Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32
Abstract
:1. Introduction
2. Cycle Description
3. Thermodynamic analysis
- One dimensional steady flow for the working fluid in the system.
- Saturated vapor and liquid at the outlet of the gas-liquid separator.
- Mixing occurs at a constant pressure, less than the inlet pressure of the suction flow.
- Expansion processes and compression processes are all adiabatic. The ejector geometry effects are assumed to be considered in terms of isentropic efficiencies of the ejector components.
- The separator offered zero pressure drop and had 100% effectiveness in separating the two-phase mixture into saturated vapor and liquid [13].
3.1. Energy Analysis
3.2. Exergy Analysis
- The property parameters at states 8 and 3 are calculated based on the given condensing temperature, evaporating temperature, subcooling and superheat.
- The property parameters at states 9 and 4 are calculated by given ηmn, ηsn, and SNPD. Fluid velocities at the corresponding states are calculated by Equations (5) and (8).
- Some value of μ is presumed.
- The property parameters and fluid velocity at state 5 are calculated by Equations (10) and (11).
- Enthalpy, pressure, vapor quality and other property parameters at state 6 are calculated by given ηdn and Equations (12)–(14).
- Steps (iii)–(v) are iterated until Equation (15) is satisfied.
- The other performance parameters are calculated by the other equations.
4. Results and Discussion
5. Conclusions
- The cycle COP of R32 and R134a EEC are at a range of 3.578–8.464 and 3.749–8.792, respectively. The R32 EEC and the R134a EEC have a 5.22%–13.77% and 6.63%–17.83% improvement in COP over the corresponding basic cycle, respectively.
- The application of an ejector instead of a throttle valve decreases the cycle’s total exergy destruction by 8.84%–15.84% and 10.16%–19.38% for R32 and R134a, respectively.
- The exergy efficiency of the R32 and R134a EEC varies from 0.2189 to 0.5081 and from 0.2346 to 0.5284, respectively. The application of an ejector instead of a throttle valve yields 5.13%–13.83% and 6.68–17.95% improvement in exergy efficiency over the corresponding basic cycle respectively for R32 and R134a.
- There exists an optimum SNPD which gives a maximum system COP and VCC under a specified condition. The value of the optimum SNPD mainly depends on the efficiencies of the ejector components, but is virtually independent of evaporating temperature and condensing temperature. The optimum SNPD varies from 0 to 3 kPa and from 0 to 17 kPa for R32 and R134a respectively. Among the components of ejector, the effect of the diffusion nozzle efficiency on the optimum SNPD is relatively more significant. In addition, the improvement of the component efficiency, especially the efficiencies of diffusion nozzle and the motive nozzle, can enhance the EEC performance.
Nomenclature
BC | basic refrigeration cycle |
COP | coefficient of performance |
CPR | compression pressure ratio |
EEC | ejector-expansion refrigeration cycle |
Ex | exergy [kJ/kg] |
h | enthalpy [kJ/kg] |
iCOP | improvement of COP |
iEx | variation ratio of exergy destruction |
iVCC | improvement of volumetric cooling capacity |
m | mass flow rate [kg/s] |
p | pressure [kPa] |
PLR | pressure lift ratio |
q | specific heat transfer rate [kJ/kg] |
s | specific entropy [kJ/(kg.K)] |
SNPD | suction nozzle pressure drop [kPa] |
t | temperature [°C] |
T | temperature [K] |
v | velocity [m/s] |
VCC | volumetric cooling capacity [kJ/m3] |
w | specific power [kJ/kg] |
x | vapor quality |
η | efficiency |
μ | entrainment ratio of ejector |
Subscripts | |
---|---|
0 | reference environment |
com | compressor |
con | condenser |
dn | diffusion nozzle |
eva | evaporator |
mix | mixing chamber |
hx | heat exchanger |
mn | motive nozzle |
r | refrigerated object |
sn | suction nozzle |
tot | totle |
tv | throttle valve |
Acknowledgments
Author Contributions
Conflicts of Interest
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Process | R32
| R134a
| ||||||
---|---|---|---|---|---|---|---|---|
BC
| EEC
| BC
| EEC
| |||||
Ex (kJ/kg) | (%) | Ex (kJ/kg) | (%) | Ex (kJ/kg) | (%) | Ex (kJ/kg) | (%) | |
Compression | 6.398 | 20.78 | 5.894 | 21.41 | 4.126 | 23.15 | 3.705 | 23.97 |
Condensing | 14.05 | 45.63 | 13.67 | 49.65 | 7.316 | 41.05 | 7.262 | 46.99 |
Ejector | – | – | 3.438 | 12.49 | – | – | 1.769 | 11.45 |
Throttling | 5.899 | 19.16 | 0.08396 | 0.31 | 3.712 | 20.83 | 0.02212 | 0.14 |
Evaporation | 4.443 | 14.43 | 4.447 | 16.15 | 2.670 | 14.98 | 2.697 | 17.45 |
Total | 30.79 | 100 | 27.53 | 100 | 17.82 | 100 | 15.46 | 100 |
ηex | 0.3194 | 0.344 | 0.3284 | 0.3631 |
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Zhang, Z.; Tong, L.; Chang, L.; Chen, Y.; Wang, X. Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32. Entropy 2015, 17, 4744-4761. https://doi.org/10.3390/e17074744
Zhang Z, Tong L, Chang L, Chen Y, Wang X. Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32. Entropy. 2015; 17(7):4744-4761. https://doi.org/10.3390/e17074744
Chicago/Turabian StyleZhang, Zhenying, Lirui Tong, Li Chang, Yanhua Chen, and Xingguo Wang. 2015. "Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32" Entropy 17, no. 7: 4744-4761. https://doi.org/10.3390/e17074744
APA StyleZhang, Z., Tong, L., Chang, L., Chen, Y., & Wang, X. (2015). Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32. Entropy, 17(7), 4744-4761. https://doi.org/10.3390/e17074744