Fluid sprinkling – spraying – and diffusing – Weather control – Snowmaking
Reexamination Certificate
2000-01-22
2002-04-30
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Weather control
Snowmaking
C239S002200
Reexamination Certificate
active
06378778
ABSTRACT:
The present invention relates to a snow gun, that is to say an apparatus for making artificially produced snow.
Today, snow guns which are included in a snow production system on ski slopes are considered to be an important and necessary element in order to ensure a stable operation of the ski area.
Considerable sums are invested in ski areas, but unpredictable and unstable weather conditions, with greatly varying amounts of precipitation in the form of snow, can easily render these capital outlays unprofitable, even in normally snowy districts.
The presence of a snow production system on a slope allows the following to be obtained:
Earlier start to the season. In many places the early part of winter is marked by frost, but little or no snow fall. These are good conditions for snow production.
The advantage of a durable underlying layer of snow. Artificial snow is heavier, denser and more durable than natural snow.
The season can be extended.
Production of snow takes place with the aid of so-called “snow guns”, by mixing water and air at high pressure and then spraying the mixture out at high velocity through a nozzle. The mixture expands in a chamber, is supercooled and then hits static surrounding cold air.
New requirements with respect to operating and energy costs have recently focused on automation and conservation of energy in such systems. The major winter sports centres and neighbouring films have gradually become dependent upon a reliable winter season with snow, Earlier, snow production systems were started up once “it was cold enough”. Therefore, new requirements have emerged with respect to the effect of the guns and equipment used under marginal conditions in order to secure a season of maximum length.
Natural snow consists of frozen water which has been crystallised in hexagonal shape, forming characteristic snow crystals. The snow crystals change continuously, the snow becomes coarser the older it is. Artificial snow that is produced in snow guns consists of frozen water droplets which have had neither the time nor the opportunity to form natural snow crystals.
The snow produced in a snow gun is formed by supplying water and air under pressure, and the small water droplets which are thrown out of the snow guns are cooled by:
Expansion of compressed air. Air which is compressed becomes warmer, and conversely, it becomes colder on expansion (only in compressed air systems).
Evaporation from the surface of the water droplets. The evaporation “steals” heat from the water droplets.
Contact with surrounding cold air.
Low water and compressed air temperature gives a better starting point for the cooling process.
An important parameter during snow production is the temperature. The production rate of snow will increase with low air temperature, low air humidity, low water temperature and increased cold air volume for expansion.
Cold, dry air will therefore give the best conditions for snow production. It is physically possible to produce snow when the temperature is above freezing. In the compressed air system, which on the expansion of air generates “its own cold”, the theoretical limit for conversion to snow at different levels of air humidity varies.
Because the snow tends to melt again at high temperatures, and at the same time the snow production becomes inefficient and expensive, there is a practical limit of +2° C. at a very low level of humidity.
Today there are three main snow gun systems:
Water/compressed air system
(formerly known as a high-pressure
system), see
FIG. 1.
Tower gun
(external mixture of water and
compressed air), see FIGS. 2a and 2b.
Fan system
(formerly known as a low pressure
system), see FIGS. 3a and 3b.
The water/compressed air system (
FIG. 1
) is based on the snow guns being supplied with air
11
at a pressure of 7-8 bar, and water
10
at a pressure of 8-10 bar. Water under pressure and compressed air are mixed in the snow gun antechamber
12
. The water is atomised in the gun by passing through a nozzle
13
, whilst air on expansion is cooled to a range of between −30° C. and −40° C. The snow particles
14
are formed in this mixture of atomised water and cooled air. When the snow particles are thrown a long distance at high speed, they will remain longer in the air and this gives increased growth and snow volume. The guns weigh about 10-50 kg.
Tower guns
20
(see
FIG. 2
a
) are often mounted on separate posts
21
, masts or the like. A water pressure in the range of about 14-50 bar is used. The water is forced through inclined nozzles
23
on each side of the tower gun (see also
FIG. 2
b
). The mixture of air
24
and water
22
takes place outside the snow gun downstream in relation to the nozzle which discharges compressed air. Because the gun is mounted above the ground (8-12 meters), the snow particles have a long fall before they reach the ground and thus a longer crystallisation process. Among the disadvantages of these tower guns are that the snow is blown away if wind directions are unfavourable, and also that an optimum mixture of the water and the expanding, cooled air is not obtained.
Fan system
30
(see
FIGS. 3
a
and
3
b
) is based on water
31
being supplied at a pressure of about 15-40 bar. The compressed air having a pressure in the range of about 8-10 bar is provided by means of a separate compressor
32
. The gun is tubular and has a relatively large diameter, wherein at the upstream end of the gun there is mounted a fan
33
powered by an electric motor
34
which sucks in and blows out air at high velocity. A large number of water and compressed air nozzles
36
,
37
are found around mouth
35
of the gun for the atomisation of the mixture and the formation of snow particles with the aid of the air of the air stream which is generated by the fan. The nozzles are often located in two or more rings
38
,
39
along the internal periphery of the mouth. Fan guns usually weigh about 400-1000 kg and require mechanical equipment (preparation machines or the like) for their displacement on a ski slope. In addition to the water supply, it is also necessary to have a substantial supply of electricity for the motor
34
. A system of this kind is described in, inter alia, DE-Al-3015020.
The present invention is directed towards a snow gun wherein the compressed air expands before atomised water is added. By using an ejector as an accessory, the snow guns according to the invention will be less affected by wind and weather, and at the same time the ejector will cause an intake of additional dry air.
The snow gun according to the invention is lighter than the existing fan and tower guns, and also generates a lower level of noise. As regards noise from snow guns, this is a problem today, especially in ski areas which are close to a built-up area. The environmental requirements set by the authorities are increasingly stringent, and this means that a number of existing snow guns cannot be operated at night because they cause an excessively high level of noise.
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Crea AS
Hwu Davis
Scherbel David A.
Young & Thompson
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