Screening of HFCs and Fluoroethers as Alternatives to R134a Using SRK EoS

S. Parashurama; D. K. Ramesha; M. S. Govindegowda

doi:10.1007/s40032-019-00501-5

Journal of The Institution of Engineers (India): Series C

pp 1–7 | Cite as

Screening of HFCs and Fluoroethers as Alternatives to R134a Using SRK EoS

Authors
Authors and affiliations

S. Parashurama
D. K. Ramesha
M. S. Govindegowda

Original Contribution

First Online: 17 January 2019

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Abstract

The volumetric and thermodynamic properties of fluorinated ethers such as trifluoromethyl-1-H-pentafluoroethylether, F-oxetane, 2-H-heptafluoropropane, pentafluorodimethylether, F-methyl methyl ether, perfluorodoxolane, pentafluorodimethoxymethane and HFCs such as trifluoroethane, heptafluoropropane, difluoroethane, pentafluoropropane, ethyl fluoride as alternatives to replace R134a have been predicted using SRK equation of state over the temperature range from − 25 °C to + 55 °C. Theoretical analysis is carried out using ten-point vapour compression cycle for screening of candidate refrigerants. The results of analysis have been used to ascertain standard refrigeration parameters in respect of each of the candidate refrigerants. The analysis indicates that the performances of difluoroethane, ethyl fluoride, pentafluorodimethylether and F-oxetane are better than that of R134a.

Keywords

Hydrofluorocarbons Fluorinated ethers Volumetric refrigeration capacity Discharge temperature Coefficient of performance Specific compressor work R134a

List of symbols

C: Clearance factor and specific heat (kJ/kg °C)
COP: Coefficient of performance
GWP: Global warming potential
ODP: Ozone depletion potential
h: Enthalpy (kJ/kg)
M: Molecular weight (kg/kg mol)
$\dot{m}$: Mass flow rate, kg/s
n: Polytropic index
P: Pressure (bar)
Q₀: Refrigerating effect (kJ/kg)
T: Temperature (K) and torque (N m)
V: Volume, cc (m³)
v: Specific volume (m³/kg)
W: Power input (W)
q: Refrigeration effect

Abbreviations

NBP: Normal boiling point (°C)
CFC: Chlorofluorocarbons
HFCs: Hydrofluorocarbons
HCFCs: Hydrochlorofluorocarbons
PFDME: Perfluorodimethyl ether
POE: Polyester oil
VP: Vapour pressure (bar)
VRC: Volumetric refrigerating capacity (kJ/m³)
SCD: Specific compressor displacement [(m³)/ton of refrigeration]

Greek symbols

γ: Specific heat ratio
η: Efficiency

Subscripts

c: Critical
fg: Vapourization
i: Inlet
is: Isentropic
k: Condenser
n: Polytropic
o: Evaporator
stg: Starting torque
v: Volumetric, vapour
0, 1, 2, etc.: State points

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Appendix

Vapour Pressure Equation

$$\ln \left( {\frac{{P_{\text{v}} }}{{P_{\text{c}} }}} \right) = \left( {1 - x^{ - 1} } \right)\left( {Ax + Bx^{1.5} + Cx^{3} + Dx^{4} } \right)$$

where $x = 1 - \frac{T}{T_{\text{c}}}.$

The parameters A, B, C and D are listed in Reid et al. [8].

Equation of State

In 1972, a modified Redlich–Kwong equation of state was proposed by Soave as given in Ried [6]. This equation has been used in calculating the tables of thermodynamic properties of refrigerants studied.

$$\begin{aligned} P & = \frac{RT}{(v - b)} - \frac{a\alpha }{v(v - b)} \\ a & = \frac{{0.42748R_{2} T_{\text{c}}^{2} }}{{P_{\text{c}} }} \\ b & = \frac{{0.08664RT_{\text{c}} }}{{P_{\text{c}} }}\;\alpha = \left[ {1 + \left( {0.48508 + 1.55171\omega - 0.15613\omega^{2} } \right)\left( {1 - \sqrt {T_{\text{r}} } } \right)} \right]^{2} \\ \end{aligned}$$

where $T_{\text{r}} = \frac{T}{{T_{\text{c}} }}$.

Acentric Factor

This is estimated using the equation proposed by Lee–Kesler as given in Ried [8].

$$\omega = \frac{{\ln p_{\text{c}} - 5.97214 + 6.09648\theta^{ - 1} + 1.28862\ln \theta - 0.169347\theta^{6} }}{{15.2518 - 15.6875\theta^{ - 1} - 13.4721\ln \theta + 0.43577\theta^{6} }}$$

where $\theta = \frac{{T_{\text{b}} }}{{T_{\text{c}} }}$.

Ideal Gas Heat Capacity

The ideal gas heat capacity needed to calculate the temperature dependence of enthalpy and entropy from SRK equation of state is estimated by using the expression proposed by Rihani and Doraiswamy [12]:

$$C_{\text{p}} = \sum\limits_{i} {n_{i} a_{i} } + \sum\limits_{i} {n_{i} b_{i} T} + \sum\limits_{i} {n_{i} c_{i} T^{2} } + \sum\limits_{i} {n_{i} d_{i} T^{3} }$$

where n_i represents the number of groups of type i.

The parameters a_i, b_i, c_i and d_i are listed in Reid et al. [6].

Liquid Specific Volume

The liquid specific volume is obtained from the following expressions proposed by Hankinson–Brost–Thomson [6] as this does not require any experimental data. $\frac{{v_{\text{f}} }}{{V^{*} }} = V_{\text{R}}^{(0)} \left[ {1 - \omega V_{\text{R}}^{(\delta )} } \right]$, where $V_{\text{R}}^{(0)} = 1 + a\left( {1 - T_{\text{r}} } \right)^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 3}}\right.\kern-0pt} \!\lower0.7ex\hbox{$3$}}}} + b\left( {1 - T_{\text{r}} } \right)^{{{\raise0.7ex\hbox{$2$} \!\mathord{\left/ {\vphantom {2 3}}\right.\kern-0pt} \!\lower0.7ex\hbox{$3$}}}} + c\left( {1 - T_{\text{r}} } \right) + d\left( {1 - T_{\text{r}} } \right)^{{{\raise0.7ex\hbox{$4$} \!\mathord{\left/ {\vphantom {4 3}}\right.\kern-0pt} \!\lower0.7ex\hbox{$3$}}}}$

$$V_{\text{R}}^{(\delta )} = \frac{{\left( {e + fT_{\text{r}} + gT_{\text{r}}^{2} + hT_{\text{r}}^{3} } \right)}}{{\left( {T_{\text{r}} - 1.00001} \right)}}$$

and 0.25 < T_r < 1.0

$$V^{*} = \frac{{RT_{\text{c}} }}{{p_{\text{c}} }}\left( {a + b\omega + c\omega^{2} } \right)\;V^{*} = \frac{{RT_{\text{c}} }}{{P_{\text{c}} }}\left( {A + B\omega + C\omega^{2} } \right)$$

where the constants a, b, c, d, e, f, g, h, A, B and C are taken from [6].

Enthalpy and Entropy

The enthalpy of the refrigerant at any temperature [14] can be determined by the equation derived using the thermodynamic property relation given below.

$$h_{2} - h_{1} = \int\limits_{1}^{2} {\left[ {T\left( {\frac{\partial p}{\partial T}} \right)_{v} + v\left( {\frac{\partial p}{\partial v}} \right)_{T} } \right]} \left( {{\text{d}}v} \right)_{T}$$

The entropy of the refrigerant at any temperature [14] can be determined by using the thermodynamic property relation given by

$$s - s^{*} = \int\limits_{1}^{2} {\left[ {C_{v} \frac{{{\text{d}}T}}{T} + \left( {\frac{\partial p}{\partial T}} \right)\left( {{\text{d}}v} \right)_{T} } \right]} .$$

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Authors and Affiliations

S. Parashurama
- 1
Email author
D. K. Ramesha
- 2
M. S. Govindegowda
- 3

1.Department of Mechanical EngineeringJSSATEBangaloreIndia
2.Department of Mechanical EngineeringUVCEBangaloreIndia
3.Vivekananda College of Engineering and TechnologyPutturIndia

Screening of HFCs and Fluoroethers as Alternatives to R134a Using SRK EoS

Abstract

Keywords

List of symbols

Abbreviations

Greek symbols

Subscripts

References

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