4 th International Conference on Hydrogen Safety

4th International Conference on Hydrogen SafetySeptember 12-14, 2011 San Francisco, California, USA

Numerical study on fast filling of 70 MPa Numerical study on fast filling of 70 MPa hydrogen vehicle cylinderhydrogen vehicle cylinder

Gesi Liu, Yongzhi Zhao, Yanlei Liu, Jinyang Zheng, Yuntang He

Institute of Process Equipment

Zhejiang University, Hangzhou, P. R. China

September 12, 2011

ICHS2011-#109

Numerical study on fast filling of 70 MPa hydrogen vehicle cylinder


Zhejiang University is located in Hangzhou which is near Shanghai, P.R. China.

Hangzhou(30°15'9.44"N, 120° 9'54.36"E) by Google Earth

180k

m

1h tr

ain




Hangzhou was honored as "the most beautiful and magnificent city in the world" by the Italian traveler Marco Polo.

The West Lake of Hangzhou has just been named as a World heritage site in June 24, 2011.


Zhejiang University was founded in 1897 as one of the oldest institutions of higher learning in China. It has always been ranked among the few top universities in China. There are five campuses: Zhijiang, Xixi, Yuquan, Huajiachi and Zijingang.

44,151 full-time students, including 24,983 undergraduates, 11,883 graduate students working for master degree, 6,050 doctoral candidates, 1,235 foreign students. Total collection of library: 6,260,000 Volume.

Welcome to ZJU and HangzhouZhijiang campus

Xixi campus Yuquan campus

Huajiachi campusZijingang campus




Contents

4

Introduction1

2

3

Mathematic model

Results and discussion

Conclusions



1. Introduction

Hydrogen has been recognized as an ideal energy carrier for stationary and mobile applications. The industrialization of hydrogen economy needs systems integration.



1. Introduction

In demands of 500 km driving range with one charge for HFCV, 70 MPa gaseous hydrogen storage system with high hydrogen storage density has become one of the most developed solution. High pressure gaseous hydrogen storage is normally achieved by two kinds of on-board cylinders (type 3 and type 4), which are made of carbon fiber reinforced polymer (CFRP) and certain liner (metal liner for type 3 cylinder, non-metal one for type 4).

HFCV CFRP cylinder



1. Introduction

For commercialization of HFCV, fast filling of on-board cylinder is necessary, which may lead to significant temperature rise within the cylinder. That may cause failure of cylinder and under-filling. So the maximum temperature within the cylinder is restricted below 85ºC by available standards and codes such as :

ISO/TS 15869 Gaseous hydrogen and hydrogen blends - Land Vehicle Fuel Tanks, International Standard Organization.

SAE J 2601 Fueling Protocols for Light Duty Gaseous Hydrogen Surface Vehicles, Society of Automotive Engineers.

To avoid risks caused by temperature rise, it is essential to conduct research on the mechanism and control methods of temperature rise.



1. Introduction

Many investigators have done experiments, simulations and theoretical studies on issues of the fast filling:

Most of the researches on fast filling concentrate on the cases with the working pressure of 35 MPa, e.g. Monde et al. (2007), Liu et al. (2010), Dicken et al. (2007, 2008), Heitsch et al. (2011), Zhao et al. (2010), Kim et al. (2010), Hiroshi et al. (2006), Toshihiro et al. (2008), etc.

Fast filling experiments of 70 MPa cylinder have been done by Hiroshi et al. (2006) and Khan et al. (2009).



1. Introduction

The aforementioned researches shows that:

For 35MPa cases with type 3 cylinder, the problem of temperature rise is relatively small.

However, normal filling procedure for type 4 cylinder may lead to higher temperature rise than that of type 3.

For 70MPa cases with both kinds of cylinders, the final maximum temperature with normal filling procedure may be unexpected high and intolerable at relatively high atmosphere temperature.



1. Introduction

Our group has been engaged in the rapid filling of HFCV for several years. Experiments and simulations on 35MPa HFCV storage system have been done. The published results on fast filling of HFCV cylinder include:

Liu et al. (2010) investigated the thermal behaviors such as temperature rise and distributions inside 35 MPa (150 L, type 3) hydrogen storage cylinders during its refueling by experiments. Zhao et al. (2010) investigated the effects of different average mass filling rates, initial pressure within cylinder and ambient temperature on the maximum temperature rise during refueling by numerical simulation.



1. Introduction

Experiment devices of 35MPa fast filling (150 L, type 3 cylinder)



1. Introduction

Hydrogen refueling station (70MPa available)



1. Introduction

Our group is now engaging in the issues of 70MPa HFCV storage system. This paper is a predicting study for the experiments of 70MPa fast filling process which has just been done few days ago. And the test cylinder (74L, type 3) and experiment devices are shown in the following pictures:



1. Introduction

Pre-cooling device Online monitoring system



Structure diagram of the test 70MPa HFCV cylinder is shown below. The volume of the type 3 cylinder is 74 L. The diameter of inlet pipe is 10 mm. The simulated cylinder is treated as a combination of two parts: fiber layer and aluminum alloy liner.

1. Introduction

aluminum alloy liner

fiber layer



2. Mathematic model

2.1 AssumptionsA 2-dimensional axisymmetrical CFD model is presented, including: A jet-modified standard k - model and a real gas model. Assumptions proposed for simplifying the model are described as follows:

Heat exchange coefficient of natural convection and the ambient temperature are considered as constant;The model is based on 2-dimensional axisymmetrical algorithm, and buoyancy effect is neglected.Temperature of inlet gas is considered as constant, which is equal to ambient temperature.Initial temperature of the whole system is considered as the ambient temperature. And the initial pressure is stable at the very beginning of the filling process. The gas inlet is treated as pressure inlet.



2. Mathematic model

2.2 Equations

( ) 0

i

i

ut x

The law of conservation of momentum yields the equations below:

2( ) ( )

3

i jji li i j ij

j i j j i l j

u uuu upu u u

t x x x x x x x

The mass conservation equation:



2. Mathematic model

2.2 Equations

The turbulence kinetic energy k and its rate of dissipation are obtained from the following transport equations:

ti k M

i j k j

kk ku G Y

t x x x

2

1 2t

i ki j j

u C G Ct x x x k k



2. Mathematic model

2.2 Equations

As the varying range of the hydrogen properties during the fast filling is quite large, a real gas model must be adopted.

The modified Benedict-Webb-Rubin equation of state has good accuracy:In the region between 250 and 450 K and at pressures from 0.1 to 300 MPa, the uncertainty in density is 0.04%. Speed of sound data are represented within 0.5% below 100 MPa. The estimated uncertainty for heat capacities is 1.0%. The uncertainty in thermal conductivity is estimated to 10% below 700 atm. The uncertainty in viscosity ranges from 4% to 15%.

In this model, the modified Benedict-Webb-Rubin equation of state is applied for calculating the properties of hydrogen gas, and the detail can be found in Younglove and Mclinden (1994).



2. Mathematic model

This model gives a good match of the previous 35 MPa experiment data of Liu et al (2010).For instance, the mass average temperature rise of gas vs. time curve is shown in left for the case, which is initialized with 3 MPa and charged with linear pressure-rise pattern. The simulation results generally agree with the experiment data. The deviation may be mainly caused by the nonlinearity of experiment pressure-rise pattern, while the pattern of simulation is exactly linear.

2.3 Comparison with previous data

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

Tem

pera

ture

ris

e (K

)

Time (s)

Simulation Experiment



2. Mathematic model

For different cases, the inlet pressure-rise patterns shown in left are set respectively.The temperature of inlet gas for all cases is assumed as the ambient temperature, and similarly initial pressure is 2 MPa.The red group of cases is analyzed for effects of different filling time .The blue group is for effects of different pressure-rise patterns.

0 30 60 90 120 150 180 210 2400

10

20

30

40

50

60

70

Inle

t gau

ge p

ress

ure

(MPa

)

Time (s)

120s 240s 180s_p1 180s_p2 180s_p3 180s_p4

2.4 Inlet settings

Red group of different filling time

Blue group of different pressure-rise patterns



3. Results and discussion

3.1 Characteristics of temperature fieldTemperature contour of the cylinder after 160 seconds for the case of 180s_p1




For instance, temperature contour in previous page shows characteristics of temperature field. And there are similar characteristics for all cases:

There is significant temperature gradient in interlaminar area between the aluminum alloy liner and CFRP layer, which may caused by the low thermal conductivity of CFRP.

The highest temperature of hydrogen gas usually appears in the near-wall space around far end enclosure.

Because of jet effect, there is also remarkable temperature gradient along the jet path.

The standard deviation of hydrogen gas temperature with cylinder (excluding the jet path) is relatively small, which shows good temperature homogeneity.

3.1 Characteristics of temperature field




As shown in left, the curves show that the maximum temperature rise decreases with the increasing of filling time. That may be caused by the discrepancy among different conditions of heat dissipation. The discrepancy means that the efficiency of cylinder heat dissipation is related to pressure-rise rate.

3.2 Effects of different filling time:

0 30 60 90 120 150 180 210 2400

10

20

30

40

50

60

70

Tem

pera

ture

ris

e (K

)

Time (s)

120s 180s 240s




As shown in left, the mass flow rate of inlet section rises rapidly to a certain limit in the first few seconds. Then the rate is falling down nonlinearly during the residual filling time, which indicates the real gas effects of hydrogen gas. And nonlinearity level of mass flow rate curve increases with the decreasing of the filling time.


0 30 60 90 120 150 180 210 2400.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Mas

s fl

ow r

ate

(kg/

s)

Time (s)

120s 180s 240s




The state of charge (SOC) curve is shown in left, which is described below:

Where ρend is the final average density after the filling process in the cylinder. ρ0 is the density of 288 K at the target pressure.The final SOC are 89.7% for 120s, 90.8% for 180s and 91.2% for 240s, which decreases with filling time. The decreasing trend affirms the potential risks of cylinder underfilling.


0 30 60 90 120 150 180 210 2400.0

0.2

0.4

0.6

0.8

1.0

SOC

Time (s)

120s 180s 240s

0

endSOC




The maximum gas temperature curve shown in the left has similar results with the experiment results found in Hirotani et al. (2006), which shows small difference of final maximum gas temperature among all cases. The difference means that the efficiency of cylinder heat dissipation is related to pressure-rise pattern.

3.3 Effects of different pressure-rise patterns:

0 30 60 90 120 150 1800

10

20

30

40

50

60

70

Tem

pera

ture

ris

e (K

)

Time (s)

p1 p2 p3 p4



4. Conclussions

A 2-dimionsional axisymmetric CFD model for predicting fast filling process of 70

MPa HFCV cylinder has been presented. And by changing the pressure-rise pattern

and the filling time, the thermodynamic response of 70 MPa fast filling process has

been explored. Some conclusions are described as follows:

Remarkable temperature gradient can be found in the jet path and interlaminar

area between the aluminum alloy liner and CFRP layer.

For linear pressure-rise pattern with different filling time, the final maximum gas

temperature increases with the decreasing of the filling time.

For different pressure-rise patterns with the same filling time, difference of the final

maximum gas temperature among the cases is small.

http://www.zhedahuaji.com Tel: +86-571-87953393 Fax:+86-571-87953393 Email: [email protected] Address: Institute of Process Equipment, Zhejiang University, 38#Zheda Road, Hangzhou, P.R. China, 310027.

4 th International Conference on Hydrogen Safety

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