[ASME ASME/JSME 2011 8th Thermal Engineering Joint Conference - Honolulu, Hawaii, USA (March...

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Proceedings of the ASME/JSME 8th Thermal Engineering Joint Conference AJTEC2011

March 13-17, 2011, Honolulu, Hawaii, USA

AJTEC2011-44393

FEASIBILITY OF VORTEX TUBE AIR-CONDITIONING SYSTEM

Mohammad O. Hamdan United Arab Emirates University

Al Ain, Abu Dhabi, UAE

Ahmed Alawar United Arab Emirates University


Emad Elnajjar United Arab Emirates University


Waseem Siddique United Arab Emirates University


ABSTRACT This paper investigates the feasibility of using vortex tube

as air-conditioning device. Series of experiments are conducted

to evaluate the design parameters and calculate the

performances of counter-flow Ranque–Hilsch vortex tube

(RHVT). The study is conducted for different inlet pressures

conditions, number of nozzle inlets, vortex chamber depth and

thermal insulation condition. The vortex tube performance is

investigated by measuring temperatures, pressures and mass

flow rates for the inlet and hot/cold exits. It is found that vortex

tube has very coefficient of performance which make it

inadequate to compete with conventional air conditioning

system.

NOMENCLATURE �� coefficient of performance

�� specific heat constant, kJ/kg-K

� vortex tube inner diameter, �

�� inlet pressure, bar

� hot mass flow rate, kg/s

� � cold mass flow rate, kg/s

� �� inlet mass flow rate, kg/s

RHVT Ranque-Hilsch vortex tube

� air gas constant, kJ/kg-K

hot outlet temperature, °�

� cold outlet temperature, °�

�� inlet temperature, °�

∆ temperature difference between the inlet and the hot

out, ∆ ��

∆ � temperature difference between the inlet and the cold

outlet, ∆ � � ��

� cold mass fraction

INTRODUCTION The Ranque-Hilsch vortex tube (RHVT) is a thermal

mechanical device that separates the energy of a compressed

gas flow two opposite streams; one stream colder than the inlet

temperature while the other stream is hotter than the inlet

temperature. The vortex tube does not have any moving part

and the separation is occurred due to swirl flow generation

without requiring any external work or heat transfer. The vortex

tube was first discovered by Ranque in 1928 while

experimenting on vortex tube pump [1-2], a metallurgist and

physicist who was granted a French patent for the device in

1932, and a United States patent in 1934. Later in 1945, Rudolf

Hilsch [3] conducted an experiment on vortex tube that focused

on the thermal performance with different inlet pressure and

different geometrical parameters.

In the recent years it was known that vortex tube is a low

cost and an effective solution for many cooling problem. The

separation mechanism inside the vortex tube was not

completely understood until today [4]. The ability to obtain

either hot or cold flow streams using compressed gas, allowed

the use of vortex tube in many engineering applications such as

cooling of electronics, cooling of food, cooling of firemen's

suit, cooling of machinery during operation. In spite of its small

capacity, the RHVT is very useful for certain thermal

management applications because it of simplicity, compactness,

Proceedings of the ASME/JSME 2011 8th Thermal Engineering Joint Conference AJTEC2011

March 13-17, 2011, Honolulu, Hawaii, USA

AJTEC2011-44393

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light weight, robustness, reliability, low maintenance cost and

safety [5]. The RHVT can be classified into two types: (1) the

counter-flow RHVT and (2) the uni-flow RHVT [6]. In the

counter flow RHVT type the cold flow move in the opposite

direction with respect to hot stream while in the second type,

the hot and cold streams flow in same direction. In general, the

counter-flow RHVT is recommended over the uni-flow RHVT

for its efficient energy separation [6].

Vortex tube is covered extensively in literatures through

experimental and numerical analysis. The experimental work of

Nimbalkar and Muller [7] indicated that there is an optimum

diameter of cold end orifice for achieving maximum energy

separation. Also, the results [7] show that the maximum value

of energy separation was always reachable at a 60% cold

fraction irrespective of the orifice diameter and the inlet

pressure. The optimum diameter to length ratio of the hot side

was investigated by Dincer et al. [8, 9]. Vortex tube

performance was investigated for three different working gases:

air, oxygen and nitrogen and results were reported using

streakline visualizations in a vortex tube made of Perspex [10].

The effect of vortex entrance condition is reported in [11]

which indicate that vortex tube can be enhanced by rounding

the entrance. It was reported [6] that cooling the vortex tube

can enhance the cooling capability by 5-9%. Xue and

Arjomandi [12] reported that the vortex angle has direct effect

on vortex tube and that a smaller vortex angle demonstrated a

larger temperature difference and better performance for the

heating efficiency of the vortex tube. Scientists worked in

improving vortex tube by redesign the nozzle, gas inlet and

utilizing diffuser vortex tube which showed reasonable

enhancement compared to current design [13]. A modification

to vortex tube was proposed [14] by introducing double-circuit

vortex tube which showed enhancement in the vortex tube

performance.

Other scientist modeled and analyzed the vortex tube

using numerical analysis with different turbulent model.

Numerical study showed acceptable agreement with published

data [15-18]. A full discuss of 3D numerical study is presented

in reference [16] which report maximum COP of the vortex

tube is found to be 0.59 as a heat engine and 0.83 as a

refrigerator. Behera et al. [16] reported numerically that the

secondary flow degrade the performance of the vortex tube. It

was reported that the magnitude of velocity angle is reversely

proportional to the vortex pipe diameter [18].

The current study investigates the effect of number of

inlet nozzles, vortex stopper location, vortex tube insulation

and inlet pressure. The effect of vortex tube in energy

separation is reported using outlets temperature and cold mass

fraction.

EXPERIMENTAL SETUP A two-dimensional cross section of used vortex tube is

shown in Fig. 1. A room temperature compressed air is used as

working fluid at different inlet pressure values. The compressed

air enters in the middle of the vortex tube to chamber that

distribute the air into multiple inlet nozzles that promote vortex

flow generation within the vortex generator. The vortex flow

get separated to two outlets where hot air leaves from the outer

parameter of the vortex while cold air leave from the center of

vortex at the opposite direction as shown in figure (1a). The

schematic diagram of the experimental setup is shown in Fig. 2.

(a)

(b) FIGURE. 1 THE VORTEX TUBE; (a) A 2-D CROSS-SECTION OF

THE VORTEX TUBE AND (b) VORTEX GENERATOR.

FIGURE. 2 A SCHEMATIC DIAGRAM OF THE TEST BED WITH

POINT OF DATA COLLECTION.

The compressed air is provided through compressor

storage tank to assure uniform pressure with minimum

variation. The compressor maximum rated pressure is 12 bars,

even though all runs where for inlet pressure of 5 bar or less.

The compressed gas passed through a humidifier and particle

separation filter to assure the use of clean dry air. The air is

expanded in the vortex tube chamber and separated into hot air

stream and cold air stream. The cold stream in the central

region flows out of the tube through the central orifice nearer to

the inlet nozzle, while the hot stream in the outer annulus

leaves the tube through another outlet farther from the inlet.

The flow rate of the inlet air is regulated through flow

rotometer valve while the pressure is controlled using a

pressure controller that is attached on the compressor tank

outlet. The volumetric flow rates of the inlet and cold streams



are both measured by flow meters. The temperatures of the

temperature of the inlet and outlet flows are measured with

three thermocouples. In the present study, the vortex tube is

made of stainless steel with inner diameter of 10mm. The

tangential inlet nozzle has a diameter of 3mm. The whole

length of the tube is 137mm. The outlet diameter of the cold

side is 4.5 mm and hot side end is around 8 mm. The inlet flow

rate is controlled through the flow meter valve which implicitly

determines the inlet pressure. In this experiment, different inlet

pressure sets were used in the test ranging from 2-5 bars with

room inlet temperature. The uncertainty of the used type-K

thermocouple is 0.3°� which is very small.

RESULTS AND DISCUSSION In the present work, the effects of the (a) inlet pressure,

(b) the number of nozzles, (c) the vortex stopper location and

(d) the vortex tube insulation on the performance of RHVT are

experimentally investigated. The behavior of vortex tube when

cold and hot outlets are brought to same outlet pressure is

shown figure (3) which shows the cold and hot outlet

temperature versus the cold mass fraction (� ). The present

experimental data, figure (3), shows a good qualitative

agreement with earlier published data [3, 6] considering the

geometry and the inlet conditions differences. As expected and

reported in literature, there is a non-monotonic relation between

outlet temperature and cold mass fraction and that there is

optimum cold mass fraction for maximum hot temperature and

minimum cold temperature. As shown if figure (3), the

optimum temperature at the cold ( ∆ � � �19.9°��

0.098) and hot outlet (∆ � 5.6°�� 0.098) does not occur at the same cold mass fraction.

FIGURE. 3 THE TEMPERATURE OF COLD AND HOT

OUTLETS VERSUS COLD MASS FRACTION FOR 5 BAR INLET

PRESSURE, 26 oC INLET TEMPERATURE AND 6 SWIRLING

JETS.

The effect of pressure on the optimum condition of the

vortex tube is shown in figure 4. It is clear that pressure

increase the maximum hot outlet temperature and decrease the

minimum outlet temperature, hence pressure has direct effect

on promoting separation of the energy of the flow to two

streams, as shown in figure 4a and 4b. Based on figure 4, it is

clear that the optimum mass fraction for cooling does not

depend on the operating inlet pressure (as shown in figure 4c)

while for the hot outlet flow, the optimum cold mass fraction

increases with the increase in the pressure (as shown in figure

4d).

FIGURE. 4 THE EFFECT OF INLET PRESSURE AT 26 oC INLET TEMPERATURE ON THE; (a) MINIMUM COLD

TEMPERATURE, (b) MAXIMUM HOT TEMPERATURE, (c)

COLD OUTLET AND (d) HOT OUTLET.

FIGURE. 5 THE EFFECT OF NUMBER OF NOZZELS AT 5 BAR INLET PRESSURE AND 26 oC INLET TEMPERATURE ON (a)

COLD OUTLET AND (b) HOT OUTLET.

It is commonly to use multiple jets to generate the vortex

flow inside the vortex generator show in figure 2b. The effect

of jet angle was discussed in literature [12] which shows that

smaller angel or tangent jets generate the maximum energy

separation. The effect of number of jet for same angle is shown



in figure 5a and 5b, which shows that as number of jet

decreases from 6 to 3 jets the optimum cold mass fraction

increases (from 10% to 22%) while the cold outlet temperature

increase marginally (by less than 1.5 degree). The single inlet

nozzle shows lower performance compare to 6 and 3 jets vortex

generator and this could be due to the uniformity of the vortex

since it is expected that as number of inlet nozzles increase, the

vortex become more stable and uniform.

The effect of vortex stopper is shown in figure 6. The

vortex stopper is a radial fin that allows the flow to move

axially in the vortex tube while stopping the vortex and

secondary flow motion as shown in figure (1a). Three different

locations of the vortex stopper are investigated and reported in

figure 6. It is clear that the location of vortex stopper has an

effect on the vortex tube performance and that as stopper move

away from the vortex generator, colder temperature is achieved.

This indicates, agreed with published work [8, 9], that the

length of the vortex chamber is directly affecting the vortex

tube performance. The vortex tube length to diameter ration is

very important design parameter which is not investigated in

this work and need more exploration. The figure (6) support the

idea that there is secondary circulation inside the vortex tube

which enhances the energy separation such in this case it is

clear that as vortex stopper move far from the vortex generator

better cooling is achieved as shown in figure (6b). The distance

from A to B and from B to C is equal to 7D.

FIGURE. 6 THE EFFECT OF NUMBER OF SWIRL STOPPER AT 5 BAR INLET PRESSURE AND 26 oC INLET TEMPERATURE ON

THE (a) COLD OUTLET AND (B) HOT OUTLET.

The effect of insulation on vortex tube is shown in figure

(7) for cold outlet, figure (7a), and hot outlet, figure (7b). The

results show that insulation has minor effect on the

performance of the vortex tube which suggest that heat loss

through the vortex tube is minimal and that most of the hear

exchange is happening inside the vortex tube where maximum

temperature difference is occurring between the cold center and

external hot vortex. It is reported in [6] that cooling the vortex

tube would promote cooling by 5-9% which was not observed

here through the insulation and no insulation case which means

that small amount of heat is lost through the vortex tube wall

and that’s why this effect was not noticeable in the current test.

FIGURE. 7 THE EFFECT OF INSULATION OF THE STEEL

VORTEX TUBE AT 5 BAR INLET PRESSURE AND 26 oC INLET

TEMPERATURE ON BOTH (a) COLD OUTLET AND (b) HOT

OUTLET.

The use of vortex tube as air conditioning device has

fascinated engineers due to its simplicity and reliability with no

moving part. The use of vortex tube as air-condition device is

not yet feasible due to low coefficient of performance as shown

in figure 8. The figure (8) shows that there is an optimum cold

mass fraction value where maximum COP exists and that as

inlet pressure decrease the COP would increase. The efficiency

of a refrigerator is expressed in terms of the coefficient of

performance (COP) which is expressed as follow, [19]:

�� !�"�#�$#�

��%# !�"&'$#�

For the vortex tube, the COP is calculated by dividing the

desired output (cooling load) on required input (compression

energy). The compression energy was calculated for isothermal

process (at constant temperature) while the cooling load was

calculated for ideal gas as shown below:

�� (() '*+(�"

&�(�,�!��)�(�$!�� ('-'�!*.�

� ��/ �� 0

�� )'/��/�2340

FIGURE. 8 THE COOLING COP VERSUS COLD FRACTION

FOR DIFFERENT INLET PRESSURE AT 26 oC INLET

TEMPERATURE.

CONCLUSION The available vortex tube is not appropriate to be used for

air conditioning system due to its low coefficient of

performance. The results show that most of the input energy is



lost as kinetic energy and small is converted to cooling heating

load. A series of experiments are conducted to investigate the

performance of vortex tube under several design parameters

mainly; (1) inlet pressure, (2) cold mass fraction, (3) number of

inlet nozzles, (4) vortex stopper location and (5) insulation. The

following were concluded from the experimental data:

1) The inlet pressure is the necessary driving force for the

energy separation. Experiments show that the higher the

inlet pressure, the greater the temperature difference of the

outlet streams.

2) The cold fraction is an important parameter influencing the

performance of the energy separation in the vortex tube.

3) The effect of number of nozzle is very important and that

for constant inlet pressure test, it is clear that increasing

number of nozzle increase the performance of the vortex

tube.

4) The vortex tube length (vortex stopper location) has direct

effect on the performance on the vortex tube. The data

shows that as vortex stopper move far from the vortex

generator the energy separation performance increases.

This is achieved when the vortex stopper move far from

the vortex generator from 0 to 15D.

5) Insulation has minimal effect on vortex tube cooling or

heating capabilities.

ACKNOWLEDGEMENTS The authors would like to acknowledge the support provided by

United Arab Emirates University. This work was financially

supported by the Research Affairs at the United Arab Emirates

University under a contract no. 01-05-7-11/09.

REFERENCES

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simultaneous exhaust of hot air and cold air”, J Phys

Radium (Paris) 1933; 4:112–4 S-115, June. Also translated

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T.F. 3294.

[2] Ranque GJ., “Method and apparatus for obtaining from a

fluid under pressure two outputs of fluid at different

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