Petra Janickova

Petra Janickova 21. February 2011

Investigation on Pressure Drop Phenomena of CO2 in Two Phase Flow

for Detector Cooling

1. Advantages of CO2 2. The test facilities3. Pressure drop measurements4. Comparison to the model 5. Conclusion


• higher latent heat, 2 times more

then C6F14

• higher operation pressure then

C3F8 (at -20˚C it has 2 bar)

smaller gas bubbles in two phase

flow

lower probability of

plugging in mini channels

• lower Global Warming Potential

CO2 = 1 ; C6F14 = 7400

• resistant to radiation

• high heat transfer coefficient

especially in two phase flow

1. Advantages of CO2


2. The different supply systemsSMALL SCALE SYSTEM: Compressing Condensing LARGE SCALE SYSTEM: Liquefying Pumping


The portable test section

Expansion Heating Measurement Heating

wall temperature

fluid temperature


3. Experimental results

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250Large scale system Small scale system

Vapor quality

Pres

sure

dro

p [m

bar]


3. Experimental results

400 500 600 700 800 900 10000

10

20

30

40

50

60

70

Mass flux [kg/m2s]

Offs

et ∆

p(∆p

) [m

bar]


3. Possible reasons for the deviation

1. blocked capillaries

2. wrong measurement of the

mass flow

3. different kind of pump

1. Measurement of the pressure drop by

means of the temperature sensors

2. Calibration of the mass flow meter in

single phase

3. Measurement of eventual pressure

oscillations in the system


3. Reasons for the deviation1. Measurement of the pressure drop by means of the temperature sensors

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10000

20000

30000

40000

50000

60000

70000

80000

Δp_measured Δp_calculated

Vapour quality x

Pres

sure

dro

p Δp

in

[Pa/

m]

Large scale

Small scale

The deviation of calculated and measured mass flow is identical at both systems


3. Reasons for the deviation2. Calibration of the mass flow meter in single phase

The coriolis mass flow meter is measuring by means of the coriolis effect Thus able to measure in liquid and gas phase

• A lower accuracy of the mass flux meter at low mass flux < 500 kg/m2s• Additional vibrations in the system can effect the measurement

0 200 400 600 800 1000 1200 14000

20

40

60

80

100

120

140

160

LIQUID GAS Prediction

Mass flux measured with the mass flow meter in cryolab G [kg/m2s]

Erro

r [%

]


3. Reasons for the deviation2. Calibration of the mass flow meter in single phase

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

300

350

Small scale Large scale calibrated

Vapor quality x

Pres

sure

dro

p ∆p

[mba

r]

→ The deviation in mass flow is not effecting the pressure drop significantly

2 4 6 8 10 12 14 16 18 20 2225

30

35

40

45

50

55

Time [min]

Pres

sure

p [b

ar]

A = 1 bar


3. Measurement of eventual pressure oscillations in the system

According to the datasheet: f = 2.33 Hz

3. Reasons for the deviation


3. Measurement of eventual pressure oscillations in the system

Measurement in the test sectionA = 25 mbar

3. Reasons for the deviation

More measurements has to be done to prove the influence of the oscillations


4. Proof of the model

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.0000

100

200

300

400

500

600

700

800

900

MODEL 300 kg/m^2*s 400 kg/m^2*s 500 kg/m^2*s 800 kg/m^2*s941 kg/m^2*s

Vapor quality x

Pres

sure

dro

p ∆p

[mba

r]



The deviation is growing bigger with higher mass flux and is negative at low mass flux

200 300 400 500 600 700 800 900 1000-20

0

20

40

60

80

100

120

140

160

180

200

220

240

Mass flux G [kg/m2s]

Offs

et ∆

(∆p)

[mba

r]



The friction factor is more depending on the mass flux: Introduction of a new friction factor with a mass flux ratio

0 10000 20000 30000 40000 50000 600000

0.0050.01

0.0150.02

0.0250.03

0.0350.04

0.045

Reynolds number ReV

Fricti

on fa

ctor

0 0.02 0.04 0.06 0.08 0.1 0.120

0.005

0.01

0.015

0.02

0.025

270 260 460460 f_calculated

Weber number WeL

Fricti

on fa

ctor

0 10000 20000 30000 40000 50000 600000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

f_measured f_calculated f_new

Reynolds number

Fricti

on fa

ctor


4. Proof of the model The model is not including the roughness Introduction of an additional part concerning the roughness

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.0000

100

200

300

400

500

600

700

800

900

1000

MODEL 300 kg/m^2*s 400 kg/m^2*s 500 kg/m^2*s800 kg/m^2*s 941 kg/m^2*s old f_M

Vapor quality x

Pres

sure

dro

p ∆p

[mba

r]


5. Conclusion

• The pressure oscillations caused by a pump can cause a problem during the operation of the cooling plant for CMS. A solution could be:• A good damping system• A not fluctuating pump (gear pump)

• The coriolis mass flow meter should be calibrated before use• The latest released model has to be improved and therefore more measurements has to be done• at high mass flow• the dryout inception• the pressure drop

• Never trust the pressure restriction of the valves while doing a pressure test!


Thank you for your attention!

Petra Janickova

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