Fluid sprinkling – spraying – and diffusing – Processes – Of weather control or modification
Reexamination Certificate
2000-05-03
2002-10-15
Ganey, Steven J. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Of weather control or modification
C062S069000, C062S074000
Reexamination Certificate
active
06464148
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to snowmaking and, more particularly, to a process whereby the use of certain organosilicone surfactant additives enhance the quality and making of the snow in vast quantities while reducing energy consumption.
BACKGROUND OF THE INVENTION
Many ski resorts have extensive snowmaking capability such that the resort has more control over the ski conditions throughout the ski season. The demand for snow has increased steadily with the large increase in the number of people involved in skiing, tubing, sledding, snowboarding, and the like sport activities. This need is especially acute at times when an insufficient supply of natural snow, particularly fresh powdered snow, is not available at winter resorts because of climatic or local weather conditions non-conducive to snowfall precipitation. It has been common practice to mechanically produce snow at such winter resorts for the aforementioned winter sports and the like by means of the atomization of water into fine droplets when ambient weather conditions are suitable for cooling the droplets to a temperature below the freezing point of water before the droplets reach the ground. In this manner, substantially all of the droplets become at least partially crystallized as snow while still airborne.
Typically in these processes, pressurized water and compressed air are exhausted through a nozzle at high speed to form vapor droplets which freeze when exposed to the ambient atmosphere.
Snowmaking methods and apparatus generally have been classified into two distinct groups, the so-called “air” and “airless” types. The former utilizes large quantities of compressed or pressurized air, usually at relatively high air pressures, which upon expansion shreds the atomized water particles from the spray nozzle into finer water particles or mist; implants seed crystals in the atomized water spray or fog; and cools the entire discharge zone to an extremely cold condition highly desirable for snowmaking. This temperature at discharge has been known to be as low as about −75° C. The airless type does not use compressed air, but instead, uses fans, a.k.a. fan guns, which blow the water as it leaves a nozzle to provide mixing and a fine dispersion which freezes to produce snow.
Because of differences in the control of water droplet breakup, propulsion, and ice nuclei generation, the air and airless snowmaking devices have different operating characteristics at various atmospheric temperatures. The airless-type devices typically excel at lower temperatures, i.e., less than about −4.5° C. The air-type snowmaking devices have operational advantages at temperatures near the freezing point of water, but are at a disadvantage at lower temperatures because their generally fixed mixing throat size, limits the amount of air which may be mixed with the water. In addition, these air devices are at a disadvantage in field use because of the relatively high air pressure—up to 100 psig or more—which is necessary to break up the water droplets to a sufficient degree.
Snowmaking apparatus, especially the snow guns, have improved dramatically over the last forty years and resorts are able to produce a large snow base as long as climatic conditions are generally cold. Most snow guns require a temperature below at least 0° C., preferably below −5° C., and most preferably below −7° C. Colder temperatures make the snowmaking process easier. Furthermore, to support many commercial winter resort operations, it is essential that these ambient conditions last for a period of time sufficient to permit snowmaking to continue until an adequate depth of snow is deposited on the area, terrain or slope desired to be covered. In areas of North Carolina and Tennessee, for example, during a typical winter sports season, there may be only 25 days with good conditions for making artificial snow. Farther north in Ohio, 30 to 40 days of snowmaking operations can ordinarily be expected and in Michigan, 50 days or more are not uncommon. Therefore, it is important for effective commercial operations that large volumes of quality snow be produced rapidly during those periods when conditions are right for mechanical, i.e., artificial snowmaking.
During the snowmaking process, heat transfer occurs primarily by two different mechanisms: convective heat transfer and evaporation of water. The role of the injected air in the snow gun, whether via compressed air or fanned air, is not to absorb the heat of fusion directly—calculations suggest that this air is directly responsible for from about 2 to 15% of the transferred heat energy—but rather to promote heat transfer from the water droplets to the cold ambient air. It does this by causing turbulence and by producing water droplets of desirable diameter. Serendipitously, compressed air supplies ice seeds upon expansion which aid in initiating the freezing process.
As an aside, a substantial amount of air is needed to freeze 10 gallons of water per minute which is the ordinary minimum production rate of commercial snow guns. If the air is bone-dry, it has been determined that the minimum amount of air required varies from 15,000 scfm at about −13.4° C. to 33,000 scfm at about −2° C. Nevertheless, such large quantities of air may be supplied by winds of even moderate velocity, i.e., about 1 to 10 feet per second. With respect to the compressed air per se being put through the orifices of the snow guns together with the water compositions, the compressed air flows at a rate amounting to a minor proportion by weight of said air with reference to the water composition.
With respect to droplet size, of course, smaller droplet size diameters yield larger area per unit mass and thus larger heat transfer. Since the residence time in the ambient air of a water droplet of a given diameter is dependent on the wind velocity, there is a practical lower limit for the droplet diameter. Thus, the droplet diameter has to be small enough to result in a sufficiently long residence time in the air and a sufficiently high heat transfer rate to complete the freezing process. However, in addition, it has to be large enough so that the water droplets will not be carried far away by the wind as mist which would cause difficulty in depositing the artificial snow on the desired areas.
Generally, commercial snow guns induce a vertical component to the droplets on the order of about 20 feet per second and thus the ambient air residence time has been estimated to be at least about 20 seconds. Therefore, the optimum size of a water droplet for snowmaking is accordingly determined by the rate of heat transfer, which must be sufficient to freeze the droplet in less than 20 seconds. Under typical atmospheric, snowmaking conditions, it has been determined that droplets ranging in diameter of from about 200 to 700 microns will freeze in less than 15 seconds and so this is generally accepted as the most desirable initial droplet size range for artificial snowmaking.
Even when the water droplet size, temperatures, droplet velocity and ambient air condition requirements are satisfied, snow may not be made satisfactorily. This is because water droplets of small size may supercool.
When a water droplet supercools, its temperature drops below 0° C. before solidification takes place; thus, the vapor pressure lowers and the overall heat transfer rate decreases. In fact, by reason of the inherent characteristics of water, in the absence of nuclei, it can supercool and remain in the liquid state even when reduced to a temperature as low as about −29° C. Furthermore, a supercooled droplet may only partially freeze before it falls to the ground. Its supercooled water is then frozen by conductive heat transfer with the cold ground, forming shells of ice instead of snow. Nuclei present in the water, such as inorganic and organic dust particles, including clay minerals, enable the water to freeze at higher temperatures, e.g., at −10° C. It is desirable to introduce nuclei which will cause the water or liqu
Costa Dominic Charles
Kostka Stanley J.
Aquatrols Holding Co., Inc.
Ganey Steven J.
Shedden John A.
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