Accepted Manuscript

Vapor-liquid equilibrium measurements and assessments of fluoroethane + N,N-dimethylformamide and fluoroethane + dimethylether diethylene glycol systems forthe hybrid refrigeration cycle

Rulei Deng, Xuye Jing, Danxing Zheng, Xiaoxiao Li

PII: S0140-7007(14)00067-X

DOI: 10.1016/j.ijrefrig.2014.04.001

Reference: JIJR 2752

To appear in: International Journal of Refrigeration

Received Date: 30 October 2013

Revised Date: 28 March 2014

Accepted Date: 1 April 2014

Please cite this article as: Deng, R., Jing, X., Zheng, D., Li, X., Vapor-liquid equilibrium measurementsand assessments of fluoroethane + N,N-dimethylformamide and fluoroethane + dimethylether diethyleneglycol systems for the hybrid refrigeration cycle, International Journal of Refrigeration (2014), doi:10.1016/j.ijrefrig.2014.04.001.

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Vapor-liquid equilibrium measurements and assessments of fluoroethane + N,N-dimethylformamide and fluoroethane + dimethylether diethylene glycol systems for the hybrid refrigeration cycle

Rulei Deng, Xuye Jing, Danxing Zheng*, Xiaoxiao Li

College of Chemical Engineering, Beijing University of Chemical Technology, Beijing,

100029, China

*Corresponding author: Tel.: +86 010 6441 6406; Fax: +86 10 64416406.

E-mail address: dxzh@mail.buct.edu.cn (D.Zheng)

Abstract

This study aimed to develop novel working pairs for the hybrid refrigeration cycle. To this

end, the vapor-liquid equilibrium data of fluoroethane (R161) + N,N-dimethylformamide

(DMF) and R161 + dimethylether diethylene glycol (DMEDEG) systems were obtained from

293.15 K to 353.15 K. Experimental data were correlated using the nonrandom two-liquid

(NRTL) activity coefficient model. The average relative pressure deviations are 1.33% and

1.45%, and the maximum relative pressure deviations are 3.68% and 3.90%, respectively.

Experimental results show that the two binary mixtures exhibit negative deviations from

Raoult’s law. Finally, the performance of R161 + DMF, R161 + DMEDEG, and R134a +

DMF systems were simulated and evaluated based on the hybrid refrigeration cycle. Results

show that both R161 + DMF and R161 + DMEDEG systems are potential working pairs for

the hybrid refrigeration cycle, and the R161 + DMEDEG system is better.

Keywords: R161; DMF; DMEDEG; Vapor-liquid Equilibrium; Hybrid refrigeration cycle;

Working pairs

Nomenclature

p pressure (kPa)

pis saturated vapor pressure of pure refrigerant (kPa)

R gas constant (J mol−1 K−1)

T temperature (K)

x, y the mole fraction of liquid phase and vapor phase

ViL the molar volume of saturated liquid (cm3

mol−1)

G12, G21 parameters of the NRTL model

N number of experimental points

COP coefficient of performance

f circulation ratio

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QE heat duty of evaporator (kW)

QG heat duty of generator (kW)

W compressor power (kW)

WP pump power (kW)

ms the mass flow rate of strong solution (kg h-1)

mr the mass flow rate of refrigerant (kg h-1)

ODP ozone depletion potential

GWP global warming potential

RHEX refrigerant heat exchanger

SHEX solution heat exchanger

vif̂ the fugacity of species i in vapor-phase

lif̂ the fugacity of species i in liquid-phase

Greek letters

α, τ012, τ1

12, τ021, τ1

21 parameters of the NRTL model

λ compressor pressure ratio

γ1 the activity coefficient of component 1

Subscripts

1, 2, i component 1, 2, and i

exp experimental value

cal calculated value

G generator

HC hybrid refrigeration cycle

s strong solution

r refrigerant vapor

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1. Introduction

The absorption refrigeration cycle is a kind of important energy saving technology. It can

be powered by low-grade solar energy so that it can decrease primary energy consumption

and minimize negative impacts on the environment (Zhai and Wang, 2009; Kameyama, 1998).

Compared with the traditional absorption cooling cycle, the hybrid refrigeration cycle can

achieve a cryogenic cooling effect, extend the operating temperature range, and improve the

coefficient of performance. Thus, this technology has gained considerable in the past decades

(Zheng and Meng, 2012; Meng et al., 2013; Fukuta et al., 2002).

The performance of the absorption cycle depends on its configuration and the

thermophysical properties of working pairs composed of a refrigerant and an absorbent

(Mehrdad et al., 2013; Sun et al., 2012). Accordingly, many researchers have attempted to

develop new working pairs for the absorption and hybrid refrigeration cycles to improve their

performance (Eiseman 1959; Jelinek, et al., 2008; Li et al., 2013). Alternative refrigerants

such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which have

excellent thermophysical properties, combined with organic absorbents are widely used in

absorption heat transformers (AHTs), absorption heat pumps, and refrigeration cycles

(Srikhirin et al., 2001). Thus far, R22 is the best fluorocarbon refrigerant used in absorption

refrigeration cycles (Bhaduri and Verma, 1988; Fatouh et al., 1995; Eiseman, 1959). Sujatha

et al. (1997 and 1999) observed that the absorption cycle based on R22 and organic

absorbents has certain advantages over ammonia + water mixtures. Environmental protection

policies mandate the restriction of CFCs and HCFCs, and HFCs are thus deemed as

alternative refrigerants. HFCs are not destructive to the ozone layer, although they slightly

contribute to global warming (Mclinden et al., 1998; Wahlstrom et al., 1997; Wahlstrom et al.,

2000). Borde et al. (1995) investigated the possibility of using R134a with different organic

absorbents as working pairs for the absorption refrigeration cycle. They concluded that the

overall performance of the R134a + DMETEG system is better than those of R134a + MCL

and R134a + DMEU. Muthu et al. (2008) performed an experimental study and revealed the

feasibility of using R134a + DMAC as working pairs in absorption machines using low-grade

heat sources. Suresh et al. (2013) performed an experimental investigation on the

performance of an absorption cooling system based on R134a + DMF system. Results

indicated that the absorption cooling system can be very competitive for applications within

the heat sources temperature range of 80 °C to 90 °C.

Fluoroethane (R161) has superior environmental performance (ODP=0, GWP=12),

excellent thermophysical properties, high energy efficiency, and good commonality with

existing systems. Thus, R161 is a promising long-term alternative refrigerant (Xuan et al.,

2005). Many studies on R161 and related refrigerant mixtures have been conducted, such as

those focusing on the saturated vapor pressure of R161 and the vapor–liquid equilibrium

(VLE) of R161 with R134a or R143a (Cui et al., 2006; Wang et al., 2010; Dong et al., 2008;

Dong et al., 2010). Han et al. (2010) performed a series of experiments on the cycle

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performance of R161 in a small-scale refrigeration system. Experimental results show that

R161 can achieve 15%-25% higher COP than R410A and R32. Given their GWP values

higher than 150, R134a and R32 can be abandoned as a refrigerant for refrigeration systems in

the coming years (Bobbo et al., 2013). Accordingly, R161 can be used as an alternative

refrigerant for R22, R134a, and R32 for use in the absorption and hybrid refrigeration cycles.

To determine the possibility of alternative working pairs in the absorption and hybrid

refrigeration cycles, VLE data of the mixtures have to be determined (Borde et al., 1997).

Wahlstrom and Vamling (2000) measured the solubility of refrigerant R152a in n-eicosane,

n-hexadecane, n-tridecane, and 2,6,10,14-tetramethyl pentadecane at different temperatures

and pressures. Yelisetty and Visco (2009) investigated the solubility of R32, R125, R152a,

and R143a in three polyols and found that both R32 and R152a have good solubility in

organic solvents. Zehioua et al. (2010a and 2010b) studied the VLE data of R134a + DMF,

R134a + DMEDEG, and R134a + DMETrEG systems for AHT. Han et al. (2011) measured

the solubility of refrigerants R134a and R32 in DMF, respectively. Their experimental data

are correlated with the NRTL activity coefficient model. Gao et al. (2012) investigated the

solubility of refrigerant R23 in DMF from 283.15 K to 363.15 K. Li et al. (2013) measured

the VLE data of R32 + DMAC, R32 + DMEDEG, and R152a + DMEDEG systems from

293.15 K to 353.15 K. Results show that the affinity of the R32 + DMEDEG system is the

best. However, no VLE literature data are available for the R161 + DMF and R161 +

DMEDEG systems.

This paper aims at the validation of whether the R161+DMF and R161+DMEDEG systems

can be used as potential working pairs in the hybrid refrigeration cycle. The VLE data of the

two systems were measured from 293.15 K to 353.15 K. Experimental data were correlated

using the NRTL activity coefficient model. Then on the basis of that, the cycle performance of

hybrid refrigeration cycle using R161 + DMF, R161 + DMEDEG and R134a + DMF systems

were also simulated and evaluated.

2. Experimental Methodology

2.1 Materials

The refrigerant R161 (C2H5F, CAS number 353-36-6) was provided by Zhejiang Lantian

Environmental Protection Hi-Tech Co., Ltd. with a declared mass fraction purity higher than

99.95%. The refrigerant R134a (C2H2F4, CAS number 811-97-2) was supplied by DuPont Co.,

Ltd. with a declared mass fraction purity higher than 99.9%. The commercial absorbents

DMF (C3H7NO, CAS number 68-12-2) and DMEDEG (C6H14O3, CAS number 111-96-6) for

this work were provided by Sigma-Aldrich Co., Ltd. with the mass fraction purity higher than

99.9%. All the materials were used without any further purification or drying.

2.2 Apparatus and Uncertainty Analysis

The schematic of the equilibrium apparatus is shown in Figure 1 (details of the apparatus

are found elsewhere) (Li et al., 2013; Meng et al., 2013). Compared with the previous

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apparatus, a circulating micropump was added to the system. This micropump can accelerate

the system to reach phase equilibrium. The inner volume of the equilibrium cell was designed

to be 150ml. The equilibrium temperature was measured with a temperature controller (model

LC-6, Julabo Co., Ltd.) using a Pt-100 resistance temperature probe. Equilibrium pressure

was measured using a pressure transducer (model PTX7533, GE Co., Ltd.). A six-way valve

(model VACLO) was used to control the sampling injection volume to as close to 5 µl as

possible each time. Liquid samples were analyzed with a gas chromatography system (model

GC-2014, Shimadzu) equipped with a flame ionization detector and a Wax-RTX-5

chromatographic column.

In this experimental system, the uncertainties are mainly caused by the measurement of

temperature (T), pressure (p) and composition (x) (Meng et al., 2013). The calculation

procedure of uncertainty was given as follows:

� Uncertainty of temperature measurement

The temperature controlled system consisted of a temperature controller (Model LC-6) and

a Pt-100 resistance temperature sensor. The measurement error of Pt-100 resistance

temperature sensor is ±(0.10+0.0017|T|)°C. The stability of the temperature controller is

±0.03°C and the resolution of temperature monitor is 0.01°C. The uncertainties of the

temperature measurement are mainly caused by measuring repeatability u1(T), the

measurement error of temperature sensor u2(T), the stability of the temperature u3(T) and the

resolution of temperature monitor u4(T) (ISO, 1993). In general, the u1(T) is calculated based

on the method of Type A evaluation of standard uncertainty(Ellison et a., 200l). The u2(T),u3(T)

and u4(T) are calculated based on Type B evaluation of standard uncertainty (Ellison et a.,

200l). Take the case of T=30°C, repeated 10 times independent observation. So the

uncertainty of temperature can be calculated as follows (Kirkup and Frenkel, 2006; JCGM

100, 2008):

( )( )( ) ( )10

11

2

=−

−=∑

= nn

TTTs

n

ii

(1)

( ) ( ) nTsTu =1 (2)

( ) 301.05.02 ×=Tu (3)

( ) 3005.03 =Tu (4)

( ) 3151.04 =Tu (5)

and then the combined standard uncertainty of temperature is defined as:

( ) ( )∑=

=4

1

2

iic TuTu (6)

Based on the above equations, the combined standard uncertainty of temperature is 0.072°C.

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� Uncertainty of pressure measurement

The equilibrium pressure was measured using a pressure transducer (Model PTX7533). The

maximum measure scale and measurement error are 6.0MPa and 0.015%, respectively. The

resolution of pressure monitor is 0.0001MPa. The uncertainties of the pressure measurement

are mainly caused by the measurement error of pressure transducer u1(T) and the resolution of

pressure monitor u2(T) (ISO, 1993). So the uncertainty of pressure can be calculated as

follows (Kirkup and Frenkel, 2006; JCGM 100, 2008):

( ) 36.00.015%1 ×=pu (7)

( ) 301.05.02 ×=pu (8)

( ) ( )∑=

=4

1

2

iic pupu (9)

Therefore, the combined standard uncertainty of pressure is 0.0006MPa.

� Uncertainty of composition measurement

The gas chromatography (GC-2014) is used to analyze the liquid composition. The

uncertainties of composition measurement are mainly caused by the stability of the carrier gas

flow rate, the baseline noise, the baseline wander and the repeatability of the FID

measurement (JJG 700, 1999).

Usually, the chromatography workstation baseline is stable at 30 mV, and the uncertainty

contribution of the baseline noise and the baseline wander are 0.33% and 0.7%, respectively.

The uncertainty contribution of the repeatability of the FID measurement is 1.2% (Shimadzu,

2012). The uncertainty of composition can be calculated as follows:

( ) ( ) 015.03

1

2 == ∑=i

ic xuxu (10)

So, the combined standard uncertainty of composition measurement is 0.015.

2.3 Experimental procedure

The equilibrium cell was first vacuumed to remove inert gas and other impurities using a

vacuum pump. The vacuum level of the cell can reach to 3 kPa. About 50 ml of DMF or

DMEDEG was then injected into the equilibrium cell. The temperature of the thermostatic

water bath was set at the designed experimental temperature, and the desired amount of

refrigerant was slowly added. The circulating micropump was opened to ensure thorough

mixing of vapor and liquid. On average, the liquid phase was circulated about 30 min. In the

following 30 min, the experimental pressure and temperature were maintained at a certain

value. The system was deemed to have reached the equilibrium state about 1 h later. At this

point, the sample was injected into the GC using the circulation micropump, and the average

pressure and temperature were recorded. By changing the experimental temperature and

repeating the above procedures, a series of experimental data were obtained. Under the

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condition of equilibrium state, the average fluctuations of temperature, pressure and mole

fraction are ± 0.03°C, ± 0.5 kPa and ± 0.013, respectively. The thermostat water

temperature fluctuation is less than ±0.03°C within 30 min with the control of Julabo

temperature controller.

2.4 Reliability validation of the apparatus

In order to validate the stability and reliability of the experimental system, the VLE data of

R134a + DMF system were measured at temperatures 303.15 K and 313.15 K. The

experimental results and reference data (Han et al., 2011) are listed in Table 1, where pexp and

plit are pressure of experiment and reference, respectively, xexp and xlit are the liquid mole

fraction of R134a of experiment and reference, respectively. The mole fraction xexp was

substituted into the NRTL equation correlated by the reference data from Han et al. (2011).

Then the p value was correspondingly obtained and compared with the p value measured by

the experiment. The average and maximum relative deviations of the pressure are 1.51% and

2.89%, respectively. The results show that the experimental apparatus has acceptable

reliability.

3. Correlation and Results discussion

In many previous works, the five-parameter NRTL activity coefficient model was always

suggested by researchers to correlate the VLE data of non-ideality binary systems, such as

HFCs and organic solvents mixtures (Han et al., 2011; Li et al. 2013; Meng et al., 2013). In

this work, all the experimental data were correlated using the NRTL activity coefficient model,

which can be described as the following equations (Renon and Prausnitz, 1968; Han et al.,

2011):

++

+=

21212

1212

2

2121

2121

221 )(

lnGxx

G

Gxx

Gx

ττγ (11)

where G12 and G21 are defined as:

)exp( 1212 ατ−=G (12)

)exp( 2121 ατ−=G (13)

where τ12 and τ21 are defined as:

RT

T )ln(121

120

12

τττ += (14)

RT

T )ln(211

210

21

τττ += (15)

In equations (11) - (13)γ1 is the activity coefficient of component 1x1 and x2 are the mole

fractions of component 1 and 2R is the gas constantα, τ012, τ1

12, τ021 and τ1

21 are the five

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parameters of the NRTL activity coefficient model and can be obtained by minimizing the

following objective function:

∑=

−=N

iicalppOBF

1

2exp )( (16)

where N is the total number of experiments datapexp is the experimental pressurepcal is the

calculated pressure.

For binary systems, the criterions of VLE as given by equation (17): l

iv

i ff ˆˆ = (17)

where the vif̂ and l

if̂ are the vapor-phase fugacity and liquid-phase fugacity for species i

respectively. If the vapor was regard as ideal gas, and after simplified the equation (17)the

criterions of VLE in this work can be expressed by the equation (Smith, 2002):

−=RT

ppVpxpy

sLs )(exp 11

1111 γ (18)

where y1 is the vapor mole fractions of component 1, p1s and V1

L is the vapor pressure and the

mole volume of the saturated liquid pure refrigerant R161, respectively.

The calculation of activity coefficient γ1 needs the values of p1s and V1

L of R161. Generally,

the values of p1s and V1

L can be obtained from literatures or calculated using software.

REFPROP is a reliable refrigerant property calculation software, which can estimate the

thermodynamic properties for HFC refrigerants (Lemmon et al., 2010). In order to verify the

reliability of REFPROP for R161, we compared the literature data (Chen et al., 2005; Grosse

et al., 1940) and calculated results of p1s and V1

L. The calculated values exhibit a good

consistent with the literature data. The results show that REFPROP can estimate the values of

p1s and V1

L for R 161.” So, the values of p1s and V1

L for R161 in the systems of R161+DMF

and R161+DMEDEG can be obtained from REFPROP. In addition, on the basis of researches

using REFPROP to estimate the values of p1s and V1

L for R161 in the systems of R161 + POE,

R161 + R143a, R161 + R134a, R161 + DMAC and R161 + NMP (Han et al., 2010; Wang et

al., 2010; Jing et al., 2013), the values of p1s and V1

L for R161 in the systems of R161 + DMF

and R161 + DMEDEG are calculated by REFPROP, which can be academically classified

into estimated results in this work. The term exp[V L

1(p-ps

1 )/RT] is the Poynting factor.

According to the calculated results, the value of Poynting factor almost equals to 1.

For the mixtures R161 + DMF and R161 + DMEDEG, the vapor phase is assumed

composed of only R161 vapor (y1=1) because of the negligible volatility of DMF and

DMEDEG in this experiment. For example, Han et al. (2011), Gao et al.(2012) and Li et al.

(2013) measured the VLE data of R134a + DMF, R32 + DMF, R23 + DMF and R32 +

DMEDEG systems and found that there were almost no DMF or DMEDEG in the vapor

phase of the mixtures at the experimental temperature ranges. Therefore, the equation (18) can

be simplified as follows:

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spxp 111γ= (19)

On the basis of the measured VLE data which is illustrated in Tables 2 and 3, the values of

the five parameters in the NRTL activity coefficient model were correlated and the results are

listed in Table 4. All the measured VLE data as well as the results calculated using the NRTL

activity coefficient model at different temperatures (293.15 K to 353.15 K) is presented in

Tables 2 and 3. The relative pressure deviations of experiment data from the calculated results

are shown in Figure 2. For the R161 + DMF and R161 + DMEDEG systems, the average

relative pressure deviations between experiment and calculated values are 1.33% and 1.45%,

and the maximum relative pressure deviations are 3.68% and 3.90%, respectively. The results

show good thermodynamic consistency between experiment data and calculated results.

Therefore, the NRTL activity coefficient model can be used to predict the VLE behaviors of

the binary mixtures R161 + DMF and R161 + DMEDEG.

The p-T-x diagrams of the R161 + DMF and R161 + DMEDEG systems are plotted in

Figures 3 and 4, respectively. Vapor pressure is found to monotonously increase with

increased mole fraction x1 at a given temperature. Similarly, the mole fraction x1 decreases

with increased temperature at a given pressure. To analyze the deviations from Raoult’s law

for binary mixtures R161 + DMF and R161 + DMEDEG, the activity coefficient γ1 is

calculated at 303.15 K, and the results are plotted in Figure 5. According to the γ1-x1 diagram,

the activity coefficients are always less than the value 1. The calculated results show that both

binary mixtures exhibit negative deviations from Raoult’s law, and the R161 + DMEDEG

system has a greater negative deviation than R161 + DMF. Thus, both absorbents DMF and

DMEDEG have good affinity with R161, and the latter is better. In addition, the activity

coefficient γ1 decreases with increased mole fraction x1 for both systems. Therefore, the

degree of negative deviations weakens with increased mole fraction x1.

4. Performance evaluations of R161 + DMF and R161 + DMEDEG systems as working pairs for the hybrid refrigeration cycle

The schematic of the hybrid refrigeration cycle is shown in Figure 6. The cycle mainly

consists of an evaporator, a condenser, a generator, an absorber, a compressor, a solution

pump, a refrigerant throttled valve, a refrigerant heat exchanger, and a solution heat exchanger.

The refrigerant vapor (1) coming from the generator and rectifier is condensed in the

condenser. The heat of condensation is removed by the cooling water. After supercooling in

refrigerant heat exchanger (RHEX), the liquid refrigerant (3) is throttled by V1 into the

evaporator to facilitate cooling. The low-pressure refrigerant vapor (5) coming from the

evaporator is superheated in solution heat exchanger (SHEX) and then proceeds into the

compressor. The compressed refrigerant vapor (7) is absorbed by the weak solution (13) from

the generator and then becomes a strong solution (8). This strong solution (8) is pumped

through the SHEX and preheated by the weak solution coming from the generator. The strong

solution enters the generator, where the refrigerant vapor is desorbed and separated from the

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solution for the next cycle. The cycle is powered by mechanical work and low-grade heat at

the compressor and generator, respectively.

The performances of the R161 + DMF and R161 + DMEDEG systems in the hybrid

refrigeration cycle have been evaluated and compared with the R134a + DMF working pair

that is commonly studied by researchers (He et al., 2009; Meng et al., 2013). The simulation

based on an Aspen Plus program built by our previous work (Zheng and Meng, 2012; Meng et

al., 2013) and the NRTL activity coefficient model which adopted the parameters in Table 4.

In the cycle simulation, the evaporator temperature, absorber temperature, and condenser

temperature are set to 263.15, 303.15, and 303.15 K (Zheng and Meng, 2012; Meng et al.,

2013). The simulation range of generator temperature is from 340 K to 410 K (Dong et al.,

2012). The detailed information of conditions for computer simulation adopted in this work is

listed in Table 5. And others assumptions are described as follows (Zheng and Meng, 2012;

Dong et al., 2012):

(1) The cycle runs in steady-state;

(2) The heat losses to environment and the pressure drops within the cycle can be neglected;

(3) The outlet temperatures of absorber and condenser are kept the same; and the solution

outlets of generator and absorber are saturated conditions;

(4) No absorbents exist in the refrigerant loops.

As the evaluation criterions, the coefficient of performance and the circulation ratio of the

cycle are defined as following equations (20) and (21):

elec

PG

EHC WW

Q

QCOP

η)( ++

= (20)

where QE, QG, W and WP are the heat input into evaporator, the heat supplied to generator, the

electricity consumption of compressor and solution pump, respectively. The ηelec has been

assumed as a reasonable average efficiency for electricity production from thermal sources

and the value is 0.38 (Ventas et al., 2010). The circulation ratio f is given by equation (21),

which is defined as the ratio of mass flow rate of strong solution from absorber to that of

refrigerant vapor generated in the generator and an important index for evaluating the hybrid

refrigeration cycle (Takada, 1987; Dong et al., 2012).

r

s

m

mf = (21)

where ms is the mass flow rate of strong solution in stream 8 (from absorber to generator), mr

is the mass flow rate of refrigerant vapor in steam 1 (from rectifier to condenser).

Figure 7 shows the variations in COPHC for the three binary mixtures R161 + DMF, R161 +

DMEDEG and R134a + DMF with varied generator temperatures in the hybrid refrigeration

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cycle. Notably, COPHC initially increases significantly with increased generator temperature,

and then the curves almost flatten at higher temperatures. As is shown in Figure 7, COPHC

follows the order R161 + DMEDEG > R161 + DMF > R134a + DMF. Similar to Figure 7,

Figure 8 shows the f values of the three systems at different generator temperatures. The R161

+ DMEDEG system has the lowest f value, followed by the R161 + DMF and R134a + DMF

systems. Simulation results show that both the R161 + DMF and R161 + DMEDEG systems

have the potential to be applied as working pairs for the hybrid refrigeration cycle. Overall,

the R161 + DMEDEG system is the best working pair from the viewpoint of COPHC and f

performances.

5. Conclusions

In this work, the binary mixtures R161 + DMF and R161 + DMEDEG were proposed as

new working pairs for the hybrid refrigeration cycle. VLE data of the two mixtures were

obtained from 293.15 K to 353.15 K. Experimental data were then correlated using the NRTL

activity coefficient model. For the R161 + DMF and R161 + DMEDEG systems, the average

relative pressure deviations between experiment and calculated values are 1.33% and 1.46%,

and the maximum relative pressure deviations are 3.68% and 3.90%, respectively. Results

show good thermodynamic consistency between experimental and calculated results.

Therefore, the NRTL activity coefficient model can be used to predict the VLE behaviors of

the binary mixtures R161 + DMF and R161 + DMEDEG.

The two binary mixtures are found exhibit negative deviations from Raoult’s law. The

negative deviation degree of R161 + DMEDEG is greater than that of R161 + DMF.

Therefore, both DMF and DMEDEG have good affinity with R161, and the latter is better.

In addition, evaluation of the performances of the R161 + DMF, R161 + DMEDEG, and

R134a + DMF systems shows that the R161 + DMEDEG system has the best performance

among the studied working pairs. Therefore, the R161 + DMEDEG system can be considered

as the best candidate working pair for the hybrid refrigeration cycle.

Acknowledgments

The support provided by the National Natural Science Foundation of China (No. 51276010),

the National Basic Research Program of China (No. 2010CB227304), the “Chinese

Universities Scientific Fund” (ZY1342) and the China Postdoctoral Science Foundation

funded project (No. 2013M540844) for the completion of the present work are gratefully

acknowledged.

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Refrigeration 20(4), 256-266.

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Figure 1. Schematic diagram of the VLE experimental apparatus. 1, gas cylinder; 2, gas

storage tank; 3, liquid injector; 4, circulation micro-pump; 5, thermostatic water bath; 6,

equilibrium cell; 7, refrigeration system; 8, temperature controller; 9, six-way valve; 10,

cushion tank; 11, vacuum pump; 12, gas chromatography; 13, computer; 14, pressure

monitor; 15, five-way valve; 16, electric stirrer.

Figure 2. Relative pressure deviations for the two binary mixtures in the

temperature range from 293.15 K to 353.15 K; �, R161 + DMF; , R161 +

DMEDEG.

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Figure 3. Solubility of R161 (1) in DMF (2) at different temperatures; �, 293.15 K; �,

303.15 K; �, 313.15 K; �, 323.15 K; �, 333.15 K; �, 343.15 K; ▲, 353.15 K; —,

calculated by using the NRTL activity coefficient model.

Figure 4. Solubility of R161 (1) in DMEDEG (2) at different temperatures; �, 293.15 K;

�, 303.15 K; �, 313.15 K; �, 323.15 K; �, 333.15 K; �, 343.15 K; ▲, 353.15 K; —,

calculated by using the NRTL activity coefficient model.

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Figure 5. Activity coefficient of R161 in DMF and DMEDEG as a function of mole

fraction at T=303.15 K; �, R161 (1) + DMF (2); �, R161 (1) + DMEDEG (2); —,

calculated by using the NRTL activity coefficient model.

Figure 6. Schematic diagram of the hybrid refrigeration cycle.

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Figure 7. Variations of the COPHC with generator temperature for three working pairs; ,

R161 + DMF; �, R161 + DMEDEG; ▲, R134a + DMF.

Figure 8. Variations of the f with generator temperature for three working pairs; , R161 +

DMF; �, R161 + DMEDEG; ▲, R134a + DMF.

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Figure captions

Figure 1. Schematic diagram of the VLE experimental apparatus. 1, gas cylinder; 2, gas

storage tank; 3, liquid injector; 4, circulation micro-pump; 5, thermostatic water bath; 6,

equilibrium cell; 7, refrigeration system; 8, temperature controller; 9, six-way valve; 10,

cushion tank; 11, vacuum pump; 12, gas chromatography; 13, computer; 14, pressure monitor;

15, five-way valve;16, electric stirrer.

Figure 2. Relative pressure deviations for the two binary mixtures in the temperature range

from 293.15 K to 353.15 K; �, R161 + DMF; , R161 + DMEDEG.

Figure 3. Solubility of R161 (1) in DMF (2) at different temperatures; �, 293.15 K; �,

303.15 K; �, 313.15 K; �, 323.15 K; �, 333.15 K; �, 343.15 K; ▲, 353.15 K; —,

calculated by using the NRTL activity coefficient model.

Figure 4. Solubility of R161 (1) in DMEDEG (2) at different temperatures; �, 293.15 K; �,

303.15 K; �, 313.15 K; �, 323.15 K; �, 333.15 K; �, 343.15 K; ▲, 353.15 K; —,

calculated by using the NRTL activity coefficient model.

Figure 5. Activity coefficient of R161 in DMF and DMEDEG as a function of mole fraction

at T=303.15 K; �, R161 (1) + DMF (2); �, R161 (1) + DMEDEG (2); —, calculated by

using the NRTL activity coefficient model.

Figure 6. Schematic diagram of the hybrid refrigeration cycle.

Figure 7. Variations of the COPHC with generator temperature for three working pairs; ,

R161 + DMF; �, R161 + DMEDEG; ▲, R134a + DMF.

Figure 8. Variations of the f with generator temperature for three working pairs; , R161 +

DMF; �, R161 + DMEDEG; ▲, R134a + DMF.

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Table 1. Vapor-liquid equilibrium data of R134a + DMFa system at T=303.15 K and T=313.15

K: x1,exp (experiment data); x1,lit (literature data) (Han et al., 2011).

Items T=303.15 K T=313.15 K

pexp/kPa 155.6 260.2 408.5 485.8 214.5 342.6 471.5 611.2

x1,exp 0.2388 0.3950 0.6026 0.6971 0.2512 0.4037 0.5302 0.6941

plit/kPa 155.8 258.9 410.7 485.7 201.5 332.2 471.5 614.1

x1,lit 0.2352 0.3836 0.5994 0.6929 0.2343 0.3828 0.5263 0.6925 a Standard uncertainties u are u(p)=0.6 kPa, u(T)=0.072 K and u(x)=0.015.

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Table 2. Experimental and calculated VLE data for R161 (1) + DMF (2)a.

T/K x1 pexp/kPa pcal/kPa δp/%b T/K x

1 pexp/kPa pcal/kPa δp/%b

293.15 0.1452 104.2 101.3 2.75 323.15 0.4287 569.9 588.1 3.19

293.15 0.2143 151.3 150.2 0.69 323.15 0.5415 745.5 759.2 1.83

293.15 0.3265 230.5 231.2 0.22 323.15 0.6392 914.3 918.8 0.50

293.15 0.3984 286.3 283.9 0.84 323.15 0.7834 1190.8 1189.5 0.11

293.15 0.4856 348.4 349.7 0.36 323.15 0.8441 1322.6 1324.9 0.17

293.15 0.5892 444.6 431.2 3.07 323.15 0.9462 1581.5 1597.1 0.98

293.15 0.6523 496.4 482.7 2.75 333.15 0.1532 240.1 241.9 0.76

293.15 0.7219 557.1 542.4 2.63 333.15 0.2253 353.6 360.3 1.91

293.15 0.8513 671.5 662.5 1.35 333.15 0.3785 616.2 622.4 1.01

293.15 0.9122 729.7 722.8 0.95 333.15 0.4845 804.5 814.2 1.20

303.15 0.1502 137.5 132.5 2.91 333.15 0.5633 953.6 964.5 1.14

303.15 0.2181 200.6 193.2 3.68 333.15 0.6721 1185.4 1188.8 0.29

303.15 0.3344 303.5 299.1 1.49 333.15 0.7374 1331.3 1338.2 0.50

303.15 0.4192 384.4 378.2 1.62 333.15 0.8173 1534.8 1545.2 0.68

303.15 0.4726 440.1 429.3 2.45 333.15 0.8736 1700.6 1716.7 0.95

303.15 0.5793 548.2 535.7 2.29 333.15 0.9491 1974.2 1994.2 1.01

303.15 0.6442 623.5 604.3 3.12 343.15 0.1548 290.2 287.7 0.86

303.15 0.7198 709.2 688.7 2.89 343.15 0.2175 408.8 411.5 0.66

303.15 0.7912 792.1 775.1 2.14 343.15 0.3126 600.4 606.5 0.94

303.15 0.8733 889.5 884.4 0.58 343.15 0.4082 795.5 809.9 1.80

303.15 0.9392 973.8 978.7 0.51 343.15 0.5045 1011.3 1024.8 1.34

313.15 0.1411 159.1 153.9 3.27 343.15 0.6621 1400.5 1408.5 0.57

313.15 0.2197 243.1 240.9 0.95 343.15 0.7374 1618.6 1616.3 0.15

313.15 0.2731 300.2 300.8 0.20 343.15 0.8292 1919.2 1912.2 0.36

313.15 0.3724 408.3 414.4 1.49 343.15 0.8995 2191.6 2197.1 0.25

313.15 0.4945 550.1 560.2 1.79 353.15 0.1519 337.4 328.3 2.69

313.15 0.5826 659.4 671.2 1.79 353.15 0.2036 463.2 450.1 2.82

313.15 0.6641 773.3 781.2 1.02 353.15 0.2942 681.8 672.3 1.39

313.15 0.7272 870.9 873.3 0.24 353.15 0.4154 990.4 984.6 0.58

313.15 0.7955 982.4 981.5 0.09 353.15 0.5263 1290.9 1286.5 0.34

313.15 0.9433 1256.2 1261.4 0.42 353.15 0.6341 1604.2 1601.4 0.20

323.15 0.1468 199.1 194.2 2.44 353.15 0.7095 1853.4 1841.8 0.62

323.15 0.2089 281.3 278.2 1.10 353.15 0.8044 2216.3 2190.6 1.16

323.15 0.3016 397.9 406.1 2.06 353.15 0.8895 2631.5 2591.2 1.53 a Standard uncertainties u are u(p)=0.6 kPa, u(T)=0.072 K and u(x)=0.015.

b Relative deviation of the pressure (δp): δp =(|pexp-pcal|/pexp)×100%.

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Table 3. Experimental and calculated VLE data for R161 (1) + DMEDEG (2)a.

T/K x1 pexp/kPa pcal/kPa δp/% T/K x

1 pexp/kPa pcal/kPa δp/%

293.15 0.1272 78.6 77.8 1.01 323.15 0.6065 745.2 752.7 1.01

293.15 0.2643 160.5 164.1 2.23 323.15 0.6664 838.7 843.6 0.58

293.15 0.3923 243.2 248.3 1.98 323.15 0.7432 960.3 974.7 1.52

293.15 0.5065 328.1 327.2 0.28 323.15 0.8543 1234.2 1220.2 1.14

293.15 0.6097 414.9 404.2 2.58 323.15 0.9432 1510.6 1519 0.55

293.15 0.6953 486.5 474.3 2.51 333.15 0.1694 237.4 238.2 0.34

293.15 0.7721 553.6 544.4 1.66 333.15 0.2761 385.1 390.6 1.42

293.15 0.8722 655.7 651.7 0.61 333.15 0.3563 509.5 507.8 0.33

293.15 0.9432 731.9 740.6 1.18 333.15 0.4741 689.8 686.6 0.47

303.15 0.1298 97.6 100.6 3.06 333.15 0.5475 816.9 804.5 1.51

303.15 0.2296 175.6 179.3 2.11 333.15 0.6572 1016.3 997.3 1.87

303.15 0.3362 259.3 265.4 2.35 333.15 0.7611 1230.9 1215.8 1.23

303.15 0.4491 362.1 360.1 0.55 333.15 0.8550 1494.5 1479.7 0.99

303.15 0.5646 467.8 463.3 0.97 333.15 0.9547 1923.2 1933.2 0.52

303.15 0.6692 577.5 566.4 1.93 343.15 0.2171 367.5 361.3 1.68

303.15 0.7456 678.2 651.7 3.90 343.15 0.3272 556.7 551.1 1.01

303.15 0.8663 830.5 819.3 1.35 343.15 0.4345 746.3 743.3 0.40

303.15 0.9424 952.8 957.7 0.51 343.15 0.5230 906.8 904.8 0.22

313.15 0.1575 147.5 151.8 2.91 343.15 0.6151 1110.2 1098.2 1.08

313.15 0.2655 250.9 257.5 2.65 343.15 0.6995 1280.2 1291.3 0.87

313.15 0.3333 315.7 325.1 2.99 343.15 0.7820 1501.2 1515.8 0.97

313.15 0.4385 421.2 433.2 2.81 343.15 0.8811 1898.6 1885.7 0.68

313.15 0.5673 564.8 573.7 1.57 343.15 0.9633 2359.7 2425.3 2.78

313.15 0.6561 683.5 680.7 0.41 353.15 0.2190 432.8 425.7 1.63

313.15 0.7516 814.8 813.2 0.19 353.15 0.3011 600.5 593.1 1.23

313.15 0.8435 960.1 973.4 1.38 353.15 0.3922 780.4 785.2 0.62

313.15 0.9253 1139.2 1166.9 2.44 353.15 0.4845 981.2 988.6 0.75

323.15 0.1361 159.8 159.7 0.08 353.15 0.6060 1260.2 1280.2 1.59

323.15 0.2790 318.3 329.6 3.54 353.15 0.7153 1560.2 1580.2 1.28

323.15 0.3935 455.5 469.5 3.08 353.15 0.8226 1989.5 1958.9 1.54

323.15 0.4614 542.3 555.4 2.42 353.15 0.9130 2490.5 2464.7 1.04

323.15 0.5350 641.5 652.5 1.71 a Standard uncertainties u are u(p)=0.6 kPa, u(T)=0.072 K and u(x)=0.015.

b Relative deviation of the pressure (δp): δp =(|pexp-pcal|/pexp)×100%.

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Table 4. Parameters of the NRTL activity coefficient model derived by correlated the

experiment data in this work.

Parameters

Values

R161 (1) + DMF (2) R161 (1) + DMEDEG (2)

α 7.55 5.40

τ120 16212.81 23277.3

τ121 -2808.73 -3983.71

τ210 14833.64 20253.19

τ211 -2696.55 -3715.19

Table 5. The specified simulation parameters of major equipments in the hybrid refrigeration

cycle.

Items Values

Minimum temperature difference for solution

heat exchangers and refrigerant heat exchanger / Κ 5 (Meng et al., 2013; Vidala et al., 2006)

Efficiency of pump / - 0.5 (Rameshkumar and Udayakumar, 2007)

Isentropic efficiency of compressor / - 0.72 (Simith et al., 2010)

Vapor fraction of outflow from evaporator / - 0.99 (Jakobsen et al., 2004)

The compressor pressure ratio λ/ - 1.5 (Meng et al., 2013)

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Highlights:

� VLE data of R161+DMF/DMEDEG systems were measured between 293.15 K

and 353.15 K.

� All the experimental data were correlated by NRTL activity coefficient model.

� Hybrid refrigeration cycle was evaluated based on R161+DMF and

R161+DMEDEG.

� R161+DMEDEG was selected as a better option for hybrid refrigeration cycle.