METHOD AND DEVICE FOR PREPARING SNOW

Abstract: The invention relates to a method for preparing snow, in particular in a hall intended for winter sports, comprising the steps of: bringing the hall to a temperature below freezing point; supplying a liquid for freezing to the hall and atomizing the liquid in the hall using a gas, wherein for atomizing purposes gas is supplied under a pressure of a maximum of 12 barg and a volume ratio between the gas and the liquid lies between 125 and 2000 Nm<3>/m<3>. The average size of the atomized liquid particles can herein amount to a maximum of 75 mu m (SMD). The hall can be divided into compartments for preparing the snow, wherein snow can then be prepared in one compartment at a time. The invention further relates to an apparatus for performing this method. In order to atomize the liquid for freezing this apparatus can be provided with one or more optionally movable spray nozzles.

Description: METHOD AND DEVICE FOR PREPARING SNOW The present invention relates to a method for preparing snow, in particular in a hall intended for winter sports, comprising the steps of: bringing the hall to a temperature below freezing point ; supplying a liquid for freezing to the hall and atomizing the liquid in the hall using a gas. Such a method is known from the American patent 5,102,044. In this patent a method is described for preparing snow wherein a mixture of water and compressed air is supplied to a number of spray nozzles in which the water and the compressed air are apparently mixed and the water atomized, so that it is sprayed into the hall in the form of droplets, wherein the droplets freeze as a result of the low temperature in the hall and fall in the form of snow crystals. It is stated that this method should produce satisfactory results at air/water ratios lying between 300 and 3000 Nm 3 /m 3 (1 Nm 3 = 1 m 3 of gas at normal ambient pressure and temperature) , but specific examples are not given. Although compared to other known methods of snow preparation, wherein for instance the atomized liquid is frozen by bringing it into contact with a cryogenic medium such as nitrogen, this method has the advantage that the costs are relatively low while in addition the dangers of working with such a cryogenic fluid in a closed space are avoided, this known method is still found not to be wholly satisfactory in practice. Atomizing of the liquid at a gas/liquid ratio in the vicinity of the lower limit stated in this patent at the described temperature in the hall is thus found to result in very coarse, slushy snow, while the energy costs for bringing the hall to the desired low temperature and generating the gas pressure required in practice are relatively high. The invention therefore has for its object to provide an improved method of the above described type. According to the invention this is achieved in that for atomizing purposes gas is supplied under a pressure of a maximum of 12 barg (measured (over) pressure, 1 barg = 2 bar absolute) and a volume ratio between the gas and the liquid of between 125 and 2000 Nm 3 /m 3 . Surprisingly, it has been found that even when use is made of a gas, generally air, at such a relatively low pressure, the liquid is still atomized in effective manner and that even at relatively low gas/liquid ratios well usable, i.e. relatively loose, snow with relatively small crystals is obtained in practice. The snow preparation at such a low pressure requires moreover relatively little power, while a sufficient capacity is nevertheless obtained. The volume ratio of the gas and the liquid preferably lies between 150 and 1200 Nm 3 /m 3 and more preferably between 165 and 500 Nm 3 /m 3 . Within this range very well usable snow can be prepared with a relatively small quantity of gas under pressure. Herein the gas is preferably supplied at a pressure of a maximum of 8 barg and more preferably a maximum of 6 barg, whereby with little power sufficient small droplets are still formed and a considerable snow-preparing capacity is also obtained. The average size of the atomized liquid particles preferably amounts to a maximum of 75 μm (SMD) , more preferably a maximum of 55 μm (SMD) and most preferably a maximum of 35 μm (SMD) , wherein SMD stands for the Sauter Mean Diameter, defined as the diameter of a droplet which has the same ratio between surface area and volume as exists between the surface area of all droplets together and the volume of all droplets . Such relatively small liquid particles result in relatively small snow crystals which ensure a good snow quality. The temperature in the hall is preferably reduced to less than -i°C and more preferably to -3°C. In order to obtain a very high snow preparing capacity it is recommended to reduce the temperature in the hall to less than -5°C. This temperature reduction can herein take place by introducing cold air into the hall, wherein the liquid mist is then preferably carried into the hall substantially transversely of the direction of flow of the cold air. An intensive contact between the liquid mist and the cold air is hereby achieved, resulting in a rapid freezing of the liquid mist. The liquid mist is preferably distributed uniformly in the hall, as calculated in surface area as well as in time. A snow layer with an even thickness is hereby formed in the hall, which is therefore relatively flat, while by applying the snow layer spread over time the maximum cooling capacity required for preparing the snow remains relatively low. The hall can herein be divided into compartments for preparation of the snow and snow can be prepared in one compartment at a time. In this manner the atmospheric conditions (in particular the temperature) can be optimally adjusted in that part of the hall where snow production is taking place. With a view to reducing the total cold capacity required for the hall during snow preparation, preparation preferably takes place in a period of decreased outside temperatures, such as at night. This has the added advantage that such a winter sports hall will generally be closed at night, whereby no heat is introduced into the hall by visitors. In addition, a large number of energy consumers such as lighting, lift systems and the like will then be switched off, whereby extra power is available for preparing snow. The invention also relates to an apparatus for preparing snow, in particular in a hall intended for winter sports, provided with cold-generating means for bringing the temperature in the hall below freezing point, means for supplying to the hall a liquid for freezing and means connected to the liquid supply means for atomizing the liquid in the hall using a gas. Such an apparatus is likewise known from the American patent 5,102,044. The invention now has for its object to adapt this apparatus such that the above described method can be performed therewith. This is achieved according to the invention in that the atomizing means are connected to a source of gas under a pressure of a maximum of 12 barg and are adapted to atomize the liquid at a gas/liquid ratio lying between 125 and 2000 Nm 3 /m 3 . The atomizing means preferably comprise at least one spray nozzle connected to the liquid supply means and the source of gas under pressure. The liquid and the gas can be mixed in this spray nozzle and they can be atomized simultaneously as a result of the high pressure thereof. In preference the spray nozzle further has mechanical atomizing means, for instance in the form of a target surface, whereby the jet of liquid flowing into the spray nozzle is already broken up into small droplets before being further atomized by the gas flow. When the spray nozzle is movable the liquid atomized thereby can be spread in even distribution across the hall. The cold-generating means are preferably adapted to blow a flow of cold air into the hall, wherein the spray nozzle is preferably directed transversely of the flow direction of the cold air in order to obtain optimum contact between the atomized liquid and the cold air flow. A plurality of alternately operable spray nozzles are preferably arranged spread over the hall, whereby snow can be prepared in the whole hall evenly and using relatively little power. In order to prevent as far as possible any heating-up of the hall at the location where snow is being prepared, displaceable partition elements can be arranged in the hall between the spray nozzles, whereby more cold can be supplied locally. The invention is now elucidated on the basis of an example, wherein reference is made to the annexed drawing, in which: figure 1 shows a schematic perspective view of a hall for winter sports with a snow preparing apparatus according to the invention, figure 2 shows a cross-section through a spray nozzle for use in the snow preparing apparatus according to the invention, figure 3 is a diagram showing the operational range of the snow preparing apparatus, and figure 4 shows a diagram of the power demand during normal use of the hall and during the snow preparation. A hall 1 for practising winter sports, such as skiing, snow boarding and the like, is provided with a slope 2, which in usual manner takes a slightly stepshaped form. In order to maintain a low temperature in hall 1 two cold machines 3 are present placed on either side of hall 1, each of which draws in air as according to arrow I and, after it has been cooled to below freezing point, distributes the air into hall 1 via a conduit 4 which is suspended from the roof 5 of hall 1 and has a number of blow-out openings 6 arranged spread in longitudinal direction. The cold air herein flows initially into hall 1 as according to arrows C and is eventually extracted by fans 11 at one of the short sides 7 of hall 1, whereby a cold air flow is established in longitudinal direction of hall 1. The extracted cold air is recirculated by the ventilators to the associated cold machine 3 and there cooled again to the desired temperature. It will otherwise be apparent that the apparatus according to the invention can also be applied in combination with other arrangements of the blow-out and extraction openings. The blow-out openings could for instance be arranged on the short sides of the hall and extraction could take place centrally in the hall . In this manner an air flow in longitudinal direction of the hall could for instance also be generated. For preparation of snow in hall 1 spray nozzles 9 are arranged on the long sides 8 thereof. In the shown embodiment these spray nozzles 9 are movable in both vertical and horizontal direction as according to arrows V and H, in order to obtain an even spraying pattern. Spray nozzles 9 are each connected to a liquid supply conduit and a source of gas under pressure, generally compressed air (not shown here) . In spray nozzles 9 the supplied liquid, usually water, is atomized under the influence of the compressed air and the internal form of spray nozzle 9, whereafter the atomized liquid is sprayed into hall 1 in the form of a cone 10. There the liquid particles freeze as a result of the low temperature and descend in the form of snow crystals. In order to enable preparation of snow only in determined parts of hall 1, displaceable partitions, for instance in the form of insulating curtains 31, are arranged at different locations in hall 1. Hall 1 can hereby be divided into compartments 12 and snow can be prepared in one compartment at a time. This is important because in the preparation of snow the freezing heat is released from the mist droplets. The temperature in the relevant compartment 12 hereby increases. By now closing all blow-out openings 6 for cold air located outside the relevant compartment 12, all available cold air can be concentrated in the compartment where the snow is being prepared, whereby warming of that compartment can be prevented. Particularly when outside temperatures are relatively high, as will be the case in summer, this is especially effective. Spray nozzle 9 can be formed by a housing 13 which has a connection 14 for a liquid supply conduit L in addition to a connection 15 for an air supply conduit A. Both connections 14, 15 are connected to a mixing chamber 16 via respectively a passage 17 and an annular chamber 18 with radial openings 19. In this mixing chamber 16 the liquid L is atomized and subsequently sprayed out in the form of a mist of very fine droplets of uniformly distributed size through a number of apertures 22 in the wall of spray nozzle 9. Because the apparatus according to the invention as described above is of extremely simple construction, it is very suitable for later incorporation into existing winter sports halls, for instance as replacement for a snow preparing apparatus on the basis of nitrogen. Large savings can hereby be achieved in respect of the raw materials used, since nitrogen as cold producer for the preparation of snow cannot be used very efficiently and is therefore relatively expensive. This is the result of the fact the in the preparation of snow an evaporation temperature in the order of -10 °C is used, while the used nitrogen will have a temperature in liquid form of about -200 °C. In addition, the working conditions in the hall during snow production are considerably improved by replacing nitrogen with compressed air. As stated, the preparation of the snow preferably takes place when the outside temperatures are relatively low, therefore usually at night. As can be seen in figure 4, the power then required to maintain the temperature in hall 1 at the desired value (area 28) is considerably lower than during the day (area 25) . The power surplus 21 of cold machine 3, which is anyway dimensioned for the power requirement during the day, can then be used for the snow preparation. No additional cooling capacity need hereby be installed for preparing the snow. The snow preparation at night has the added advantage that at that time other energy consumers, such as the lighting and the ski lifts (area 26) , as well as the electricity supply for secondary work areas, such as catering facilities (area 27) , will also be switched off, so that the total quantity of power drawn by the total installation from the mains electricity will also be lower at that moment. This power surplus 20 can then also be used for snow preparation without this resulting in extra peak loads on the mains and the associated cost to the user. The examples below indicate some working points of the snow preparing apparatus according to the invention which show how relatively large quantities of high- quality snow can be made at relatively low pressures and small quantities of air. EXAMPLE 1 Air at a temperature of 24 °C and a pressure of 7.5 barg is taken as starting point. This compressed air is supplied to spray nozzle 9 and used to atomize water supplied at a temperature of 12 °C. The air/water ratio is set at 600 Nm 3 /m 3 . The temperature in hall 1 amounts to -4.5 °C. In these conditions a mist is created with an average droplet size of 30 μm (SMD) . When this mist is frozen, snow crystals are formed which can be designated as "powder snow", which is very suitable as top layer. EXAMPLE 2 The starting point here is air at the same temperature of 24 °C but with a pressure of 7.0 barg. This compressed air is again supplied to spray nozzle 9 and used to atomize water supplied at a temperature of 14 °C. The air/water ratio is now set at 250 Nm 3 /m 3 . The temperature in hall 1 amounts to -2.0 °C. Under these conditions a mist is created with an average droplet size of 50 μm (SMD) which, when frozen, forms snow crystals which can be designated as "compact snow". This snow type is also very suitable to function as upper layer. EXAMPLE 3 In this example air at a temperature of 26 °C and a pressure of 6.4 barg is supplied to spray nozzle 9 and used to atomize water which is once again supplied at a temperature of 14 °C. The air/water ratio is herein set at 140 Nm 3 /m 3 . The temperature in hall 1 is reduced to -3.0 °C. A mist is now formed with an average droplet size of 65 μm (SMD) which, when frozen, forms snow crystals which can be designated as "slushy snow". This snow is suitable to serve as bottom layer and is therefore made specifically at the beginning of a snow preparation cycle so as to arrange as thick a snow layer as possible on the base floor in a relatively short time. The above described measurement points are shown in the diagram of figure 3 , which clearly shows that the "looseness" of the snow, which is of course closely related to the average size of the atomized droplets, increases as the gas/liquid ratio increases and the temperature decreases. The hatched areas 23 and 24 herein represent those combinations of parameters wherein respectively powder snow and compact snow are obtained, while the values of the parameters in the area on the left-hand side and above line 29 correspond with the preparation of slushy snow. Although the invention is elucidated above with reference to a number of embodiments, it will be apparent to the skilled person that it is not limited thereto. The scope of the invention is therefore determined solely by the following claims .

Claims: CLAIMS 1. Method for preparing snow, in particular in a hall intended for winter sports, comprising the steps of: bringing the hall to a temperature below freezing point ; supplying a liquid for freezing to the hall and atomizing the liquid in the hall using a gas, characterized in that for atomizing purposes gas is supplied under a pressure of a maximum of 12 barg and a volume ratio between the gas and the liquid lies between 125 and 2000 Nm 3 /m 3 . 2. Method as claimed in claim 1, characterized in that the volume ratio of the gas and the liquid amounts to between 150 and 1200 Nm 3 /m 3 and preferably to between 165 and 500 Nm 3 /m 3 . 3. Method as claimed in claim 1 or 2, characterized in that the gas is supplied at a pressure of a maximum of 8 barg and preferably a maximum of 6 barg. 4. Method as claimed in any of the foregoing claims, characterized in that the average size of the atomized liquid particles amounts to a maximum of 75 μm (SMD) . 5. Method as claimed in claim 4, characterized in that the average size of the atomized liquid particles amounts to a maximum of 55 μm (SMD) and preferably a maximum of 35 μm (SMD) . 6. Method as claimed in any of the foregoing claims, characterized in that the temperature in the hall is reduced to less than -1°C and preferably to less than -3° C. 7. Method as claimed in claim 6, characterized in that the temperature in the hall is reduced to less than -5°C. 8. Method as claimed in any of the foregoing claims, characterized in that the temperature in the hall is reduced by introducing cold air into the hall and the liquid mist is carried into the hall substantially transversely of the direction of flow of the cold air. 9. Method as claimed in any of the foregoing claims, characterized in that the liquid mist is carried into the hall in even distribution. 10. Method as claimed in any of the foregoing claims, characterized in that the hall is divided into compartments for preparing the snow and snow is prepared in one compartment at a time. 11. Method as claimed in any of the foregoing claims, characterized in that preparation takes place at low outside temperatures, and preferably at night. 12. Method as claimed in claim 11, characterized in that energy-consuming and heat-generating equipment present in the hall is switched off during preparation of the snow . 13. Apparatus for preparing snow, in particular in a hall intended for winter sports, provided with cold- generating means for bringing the temperature in the hall below freezing point, means for supplying to the hall a liquid for freezing and means connected to the liquid supply means for atomizing the liquid in the hall using a gas, characterized in that the atomizing means are connected to a source of gas under a pressure of a maximum of 12 barg and are adapted to atomize the liquid at a gas/liquid ratio lying between 125 and 2000 Nm 3 /m 3 . 14. Snow preparing apparatus as claimed in claim 12, characterized in that the atomizing means comprise at least one spray nozzle connected to the liquid supply means and the source of gas under pressure. 15. Snow preparing apparatus as claimed in claim 14 , characterized in that the spray nozzle has mechanical atomizing means. 16. Snow preparing apparatus as claimed in claim 14 or 15, characterized in that the spray nozzle is movable. 17. Snow preparing apparatus as claimed in any of the claims 12-14, characterized in that the cold- generating means are adapted to blow a cold air flow into the hall, and the spray nozzle is directed substantially transversely of the flow direction of the cold air. 18. Snow preparing apparatus as claimed in any of the claims 14-17, characterized in that a plurality of alternately operable spray nozzles are arranged spread over the hall . 19. Snow preparing apparatus as claimed in claim 18, characterized in that displaceable partition elements are arranged in the hall between the spray nozzles.

Inventors: DE GRAAF JAN DOUWE, DE GRAAF, JAN, DOUWE
Applicants: GRAAF JAN DOUWE DE, DE GRAAF, JAN, DOUWE
Application year: 1998
Main classification: F25C3
IPC codes: F25C3