Paper on

CFD ANALYSIS TOWARDS OPTIMIZING THE

PARAMETERS OF VORTEX TUBE

PREPARED BY

K.SARATHKUMAR P.IYAPPAN

E. Mail:sarathnirmala@gmail.com E. Mail: iyappan2k@gmail.com

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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