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CFD ANALYSIS TOWARDS OPTIMIZING THE
PARAMETERS OF VORTEX TUBE
PREPARED BY
K.SARATHKUMAR P.IYAPPAN
E. Mail:[email protected] E. Mail: [email protected]
Second year mechanical Second year mechanical
KCG College of technology. Chennai PSNA college of Engg.Dindigul
Mobile no: 9786375113 Mobile no: 9003882559
SUBMISSION FOR
RITZKAIZEN’9
National level technical symposium
Regency Institute of Tech.,
Pondicherry
ABSTRACT
In today’s complex manufacturing processes, there is a need for efficient means of
production which has led all manufacturing companies to run the machines continuously. Due to
which there is failure in cutting tools may occur due to wear, improper handling of tools or due to
thermal shocks. The cutting tool failure due to thermal shocks is because improper cooling. Other
than that rust formation is an important thing to be considered. This happens because of the
continuous contact of liquid coolant on the surface of cutting tools. Because of these reasons the
tool gets failed.
The industries are going for replacement of failed tools with new ones without analyzing
the cause of failure and rectifying them. So to stop the failure of cutting tools due to thermal
shocks and rust formation the quality of tools must be improved. On the contrary by providing
vortex cooling system which makes the tool free from the above said failures. Temperature
distribution across the axial direction of the vortex tube is being studied and has been proved that
the sub zero temperatures are obtained for cooling. CFD techniques are used to simulate the
phenomenon of flow pattern, thermal separation, and pressure gradient. In the present study CFD
is used as a tool for obtaining optimal design of vortex tube.
INTRODUCTION:
In the increasingly globalised economy due to the mass production there is continuous
running of machines which leads to the failure in cutting tools. These failures of cutting tool are due
to improper handling of tools or due to thermal shocks. The cutting tool failure due to thermal shocks
is because of improper cooling. Other than that rust formation is an important thing to be considered.
This happens because of the continuous contact of liquid coolant on the surface of cutting tools.
Because of these reasons the tool gets failed. So a vortex tube could be employed for cooling
purposes.
VORTEX TUBE:
The Vortex Tube (VT) cooler is a device that generates cold and hot gas from compressed
gas, as shown in Fig.2.1. It contains the following parts: one or more inlet nozzles, a vortex chamber,
a cold-end orifice, a hot-end control valve and a tube. When high pressure gas (6 bars) is tangentially
injected into the vortex chamber via the inlet nozzles, a swirling flow is created inside the vortex
chamber. At the hot exhaust, the gas escapes with a higher temperature, while at the cold exhaust, the
gas has a lower temperature Vortex Tube (RVT), Hilsch Vortex Tube (HVT) and Ranque compared
to the inlet temperature.
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IDENTIFICATION OF THE PROBLEM:
In the case of RHVT temperature of air at both cold and hot outlets are taken as the broad area
of interest in this project. In such circumstances both the inlet pressure and dimensional parameters
should be considered. Varying the pressure at inlet can be easily done with the aid of a pressure
regulator. Optimization of dimensional parameters of RHVT would give better performance.
A thorough study or recent literary reviews implies that, the critical parameters that affect the
outlet temperatures are L/D ratio and cold end diameter. For lower values of L/D ratios the swirl
intensity extends beyond the length of hot end exit of the tube. L/D ratio should be in a range such
that the stagnation point is within the tube. So increase in the length of tube enhances the temperature
separation up to the condition that stagnation point is within the length of tube. Also secondary
circulation flow in vortex tube has its influence on temperature separation.
PROBLEM STATEMENT
Analysis of temperature distribution across three dimensional model of Ranque Hilsch
Vortex Tube(RHVT) using Fluent 6.1 package with the help of Gambit preprocessor. The three
dimensional model is shown in figure 3.1
ASSUMPTIONS
In order to analyze the problem, the following assumptions are made
The temperature variation is three dimensional
The material properties are constant(Isotropic)
Room temperature is assumed to be maintained at 270C
BOUNDARY CONDITIONS
For the computational domain shown in fig 3.1, the boundary conditions are listed below
INLET NOZZLE COLD END HOT END
Pressure, Pin =0.5422 MPa Pressure, Pc =0.136 MPa Hot gas fractio=20, 40, 50, 60, 80%
Temperature, Tin =300 K
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RESULTS AND DISCUSSION
The thermal behavior of vortex tubes of various dimensions has been taken into
consideration. They are grouped into three types based on the dimensions varied. The types of vortex
tubes taken for analysis are
Type1
RHVT with cold outlet diameter Dc=6 mm, L/D ratio = 05 mm, L/D ratio = 10 mm, L/D ratio =
20 mm, L/D ratio = 25 mm
Type2 RHVT with cold outlet diameter Dc=7 mm, L/D ratio = 05 mm, L/D ratio = 10
mm, L/D ratio = 20 mm, L/D ratio = 25 m
Type3 RHVT with cold outlet diameter Dc=8 mm, L/D ratio = 05 mm, L/D ratio = 10 mm,
L/D ratio = 20 mm, L/D ratio = 25 mm
PARAMETERS STUDIED
The inlet pressure and the velocity of air entering the vortex chamber are kept constant and
the dimensional parameters (Dc and L/D) are varied. Then three dimensional model of the vortex
tube with optimum design has been investigated by varying hot (mh) and cold gas fractions (mc). By
varying the hot gas fraction the temperature of outlet air both at hot and cold ends are noted.
The performances of all the cases of vortex tubes based on CFD and thermal analysis made
in the FLUENT 6.1 are to be presented in this chapter. The temperature of the air at the cold outlet
for various dimensions of vortex tube is the area of interest in this project.
TEMPERATURE DISTRIBUTION ACROSS THE VORTEX TUBE
Type I: Initial CFD analysis has been carried out for RHVT of diameter D=12mm, cold end
diameter (Dc) =6mm for various L/D ratios. The L/D ratio is varied as 5, 10, 20 and 25mm. the
compressed air from the nozzle enters the vortex generation chamber and gets expand. This is the case
where airflow patterns and the temperature distribution are to be analyzed. For each L/D ratio
individual contour diagrams for static temperature has been obtained and the values are tabulated. The
analysis shows that, for a RHVT of Dc =6mm the minimum cold end temperature of -17oCand a
maximum hot end temperature of 76oCcan be obtained.
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Type II : Secondly CFD analysis has been carried out for RHVT of diameter D=12 mm, cold
end diameter (Dc) =7 mm for various L/D ratios as in the previous case. The analysis shows
that for a RHVT of Dc=7 mm the minimum cold end temperature of 100C and a maximum hot
end temperature of 850C can be obtained.
Type III: Finally CFD analysis has been carried out for RHVT of diameter D=12 mm, cold end
diameter (Dc) =8 mm for various L/D ratios. The analysis shows that for a RHVT of Dc=8 mm
the minimum cold end temperature of -70C and a maximum hot end temperature of 710Ccan be
obtained.
RESULTS OBTAINED FOR THE VARIOUS TYPES OF Dc VALUES
L/D
RATIO
COLD GAS TEMP(C) HOT GAS TEMP(C) TEMPERATURE
DIFFERENCE(C)
TYPE1 TYPE2 TYPE3 TYPE1 TYPE2 TYPE3 TYPE1 TYPE2 TYPE3
5 7 10 12 59 62 60 52 52 48
10 -8 -2 5 65 74 66 73 76 61
15 -17 -10 -7 76 85 71 93 95 78
20 -12 -5 -5 74 79 68 86 84 73
COMPARISION OF VORTEX TUBES
Here the results obtained from the CFD analysis are compared for all the three cases to choose the
optimum design parameters for a 12 mm diameter vortex tube. The graph illustrate that in all the
cases the L/D ratio of 20 has made the greater temperature difference over the other ratios. But
among the three cold end diameter used, Dc=7 mm shows the higher difference in temperature. This
is shown in the following figure
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But the maximum hot gas temperature of 850C is attained by using Dc=7 mm as shown in the
following figure. Therefore choosing Dc depends on the application. Here we use RHVT for the
purpose of cooling cutting tool. So as far as our case is concerned Dc of 6mm and L/D of 20 are
optimum.
VELOCITIES AND FLOW PATTERN
The core flow takes place at stagnation point at an axial distance from the inlet. The point at
which the axial velocity goes negative is called stagnation point. The analysis shows that the forced
and free vortex components up to the stagnation point. In this case the air entering the system never
leaves the cold outlet directly. After reaching the stagnation point the temperature separation takes
place and there it takes negative direction towards cold end.
EFFECTS OF HOT GAS FRACTION
Vortex tube performance varies when hot gas fraction has been varied. This has been
proved in CFD with the help of FLUENT 6.1. For a specific RHVT of Dc=6 mm and L/D=20(optimized
values from earlier analysis), an investigation has been carried out. Hot gas fractions have been
varied as 20, 30, 40, 50, 60, 70 and 80 percentages. The static temperature contours obtained for a
hot gas fraction of 40% proves that if the hot fraction increases, the cold gas temperature gets
lower.
CONCLUSION
From the CFD analysis conducted for vortex tubes of various dimensions, the minimum cold
gas temperature achievable is -170C and is obtained for RHVT of cold end diameter of 6 mm and L/D
ratio of 20. With this optimum design, a minimum cold gas temperature of -310C is obtained at 80%
hot gas fraction. This optimum design of vortex tube can be used for various industrial cooling
applications.
REFERENCES
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1.Fundamentals of Compressible Flow with Aircraft & Jet Propulsion - S.M.Yahya,
New Age International Publishers.
2.Computational Fluid Dynamics-T.J. Chung, Cambridge university press.
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