Patent Application
20250164194
This patent application claims priority from Italian Patent Application No. 102022000003092 filed on Feb. 18, 2022, the entire disclosure of which is incorporated herein by reference.
The present invention relates to thermal control systems, and particularly to the thermal control of aerospace systems. In the present description reference will be made to this preferred, although not exclusive, field of application.
Specifically, the present invention relates to a modular evaporator for a Loop Heat Pipe (LHP) system.
LHP systems are highly efficient passive heat transfer devices based on liquid/vapor phase change in a closed and hermetically sealed loop. Fluid circulation inside the loop is produced by capillary effect. LHP systems are used as cooling devices in the thermal control of space systems.
A LHP system 100 is schematically shown in
The evaporator assembly 102 (
The capillary pump 111 is usually provided with a saddle 112 for attachment to a heat source (not shown) from which a heat flow 113 is extracted by conduction.
The capillary pump 111 includes a first micro-porous medium or primary wick 115 that surrounds, and sucks liquid from, a second porous medium or secondary wick 116 that extends throughout the compensation chamber 110 and the capillary pump 111. Secondary wick 116 is hollow and houses an inner tubing 114.
The inlet port 108 of the evaporator assembly 102 is connected to the liquid line 109 and communicates with the inner tubing 114 of the secondary wick 116.
The capillary pump 111 includes a plurality of circumferential (not shown in the Figures) and axial vapor channels 117 located on a perimeter surface of the primary wick 115 constituting a vapor-liquid interface where evaporative heat transfer takes place. Vapor flows from channels 117 to the outlet port 104, and hence to the condenser 3 through vapor line 106.
Vapor is condensed in the condenser 103, thus releasing the heat absorbed in the evaporator assembly 102. The primary wick 115 forces the liquid to return back from the condenser 103 to the evaporator assembly 102 via the liquid line 109 by capillary action. The returned liquid passes though the inner tubing 114 located inside the compensation chamber 110, cooling down the liquid in the compensation chamber 110. The compensation chamber 110 is used as a volume buffer compensator for accumulation of liquid excess during LHP operation due to temperature variations and for ensuring LHP start-up from non-operational conditions.
LHP system are simple and reliable, but suffer limitations that limit their use.
One of such limitations is the limited pumping capability of the secondary wick 116, which is not as powerful as the primary wick 115 and can pump the fluid against gravity only if the elevation difference is not more than 5-50 cm, depending on the surface tension properties of the working fluid.
Another important drawback of the limited pumping capability of the secondary wick 116 is the impossibility to create an evaporator design with multiple capillary pumps, which can cover large area for heat collecting, e. g. because the distance from the compensation chamber to the furthest capillary pump can be a restrictive factor for the LHP system performance. In this case, in fact, the elongated secondary wick can be unable to provide the necessary flow rate of liquid from the compensation chamber to the furthest capillary pump, which would lead to the primary wick dryout and, consequently, to failure in LHP operation.
Thus, the limited pumping capability of the secondary wick in the known designs of capillary pump-compensation chamber assemblies poses restrictions on the orientation of the evaporator assembly in a gravitational field and does not allow to construct long multiple evaporator assemblies.
This is clearly shown in
Another issue is that heat is extracted only by conduction through the small footprint of the evaporator saddle 12, which makes this solution unfit for extracting heath from large areas and/or a gas flow.
EP 3376348 A1, on the disclosure of which is based the preamble of claim 1, discloses modular evaporator units in which a plurality of evaporator assemblies of the type described above are series-connected and combined in different linear configurations.
An object of the present invention is to provide an improved modular evaporator assembly which overcomes the problems of the prior art LHPs specified above, and specifically allows to significantly extend the limits of LHP operation in any orientation in a gravity field.
A further object of the present invention is to create evaporator units configured to cover large areas and to grab heat from a gas flow.
The above object is attained by an evaporator assembly including at least one compensation chamber and at least one capillary pump including a primary wick, the evaporator assembly including a secondary wick extending through the compensation chamber and the capillary pump and contacting the primary wick, wherein the least one compensation chamber and the at least one capillary pump are arranged parallel to one another along respective distinct axes.
The parallel arrangement of compensation chamber(s) and capillary pump(s) removes the orientation constraints in a gravity field.
Preferably, the evaporator assembly includes a plurality of compensation chambers and a plurality of capillary pumps extending along respective axes that are distinct and parallel to one another.
By combining a plurality of compensation chambers and capillary pumps in different arrangements, it is possible to obtain an evaporator assembly in the form of a large “cold plate” that can be used to extract heat from an extended area and/or multiple sources.
According to an embodiment, the evaporator assembly includes a plurality of parallel branches, each branch including at least two compensation chambers or capillary pumps.
This further enhances the ability of the assembly to cover extended areas.
According to further embodiments of the invention, the evaporator assembly includes a first manifold connected to a liquid inlet port and to first ends of the compensation chambers, and a second manifold connecting respective second ends of the compensation chambers and first ends of the capillary pumps.
This arrangement simplifies connection and allows easy integration of compensation chambers and capillary pumps into a “cold plate” arrangement.
Optionally, where the system includes a plurality of branches each having two or more compensation chambers or capillary pumps, a third manifold connecting intermediate nodes of the branches can be used. This enhances a balanced liquid feed and improves the performance in transients.
According to a preferred embodiments, the compensation chambers are disposed at the opposite ends of the evaporator, and capillary pumps are arranged between the compensation chambers. Grouping the capillary pumps in a middle area of the evaporator assembly simplifies connection of the vapor outlet ports of the compensation chambers, and allows the capillary pumps to be integrated into a finned heat exchanger. This enables heat collection from a gas flow by convection.
The present invention also relates to an LHP system including at least one evaporator assembly as previously defined and at least one condenser.
A modular LHP system according to the present invention can be provided as a system that can be finally assembled and filled as a part of the integration activities of the spacecraft, as opposed to standard LHP systems that are supplied as a single-piece filled and sealed circuit, the integration of which is tricky on satellites and substantially impossible across a pressurized shell.
For a better understanding of the present invention, a plurality of preferred embodiments are described herein by way of non-limiting examples and with reference to the accompanying drawings, wherein:
A LHP system 1 according to the present invention, in its simplest form, is schematically shown in
As known in the art, system 1 comprises an evaporator assembly 2 and a condenser 3. An outlet port 4 of the evaporator assembly 2 is connected to an inlet port 5 of condenser 3 by a vapor line 6; an outlet port 7 of condenser 3 is connected to an inlet port 8 of evaporator assembly 2 by a liquid line 9. Evaporator assembly 2 (
According to the present invention, and as clearly shown in
In the specific embodiment of
Capillary pump 11 includes a first micro-porous medium or primary wick 15 that surrounds, directly contacts, and sucks liquid from, a second porous medium or secondary wick 16 extending throughout the evaporator 2, including compensation chamber 10 and manifolds 18, 19. Primary wick 15 has a typical pore size of 1-10 μm.
For example, primary wick 15 may be made of sintered metal ceramic, preferably from the mixture of stainless steel powder and fiber.
Secondary wick 16 is flexible and more permeable than primary wick 15, and has a typical pore size around 20-60 μm. Secondary wick 16 serves the purpose of supplying the primary wick 15 with liquid in case of transients due to rapid changes in power or condenser temperature.
For example, secondary wick can be made of stainless steel mesh or braided stainless steel fiber. Inlet port 8 is located at a midpoint of compensation chamber 10 and is connected to liquid feed inner tubing 14 extending through secondary wick 16 from inlet port 8 to capillary pump 11.
Specifically, liquid feed inner tubing 14 (also known as “bayonet tubing”) extends within secondary wick 16 through compensation chamber 10 from inlet port 8 to opposite ends thereof, pass through manifolds 18, 19 and enters opposite ends of capillary pump 11 through secondary wick 16. Therefore, capillary pump 11 communicates with inlet port directly through liquid feed inner tubing 14 and with compensation chamber 10 only indirectly through secondary wick 16.
Capillary pump 11 includes a plurality of circumferential (not shown in the Figures) and axial vapor channels 17 located on a perimeter surface of primary wick 15 constituting a vapor-liquid interface where evaporative heat transfer takes place. Vapor flows from channels 17 to outlet port 4, and hence to condenser 3 through vapor line 6.
Vapor is condensed in the condenser 3, thus releasing the heat absorbed in the evaporator assembly 2. Primary wick 15 forces the liquid to return back from the condenser 3 to the evaporator assembly 2 via the liquid line 9 by capillary action. The returned liquid passes though inner tubing 14 located inside the compensation chamber 10, cooling down the liquid in the compensation chamber 10. The compensation chamber 10 is used as a volume buffer compensator for accumulation of liquid excess during LHP operation due to temperature variations and for ensuring LHP start-up from non-operational conditions.
For proper operation, the compensation chamber 10 always has two phases inside, liquid and vapor, which are separated by a vapor-liquid interface. The compensation chamber 10 plays a critical role during transients such as rapid input power drop down or rise up and/or quick variations of the condenser temperature.
As shown in
Evaporator assembly 2 of
In the embodiment of
The secondary wick 16 extending along compensation chambers 10, capillary pump 111 and manifolds 18, 19 is shown schematically by dotted lines.
The embodiment of
The embodiment of
It is clear that this modular approach can be further extended by combining a number of elementary modules to form an evaporator assembly 2 of any dimensions.
Evaporator assembly 2 of
Manifolds 18, 19 connect respective first ends and second ends of the branches 20, 21. An additional manifold 24 connects intermediate nodes of the branches 20, 21, in between each pair of compensation chambers 10 and capillary pumps 11. Manifold 18 is connectable to liquid line 9. Vapor outlet ports 4 of each of the capillary pumps 11 are connected to a vapor manifold 25, which is in turn connectable to vapor line 6).
The parallel arrangement of the capillary pump branches 21 allows the latter to be incorporated as a tube bundle in a finned heat exchanger 22 having a pack of parallel fins 26, of which only a few are schematically depicted in
Finally, it is evident that further configurations and modifications of the evaporator assembly 2 and the resulting LHP system are possible without departing from the scope of the present invention as defined by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22425006.8 | Feb 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/051492 | 2/18/2023 | WO |
