Vaporization device under microgravity conditions

Abstract

The present invention relates to a satellite, preferably a resistojet, comprising a device for vaporizing a fluid under microgravity conditions, comprising: • a fluid inlet (I1), • a fluid outlet (U1), • a heater (R1), • a nozzle (T1) fluidly connected to the outlet (U1), • a hollow fluidic swirling element (S1) having an inner surface and an outer surface; said swirling element (S1) being made of a thermally conductive material thermally connected with the heater and fluidly connected with the inlet (I1) and the outlet (U1), wherein the fluid wets the inner surface of the swirling element (S1) by centrifugal force, achieving—when the swirling element is heated by the heater (R1)—a percentage conversion of the fluid into vapor of at least 99% at the outlet (U1), thereby producing a thrust force exiting from the nozzle (T1).

Description

[0001] Vaporization device under microgravity conditions DESCRIPTION

[0002] TECHNICAL FIELD

[0003] The present invention relates to a propulsion system for a satellite, preferably a resistojet, in particular a resistojet for a fluid, preferably demineralized water, comprising a vaporization chamber with an initial swirling element, preferably followed by a lattice element, for effectively heating the fluid under microgravity conditions.

[0004] BACKGROUND ART

[0005] A resistojet or electrothermal thruster is a propulsion technology for space applications based on the conversion of electrical energy into thrust through the heating of a fluid.

[0006] Although this technology has already been employed since the 1960s, resistojets still present disadvantages, in particular relating to the propellant fluid and the efficiency of heating under microgravity conditions.

[0007] It is known, in fact, to use organic propellants such as hydrazine, currently the most commonly used propellant, which however is extremely toxic, difficult to handle, and known to have heat transfer issues, particularly in the region of the nozzle and the vaporization chamber. Other non-organic propellants may include hydrogen and ammonia; however, hydrogen is difficult to store, and it is known that flow losses occur due to gas expansion in the nozzle, leading to its condensation. As for ammonia, it decomposes into low-molecular-weight products that introduce flow losses .

[0008] Moreover, this technology requires the heater to reach high temperatures in order to vaporize the fluid, since under microgravity conditions heat conduction is a known problem. This entails safety issues, as there is a high-temperature element onboard the satellite, as well as an energy cost issue, since heating to high temperature requires considerable energy. Furthermore, the high temperature necessitates that the heater be made of a material capable of withstanding such temperatures, introducing design constraints for the system.

[0009] There is therefore a need for a resistojet in which the propellant is safe, easily storable, and that does not present, or at least limits, flow losses in the nozzle. Furthermore, there is a need for a heating system capable of effectively vaporizing the entirety of the fluid under microgravity conditions.

[0010] OBJECTS AND SUMMARY OF THE INVENTION

[0011] The object of the invention is therefore to provide a satellite, preferably a resistojet or electrothermal thruster, whose design overcomes at least in part the disadvantages of the prior art described above.

[0012] This is achieved through a satellite for vaporizing a fluid, preferably demineralized water, under microgravity conditions, comprising :

[0013] • an inlet for the fluid,

[0014] • an outlet for the fluid,

[0015] • a heater, preferably an electric heater,

[0016] • a nozzle fluidly connected to the outlet, and

[0017] • a hollow fluid swirling element, preferably a coil, having an internal surface and an external surface; said swirling element being made of a thermally conductive material, preferably metallic, thermally connected to the heater and heated by conduction, and fluidly connected to the inlet and the outlet, in such a way that the fluid, when passing through the coil, is heated homogeneously.

[0018] This is achieved because the fluid wets the internal surface of the swirling element by centrifugal force, obtaining, when the swirling element is heated by the heater, a conversion of at least 99% of the fluid into vapor at the outlet, thereby producing a thrust force exiting the nozzle.

[0019] Furthermore, said satellite comprises a second chamber, positioned between the outlet, i.e., the terminal portion, of the coil and the outlet for the fluid, such that when the fluid is vaporized in the coil, it enters the second chamber, where it occupies the entire volume; from this chamber, the vapor is then free to exit through the fluid outlet. This second chamber serves to reduce pressure fluctuations of the vapor and to limit backpressure, which would otherwise make it more difficult for new fluid to enter the coil.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Preferred embodiments of the present invention will be described below purely by way of non-limiting example, with reference to the accompanying drawings, in which:

[0022] Figure 1A. 3D model of the vaporization chamber (left) and schematic view of the same (right) ;

[0023] Figure IB. 3D model and various views of a second embodiment of the vaporization chamber;

[0024] Figure 2. Schematic view of the space module according to a first embodiment;

[0025] Figure 3. Schematic view of the space module according to a second embodiment;

[0026] Figure 4. Schematic view of the space module according to a third embodiment;

[0027] Figure 5. Schematic view of the space module according to a fourth embodiment;

[0028] Figure 6. Front view (left) , side view (right) , and top view (below) of the fluid container;

[0029] Figure 7. 3D model of the nozzle.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention concerns a satellite, preferably a resistojet comprising a vaporization device, preferably a vaporization chamber or, more generally, a heat exchanger, for space applications or applications under microgravity conditions.

[0032] The chamber is shown in Figure 1. It comprises an inlet II for the liquid to be vaporized, preferably demineralized water, and an outlet U1 for the vapor. The phase transition from liquid to vapor occurs within a swirling element, preferably a coil SI. The coil is fundamental for solving the technical problem of heating a liquid under microgravity conditions, i.e., a particular condition in which a system is subject to a gravitational field of low magnitude. It is known that under such conditions, heat conduction is difficult because, in the absence of gravity, the buoyancy effect is absent; therefore, the fluid to be heated does not move away from the heat source once heated, making room for colder fluid. In fact, in the absence of gravity or under reduced gravity conditions, there is no weight difference between more or less dense fluids, i.e., hotter or colder fluids, and consequently, there is no circulation of the fluid in the heater; therefore, the fluid is not efficiently heated.

[0033] The coil structure SI according to the present invention solves this problem by exploiting centrifugal force. Indeed, as the fluid flows through the coil, it is subjected to a centrifugal force that enforces contact between the liquid and the heated wall of the coil by conduction, and in this way, the fluid is heated homogeneously and can be completely converted into vapor.

[0034] The vaporization chamber has a central body Cl, hollow inside, within which the heater (not shown in Figure 1A) is housed. This hollow body defines a first internal wall Pl, within which the coil is housed, followed by a second wall P2. The coil is thus in thermal contact by conduction with the heater.

[0035] At the base of the hollow body there is a chamber C2 with an oblong structure; this structure is optional and serves to homogenize the vapor pressure, i.e., the pressure oscillations are thus damped, and the backpressure value that would hinder the flow of liquid water entering the vaporization cell is reduced. In this way, the vapor exits from the coil and fills this homogenization volume, and once pressurized, exits through the outlet U1.

[0036] The chamber further comprises inlets for temperature and pressure sensors, respectively STI and SP1, to measure the pressure and temperature values of the fluid. These sensors are connected to an electronic processing unit which controls the temperature of the heater and may optionally control the incoming fluid volume ( this aspect will be described later in the description of the exemplary embodiment ) .

[0037] Overall , the vapori zation chamber under microgravity conditions comprises an inlet for a fluid, preferably deminerali zed water, in fluid communication with a coil within which the flow is converted into vapor by means of a heater . The chamber further comprises an outlet for extracting the vapor produced in the coil , a pressure sensor, and a temperature sensor . Optionally, the chamber may comprise a homogeni zation volume to regulate the pressure of the gas at the outlet .

[0038] According to another embodiment , the cell has the same components but a new geometry, shown in Figure IB .

[0039] In the second embodiment , the vapori zation cell comprises a main body having prismatic geometry, preferably with a polygonal base , provided with lateral proj ections suitable for fastening . Inside the body, an axial bore is formed, suitable for housing a removable heater . Around said bore , a coil is arranged, configured as a concentric helical conduit , intended to convey the fluid entering through a lateral threaded connection and conduct it to the outlet located at the upper part of the body .

[0040] Downstream of the coil , a pressure homogeni zation chamber is provided, defined radially around the terminal portion of the coil . Said chamber is provided with an internal lattice which increases the heat exchange surface and ensures a uni form distribution of the fluid before its discharge . Said lattice has a geometry that enhances the capillary ef fect of any recondensed water, as well as increasing the heat exchange surface for the vapor portion . The chamber is therefore suitable for promoting the stabili zation of the fluid pressure conditions and for completing its vapori zation .

[0041] The main body further has additional radial and frontal threaded ports intended for hydraulic connections and for the insertion of sensors . Such ports include inlet and outlet connections for the fluid as well as seats for accommodating pressure and temperature measuring instruments . The arrangement of the connections along directions orthogonal to the main axis allows simplified integration within fluidic systems.

[0042] The cell has overall dimensions, given by way of example and without limitation, on the order of 31 millimeters in height and 26 millimeters in width, with threaded connections M5x0.8 and M8xl, compliant with ISO 6149-2, for the fluidic connections, and M3xQ.5 threads for fastenings and accessories.

[0043] The homogenization chamber maintains proportions in which the internal diameter is greater than that of the coil, and the height is such as to ensure a useful volume for pressure equalization, being further enhanced by the internal lattice.

[0044] In the known art, vaporization systems are known in which, at the end of the heating element, there is a rectifying chamber, the role of which is to make the fluid path linear. In contrast, in the present invention, the homogenization chamber, either with or without the lattice, is intended to uniform the pressure of the fluid downstream of the coil.

[0045] To support this function, the structure of the chamber according to the present invention is configured as an annular or cylindrical volume arranged radially around the coil. It is directly in fluid continuity with the path of the coil and constitutes a collection cavity for the fluid, in which the flow coming from multiple turns of the spiral mixes. Inside it, a lattice or internal structure is integrated, which creates an extended surface of contact with the fluid and promotes heat exchange .

[0046] Conversely, rectifying chambers are located downstream of the axial outlet of helical conduits, that is, in direct continuation along the longitudinal axis of the body of the coil. The rectifying chamber is defined as a hollow section having walls extending axially, and above all, it must be free of internal components. Typically, the configuration is that of a free cylindrical volume intended solely to straighten the flow and direct it toward the nozzle. The method for the conversion from fluid to vapor comprises the following steps : supplying a fluid, preferably deminerali zed water, to the inlet of the vapori zation chamber ; heating said fluid inside the coil by means of a heater so as to obtain the phase transition from fluid to vapor .

[0047] In one embodiment , the vapori zation chamber is used in a steam propulsion space module ( shown in Figure 2 ) .

[0048] The inlet to the module is regulated by a valve VI , through which the fluid, preferably deminerali zed water, is introduced into the main fluid container MWT . Inside the MWT , the fluid is heated so that it does not freeze ; indeed, under the pressure and temperature conditions of space , freezing is a known problem . In the MWT , the liquid is therefore maintained at low pressure and at a temperature of approximately 30 ° C .

[0049] From the MWT , the fluid is extracted either by means of a pump ( as shown in Figure 2 ) or through a sel f-pressuri zation system ( as shown in Figure 3 ) .

[0050] In particular, the latter comprises a branch in the outlet tube of the MWT ; this branch has a smaller diameter than the main tube , so that only a fraction of the liquid exiting the MWT enters the branch . Inside this branch, the liquid is heated by means of a foil heater, so that the fluid is converted into vapor which is re-introduced into the MWT , within which it exerts pressure on the fluid, thereby pushing it out of the MWT and into the main tube .

[0051] Thus , the fluid is extracted from the MWT , and this extraction can occur either downstream by means of a pump, that is , through a suction force , or upstream by means of the pressure exerted by the vapor on the fluid, that is , through a compression force .

[0052] The fluid extracted from the MWT passes through the main tube and through a filter Fl ; this is a commercial filter used to eliminate potential contaminants in the fluid . Fluidly connected to the filter is a mass flow meter (MFM) , which measures the flow rate ; based on this measurement , the energy supplied to the heater of the vapori zation chamber is calibrated . At the outlet of the MFM, there is a valve V2 . This valve can be opened or closed and allows the module to be used in continuous or pulsed mode . In particular, i f the valve remains open, the module operates with a continuous vapor flow; however, the valve can be closed to accumulate a predefined aliquot of flow to be sent into the vapori zation chamber, and consequently, the module will use only that aliquot . The process can be repeated, resulting in a pulsed-type propulsion .

[0053] The valve is fluidly connected with the inlet I I of the vapori zation chamber . The fluid enters the coil and is heated by the heater . The amount of energy to be supplied to the heater is determined both by the MFM and by the temperature and pressure sensors inside the chamber, which are connected to a control unit , for example an Arduino control unit or an avionic unit configured ad hoc for the present invention .

[0054] Inside the coil , thanks to the helical structure , contact between the fluid and the heated walls is maximized, obtaining a conversion from fluid to vapor of at least 99% , preferably 100% .

[0055] The vapor exiting the coil enters a homogeni zation volume ; as the vapor expands , it completely occupies the homogeni zation volume and exits the vapori zation chamber through the vapor outlet U2 . The vapor is then puri fied again by means of a commercial filter F2 . Downstream of the filter, there is a system with at least one valve ; however, two valves are preferred, since they introduce redundancy into the system . The concept of redundancy is central in space applications , as on-site maintenance is not always possible , and therefore it is advantageous to have redundancy to maintain correct operation . It should be noted, however, that such redundancy is not limiting, but a technical improvement . Similarly, the valve V3 can be used to control the type of propulsion of the space module , i . e . , continuous or pulsed . At the outlet of V3 , the vapor enters the noz zle , which is provided with a heater and with pressure and temperature sensors . The heater enables the vapor to be heated to a temperature approximately 250 ° C higher than the inlet vapor temperature , and since the volume of the thruster does not change during this process , the increase in vapor temperature results in a greater propulsion force .

[0056] The foregoing embodiment comprises an electronic processing unit , i . e . , an Arduino electronic processing unit , which receives as input the information from the flow meter and from the pressure and temperature sensors , and which produces as output a signal corresponding to the control of the temperature of the heaters .

[0057] In particular, each heater can be controlled independently . That is , the heater of the MWT can be controlled independently from the heater of the vapori zation chamber, and both can, in turn, be controlled independently from the heater of the thruster .

[0058] Furthermore , i f the module is configured as shown in Figure 3 , that is , with the branch for sel f-pressuri zation, the heater of the branch can be controlled independently of all the other heaters and vice versa .

[0059] The valves V2 and V3 are controlled by a second electronic processing unit , and this latter unit is itsel f controlled by the first electronic processing unit , i . e . , the Arduino electronic processing unit .

[0060] According to one aspect of the invention, a custom PCB electronic board is adopted, configured to control the propulsion unit autonomously ( see Figures 4 and 5 ) . The control board is electrically connected to the power bus of the satellite for power supply, and to the command and telemetry system of the satellite for the reception of maneuver commands .

[0061] Thanks to software that utili zes the state machine principle , the thruster is configured to perform the entire procedure of firing preparation, firing, and shutdown, regulating time and thrust according to the received maneuver commands .

[0062] The control system is capable of closed-loop control using FID control laws and through filters , for example , electronic filters , to regulate the fluid flow rate .

[0063] Furthermore , it is capable of performing various types of firing ( continuous or pulsed) , of closed-loop control of the heaters by means of PWM control, and of simultaneously monitoring all operating parameters of the system, such as, for example, pressure, temperature, voltage, current, and flow.

[0064] In Figure 6 a complete view of the MWT is shown. In particular, the configuration with the self-pressurization system is illustrated. The MWT presents, on the upper wall, a plurality of inlets for pressure sensors SP2 and temperature sensors ST2, and an inlet for introducing the fluid into the MWT.

[0065] On the lower part of the wall perpendicular to the wall bearing the sensors, there is the main tube for the outlet of the fluid from the MWT. From this tube, it is possible to see the branch for self-pressurizing the MWT.

[0066] The branch includes, at its base, a heater R2 designed to heat and vaporize the incoming fluid. The branch runs along the wall and has the discharge point at the upper part of the MWT wall, so that the vapor enters the head of the MWT, exerting pressure on the loaded fluid.

[0067] In Figure 7, a schematic view of the nozzle is shown.

[0068] The nozzle has a central body through which the vapor, obtained from the vaporization chamber, passes. The central body has two transverse hollow bodies, which serve as inlets for the pressure sensors SP3 and temperature sensors ST3.

[0069] Furthermore, the central body has at least one groove on the external surface, within which the heater (not shown in the figure) is housed.

[0070] In addition, the nozzle has inside it a spiral vane structure designed to increase gas turbulence and heat exchange.

[0071] Advantageously, the present invention does not require rotating systems to generate the centrifugal force necessary to maximize contact between the fluid and the walls of the heated coil .

[0072] Moreover, the absence of a rotating element eliminates the need for a power supply system, which would compromise the energy efficiency of the space module. Advantageously, the present invention can use deminerali zed water as the propulsion fluid and does not require— although it would be possible— the use of fluids such as organic compounds , for example hydrazine , or pressuri zed gases or cryogenic fluids , which are widely used in propulsion systems .

[0073] Advantageously, the water used as the fluid does not have to be pressuri zed previously to high pressures . In fact , pressures above a certain threshold are a signi ficant source of risk . Furthermore , the low pressure allows the transition from liquid to vapor at temperatures lower than the temperatures required for the same transition at atmospheric pressure .

[0074] Advantageously, water has a density higher than other propellants , for example pressuri zed gases , allowing improved storage and consequently the possibility of having a greater quantity of propellant available .

[0075] Advantageously, the present invention has reduced dimensions , preferably 10 x 10 x 6 cm, making it usable both as a primary thruster for CubeSat with total volumes starting from 2U and as a secondary thruster for SmallSats , i . e . , systems with a mass less than 500 kg .

Claims

CLAIMS1. Satellite comprising a device for vaporizing a fluid under microgravity conditions, comprising:• a fluid inlet (II) ,• a fluid outlet (Ul) ,• a heater (R1 ) ,• a nozzle (Tl) fluidly connected to the outlet (Ul) ,• a hollow fluidic swirling element (SI) having an inner surface and an outer surface; said swirling element (SI) being made of a thermally conductive material thermally connected with the heater and fluidly connected with the inlet (II) and the outlet (Ul) ;• a chamber (C) being interposed between the terminal portion of the swirling element (SI) and the fluid outlet (Ul) , such that the fluid vaporized in the element (SI) flows into the chamber (C) before exiting through the fluid outlet (Ul) ,in order to reduce the pressure fluctuations of the vapor exiting from the fluid outlet and to reduce the back pressure of the vapor within the element (SI) , wherein the fluid wets the inner surface of the swirling element (SI) by centrifugal force, obtaining— when the swirling element is heated by the heater (Rl)— a percentage conversion of the fluid to vapor of at least 99% at the outlet (Ul) and thereby producing a thrust force exiting from the nozzle (Tl) .

2. Satellite according to claim 1, comprising a reservoir for the fluid and wherein the fluid is demineralized water.

3. Satellite according to claim 1, wherein the swirling element is a coil.

4. Satellite according to claim 1, further comprising a pressure sensor (SP1) for measuring the pressure of the fluid.

5. Satellite according to claim 1, further comprising a temperature sensor (STI) for measuring the temperature of the fluid .

6. Satellite according to claims 4 and 5, further comprising an electronic processing unit in data communication with the pressure and temperature sensors, configured to regulate the energy supplied to the heater based on the pressure and temperature data.

7. Satellite according to claim 1, wherein the heater is electric .

8. Method for vaporizing a fluid under microgravity conditions, comprising the steps of:• providing a hollow swirling element (SI) having an inner surface and an outer surface, said swirling element (SI) being made of a thermally conductive material thermally connected with the heater and fluidly connected with a fluid inlet (II) and a fluid outlet (Ul) ;• supplying to the inlet of the swirling element a pressurized fluid to be vaporized;• generating thermal energy by means of the heater connected to the swirling element;• conveying the vaporized fluid into the chamber outlet.

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