LIQUID
NITROGEN
N2
Nitrogen
Nitrogen is mainly found as a gas in the atmosphere, where it accounts
for 78 % by volume.
Nitrogen is also found:
- In the Earth's
crust, to a limited extent (in the form of nitrates, etc.),
- In organic form
(in the living or dead plants and organisms which form humus)
- In mineral form
(ammonia), and thus contributes to soil fertility.
In gaseous form, nitrogen is a neutral, colorless gas. It is inert
and does not sustain life.
Handling
& Use
Liquid
Nitrogen, often abbreviated as LN2 is used extensively in all fields
of research
and industry. The important things to remember is
that as a liquid its boiling point is around -195°C (-320°F)
at normal pressure which means that unless its temperature is kept
below that temperature, it will boil and turn into Nitrogen Gas. Increasing
the
pressure under
which it is stored increases the boiling point. At -147°C (-232.6°F)
it reaches the critical temperature above this temperature, the gas
cannot be liquefied by pressure alone.
Practically
this means that storage of LN2 requires the best heat insulation
possible. For this purpose Dewar
Flasks or vacuum insulated
flasks and containers are used. The Dewar Flask principle is to reduce
heat transfer and therefore boiling of the LN2 by minimizing conduction
of heat ( the vacuum space and the normal material glass are poor conductors
of heat), by minimizing radiation, dewar flasks are coated with silver
on their inside walls and by minimizing convection ( the vacuum space
has very little gas to allow heat convection .
The main
concern in safe handling is to realize that LN2 is very cold and
will freeze most items that are placed in it, including human tissue,
fingers and such like. The gas boiling off the LN2 is not toxic but
will not support life so don't boil LN2 in quantities in small closed
spaces. The gas escaping can be very cold and should be handled with
care. Use gloves, and eye protection, use proper Dewar
Flasks for containing,
transport and use of LN2
Physical
Characteristics
| Critical point |
|
| Critical temperature |
-147 °C |
| Critical pressure |
33.999 bar |
| Critical density |
314.03 kg/m3 |
| Triple point |
|
| Triple point temperature |
-210.1 °C |
| Triple point pressure |
0.1253 bar |
| Solid
Phase |
|
| Molecular weight |
28.0134 g/mol |
| Solid Phase |
|
| Melting point |
-210 °C |
| Latent heat of fusion (1,013 bar, at triple point) |
25.73 kJ/kg |
| Liquid Phase |
|
| Liquid density (1.013 bar at boiling point) |
808.607 kg/m3 |
| Liquid/gas
equivalent (1.013 bar and 15 °C (59 °F)) |
691 vol/vol |
| Boiling point (1.013 bar) |
-195.9 °C |
| Latent heat of vaporization (1.013 bar at boiling point) |
198.38 kJ/kg |
| Gaseous phase |
|
| Gas density (1.013 bar at boiling point) |
4.614 kg/m3 |
| Specific gravity
(air = 1) (1.013 bar and 21 °C (70 °F)) |
0.967 |
| Specific volume
(1.013 bar and 21 °C (70 °F)) |
0.862 m3/kg |
| Ratio
of specific heats (Gamma:Cp/Cv) (1.013 bar and 25 °C
(77 °F)) |
1.403846 |
| Thermal conductivity
(1.013 bar and 0 °C (32 °F)) |
24 mW/(m.K) |
| Compressibility
Factor (Z) (1.013 bar and 15 °C (59 °F)) |
0.9997 |
DOWNLOAD AIR LIQUIDE SAFETY
INSTRUCIONS use at your own risk.
Finemech takes no responsibilty
for the use or hadling of liquid nitrogen in any container or Dewar flask
that it sells. This page is provided for information only
|
