Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
NOZZLES
FIELD OF THE INVENTION
This invention relates to nozzles and more
particularly to flat jet nozzles especially, but not
exclusively, for use in snowmaking equipment. The
invention also relates to snowmaking equipment.
BACKGROUND OF THE INVENTION
There are many tyges, designs and configurations
of nozzles that are particularly used in industrial
situations for the spraying of fluids. Nozzles of this
kind are used in the irrigation, cleaning~ painting and
fire extinguishing industries. Spraying systems
incorporating no~~les of this kiaid have ~ri~.e ranging
industrial applications. Nozzles are also used in
snowmaking equipment and the nozzle that is the subject of
this invention has its primary use in saaowa~aking
equipment.
Flat jet nozzles that produce a flat spray
pattern are known. They distribute liquid as a flat or
sheet type spray. Some use elliptical orifices with the
axis of the spray pattern being a continuation of the axis
of the inlet pipe connection. Others use a deflector, the
deflecting surface diverting the spray pattern away from
the axis of the inlet pipe connection. There are a number
of different nozzles that provide a flat spray pattern.
Variations of these nozzles provide considerable
variations in the spray pattern.. The adjustability of
nozzles of this kind is usually confined to variation in
the liquid pressure.
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There are a number of parameters that contribute
to successful snowmaking. The constant fluctuations in
these parameters means that efficient snowmaking equipment
needs to be continually adjustable to ensure optimum
efficiency. The adjustability and resultant efficiency is
critical to successful snowmaking and often critical to
the economics of a ski resort.
It is the issues surrounding the design of
nozzles that produce a flat spray pattern and the issues
of snowmaking equipment that have brought about the
present invention and its derivatives.
SUM~2ARY OF THE INVENTION
In accordance with one aspect of the present
invention there is provided a nozzle for producing a flat
spray patterne the nozzle comprising a fluid passageway
tera~inatiga.g in aa~. end ~~~.11 having an o~a.tlet ~,perture~ the
fluid passageway having at least one deflector that
deflects the fluid towards the aperture; and adjustable
anea~ns to vary the cross section of the aperture.
Frefer~,bly~ the fluid passageway has at least two wall
portions that converge towards the aperture. The means to
~5 vary the cross section of the aperture may comprise
displaceable shutters that move from opposite sides of the
aperture to close off or increase the aperture of the
cross section.
Preferably, the end wall is furnished by a cross
member that extends across the end of the fluid
passageway, the tube supporting axially displaceable pins
adapted to move across the aperture to decrease or
increase the cross section of the aperture.
In a preferred embodiment means is provided to
control the axial displacement of the pins.
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In a preferred embodiment the nozzle comprises a
T-piece, the leg of which is a pipe defining a fluid
passageway and the head of the T being a pipe positioned
across the end of the fluid passageway, an aperture is
positioned in the head of the T-piece axially aligned with
the fluid passageway, and a pin terminating in a planar
face is positioned at each end of the head of the T-piece
to be displaceable along the T-piece so that the end faces
of the pin can move across the aperture to vary the cross
section of the aperture.
In the preferred embodiment the fluid passageway
and cross member are circular and the diameter of the
fluid passageway is the same as the diameter of the cross
member. It is also preferable that in adjusting the cross
section of the aperture the pins move the same distance in
opposing directions.
~.ccording to a further aspect of the present
invention there is provided snowmaking equipment
comprising at least one flat jet water nozzle inclined
upwardly to, in use~ project a plume of water droplets,
the nozzle being positioned adjacent a jet of compressed
air, the nozzle having an outlet aperture, and means to
vary the cross section of the aperture to adjust the
characteristics of the plume to suit the ambient
conditions.
Preferably, the jet of compressed air is placed
downstream of the nozzle. The jet of compressed air
preferably comprises an array of apertures. The width of
which equates to the width of the plume at the air jet.
Preferably, four flat jet water nozzles are
positioned spaced apart in a horizontal plane, the spacing
of the nozzles equating to the maximum width of each
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plume.
In accordance with a still further aspect of the
present invention there is provided snowmaking equipment
comprising a rotatable mast that supports a head, the head
comprising at least two spaced apart flat jet water
nozzles, each nozzle having an outlet aperture, each
nozzle being positioned adjacent a jet of compressed air
and means to vary the cross section of each aperture to
vary the output of each nozzle.
Preferably, the head is vertically adjustable
whilst maintaining the angle of inclination of water and
air nozzles. In a preferred embodiment, the plume of
water droplets escaping from each nozzle is directed
tangentially against the underside of the air jet. The air
jet preferably has an array of ~, plura.lity of spaced
outlet spartures~ the width of the array being
substantially the same a.s the wic~.tra, of the plume at the
air jet.
Preferably~ the head includes four nozzles spaced
so that the plua~,es ax~.eet a.t their ~~idest points .
DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be
described by way of example only in which:
Figure 1 is a perspective view of snowmaking
equipment,
Figure 2 is a side elevational view of the
snowmaking equipment in three different vertical
positions,
Figure 3 is a plan view of the snowmaking
equipment,
Figure 4 is a side elevational view of the
snowmaking equipment when supported on an uneven inclined
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surface,
Figure 5 is a detailed perspective view of the
head of the snowmaking equipment shown in Figure 1,
Figures 6a, 6b and 6c are cross sectional views
taken along the lines 6-6 of Figure 5 showing a water jet
and air nozzle in three different relative positions,
Figure 7 is an enlarged cross sectional view of
part of the head enclosed by the circle 7 in Figure 5,
Figure 7a is a cross sectional view of two
adjacent nozzles illustrating a means of adjusting the
nozzles,
Figures 8a and 8b are cross sectional views taken
along the lines 8-8 of Figure 7 showing the outlet of the
water jet in two positions,
Figure 9 is a cross sectional view taken along
the lines x and showing the physical association of a
water jet with an air jet,
Figure 10 is a cross sectional view illustrating
the associ~.tion of a plume of eater contacting the a.ir
bet,
Figure 11 is a perspective underside view of the
air jets
Figure ~.~ is s, perspective view of a head for
snowmaking equipment of a second embodiment,
Figure 13 is a plan view of the head,
Figures 14a and 14b are plan views of the head
illustrating movement of mechanisms to adjust flat jet
nozzles,
Figure 15 is an enlarged perspective view within
the area 15 of Figure 13 illustrating the adjustment
mechanism of the flat jet nozzle, and
Figure 16 is an enlarged perspective view within
the area 16 of Figure 13 illustrating the relationship
between the flat jet water nozzle and air nozzle.
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The preferred embodiments that are illustrated in
the accompanying drawings relate to snowmaking equipment
that incorporates an adjustable flat jet nozzle. The
invention covers both the nozzle per se applicable to many
spraying industries as well as snowmaking equipment that
incorporates a nozzle, it is however understood that the
snowmaking equipment has many other features that
contribute to its improved design and operation.
The nozzle 10 is shown in detail in Figures 7 and
8. Although it is shown in association with snowmaking
equipment it is understood that this nozzle is applicable
to many fields totally unrelated to snowmaking. The
nozzle has applicability in any industrial spraying
application where there is a need for a variable flat jet
nozzle.
~.s shown in Figures 7 to 10 of the accompanying
drawings~ an a~.jia.stable n~~zle 10 com~arises a T-~aiece 11~
the leg 12 of which is a cylindrical fluid passageway that
is secured to a rectangular mounting plate 13. Welded
across the end of the leg 12 is a piece of cylindrical
pi~ae 15 ~~itla a circular outlet aperture 20 positioned co-
axially with the as~is of the fluid passageway. The pipe
15 is hollow to accommodate a pair of cylindrical pins 21,
22. Each pin is cylindrical and terminates in a planar
face 23 at one end. An O-ring 24 is located in a groove
25 on the exterior of the pin spaced from but close to the
face 23. The other end of the pin is provided with an
external thread 26 that is arranged to be a screw fit
within a threaded sleeve 30 which is in turn welded to a
radial flange 31 that joins a larger hollow sleeve 32 that
operates as a pin guide. As shown in Figure 10, the
circular cross section~of the T-piece head 15 provides two
converging surfaces 3 and 4 that cause water flowing
towards the aperture 20 to converge towards the aperture.
The planar ends 23 of the pins 21, 22 operate to vary the
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cross section of the aperture 20. As the pins move in the
pipe the ends progressively close off the aperture 20 as
shown in Figures 8a and 8b.
In other options the T-piece head (not shown)
could be of triangular cross section with opposed sides
converging towards the aperture. A square tube with the
aperture in one corner also provides the two converging
walls.
In other embodiment the head could be a
rectangular block with an elongate groove with an aperture
in the base of the groove. The pins are in block form to
slide in the groove. The adjacent end of the pins are
bevelled to define converging surfaces with the straight
edges of the pins being adjacent the aperture to define an
adjustable slit across the aperture.
The no~~le described ~.bovr~ ~arovides a flat s~aray
profile. The exact profile varies in dependence with the
position of the pins 21, 22 in the aperture 20.
Dis~alacement of the pin guides 3~ causes
displacement of the pins ~1~ ~~ to vary the cross section
of the aperture 20. If the pin guides are coupled to a
suitable servo mechanism the nozzle can have a constantly
variable output depending on the position of the pins.
Ideally, each pin moves by the same amount in opposite
directions..
The nozzle has the advantage that its output can
be varied whilst maintaining full input fluid pressure.
This differs from most flat jet nozzles where the
adjustability is either by variation of the input fluid
pressure or by changing the nozzle aperture by replacing
the end of the nozzle.
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Although in the preferred embodiment the outlet
aperture 20 of the nozzle is circular, it is understood
that other shapes are envisaged. A larger diameter
aperture provides a small spray angle whilst a smaller
aperture diameter increases the spray angle. A wide slot
on the other hand provides a very wide spray angle. The
fluid flow can be increased by increasing the width of the
aperture 20 by moving the pins apart 21, 22. Conversely,
a decrease in fluid flow is achieved by moving the pins
21, 22 together. Preferably, the pressure always remains
constant, namely at its maximum. Use at maximum pressure
results in higher velocity and smaller spray particle °
size. The closer the pins are together results in small
spray particles and less fluid flow which is ideal for
snowmaking.
Although the variable flat nozzle 10 described
above is specifically designed for use with snowmaking
equipment~ it is understood that this n~zzle c~u.ld, be used
in a wide range of other industrial applications. The
adjustability of the nozzle could be manual through use of
a. spanner~ Allen key or similar such tool to displace the
pins or through more automated means by driving the pin
guides as shown in Figure 7.
Figures 1 to 11 illustrate snowmaking equipment S
utilising a bank of four nozzles 10 of the kind described
above. As shown in Figure 3, the nozzles 10 are mounted
spaced apart so that the plumes of water particles that
are ejected from the nozzles meet at their maximum width.
As shown in Figure 5, the snowmaking equipment S
comprises a mast M that is pivotally rotated about an
adjustable base structure B that comprises three legs 51,
52, 53 mounted on adjustable skids 55 that extend
outwardly by about 2 metres and are equally spaced around
a common pitch circle. The legs 51, 52, 53 support an
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adjustable triangular bracing structure 60 on which the
mast M is rotatably mounted. The mast comprises a
vertical column 61 that is mounted centrally of the base
structure B, the vertical column 61 has a rearwardly
trailing arm 62 that terminates in a mounting bracket 63
that in turn pivotally supports two closely spaced
parallelogram linkages 64, 65. The parallelogram linkages
64, 65 pivotally supports a head assembly H that is in the
form of, a pair of triangular support frames 66, 67 that
are rigidly secured to the spray head H.
The spray head H is shown in Figure 5 and
essentially comprises an elongate water pipe 71 referred
to as a manifold that has projecting therefrom four
adjustable nozzle assemblies 10 of the kind described
above and shown in Figures 7 to 9. Each nozzle 10 is also
associated with a~ compressed air jet 75 as shown in Figure
5. The jets 75 are interconnected by pipe 76 and fed by a
common source of compressed. air. The array of nozzles 5.0
and air jets 75 support a rectangular wind vane 74 shown
in Figures 1 and 3. The compressed air and water are
supplied to the head H by flez~ible pipes that run down. the
mast ~3 to the ground a.s sho~aaa in Figure 4.
The parallelogram linkages 64, 65 are in a
parallel closely spaced configuration. Each parallelogram
linkages 64, 65 as shown in Figure 4 comprises two
elongate arms 68, 69 that are pivoted at one end to the
mounting bracket 63 on the mast M and the triangular frame
66 or 67 on the spray head H at the other end. The
parallelogram linkage has the opportunity of assuming a
variety of vertical positions as shown in Figure 2. At
the highest position the arms 68, 69 extend vertically
whilst at a lowest position the arms 68, 69 are slightly
extended below the horizontal. In each case the
triangular support for the jet assemblies remains at the
same angle to the horizontal. The triangular frames 66,
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67 can be covered in sheet material to act as a subsidiary
wind vane to the primary vane 74. The parallelogram
linkages are attached to trailing arm 80 that is coupled
to a spring 81 that is in turn attached to rearwardly
extending flange 82 on the base of the mast M. The spring
81 acts to urge the parallelogram linkages 64, 65 to
assume the vertical position and the lower positions are
caused by wind impinging on the vane 74 to deflect the
assembly down against the spring. It is understood that
the spring could be adjustable and it is further
understood that other mechanisms such as pneumatic or
hydraulic dampers could replace the spring. The maximum
height of the assembly S is approximately 6 metres.
As mentioned above, the spray head H incorporates
four adjustable flat nozzles, each associated with a
compresses air jet. The association of each adjustable
flat nozzle 10 with the compressed air is illustrated in
Figures 9 to 11. The air jet 75 is in the form of a.
tapered jet body 76 of triangular cross section that is
inclined downwardly from the horizontal by 21°. The jet
body 75 terminates in a plurality, preferably between
three and fourteen sms.ll apertures 77. The ~.a.ndersic~e of
each aperture 77 has a trailing scalloped groove 78 that
is cut out of the underside of the air jet and the
arrangement of the water jets 10 is such that, as shown in
Figure 10, the water first hits the underside of the air
jet 75 as it tangentially passes the ends of the air jets
and the apertures 77. The holes 77 in the end 79 of the
tapered nozzle body are drilled so that they extend to the
bottom surface to merge with the trailing scalloped
grooves 78. The thin edge that is defined at the top of
the apertures reduces the surface area for ice to adhere.
Furthermore, the velocity of the water plume P, as it
passes the apertures, clears the ice away.
Figures 6a to 6c illustrates the adjustability of
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the air nozzle 75 and water jets 10. The air tube 76 is
mounted on a elongate shaft 101 that is axially
displaceable about a sleeve 102 that is held to a support
bracket via a screw 103. The jets 75 are in turn mounted
to the shaft to be rotatable about a substantially
horizontally axis as shown in Figures 6a and 6c. The jets
75 can also be inclined relative to the air tube 76
through a flange bracket assembly 105 shown in Figure 6c.
The position of the water jets and water supply arm are
substantially fixed to the support bracket as shown in
Figures 6a, 6b and 6c.
The adjustment of the nozzle orifice size is
carried out by displacement of the pins 21, 22. As shown
in Figures 7 and 8. To displace the pins to vary the
cross section of the outlet aperture 20 of each nozzle 10,
the pin support sleeves 30 are connected to slides 32 via
webs 39. The slides are positioned co-axial of the: air
pipe 76 and, as sho~ax~. in Fic~~are 7a, each sleeve 32 is
arranged to be a sliding fit on the air pipe 76. All the
left hand sleeves 30 of the adjustable nozzles 10 are
connected. to a. first elongate rod 90 and a.ll the right
hand sleeves 30 are connected to a second elongate rod 91.
The rods 90 and 91 are bolted to the respective sleeves 32
so that displacement of the rods 90, 91 has the effect of
moving the sleeves 32 to in turn move the pins 21 or 22 in
and out of the aperture 20 of each nozzle 10.. The rods 90
and 91 are coupled to threaded bosses 97B 98 that support
externally threaded rods 92, 93 that extend from opposite
sides of a bevel gear 94. The bevel gear 94 meshes with a
second bevel gear 95 connected to a shaft 96 that extends
down the mast so that it can be driven from the base of
the mast. Thus, rotation of the shaft 96 imparts rotation
to the two rods 92, 93 extending from the beveled gear 94.
The two shafts 92, 93 have opposite threads so that the
left hand shaft has a left hand thread that has the effect
of moving the boss 97 to displace the first rod 90 in one
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direction and the right hand shaft 93 has a right hand
thread to move the boss 98 to displace the rod 91 in the
opposite direction.
As shown in Figures 8a and 8b, fine tuning of the
position of the pins 21, 22 can be done by adjusting the
threaded end 26 of the pins in their sleeve by use of an
Allen key.
Figures 12 to 16 illustrate a second embodiment
of a head 110 for use with snow making equipment. It is
understood that the head would be supported by a mast
assembly of the kind described earlier.
The head 110 comprises four spray head assemblies
111-114 mounted across a main beam 115 that is in the form
of a substantially rectangular aluminium extrusion. The
main besm 115 provides a. firm base for each spra;~ head
~.sse~bly 111-114 and also su~a~aorts a centrall~~ ~aositione~.
wind mechanism 120 that facilitates the adjustment of the
flat water jet nozzles 10. A pair of elongate drive rails
116~ 11'7 that are also extruded in aluminium are
positioned in a parallcl array direction behind the main
beam 115 to be driven by the wind mechanism 120 to in turn
move the adjustment pins 21, 22 of the nozzles 10.
As shown in Figure 12 the wind mechanism 120 is
positioned centrally of the beam 115 and the four nozzle
assemblies 111-114 are positioned equally spaced along the
beam 115. The winder mechanism 120 which is shown in
greater detail in Figure 15 comprises a winding shaft (not
shown) that comes up from beneath the head. The shaft
enters a wind block 121 and through bevelled gears (not
shown) drives two co-axially extending shafts 123, 124
that project from either side of the wind block parallel
to the rails. The gears provide a 7:1 ratio to introduce
fine control and a mechanical advantage. Each shaft is in
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turn threadedly engaged with a drive block 125, 126 that
is secured to a rectangular bracket 130, 131 that is a
sliding fit on the main beam 115. Each block 125, 126 is
reverse threaded so that rotation of the shafts 123, 124
in the same direction imparts linear movement of the
blocks 125, 126 and a sliding movement of the brackets
130, 131 in opposed directions. Each bracket 130, 131 is
in turn bolted to different drive rails so that, as shown
in Figure 5, the left hand bracket 130 drives the outer
rail 117 and the right hand bracket 131 drives the inner
rail 116. In this way rotation of the shaft that comes
into the base of the mast has the effect of displacing the
drive rails 116, 117 in opposite directions.
Each nozzle 111 to 114 assembly is the same and
one 111 is shown in greater detail in Figure 16. The
nozzle assembly 111 includes a fi,~ed central bracket 140
that is bolted to the main beam 115. The central bracket
140 has a :ear face 141 that is in turn gelded to a flange
142 and a pair of upstanding columns 143, 144 that engage
a nozzle arm support 150. The central bracket 140 also
supports a water jet body 145 that is in the form of a
rectangular block. The water jet bod;~r 145 includes a
water inlet passage 146 coming from a water inlet pipe 147
and a head passage 148 in the manner of the earlier
embodiments. The head passage 148 supports two adjustment
pins 21, 22 that are aacially displaceable across an outlet
aperture 20 in a similar manner to the earlier
embodiments. The end of each pin 21, 22 is bolted to a
flange 152, 153 that is in turn supported by a pin drive
154, 155 that surrounds the main beam 115 to be slidable
thereon. The pin drives 154, 155 are also secured to
flanges 156, 157 that are respectively bolted to the drive
rails 116, 117 so that movement of that drive rails
imparts movement to the pin drives.
The air nozzle 75 is coupled through a nozzle arm
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160 into the nozzle arm support 150 to be coupled to an
air supply pipe 161. The nozzle arm support 150 is
adjustable vertically through a nut 163 that engages the
column 143, horizontally through a screw threaded coupling
164 along the length of the arm and rotationally through
two different planes due to a pivotal linkage 165 of the
air nozzle to the arm. This universal adjustability
allows fine tuning between the relationship of the air
nozzle 75 and the flat jet water nozzle 10. The
relationship is the same as described earlier in the
specification.
As described with reference to Figure 15,
operation of the wind mechanism 20 causes opposed movement
of the drive rails 116, 117 to in turn cause opposed
movements of the pin drives 154~ 155 to effect
displacement of the pins ~1~ 2~ to vary the cross section
of the outlet aperture ~0 of the flat jet nozzle 10.
Figures 14a and 14b illustrate the drive to disple.ce the
pins towards one another in Figure 14A and away from one
another in 14b.
The assembly has the advantage that the ~.se of
square tubing provides positive guidance to the
componentry as well as a sturdy support on which. the
nozzle assemblies can be mounted. The nozzle assemblies
are also secured to the main support with a degree of
axial adjustability so that in setup, the position of the
nozzles along the length of the main support can be
altered. Since the pin movement is about a maximum of 4mm
the mechanism must have a level of accuracy to provide the
precise incremental changes. This is achieved by the use
of the square tubing and bracket arrangement of a Zm head.
In order to explain the operation of the
snowmaking equipment described above and, in particular,
the sophistications and important characteristics that
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result in an improved snowmaking technique. it is first
necessary to consider, in general terms, the science of
snowmaking.
SNOWMAKING
Snowmaking is a heat exchange process. Heat is
removed from snowmaking water by evaporative and
convective cooling and released into the surrounding
environment. This heat creates a micro-climate inside the
snowmaking plume that is very different from ambient
conditions. There are many variables that affect
snowmaking. Three of the most important variables are wet
bulb temperature, nucleation temperature and droplet size.
Wet bulb temperature. the temperature of a water droplet
exiting a snow gun is typically between +1°C and +6.5°C.
Once a water droplet passes a, nozzle and is released into
the air, its tempere.ture falls rapidly due to expansive
~,nd, convecti~e cooling and. eva~aore,tive effects. The
droplet's temperature will continue to fall until
equilibrium is reached.
This is the wet bulb temperature a,nd it is as
important as dry bulb (ambient) temperature in predicting
snowmaking success. For example, snowmaking temperatures
at -2°C and 10% humidity are equivalent to those at -7°C
and 90a humidity.
Once the wet bulb temperature is known, there
must be a way to predict whether water droplets will
actually freeze at that temperature. Ice is the result of
a liquid (water) becoming a solid (ice) by an event called
nucleation. In order to freeze, a water droplet must
first reach its nucleation temperature. There are two
types of nucleation, homogeneous nucleation and
heterogeneous nucleation.
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Homogeneous nucleation occurs in pure water in
which there is no contact with any other foreign substance
or surface. With homogeneous nucleation, the conversion of
the liquid state to solid state is done by either lowering
temperatures or by changes in pressure. However,
temperature is the primary influence on the conversion of
water to ice or ice to water. In homogeneous nucleation,
the nucleation begins when a very small volume of water
molecules reaches the solid state. This small volume of
molecules is called the embryo and becomes the basis for
further growth until all of the water is converted. The
growth process is controlled by the rate of removal of the
latent heat being released. Molecules are attaching and
detaching from the embryo at roughly equal and very rapid
rates. As more molecules attach to the embryo, energy is
released causing the temperature of the attached molecules
to be lower than the temperature of the uns.ttached
molecules. The growth. rate continues until all the
molecules are attached. At this poiaat, the solid state
(ice) is established. Many people think that pure water
freezes at 0°C or 32°F. In fact, the nucleation event
(freezing) for pure water will take place as low as minus
~:0°C or minus ~;0°1~. This is most likely to occur in
laboratory e:~periments or high in the upper atmosphere
(upper troposphere).
Heterogeneous nucleation occurs when ice forms at
temperatures above minus 40°C or minus 40°F due to the
presence of a foreign material in the water. This foreign
material acts as the embryo and grows more rapidly than
embryos of pure water. The location at which an ice embryo
is formed is called the ice-nucleating site. As with
homogeneous nucleation, heterogeneous nucleation is
governed by two major factors: the free energy change
involved in forming the embryo and the dynamics of
fluctuating embryo growth. In heterogeneous nucleation,
the configuration of molecules and energy of interaction
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at the nucleating site become the dominating influence in
the conversion of water to ice. Snowmaking involves the
process of heterogeneous nucleation. There are many
materials and substances which act as nucleators; each one
promotes freezing at a specific temperature or nucleation
temperature. These nucleators are generally categorised as
a high-temperature (i.e. silver iodide, dry ice, ice and
nucleating proteins) or low-temperature (i.e. calcium,
magnesium, dust and silt) nucleators. It is low-
temperature nucleators that are found in large numbers in
untreated snowmaking water. The nucleation temperature of
snowmaking water is between -10°C and -7°C.
Research has demonstrated that 950 of natural,
untreated water droplets will freeze at widely different
temperatures, the average temperature being 18.2°F.
Introducing a consistent high temperature nucleator into
the water will raise the freezing point. ~,s a ws.ter
droplet cools, heist enr~rgg~ is released into the s.tmosphere
at a rate of one calorie per gram of water. As it freezes
into an ice crystal, the water droplet will release
additional energy at a rate of 80 calories per gram of
water. This quick relee,se of energy raises the water
droplet temperature to 32° ~'~ where it will remain while
freezing continues. This is one reason why we are
accustomed to thinking that water freezes at 32°F or O°C.
The water will continue to freeze as long as it remains at
or below 32°F or 0°C, but only after it has first cooled to
its nucleation temperature. Any excess energy will be
dissipated into the atmosphere. Since the distribution of
various nucleators in a given volume of water is totally
random, the size of the water droplet or the number of
high-temperature nucleators has a significant effect on
the temperature at which freezing occurs (nucleation
temperature). In natural water, as the size of the water
droplet decreases, the likelihood that the droplet will
contain a high-temperature nucleator also decreases.
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Conversely, larger water droplets stand a better chance of
containing high-temperature nucleators. The optimum
situation for snowmakers is one in which every droplet of
water passing through the snow gun nozzle contains at
least one high-temperature nucleators and freezes in the
plume.
The relationship between the variables of
nucleation temperature and droplet size is summarised in
two statistically valid conclusions. First, a 50% increase
in the droplet size results in a one-degree, F increase in
nucleation temperature. Second, a 50% decrease in droplet
size results in a three-degree, F decrease in nucleation
temperature. These conclusions are based on an average
droplet size of 300 microns, and indicate that decreasing
the droplet size can be counter-productive to promoting
high-temperature nucleation, unless enough high-
temper~.ture nucleators are present. Looking at the
relationship bet~,~een droplet size ~,n~, evaporation,
research in cloud seeding shows that:~P~ 50% decrease in
droplet size produces, a four-fold increase in the
evaporation rate. *~. droplet that is 50~ smaller will
evaporate to nothing after f~.lling just one-eighth the
distance that the average 300 micron droplet falls. These
conclusions further point out the undesirable results from
using very small droplets, especially in areas where water
loss is a critical issue. Relating droplets size to
nucleation temperature, it is possible to increase
snowmaking production and efficiency by using high-
temperature nucleators with larger water droplets. This
method frequently allows for increased water flow, reduces
evaporation, and yields more snow on the ground. In fact,
studies indicate that a 20% increase in water flow can
increase snow volume up to 40o if droplet size and
nucleation temperature are optimised.
Summary
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The snowmaking process involves spraying water
droplets into the cold ambient air, heat from the water
droplets is transferred into the ambient air and the water
droplets begin to freeze. If there is sufficient
temperature differential between the water droplets and
sufficient hang time the water droplet will freeze before
hitting the ground. The volume of water that can be
converted into snow depends on many factors.
Initial Water Temperature - a higher temperature
of the water means that more heat needs to be removed
before freezing can occur.
High-Temperature Nucleators - Once a water
droplet achieves a temperature of 0°C it needs a high
temperature nucleator to be present before the water
droplet will give off its la.tega.t heat and convert to snow.
Droplet Size - The size of the water droplet
determines its ability to convert to snow. There are many
methods to con~°ert a water strew. int~ water droplets ~f
var~°ir.g sizesa use of water nozzles a~ad c~mpressed air acre
two of the predominant methods. Small water droplets
offer more surface area to the ambient air but are prone
to evaporation in low humidity and are less likely to have
high temperature nucleators present. Being smaller they
have less mass and are vulnerable to high winds which can
carry them away - smaller particles also have a lower
velocity and a greater hang time. Small water droplets are
desirable at marginal snowmaking temperatures due to the
larger surface area and a greater hang time which aids
when there is a low temperature differential with the
ambient air. The larger surface area also assists the
evaporative cooling effect.
Larger water droplets have less surface area,
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greater mass, higher velocity and have a higher chance of
having high temperature nucleators present. When the
ambient air is colder the temperature differential is
greater with the particle temperature therefore a greater
heat exchange occurs. The latent heat that is given off by
the water particles is easily dissipated into the
surrounding ambient air. The higher the velocity the
greater the heat exchange.
A snowmaking gun should therefore produce a small
droplet size in marginal conditions and a larger particle
in colder conditions.
Hang Time - The longer the water droplet is in
contact with the ambient air the more chance the particle
has to freeze. A snowmaking gun has a greater production
the higher it is in the air. Droplets projected at a
high.~:r velocity ~e~ill also achieve a greater hang. gt is
imperative to get a snowmaking guxx ~.s high as possible and
project the particles as fast as possible.
Water '~~'olume - Given the above factors there is
onl~,~ a certain volume of water that c~.n be converted. in
snow depending ~n the efficiencies of the above factors.
Control of the water volume needs to be incorporated into
any snowgun design to compensate for the change in ambient
temperatures.
High Temperature Nucleation - Most snowmaking
guns have a system that produces high temperature
nucleators mostly in the form of ice crystals. This is
usually achieved by combining water and compressed air.
Compressed Air - Air is a gas - or more
accurately, a mix of gases. Unlike liquids, gases are
compressible; a given volume of air can be contained in a
much smaller space. In order to fill that smaller space,
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however, the gas will exist at a higher pressure. A basic
law of physics indicates that the pressure of a gas and
its volume are related to its temperature; when pressure
goes up, so does the temperature. But the temperature
doesn't necessarily stay high - it can be decreased.
When a compressed gas is released and goes back
to its original pressure, a great deal of mechanical
energy is released. At the same time, a great deal of heat
is absorbed. It is these last two characteristics that
make compressed air such important factor in snowmaking.
The mechanical energy released by the air disrupts the
stream of water in tiny droplets, and then propels them
into the atmosphere. As compressed air escapes the gun, it
absorbs heat - in other words, cools.
Current Art of Snowmaking
Currentlgr there are four different methods of snowmakings
1. Fan Guns
2. Tnterns.l mia~ Air water guns
3. E~~ternal mi~~ - Air water guns
4. Water only guns
Fan Guns consist of a large barrel with an
enclosed electric fan that forces large volumes of ambient
air through the barrel. On the end of the barrel there is
a configuration of water nozzles usually arranged in banks
that can be turned on independently of each other. Each
bank can consist of up to 90 small capacity hollow cone
nozzles which produce very fine particles. The water
particles are projected into the ambient air by the large
volume of air that the fan produces. Fan Guns usually have
an outer ring that is called the nucleating ring. This
ring has a small number of miniature air/water nozzles
that operate in the same way as an internal mix air/water
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gun. An onboard compressor is used to operate this ring.
The nucleating ring's primary role is to produce ice
crystals. The ice crystals are carried along the outside
of the bulk water plume for a distance before becoming
ingested into the plume thus nucleating the bulk water
plume. Operation of the fan gun is achieved by opening one
bank of nozzles at a time and altering the water pressure
to the nozzles. Once full pressure is achieved on a bank
another bank is opened and the water pressure is adjusted.
Internal Mix Air/Water Guns - consist of a
compressed air line and a water line converging into a
common chamber with an exit orifice. Compressed air enters
the common chamber and expands breaking up the water
stream into smaller particles and projecting them into the
ambient air. Operation of the gun is achieved by
regulating the water pressure entering the common chamber.
A common feature ~f the internal mi~~ gun is that ~~Then
water floe is increased. air flow is decreased and visa
versa. f~TTater pressure cannot usually exceed the air
pressure which is usually 80 - 125psi. There are a
multitude of orifice and mixing chamber shapes that
produce a wide variety of plumes and droplet sues.
External Mix Air/rsolater Guns - usually consist of
a configuration of fixed orifice flat jet nozzles arranged
on a head that spray water into the ambient air. The head
is usually put on a mast in order to give the water
droplets more hang time due to the fact there is no
compressed air to break the water droplets into smaller
particles or to propel them. As with the fan guns the
external mix guns have nucleating nozzles that use small
internal mix nozzles to produce ice crystals which are
directed into the bulk water plume. Control of the gun is
by changing the fixed orifice flat jet nozzles for a
different size or opening banks of nozzles as with the fan
gun.
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Water Only Guns - Water only snow guns have no
compressed air or nucleating nozzles. The head comprises a
number of flat jet nozzles assembled on a high mast,
usually a minimum of 6 metres in height. Snowguns of this
type can only be used at temperatures starting at -6°C and
work better with a high temperature nucleation additive.
THE PREFERRED EMBODIMENTS
The snowmaking equipment that is the subject of
this application differs from the existing technology by
the fact that it uses the maximum efficiencies of each
component involved in the process. The snowmaking
equipment S is an external mix air/water gun utilising a
bank of four variable nozzles 10 that provide a flat
output pe.ttern for the water to configure on a flat
horizontal plan. Compressed air is introduced into the
water plume P in a flat configuration a~ad. ha.s the same
dimensions as the water plume at the point of
intersection. A significant feature of this snowmaking
equipment is that control of the gun is by adjusting the
n~zzle orifice size and thus chs,nging the water flow.
This allows the maximum pressure of the water to be
utilised creating a consistent droplet size with a higher
velocity and throw than the conventional snowmaking guns.
The compressed air is introduced into the water
plume P directly at the point where the compressed air has
the most energy. The maximum energy from the compressed
air greatly increases the atomization of the water
particles, and gives the maximum cooling and projection of
the water droplets. The temperature directly at the exit
of the air orifices can be as low as -40°C which drops the
bulk water plume to around 0°C and lower, the extreme cold
air also creates ice crystals, some which are carried in
the bulk water plume while some are blown out of the plume
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and are re-ingested at a further distance. This high
concentration of ice crystals ensures that there is an
abundance of high temperature nucleators to seed the
majority of the water droplets.
If ice crystals are injected into the bulk water
plume before the plume temperature is 0°C the ice crystals
will melt, this is why other external mix guns project the
ice crystals that are produced into the plume at a further
distance away from the water nozzle so that the bulk water
has had enough time for the heat in the water to be
carried away by the ambient air before they are
introduced. In windy conditions some of these ice crystals
can be carried away reducing the nucleation of the bulk
water.
Internal mix guns utilise the compressed air in
the s~.me way with the e~~ception th~.t the energy of the
water prr~ssure is not utilised as it is regulated. to
control the water flow. The maximum water pressure for
most internal mix guns usually does not exceed the
compressed air pressure (that is 7 bar - whereas the
variable flat jet cs,n operate at pressures e,~~,ceeding 40
bar). The nature of a fixed chamber dictates that the more
water is used the less air that can be in the cham'her by
volume and the same in reverse. The compressed air is the
only means for projection and atomisation of the water;
when the amount of compressed air is limited by a greater
water flow efficiencies are decreased. Because the energy
of the water is riot utilised there has to be an increase
in the volume of compressed air that is used making the
gun more expensive and noisy to run.
The snowmaking equipment of the preferred
embodiments uses the same amount of compressed air no
matter what the water flow giving a more linear curve and
allowing greater production per gun and because it has
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lower consumption of compressed air applied directly into
the plume using smaller air orifice size resulting in
considerably quieter operation. The synergy of these two
mediums gives the most efficiency that can be obtained
creating a consistent plume of homogenous medium sized
water particles that have the highest possible velocity
and high temperature nucleators (ice crystals) possible.
Because external mix guns do not use compressed
air to atomise the water plume the droplets that are
formed are much larger with a greater range of differing
sizes within the plume. At lower pressures the droplets
can be as large as 1000 to 4000 microns where as the
preferred embodiment produces droplets in the 300 to 600
micron range.
The preferred embodiments leave a v~:rg~ high plume
velocity and surface area which. causes more ambient air to
be inducted ixa,to the ~alu~.n giving added cooling. The shape
of the wind vane °~4 on the head H resembles a tilted
airplane wing and directs the wind from behind the head to
accelerate over the nozzle outlet increasing the amount of
cold air into the plume and helping to accelerate its
velocity.
The preferred embodiments utilise a portable mast
arrangement that allows the head to be positioned 1 metre
to 6 metres above the ground. The main mast members form a
parallelogram to which the head is attached to the top,
when the mast is lowered and raised the head maintains a
constant angle giving a consistency in the trajectory of
the plume. Other snowgun masts have a fixed mast so that
when the mast is lowered the angle of the head points
progressively more into the ground decreasing the snowguns
efficiency. Most external mix guns cannot be lowered as
they rely on the height of the mast to produce sufficient
hang time for the water droplets to freeze. The apparatus
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of the preferred embodiment can produce snow efficiently 1
metre above the ground - the efficiency increases with
height.
Most 6 metre masts for snowguns are in
permanently fixed ground positions. The apparatus of the
preferred embodiment can be towed by a snowmobile and set
up at different locations. The legs of the mast has skids
attached so that it can be easily towed; the legs are also
adjustable so that the mast can be levelled on uneven
terrain, see Figure 4. The flat profile of the legs
reduces the hazard to skiers. The main mast swivels at
the base which allows the head to be turned with the wind.
The wind vane 74 on the head H catches the wind and pushes
the head downwind in the same way a weather vane works.
This increases the gun's efficiency as cross winds affect
the ~fflclenCy ~f the plume by blowing the bulk ~~~ater
together lessening the surface area and velocity. The
mast is couaaterbalanced. by ~? spring ~1 which a ~,ick~ easy
~0 raising and lowering of the mast. The wind vane 74 is
tilted upward and in the event of high winds this
automatically lowers the height by pushing the head closer
to the ground. This .ids in more s~a.o~~ beira.c~ deposited ~n
the ski run; if the mast were to remain at its maximum.
height in high winds the snow produced would be more
likely t~ be carried away.
In the event of heavy ice conditions the head
lowers itself under the weight of the ice so that it can
be easily de-iced by staff.
The apparatus of the preferred embodiments has
the same efficiency and production as a fan gun but
produces larger water particles. Fan guns are more
expensive to purchase and need more electrical
infrastructure on the mountain therefore limiting their
movement. Movement of fan guns require the use of
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expensive snow grooming machines because of their size and
weight. Expensive permanent tower designs are necessary
to raise a fan gun 6 metres into the air which introduces
additional risks to the staff as the fan guns require
staff to perform duties at height e.g. taking off covers,
de-icing of controls.
In a more sophisticated version of the equipment,
a wet bulb temperature sensor is incorporated with an
ambient temperature sensor that also sensors the
temperature of the water. A water pressure sensor is also
included. A computer constantly monitors the readings of
the sensors and selectors a nozzle aperture size that it
is optimum to produce snow most efficiently in the set
conditions. The use of electrically powered servo motors
thus allows continual adjustment of the nozzle apertures
in dependcrace on changes ice. the ambient conditions.
Changes in direction and strength of the wind is
acco~odatec. by the vane ova. the head of the mast that
causes the mast point down wind and the head to assume the
appropriate height as directed by the wind. The parallel
linkage ensures tb.at the nozzles are inclined at the right
angle to the horizontal reg~:rdless of the effective height
of the mast.
