Natural circulation loop (NCL) is simple and reliable due to the absence of moving components and is preferred in applications where safety is of foremost concern, such as nuclear power plants and high-pressure thermal power plants. In the present study, optimum operating conditions based on the maximum heat transfer rate in NCLs have been obtained for subcritical as well as supercritical fluids. In recent years, there is a growing interest in the use of carbon dioxide (CO2) as loop fluid in NCLs for a variety of heat transfer applications due to its excellent thermophysical environmentally benign properties. In the present study, three-dimensional (3D) computational fluid dynamics (CFD) analysis of a CO2-based NCL with isothermal source and sink has been carried out. Results show that the heat transfer rate is much higher in the case of supercritical phase (if operated near pseudocritical region) than the subcritical phase. In the subcritical option, higher heat transfer rate is obtained in the case of liquid operated near saturation condition. Correlations for optimum operating condition are obtained for a supercritical CO2-based NCL in terms of reduced temperature and reduced pressure so that they can be employed for a wide variety of fluids operating in supercritical region. Correlations are also validated with different loop fluids. These results are expected to help design superior optimal NCLs for critical applications.

References

References
1.
Wang
,
K.
,
Magnus
,
E.
,
Yunho
,
H.
, and
Radermacher
,
R.
,
2010
, “
Review of Secondary Loop Refrigeration System
,”
Int. J. Refrig.
,
33
(
2
), pp.
212
234
.
2.
Kumar
,
K. K.
, and
Ram Gopal
,
M.
,
2009
, “
Carbon Dioxide as Secondary Fluid in Natural Circulation Loops
,”
Proc. Inst. Mech. Eng., Part E
,
223
(
3
), pp.
189
194
.
3.
Yadav
,
A. K.
,
Bhattacharyya
,
S.
, and
Ram Gopal
,
M.
,
2014
, “
On the Suitability of Carbon Dioxide in Forced Circulation Type Secondary Loops
,”
Int. J. Low Carbon Technol.
,
9
(
1
), pp.
85
90
.
4.
Kreitlow
,
D. B.
, and
Reistad
,
G. M.
,
1978
, “
Thermosyphon Models for Downhole Heat Exchanger Application in Shallow Geothermal Systems
,”
ASME J. Heat Transfer
,
100
(
4
), pp.
713
719
.
5.
Torrance
,
K. E.
,
1979
, “
Open-Loop Thermosyphons With Geological Application
,”
ASME J. Heat Transfer
,
100
(4), pp.
677
683
.
6.
Rieberer
,
R.
,
2005
, “
Naturally Circulation Probes and Collectors for Ground-Coupled Heat Pumps
,”
Int. J. Refrig.
,
28
(
8
), pp.
1308
1315
.
7.
Zhang
,
X. R.
, and
Yamaguchi
,
H.
,
2007
, “
An Experimental Study on Evacuated Tube Solar Collector Using Supercritical CO2
,”
Appl. Therm. Eng.
,
28
(10), pp.
1225
1233
.
8.
Zimmermann
,
A. J. P.
, and
Melo
,
C.
,
2014
, “
Analysis of a R744 Two Phase Loop Thermosyphon Applied to the Cold End of a Stirling Cooler
,”
Appl. Therm. Eng.
,
73
(
1
), pp.
549
558
.
9.
Rieberer
,
R.
,
Karl
,
M.
, and
Hermann
,
H.
,
2004
, “
CO2 Two-Phase Thermosyphon as a Heat Source System for Heat Pumps
,”
6th IIR-Gustav Lorentzen Natural Working Fluids Conference
,
Glasgow
, UK, Aug. 29–Sept. 1 pp.
1
8
.
10.
Ochsner
,
K.
,
2008
, “
Carbon Dioxide Heat Pipe in Conjunction With a Ground Source Heat Pump (GSHP)
,”
Appl. Therm. Eng.
,
28
(
16
), pp.
2077
2082
.
11.
Sarkar
,
M. K. S.
,
Tilak
,
A. K.
, and
Basu
,
D. N.
,
2014
, “
A State-of-the-Art Review of Recent Advances in Supercritical Natural Circulation Loops for Nuclear Applications
,”
Ann. Nucl. Energy
,
73
, pp.
250
263
.
12.
Yadav
,
A. K.
,
Ram Gopal
,
M.
, and
Bhattacharyya
,
S.
,
2012
, “
CO2 Based Natural Circulation Loops: New Correlations for Friction and Heat Transfer
,”
Int. J. Heat Mass Transfer
,
55
(
17–18
), pp.
4621
4630
.
13.
Sabersky
,
R. H.
, and
Hauptmann
,
E. G.
,
1967
, “
Forced Convection Heat Transfer to Carbon Dioxide Near the Critical Point
,”
Int. J. Heat Mass Transfer
,
10
(
11
), pp.
1499
1508
.
14.
Yamagata
,
K.
,
Nishmawa
,
K.
,
Hasegawa
,
T. S.
,
Fuji
,
T.
, and
Yoshida
,
M. S.
,
1972
, “
Forced Convective Heat Transfer to Supercritical Water Flowing in Tubes
,”
Int. J. Heat Mass Transfer
,
15
(
12
), pp.
2575
2593
.
15.
He
,
S.
,
Kim
,
W. S.
, and
Jackson
,
J. D.
,
2008
, “
A Computational Study of Convective Heat Transfer to Carbon Dioxide at a Pressure Just Above the Critical Value
,”
Appl. Therm. Eng.
,
28
(
13
), pp.
1662
1675
.
16.
Hua
,
Y. X.
,
Wang
,
Y. Z.
, and
Meng
,
H.
,
2010
, “
A Numerical Study of Supercritical Forced Convective Heat Transfer of n-Heptane Inside a Horizontal Miniature Tube
,”
J. Supercrit. Fluids
,
52
(
1
), pp.
36
46
.
17.
Du
,
Z.
,
Lin
,
W.
, and
Gu
,
A.
,
2010
, “
Numerical Investigation of Cooling Heat Transfer to Supercritical CO2 in a Horizontal Circular Tube
,”
J. Supercrit. Fluids
,
55
(
1
), pp.
116
121
.
18.
Yadav
,
A. K.
,
Ram Gopal
,
M.
, and
Bhattacharyya
,
S.
,
2012
, “
CFD Analysis of a CO2 Based Natural Circulation Loop With End Heat Exchangers
,”
Appl. Therm. Eng.
,
36
, pp.
288
295
.
19.
Yoshikawa
,
S.
,
Smith
,
R. L.
, Jr.
,
Inomata
,
H.
,
Matsumura
,
Y.
, and
Arai
,
K.
,
2005
, “
Performance of a Natural Convection Circulation System for Supercritical Fluids
,”
J. Supercrit. Fluids
,
36
(
1
), pp.
70
80
.
20.
Seetharam
,
T. R.
, and
Sharma
,
G. K.
,
1979
, “
Free Convective Heat Transfer to Fluids in the Near-Critical Region From Vertical Surfaces With Uniform Heat Flux
,”
Int. J. Heat Mass Transfer
,
22
(
1
), pp.
13
20
.
21.
Liao
,
S. M.
, and
Zhao
,
T. S.
,
2002
, “
Measurements of Heat Transfer Coefficients From Supercritical Carbon Dioxide Flowing in Horizontal Mini/Micro Channels
,”
ASME J. Heat Transfer
,
124
(
3
), pp.
413
420
.
22.
Yamamoto
,
S.
,
Furusawa
,
T.
, and
Matsuzawa
,
T.
,
2011
, “
Numerical Simulation of Supercritical Carbon Dioxide Flows Across Critical Point
,”
Int. J. Heat Mass Transfer
,
54
(
4
), pp.
774
782
.
23.
Yang
,
J.
,
Oka
,
Y.
,
Ishiwatari
,
Y.
,
Liu
,
J.
, and
Yoo
,
J.
,
2007
, “
Numerical Investigation of Heat Transfer in Upward Flow of Supercritical Water in Circular Tubes and Tight Fuel Rod Bundles
,”
Nucl. Eng. Des.
,
237
(
4
), pp.
420
430
.
24.
Lisboa
,
P. F.
,
Fernandes
,
J.
,
Simoes
,
P. C.
,
Mota
,
J. P. B.
, and
Saatdjian
,
E.
,
2010
, “
Computational-Fluid-Dynamics Study of a Kenics Static Mixer as a Heat Exchanger for Supercritical Carbon Dioxide
,”
J. Supercrit. Fluids
,
55
(
1
), pp.
107
115
.
25.
Vijayan
,
P. K.
, and
Austregesilo
,
H.
,
1994
, “
Scaling Laws for Single-Phase Natural Circulation Loops
,”
Nucl. Eng. Des.
,
152
(
1–3
), pp.
331
347
.
26.
Launder
,
B. E.
, and
Spalding
,
D. B.
,
1974
, “
The Numerical Computation of Turbulent Flows
,”
Comput. Methods Appl. Mech. Eng.
,
3
(
2
), pp.
269
289
.
27.
Yadav
,
A. K.
,
Ram Gopal
,
M.
, and
Bhattacharyya
,
S.
,
2014
, “
Transient Analysis of Subcritical/Supercritical Carbon Dioxide Based Natural Circulation Loops With End Heat Exchangers: Numerical Studies
,”
Int. J. Heat Mass Transfer
,
59
, pp.
24
33
.
28.
Kumar
,
K. K.
, and
Ram Gopal
,
M.
,
2009
, “
Steady-State Analysis of CO2 Based Natural Circulation Loops With End Heat Exchangers
,”
Appl. Therm. Eng.
,
29
(
10
), pp.
1893
1903
.
29.
Zhang
,
X.
,
Chen
,
L.
, and
Yamaguchi
,
H.
,
2010
, “
Natural Convective Flow and Heat Transfer of Supercritical CO2 in a Rectangular Circulation Loop
,”
Int. J. Heat Mass Transfer
,
53
(
19–20
), pp.
4112
4122
.
30.
NIST,
2013
, Standard Reference Database-refprop, Version 9.1, National Institute of Standards and Technology, Gaithersburg, MD.
31.
Vijayan
,
P. K.
,
2002
, “
Experimental Observations on the General Trends of the Steady State and Stability Behaviour of Single-Phase Natural Circulation Loops
,”
Nucl. Eng. Des.
,
215
(
1–2
), pp.
139
152
.
You do not currently have access to this content.