Abstract:
A snow making apparatus comprises at least one water/air nozzle for ejecting a water/air mixture. The snow making apparatus comprises at least one jet pump which operates with water as a driving medium and mixes air with the water and compresses the water/air mixture in order to form the water/air mixture which is supplied to the at least one water/air nozzle. A method of operating a snow making apparatus comprises corresponding features. The snow making apparatus and method enables unused energy to be used in a particularly effective manner.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a snow making apparatus comprising at least one water/air nozzel which is adapted to eject a water/air mixture. The invention further relates to a method of operating a snow making apparatus. 
   2. Description of the Related Art 
   Snow making apparatuses (so-called “snow cannons”) of various configurations are used in winter sports areas. DE 196 27 586 A1 gives an overview of known types of construction of snow making apparatuses. These include, in particular, high-pressure cannons close to the ground, high-pressure cannons of a lance type of construction (tower construction) and low-pressure cannons with a propeller. 
   High-pressure cannons close to the ground use compressed air to produce a water/air mist which is expelled at high speed in order to achieve the desired throwing range and active cooling due to rapid air expansion. Considerable quantities of compressed air are required. A central compressor is generally provided for a plurality of cannons, the compressor having a power rating of, for example, 15 to 20 kW. 
   With high-pressure cannons of lance form, the water/air nozzles are arranged at a height of 8 to 12 m above the piste. Lower expulsion rates may be employed, owing to the prolonged falling path. Therefore, the air compressor may have only, for a high-pressure cannon, a relatively low power rating of, for example, 5 kW per lance. A cannon of this design is shown in DE 196 27 586 A1. 
   With low-pressure cannons, a propeller produces a main air stream into which freezing nuclei are sprayed by means of nucleator nozzles and small water droplets are spayed by means of water nozzles. The nucleator nozzles are constructed as water/air nozzles. They are operated with compressed air and water under pressure and atomise a water/air mixture. The compressed air relaxes as it issues from the nucleator nozzles and thus cools water droplets of the water/air mixture to well below the freezing point so that small ice crystals are formed. The droplets discharged by the water nozzles settle on these freezing nuclei and thus form the snow crystal. With cannons of this design, compressed air which typically, as with the other designs mentioned, has to have a pressure of approximately 4 to 10 bar is required only for the nucleator nozzles. A compressed air power rating of about 4 to 5.5 kW is typically required. DE 41 31 857 A1 shows one such snow cannon with a screw compressor flanged on to the main motor. 
   With all the designs described hitherto, the snow making apparatus requires compressed air which has to be provided by a local or central compressor. This causes additional, considerable energy consumption. The compressor increases the production costs, requires maintenance and causes noise. In addition, proper working is not always ensured, in particular, at low temperatures. A compressor mounted on the snow making apparatus increases the weight thereof by about 120 kg, whereas a central compressor necessitates the laying of compressed air lines. 
   DE 44 23 124 A1 discloses a snow making apparatus of a propeller type of construction, which does not require an additional source of compressed air. The freezing nuclei are formed here by an auxiliary nozzle which is arranged in the main air stream. With this apparatus, which is dependent on the propeller type of construction, a propeller drive has to be provided that is dimensioned correspondingly more powerful. 
   SUMMARY 
   Broadly speaking, the present invention avoids the drawbacks described above by providing, in one embodiment, a snow making apparatus which does not require an air compressor or only requires an air compressor with a relatively low output. Advantages of the snow making apparatus will become apparent from the following detailed description, and may include, without limitation, efficient use of energy, which is wasted and converted into heat in snow making apparatuses according to the prior art; low production costs; light weight; high reliability, and requiring only minimal maintenance. 
   The present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below. 
   In one embodiment, a snow making apparatus is provided. The snow making apparatus includes at least one water/air nozzle which is adapted to eject a water/air mixture. The snow making apparatus comprises at least one jet pump which operates with water as a driving medium, and mixes air with the water and compresses the water/air mixture in order to form the water/air mixture which is supplied to the at least one water/air nozzle. 
   In another embodiment, a method of operating a snow making apparatus is provided. The method includes producing a water/air mixture using at least one jet pump. The at least one jet pump operates with water as a driving fluid and the at least one jet pump compresses the air and mixes the air with the water. The method further includes ejecting the water/air mixture through at least one water/air nozzle. 
   In yet another embodiment, a method of operating a snow making apparatus is provided. The method includes producing a water/air mixture using at least one jet pump. The at least one jet pump operates with water as a driving fluid and the at least one jet pump mixes the air with the water and compresses the water/air mixture. The method further includes ejecting the water/air mixture through at least one water/air nozzle. 
   The invention embarks from the basic idea of using at least one jet pump (liquid jet gas compressor) for producing the water/air mixture expelled by at least one water/air nozzle. The jet pump operates without moving parts and is inexpensive, light and reliable. Ambient air or air which has been precompressed by a compressor is supplied to the jet pump, depending on the effective working pressure of the water available for the jet pump. In the first case, the air compressor which is usually required in the prior art is completely dispensed with; in the second case, the compressor may be correspondingly smaller and more cost-efficient in design. 
   The energy required to operate the jet pump is supplied to the snow making apparatus according to the invention via the operating pressure of the water supply. A surprising synergistic effect of the solution according to the invention is that energy which is wasted in prior art systems may be utilised on most snow making apparatuses in typical applications, namely for providing ski pistes with snow. This is because water is usually supplied to the snow making apparatuses arranged on a slope by a pump system located in the valley. The pump system supplies a pressure line which leads to the mountain and to which the snow making apparatuses are connected. The line pressure required for the snow making apparatus, for example 15 to 20 bar, must be available even at the highest point of the pressure line. Depending on the difference in height that the pressure line overcomes, the line pressure is much higher in the lower and middle region of the piste and is, for example, 40 to 80 bar or higher. 
   In systems according to the prior art, the connecting points of the pressure line comprise what are known as hydrants which correspondingly limit the operating pressure for the connected snow making apparatuses, in the manner of a throttle valve. The hydrants convert considerable amounts of energy into heat. For example, the throttle power is about 16 kW at a line pressure of 40 bar, an operating pressure of the snow making apparatus of 10 bar and a water consumption of 20 m 3 /h. This energy, which remains unused in systems according to the prior art, may be utilised by the invention. 
   As already mentioned, ambient air or already pre-compressed air may be supplied to each jet pump. In some configurations of the invention, at least one multi-stage jet pump is used in order to obtain particularly high air compression. The jet pump (or at least one stage of the multi-stage jet pump) preferably comprises a driving nozzle for the water, a suction nozzle for the air, a mixing chamber for mixing the water issuing from the driving nozzle with the air flowing through the suction nozzle, and a diffuser for compressing the water/air mixture. A swirl member is provided in the suction nozzle in some configurations. 
   In particularly preferred embodiments, more than 50% or more than 75% or more than 90% or substantially all of the water throughput of the snow making apparatus passes through the jet pump or jet pumps and is expelled through the water/air nozzle or the water/air nozzles as a water/air mixture. In these configurations, the energy provided by the water is utilised particularly well. Preferably, more than 50% or more than 75% or more than 90% or substantially all of the nozzles of the snow making apparatus are configured as water/air nozzles (in contrast to mere water nozzles as in low-pressure cannons according to the prior art). A particularly large quantity of freezing nuclei is then produced. 
   To achieve particularly good compression of the water/air mixture, the effective working pressure of each jet pump, (i.e. the pressure difference which is available to the jet pump and is often also described as the effective driving fluid pressure) is preferably at least 10 bar or at least 20 bar or at least 30 bar. In preferred configurations, the snow making apparatus is preferably adapted for unthrottled or direct connection to a water pressure line having a line pressure of more than 20 bar or more than 30 bar or more than 40 bar. 
   In preferred configurations, the at least one jet pump comprises a nozzle needle for varying the water throughput and/or the mixing ratio of the expelled water/air mixture (and therefore the constitution of the snow produced). The nozzle needle may be adjusted by a motor or manually, taking into account, in particular, ambient parameters such as temperature, air humidity, etc. In some further developed configurations, the nozzle needle has an axial bore to increase the air throughput of the jet pump. 
   In further advantageous configurations of the invention, during operation of the snow making apparatus, different water/air nozzles or groups of water/air nozzles may simultaneously be supplied with water/air mixtures having different mixing ratios. This measure leads to snow having particularly good qualities. The water/air mixtures may be produced by jet pumps having different constructions or adjustments, or they may be derived from a single jet pump (for example at different points of the mixing chamber or diffuser). 
   To enable the water throughput to be adapted step-by-step to the requirements of snow production and environmental conditions, a plurality of water/air nozzles that may individually be turned on and/or a plurality of groups of water/air nozzles that may individually be turned on are provided in preferred configurations. These nozzles or nozzle groups may be connectable to an individual jet pump or to a group of jet pumps via a distributor. Preferably, however, at least one respective individual jet pump is provided for each nozzle or nozzle group that may individually be turned on. 
   The snow making apparatus according to the invention may be configured in any known type of construction. In particular, variants with a lance type of construction and as a propeller machine are provided. With the propeller type of construction, the snow making apparatus preferably comprises a motor-driven propeller for producing a main air stream, and the water/air nozzles are arranged in one or more nozzle rings so that they discharge the water/air mixture into the main air stream. With the lance type of construction, a vertical or oblique lance rod of which the end remote from the ground comprises a nozzle head with one or more water/air nozzles is provided in preferred configurations. The at least one jet pump may be arranged at the nozzle head or at the end of the lance rod close to the ground. The lance rod is preferably constructed as a pipe through which the water supply is conveyed in the first case and the water/air mixture is conveyed in the second case. 
   In preferred configurations, the method according to the invention is developed by features which correspond to the aforementioned features and/or the features mentioned in the dependent apparatus claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features, advantages and objects of the invention will emerge from the following description of a plurality of embodiments and variants. Reference is made to the schematic drawings, in which: 
       FIG. 1  is a basic sketch of an embodiment according to the invention, 
       FIG. 2  is a side view of a first embodiment of the invention in the form of a propeller machine, 
       FIG. 3  is a front view of the propeller machine of  FIG. 2  in the direction of the arrow III, 
       FIG. 4  is an enlarged bottom view in the direction of the arrow IV of the pump module shown from the side in  FIG. 2 , 
       FIG. 5  is an enlarged section of the region V of  FIG. 2  along the line V-V in  FIG. 4 , 
       FIG. 6  is a further enlarged section of the pump tube shown in  FIG. 5 , 
       FIG. 7  is a side view of a second embodiment of the invention of lance type of construction, 
       FIG. 8  is an enlarged side view of the region VIII of  FIG. 7  in a section along the longitudinal axis, 
       FIG. 9  is an enlarged side view of the region XI of  FIG. 7  in a section along the longitudinal axis, 
       FIG. 10  is a cross-section through the nozzle head shown in  FIG. 9 , along the line X-X, 
       FIG. 11  is a perspective oblique top view of a nozzle head and jet pumps according to a further embodiment of the invention, 
       FIG. 12  is a front view of the nozzle head according to  FIG. 11 , 
       FIG. 13  is a top view of the nozzle head according to  FIG. 11 , 
       FIG. 14  is a longitudinal section along the line XIV-XIV in  FIG. 12 , 
       FIG. 15  is a transverse section along the line XV-XV in  FIG. 13 , and 
       FIG. 16  is a transverse section along the line XVI-XVI in  FIG. 13 . 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The basic sketch in  FIG. 1  shows certain elements of a snow making apparatus according to one embodiment comprising a jet pump  10  and a plurality of water/air nozzles  12 . The jet pump  10  is formed in a manner known per se with a driving nozzle  14  and a pump tube  16 , the pump tube  16  comprising suction nozzles  18 , a mixing chamber  20  and diffuser  22 . In the embodiment described here, the driving nozzle  14  comprises a circular nozzle opening having a diameter of, for example, 4 mm or 5 mm. In the present example, the suction nozzles  18  are configured as bores with a diameter of 12 mm in the pump tube  16 , and the mixing chamber  20  here is a mixing tube with a constant cross-section. In some embodiments of the jet pump  10 , a swirl member (not shown) is arranged in the driving nozzle  14 . 
   During operation of the snow making apparatus, water W is supplied to the jet pump  10  via a pressure line (not shown) at a pressure of about 25 to 40 bar or higher. The water W serves as a driving medium here; the path of the driving water stream is designated by a continuous arrow in  FIG. 1 . The water W issues from the driving nozzle  14  as a high speed jet and entrains air A which enters the pump tube  16  through the suction nozzles  18  (the entry direction of the air A is illustrated by dotted arrows in  FIG. 1 ). The speeds of the water W and the air A become the same in the mixing chamber  20 , and the two media mix intensively. The high speed of the resultant water/air mixture M is partially converted into pressure again in the diffuser  22 . 
   The water/air mixture M now passes to the water/air nozzles  12  through which it is expelled (the flow path of the mixture M is indicated by the dot-dash arrows in  FIG. 1 ). The air expands abruptly as it leaves the water/air nozzles  12  and cools the finest water droplets to well below the freezing point. At suitably low ambient temperatures, further droplets of the water/air mixture M settle on these freezing nuclei and form snow crystals. 
   The snow making apparatus shown in  FIG. 2  has a main tube  24  in which there is arranged an electric motor  26  with a flange-mounted propeller  28 . During operation, the propeller  28  driven by the electric motor  26  with a power rating of approximately 5 to 15 kW produces a main stream S of which the direction is indicated in  FIG. 2  by a dashed arrow. The main tube  28  tapers in the flow direction to a diameter of about 56 cm. 
   A nozzle module  30  connected to the outlet side of the main tube  24  contains a number of water/air nozzles  12  ( FIG. 1 ), which are arranged in a plurality of nozzle rings  32 A,  32 B,  32 C,  32 D. A distributor  34  is connected, on the one hand, to the nozzle module  30  and, on the other hand, to a plurality of jet pumps  10 , only one of which is visible in  FIG. 2 . In the present embodiment, the snow making apparatus comprises only water/air nozzles  12  which are supplied with the water/air mixture M produced by the jet pumps  10 . Water-only nozzles are not provided. 
   The front view in  FIG. 3  shows, in particular, the concentric arrangement of the four nozzle rings  32 A,  32 B,  32 C,  32 D. In the present example, each of the nozzle rings  32 A,  32 B,  32 C,  32 D is configured as an octagon with 64 or 72 water/air nozzles  12 . A circumferential channel of each nozzle ring  32 A,  32 B,  32 C,  32 D is connected to the distributor  34 . 
   The enlarged view of the pump module in  FIG. 4  shows the distributor  34  and three jet pumps  10  which are connected to the compressed water supply via a connecting piece  36 . Each jet pump  10  supplies a respective nozzle ring  32 A,  32 B,  32 C with the water/air mixture M via an associated connecting duct  38 A,  38 B,  38 C. The nozzle ring  32 D is connected to a further jet pump  10  (not shown in  FIG. 4 ) via two further connecting ducts  38 D,  38 E. 
   Whereas all jet pumps  10  are always operated in the embodiment of  FIG. 4 , valves are provided in variations, which valves may be arranged on the inlet side in the connecting piece  36  or on the outlet side in the distributor  34 . The nozzle rings  32 A,  32 B,  32 C,  32 D may be turned on and off individually by suitably controlling these valves, so that it is possible that one or more or all nozzle rings  32 A,  32 B,  32 C,  32 D are active in each case. In this configuration, the water throughput and therefore the snow production level may be regulated in a cost-effective manner. 
     FIG. 5  shows, by way of example, a section through the nozzle module  30  which extends through a respective nozzle bore  40  of the four nozzle rings  32 A,  32 B,  32 C,  32 D. The nozzle bores  40  are provided for receiving the water/air nozzles  12 , for example in the construction shown in  FIG. 1 . Suitable water/air nozzles  12  are commercially available as inserts for the nozzle bores  40  and, as such, do not form the subject of the present invention. 
   The pump tube  16  is shown on an enlarged scale in  FIG. 6 . The pump nozzles  18  are arranged as four bores offset radially by 90° each in the inlet-side portion of the pump tube  16 . 
   In the embodiment of  FIG. 7 , the snow making apparatus is configured as a lance type of construction. An anchor  42  located in the ground fixes a holder  44  comprising two hingedly connected support rods  46 ,  48 . The snow making apparatus in the stricter sense is fastened on the upper support rod  48 . It has a lance rod  50  which is, for example, 8 to 12 m long, is formed as a pipe, and at the upper end of which there is arranged a nozzle head  52  and at the lower end of which there is arranged a pump element  54 . 
   As shown in  FIG. 8 , the pump element  54  comprises a jet pump  10 ′ and a connecting elbow  56  connected thereto. The compressed water W required for operation is supplied to the jet pump  10 ′ via the connecting elbow  56 . Similarly to the jet pump  10  in  FIG. 1 , the jet pump  10 ′ is configured with a driving nozzle  14 ′ and a pump tube  16 ′ with a mixing chamber  20 ′ and diffuser  22 ′. A connecting piece  58  comprises bores for admitting ambient air A which act as suction nozzles  18 ′. The connecting piece  58  connects the connecting elbow  56 , the driving nozzle  14 ′ and the pump tube  16 ′ to a module. On the outlet side, the jet pump  10 ′ is connected via a sleeve  64  to the pipe-shaped lance rod  50 . 
   The jet pump  10 ′ further comprises a nozzle needle  60  which comprises a through-bore and is supported in a longitudinally displaceable manner in a guide  62 . The pump properties of the jet pump  10 ′ can be adapted to the requirements by appropriate adjustment of the nozzle needle  60 ; in particular, it is possible to vary the water throughput and/or the mixing ratio of water and air in the water/air mixture M. Adjustment can be carried out manually (for example during installation or maintenance of the system) or automatically (for example depending on the desired quantity of snow or weather conditions). In the present example, the nozzle needle  60  has a through-bore along its longitudinal axis, so further ambient air A can be introduced into the driving jet of the jet pump  10 ′ in order to increase the pump capacity. However, variations comprising a nozzle needle  60  which does not have a through-bore are also provided and still have the advantage of improved adjustability. 
   The nozzle head  52  shown in detail in  FIG. 9  is detachably connected to the upper end of the lance rod  50  ( FIG. 7 ) by a connecting and sealing module  66 . As shown in  FIG. 9  and the cross-section of  FIG. 10 , the nozzle head  52  in the present example has a total of six bores  68 , each for receiving a respective water/air nozzle  12  ( FIG. 1 ) in the form of a nozzle insert known per se. 
   During operation, the water/air mixture M produced by the jet pump  10 ′ is fed into the lance rod  50  and from there into the nozzle head  52 . The water/air mixture M issues from the water/air nozzles  12  ( FIG. 1 ) as a fine spray mist. Expansion leads to freezing nuclei from which snow crystals are created by the deposition of further water droplets during the relatively long falling path to the ground. In the configuration described here, the pipe-shaped lance rod  50  serves to convey the water/air mixture M from the jet pump  10 ′ to the nozzle head  52 . Further lines, whether for compressed air or for water, are not required. It is merely necessary to establish a connection between the connecting elbow  56  and a water pressure line which is already laid next to the piste in existing piste installations. 
   In further variations, jet pumps  10 ′ as shown in  FIG. 8  are also used in the propeller machine according to  FIG. 2 , in order to also obtain the possibilities for adjustment afforded by the nozzle needle  60 . Conversely, the snow making apparatuses in lance form according to  FIG. 7  may also be equipped with the simpler jet pumps  10  according to  FIG. 1 . 
     FIG. 11  to  FIG. 16  show, as a further embodiment of the invention, a nozzle head  52 ′ which forms a compact module together with two jet pumps  10 ″. The module is intended to be mounted on the towering end of a lance rod, at a height of, for example, 10 m. In other words, the present embodiment represents a modification of the embodiment of  FIG. 7  in that the nozzle head  52  in  FIG. 7  has now been replaced by the nozzle head  52 ′ and in that the pump element  54  in the form of the jet pumps  10 ″ has been mounted directly on the nozzle head  52 ′. Owing to the constructional combination of the jet pumps  10 ″ with the nozzle head  52 ′, separation of the water/air mixture M—which might possibly occur in the lance rod  50  with the embodiment of FIG.  7 —is avoided. 
   Referring to  FIG. 11  to  FIG. 16 , the jet pumps  10 ″ according to the present embodiment each comprise a driving nozzle  14 ″ and a plurality of suction nozzles  18 ″. The nozzle head  52 ′ is provided with a total of ten screw-in water/air nozzles  12 ′ of which the four shown on the right of  FIG. 11  to  FIG. 14  form a first group and the six shown in the middle of  FIG. 11  to  FIG. 14  form a second group. The driving nozzles  14 ″ of the two jet pumps  10 ″ have different diameters, and therefore different water throughputs. The jet pump  10 ″ with the smaller driving nozzle diameter supplies the first group of the four water/air nozzles  12 ′, and the jet pump  10 ″ with the greater driving nozzle diameter supplies the second group of the six water/air nozzles  12 ′. In total, therefore, three-stage water regulation is achieved by activating either only the first group of driving nozzles  14 ″ or only the second group of driving nozzles  14 ″ or both groups of driving nozzles. 
   Flat nozzles are used as water/air nozzles  12 ′ in the present embodiment, to achieve the fastest possible relaxation of the air and therefore to cool the smallest water droplets which then freeze and therefore form the freezing nuclei for the remaining water. 
   A further advantage of the configuration according to  FIG. 11  to  FIG. 16  over that of  FIG. 7  resides in the better utilisation of energy. As the jet pumps  10 ″ preferably operate with a pressure ratio of approximately 3:1, the pressure drop of about 1 bar in the lance pipe  50  which towers upwardly by about 10 m has to be compensated by a pressure which is about 3 bar higher at the driving nozzle  14 ′ of the jet pump  10 ′ in the embodiment of  FIG. 7 . With the embodiment of  FIG. 11  to  FIG. 16 , on the other hand, an additional water pressure of only about 1 bar is required to achieve the desired driving nozzle pressure. 
   A large number of further modifications, in particular with respect to the dimensioning of the individual components and/or the number or configuration of the jet pumps  10 ,  10 ′,  10 ″ or of the water/air nozzles  12 ,  12 ′ is immediately apparent to the person skilled in the art.