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: behera@iisc.ac.in

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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