Thermal-Hydraulic Performance of Printed Circuit Heat Exchanger in ...

Thermal-Hydraulic Performance of
Printed Circuit Heat Exchanger
in Supercritical CO 2 Cycle
K. Nikitin, Y. Kato, L. Ngo
Research Laboratory for Nuclear Reactors
Tokyo Institute of Technology

Study Incentives
o Supercritical CO 2 cycle demonstrates some advantages
in comparison to He cycle
- higher cycle efficiency (Y. Kato, 2003),
- better turbomachinery (Y. Muto, 2003),
- power generation cost is expected to be smaller.
o High efficiency recuperator is a crucial component of
supercritical CO 2 cycle. The targeted recuperator
effectiveness is as high as 95%.
o PCHE is a promising heat exchanger because it
- is able to withstand the pressure up to 50 MPa and the temperature up
to 700 o C (reliability ),
- has a high compactness and high efficiency (cost reduction).
PCHE = Printed
Circuit
Heat
Exchanger
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What is the PCHE?
Fluid flow channels are etched chemically on metal
plates.
- Typical plate: thickness = 1.6mm,
width = 600mm, length = 1200mm,
- Channels have semi-circular profile with
1-22 mm diameter.
Etched plates are stacked and diffusion bonded
together to fabricate a block
The blocks are then welded together to form the
complete heat exchanger core
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Construction of PCHEs
Plate stacking
Diffusion bonding
the bond strength is achieved by
pressure, temperature, time of contact,
and cleanliness of the surfaces
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Advantages of PCHE
Photo-etching technology:
Micro channels with smaller hydraulic diameter D h :
Pressure capability
PD
in excess of 50 MPa.
= h
.
Compact size (L)(
) or Higher efficiency (98%).
L =
Dh
4 j
Pr
2/3
No plate-fin brazing:
Manufacturing cost reduction.
N
σ
2t
( T
where
o
−Ti
)
N = .
∆T
LMTD
Diffusion bonding technology:
Maintain parent material strength:
Extreme temperature from cryogenic up to 700 o C.
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From HEATRIC homepage
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Experimental Facility
Oil Separator
Heater
Cooler
Compressor
PCHE (3kW)
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Experimental Loop
Cooler 2
∆P
CO 2 tank
FR
T
PCHE
T,P
T,P
∆P
T
FR
Compressor
Pressure
Reducer
Cooler 1
Oil
Separator
Heater 1 Heater 2
T :thermocouple, P :pressure meter, ∆P :differential pressure meter, FR : flow rate meter
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PCHE Test Section
Dimension of 896 x 76 x 71 mm and a dry mass of 40 kg
Channel geometry (mm) Area, (m 2 )
Channels
number, n
Diameter,
D
Active
length, L
Hydraulic
diameter, D h
Heat
transfer, A
Free flow, A c
Hot side 144 1.69 1062
1.03
0.664
64 0.00016
Cold
side
66 1.69 1170
1.03
0.336
36 0.000074
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Experimental Conditions
Pressure, MPa
No. 1 2 3 4 5
Cold
side
6.5 7.4 8.5 9.5 10.2
Hot side 2.2 2.5 2.8 3.0 3.3
Temperature,
o
C
Cold
side
90-108
Hot side 280-300
Flow rate, kg/h - From 40 to 80 with 5 kg/h increment
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Overall Heat Transfer Coefficient, U
‣ LMTD method:
where
U
1 ( Q )
2
c
+ Qh
=
Qc
= Wc
( hc
,
)
( Th,
i
− Tc,
o
) − ( Th,
o
− Tc,
i
)
, o
− hc
i
Ah
FG
ln (
Q = W h − h )
[ T − T ) /( T − T )]
h,
i
c,
o
h,
o
c,
i
h
h( h, o h,
i
1500
A - Heat transfer area, 0.664 m 2
C
p
, J/(kg*K)
1400
1300
1200
1100
1000
Hot side
Cold side
P, MPa:
10.2
6.5
3.3
2.2
F G
- Geometric factor, 0.9624
h, c - hot, cold side
o, i - outlet, inlet
120 160 200 240 280
CO 2
temperature, o C
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Heat Loss Estimation (1)
Total value:
1) From outer surface temperature of PCHE insulator
Q
loss
= ∑
i=
1,10
A
ins
i
[
4 4
εσ ( T − T ) + h ( T − T )] ≈ 110 ~ 120 [ ]
s, i surr conv , i s,
i surr
W
2) From heat balance
Q
loss
= Q h
− Q c
Heat loss, [W]
150
140
130
120
110
100
From heat balance
Pressure range, [MPa]
6.5-2.2
7.4-2.5
8.5-2.8
9.5-3.0
10.2-3.3
90
40 50 60 70 80 90
Flow rate, [kg/h]
From outer surface temperature
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Heat Loss Estimation (2)
Effect on the outlet temperatures:
3) From 2D FLUENT CFD calculations (with(2)/without(1) heat loss)
(1) (2)
4) From the heat loss compensation experiments
PCHE
PCHE−surf
Insulator Q ≈ 0
Heaters
T
k
k
= Tnear−heater−surf
loss
∆T
Thot
, out +∆Thot
, out
Tcold
, out +∆Tcold
, out
'
hot, out
: Whot
× ∫ Cp(
P(
T ), T ) dT = −0.35Qloss;
∆Tcold,
out
: Wcold
× ∫ Cp(
P(
T ), T ) dT = −0.
65
T
T
hot , out
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cold , out
Q
'
loss

Overall heat transfer coefficient, U
U, [W/m 2 K]
650
600
550
500
450
400
350
300
Pressure, [MPa]
6.5-2.2
7.4-2.5
8.5-2.8
9.5-3.0
10.2-3.3
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Reynolds number × 10 -3
U =
3
( 18.6 ± 6.8) + (0.105±
0.002) × Re, 2×
10 < Re < 6×
10
3
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Pressure factor, f P
0.07
Pressure factor, f P
0.06
0.05
0.04
0.03
hot side
cold side
Pressure range, [MPa]
6.5-2.2
7.4-2.5
8.5-2.8
9.5-3.0
10.2-3.3
0.02
2 4 6 8 10 12
Reynolds number × 10 -3
−6
−8
3
3
f P ,
= ( 0.032±
0.002) −(1.01×
10 ± 6×
10 ) × Re, 2×
10 ≤ Re≤6×
10
hot
−6
−8
3
3
f P ,
= ( 0.066±
0.001) −(1.11×
10 ± 7×
10 ) × Re, 6×
10 ≤ Re≤12×
10
cold
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PCHE cross-section
section
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Head loss in PCHE
∆p
=
ρg∆H
=
115 o 100 o
∑
m
ρ K
m
b
U
2
2
m
+
∑
m
ρ 0.316Re
m
−0.25
loss in elbows + loss in a straight pipe
La
U
md 2
2
m
I. K b =K 1 *K 2 *K 3
from Hydraulic Engineering, A.
II.
from Hydraulic Engineering, A. Lencastre, , 1987
from JSME Textbook, 2003
III. CFD FLUENT
:
∆
p calc
∆p
− ∆p
exp
exp
= 14 − 37%
2⎛θ
⎞
4⎛θ
⎞
∆p K = 0.946sin ⎜ ⎟ + 2.047sin ⎜ ⎟
:
calc
− ∆pexp
= 6 − 32%
b
⎝ 2 ⎠ ⎝ 2 ⎠
∆pexp
: N/A yet
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Effectiveness:
PCHE’s Effectiveness
Q&
η =
Q &
max
C
=
C
c
min
( Tc , o
−Tc
, i)
( T −T
)
h , i
c , i
1.000
Effectiveness, η
0.995
0.990
0.985
0.980
0.975
0.970
Pressure range, [MPa]
10.2-3.3
9.5-3.0
8.5-2.8
7.4-2.5
6.5-2.2
0.965
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Reynolds number × 10 -3
PCHE’s effectiveness reaches value up to 98.7%.
1% of recuperator effectiveness the gas turbine cycle efficiency 0.6%
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MUSE Code Simulation
‣Developed for plate-fin heat
exchanger,
‣Use Wavy fin plate heat
exchanger model,
‣This model is the most similar
model to our tested PCHE.
Various plate-fin models
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Experimental data & MUSE Calculations
700
600
Experimental Data
U, [W/m 2 K]
500
400
300
200
40 50 60 70 80 90
Flow rate, [kg/h]
The different slopes may be due to:
MUSE Calcualtions
- Difference of PCHE from wavy fin model,
- Neglect of cross flow in the distributor sections.
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Conclusions
‣ The overall heat transfer coefficient and pressure loss factor of o
PCHE were investigated both experimentally and numerically; the
empirical correlations are proposed.
‣ The method to take into account the heat loss for overall heat
transfer coefficient estimations has been established.
‣ The overall heat transfer coefficient varies from 300 to 650
W/m 2 K while the heat transfer effectiveness reaches up to 98.7 %.
‣ PCHE might be judged as a promising compact heat exchanger
for the high efficiency recuperator.
‣ The experimental data are currently used for CFD FLUENT
code verification and developing the new heat exchanger type.
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