A.P. Sasmito, E. Birgersson, K.W. Lum, A.S. Mujumdar
Paper Code :217Title :Simulation Analysis of 2 Stages CO2 Heat Pump Water Heater
Author :Pramote Laipradit, Wimonnad Charote, Kusuma Suntornprasert, Khanida Koupratoom
Room 3 Wednesday, 10 February 2010
RCMeAe
SESSION 2Energy System14.00 - 16.15
Paper Code :202Title :Mathematical Modelling of Combustion Rate Using Carbon Deposit On a Wastes
Bubbling Fluidized Bed ReactorAuthor :I Nyoman Suprapta Winaya
Paper Code :223Title :
Author :Yatna Yuwana Martawirya,Nathanael Panagung Tandian, Aries Karyadi
Preliminary Study Of Web-based Software Of Information System And Simulation For Components Of Kamojang Geothermal Power Plant
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Paper Code :221Title :Upgrading of Municipal Solid Waste as Solid Fuel to Subbituminous Coal Grade
by Torrefaction ProcessAuthor :Toto Hardianto, Amrul, Aryadi Suwono, Ari Darmawan Pasek
Paper Code :207Title :Design and Simulation of Combustor for Turbocharger Based Micro Gas Turbine
System Using LPG and BiogasAuthor :T. A. Fauzi Soelaiman, N. P. Tandian, R. Febrianda
Paper Code :334Title :Early Design Optimization In Hot Briquetting MachineAuthor :Asep Indra Komara, I Wayan Suweca
Paper Code :209
Title :Application of ejectors to closed-cycle OTEC and SOTEC powerplantsAuthor :Menandro Serrano Berana and Masafumi Nakagawa
Regional Conference on Mechanical and Aerospace Technology
Bali, February 9 – 10, 2010
112-1
CFD Assessment of a Combined Ejector Performance
Analysis Method Applied with HCs Working Fluid
Sarin Chan
(a,c), Aryadi Suwono
(a), I Made Astina
(a), Prihadi Setyo Darmanto
(a) ,
Haruki Sato(b)
(a) Mechanical Engineering Dept., Faculty of Mechanical and
Aerospace Engineering, Institut Teknologi Bandung,
Jl. Ganesha No. 10, Bandung 40132 INDONESIA
Tel: (62-22) 250 6447, Fax: (62-22) 253 4099
(b) Faculty of Science and Technology, Keio University,
3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522 JAPAN
Tel/Fax: (81-45) 566-1729, E-mail: [email protected]
(c) Mechanical and Industrial Dept, Institute of Technology of Cambodia,
Pochentong Boulevard, P.O. Box 86, Phnom Penh, CAMBODIA
E-mail: [email protected]
Abstract : This paper presents the results of using CFD method to study the
performance of an actual ejector operated with Propane. Referred to the CFD results, the
combined theoretical method is assessed. The absence of normal shock wave predicted by
the combined theoretical method is confirmed by CFD results. It is pointed out that the
efficiency values included by the theoretical method depend on fluid type and ejector
design. The combined theoretical method would be used in the preliminary studies of the
system performance with respect to large or new working candidates and wide range of
operating conditions. CFD studies would then be used to optimize the ejector design and
anticipate or troubleshoot the problems of the ejector.
Keywords : ejector, CFD, combined theoretical method, performance analysis
1. Introduction
A method based on a combination between
constant-area-ejector mixing theory and the so-
called shock-circle definition has been
implemented by our group in the analysis of
ejector refrigeration system [1,2]. The calculated
results are found to have good agreement with the
reported available experimental data of R-141b
and R-11, for both entrainment and compression
ratios. The method has been used in our previous
works to study the performance of simple and
novel ejector refrigeration cycles with various
HCs refrigerants. Interesting results suggest that
Propane appear to be the best refrigerant
especially for heat source temperatures lower than
95oC. As the method utilizes some empirical
constants, the calculation results must be assessed
when studying the fluid differed from the original
fluid when the method was being developed.
Available literatures reported the capability of
CFD analysis in dealing with the complex flows
inside ejector and providing good overall
performance prediction in all operating modes of
ejector [3-7]. The CFD method also takes into
account the complex effects of physical geometry
of ejector.
Zhu, et al. [3] established CFD models of their
actual ejector working with R-141b and
performed validation of the models with the
testing data. Three turbulent models were tested
and the results show that “RNG k- model” is the
best one describing the experimental data with
only 9.29% of maximum deviation. Seven data
points of different operating conditions were
compared. The authors also report the effects of
mixing section converging angle and the nozzle
exit position on the ejector performance based on
their extensive CFD testing results. The
comparisons of the CFD and the experiments of
supersonic air ejector were carried out by Hemidi,
et al. [8]. Good prediction of the entrainment
ratios by CFD calculation was confirmed and the
overall deviation was less than 10% for k- model.
Regional Conference on Mechanical and Aerospace Technology
Bali, February 9 – 10, 2010
112-2
The inconsistency of local flow feature of
different turbulent models was observed, however
the ejector performance indicator, entrainment
ratio, was still well reproduced. The studies on
steam ejectors were reported by some researchers
[9, 6, 10]. Based on the independent comparisons
with their respective measurements data, CFD
analysis is confirmed to be a reliable tool for
studying and troubleshooting the ejector
performance. The CFD method was also tested
with other fluids like R-141b and methanol.
Rusly, et al. [7] studied the performance of four
ejectors of Haung, et al. [11], using CFD
technique and they found that errors of calculated
entrainment ratio are less than 10%. Riffat, et al.
[12] reported their experimental results and the
CFD analysis for the ejector working with
methanol.
Due to the lack of experimental data, CFD
analysis will be used in this study to assess the
reliability of the combined theoretical method of
constant-area mixing theory and the shock-circle
definition, applied for hydrocarbons (HCs) as
working fluids.
2. Combined Theoretical Method
The schematic of an ejector which is the main and
dominating component in the ejector refrigeration
cycle is shown in Fig. 1. The high-pressure vapor
known as primary fluid is expanded through
converging-diverging nozzle where its pressure
energy is converted into kinetic energy. The flow
leaving the nozzle with supersonic velocity and
very low pressure, provoke the entrainment of
secondary fluid from suction chamber. In the
constant-area section, the two flows mix and then
the mixed flow may experience succession
shockwaves at the end of constant area section
depending on the flow condition and the
geometrical design of ejector. Finally, the mixed
flow is further decelerated in the diffuser and
pressure is further recovered after some pressure
recovery has happened in the constant area
section. In the unfavorable design, the normal
shockwave may happen in the diffuser.
To simplify the complex flow phenomena
happened inside the ejector, the following
assumptions are made:
1. The flows are one-dimensional (except at
first interaction section A-A),
compressible and steady inside adiabatic
wall
2. The flow velocities at the inlet of primary
nozzle and suction chamber; and at the
outlet of diffuser, are considered
negligible
3. Constant coefficients are used to account
for the losses
4. The primary and secondary fluids are
completely mixed at the end of constant-
area section.
Primary
flow
Constant area
sectionDiffuser
Secondary
flow
Discharged
mixed flow
A
A
Suction
chamber
Dpm
Dt
Dcax
r
Figure 1. Schematic Diagram of Ejector
Based on the assumptions, the analytical
equations derived from mass, momentum and
energy balances are determined for solving the
flow problem. The constant-area-ejector theory
describes the mixing of primary jet flow from the
nozzle and entrained secondary flow, as
undergone inside constant cross sectional tube.
Incorporating the mixing theory with the so-called
shock-circle definition by [13] which prescribes
the conditions at the mixing starting point, section
A-A, the coupled equations can be solved to
determine the ejector entrainment ratio and the
thermodynamic state at the discharged of ejector.
The detail information on the combined
theoretical method can be found in our previous
reports [2, 1].
3. Ejector Design
An actual ejector have been designed and
manufactured for the experimental study on the
performance of ejector refrigeration system. The
dimensions of the main ejector parts, including
nozzle throat diameter and the constant-area
section diameter were determined by our
combined analysis method. The input parameters
are the required cooling capacity and the design
operating condition. Other physical dimensions of
the ejector were chosen based on the survey of the
existing ejectors reported in available literatures.
Regional Conference on Mechanical and Aerospace Technology
Bali, February 9 – 10, 2010
112-3
The ejector has movable nozzle and the position
of the nozzle can be altered even the system is in
operation. The ejector was designed for Propane
at the operating condition of Tg=70oC, Tc=35
oC
and Te=5oC. The efficiency values used in the
calculation with the combined method are 0.95 for
primary nozzle, 1 for suction nozzle, 0.82 for
effective expended flow, 0.92 for constant-area
mixing section and 0.95 for the diffuser. The
above efficiency values were obtained from
experimental data of reference [11] which can be
reproduced by our combined analysis method
with relative error within 15% for entrainment
ratios and 5% for critical discharged temperature.
Figure 2. Actual Ejector Design
4. CFD Modeling
The ejector shown in Fig. 2 is modeled as 2D
asymmetric problem. The CFD commercial
package, including grid generator, Gambit 2.3 and
solver, Fluent 6.3, are used in this study. There are
approximately 46000 elements of structured
quadrilateral meshes used on the ejector model.
The grids are at highest density in the jet entrained
zone which is between nozzle outlet and the inlet
of constant-area section. The grid structure of
ejector model is shown in Fig. 3.
The pressure-based implicit solver is selected in
Fluent. The renormalization group (RNG) k-
turbulent model is applied with standard near wall
treatment. Pressure inlet is used for boundary
conditions of both primary and secondary fluids
inlets. For the ejector discharged condition,
pressure outlet boundary condition is used.
Density of fluid is assumed as ideal gas while
other fluid properties use temperature dependent
polynomial functions which were fitted to data
calculated from real-gas equation.
5. Results and Discussion
Figure 4 shows the COPs of simple ejector cycle
with different HCs. The results were calculated by
the combined theoretical analysis method with the
same values of efficiencies given in the previous
section. The calculated results are independent of
ejector size. According to the figure, among all
studied HCs fluids, Propane provides the highest
COP.
0
0.1
0.2
0.3
0.4
0.5C
OP
Tg= 80oC
Tc= 35oC
Te= 10oC
Figure 4. COPs of Simple Ejector Cycle with
Different HCs Working Fluids
The performance of Propane predicted by the
combined analysis method is very convincing, as
good COP can be achieved under low generator
temperature heat source. However, the results
could be misleading due to the fact that the
combined theoretical method uses the efficiency
values that were derived exclusively from data of
R-141b. Therefore, CFD analysis will be used to
assess the combined theoretical method for the
case of Propane.
Regional Conference on Mechanical and Aerospace Technology
Bali, February 9 – 10, 2010
112-4
GridFLUENT 6.3 (axi, dbns imp, ske)
Jan 25, 2010
Figure 3. Grid arrangement of ejector model
The size of ejector including nozzle and constant-
area section diameters are provided as input data
to the combined analysis method along with the
generator and evaporator temperatures. With this
input set, the entrainment ratio and the critical
back pressure are calculated. It should be notified
that the theoretical analysis method can only
calculate ejector performance parameters at the
critical point.
Contours of Mach NumberFLUENT 6.3 (axi, pbns, rngke)
Jan 26, 2010
2.12e+00
2.03e+00
1.95e+00
1.87e+00
1.79e+00
1.71e+00
1.63e+00
1.55e+00
1.46e+00
1.38e+00
1.30e+00
1.22e+00
1.14e+00
1.06e+00
9.76e-01
8.95e-01
8.14e-01
7.32e-01
6.51e-01
5.70e-01
4.88e-01
4.07e-01
3.25e-01
2.44e-01
1.63e-01
8.14e-02
6.15e-05
Figure 5. Contours of Mach number for Ejector
Operated at Critical Discharged Pressure
0
0.5
1
1.5
2
2.5
0 50 100 150 200
Ma
ch N
um
ber
Axial Position, mm
Figure 6. Mach number along the Center Line of
Ejector Operated at Critical Discharged Pressure
0
0.2
0.4
0.8 1 1.2 1.4 1.6 1.8E
ntr
ain
men
t R
ati
o
Ejector Discharged Pressure, MPa
Tg= 60oC
Tg= 70oC
Tg= 80oC
Te= 10oC
Figure 7. CFD results for Ejector Performance
According to Figs. 5 and 6, there are successive
shock waves occurring after the primary fluid
leaving the nozzle, however there is no normal
shock wave at the exit of constant-area section.
This behavior agrees well with the prediction of
the combined theoretical method.
Figure 7 shows the CFD results of the ejector
performance worked with Propane. Differed from
theoretical method, CFD can calculate the
performance of ejector in all operating modes.
This is an advantage of the numerical method
compared to the analytical approach.
The critical entrainment ratios and discharged
pressures of ejector for generator temperatures of
60, 70 and 80oC, and for evaporator temperature
of 10oC, resulted from the CFD analysis are listed
in Table 1.
The calculation results from the combined
theoretical analysis method are also listed in Table
1. The data of entrainment ratios from CFD and
the combined theoretical method have very
different values. In case of critical discharged
pressure, the calculated results from the two
methods are in better agreement.
Table 1. Calculated data of Ejector Critical
Entrainment Ratio and Discharged Pressure
Regional Conference on Mechanical and Aerospace Technology
Bali, February 9 – 10, 2010
112-5
Tg
[oC]
CFD Combined
Theoretical Method
µ Pc*
[MPa]
µ Pc*
[MPa]
60 0.31 1.053 0.49 1.119
70 0.26 1.277 0.33 1.283
80 0.16 1.569 0.20 1.483
Better agreement of the calculated entrainment
ratios from CFD and the combined theoretical
methods can be achieved by changing the
efficiency values used in the combined analysis
method. Based on the results, it confirms that the
efficiency values derived from the experimental
data of R-141b ejectors would not valid for all
working fluids and ejectors. Besides working
fluid, the ejector design also contributes to the
value of efficiencies.
6. Conclusion
The CFD model of an actual ejector have been
created and analyzed to determine the
performance parameters including critical
entrainment ratio and discharged pressure of the
ejector. The CFD results of the ejector worked
with Propane are used to assess the combined
theoretical method. Concerning to the flow
situation at the exit of constant-area section when
the ejector operated at critical discharged
pressure, the combined theoretical method well
predicts that there is no normal shock as the flow
is already subsonic. This behavior is confirmed by
the CFD results. The theoretical method has
strong dependency on the values of efficiency
used for representing the losses occurred in the
components of ejector. The efficiency values
should be different for different working fluid and
ejector design. More rational values of the
efficiencies with respect to fluid in use and ejector
design are required. Because CFD analysis is very
time consuming, the reliable theoretical analysis
method should be used in the preliminary studies
of ejector system performances with large amount
of working fluids and operating conditions to
narrow down the working fluids candidates and
good operating conditions. The CFD should be
applied to have better performance prediction
incorporating with the effects geometric
parameters which are vital for the actual ejector
design.
Acknowledgement
The authors are grateful to the AUN/SEED-net
program and the Global COE program of Keio
University for supporting this study.
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