a generalized correlation for refrigerant mass flow rate through adiabatic capillary tubes

A generalized correlation for refrigerant mass flow ratethrough adiabatic capillary tubes

Jongmin Choi, Yongchan Kim*, Ho Young Kim

Department of Mechanical Engineering, Korea University, Anam-Dong, Sungbuk-Gu, Seoul, 136-701, South Korea

Received 24 March 2003; received in revised form 26 May 2003; accepted 26 May 2003

Abstract

A capillary tube is a common expansion device used in small sized refrigeration and air-conditioning systems. Ageneralized correlation for refrigerant flow rate in adiabatic capillary tubes is developed by implementing dimensionlessparameters based on extensive experimental data for R-22, R-290, and R-407C measured in this study. Dimensionless

parameters are derived from the Buckingham Pi theorem, considering the effects of tube inlet conditions, capillary tubegeometry, and refrigerant properties on mass flow rate. The generalized correlation yields good agreement with thepresent data for R-22, R-290, and R-407C with average and standard deviations of 0.9 and 5.0%, respectively.

Approximately 97% of the present data are correlated within a relative deviation of �10%. Further assessments of thecorrelation are made by comparing the predictions with measured data for R-12, R-134a, R-152a, R-410A, and R-600ain the open literature. The correlation predicts the data for those five refrigerants with average and standard deviationsof �0.73 and 6.16%, respectively.

# 2003 Elsevier Ltd and IIR. All rights reserved.

Keywords: Air conditioner; Domestic refrigerator; Refrigerant; Flow; Capillary tube; Expansion device; Simulation; R-22; R-407C;

R-290

Correlation generale pour les flux massiques de frigorigenesen ecoulement a l’interieur de tubes capillaires adiabatiques

Mots cles : Conditionneur d’air ; Refrigerateur domestique ; Frigorigene ; Debit ; Capillaire ; Detente ; Simulation ; R-22 ; R-407C ;

R-290

1. Introduction

Due to environmental concerns on the depletion ofthe ozone layer and global warming, CFC (chloro-

fluorocarbon) and HCFC (hydrochlorofluorocarbon)are being phased out from the refrigeration industry. As

a result, HFC (hydrofluorocarbon), HC (hydrocarbon),and HFC mixtures have emerged as alternatives of R-12and R-22. A capillary tube is a constant area expansiondevice, which has been widely used in small vapor-com-

pression refrigeration and air-conditioning systems.Since an improperly sized capillary tube can significantlyreduce the performance of a refrigeration system [1,2], the

0140-7007/$35.00 # 2003 Elsevier Ltd and IIR. All rights reserved.

doi:10.1016/S0140-7007(03)00079-3

International Journal of Refrigeration 26 (2003) 881–888

www.elsevier.com/locate/ijrefrig

* Corresponding author. Tel.: +82-2-3290-3366; fax: +82-

2-921-5439.

E-mail address: [email protected] (Y. Kim).

http://www.elsevier.com/locate/ijrefrig/a4.3d

mailto:[email protected]

capillary tube working with alternative refrigerants mustbe redesigned. In order to provide an appropriate tool todesign a capillary tube, a generalized flow correlation for

alternative refrigerants must be developed.In the past, many theoretical studies on capillary

tubes have been published [3–13]. Most of the theo-

retical capillary tube models modified the friction factoror delay of vaporization to obtain consistent results withthe measured data. Experimental studies for not only

explaining flow phenomena in capillary tubes but alsopredicting refrigerant flow rate were extensively per-formed by many researchers [14–24]. Wolf et al. [22]developed generalized correlations for subcooled and

two-phase inlet conditions by using the Buckingham Pitheorem [23] with the test data for R-22, R-134a, andR-410A. Melo et al. [3] also presented empirical correl-

ations for adiabatic capillary tubes using the data ofR-12, R134a, and R-600a. Recently, Kim et al. [24]developed a dimensionless correlation for straight and

coiled capillary tubes using R-22, R-407C, and R-410Ain a similar format as the Wolf et al. correlation.The existing correlations in the literature do not suf-

ficiently cover possible alternative refrigerants of R-12and R-22 due to narrow spectrum of database and/orpoor validation of the model with these refrigerants. Inaddition, some existing correlations include complicated

dimensionless parameters due to an inclusion of repeat-ing variables such as viscosity and specific volume whengenerating dimensionless Pi-groups. The objective of

this study is to develop a generalized correlation in asimple form that can be used in the prediction of massflow rate of alternative refrigerants in adiabatic capillarytubes. Combining dimensionless parameters derived

from extensive experimental data for R-22, R-290, andR-407C measured in this study develops a generalizedcorrelation for alternative refrigerants. The predictions

from the present correlation are compared with experi-mental data and the correlations of other researchers.Besides, further assessments of the correlation are made

by comparing predictions with measured data in the lit-erature with R-12, R-22, R-134a, R-152a, R-410A, andR-600a.

2. Experiments

The experimental setup shown in Fig. 1 was used tomeasure the performance of various adiabatic capillarytubes. A self-lubricating diaphragm pump with a vari-

able-speed motor was used to provide a wide range ofrefrigerant mass flow rates. A bypass line with a needlevalve was installed between the pump and downstream

of the test section to provide precise control of testconditions and system stability. The inlet pressure of thetest section was controlled by adjusting pump speed.

Refrigerant subcooling entering the test section was setby a water-heated heat exchanger. The two-phaserefrigerant exiting the test section was condensed andsubcooled in a water/glycol cooled heat exchanger, so

that the refrigerant pump had only liquid at its suctionside. The exit pressure of the test section was controlledby adjusting temperature and flow rate of the chilled

water/glycol mixture entering the water/glycol cooledheat exchanger.The refrigerant flow rate was measured by a Coriolis

effect mass flow meter with an uncertainty of �0.2% ofreading. The pressures and temperatures of the refriger-ant at the inlet and outlet of the test section were mon-itored using pressure transducers with an uncertainty of

�0.2% of full scale (3447 kPa) and T-type thermo-couples with an uncertainty of �0.2 �C, respectively.The length of a capillary tube was measured by a dial

caliper with an uncertainty of �0.013 mm. The tubediameter was measured using a precision plug gauge setwith an uncertainty of �0.013 mm. The measured data

were recorded using a data acquisition system aftersteady state conditions were reached.Table 1 shows the specification of capillary tubes and

test conditions in this study. Nine capillary tubes madeof copper were tested with three refrigerants: R-22,R-290, and R-407C. Test conditions were chosen tocover a wide range of operating conditions for capillary

tubes used in small sized residential air-conditioners.The inlet refrigerant pressure of the capillary tube wasadjusted to the saturation pressure corresponding to the

Nomenclature

D Inner diameter (m)hfg Heat of vaporization (J/kg)

L Length (m)m:

Mass flow rate (kg/s)Pc Critical pressure (Pa)Pin Inlet pressure (Pa)

Psat Saturated pressure (Pa)Tc Critical temperature (�C)DTsub Degree of subcooling (�C)

Greek letters� Density (kg/m3)

� Dimensionless parameter group� Surface tension (N/m)� Viscosity (Pa.s)

Subscriptsf Saturated liquidg Saturated vapor

meas Measuredpred Predicted

882 J. Choi et al. / International Journal of Refrigeration 26 (2003) 881–888

condensing temperatures of 38, 45, and 52 �C, whilethe exit pressure of the capillary tube was maintained atthe saturation pressure corresponding to the evaporating

temperature of 7 �C. For each condensing temperature,the degree of subcooling at the capillary tube inlet wasvaried at 1, 4, 9, and 14 �C. Condensing temperature of

R-407C was determined by averaging dew point andbubble point temperatures at constant pressure.

3. Development of a generalized correlation

3.1. Data analysis

Experimental data for R-22, R-290, and R-407C areanalyzed with respect to inlet conditions (pressure and

subcooling) and dimensionless parameters for capillarytube geometry, viscosity, and surface tension, which are

derived by the Buckingham Pi theorem [23] and given inTable 2. Fig. 2 shows the variations of mass flow rate asa function of condensing temperature and dimensionless

viscosity in the capillary tube with an inner diameter of1.21 mm and a length of 1000 mm. For each refrigerantat a given dimensionless viscosity, the mass flow rate

increases with a rise of condensing temperature from 38to 45 �C due to an increase of inlet pressure (or con-densing pressure), which was also observed in previous

researches conducted with R-12, R-22, R-134a, R407C,and R-410A [5,10,22,24]. R-407C shows the highestmass flow rate for given condensing temperatures due toits higher vapor pressure than other refrigerants at the

same average condensing temperature. Besides, the massflow rates for given condensing temperatures arestrongly dependent on dimensionless viscosity

ð�f � �gÞ=�g, which is calculated using saturationproperties for a given inlet temperature. It should benoted that the dimensionless viscosity becomes higher

with an increase of inlet subcooling at a given conden-sing temperature.Fig. 3 represents mass flow rates as a function of inlet

subcooling and dimensionless surface tension in thecapillary tube with an inner diameter of 1.21 mm and alength of 1000 mm. As the inlet subcooling becomeshigher at a given dimensionless surface tension, the mass

flow rate increases because the flashing point movestoward the capillary exit. The delay of the flashing pro-vides more liquid portion in the capillary tube. This

Fig. 1. Schematic diagram of the experimental setup.

Table 1

Test conditions

Refrigerants
R-22, R-290, R-407C
Capillary tube length (mm)
700, 1000, 1300
Capillary tube I.D. (mm)
0.96, 1.21, 1.36
Condensing temperature (�C)
38.0, 45.0, 52.0
Evaporating temperature (�C)
7
Degree of subcooling (�C)
1.0, 4.0, 9.0, 14.0
J. Choi et al. / International Journal of Refrigeration 26 (2003) 881–888 883

trend was also observed by previous researchers[10,18,22,24]. Besides, the mass flow rates for given inletsubcoolings are linearly reduced with an increase of

dimensionless surface tension �=ðDPinÞ. The surfacetension, which increases with a reduction of saturationtemperature, contributes on flow friction and bubble

nucleation in capillary tube flow.Fig. 4 shows the effects of capillary tube geometry on

mass flow rate at a condensing temperature of 45 �C.

The mass flow rate was approximately proportional tothe square of the capillary tube diameter, while it wasapproximately inversely proportional to the capillarytube length. As the dimensionless geometric parameter

of L=D increases, the mass flow rate for a given sub-cooling rapidly decreases due to a rise of flow restric-tions. However, as the L=D increases over a certain

value, the drops in mass flow rate become insignificant.As shown in Fig. 4, all refrigerants show the same trendsof mass flow rates with respect to L=D.

3.2. Generalized correlation

In order to generate appropriate dimensionless para-

meters for the generalized correlation, variables influen-cing mass flow rate through capillary tubes are selectedbased on data analysis. Operating parameters con-

sidered in this study are inlet pressure Pin, degree ofsubcooling DTsub, and saturation pressure Psat corre-sponding to inlet temperature. The saturation pressure

Psat is included to consider the effects of the pressuredifference between Pin and Psat in subcooled liquid state.The pressure difference Pin � Psat shows strong influenceon refrigerant mass flow rate through a capillary tube

because it determines the length of the liquid portion inthe capillary tube [20]. The exit pressure is not includedsince choking flow conditions are easily established in

capillary tubes for typical steady-state applicationswhere the exit pressure is lower than saturation pressurePsat [5,22,24].

The existence of the metastable region increasesrefrigerant mass flow rate through a capillary tube due

Fig. 2. Effects of flow patterns on heat transfer coefficients.

Fig. 3. Effects of subcooling and dimensionless surface tension.
Fig. 4. Effects of L/D.

to a relatively higher fluid density. The influence ofmetastable flow can be represented as a function of sur-face tension, pressure drop, and surface geometry withwhich the liquid is in contact [20]. Therefore, the selec-

ted properties associated with metastable flow and fric-tion are viscosity � and density � of both the liquid andvapor phases, and surface tension �. In addition to these

variables, critical temperature Tc and heat of vaporiza-tion hfg are also included to non-dimensionalize inletsubcooling DTsub and to consider potential effect of

vapor bubble formation and growth, respectively.Capillary tube diameter D and length L are included toconsider geometric effects on mass flow rate. Surfaceroughness of inner wall affects the friction loss, the

inception of flash, and the mass flow rate. However, thesurface roughness is not included in the dimensionlessparameter because the commercial tubes are available

only in a limited band of surface roughness. The surfaceroughness of the commercial capillary tubes tested inthis study ranges from 0.09 to 0.15 mm. Finally, the

mass flow rate can be represented by

m:¼ f ððPin � PsatÞ;DTsub;L;D; �f ; �g; �f ; �g; �; hfg;TcÞ

ð1Þ

Eight dimensionless Pi-groups are derived by com-

bining selected variables in Eq. (1) with the four repeat-ing variables D; �f ; �f , and Tc based on theBuckingham Pi theorem [23]. The definition and effect

of each Pi-group on capillary tube flow are given inTable 2. To generate a simple form of dimensionless Pi-groups, the complicated repeating variable �2

f =ð�fD2Þ

included in original parameters is replaced by Pin, Pc, or

Psat in modified parameters. Besides, the original �5

group �g=�f is modified as ð�f � �gÞ=�g since themodified parameter shows better dependence on mass

flow rate during data analysis.The generalized correlation for the dimensionless

mass flow rate �8 is generated in a power law form of

the remaining Pi-groups. The power law form was alsoused in Refs. [22,24]. The coefficient and exponents ofthe seven independent Pi-groups are determined using a

non-linear regression technique along with the experi-mental data for R-22, R-407C, and R-290 measured inthis study. All properties of the refrigerants were calcu-lated using REFPROP [25]. Finally, the generalized

correlation for refrigerant mass flow rates throughadiabatic capillary tubes is given as

�8 ¼ 1:313�

10�3 ��0:0871 �0:188

2 ��0:4123 ��0:834

4 �0:1995 ��0:368

6 �0:9927

ð2Þ

4. Verification and extension of the generalized

correlation

4.1. Comparison with test data for R-22, R-290, and

R-407C

The generalized correlation is verified by comparing

predicted mass flow rates using Eq. (2) with the mea-sured data for R-22, R-290, and R-407C. These resultsare represented in Fig. 5. Approximately 97% of the

experimental data are correlated within a relativedeviation of �10%. Generally, the correlation yields

Fig. 5. Comparison of predicted mass flow rate with measured

data in this study.

Table 2

Dimensionless Pi-groups

Pi-

group

Original

parameter

Modified

parameter

Effect

�1
ðPin � PsatÞ�fD
2

�2f

Pin � Psat

Pc
Inlet pressure
�2
DTsub
Tc

DTsub

Tc
Subcooling
�3
L
D

L

D
Geometry
�4
�f�g
�f�g

Density

�5
�g
�f

�f � �g

�g
Friction,
bubble growth

�6
��fD
�2f

�

DPin
Friction,
bubble growth

�7
hfg�
2fD

2

�2f

�fhfgPsat

Vaporization

�8

m:

D�f

m:

D 2ffiffiffiffiffiffiffiffiffiffiffi�fPin

p
Mass flow rate

good agreement with the measured data in all test con-ditions for R-22, R-290, and R-407C with average andstandard deviations of 0.90 and 5.0%, respectively.The validity of the correlation is further assessed by

comparing predicted mass flow rates with R-22 usingEq. (2) with the measured data of Wolf et al. [22] thatare not used in developing correlation. As shown in

Fig. 6, approximately 98% of predicted mass flow ratesare consistent with the measured data for R-22 within arelative deviation of �10%. Even though Wolf et al.’s

data [22] cover higher mass flow ranges beyond the pre-sent data used in developing the correlation, the corre-lation yields good prediction results for R-22 with

average and standard deviations of 0.88 and 5.70%,respectively.

4.2. Extension of the correlation to other refrigerants

To extend application limits of the correlationimposed by data source, the predicted mass flow rates

using Eq. (2) are compared with the measured datareported by previous investigators [3,11,22] with R-12,R-134a, R-152a, R-410A, and R-600a that are not used

in the development of the present correlation. Fig. 7shows the comparison of the predicted with measuredmass flow rates for R-12, R-134a, R-152a, R-410A, and

R-600a. Approximately 96.4% of the data are corre-lated within a relative deviation of �15%, while 89.2%data fall within a relative deviation of �10%. In addi-tion, the correlation predicts test data for those five

refrigerants with average and standard deviations of�0.73 and 6.16%, respectively.Figs. 8 and 9 show relative deviations of the predicted

data using Eq. (2) from the measured data for HFC andHC refrigerants, respectively, with respect to inlet pres-sure. The present correlation predicts the data for HFC


data for R-22.


data in open literature.

Fig. 8. Deviations of predicted mass flow rate from measured

data for HFC refrigerants.

Fig. 9. Deviations of predicted mass flow rate from measured

data for HC refrigerants.


bStan: dev: ¼

n 1½ðm:pred �m

:measÞ � 100Þ=m

:meas

2�Ave: dev:2.

refrigerants ranging from �10 to +15% at all test

conditions. Relative deviations of the experimental datafor HC refrigerants from the predicted values are from�17 to +15% at all test conditions. The deviations inthe predictions for R-290 are relatively high as com-

pared to Melo et al.’s data [11] due to lower flow rangesand higher experimental uncertainties.Average and mean deviations of the present corre-

lation, the Wolf et al. correlation [22], and the Melo etal. correlation [3] from the database for eight refriger-ants in the open literature [3,11,22] are represented in

Table 3. The Wolf et al. correlation [22] shows relativelyhigher average and mean deviations for all refrigerantgroups. Their correlation yields average deviations of6.9% for HCFC and 10.02% for HFC refrigerants.

However, it significantly over-predicts the data of CFCand HC refrigerants with average deviations of 16.24and 25.22%, respectively, due to the limited database

for these refrigerants. The Melo et al. correlation alsoyields good predictions for HCFC and HFC refrigerantswith average deviations of 2.96 and �0.14%, respec-

tively, but it shows large over-predictions for HCrefrigerants with an average deviation of 16.38%. Thepresent correlation yields relatively good agreement

with the experimental data for all refrigerant groups.The maximum average and standard deviations of thepresent correlation are �4.4% for CFC and 6.61% forHC refrigerants, respectively. Based on these compar-

isons, it can be concluded that the selected dimension-less parameters in a simple form are appropriate for allrefrigerant groups considered in this study.

Basically, the generalized form of the correlation can

be applied to predict refrigerant mass flow rate throughadiabatic capillary tubes with extensive ranges of oper-ating conditions and refrigerants. However, the accu-racy of the correlation cannot be guaranteed when the

correlation is applied beyond the ranges of the database.Limitations on the application of the present correlationinclude capillary tube lengths from 508 to 5080 mm,

capillary tube inner diameters from 0.66 to 3.05 mm,inlet pressures from 532 to 2990 kPa, and inlet subcool-ings from 0.7 to 18.9 �C. The working fluids can be

extended to R-12, R-134a, R-152a, R-410A, and R-600abecause the correlation was verified with those refriger-ants based on other researchers’ data. It should be notedthat the correlation is only applicable for the refriger-

ants without oil.

5. Conclusions

The performance of the adiabatic capillary tubes with

R-22, R-407C, and R-290 was measured by varying tubeinlet conditions and tube geometries. Based on thesedata, a generalized correlation to predict refrigerant

mass flow rate through adiabatic capillary tubes isdeveloped by implementing dimensionless parametersthat were created using the Buckingham Pi theoremconsidering the effects of tube inlet conditions, tube

geometries, and refrigerant properties. The generalizedcorrelation yields good agreement with the present datafor R-22, R-290, and R-407C with average and standard

Table 3

Comparison of the correlations with experimental data

Correlations

Wolf et al. [22]
Melo et al. [3] Present
Data source
Ave. dev.a Stan. dev.b Ave. dev. Stan. dev. Ave. dev. Stan. dev.
CFC
Melo et al. R-12 16.24 5.12 �0.36 3.93 �4.40 3.51
HCFC
Present R-22 6.90 11.41 2.96 9.32 0.88 5.70
Wolf et al.
R-22
HFC
Present R-407C 10.02 16.80 �0.14 12.29 0.98 4.87
R-134a

Wolf et al.
R-152a
R-410A

Melo et al.
R-134a
Dirik et al.
R-134a
HC
Present R-290 25.22 8.63 16.38 10.12 �1.11 6.61
Melo et al.
R-600a
X
aAve: dev: ¼
1

n

n

1½ðm:pred �m

:measÞ � 100Þ=m

:meas.

1Xn


deviations of 0.90 and 5.0%, respectively. Further ver-ifications of the correlation are made by comparing thepredictions with measured data reported by previousresearchers with R-12, R-134a, R-152a, R-410A, and

R-600a. Average and standard deviations of the corre-lation from the data for those five refrigerants are—0.73and 6.16%, respectively. The correlations of Wolf et al.

[22], and Melo et al. [3] show large over-predictions forHC refrigerants with average deviations of 25.22 and16.38%, respectively.

Acknowledgements

This work was supported by the Carbon DioxideReduction & Sequestration Center, one of the 21stCentury Frontier R&D Programs in the Ministry of

Science and Technology of Korea, and the KoreaScience & Engineering Foundation (Grant No. R01-2002-000-00481-0).

References

[1] Bansal PK, Rupasinghe AS. An empirical correlation for

sizing capillary tubes. Int J Refrigeration 1996;19(8):497–

505.

[2] Choi JM, Kim YC. The effects of improper refrigerant

charge on the performance of a heat pump with an elec-

tronic expansion valve and capillary tube. Energy 2002;

27(4):391–404.

[3] Melo C, Ferreira RTS, Neto CB, Goncalves JM, Mezavila

MM. An experimental analysis of adiabatic capillary

tubes. Applied Thermal Eng 1999;19:669–94.

[4] Bittle RR, Pate MB. A theoretical model for predicting

adiabatic capillary tube performance with alternative

refrigerants. ASHRAE Trans 1996;102(2):52–64.

[5] Bolstad NM, Jordan RC. Theory and use of the capillary

tube expansion device; part II, non-adiabatic flow.

Refrigerating Eng 1949;57(6):572–83.

[6] Marcy GP. Pressure drop with change of phase in a

capillary tube. Refrigerating Eng 1949;57(1):53–7.

[7] Hopkins NE. Rating the restrictor tube. Refrigerating Eng

1950;58(11):1087–95.

[8] Whitesel HA. Capillary two-phase flow. Refrigerating Eng

1957;65(9):35–47.

[9] Milkol EP. Adiabatic single and two-phase flow in small

bore tubes. ASHRAE Journal 1963;5(11):75–86.

[10] Kuehl SJ, Goldschmidt VW. Modeling of steady flow of

R-22 through capillary tubes. ASHRAE Trans 1991;97(1):

139–48.

[11] Dirik E, Inan C, Tanes MY. Numerical and experimental

studies on adiabatic and non-adiabatic capillary tubes

with HFC-134a. In: Proceedings of the Int. Refrigeration

Conf. at Purdue, West Lafayette, Indiana, USA; 1994. p.

365–70.

[12] Wong TN, Ooi KT. Adiabatic capillary tube expansion

devices: a comparison of the homogeneous flow and

separated flow models. Applied Thermal Engineering

1996;16(7):625–34.

[13] Escanes F, Perez-Segarra CD, Oliva A. Numerical simu-

lation of capillary-tube expansion devices. Int J Refrig-

eration 1995;18(2):113–22.

[14] Stabler LA. Theory and use of a capillary tube for liquid

refrigerant control. Refrigerating Eng 1948;55(1):55–9.

[15] Lathrop HF. Application and characteristics of capillary

tubes. Refrigerating Eng 1948;56(2):1–33.

[16] Prosek JR. A practical method of selecting capillary tubes.

Refrigerating Eng 1953;61:644–7.

[17] Cooper I, Chu CK, Brisken WR. Simple selection method

for capillary derived from physical flow conditions.

Refrigerating Eng 1957;65(7):37–41.

[18] Koizumi H, Yokoyama K. Characteristics of refrigerant

flow in a capillary tube. ASHRAE Trans 1980;86(2):19–

27.

[19] Li RY, Lin S, Chen ZH. Numerical modeling of thermo-

dynamic non-equilibrium flow of refrigerant through

capillary tubes. ASHRAE Trans 1990;96(1):542–9.

[20] Chen ZH, Li RY, Lin S, Chen ZY. A correlation for

metastable flow of refrigerant 12 through capillary tubes.

ASHRAE Trans 1990;96(1):550–4.

[21] Wijaya H. Adiabatic capillary tube test data for HFC-

134a. In: Proceedings of the Int. Refrigeration Conf. at

Purdue, West Lafayette, Indiana, USA; 1992. p. 63–71.

[22] Wolf DA, Bittle RR, Pate MB. Adiabatic capillary tube

performance with alternative refrigerants. ASHRAE RP-

762, 1995.

[23] Buckingham E. On physically similar systems: illustrations

of the use of dimensional equations. Physical Review

1914;4(4):345–76.

[24] Kim SG, Kim MS, Ro ST. Experimental investigation of

the performance of R22, R407C, and R410A in several

capillary tubes for air-conditioner. Int J Refrigeration

2002;25:521–31.

[25] McLinden MO, Klein SA, Lemmon EW, Peskin AP.

NIST thermodynamic and transport properties of refrig-

erant and refrigerant mixtures (REFPROP). Version 6.01.

Gaithersburg, MD: NIST, 1998.


a generalized correlation for refrigerant mass flow rate through adiabatic capillary tubes

Documents