149
| www.lakeshore.com
Appendix B: Handling Liquid
Helium and Nitrogen
B.1 General
Use of liquid helium (LHe) and liquid nitrogen (LN
2
) is often associated with the
Model
335 temperature controller. Although not explosive, there are a number of
safety considerations to keep in mind in the handling of LHe and LN
2
.
B.2 Properties
LHe and LN
2
are colorless, odorless, and tasteless gases. Gaseous nitrogen makes up
about 78 percent of the Earth’s atmosphere, while helium comprises only about
5
ppm. Most helium is recovered from natural gas deposits. Once collected and iso-
lated, the gases will liquefy when properly cooled. A quick comparison between LHe
and LN
2
is provided in TABLE B-1.
B.3 Handling
Cryogenic Storage
Dewars
Cryogenic containers (Dewars) must be operated in accordance with the manufac-
turer instructions. Safety instructions will also be posted on the side of each Dewar.
Cryogenic Dewars must be kept in a well-ventilated place where they are protected
from the weather and away from any sources of heat. A typical cryogenic Dewar is
shown in
FIGURE B-1.
B.4 Liquid Helium
and Nitrogen
Safety Precautions
Transferring LHe and LN
2
and operation of the storage Dewar controls should be in
accordance with the manufacturer/supplier's instructions. During this transfer, it is
important that all safety precautions written on the storage Dewar and recom
-
mended by the manufacturer be followed.
Property Liquid Helium Liquid Nitrogen
Boiling Point at 1 atm 4.2 K 77 K
Thermal Conductivity (Gas), w/cm-K 0.083 0.013
Latent Heat of Vaporization, Btu/L 2.4 152
Liquid Density, lb/L 0.275 0.78
TABLE B-1 Comparison of liquid helium and liquid nitrogen
FIGURE B-1 Typical cryogenic storage
Dewar
To Next Page
Loading...
