Properties Of Hydrogen

Definition o

f Units f

or Table of Properties

NBP

-

Normal boiling point

NTP

=

Normal temp, and pressure latm at 293.15 Kelvin

amu

=

Atomic mass unit

atm

=

Atmospheric pressure

£

=

Gram

cm

=

Centimeter

m

=

Meter

ml

=

Milliliter

m3

=

Cubic meter (kiloliter)

L

=

Liter

J

=

Joule

KJ

=

Kilojoule

Cp

=

Specific heat at constant pressure

Cv

=

Specific heat at constant volume

sec

=

Second

mW

Milliwatt

N

=

Newton

MN

=

Meganewton

MJ

=

Mega Joules

km

=

Kilometer

min

Tab

Minute le 5.3 Units Used in Table 5.4

When hydrogen is cooled to a temperature of 20 Kelvin it condenses to a liquid. A gas stored as a liquid at low temperatures (below 200 Kelvin) is termed a cryogen. As a cryogenic liquid, hydrogen can be stored and handled on a large scale using current technology handling equipment. In this form, it is far denser than it is in the gaseous state. However, its low-density characteristics, as compared to other fuels, are still a challenge. A volume of liquid hydrogen weighs only 10% as much as the same volume of gasoline. For equal weights of hydrogen and gasoline, hydrogen has 290% more energy. For equal volumes of hydrogen and gasoline, hydrogen has only 29% as much energy. Its very low temperature (20 to 30 Kelvin) presents a handling problem not encountered with current common fuels.

Current technology equipment is available for handling and storage of liquid hydrogen. Research to improve storage methods and technology will provide techniques that will ease the adoption of hydrogen as the general-purpose fuel. This work must be directed at the development of improved solutions to the handling and storage problems created by liquid hydrogen's low temperature and density in both the gaseous and liquid state. The low density of hydrogen and its low boiling point present the major research challenge in the development of the new energy system.

A wealth of information covering hydrogen and hydrogen use technologies is available from the International Association for Hydrogen energy. 173 The BMW Corporation's liquid hydrogen fueling

172 "National Bureau of Standards, Technical Note 690", J. Hord, U. S. Department of Commerce, October 1976

173 The International Association for Hydrogen Energy (IAHE), P. O. Box 248266,Coral Gables, Florida 33124 IAHE resources include: The International Journal Of Hydrogen Energy (13 volumes), and the proceedings of The 7 World Hydrogen Energy Conferences. (http:/Avww. iahe, org/)

system for passenger automobiles will be discussed in Chapter 7. Their system has performed satisfactorily and may provide an adequate system for future liquid hydrogen fueled automobiles.

HYDROGEN PROPERTIES

VALUE

UNITS

Molecular weight

2.0159

amu

Triple point pressure

0.0695

atm

Triple point temperature

13.803

Kelvin

Normal boiling point

20.268

Kelvin

Critical pressure

12.795

atm

Critical temperature

32.976

Kelvin

Density at critical point

0.0324

g/ml

Density of liquid at triple point

0.0770

g/ml

Density of solid at triple point

0.0865

g/ml

Density of vapor at triple point

125.60

g/m3

Density of liquid at NBP

0.0708

g/ml

Density of vapor at NBP

134.0

g/m3

Density of gas at NTP

83.746

g/m3

Density ratio: NBP liquid-to-NTP gas

845

Ratio

Heat of fusion

58.23

J/K

Heat of vaporization

445.59

J/g

Heat of sublimation

507.39

J/g

Heat of combustion: to steam at 100 C

119.93

MJ/kg

Heat of combustion: to water at 0 C

141.86

MJ/kg

Specific heat (Cp) of NTP gas

14.89

J/(g)(Kelvin)

Cp of NBP liquid

9.69

J/(g)(Kelvin)

Cp/Cv of NTP gas

1.383

Ratio (gamma)

Cp/Cv of NBP liquid

1.688

Ratio (gamma)

Viscosity of NTP gas

8.75X10'

g/(cm)(sec)

Viscosity of NBP liquid

1.33X10'4

g/(cm)(sec)

Thermal conductivity of NTP gas

1.897

mW/(cm)( Kelvin)

Thermal conductivity of NBP liquid

1.00

mW/(cm)( Kelvin)

Surface tension of NBP liquid

1.93X10"3

N/m

Dielectric constant of NTP gas

1.00026

Dielectric constant of NBP liquid

1.233

Index of refraction of NTP gas

1.00012

Index of refraction of NBP liquid

1.110

Adiabatic sound velocity in NTP gas

1294

m/sec

Adiabatic sound velocity in NBP liquid

1093

m/sec

Compressibility factor (z) in NTP gas

1.0006

Compressibility factor 2 (z) in NBP liquid

1.712X10"

Gas constant (R)

40.7037

(ml)(atm)/(g)( Kelvin)

Isothermal bulk modulus of NBP liquid

50.13

MN/m3

Volume expansivity of NBP liquid

1.658X10''

Limits of flammability in air

4 to 75

Volume %

Limits of detonatability in air

18.3 to 59

Volume %

Stoichiometric composition in air

29.53

Volume %

Minimum energy for ignition in air

0.020

MS

Auto ignition temperature in air

858

Kelvin

Hot air jet ignition temperature

943

Kelvin

Flame temperature in air

2318

Kelvin

Thermal energy radiated from flame

17 to 25

%

Burning velocity in NTP air

265 to 325

cm/sec

Detonation velocity in NTP air

1.48 to 2.15

km/sec

Diffusion coefficient in NTP air

0.61

cm2/sec

Diffusion velocity in NTP air

2

cm/sec

Buoyant velocity in NTP air

1.2 to9

m/sec

Maximum experimental safe gap in NTP air

8X10'J

cm

Quenching gap in NTP air

4.6X10'J

cm

Detonation induction distance in NTP air

100

length/diameter

Limiting oxygen index

5.0

volume %

Vaporization rate of liquid pools

2.5 to 5.

cm/min

Burning rate of spilled liquid pools

3.0 to 6.6

cm/min

Table 5.4 Detailed Properties of Hydrogen

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