Abstract:
A valve for one-time opening a fluid line for venting a technical system includes an inlet for connecting to the fluid line, an outlet, and a controllable closure arranged between the inlet and the outlet. In the non-activated state the controllable closure closes a passage between the inlet and the outlet. The closure includes a material that changes its phase state in dependence on a control parameter, whereby the passage is irreversibly opened in the activated state.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to German application number 10 2013 001 992.3, the entire disclosure of which is herein expressly incorporated by reference. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention relate to a valve for one-time opening of a fluid line, in particular for venting a technical system. The invention further relates to a technical system, in particular of a spacecraft component. 
     Valves adapted for switching only a single time are frequently used in space travel. The function of the valves is to ensure a defined opening or closing of a fluid line at a given time. For this purpose, the valves have an actuator. In most cases, pyrotechnical igniters are used as actuators. A disadvantage of such actuators is that when actuating them, a so-called gyro-shock occurs, which can damage other components of the technical system. Pyrotechnical igniters normally have a limited warranted lifetime of, for example, 8 years. Since spacecrafts such as, for example, communication satellites typically stay longer than 15 years in geostationary orbit, a reliable actuation of the valve at the end of the lifetime of the system is not ensured. 
     Currently, one-time-switching valves on the basis of wax actuators are under development. In these actuators, a pre-loaded spring is embedded in wax. The solidified wax prevents the spring from relaxing. For actuating the valve, the wax is heated and thus liquefied. Due to the liquefied wax, the spring is no longer blocked and the actuator opens the cap of a capillary tube, for example by means of shear forces. The function of such an actuator requires the presence of a shear blade. 
     Exemplary embodiments of the present invention are directed to a valve that is to be opened only once and that allows in a cost-effective and reliable manner to open a fluid line, in particular for venting a technical system. 
     In accordance with the present invention the valve comprises an inlet for connecting to the fluid line, an outlet, and a controllable closure. The controllable closure is arranged between the inlet and the outlet and closes in the non-activated state a passage between the inlet and the outlet. The closure comprises a material that changes its phase state depending on a control parameter, as a result of which the passage is irreversibly opened in the activated state. 
     The valve according to the invention enables the one-time opening of a fluid line without a mechanical actuator. Through this, the valve can be produced with low complexity and therefore at low costs. Its reliable function is ensured over a lifetime of more than 15 years, as required in space applications. 
     The technical system can involve, for example, a space travel downthrust system with storable fuels. The proposed valve can be used, for example, to passivate satellite tanks and satellite lines, which serve for providing fuel and compressed gas, at the end of a mission. Through this, explosions can be prevented during a later re-entry of the spacecraft or in the event of debris impacts. 
     According to an advantageous configuration, the phase change of the material (so-called phase-change material) can be effected by heat supply, wherein the material transitions under heat supply from a solid state into a liquid state and thereby opens the closure. In order to achieve the phase change of the material, a so-called phase-change temperature has to be reached. The material is preferably selected such that the difference between an ambient temperature or an operating temperature of the valve and the phase-change temperature excludes unintentional actuation of the valve. Such unintentional actuation could be caused by solar radiation or waste heat of other components. Expediently, the phase-change material comprises a metal or consists of metal. Preferably, indium is used, which has a melting temperature of more than 157° C. and therefore meets the requirements placed upon space travel applications. The concept of metal is to be interpreted broadly. It is in particular to be understood that this also includes metal alloys. 
     According to a further advantageous configuration, the closure comprises a heating device that can be switched on by means of a control device so as to activate the closure. By means of the heating device, the material can be brought from the solid state, in which the closure closes a passage between the inlet and the outlet, into a liquid or gaseous aggregation state, whereby the one-time opening of the valve is enabled. The heating device can be configured as a resistance heating. A resistance heating system is known in fields related to space travel applications, for example, in connection with hydrazine jet engines. Such a heating device comprises a heating element, a feed line and an electrical connection. 
     Expediently, the heating device in the closure is arranged in spatial proximity to the phase-change material. This ensures that the reaction time for changing the phase state of the phase-change material is short. 
     In the non-activated state of the valve, the phase-change material closes at least one passage channel of the closure. In other words, this means that the closure has one or a plurality of passage channels in which, in the non-activated state, the solid phase-change material is arranged. After activating the valve, the fluid contained in the fluid lines flows through the passage channel or channels for venting the technical system. 
     According to an advantageous configuration, a wall of the at least one passage channel, in a longitudinal section through the closure or through the evacuation valve, is formed to be conical or stepped at least in sections so that the material is pressed against the wall by the pressure prevailing in the technical system. This ensures that the pressure prevailing during the operation of the technical system cannot displace the sealing phase-change material when the evacuation valve is not activated, which otherwise could result in leakages of the technical system. 
     In a further configuration, the outlet has an outlet nozzle that has at least one opening, wherein the outlet nozzle protrudes into a volume of the valve, which volume is arranged between the passage and the outlet, wherein the material that is liquefied by activation can be absorbed by the volume, and the at least one opening of the outlet nozzle is fluidically connected to the inlet by passing through the passage. Here, the at least one opening is connected to an exit of the outlet. The volume formed in the housing of the valve thus is dimensioned in terms of its size in such a manner that the material that changes its phase state during heating can be completely absorbed by said volume. At the same time, the outlet nozzle is arranged in the volume in such a manner that the at least one opening of the outlet nozzle is not closed by the phase-change material, and the connection between the inlet of the evacuation valve and the outlet of the evacuation valve is therefore ensured. 
     The outlet can be formed such that it has at its exit a tube for connecting. Alternatively, the outlet can comprise a nozzle at its exit. The nozzle can be connected here as a separate component to the outlet of the evacuation valve. Likewise, the outlet of the evacuation valve can be configured such that the exit of the outlet has the shape of a nozzle. In a further variant, the outlet can comprise at its exit a plurality of outlets which enables the fluid to discharge symmetrically, in particular along a longitudinal axis of the evacuation valve. This ensures that during discharging of the fluid, no thrust vector or no moment is generated that acts on the technical system, for example, a satellite or a spacecraft. Such an arrangement is also designated as “zero-force-outlet”. 
     For limiting the fluid flow rate when the valve is open, an orifice can be arranged between the inlet and the closure. This orifice limits the cross-section through which the fluid can flow during venting of the technical system. Corresponding to this, alternatively or additionally, an orifice for limiting the fluid flow rate can also be arranged between the outlet and the closure. 
     When reference to a fluid is made in the present description, this is to be understood as both a liquid medium and a gaseous medium, for example, a fuel. 
     The technical system involves in particular a spacecraft component that comprises an evacuation valve that is configured as described above. Here, as long as the valve is not open, the medium in the technical component is typically pressurized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention is explained in greater detail below by means of an exemplary embodiment in the drawing. In the figures: 
         FIG. 1  shows a schematic cross-sectional illustration of a valve according to the invention in the form of an evacuation valve, 
         FIG. 1 a    shows another schematic cross-sectional illustration of a valve according to the invention in the form of an evacuation valve, 
         FIG. 2  shows a schematic illustration of a zero-force-outlet that can be arranged at an outlet of the evacuation valve, 
         FIG. 3  shows a nozzle for arranging at the outlet of the evacuation valve shown in  FIG. 1 , 
         FIG. 4  shows a schematic illustration of an evacuation valve according to the invention in a side view, in which components of a heating device are shown, and 
         FIG. 5  shows a top view onto the evacuation valve of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic cross-sectional illustration of an evacuation valve  1  according to the invention. The evacuation valve  1  comprises a housing  2 . The housing  2  consists of a first housing section  2   a  and a second housing section  2   b . The two housing sections  2   a ,  2   b  are connected to one another by a connecting section  2   c . The first and second housing sections  2   a ,  2   b , for example, have a circular cross-section. The diameter of the first housing section  2   a  in the exemplary embodiment is larger than the cross-section of the second housing section  2   b , although this not required. This results in a conical shape of the housing section  2   c . In the exemplary embodiment, the diameter of the second housing section  2   b  is dimensioned according to the cross-section of an inlet  3  of the evacuation valve  1 . At its opposite end, the housing  2  has an outlet  4 . The inlet  3  is connected to a fluid line (not illustrated) of a technical system, for example, a space propulsion. The outlet  4  is fluidically connected to the surroundings or another piping system or container. 
     Between the inlet  3  and the outlet  4 , a controllable closure  5  is arranged. The closure  5  has at least one passage channel  7 ,  8 . In the illustration of  FIG. 1 , two passage channels  7 ,  8  are shown. Between the two passage channels  7 ,  8 , a heating device  9  is arranged in the closure. The two passage channels  7  are filled with a phase-change material  6 . The phase-change material  6  consists in general of a solid meltable material. Preferably, a metal such as, for example, indium is used as a phase-change material. The melting temperature of indium is above approximately 157° C. A phase change of the phase-change material  6  thus only takes place upon activation, but not due to solar radiation or waste heat of other components in the proximity of the evacuation valve. This is ensured by the sufficiently large temperature difference between ambient temperature/operating temperature of the evacuation valve and the phase-change temperature. 
     If the heating device  9  is not in operation, the phase-change material  6  keeps its solid form. By putting the heating device  9  into operation, the phase-changing material  6  is made to melt. In the housing  2 , between the outlet  4  and the closure  5 , a volume  13  is provided into which the molten phase-change material can flow. The volume  13  is a closed intermediate space between the outlet  4  and the closure  5 . The outlet  4  comprises an outlet nozzle  10  that protrudes into the volume  13 . The outlet nozzle  10  comprises, at least on the outer circumference, one or more openings  11  which are connected to an exit  12  of the outlet nozzle  10 . The exit  12  is connected with the surroundings or another piping system or container. 
     Upon activating the heating device  9 , the phase-change material  6  is liquefied and is flushed into the volume  13  by means of a residual pressure of the technical system, which residual pressure prevails on the inlet side. In the downstream volume  13 , the molten phase-change material  6  deposits on the bottom  14  of the volume. The fluid to be discharged can now flow through the openings  11  of the outlet nozzle  10  until the technical system is at ambient pressure. 
     In order to prevent the evacuation valve  1  from leaking when the heating device is not activated and the evacuation valve therefore is not actuated, the passage channels  7 ,  8  are configured in such a manner that the solid phase-change material  6  is sealingly pressed against a respective wall of the passage channel  7 ,  8 . In the exemplary embodiment shown in  FIG. 1 , the passage channels  7 ,  8  each have a first narrow section  7   a ,  8   a  and a second, comparatively wider section  7   b ,  8   b . The resulting step  7   c ,  8   c  prevents that the phase-change material can be pressed out of the passage channels  7 ,  8  when the valve is closed and high pressure prevails in the technical system. On the contrary, the higher the pressure is in the technical system and therefore on the inlet side of the evacuation valve  1 , the better the phase-change material  6  is pressed against the walls of the passage channels  7 ,  8 . The same effect can be achieved if the passage channels  7 ,  8  have a conical shape (see  FIG. 1 a   ). 
     The flow rate of the medium when the evacuation valve  1  is open can be limited by orifices that are optionally arranged at the inlet  3  and/or outlet  4 . Only as an example, such an orifice  15  is arranged at the inlet  3 . This results in a cross-section  16  that is reduced with respect to the inlet cross-section  3 . If such an orifice is to be arranged at the outlet  4 , this orifice can be provided at the exit  12  of the outlet nozzle  10 . 
     If the evacuation valve  1  is to be used in space travel applications, it is advantageous to provide the exit  12  of the outlet nozzle with a so-called zero-force outlet  20 , which is exemplary shown in  FIG. 2 . The latter can be connected, for example, to a receptacle  17  of the outlet  4 . It is principally also possible to form the zero-force-outlet  20  integrally with the outlet  4  of the evacuation valve  1 . 
     The zero-force-outlet  20  comprises a connecting section  21  which can be inserted into the receptacle  17  of the outlet pipe  4 . The type of connection (non-positive- and/or positive-locking fit or adhesive bond) is of subordinate importance here. An inlet  22  is now fluidically connected to the exit  21  of the outlet nozzle  10 . In the drawing, two further sections  21   a ,  21   b  extend in opposite directions from the connecting section  21  so that the respective outlets  23 ,  24  enable the fluid to discharge symmetrically. The number of outlets  23 ,  24  can principally also be selected differently. It only has to be ensured that the fluid discharges symmetrically, in particular with regard to a longitudinal axis of the evacuation valve, which extends in  FIG. 1  in the plane of projection from left to right. This ensures that no thrust vector or moment can occur that acts on the technical system. 
     Alternatively, a nozzle  30  can be connected to the outlet  12 . The nozzle  30 , which is illustrated in  FIG. 3 , comprises a connecting section  31  which, in turn, can be connected to the receptacle  17  of the exit  12  of the outlet  4 . The connection can be formed in a detachable manner, a nonpositive-locking and/or positive-locking manner or firmly bonding manner. Also, the nozzle  30  could be an integral part of the outlet  4 . At an end opposite to the inlet  32 , an outlet  33  with a nozzle widening  34  is provided. 
     As described above, the closure  5  is heated by the heating device  9 . As is apparent from  FIG. 1 , the heating device  9  is located in the closure near the phase-change material  6 . Heating devices of this type are used, for example, for hydrazine jet engines. The heating device  9  consists of a heating element (H), a heater-inherent feed line  18  and an electrical connection  19 . This is schematically illustrated in the  FIGS. 4 and 5 , wherein  FIG. 4  illustrates a side view of the evacuation valve  1  according to the invention, and  FIG. 5  illustrates the arrangement from above, with the feed line  18  and the electrical connection  19 . The location of the closure with the heating device  9  arranged therein is in each case illustrated hatched and indicated by the reference number  5 . 
     The described evacuation valve has the advantage of low costs, durability, reliable function in the case of activation, and low complexity due to the absence of mechanical elements. The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
     REFERENCE LIST 
       1  Evacuation valve 
       2  Housing 
       2   a  First housing section 
       2   b  Second housing section 
       2   c  Connecting section 
       3  Inlets 
       4  Outlets 
       5  Closure 
       6  Phase-change material 
       7  Passage channel 
       7   a  First, narrow section of the passage channel  7   
       7   b  Second wide section of the passage channel  7   
       7   c  Step 
       8  Passage channel 
       8   a  First narrow section of the passage channel  8   
       8   b  Second wide section of the passage channel  8   
       8   c  Step 
       9  Heating device 
       10  Outlet nozzle 
       11  Opening 
       12  Exit of the outlet nozzle 
       13  Volume 
       14  Bottom of the volume 
       15  Orifice 
       16  Cross-section 
       17  Receptacle for orifice, nozzle or zero-force-outlet 
       18  Feed line 
       19  Electrical connection 
       20  Zero-force-outlet 
       21  Connecting section 
       21   a  Section 
       21   b  Section 
       22  Inlet 
       23  Outlet 
       24  Outlet 
       30  Nozzle 
       31  Connecting section 
       32  Inlet 
       33  Outlet 
       34  Nozzle widening