U.S. patent number 3,703,991 [Application Number 05/165,688] was granted by the patent office on 1972-11-28 for snow precipitator.
This patent grant is currently assigned to Hedco, Inc.. Invention is credited to William E. C. Eustis, Wallace E. Howell.
United States Patent |
3,703,991 |
Eustis , et al. |
November 28, 1972 |
SNOW PRECIPITATOR
Abstract
In a snow-making machine which includes a tunnel-like housing,
ice nuclei are generated by homogeneous nucleation in a separate
zone or part of the air stream within the housing by injecting
propane or other refrigerants into a stream of moist air. A
propeller at one end of the tunnel moves an air mass through the
tunnel carrying the ice nuclei with it. Water slightly above its
freezing temperature is discharged through a nozzle disposed in the
tunnel and is broken up into droplets. The droplets are discharged
in a direction countercurrent to the flow of the air mass and ice
nuclei. The air mass supercools the droplets, and they are then
infected with the ice nuclei. The ice-infected droplets are then
dispersed through a large volume of air to effect the removal of
latent heat from the drops to form snow-like particles.
Inventors: |
Eustis; William E. C.
(Cambridge, MA), Howell; Wallace E. (Lexington, MA) |
Assignee: |
Hedco, Inc. (Bedford,
NJ)
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Family
ID: |
22600018 |
Appl.
No.: |
05/165,688 |
Filed: |
July 23, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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854103 |
Aug 29, 1969 |
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Current U.S.
Class: |
239/2.2 |
Current CPC
Class: |
F25C
3/04 (20130101); F25C 2303/046 (20130101); F25C
2303/0481 (20130101) |
Current International
Class: |
F25C
3/04 (20060101); F25C 3/00 (20060101); A01g
015/00 (); E01h 013/00 () |
Field of
Search: |
;239/2S,14,399 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: King; Lloyd L.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of Ser. No. 854,103, filed Aug.
29, 1969, now abandoned.
Claims
Having described our invention, what we claim is:
1. A method for making snow which comprises:
a. disintegrating a water stream to form water droplets at a
temperature of greater than 0.degree.C in a first zone;
b. supercooling the droplets so formed to less than 0.degree.C by
flowing a mass of ambient air about the droplets;
c. forming ice nuclei in a second separate zone independent of the
formation of the water droplets;
d. infecting the water droplets with the ice nuclei in a third zone
distinct from the first and second zones;
e. discharging the ice-infected water droplets through a large
volume of the ambient air; and
f. removing progressively the latent heat of the ice-infected water
droplets until the water droplets are more or less substantially
completely frozen and in a snow-like state.
2. The method of claim 1 where the ice nuclei are formed by
injecting into a separate stream of moist cold air a refrigerant
adapted to lower the temperature of the moist stream to less than
about -40.degree.C whereby the ice nuclei are formed by homogeneous
nucleation.
3. The method of claim 2 which includes bleeding water into the
moist stream of air and wherein the refrigerant is an expanding
gas, and further which includes forming the water droplets in the
first zone by flowing the water through a nozzle.
4. The method of claim 1 wherein the ice nuclei are formed by the
expansional cooling of saturated compressed air.
5. The method of claim 1 wherein the ice nuclei and the ambient air
flow countercurrent to the direction of flow of the water droplets
thereby increasing the rate of transfer of the heat from the water
drops to the air to provide increased supercooling.
6. The method of claim 1 wherein the size of the ice nuclei are
between about 0.1 to 1 microns and the size of the water droplets
are between 100 to 500 microns and further where the water droplets
are initially disintegrated at a temperature of about 4.degree.C
and supercooled to less than 0.degree.C.
7. A method for making snow which comprises:
a. disintegrating a water stream to form water droplets at a
temperature of greater than 0.degree.C;
b. supercooling the droplets so formed to less than 0.degree.C by
flowing an air stream about the droplets;
c. forming ice nuclei;
d. controlling the formation of ice nuclei as a step separate from
and independent of the formation of the water droplets;
e. infecting the water droplets with the ice nuclei;
f. discharging the ice-infected water droplets through a large
volume of the air stream; and
g. removing progressively the latent heat of the ice-infected water
droplets until the water droplets are more or less substantially
completely frozen and in a snow-like state.
8. The method of claim 7 wherein the control of the formation of
the water droplets and the ice nuclei as separate steps is
accomplished by:
disintegrating the water stream to form the water droplets in a
first zone; and
controlling the formation of the ice nuclei as a separate step in a
second zone distinct from the first zone.
9. The method of claim 8 which includes infecting the water
droplets with the ice nuclei in a third zone distinct from the
first and second zones.
10. The method of claim 8 wherein the controlled formation of the
ice nuclei is accomplished by injecting into a separate stream of
moist cold air a refrigerant adapted to lower the temperature of
the moist stream to less than about -40.degree.C whereby the ice
nuclei are formed by homogeneous nucleation.
11. The method of claim 10 which includes bleeding water into the
moist stream of air and where the refrigerant is an expanding
gas.
12. The method of claim 7 which includes controlling the formation
of the ice nuclei through expansional cooling of saturated
compressed air.
13. The method of claim 7 wherein the ice nuclei and air stream
flow countercurrent to the direction of the water droplets thereby
increasing the rate of transfer of heat from the water droplets to
the air to provide increased supercooling.
14. The method of claim 7 wherein the ice nuclei and air stream
flow concurrently with the direction of flow of the water droplets.
Description
SUMMARY OF THE INVENTION
The purpose of a snow-making apparatus is to emit at least
partially frozen particles which will gather on the ground as a
more or less loose snow-like mass suitable for skiing. An essential
property of any snow-making device is that it effects the
initiation of the freezing process in a large proportion of the
water particles generated, otherwise the spray produces an
artificial ice storm.
In the state of the art today, the proper role of nucleation as the
necessary initiation of freezing has not generally been recognized
or clearly identified. The prior art in at least one instance
discloses combining compressed air and pressurized water in a
helically moving chamber and discharging the mixture through a
nozzle. Upon discharge, the mixture forms ice crystals. (See U.S.
Pat. No. 3,301,485). Also a mixture of water and crushed ice
discharged through a nozzle into an ambient stream of air at less
than 0.degree.C to precipitate snow crystals has been suggested.
(See U.S. Pat. No. 2,968,164).
The primary drawbacks of the present methods and apparatus for snow
making are that the nucleating portion of the snow-making process
and the crystallization of the water droplets in the air stream
have been performed substantially simultaneously or more or less
accidentally by unrecognized "brute force," without regard to
controlling the sets of parameters which affect each step in the
process. This results in uneconomical and inefficient apparatus for
making snow, with the attendant high cost.
To form frozen particles more is required than simply the cooling
of the water to a temperature below 0.degree.C in the course of its
emission and subsequent fall, for water when it is cooled below
0.degree.C does not start to freeze until a nucleus of the frozen
phase appears. This nucleus may arise through collision between the
cooling water particles and a bit of natural ice (isomorphic
nucleation), or through the action of a foreign particle of some
other substance, the crystalline, molecular or other structure of
which somewhat resembles ice or otherwise effects the onset of the
ice phase (heterogeneous nucleation), or through cooling of the
liquid phase to such a low temperature that the ice phase appears
spontaneously without the introduction of any foreign matter
(homogeneous nucleation), which in water at atmospheric pressure
occurs at about -40.degree.C. Unless the onset of freezing is
initiated in one of these three ways, the water particle below
0.degree. C remains in a supercooled state until it strikes the
ground, where it freezes in the form of glaze or ice, generally too
hard for skiing and too rough for skating.
In our invention, the production of ice nuclei is separated from
the function of disintegrating the water stream and of cooling the
resulting water droplets and is accomplished by cooling of moist
air below the temperature of homogeneous nucleation in a separate
zone, either by adiabatic expansion of moist compressed air in an
efficient nozzle, or by injection into moist cold air of a
refrigerant, such as liquid propane, or both; and the zone is so
designed as to permit ice nuclei to grow to such a size that they
may survive the few fractions of a second during which they are to
become mixed with the droplet spray.
Likewise, the zone in which the droplet spray is generated is so
designed that the bulk water may be brought to a temperature just
barely above 0.degree.C before leaving a nozzle and may be mixed
with a stream of cold air and so be brought to a supercooled state
within a very short distance after leaving the nozzle. After each
separate step has been accomplished, mixture of the drop spray with
the nucleus cloud is then effectuated. Finally, the spray is mixed
with a rapidly moving air stream propelled from a blower in such a
way as to spread it through a large volume of the atmosphere, with
which it exchanges latent heat during the freezing of the drops.
The ice crystals then formed fall to the ground as more or less
completely frozen snow-like particles.
Accordingly, in our invention the individual steps required for
making snow are each controlled to ensure economic and efficient
results.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic and partially sectional view of our snow
precipitator; and
FIG. 2 is an alternative embodiment of our invention; and
FIG. 3 is a further alternative embodiment of our nucleating
chamber.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the snow precipitator is shown generally at 10
and includes a housing or tunnel-like conduit 12 together with a
propeller or fan 14 secured to the housing by a bracket 16, to move
air through the housing and carry the ice crystals into the
atmosphere. Disposed in the downstream or high pressure side of the
propeller 14 is a nucleating zone 18 used to form the ice nuclei.
The zone 18 comprises a feed conduit 20 for the introduction of a
moist air stream and a diaphragm 22 to provide for the introduction
of propane, or similar gas, into the moist air stream. The conduit
20 passes through the housing and as shown is L-shaped. The
diaphragm 22 is disposed in the discharge end of the conduit 20 and
further is connected to a conduit 24 which passes through the
housing 12. In communication with the conduit 20 is a feed line 26
to bleed water into the air stream.
Located downstream of the propeller 14 or on the high pressure side
and axially spaced apart from and generally axially aligned with
the nucleating zone 18 is a nozzle 28 which faces into the
direction of the flow of air created by the propeller 14. The
nozzle is connected to a water supply by conduit 30 which passes
through the housing 12. Water flowing through the conduit 30 and
the nozzle 28 is broken up into droplets.
In the operation of the snow precipitator, the propeller 14 is
actuated by a motor or other means (not shown) to move ambient air
at less than 0.degree.C, and at atmospheric humidity through the
housing. Compressed air at any humidity, including a high humidity,
and at a convenient pressure, say 10 to 15 psi in introduced into
conduit 20. Water at a rate determined by the relative humidity of
the atmosphere but typically perhaps of from 0.1 quarts to 20
quarts/minute is bled into the compressed air through feed line 26.
Liquid propane at a rate determined by the desired production rate
of snow and typically from about 0.5 to 15 lbs/hour say for example
2 lbs/hour is discharged through the diaphragm 22, which has an
orifice of about 0.010 inches, and into the saturated air stream.
When discharged into the air stream the propane goes through a
phase change into gas and absorbs heat from the air stream. If
desired, other expanding gases or refrigerants which have a high
heat of vaporization and would lower the temperature of the air
stream to below about -40.degree.C on expansion or in a phase
change may be used. For example, other hydrocarbons like butane,
ethane, methane, and other liquified gases such as liquid oxygen,
halocarbons like freon, carbon dioxide, etc. may be used, as well
as ammonia, and sulfur dioxide. The refrigerant may incur a phase
change from a liquid to a gas or may simply be an expanding gas.
Other typical refrigerants are set forth in the Handbook of
Chemistry and Physics, 47th Edition, Section E, pages 17-25.
The expanding propane cools a portion of the saturated air below
-40.degree.C and causes the formation of generally uniform ice
nuclei by homogeneous nucleation within the air stream. The average
particle size of the ice nuclei formed without addition of bleed
water is generally between about 0.1 to 10 microns say for example
less than one micron and with bleed water may be increased to
between about 125 to 250 microns say about 150 microns. The nuclei
are then discharged into the air stream.
Water enters the conduit 30 and flows through the nozzle at any
temperature in excess of 0.degree.C and generally between 1.degree.
to 15.degree.C say about 4.degree.C at a rate of between 1-300
gallons/minute for example 15 gallons/minute and is forced through
the nozzle 28 at any rate to produce the desired particle size
between about 40 and 100 psi for example 80 psi. This temperature
is advantageous in that it prevents anchor ice from forming in the
conduit 30 and in the nozzle. The nozzle breaks the water into
droplets of suitable size say between 100 and 500 microns for
example about 200 microns, and they are discharged countercurrent
and directly into the flow of air and ice nuclei. The droplets are
supercooled to below 0.degree.C by the ambient air flowing through
the housing.
These supercooled droplets are then infected by collision with the
ice nuclei previously formed which have traveled a short distance
say between 2 to 8 inches. When a drop is infected with an ice
nuclei, spicules of ice form very rapidly within it, releasing
latent heat until the droplet becomes an ice water mixture at a
temperature of about 0.degree.C remaining at this temperature until
the freezing process is completed through the exchange of heat to
the surrounding atmosphere. This exchange of heat with the
surrounding atmosphere progressively continues both while the
droplet is within the precipitator and after the ice crystals are
discharged from the end of the housing into the atmosphere where
the freezing process is continued until the droplet is all or
largely all frozen and the particles fall to the ground as
snow.
It has been found advantageous to spray the water drops
countercurrent to the flow of ice nuclei and ambient air since the
probability of collision between the drops and the nuclei is
significantly enhanced. Also, the effective velocity of the drops
relative to the countercurrent flow of air is increased; and,
accordingly, the rate of heat exchange between the drops and the
surrounding air is about three times greater than in concurrent
operation, hastening the supercooling process.
Although the nucleating zone 18 has been shown to include an
L-shaped conduit with the diaphragm located near the discharge end
of the conduit carrying the moist air, it is possible for it to
take other forms. For example, the moist air may flow through a
venturi passage and the refrigerant injected prior to the
constriction as shown in FIG. 3 at the constriction or just beyond
the constriction. Also the nucleating zone may be of a non-unitary
construction and the diaphragm disposed adjacent to the discharge
end of the conduit 20.
When compressed air is allowed to expand adiabatically, the
temperature of the air falls about 10.degree.C for each 8 percent
decrease in pressure. Therefore, if the air is initially at a
temperature near 0.degree.C expansion from a modest pressure of
20lbs/inch is more than sufficient to bring the temperature below
-40.degree.C. If the atmospheric air initially has a relative
humidity higher than about 50 percent, it will become saturated in
the course of this expansion. In this situation, in the initial
instant after the temperature falls below -40.degree.C, very large
numbers of very small ice nuclei, say for example, in the range of
40 to 60 angstroms form spontaneously.
Accordingly, in FIG. 2, in an alternative embodiment of the
invention, the nucleating zone comprises a feed conduit 34 and a
nozzle 36 in communication with the conduit 34. The nozzle 36 is
adapted to release saturated compressed air through a nozzle to
spontaneously form ice nuclei. Also, in this embodiment the flow of
air and ice nuclei may be concurrent with the flow of the drops
discharged from the nozzle 36. Again, an efficient economic
operation is provided when the formation of ice nuclei and the
water drops are separately created and then combined to form the
ice-infected droplets.
Our invention has been described in reference to homogeneous
nucleation when a refrigerant such as propane or carbon dioxide is
injected into a stream of saturated air to lower the temperature to
below about -40.degree.C to form the ice nuclei as shown in FIG. 1
or when compressed air is cooled by expansion as shown in FIG. 2.
It is also within the scope of this invention that heterogeneous or
isomorphic nucleation may be used to form the ice nuclei in the
nucleating chamber, as for example by the introduction of silver
iodide smoke or comminuted natural ice. Referring again to FIG. 1,
the saturated air stream flows through the feed conduit 20 at a
temperature of less than 0.degree.C. A finely foreign nucleating
agent such as a solid particle or product like a silver salt such
as silver iodide is injected into this air stream such as through
line 26. The silver iodide or other nucleating agent initiates the
formation of ice crystals in a supercooled saturated air stream.
Also, the air stream may be treated with foreign crystalline
substances which may normally have a hemimorphic hexagonal
crystalline structure similar to that of ice. For example, wurtzite
has been found to be satisfactory. Also various natural minerals in
a finely divided state may be similarly employed to initiate
crystallization in the supercooled air stream; namely, zincite,
nephelite, and lead iodide may also be used. If desired, ice nuclei
per se may also be injected into the saturated stream. Also,
certain resinous compounds, such as urea, have also been
effective.
Although our invention has been described in reference to
particular embodiments wherein the steps for the formation of ice
nuclei and water droplets are controlled separately, it is to be
understood that although the embodiments described showed a single
nucleating zone and nozzle there may be employed in a particular
operation a plurality of nucleating zones and nozzles within a
housing and the orifice sizes may vary. Also depending upon the
amount of snow to be generated, the flow rates of compressed air,
propane, bleed water, ambient air, etc., will vary.
* * * * *