Nitrogen Notes #1
General Information about Liquid Nitrogen
What is Nitrogen?
Nitrogen is the most plentiful gas in the atmosphere. It is colorless,
odorless, non-flammable, and non-toxic. Over 78% of the atmosphere is nitrogen. Gaseous
nitrogen is usually referred to as "N2" or simply N2. Back
to Top
What is Liquid
Nitrogen?
Liquid Nitrogen is chilled, condensed gaseous nitrogen. It is also
colorless, odorless, non-flammable, and non-toxic. It is also extremely cold (LN2 boils at
-324° F or -210° C) and because of this intense cold, handling this material requires
the use of protective gloves and goggles. Liquid Nitrogen is normally referred to as
"LN2". Back to Top
How much
does Liquid Nitrogen cost?
The process of making liquid nitrogen consists of condensing atmospheric
gases (principally nitrogen and oxygen), separating the liquefied gases, packaging and
handling, and delivering the liquids. The most expensive part of this process is packaging
and handling. This is reflected in the relative costs for "cylinder" and
"bulk" gas prices. In the US, liquid nitrogen usually costs about $2/gallon when
delivered in dewars and about $.50/gallon when delivered and pumped into a bulk storage
tank. Prices tend to be higher the farther away from the condensing plant you are and
outside the continental United States. Back to Top
Where
do I get Liquid Nitrogen and how is it delivered?
Liquid Nitrogen is readily available from the same industrial gas suppliers
who sell welding gases (oxygen, acetylene and argon). It is frequently available from
companies which sell compressed carbon dioxide that is used for soda fountains.
LN2 for effects work is usually delivered on open
trucks in portable 180 liter or 240 liter dewars (that is, 45 and 60 gallons,
respectively). LN2 can also be delivered in insulated tank trucks and be pumped directly
into a bulk tank at your facility. Back to Top
How
do I choose between portable vessels (dewars) and a bulk storage tank?
Touring productions and Industrial Theatre generally uses LN2 delivered in
portable dewars. Permanent applications such as theme parks and most casino showrooms
choose to use bulk storage tanks. There is a significant cost for installing and leasing a
bulk tank. However, if your application uses enough LN2, installing a bulk tank may be a
cost-effective choice. We can advise you on the desirability for installing a bulk tank
for your application but the final decision will have to be made in conjunction with your
local gas supplier. Back to Top
How
do I distribute LN2 from my portable vessels (dewars) or bulk storage tank to my effects
equipment?
LN2 can be distributed in several ways. You can use flexible stainless steel
transfer hose, insulated pipe, flexible vacuum-jacketed hose, rigid vacuum-jacketed pipe,
or a combination of these means.
Stainless steel flexible transfer hose is usually used
in short lengths of less than 10’. Its ribbed inner surface creates turbulence in the
LN2 as it flows through the hose. This turbulence can cause spontaneous vaporization of
the liquid creating gas bubbles in the LN2. These gas bubbles cause "slugging"
or irregular effects when the nitrogen is used. Liquid nitrogen Burst effects, which
disburse LN2 directly into the atmosphere, are most sensitive to this condition. This
in-line gas can be removed by using a phase separator or Auto-Purge™
.
Insulated pipe is frequently a suitable,
cost-effective method for distributing cryogenic, or liquefied, gases. We manufacture a
modular, insulated, stainless steel pipe encased in a hard plastic outer shell which is
used for distributing liquid nitrogen. This pipe (Cold Pipe™ )
is manufactured in 5’ and 10’ lengths. It can be assembled in a few minutes with
two wrenches and the insulation process requires only a utility knife, a roll of black
gaffers tape, and a flexible insulation wrap which we provide. Stainless steel tubing is
used because it retains its toughness even at very low temperatures and is a poor
conductor of heat. Sophisticated distribution systems can be assembled with straight
sections of Cold Pipe™ interspersed with short pieces of
stainless steel Flexi-Cold Pipe™ for turning corners.
Rigid vacuum-jacketed pipe and vacuum-jacketed hose
are the most efficient means of distributing LN2. Unfortunately, they also present several
drawbacks. This technology costs significantly more than modular insulated pipe, must be
engineered specifically for each installation, and usually requires a lead-time of at
least six weeks to allow for manufacture. Large, permanent installations frequently use
vacuum-jacketed pipe for their main LN2 distribution system. There are also at least two
different types of vacuum-jacketed equipment design. We recommend static vacuum-jacketed
systems for entertainment applications. Back to Top
Nitrogen
Notes #2
General Information about Liquid Nitrogen Effects
What are Liquid
Nitrogen effects and how do they work?
LN2 effects work by manipulating conditions of temperature, pressure, and
humidity to create areas which hold more water vapor than they are allowed to under normal
atmospheric conditions. This is the same type of atmospheric manipulation which leads to
the natural formation of clouds, foggy days, and mist formation over ponds and other
bodies of water. The difference in this case is that you are able to choose when and where
your clouds will appear.
Dry Foggers® create this
"super-saturated" air (or fog) within the Dry Fogger® machine. Nitrogen
Burst, or Fog Stick™ , effects create this condition in a mini-weather system
around each effects nozzle. This is done by distributing pressurized LN2 to each effects
head and spraying it directly into the atmosphere. It is imperative with both of these
technologies that safety standards are maintained while equipment is being installed and
the effects are produced. Back to Top
What
are the health and safety concerns of Liquid Nitrogen effects?
Liquid Nitrogen is extremely cold and any material coming into direct
contact with LN2 also becomes very cold. Protective gloves and glasses should be worn at
all times. When large amounts of gaseous nitrogen are added to an enclosed room or
theatre, it is possible to displace or dilute the room’s oxygen and create an unsafe
environment for workers and audience members. This condition is called Oxygen Deficiency
Hazard (ODH) and every LN2 effects application must be evaluated with this concern in
mind. OSHA (The Occupational Safety and Health Administration) requires that the
atmosphere contain at least 19.5% of oxygen (usually written as O2 or O2).
Large, permanent LN2 effects installations may require gas sensing monitors to insure that
this O2 level is maintained at all times. Back to Top
Why
can’t I use liquefied air and avoid concerns about ODH?
Most industries require the use of either nitrogen or oxygen separately.
Because of this, industrial gas suppliers take great pains to insure the purity of their
products. Gas separation plants, bulk storage tanks, delivery trucks, and even portable
dewars are designed to maintain this separation. Because the industrial gas industry is so
focused on single gas purity, they are not equipped to provide liquefied air for effects
applications. Back to Top
What
system pressure should I use for the LN2 system?
Liquid Nitrogen dewars are usually classified as "low pressure"
(with a 22 psig relief valve) and "high pressure" (usually with a 250 psig
relief valve). You MUST use a high pressure dewar. Low pressure dewars are unable to
deliver sufficient LN2 to a Dry Fogger to create fog. Low pressure dewars can only
make steam with a Dry Fogger. Nitrogen effects systems only using Dry Fogger
equipment and being fed through a 1/2" hose are usually set for 100 psig. LN2 effects
systems including burst effects are usually set for 125-150 psig. Under no circumstances
can Burst effects be operated at less than 100 psig since this can lead to incomplete
vaporization of the LN2. When ordering LN2 dewars you MUST specify that you need a
"high pressure dewar" and that you must be able to draw liquid nitrogen from the
dewar at over 100 psig. Back to Top
How can I
estimate LN2 consumption for atmospheric effects?
Portable Dry Foggers® use 1-2 gallons of LN2 per minute of operation
and Dry Fogger Mammoths® use 2-3 gallons/minute. This includes the
start-up period when steam is being purged from the effects system.
Nitrogen Burst LN2 consumption is more difficult to
estimate. A Burst system first must be chilled to a sub-zero temperature so that liquid
nitrogen (not gaseous nitrogen) can be sprayed from each effects nozzle. System size,
design, and quality of insulation all affect the LN2 needed to achieve and maintain this
low temperature. Different nozzle sizes and designs demand a wide range of LN2 flow rates.
Because of these system variables, it is difficult to establish broad, rules-of-thumb for
estimating LN2 needs for generic Nitrogen Burst systems. Generally, we estimate 2-5
gallons/nozzle/minute (gallons-per-nozzle-per- minute) for effects use and estimate LN2
for system chill cycles on an system-by-system basis. This provides us with a place to
start in refining overall system design parameters. Most LN2 Burst effects are used for
short periods of time so that this high flow rate does not usually translate into high LN2
consumption. LN2 Burst consumption is also significantly affected by local humidity since
higher relative humidity makes each effect larger and longer lasting. This allows you to
use less LN2 in regions of high temperature and humidity (Florida, Hawaii, etc.). Back to Top
Nitrogen
Notes #3
General Information about Dry Fogger® Systems
How
far from the Dry Fogger® can I distribute dry fog?
We recommend that fog from a Dry Fogger Portable® not be distributed
farther than 75’ horizontally and no more than 150’ from a Dry Fogger
Mammoth® . There are several factors to consider in designing a fog distribution
system. The longer fog stays in a distribution system the more it warms up. This shortens
the life span of the fog once it comes out of the pipe or hose. Also, fog travels better
through pipe because of the smooth inner surface. The corrugated inner surface of flexible
hose creates turbulence causing moisture to fall out of the fog which shortens the
fog’s life span. And finally, sending fog to a height significantly above its height
of origin compresses the fog which also shortens its life. A well designed fog
distribution system balances these factors with facility design and the production’s
effects requirements. Back to Top
How
is fog from a Dry Fogger® distributed?
In the simplest systems, fog from a Dry Fogger® is delivered through
sections of 6" diameter flexible hose. (Note: We have found that 4" diameter
hose does not work well in distributing this type of fog.)
More sophisticated systems use 6" rigid plastic
piping for long lengths and convert to flexible hose whenever complex angles must be
turned. Manually operated gates can be installed in these systems to balance fog
distribution to a variety of locations. We ALWAYS include a short section of flexible hose
at the beginning of a distribution system. This provides a pressure relief valve so that
if all of the fog outputs become clogged, the hose will rupture before an unsafe condition
is created.
Distribution systems can be designed using pneumatic Fog
Diverters™ to automatically purge steam which is formed when a Dry Fogger® is
first turned on and to distribute the Dry Fog to a variety of locations. These automated
systems allow a few fog machines to provide fog to a wide variety of effects locations. Fog
Diverters™ can be remotely controlled by a variety of control signals, including:
DMX-512, 24 VDC, 120 VAC and, 240 VAC. These pneumatic systems can be powered with
compressed air or by withdrawing small amounts of LN2, converting it to gaseous nitrogen,
regulating its pressure and sending it on to the Diverter Controller.
Fog nozzles provide the final step in fog
distribution. Our vacu-formed nozzles can be mounted within a staircase to direct fog so
that it covers the stairway evenly and smoothly. These nozzles can also be used to control
fog for a smooth ground fog effect.
Custom, metal nozzles can be mounted in a stage floor
for a variety of effects, and pneumatic, pop-up nozzles can be built into a stage floor so
that between uses the nozzles retract, leaving a smooth stage floor with no obstructions
between effects cues.
The first step, though, is to design the effects, or
"looks", that you want. The technology can be designed to meet your needs. Back to Top
Nitrogen
Notes #4
Liquid Nitrogen Burst Effects
What are
Nitrogen Burst effects?
Nitrogen Burst effects use liquid nitrogen in conjunction with humidity in
the surrounding air to create dense, white, very active fog jets. These effects frequently
resemble steam bursts and are much sharper than Dry Fog effects. Back to
Top
Why
should I consider using LN2 Burst Effects?
Burst Effects are frequently selected as visual "punctuation" for
a larger scene or effect. Sound created at the effects nozzle can draw desired attention
to the effects area. Burst Effect Curtains generally form, fall and dissipate more rapidly
than Dry Fogger curtains. Burst Effects can be more accurately "shaped" and more
easily controlled than Dry Fog effects. Back to Top
What
are the drawbacks to using Burst Effects?
Burst Effects generally use more LN2 than Dry Fog Effects and require
significantly better insulation. Depending on the specific application, these LN2
distribution systems can be very expensive. Back to Top
How does Burst work?
Liquid Nitrogen is sprayed directly into the atmosphere. The
atmosphere’s warmth causes the very cold liquid nitrogen to vaporize and mix with the
air. The LN2’s intense cold drives the resulting nitrogen/air mixture below dew
point. So long as the cold air is below dew point it is opaque. As soon as the fog warms
up so that it is above dew point, it becomes transparent and the fog effect disappears. Back to Top
What is Dew Point?
Dew point is the point at which air reaches 100% relative humidity. Back to Top
How are
Nitrogen Burst effects different from Dry Fog effects?
Nitrogen Burst techniques create effects by using the intense cold of liquid
nitrogen and the humidity that is present in the air. These effects are created directly
at the nozzle where LN2 is sprayed into the air. Dry Fog effects (that is, effects created
with a Dry Fogger LN2 fog machine) use fog which is generated inside a Dry
Fogger and is then distributed through pipe and/or hose for use as ground fog, a fog
curtain, fog waterfall or other visual effects.
Dry Fog effects tend to create soft,
"cloud-like" effects. They are essentially silent since fog is created and moved
from the Dry Fogger machine by the vaporization of the liquid nitrogen. This rapid
conversion from cryogenic liquid (LN2) to cold gas forces the fog from the Dry Fogger
without the need of fans or any other mechanical device. Nitrogen Burst effects are
created directly at the fog nozzle where liquid nitrogen combines with air, vaporizes and
the nitrogen’s intense cold drives the resulting gaseous mixture below dew point.
This process creates very vigorous fog effects which can be used to simulate steam, create
a very rapid fog curtain or waterfall, create fog geysers or a variety of other effects.
Because of the rapid flow of LN2 through the effects nozzle these effects tend to be
fairly noisy. Burst effects generally consume more liquid nitrogen than Dry Fogger
effects since Burst effects are created in the open air which is not as humid as the
inside of a Dry Fogger and, therefore, is a harder environment for fog generation. Back to Top
Do
Burst Effects systems require any preparation before fog can be created?
Yes, since Burst effects depend on spraying liquid nitrogen from the
nozzle, all LN2 distribution system components (pipes, hoses, solenoids and nozzles) must
be chilled before fog can be created. If this is not done, the effects solenoids will be
opened and only cold nitrogen gas will come out. This pre-effect system chill is usually
achieved by running LN2 through the entire length of the effects system and evacuating the
cold waste nitrogen gas either through the effects solenoids or through a Purge solenoid
which is included in the effects system specifically for this purpose. Because of the need
to maintain very low temperatures throughout the entire effects system special insulation
techniques are frequently used. These include vacuum-jacketed pipes and hoses to minimize
heat leaks into the LN2 as it travels to the effects solenoids, phase separators
(keep-fulls) to remove nitrogen gas bubbles which may accumulate within the LN2
distribution system, and foam insulated pipe with vapor barriers in some instances as a
lower-cost means for distributing LN2 for some short term applications. Back
to Top
Should
Burst systems use bulk tanks for their LN2 supply?
While Burst systems can use LN2 supplied by dewars, the effect’s high
flow requirements usually limit the number of effects supplied by a single dewar. Back to Top
How are Burst
Systems controlled?
Large Burst systems are frequently controlled with 24VDC signals from a show
control PLC while small systems can be operated with 120VAC line voltage (220-240VAC in
some parts of the world). Some systems are controlled by theatrical dimmers which have
been set to operate in a "non-dim" mode. Back to Top |
