Design optimization and Calibration of a void fraction measurement
capacitance sensor for LN2 flow H.N. Nagendra1, 2, Ravi Verma1, 2,4, Pankaj Sagar1, 2, Kashif Akber1, S. Kasthurirengan1, N.C. Shivaprakash2 ,
A.K. Sahu3 and Upendra Behera1,* 1Centre for Cryogenic Technology, Indian Institute of Science, Bangalore, India
2Instrumentation and Applied Physics, Indian Institute of Science, Bangalore, India 3Institute for Plasma Research, Bhat, Gandhinagar, India
4Presently at School of Mechanical Engineering, VIT University, Vellore, India
E-mail: [email protected]
ACKNOWLEDGEMENT
INTRODUCTION
• Transfer of cryogenic fluids from the storage Dewar to the end applications is
a daily occurrence in laboratories / industries.
• Vacuum or Super-insulated transfer lines are efficiently used for the above
applications.
• Most of the time two-phase flow occurs during the transfer process.
• It is very important to measure void fraction (liquid hold up).
SELECTION OF TUBE MATERIAL FOR CAPACITANCE
SENSOR
This work was carried at Centre for Cryogenic Technology, Indian Institute of Science, Bangalore with financial support of Board of Research in Nuclear Sciences (BRNS), India.
MEASUREMENT OF DIELECTRIC CONSTANT OF BAKELITE
EXPT. SETUP FOR SENSOR CALIBRATION
• Glass tube deformation is minimum among other insulating tube
materials. Handling and making end connections for glass tubes is quite
difficult.
• Deformation of Bakelite material is next to glass and is considered for the
capacitance sensor development.
Fig. 1. Deformation on outer diameter.
An attempt has been made to develop simple capacitance sensors for
measuring the void fraction for LN2 flow.
Thermo-structural analysis has been done for different insulating materials.
Bakelite has been selected as the insulating materials.
Experimental setups have been developed to measure the dielectric
constant and the capacitance of the developed sensors at 77 K.
Capacitance simulation has been done with the developed sensors by
ANSYS Maxwell software and the results are in good agreement with the
experimental results.
The developed capacitance sensors are calibrated with standard sensor.
These simple sensors will be very useful for void-fraction measurement of
LN2 flow.
REFERENCES
Fig. 4. (a) Sample Chamber. (b) Experimental setup.
Fig. 5. Cross sectional
view of a concave
capacitance sensor.
Fig.10. Schematic of Expt. Setup for calibration of Capacitance sensors.
CONCLUSIONS
MOTIVATION
• Many techniques are available to measure the void fraction.
• Implementation of these techniques to cryogenic fluid flow is
sometimes difficult and expensive.
• An attempt has been made to develop simple capacitance sensors for
measuring the void fraction for LN2 flow.
Abstract ID
C2Po1A-06[20]
DESIGN OF CAPACITANCE SENSOR
Fig. 6. Simulation results for C1,
C2 and C3.
CALIBRATION CURVE
20 25 30 35 40 45 50
-0.40
-0.35
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
De
form
atio
n o
n o
ute
r d
iam
ete
r (m
m)
Outer diameter of the tube (mm)
Glass
Bakelite
Teflon
FRP
Nylon
20 25 30 35 40 45 50
-0.18
-0.16
-0.14
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
De
form
atio
n o
n in
ne
r d
iam
ete
r (m
m)
Outer diameter of the tube (mm)
Glass
Bakelite
Teflon
FRP
Nylon
Fig. 2. Deformation on inner diameter.
Fig. 3. Total deformation on 19 mm ID and 25 mm OD Bakelite tube.
0 20 40 60 80 100
3.8
4.0
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
Ca
pa
cita
nce
(p
F)
LN2 volume (%)
C1
C2
C3
Sl. No Capacitor D1 in mm D2 in mm L in mm
1 C1 19 26.2 50
2 C2 19 31.6 50
3 C3 19 38.0 50
Table 1: Capacitance sensor dimensional parameters at β = 160 ̊
0 500000 1000000 1500000 2000000
0
2
4
6
8
10
12
14
16
18
20
Ca
pa
cita
nce
(p
F)
Frequency (Hz)
300K
77K 0% LN2
77K 100% LN2
0 500000 1000000 1500000 2000000
0
5
10
15
20
Ca
pa
cita
nce
(p
F)
Frequency (Hz)
300K
77K 0% LN2
77K 100% LN2
0 100000 200000 300000 400000 500000
0
2
4
6
8
10
12
14
16
18
20
Ca
pa
cita
nce
(p
F)
Frequency (Hz)
300K
77K 0% LN2
77K 100% LN2
120 130 140 150 160 170 180 190 200 210
28.55
28.60
28.65
28.70
28.75
28.80
Ca
pa
cita
nce
(p
F)
LN2 level (mm)
Capacitance 1 Vs Level
Polynomial Fit
Equation y = Intercept + B1*x^1 + B2*x^2
Plot Capacitance
Weight No Weighting
Intercept --
B1 --
B2 --
Residual Sum of Squares 2.92799E-4
R-Square(COD) 0.99514
Adj. R-Square 0.99439
620 630 640 650 660 670 680 690 700
19.65
19.70
19.75
19.80
19.85
19.90
19.95
Capcitance 2 Vs Level
Polynomial Fit
Ca
pa
cita
nce
(p
F)
LN2 level (mm)
Equation y = Intercept + B1*x^1 + B2*x^2
Plot Capacitance
Weight No Weighting
Intercept --
B1 --
B2 --
Residual Sum of Squares 0.00182
R-Square(COD) 0.98634
Adj. R-Square 0.98463
310 320 330 340 350 360 370 380
20.875
20.900
20.925
20.950
20.975
21.000
21.025
21.050
21.075
Capicitance 3 Vs Level
Polynomial Fit
Ca
pa
cita
nce
(p
F)
LN2 level (mm)
Equation y = Intercept + B1*x^1 + B2*x^2
Plot Capacitance
Weight No Weighting
Intercept --
B1 --
B2 --
Residual Sum of Squares 9.60573E-5
R-Square(COD) 0.99674
Adj. R-Square 0.99615
440 460 480 500 520 540 560
16.8
17.0
17.2
17.4
17.6
17.8
18.0
18.2
Ca
pa
cita
nce
(p
F)
LN2 Level (mm)
Capacitance 4 Vs Level
Polynomial Fit
Equation y = Intercept + B1*x^1 + B2*x^2
Plot B
Weight No Weighting
Intercept --
B1 --
B2 --
Residual Sum of Square 0.01188
R-Square(COD) 0.99733
Adj. R-Square 0.99721
Fig. 7. Capacitance vs.
Frequency for C1. Fig. 8. Capacitance vs.
Frequency for C2.
Fig. 9. Capacitance vs.
Frequency for C3.
Fig .11.
Calibration
curve for C1.
Fig. 12.
Calibration
curve for C2.
Fig.13.
Calibration
curve for C3.
Fig. 14.
Calibration
curve for C4
(FRP tube).
Sl. No Capacitor Cmax pF Cmin pF ΔC pF Experimental
ΔC pF Simulation
1 C1 5.1 4.84 0.26 0.23
2 C2 6.26 5.93 0.33 0.31
3 C3 4.17 3.99 0.18 0.16
Table 2. Cmax, Cmin and ΔC for developed sensors
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