karŞit akiŞli ranque-hilsch vorteks tÜpÜnÜn deneysel...

ULIBTK’17 21. Ulusal Isı Bilimi ve Tekniği Kongresi 13-16 Eylül 2017, ÇORUM

KARŞIT AKIŞLI RANQUE-HILSCH VORTEKS TÜPÜNÜN DENEYSEL ANALİZİ

İlhami Ilgaz AYDOĞDU, Canberk FİDAN, Barbaros ÇETİN İ.D. Bilkent Üniversitesi University, Mechanical Engineering Department

06800 Çankaya, Ankara [email protected], [email protected], [email protected]

Özet: Henüz tüm yönleriyle keşfedilmemiş olan Ranque-Hilsch vorteks tüpü, bir soğutma aracıdır. Elektronik parçalar, soğutucu sıvıların ve hareketli parçaların olmaması ve küçük boyutu, vorteks tüpünü güvenilir bir soğutma ve ısıtma alternatifi yapar. Basınçlı hava tüpe basılır ve bu enerji zıt uçlarda sıcak ve soğuk hava elde etmek için kullanılır. Projenin amacı; basılan havanın debisinin, kontrol valfi (iç vorteksi sağlayan parça) geometrisinin ve soğuk kütle oranının vorteks tüpünün verimine etkisini araştırmaktır. Giriş ve çıkışlarda ölçülen sıcaklıklar ve debi verileriyle belirtilen parametrelerin vorteks tüpünün verimine etkisi hesaplanmıştır. Anahtar Kelimler: Ranque-Hilsch Vorteks Tüpü, control valfi gemetrisi, soğuk kütle oranı

EXPERIMENTAL INVESTIGATIONS ON COUNTER FLOW RANQUE-HILSCH VORTEX TUBE

Abstract: Ranque-Hilsch vortex tube is a cooling device which is yet to be fully explored. The compact size of the vortex tube and the absence of electronics, refrigerants and moving parts make the vortex tube a reliable alternative for cooling and heating applications. It uses pressurized working fluid and dissipates the energy entered to generate cold and hot temperature at opposite ends. The aim of this article is to observe and determine how the mass flow rate that enters the vortex tube, the geometry of the control valve which is used to create the inner vortex and adjustments on the cold mass fraction, affect the efficiency of vortex tube. In the light of the measured temperature and mass flow rate data at the inlet and the outlets, the effect of mentioned parameters to efficiency of the vortex tube is examined. Keywords: Ranque-Hilsch Vortex Tube (RHVT), control valve geometry, cold mass fraction INTRODUCTION The phenomenon of vortex in a flow has become a popular area of interest for research for the past decades. Nonetheless, the behaviour of the flow of a vortex is still coarsely explored due to the vortex flow’s characteristics. This flow type has many applications to be applied in many industry fields. One special application for the industrial usage is the vortex tube. The vortex tube also known as Ranque-Hilsch vortex tube is a mechanical device that is used as a cooling mechanism which only demands pressurized gas at its inlet and creates hot and cold temperatures at its outlets. It is founded and experimented by Georges J. Ranque in 1933 (Ranque, 1933). Rudolf Hilsch who was also a German engineer improved Ranque’s tube in 1947 (Hilsch, 1947) which is the reason that it is also known as the Ranque-Hilsch vortex tube. A Ranque-Hilsch vortex tube enables locally focused cooling or heating

by only using compressed gas as the operating gas. The absence of electronics, any kind of refrigerants, moving parts and being compact causes the vortex tube to be a reliable and safe alternative mainly for cooling and heating applications in the industry. Commercially, the main area of usage of the vortex tubes is local cooling applications. Some examples of its applications include cooling fireman’s suits (Colgate, Buchler, 2000), cooling the laboratory equipment where explosive hazards are present (Bruno, 1992), cooling machining and CNC parts, cooling special electronic components such as microchips, cooling of low-temperature magic angle spinning nuclear magnetic resonance (NMR) (Martin, Zilm, 2004), dehumidifying gas samples, liquefaction of natural gas (Fin’ko, 1983), test temperature sensors (Riu et al., 2004) and separating particles in the waste gas industry.


WORKING PRINCIPLE OF VORTEX TUBE A vortex tube is a device which only has an inlet and two outlets. Compressed gas enters the vortex tube eccentrically from the inlet and due to the geometry of the vortex tube, vortices are generated and stream follows a vortex flow until it reaches the end of the length of the hot end. Some portion of the flow goes out from the gaps at the end of the hot end although rest of the flow hits the control valve and returns. The returning flow follows a path towards the cold end exit. This flow is observed as a vortex type of flow where its temperature decreases during its path. The phenomena of this behaviour is still unclear yet there are plenty of researches done on this topic. To summarize, from the inlet, pressurized gas flows in and creates flows with lower and higher temperature values at cold end outlet and hot end outlet, respectively, compared to the inlet temperature. (Xue et al., 2013)

The vortex tube does not have any moving parts or electronics. That is why cold and hot streams are generated entirely because of the geometry of the vortex tube.

Figure 1. Working principle of vortex tube (Eiamsa-ard, Smith, and Promvonge, 2008)

DESIGN OF THE VORTEX TUBE A broad literature search had been done to determine the dimensions of the RHVT. From the previous articles that had been written on this specific subject, the most critical parameters that affect the performance and efficiency of the Ranque-Hilsch vortex tube are found as the L/D (the length of the hot tube to the diameter of the hot tube) and d/D (the diameter of the cold tube to the diameter of the hot tube) ratios. The geometry of RHVT is based on the article written by Nimbalkar (Nimbalkar et al., 2009) and also Promvonge (Promvonge et al., 2005). However, some adjustments have been made on the vortex tube. L/D and d/D ratios are selected as 11.5 and 0.4, respectively. Unlike the commercial vortex tubes, this vortex tube is manufactured in a larger geometrical manner and the reason behind this is for the ease of manufacturing process. The length of the hot tube, L=290mm whereas

the inner diameter of the cold end, d=10mm and the inner diameter of the hot end, D=25mm. Aluminium is selected as the material to manufacture the vortex tube.

Figure 2. Rendered image of the designed vortex tube EXPERIMENTAL SETUP AND PROCEDURE Two different experimental setups are arranged since the experiments are conducted under two mass flow rates. In both of the setups, the pressurized air is supplied from the compressors and the temperature data are obtained with thermocouples. Three thermocouples are used and placed at the inlet, the cold end and the hot end, respectively. Pressure values of the compressed air at the inlet of the vortex tube are obtained by using regulators. Pressure data for 1.1 kg/s is gathered with Krohne Optiswirl 4200c regulator. The inlet pressure used in the experiments is 8 bar, however the pressure goes down up to 6 bar in low mass flow rate experiments because of the lack of flow rate. Throughout the experiments, inlet pressure, temperatures of the inlet, cold end and hot end are recorded simultaneously. For the experiments with high mass flow rates, E+E Elektronik EE772 flow meter is used to record total flow that enters the vortex tube. Total flow is then divided by the experiment duration to get the flow rate and multiplied by the density of the air for mass flow rate. Experiments with the low mass flow rates were conducted at Bilkent University laboratories without a flowmeter. In these experiments, the mass flow rate was estimated by filling a closed system and measuring the mass difference of the system and dividing by the filling duration therefore, the estimation may have error because of the leakage and increasing pressure of the system. Still, the measurement is appropriate to obtain mass flow rate data in the order of magnitude. Temperature data are collected by a data acquisition system and transferred to a daqbook. Data recording starts when the valve that controls the flow rate is opened. The experiments and the data recording continued until the system reached a steady state. The temperature data used in analysis is steady state data.


Figure 3. Parts of the vortex tube

A total of six experiments were conducted to achieve the desired goals of the experiment. For each flow rate case, variable parameter is selected as the control valve’s cone angle. 30, 45 and 70-degree cone angled control valves were used to investigate the effect of the control valve’s angle on the performance and efficiency of the vortex tube.

Figure 4. Control valves THERMODYNAMIC ANALYSIS OF THE VORTEX TUBE Isentropic efficiency, cold fraction and energy splitting effect are calculated to evaluate the performance of the vortex tube. Throughout the calculations, the system is assumed to be isentropic.

Isentropic efficiency is calculated as,

!"# =%&'%((*%)&,

(1)

."and ./ are the actual inlet and cold end temperatures and (Δ.)"# is the isentropic temperature difference. It is calculated as,

(Δ.)"# = ." 1 − 34563&7

89:8 (2)

Where,;<=> and ;"? are atmospheric and inlet pressures and @ is the specific heat ratio of the gas (for air, @ ≈1.4). Cold fraction, the ratio of mass flow rate of the cold outlet to the mass flow rate of the inlet, is calculated for evaluations. To calculate cold fraction, energy equation is solved initially.

ABA=+ AD

A== A>&7

A=ℎ"? +

F&7G

H+ IJ"? −

A>K

A=ℎL +

FKG

H+ IJL +A>(

A=ℎ/ +

F(G

H+

IJ/ (3)

Because of the fact that the data is taken at a steady state, rate of change of energy is cancelled. System is assumed to be adiabatic and no work is done by the system. Therefore M and N terms are cancelled. Change in potential energy and contribution of kinetic energy is also assumed to be negligible. The remaining equation is

A>&7A=

ℎ"? = A>K

A=ℎL +A>(

A=ℎ/ (4)

Therefore, the cold fraction is calculated as

O = LK'L&LK'L(

(5)

Energy splitting effect is a different efficiency calculation type based on temperature difference at hot and cold ends (Nimbalkar et al., 2009). It is calculated with the formula below.

/P(%K'%()

QB∗ 100 (6)

where TU is specific heat of air, .Land ./ are the hot and cold end temperatures and VN is compressor work used to pressurize the air. VN is calculated as,

VN = WW'X

Y.<=>3&

3456

Z9:Z − 1 (7)

where k is TU/T\. The formula is found through literature search. Nimbalkar (Nimbalkar et al., 2009) also uses the same formula to evaluate performance of the vortex tube according to the experimental results. RESULTS AND DISCUSSION According to the temperature data obtained from experiments, performance of the vortex tube is evaluated by temperature difference, isentropic efficiency and energy splitting effect of the vortex tube.


Figure 5. Change in temperature for different cold fraction

From the previous papers, it is understood that, the optimal cold mass fraction range to obtain better temperature differences is between 0.4 to 0.65 (Subudhi et al., 2015) thus the experiments focused on observing the temperature differences and efficiencies around that range. Figures that are shown in this paper, are chosen with respect to the data that provide the optimal cases. The figure given above displays the variation of the temperature differences with respect to the cold mass fraction. For the high mass flow rate cases, better temperature difference values are obtained at the cold mass fractions values that are mentioned above. For the high mass flow rate cases, the acquired cold fraction values were calculated as 0.41, 0.45 and 0.52, respectively. The differences in cold mass fraction occurred due to the change in the control valve’s angle. However, for the low flow case experiments, the cold mass fractions values are found to have larger values than it was proposed. These cold mass fractions are 0.6, 0.68 and 0.72, respectively. The interpretation drawn from this is; for the magnitude of the flow rate, the system’s characteristics differ from one another. In addition to that, when comparing these two different cases, it is clearly seen that the experiments that are under the effect of high mass flow rate, have smaller cold mass fraction values and better temperature differences compared to the other experiments that have higher cold mass fraction and smaller temperature differences. It can be concluded as; with larger mass flow rates, the outlet temperature values will be more optimal. In addition to that, as the cold mass fraction increases, the temperature differences occurred at both outlets of the vortex tube decreases but the temperature difference obtained at the hot end outlet of the RHVT is larger compared to the cold end outlet. The effect of control valve angle and mass flow rate are investigated by experimenting with three different angled control valves in two different mass flow rates. The valve angles are 30, 45 and 70-degree and mass

flow rates are 1.1 kg/s and 0.002 kg/s. The results of these experiments are compared with results from the paper of Tufekci (Tufekci, 2009), who used the same experimental setup at Dalgakıran Kompresör. The results taken from Tufekci are the results with cold fraction 0.45-0.55 which is the region of the experiments conducted. The results of experiments are given in graph below.

Figure 6. Change in temperature for different valve angles When results of 1.1 kg/s and 0.002 kg/s are compared, it is observed that experiment with the higher mass flow rate has higher temperature difference in both ∆. hot and ∆. cold. As flow rate increases, cooling and heating rate also increases. At steady state, the tube temperature is in equilibrium with ambient temperature. Cold air decreases the temperature of the tube and the ambient increases it at cold end and does the opposite at hot end. As mass flow rate increases, the equilibrium is conducted at more distinct temperatures. For 45° valve angle,∆. hot increases from 8.8 to 18.8 and ∆. cold increases from 6.4 to 20.2. This leads to higher isentropic efficiency, energy splitting effect and COP. The effect of increase in mass flow rate is not equal in ∆. hot and ∆. cold. As seen in graph, increase in mass flow rate increases ∆. cold more than ∆. hot.

The effect of control valve angle is also derived from graph. At 1.1 kg/s mass flow rate ∆. cold is not affected much from change in valve angle. The effect can be considered as negligible. However, there is significant increase at 45° compared to other angles. This makes 45° the most efficient angle at 1.1 kg/s mass flow rate. At other valve angles, one of the streams (hot or cold) is dominant to the other one. This prevents from the formation of a homogenous and steady flow in the tube. 45° creates an equal division because of its symmetrical geometry which in return provides a better performance. At 0.002 kg/s mass flow rate, vortex tube has different characteristics and gives different results. The best ∆.


cold value is obtained at 30° and best ∆. hot value is obtained at 70°. This reveals that there is not an optimum valve angle for vortex tube. The most efficient valve angle depends on the mass flow rate in the vortex tube. When compared with results of Tüfekci (2009), similar values are obtained at 45° valve angle. However change in ∆. hot is not as sharp as this experiment. This may be caused by the difference in mass flow rate. The mass flow rate of the experiments of Tüfekci (2009) is 0.011 kg/s. This is lower than the mass flow rate of the experiment in the order of magnitude. It may cause changes in the characteristic of the vortex as mentioned before. Therefore, different slope is obtained in the graph. Also it should be noted that the slope of the ∆. cold of the Tufekci is similar to the slope of experiment with 0.002 kg/s. As these mass flow rates are close, the vortex tube acts similarly and similar slopes are obtained in ∆. cold. The best ∆. cold is obtained at 40°. 40° control valve angle is not used in this experiment. So, it could be more efficient for this level of cold fraction. Isentropic efficiency of the tube is calculated according to the results of three different angled control valves in two different mass flow rates. The results are also compared with the maximum isentropic cooling efficiency of Tufekci.

Figure 7. Isentropic efficiency of vortex tube

The isentropic efficiency of high mass flow rate (1.1 kg/s) is clearly higher compared to that of low mass flow rate (0.002 kg/s), like ∆. hot and ∆. cold. The maximum increase is at 45°, from 5.5% to 15.5%. Maximum isentropic efficiency is obtained at 45° for 1.1 kg/s mass flow rate whereas it is obtained at 30° for 0.002 mass kg/s flow rate. This is caused by the change of characteristics of the vortex tube as mentioned before.

Although the mass flow rate Tufekci (Tufekci, 2009) uses is lower than 1.1 kg/s, its isentropic efficiency is higher. The reason of this is the L/D ratio of the tube he used. The vortex tube used in these experiments has a L/D ratio of 11.5 and L/D ratio of Tufekci is 20. That is why its efficiency is higher and the efficiency of the current vortex tube can be further enhanced by increasing L/D ratio. Energy splitting effect of the tube is calculated according to the results of three different angled control valves in two different mass flow rates.

Figure 8. Energy splitting effect of vortex tube

Energy splitting effect depends on temperature difference between cold end and hot end. That’s why the slope is different from the isentropic efficiency graph and it is significantly higher for the higher mass flow rate (1.1 kg/s) than the lower mass flow rate (0.002 kg/s). The effect of ∆. hot on energy splitting effect is observed clearly on 45° valve angle. There is a significant increase at 45° because of the increase in ∆. hot at high mass flow rate. As mentioned before the characteristic changes with mass flow rate, thus different slopes are obtained and 45° has the best energy splitting effect at 1.1 kg/s whereas worst energy splitting effect at 0.002 kg/s. Also it should be noted that vortex tube has a significant temperature increase at hot end which makes it considerable for heating applications. Kevser Dincer and Şenol Baskaya (2009) also investigated the efficiency of a RHVT with respect to control valve angle. They concluded that the most efficient control valve angle is 90° angle. The angle used in that study was the angle of top side of the valve. However, the angle used in this study is the complementary angle of the base angle, which makes 90° angle in their study to be 45° in our system which is in line with our findings. However, since the flow rate


was not reported explicitly, a detailed comparison is not possible. CONCLUSIONS Experimental studies on the RHVT have been accomplished on the effect of the flow rate and the geometry of the control valve’s angle. The experimental results have been compared with one of the previous articles written by Tufekci., The findings can be summarized as follows: • Under higher flow rate, the vortex tube has better

efficiency and temperature values. • For the high flow rate cases, the optimal control

valve angle is 45° compared to 30 ° and 70 ° control valves. Under the effect of low flow rate cases, the maximum efficiency and temperature difference values are obtained when 30 ° control valve is attached to the vortex tube. This difference arises because the characteristics of the low flow rate on the vortex tube vary for the high flow rates.

• The selected L/D ratio which is currently equal to 11.5 can be optimized by increasing the ratio to 20 since during experiments it is observed that the partial stagnation region at hot end and the cold core region at cold end were mixed into each other. Therefore, the separated temperature is wasted by mixing the cold and hot air.

• As mentioned in Experimental Setup and Procedure section, the experiments with low flow rate were conducted without flowmeter and may have error. In order to investigate effect of flow rate more accurately, further measurements should be performed with a flowmeter.

NOMENCLATURE TU specific heat at constant pressure (kJ/kg K) _ mass flow rate (kg/s) ` hot outlet diameter (mm) d cold outlet diameter (mm) L length of the hot tube (mm) M rate of heat transfer (kJ/s) ; pressure (Pa) .temperature (K) N rate of work (kJ/s) Y gas constant (kJ/kg K) VN compressor work per unit mass (kJ/kg) ℎ enthalpy (kJ/kg) a specific heat ratio b velocity (m/s) J height (m) O cold mass fraction

Subscripts atm atmosphere c cold air h hot air in inlet air ACKNOWLEDGEMENTS The project team would like to thank Dalgakıran Kompresör A.Ş. for their support and Mr. Mert Alpagut and Mr. Eren Çakır for their assistance throughout the experiments. REFERENCES Bruno TJ., 1992, Applications of the vortex tube in chemical analysis. Process control and quality 3. Amsterdam: Elsevier Science Publishers BV; p. 195–207 Colgate SA, Buchler JR., 2000 Coherent transport of angular momentum-the Ranque–Hilsch tube a paradigm, Astrophysical Turbulence and Convection. Ann. NY Acad., 898:105–12. Dincer, K., & Baskaya, S., 2009. Assessment of plug angle effect on exergy efficiency of counterflow ranque-hilsch vortex tubes with the exergy analysis method. J. Faculty Eng. Archit. Gazi University, 24(3), 533-538. Eiamsa-ard, Smith, and Promvonge P., 2008. Review of Ranque–Hilsch effects in vortex tubes. Renewable and Sustainable Energy Reviews, 12.7: 1822-1842. Fin’ko VE., 1983, Cooling and condensation of a gas in a vortex flow. Sov Phys: Tech Phys ;28 (9): 1089. Hilsch R., 1947, The Use of the Expansion of Gases in a Centrifugal Field as Cooling Process, The Review of Scientific Instruments, Vol. 18, No. 2, pp. 108–113. Martin RW, Zilm KW, 2004. Variable temperature system using vortex tube cooling and fiber optic temperature measurement for low temperature magic angle spinning NMR. J Magn Reson;168(2): 202–9. Nimbalkar, Sachin U., and Muller M R, 2009, An experimental investigation of the optimum geometry for the cold end orifice of a vortex tube. Applied Thermal Engineering 29.2 (2009): 509-514. Promvonge P., Pongjet, and Smith Eiamsa-ard., 2005, Investigation on the vortex thermal separation in a vortex tube refrigerator. ScienceAsia 31.1: 215-223.


Ranque G., 1933, Expériences sur la Détente Giratoire avec Productions Simultanées d'un Echappement d'air Chaud et d'un Echappement d'air Froid, J. de Physique et Radium 4(7), 112S. Riu K, Kim J and Choi IS., 2004, Experimental investigation on dust separation characteristics of a vortex tube. Trans JSME Ser B: Therm Fluid Mech; 47(1):29–36. Subudhi, Sudhakar, and Sen M, 2015, Review of Ranque–Hilsch vortex tube experiments using air. Renewable and Sustainable Energy Reviews 52: 172-178. Tufekci, Y., 2009, An Experimental Investigation of Vortex Tube Performance Characteristics, M.Sc. Thesis, Yeditepe University, Istanbul, Turkey Xue, Yunpeng, Arjomandi M., and Kelso R., 2013, The working principle of a vortex tube. J. Refrigeration 36 (6), 1730-1740.

AUTHORS’ BIOGRAPHY İlhami Ilgaz Aydoğdu has graduated from İ.D. Bilkent University Mechanical Engineering B.Sc. in 2017. His research interests are thermodynamics and machinery dynamics. He is going to start his graduate studies in Politecnico di Milano University by Fall 2017. Canberk Fidan has graduated from İ.D. Bilkent University Mechanical Engineering B. Sc. in 2017. His research interests are on renewable energy and thermodynamics. Barbaros ÇETİN is is a faculty member in the Mechanical Engineering Department at Bilkent University, Ankara, Turkey. He received his Ph.D. in the Department of Mechanical Engineering at Vanderbilt University. His research focuses on the electrokinetic transport and particle manipulation in lab-on-a-chip devices for biomedical applications, and modeling and experimentation of grooved heat pipes. He has co-authored more than 80 refereed journal, conference publications and encyclopedia entries. He has recently received Bilkent University Distinguished Teaching Award (2015) in recognition of excellence in teaching.

APPENDIX

Table 1: Table of the experimental results of the RHVT for L=11.5D and D=25mm

Experiment Number

Pi (bar)

Ti (Co)

_ (kg/s)

Control Valve Angle

(o)

Tc (Co)

TH (Co)

TH-Ti (Co)

Ti-Tc (Co) µC

Ƞisen (%)

Energy Spitting

Effect (%)

1 7.8 28.7 1.1 30 9.2 40 11.3 19.5 0.42 14.6 12.8

2 7.9 30.2 1.1 45 10 49 18.8 20.2 0.52 14.9 16.1

3 7.9 29.5 1.1 70 9.5 43 13.5 20 0.45 14.8 13.8

4 6 18.5 0.002 30 9.8 27.7 9.2 8.7 0.6 7.4 8.9

5 6 17.8 0.002 45 11.4 26.6 8.8 6.4 0.69 5.5 7.5

6 6 18.8 0.002 70 12.2 29.8 11 6.6 0.72 5.6 8.7

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