1d analysis of co2 sub-cooled/supercritical ejector refrigeration cycle

different pressures: the upstream pressure is higher than the saturation pressure and, downstream the
throat, CO 2 is in two-phase flow.
P gc (MPa)
d eff (mm)
12
11
10
9
8
7
28 30 35 40
6
-15 -10 -5 0 5 10 15
3
2.5
2
1.5
1
0.5
T ev (°C)
Q ev (W)
28 30 35 40
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
-15 -10 -5 0 5 10 15
T ev (°C)
a. Gas cooler outlet pressure. b. Evaporator capacity.
28 30 35 40
0
-15 -10 -5 0 5 10 15
T ev (°C)
%COP
28 30 35 40
20%
10%
0%
-10%
-20%
-30%
-40%
-50%
-60%
-70%
-15 -10 -5 0 5 10 15
c. Effective diameter. d. Cop improvement.
Figure 13: Variation of ejector parameters with the evaporation temperature T ev for different gas
cooler outlet temperatures, SH = 5 K.
For the tested bodies, it has been found that:
- The CPC length does not affect the ejector performance.
- The 1D model of the ejector has been adapted by introducing a surface efficiency ettas and a
mixing efficiency m . These efficiencies are expressed as functions of the flow and the ejector
parameters.
- There is a critical constant area diameter above which the ejector performance is constant. For
constant area diameter lower than the critical diameter, the ejector performance will be
hampered.
A parametric study of the ejector refrigeration system has been performed as a function of the
evaporating temperature, the gas cooler outlet temperature, and the evaporator outlet superheat. The
COP improvement of the ejector refrigeration system is about 12% for T gc = 30 °C, T ev = 2 °C and
SH = 5 K.
REFERENCES
[1]. J.P. Chen , J.P. Liu, Z.J. Chen, Y.M. Niu: “Trans-critical R744 and two-phase flow through short
tube orifices”, International Journal of Thermal Sciences 43 (2004) 623–630.
[2]. Somchai Wongwises, Somjin Disawas: Performance of the two-phase ejector expansion
refrigeration cycle”, International Journal of Heat and Mass Transfer 48 (2005) 4282–4286.
[3]. Da-Wen Sun: “Comparative study of the performance of an ejector refrigeration cycle operating
with various refrigerants”, Energy Conversion & Management 40 (1999) 873 – 884.
[4]. Daqing Li, Eckhard A. Groll. "Transcritical CO2 refrigeration cycle with ejector-expansion
device". International Journal of Refrigeration 28 (2005) 766–773.
[5]. Somjin Disawas, Somchai Wongwises. "Experimental investigation on the performance of the
refrigeration cycle using a two-phase ejector as an expansion device". International Journal of
Refrigeration 27 (2004) 587–594.
[6]. J.M. Chang, B.J. Huang : "Empirical correlation for ejector design”, International Journal of
Refrigeration 22 (1999) 379–388.
[7]. K. Martin, R. Rieberer, J. Hager : "Modelling of Short Tube Orifices for CO 2 ”, R111,
International Refrigeration and Air Conditioning Conference at Purdue, July 17-20, 2006.
T ev (°C)
8 th IIR Gustav Lorentzen Conference on Natural Working Fluids, Copenhagen, 2008 8