DATE: 2019.05 - Computational analysis of a vortex tube - Developing boundary conditions for heat transfer analysis - CAD by creating a suitable model for heat transfer analysis - CFD analysis by using ANSYS FLUENT - Literature survey for recent academic studies ABSTRACT: Vortex tubes are simple and common devices which separates a high-pressure gas flow as two different lower gas flows. One of the outlets has a higher temperature than the inlet high pressure gas and other outlet has lower. Most common types of the vortex tubes are counter and parallel flow types. In counter flow type vortex tubes the cold and hot outlets are on opposite sides and in parallel flow type both the outlets are on the same side. Since it is a simple, well known, compact, portable, highly reliable and has a few initial costs, it could be desirable for the specific heating or cooling and refrigeration applications.

1. Vortex Tube Usage in Cooling and Liquification Process of Excess Gases in
Gheothermal Energy Plants: A Computational Study
A.B. Karsan, D.A. Yılmaz, S. Baykul
Department of Mechanical Engineering, Middle East Technical University
Abstract
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Keywords
Vortex tube, cfd analysis of the vortex tube, ranque-hilsch vortex tube, geothermal gases.
1 INTRODUCTION
Vortex tubes are simple and common devices which
separates a high-pressure gas flow as two different lower
gas flows. One of the outlets has a higher temperature
than the inlet high pressure gas and other outlet has
lower. Most common types of the vortex tubes are
counter and parallel flow types. In counter flow type
vortex tubes the cold and hot outlets are on opposite sides
and in parallel flow type both the outlets are on the same
side. Since it is a simple, well known, compact, portable,
highly reliable and has a few initial costs, it could be
desirable for the specific heating or cooling and
refrigeration applications.
2 BACKGROUND
Vortex Tube
Hilsch, has described a vortex tube of good efficiency in
which the expansion of a gas in a centrifugal field produces
cold for the first time. He has discussed important
variables in construction and operation and found data for
several tubes under various operating conditions are
given. He has found that low pressure gas, 2 to 11
atmospheres, enters the tube and two streams of air, one
hot and the other cold, emerge at nearly atmospheric
pressure. He has found that the cold stream may be as
much as 68oC below inlet temperatures. [1]
Arnorsson, has described the temperature dependence of
pressures of dissolved gases in geothermal systems. He
has concluded some functions about the partial pressures
of these gases. [2]
Groves & Ahlborn have used a novel pitot probe to
measure the axial and azimuthal velocities in a vortex
tube. They have monitored stagnation and reference
pressure sequentially as the probe is rotated around its
axis. From the measured velocity field in the 25mm
diameter vortex tube, they have determined and observed
that the return flow at the center of the tube is much
larger than the cold mass flow emerging out of the cold
end. Therefore, they have decided that the vortex tube
must have a secondary circulation imbedded into the
primary vortex, which moves fluid from the back-flow core
to the outer regions. [3]
Fröhlingsdorf &Unger have simulated the compressible
flow and energy separation phenomena numerically by
using the code system CFX. In order to calculate the energy
separation successfully, they have extended the numerical
model by integrating relevant terms for the shear-stress-
induced mechanical work. They have developed an
axisymmetric model, allowing a successful post-
calculation of experimental results. [4]
Aljuwayhel et al. have used a computational fluid
dynamics (CFD) model to investigate the energy
separation mechanism and flow phenomena within a
counter-flow vortex tube. They have developed a two-
dimensional axi-symmetric CFD model that exhibits the
general behavior expected from a vortex tube. The model
is subsequently used to investigate the internal thermal-
fluid processes that are responsible for the vortex tube’s
temperature separation behavior. They have concluded
that the energy separation exhibited by the vortex tube
can be primarily explained by a work transfer caused by a
torque produced by viscous shear acting on a rotating
control surface that separates the cold flow region and the
hot flow region. [5]
Skye et al. have compared the performance predicted by a
computational fluid dynamic (CFD) model and
experimental measurements taken using a commercially
available vortex tube. They have verified both the data and
the model by using global mass and energy balances. They
have used ANSYS-FLUENT software in CFD modelling. They
have provided a powerful tool that can be used to optimize
vortex tube design as well as assess its utility in the context
of new applications. [6]
Behera et al. have developed a three-dimensional
numerical model of Ranque-Hilsch vortex tube using the
commercial CFD code (Star-CD) to analyze the flow
parameters and energy separation mechanism inside the
tube. The have investigated the variation of fluid
properties and flow parameters as the fluid particles
progress in the flow field by tracking different particles
exiting through the hot and cold end. They have discussed
possible energy transfer mechanisms and estimated the
magnitude of energy transfer from the cold end exit flow
to hot end exit flow. [7]

2. 2
Agrawal et al have experimentally investigated the
Ranque-Hilsch vortex tube (RHVT). The have investigated
influential parameters such as L/D ratio, cold mass
fraction, inlet pressure etc. They have also tested three
different working media (air, nitrogen and carbon dioxide).
They have obtained a value for optimum performance and
they have decided that vortex tube performs better with
carbon dioxide as working fluid. [8]
Xue et al. have proposed an explanation for the
temperature separation in a vortex tube based on an
experimental study focusing on the flow structure and
energy analysis inside the tube. They have calculated the
exergy density distribution along the vortex tube by using
the measured flow properties inside the tube. They have
concluded that the temperature drop at the cold end is
caused by the pressure gradient in the front part of the
vortex tube and the temperature rise at the hot end is the
result of partial stagnation and mixture due to the multi-
circulation flow structure in the rear part of the tube. [9]
Jejurkar & Shukla have reintroduced the vortex tube and
its usage and highlighted a few applications. They have
investigated vortex tube’s usage in machining tools
cooling and laser cutting systems. They finally have
highlighted vortex tube’s importance as an alternative way
to conventional refrigeration in some applications. [10]
Jafargholinejad & Heydari, have done a simulation on a 3D
model of vortex tube and they have solved the governing
equations using ANSYS-FLUENT software. They have
concluded that there is a little difference between air and
natural gas as a working fluid. They have found that the
temperature difference between hot and cold ends for air
flow was little more than natural gas. Based on the results
obtained in their work, they have concluded that vortex
process based on pressurized natural gas can be used in
city gas stations as a heat exchanger for high efficiency
operation and energy saving purposes. [11]
Devade & Pise, have reviewed the scientific community’s
extensive experimental and theoretical studies since
invention of vortex tube. Their review takes into account
effect of almost 14 parameters on performance of vortex
tube. They have aimed to discuss efforts made in order to
enhance the refrigeration effect so that, missing links
could help for future research. [12]
Abdelghany & Kandil, have investigated the effects of
different geometrical parameters such as the tube length
to diameter ratio and the cold orifice size on the
coefficient of performance of the tube. They have
concluded that the coefficient of performance (COP) of the
tube is highly affected by the tube length to diameter ratio
(L/D), and this effect varies when operating at different
cold mass fractions where the maximum COP occur at cold
mass fraction of 0.64. [13]
Geothermal Fluids
Although geothermal energy plants are one of the
important renewable energy applications, they have some
environmental disadvantages. In the applications, some
amount of the geothermal fluid is emitted to the
atmosphere in gaseous form. This geothermal gases
consists different chemical elements in addition to the
water vapour.
One of the most important chemical component
after water vapour is the carbon dioxide (CO2). Although
it is not a toxic gas it has a very high Global Warming
Potential (GWP) and reducing CO2 emission is a very
important issue according to the Kyoto Prothocol. One of
the beneficial method to be able to reduce the CO2
emission is the resolubizing the CO2 in the geothermal
water. In addition to its positive effects over the
atmosphere, it also increases the life cycle of the
geothermal veil and the efficiency of the plant. [14]
Apart from the CO2, geothermal fluids also
consists different chemicals such that hydrogen sulfur
(H2S), ammonia (NH3), nitrogen (N2), hydrogen (H2),
mercury (Hg), boron vapour (B), radon (Rn) and methane
(CH4) with variable amounts. [15] These chemicals may
cause different environmental problems in addition to
warming effect and their influence could be restricted by
a smaller area instead of the whole atmosphere. For
instance, the effect of the CO2 is global because of the its
high GWP; however, the effect of the H2S emission is local
and it is depends on the topography, wind speed and
direction and the usage of the terrain. It could cause tool
corrosion, acid rains and problems in respiration system.
B, NH3 and Hg pollute the air and the soil, and harms the
flora. They also have negative effects over the surface
waters and the water ecosystem. [16]
Geothermal wastes also has negative effects over the
agricultural products. For instance, researches about the
this effect over the Sarılop fig in the Aegean Region in
Turkey shows that successful planting ratio changes about
between %24.8-%63.3. In Aydın Erbeyli, offshoot length of
the Sarılop fig trees changes about between 7.32-8.95 cm,
offshoot thickness about 1.00-1.02 cm and the internode
numbers about 7.90-7.67. Studies also shows that these
negative effects increases while closing to the geothermal
plant area.
In different geothermal plants there is a different chemical
distribution in the excess steam. Although this difference
could be slightly considerable for CO2, H2, and H2S, it is
negligible for other components. The variation of the
percentage of the CO2, H2, H2S and the CH4 could be seen
in Table 1. for two different geothermal plants in
Hellisheiði and Nesjavellir [17].
3 PROBLEM STATEMENT
Although vortex tubes have several benefits which are
mentioned above, they also have some disadvantages. It
has relatively low coefficient of performance, it has a very
limited capacity due to its very special geometrical
constraints and it needs a high-pressure gas source for the
inlet state. In most of the open literature, air is used as
working fluid of the vortex tube and mostly it is
compressed by compressors which need a power supply.
Only a few researches overlook different working fluid
usage such as natural gas in city gas stations as a high-

3. pressured inlet working fluid. In this study, it will be
determined that what could be results if the excess gases
in geothermal power plants as a high-pressure working
fluid in a vortex tube application. To be able to reach the
desired results following questions should be answered:
 What are the excess gases in the geothermal
power plants what are their properties?
 What will be the exit properties of the gases from
the vortex tube?
 At the cooling side of the vortex tube, excess gas
will condense or only will cool but still be in the
gaseous form?
 At the heating side of the vortex tube, what will
be the maximum temperature, and will it be
possible that safely transfer it?
 What could be the advantages of using this device
with the calculated results in economics and
environmental perspectives?
4 ANALYSIS
ANSYS Fluent 16.0 software package was used to create
the CFD model of the investigated vortex tube. The vortex
tube type is adapted from a strong study [18] to validate
the accuracy of the model. The model is two-dimensional,
axi-symmetric (with swirl), steady state and turbulence
model. The dimensions of the geometric model of the
vortex tube is given in the Fig 1.
Figure 1 Dimensions of the vortex tube model
Where:
 The length of the vortex tube c-e is 120mm
 The radius of the vortex tube a-c is 8mm
 Inlet boundary c-d is 1.6mm
 Cold outlet boundary a-b is 3.5mm (This is varied
to acquire different cold mass fractions.
 Hot outlet boundary e-f is 2mm
The geometric model was created using the Ansys
SpaceClaim software. Fig 2 shows the designed model.
Figure 2 Geometric model of the vortex tube
Meshing was done using the Ansys Meshing software.
Mesh sizing was employed with the 40,969 cells to be on
the safe size. As observed in the Jafargholinejad [11], there
is not much benefit in increasing the number of cells
beyond 40,000 while investigating the Ranque-Hilsch
vortex tube. The mesh generated is showed in Fig 3.
Figure 3 Meshed geometry
The turbulent model was chosen to be the k-epsilon model
as it is suggested to be the most effective model in
Jafargholinejad [11]. The body fluid in the analysis is the
composition of the gases from the Nesjavellir geothermal
power plant, this gas properties can be found in the above
Table 1. The inlet boundary conditions were given
according to this power plant’s excess steam values, which
are the pressure of 12 bars and temperature of 463K.
Outlets of the vortex tube were set as a pressure outlet. In
the solution method, the governing equations are
discretized by the second order upwing scheme as
suggested in [18]. Finally the solution is initialized based
on the inlet boundary conditions.
5 RESULTS
Temperature and pressure distributions against the cold
mass fraction will be graphed. Aim is to see with using this
graph which component of the excess steam of the power
plant will liquidify at what cold mass fraction.
6 DISCUSSION AND CONCLUSION
7 REFERENCES
[1] Hirsch R. The Use of the Expansion of Gases in a
Centrifugal Field as a Cooling Process, Review of Scientific
Instruments, 1947.
[2] Arnórsson S. Gas pressures in geothermal systems,
Chemical Geology, Volume 49, Issues 1–3, 1985: 319-328.
[3] Ahlborn B., Groves S. Secondary Flow in Vortex Tube,
progress in Fluid Dynamics Research, 1997.
[4] Fröhlingsdorf, W., & Unger, H. Numerical investigations
of the compressible flow and the energy separation in the
Ranque-Hilsch vortex tube. International Journal of Heat
and Mass Transfer, 42, 1998: 415-422.
[5] Aljuwayhel, N. F., Nellis, G. F., & Klein, S. A. Parametric
and internal study of the vortex tube using a CFD model.
International Journal of Refrigeration, 28, 2004: 422-450.
[6] Skye, H. M., Nellis, G. F., & Klein, S. A. Comparison of
CFD analysis to empirical data in a commercial vortex tube.
International Journal of Refrigeration, 29, 2005: 71-80.
[7] Behera, U., Paul, P. J., Dinesh, K., Jacob, S. Numerical
investigations on flow behavior and energy seperation in

4. 4
Ranque-Hilsch vortex tube. International Journal of Heat
and Mass Transfer, 51, 2008: 6077-6089.
[8] Agrawal, N., Naik, S. S., Gawale, Y. P. Experimental
investigation of vortex tube using natural substances.
International Communications in Heat and Mass Transfer,
52, 2014: 51-55.
[9] Xue, Y., Arjomandi, M., Kelso, R. Energy analysis within
a vortex tube. Experimental Thermal and Fluid Science, 52,
2014: 139-145.
[10] Jejurkar, A. N., Shukla, A. N. An Overview on Vortex
Tube Applications, 2015.
[11] Jafargholinejad S., Heydari N. Simulatıon Of Vortex
Tube Using Natural Gas As Working Fluid With Application
In City Gas Stations, 2016.
[12] Devade, K., Pise, A. T. Parametric Review of Ranque-
Hilsch Vortex Tube. American Journal of Heat and Mass
Transfer, 4, 2017: 115-145.
[13] Abdelghany, S. T., Kandil, H. A. Effect of Geometrical
Parameters on the Coefficient of Performance of the
Ranque-Hilsch Vortex Tube. Open Access Library Journal,
5, 2018
[14] Aksoy, N., Mutlu, H., Gök, Ö., Kılınç, G., Carbon
Emission of the Geothermal Power Plants and Carbon
Sequestration, 13th National Congress of Plant
Engineering, 2017/İzmir.
[15] El­WAKIL, M.M., Power Plant Technology,
McGraw­Hill Inc., 1984.
[16] Çakın, A., Gökçen, G., Eroğlu, A., Jeotermal
Uygulamalarin Çevresel Etkı̇lerı̇: Balçova Jeotermal
Bölgesel Isitma Sı̇stemı̇ Örneğı̇, 7th National Congress of
Plant Engineering, 2005/İzmir.
[17] Bassania, A., Previtalia D., Pirolab C., Bozzanoa G.,
Nadezhdinc I. S., Goryunovc A. G., Manentia, F., H2S in
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Resource for Energy and Environment, The Italian
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ENGINEERING TRANSACTIONS VOL. 70, 2018.
[18] P. Kumar, CFD Analysis of Ranque-Hilsch Vortex Tube,
National Institute of Technology Jamshedpur, 2017.
8 ACKNOWLEDGEMENT
The acknowledgement can include reference to grants,
colleagues, institutions etc. important for the support,
research and writing the paper.