Experimental Investigation of Nonideality and Nonadiabatic ... · Very good agreement of experimental data and theoretical calculations ... This was the reason why we did not reach

KIT – University of the State of Baden-Württemberg andNational Large-scale Research Center of the Helmholtz Association

Institute for Nuclear and Energy Technologies

www.kit.edu

Experimental Investigation of Nonideality and Nonadiabatic Effects under High Pressure Releases

Kuznetsov M., Pariset S., Friedrich A., Stern G., Jo rdan T.

International Conference on Hydrogen Safety (ICHS)

"Progress in safety of hydrogen technologies and in frastructure: enabling the transition to zero carbon energy"

September 9-11, 2013 Brussels - Belgium

2 9.09.2013Dr. Mike Kuznetsov, IKET

Problems to be solved: nonideality of the blow-down process (two-phase flow); non adiabatic character of the discharge process

Background

The problem is related to the high pressure hydrogen releases in order to evaluate proper dynamics of the discharge and characteristic discharge time

Temperature – entropy (T-S) – diagram of state of rea l para-hydrogen (NIST+icefuel data)


The idea is to properly calculate the blow down mass flow rate for high pressure releasesValidation against experiments to evaluate the CD taking into account nonideality (two phase) and non adiabatic character of blow down process

Blow down mass flow rate

−= ∫

−2

1

1 1

2

1

1

2

1

122

1

2

2·max·p

p

D p

pd

pACm

ρρ

ρρ&

Solution of Bernoulli equation (integral form):

theor

D

m

mC

.

exp

.

=

1, u – upstream conditions2, d – downstream conditions

+>

−

−

+≤

+

=

−+

−−+

12

112

12

1

1

1

2

1

2;

1

2

1

2;

1

2

u

u

u

u

u

u

u

u

u

uu

d

u

d

u

d

u

uuu

uu

d

uuuu

D

p

p

p

p

p

pp

p

pp

ACm

γγ

γγ

γ

γγ

γγ

γγγρ

γγργ

&

critical (chocked) flow

subcritical flow


The objective of current work is to obtain detailed experimental data on the high-pressure releases in wide range of initial pressures and nozzle diameters to take into account nonideality of the process. In order to simplify the conditions for two-phase flow and for safety reasons, nitrogen will be used instead of the pressurized hydrogen. With this work, a capability of numerical and theoretical models for high pressure hydrogen releases will be validated against time-dependent experimental data

Objectives


A gaseous system of DISCHA facility for transient t wo-phase blow-down tests with gaseous nitrogen instead of hy drogen

Size of internal volume: 2.81 dm3

Initial pressure: 5 … 200 barInitial temperature 300KTwo nozzle positions D1, D2Nozzle diameters 0.5, 1, 2, 3, 4 mm

2 piezo-resistive pressure transducers (P1, P2)3 thermocouples (T1-T3)1 force transducer (F)1 scales (M)

Experimental facility

Outdoor

Nitrogen 200bar

P1

P2

T3

T2

M

T1

F

Nitrogen 80K

Data controlled

T1 T2 T3 P1

P2 M F

V1

V5

V4

V3

V2

V7

V6

Safety valve

D2

D1

Vacuum pump

Legends

Vi: Valve

Ti: Thermoelement

Di: Nozzle

F: Dynamometer

M: Weight

Pi: Pressure sensor

V11

V12 V13

Outdoor


Size of internal volume: 2.81 dm3

Initial pressure: 5 … 200 barInitial temperature 300KTwo nozzle positions D1, D2Nozzle diameters 0.5, 1, 2, 3, 4 mm

2 piezo-resistive pressure transducers (P1, P2)3 thermocouples (T1-T3)1 force transducer (F)1 scales (M)

Experimental facility (side view)

M

FP, T

holder (di = 4 mm)

Thermocouples (Type “K”, d = 0.25 mm)


1 Pre-evacuation and gas filling2 Equilibrium of state (P, T)3 Blow down process(T, P, F, M)

Test procedure

Measurements:T PM F

Nitrogen

F

FF

M

M

M

Simultaneous temperature, pressure, force and weight measurements provide independent measurements of mass flow rate


Experimental results: pressure dynamics

Very good reproducibility of the pressure behaviorCharacteristic pressure discharge time changes from 8 sec for 4-mm nozzle to 600 sec for 0.5-mm nozzle almost independent of initial pressure

0

50

100

150

200

0 1 2 3 4 5 6 7 8

Zeit [s]

Dru

ck [b

ar]

30 bar50 bar75 bar100 bar150 bar200 bar

pres

sure

[bar

]

time [s]


Calculations: a comparison with pressure measurements

Very good agreement of experimental data and theoretical calculationsThe discharge coefficient changes from 0.9 to 0.75 with nozzle diameter decrease from 4 to 1 mm inner diameter

N2(293K, 200 bar), d=4mm

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8

time [s]

pres

sure

[bar

]

Pressure(Kistler)

Pressure(PCB)

Calculations

CD=0.92

1

12

1

1 2 22 2

1 1 11

max 2

p

p

D

p pm C A d

p

ρρρ ρ

−

= ⋅ ⋅ −

∫&

0

50

100

150

200

250

0 20 40 60 80 100 120 140

pres

sure

[bar

]

time [s]

N2(293K, 200 bar), d=1mm

Pressure(Kistler)

Pressure(PCB)

Calculations

CD=0.752

1

12

1

1 2 22 2

1 1 11

max 2

p

p

D

p pm C A d

p

ρρρ ρ

−

= ⋅ ⋅ −

∫&


Experimental results: thrust measurements

Experimental dependencies of thrust data vs. time behave according to the initial pressureSome oscillating process was observed due to mechanical vibration of the system

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6 7 8

thru

st [N

]

time [s]

N2(293K), d=4mm

200 bar

150 bar

100 bar

75 bar

50 bar

30 bar


Calculations: a comparison with thrust measurements

Experimental data on thrust measurements fit very well with theoretical calculations using the same discharge coefficient as for pressure dynamics

N2(293K, 200 bar), d=4mm

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6 7 8

time [s]

thru

st [N

]

Force

Calculations

CD=0.9 2

1

12

1

1 2 22 2

1 1 11

max 2

p

p

D

p pm C A d

p

ρρρ ρ

−

= ⋅ ⋅ −

∫&

eee AppVmF )( 0++= &


A comparison of experimental temperature measurements and calculations

The biggest deviation of theoretical and experimental values was found for temperature measurements Main reason was the nonadiabatic process due to heat exchange gas – solid wallsThe longer was the blow-down process, the higher deviation occurred

N2(293K, 200 bar), d=4mm

-250

-200

-150

-100

-50

0

50

0 1 2 3 4 5 6 7 8

time [s]

tem

pera

ture

[oC

]

T1 (125 mm)T2 (75 mm)T3 (25 mm)Calculations

CD=0.9


Experimental data analysis

2 3 4 5 6 7

100

150

200

250

300

Saturation 1 bar 5 bar 10 bar 20 bar 30 bar 50 bar 75 bar 100 bar 150 bar 200 bar

NIST Nitrogen Equation of State

Tem

pera

ture

(K

)

Entropy (kJ/kg*K)

Temperature – entropy (T-S) – diagram of state of rea l nitrogen (NIST)

At initial pressure above 100 bar two-phase flow may occur


For 4-mm nozzle the entropy deviation appears when temperature difference reaches 120 – 150K due to heat transfer gas – solid wallNon- adiabatic blow down process occurs approaching subcritical blow down regime This was the reason why we did not reach the two-phase blow down process

Experimental data analysisReal nitrogen release at different initial pressure s (4-mm nozzle)

2 3 4 5 6 7

100

150

200

250

300 Saturation 1 bar 5 bar 5 bar(4 mm Exp) 10 bar 20 bar 30 bar 50 bar 50 bar(4 mm Exp) 75 bar 100 bar 100 bar(4 mm Exp) 150 bar 200 bar 200 bar(4 mm Exp)

Tem

pera

ture

(K

)

Entropy (kJ/kg*K)


Experimental data analysisReal nitrogen release at 200 bar and different nozz le diameter

2 3 4 5 6 7

100

150

200

250

300

0.5 mm nozzle

1 mm nozzle

2 mm nozzle

Saturation 1 bar 5 bar 10 bar 20 bar 30 bar 50 bar 75 bar 100 bar 150 bar 200 bar 200 bar(0.5 mm Exp) 200 bar(1 mm Exp) 200 bar(2 mm Exp) 200 bar(4 mm Exp)

Tem

pera

ture

(K

)

Entropy (kJ/kg*K)

4 mm nozzle

The less nozzle diameter and the longer the blow down process, the lower the temperature when non adiabatic effect or entropy deviation appears (at 200 bar):0.5-mm nozzle ∆T = 40K ; 1-mm nozzle ∆T = 60K ; 2-mm nozzle ∆T = 120K ; 4-mm nozzle ∆T = 170K ;


Scaling of transient discharge pressures

Scaling by dimensionless p+ and t+ results in very good agreement of the tests with different initial pressures for the nozzle diameter more than 2 mm.There is some difference appears for smallest nozzle diameters due to the above discussed heat transfer effects and the discharge time. The slowest experiments (0.5 and 1 mm nozzles) show the highest values for p+(t+).

( )( )

1

2

12

1

2

1

2

11

−−

+−+−

+

⋅

+

−+=γ

γ

γγ

γγtp

p+ = p(t)/p0 - dimensionless pressure;

t+ = t/tchar - characteristic release time;

tchar = V/(A·c0) - characteristic release time

N2(293K, 200 bar)

0

50

100

150

200

250

0 20 40 60 80 100 120 140 160 180 200

time [s]

pres

sure

[bar

]

d=0.5 mmd=1 mmd=2 mmd=3 mmd=4 mm

N2(293K, 200 bar)

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12 14 16 18 20

t+

p+

d=0.5 mmd=1 mmd=2 mmd=3 mmd=4 mm


Scaling of transient discharge pressures

( )( )

1

2

12

1

2

1

2

11

−−

+−+−

+

⋅

+

−+=γ

γ

γγ

γγtp

p+ = p(t)/p0 - dimensionless pressure;

t+ = t/tchar - characteristic release time;

tchar = V/(A·c0) - characteristic release time

0

0.2

0.4

0.6

0.8

1.2

0 1 2 3 4 5 6 7 8 9 10t+

p+

30 bar50 bar100 bar150 bar200 bar

1 nozzle 2.0 mm

0

0.2

0.4

0.6

0.8

1.2

0 1 2 3 4 5 6 7 8 9 10

t+

p+

nozzle 4.0 mm 30 bar50 bar100 bar150 bar200 bar

1

Characteristic time t+ includes the sound speed of the gas c0 in its initial state p0/T0, which varies significantly with the initial pressure. Independent of that the scaling equation was originally derived for ideal gases with constant γand constant sound speed c0 during the blow-down process it allows a very good scaling of the present non-ideal high-pressure discharge experiments with nitrogenThe measured pressures p+(t+) were scaled well from the initial pressure p0 down to pend = 3 bar to remain in the choked flow regime, but even further the difference is rather small


Conclusions • A small-scale facility for transient discharge of c ryogenic nitrogen was

fabricated and tested with gaseous nitrogen as an i nert hydrogen substitute. Different orifice sizes (0.5, 1, 2, 3, 4 mm) and in itial N2 pressures (30 – 200 bar) were investigated.

• The measured time-dependent data for vessel dischar ge pressure, thrust, discharge mass flow, and gas temperatures could be well reproduced using the NIST database for the real gas equation-of-state of nitrogen. This verification for nitrogen also assures the EOS for hydrogen, whi ch is based on the same methodology.

• The newly developed critical discharge analysis met hod for a pure substance predicts correctly the transient blow-down of a hig h-pressure gas system. The measured pressure histories could be scaled very we ll using initial pressure and sound speed of the gas, vessel volume and nozzl e area as characteristic quantities.

• New results about the heat transfer effects in blow -down of gaseous high-pressure systems have been obtained. For relatively small nozzle diameter and lower initial pressure the heat from surrounding ma y completely eliminate the two-phase scenario of high pressure release.

• The facility is ready for extension of the experime nts to liquid nitrogen and investigation of cryogenic two-phase discharge in a future phase

Documents

Experimental Investigation of Nonideality and Nonadiabatic ... · Very good agreement of experimental data and theoretical calculations ... This was the reason why we did not reach