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)
3 9.09.2013Dr. Mike Kuznetsov, IKET
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
4 9.09.2013Dr. Mike Kuznetsov, IKET
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
5 9.09.2013Dr. Mike Kuznetsov, IKET
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
6 9.09.2013Dr. Mike Kuznetsov, IKET
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)
7 9.09.2013Dr. Mike Kuznetsov, IKET
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
8 9.09.2013Dr. Mike Kuznetsov, IKET
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]
9 9.09.2013Dr. Mike Kuznetsov, IKET
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
−
= ⋅ ⋅ −
∫&
10 9.09.2013Dr. Mike Kuznetsov, IKET
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
11 9.09.2013Dr. Mike Kuznetsov, IKET
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++= &
12 9.09.2013Dr. Mike Kuznetsov, IKET
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
13 9.09.2013Dr. Mike Kuznetsov, IKET
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
14 9.09.2013Dr. Mike Kuznetsov, IKET
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)
15 9.09.2013Dr. Mike Kuznetsov, IKET
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 ;
16 9.09.2013Dr. Mike Kuznetsov, IKET
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
17 9.09.2013Dr. Mike Kuznetsov, IKET
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
18 9.09.2013Dr. Mike Kuznetsov, IKET
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