Experimental Thermal and Fluid Science 28 (2004) 557–563

www.elsevier.com/locate/etfs

Experimental study of the inert effect of R134a and R227eaon explosion limits of the flammable refrigerants

Yang Zhao *, Liu Bin, Zhao Haibo

Thermal Energy Research Institute, Tianjin University, 92 Weijin Road, Nankai, Tianjin 300072, China

Received 1 June 2002; accepted 30 June 2003

Abstract

Experimental studies of the inert effect of R134a and R227ea on explosive limits of the flammable refrigerants were carried out.

The ranges of the explosive limits of the mixture of R134a, R227ea and other six flammable refrigerants of HFCs and HCs were

obtained. The critical suppression explosive concentrations of these mixtures can be found from the envelopes. A model about the

explosive limits of the mixtures containing nonflammable component was proposed and can be used to estimate the flammability

limit of the mixtures.

� 2003 Elsevier Inc. All rights reserved.

Keywords: Flammable refrigerant; Explosion limit; Critical flammable concentration

1. Preface

Recently, owing to the banning of CFCs and some

HCFCs, their replacements’ fire and toxicity safety is

strongly interested now. De Smedt compared two test

methods for determining the mixture explosion [1].Yang defined two parameters to describe the mixture

explosion [2] and Shigeo proposed a new index to assess

the mixture combustion hazards [3]. Bolk studied the

flammability limit of ethene–air–nitrolien mixtures [4].

Robin studied the inert effect of HFC-227ea on flam-

mable refrigerants [5].

HCs such as R290, R600, R600a and HFCs such as

R32, R134a, R152a, R125, R227ea have been consid-ered as alternative refrigerants for CFCs and HCFCs

because of their zero ODP, acceptable GWP, high COP,

low discharging pressure less than 2.5 MPa and low

discharging temperature less than 150 �C. However,

their applications are limited because of their flamma-

bility [6–8]. An understanding of their flammability and

their inertion by the nonflammable component such as

HFCs is important in developing new refrigerants. So,

*Corresponding author. Tel.: +86-222-7890627; fax: +86-222-7404-

741.

E-mail address: zhaoyang@tju.edu.cn (Y. Zhao).

0894-1777/$ - see front matter � 2003 Elsevier Inc. All rights reserved.

doi:10.1016/j.expthermflusci.2003.06.005

the flammability experiments of these mixtures were

carried out.

2. Experimental results and discussion

According to National Standard GB/T12474-90, an

experimental set of the explosion limit of flammable

refrigerants was designed, as seen in Fig. 1 [9]. The

vessel is a vertical glass cylinder that is 1500 mm in

height and 50 mm in inner diameter. The ignite energy

is not more than 100 J. More details can be referred to

GB/T12474-90. Experiments of the explosion limit of

mixtures composed of one of the two nonflammablesubstitutes––R134a, R227ea and one of the flammable

refrigerants––R290, R600, R600a, R32, R134a, R152a

were made respectively and the results are depicted in

Fig. 2.

2.1. Explosion limit of mixture composed of R227ea and

one of R290, R600, R600a, R32, R134a, R152a

From Figs. 3 and 4, it can be seen that mixtures

composed of R227ea and HFCs have a higher volu-

metric ratio than mixtures composed of R227ea and

HCs.

Nomenclature

A one flammable componentB one flammable component

C one nonflammable component

D one nonflammable component

EAC the explosion limit when the volumetric ratio

of the mixture of A to C is equal to VC=VA (%)

EACR the critical explosion limit of the mixture

composed of A and C (%)

EADR the critical explosion limit of the mixturecomposed of A and D (%)

EB the explosion limit of BEBC the explosion limit when the volumetric ratio

of B to C in the mixture is equal to VDC=VB (%)

LFL the low flammable limit

RAC the ratio of VCAR to VAR0AC the ratio of VC to VADR

RAD the ratio of VD to VADRRBC the ratio of VCBR to VBUFL the up flammable limit

VA the volumetric fraction of VA

VADR the volumetric fraction of A when the mixturecomposed of A and D reaches the critical

flammable volumetric ratio (%)

VAR the critical volumetric fraction of A (%)

VB the volumetric fraction of VBVC the volumetric fraction of VCVCAR the volumetric fraction of C when the mixture

composed of A and C reaches the critical

flammable volumetric ratio (%)VCBR the volumetric fraction of the C when the

mixture composed of B and C reaches the

critical flammable volumetric ratio (%)

VCR the critical volumetric fraction of CVD the volumetric fraction of DVDA the remaining volumetric fraction of AVDC the remaining volumetric fraction of CX the ratio of VA to VBY the ratio of VD to VCb the ratio of the number of atom F to atom H

in the molecule

Fig. 1. The scheme of the test.

Nonflammable/flammable gas

II

III

I

UFL

LFL

The critical flaming point IV

The critical suppression line

The

vol

umet

ric

rati

o of

mix

ture

in a

ir (

%)

Fig. 2. The explosion limit of a mixture composed of two components.

558 Y. Zhao et al. / Experimental Thermal and Fluid Science 28 (2004) 557–563

2.2. Explosion limit of mixture composed of R134a and

one of R290, R600, R600a, R32, R134a, R152a

From Figs. 5 and 6, it can be found that the mixtures

composed of R134a and HFCs have a higher volumetric

ratio than the mixtures composed of R134a and HCs.

2.3. Experimental results and discussion

(1) For HCs such as R290, R600, R600a, there is little

disparity between their ranges of the explosive lim-

its. Little changes happen after the addition of sup-

pression flammable component to pure HCs.

(2) For HFCs, the flammable refrigerants such as R32,

R134a, R152a, the explosion limit is affected by the

0 1 2 3 4 50

5

10

15

20

25

R290

R600

R600a

R134/HC

The

vol

umet

ric

rati

o of

mix

ture

in a

ir (

%)

Fig. 5. The explosion limit of R134a/HC.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

5

10

15

20

25

30

35

R32

R143a

R152a

R134a/HFC

The

vol

umet

ric

rati

o of

mix

ture

in a

ir (

%)

Fig. 6. The explosion limit of R134a/HFC.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

2

4

6

8

10

12

14

16

R600

R600a

R290

R227ea/ HC

The

vol

umet

ric

ratio

of

mix

ture

in a

ir (

%)

Fig. 3. The explosion limit of R227ea/HC.

0.0 0.5 1.0 1.5 2.0 2.50

5

10

15

20

25

30

35

R32

R143a

R152a

R227ea/HFC

The

vol

umet

ric

rati

o of

mix

ture

in a

ir (

%)

Fig. 4. The explosion limit of R227ea/HFC.

Y. Zhao et al. / Experimental Thermal and Fluid Science 28 (2004) 557–563 559

parameter b, the ratio of the number of atom F to

the number of atom H in the molecule. With the in-

crease of b, the UFL (the up flammable limit) andLFL (the low flammable limit) increase and the

explosive danger reduces. After adding the nonflam-

mable component, the trend of explosion limit curve

is similar to that of the pure HFCs, and the differ-

ences between them become larger.

(3) In comparison with Figs. 3–6, it can be found that

the inert effect of R227ea is better than that of

R134a.(4) The results of the experiments have a good repro-

ducibility. So, they can be used for determining

flammability of the twelve groups of mixtures dis-

cussed in the paper, or for calculating the explosionlimit of tri-component refrigerant mixtures com-

posed of the above components.

3. Estimation of the explosion limit of mixtures containing

the nonflammable component

(5) Here, two mixtures were discussed. One was com-posed of one nonflammable component and two

flammable components, and the other was com-

posed of two nonflammable components and one

flammable component.

560 Y. Zhao et al. / Experimental Thermal and Fluid Science 28 (2004) 557–563

3.1. Mixture of two flammable components and one

nonflammable component

Supposing that A, B and C denote the three compo-

nents, A and B are flammable components while C isnonflammable. According to the different concentration

of the nonflammable component in the mixture, the

calculations of the explosion limit E (UFL or LFL) are

classified into three categories as follows:

(1) If the volumetric ratio of C to A or B is less than the

critical flammable volumetric ratio, C with A or Bcan form a new mixture. From the corresponding

explosion limit curve in the paper, its explosion limit

can be found. Then E can be calculated by the fol-

lowing equation according to the blend rule of

explosion limit [10]:

E ¼ 100VAþVCEAC

þ VBEB

ð1Þ

The calculated result and the difference between the

calculated and the experimental result of the mix-

ture composed of two flammable components andone nonflammable component are shown in Table 1.

(2) If the volumetric ratio of C to A or B is larger than

their critical flammable volumetric ratio and the ra-

tio to the other is less than their critical flammable

Table 1

The calculated and experimental results of mixtures composed of R600a, R2

Name Volumetric fraction Mixture

R600a/R290/R227ea 30/30/40 R600a+R227ea, R29

R290+R227ea, R600

R600a/R290/R134a 30/30/40 R600a+R134a, R290

R290+R134a, R600a

Table 2

The calculated and experimental results of some mixtures

Name Volumetric ratio Mixture

R143a/R290/R134a 30/30/40 R290+R134a, R143a

R152a/R290/R134a 20/30/50 R290+R134a, R152a

R32/R152a/R227ea 30/30/40 R152a+R227ea, R32

Table 3

The calculated and experimental results of mixtures composed of R143a, R1

Name Volumetric ratio Mixture concentration (%

R143a/R152a/R134a 20/15/65 R143a+R34a¼ 10+ 10.5

R152a+R43a¼ 20+ 59.5

R143a/R152a/R227ea 20/30/50 R143a+R227ea¼ 20+ 2

R152a+R227ea¼ 30+ 2

volumetric ratio, a new mixture can be formed by

the nonflammable component and the latter flam-

mable component. Its explosion limit can be calcu-

lated by Eq. (1). The calculated result and the

difference between the calculated and the experimen-tal result are shown in Table 2.

(3) If the volumetric ratio of C to A or B is larger than

their corresponding critical flammable volumetric

ratio, C is divided into two parts such that the ratio

of part of C to A or B is equal to the critical flamma-

ble volumetric ratio. The volume fraction of the

nonflammable component can be defined as

VC ¼ VCAR þ VDC ð2ÞIf VDC=VB > RBC, the mixture is nonflammable; if

VDC=VB 6RBC, from the corresponding explosionlimit curve in this paper, their explosion limits can

be found. Then E can be calculated by the following

equation [10]:

E ¼ 100

VA þ VCAREACR

þ VB þ VDC

EBC

ð3Þ

The calculated result of the explosion limit and the

difference between the calculated and the experimental

result of the mixture composed of R143a, R152a and

R125 are listed in Table 3.

90 and R227ea or R134a

Value of calculating

LFL/UFL

Value of experiment

LFL/UFL

Percent

difference

0 3.39/10.8 3.3/11.2 2.7/3.6

a 3.32/10.95 0.6/2.2

3.1/11.06 3.38/11.6 8.3/4.7

3.23/10.34 4.4/2.4

Value of calculating

LFL/UFL

Value of experiment

LFL/UFL

Percent

difference

5.5/14.5 5.1/15.6 )7.8/7.15.39/14.69 4.97/15.4 )10.2/4.612.44/25.6 13.2/25.2 5.8/)1.6

52a and R134a or R227ea

) Value of calculating

LFL/UFL

Value of experiment

LFL/UFL

Percent

difference

19.86/24.9 21.3/24.1 6.8/)3.3

2 11.02/27.9 12.3/26.7 10.04/)4.58

Table 4

The calculated and experimental results of mixture composed of R290, R134a and R227ea

Name A=D=C Volumetric ratio Calculating parameter Value of calculating

LFL/UFL

Value of experiment

LFL/UFL

Percent

difference

R290/R134a/R227ea 40/30/30 RAD ¼ 4:05, VDA ¼ 32:6 6.3/12.6 6.7/13.1 6.0/3.05

VADR ¼ 7:4, EADR ¼ 13:1

EACL ¼ 4:8, EACU ¼ 12:3

Y. Zhao et al. / Experimental Thermal and Fluid Science 28 (2004) 557–563 561

3.2. Mixture of one flammable component and two

nonflammable components

Supposing that A, C and D denote the three compo-

nents, A is flammable components while C and D are

nonflammable. Because the nonflammable components

are more than the flammable component, the explosion

limit cannot be calculated by the above method. But itcan be obtained in the following way: the flammable

component is divided into two parts such that the ratio

of part of A to D or C is equal to the critical flammable

volumetric ratio. The volume fraction of the flammable

component can be defined as

VA ¼ VADR þ VDA ð4ÞIf VC=VDA > RAC, the mixture is nonflammable; if

VC=VDA 6RAC, from the related envelopes of the explo-

sion limit in this paper, their explosion limits can be

found. Therefore, E can be calculated by the followingequation [10]:

E ¼ 100VDþVADREADR

þ VCþVDAEAC

ð5Þ

The calculated result and the difference between thecalculated and the experimental results of some mixtures

are listed in Table 4.

From Tables 1–4, it can be seen that the calculated

results are consistent with the experimental results, and

the differences are less than 10%. It also can be found

that R227ea has a better inert effect than R134a has.

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.0

0.2

0.4

0.6

0.8

1.0

R13

4a

R290

R32

Flammable zone

The critical flammable line

Nonflammable zone

Fig. 7. The flammable range of R32/R290/R134a.

4. Calculation of the critical suppression explosion

concentration of the mixture containing nonflammable

components

It is important to determine the critical suppression

explosion concentration in the application of the mix-

ture containing flammable compounds. A method of

rearranging the components of the mixtures to make thenumber of the nonflammable components equal to that

of the flammable ones is proposed in this part.

4.1. Mixture of two flammable components and one

nonflammable component

If the value of VA=VB is known, VA, VB and VCR can be

calculated by Eqs. (7) and (8). That is, given

VAVB

¼ X ð6Þ

one has

VA þ VB þ VCR ¼ 100 ð7ÞVCR ¼ VCAR þ VCBR ð8Þ

Transforming Eqs. (6)–(8) yields the following set of

equations:

VBðIÞ ¼100

X ðIÞ þ X ðIÞ � RAC þ RBC þ 1

VAðIÞ ¼ X ðIÞ � VB I ¼ 1; 2; 3; . . . ; nVCRðIÞ ¼ 100� VAðIÞ � VBðIÞ

8>><>>:

ð9Þ

Eq. (9) is an iterative form for different values of X .

The calculation examples are shown in Figs. 7 and 8.

Fig. 7 depicts the flammable zone of the mixture

composed of R134a, R290 and R32. Fig. 8 shows the

flammable zone of the mixture composed of R227ea,

R143a and R290.

4.2. Mixture of one flammable component and two

nonflammable components

If the value of VD=VC is known, VA, VD and VAR can be

calculated by Eqs. (11) and (12). That is, given

VDVC

¼ Y ð10Þ

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.0

0.2

0.4

0.6

0.8

1.0

R13

4a R227ea

R600a

Nonflammable zone

Flammable zone

The critical flammable line

Fig. 10. The flammable range of R600a/R227ea/R134a.

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.0

0.2

0.4

0.6

0.8

1.0

R22

7ea

R143a

R290

Flammable zone

Nonflammable zone

The critical flammable

Fig. 8. The flammable range of R290/R143a/R227ea.

562 Y. Zhao et al. / Experimental Thermal and Fluid Science 28 (2004) 557–563

one has

VAR þ VD þ VC ¼ 100 ð11Þ

VAR ¼ VADR þ VACR ð12ÞTransforming Eqs. (10)–(12) yields the following set

of equations:

VCðIÞ ¼100

Y ðIÞ þ Y ðIÞ=RAD þ 1=R0AC þ 1

VDðIÞ ¼ Y ðIÞ � VCðIÞ I ¼ 1; 2; 3; . . . ; n

VARðIÞ ¼ 100� VDðIÞ � VCðIÞ

8>>><>>>:

ð13Þ

Eq. (13) is an iterative form for different values of X .

The calculation examples are shown in Figs. 9 and 10.Fig. 9 shows the flammable zone of the mixture

composed of R134a, R227ea and R290. Fig. 10 illus-

trates the flammable zone of the mixture composed of

R134a, R227ea and R600a.

From Figs. 7–10, it can be found that with the in-

crease of the number of nonflammable components in

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.0

0.2

0.4

0.6

0.8

1.0

R13

4a R227ea

R290

Nonflammable zone

The critical flammable line

Flammable zone

Fig. 9. The flammable range of R290/R227ea/R134a.

refrigerant mixtures, the area of the nonflammable zone

expands. It means that the safety of the mixture in-creases.

5. Conclusions

New HCs and HFCs mixtures containing nonflam-

mable components were developed to substitute ozonedepleting CFCs and HCFCs mixtures. Our results show

that the R227ea has a better inert effect than that of

R134a. It provides a guidance to develop new refriger-

ants with low ODP. But other characters such as ther-

modynamic properties, compatibility with equipments,

economics, etc., still need to be further studied.

The approaches of calculating the explosion limit

presented here can be applied to any mixture, with nolimitations to the number of flammable and nonflam-

mable components. Differences between results obtained

by mathematical methods and experiments are presented

in this paper, which show that the approaches are reliable.

Acknowledgements

This project (No. 50376048) is supported by NSFC,

by the National Education Department for doctor cen-

tre foundation and by the Tianjin Science and Tech-

nology Committee for Scientific and Technical

Development.

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