Pump with positive displacement

Pumps – Motor driven – Electric or magnetic motor

Reexamination Certificate

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Details

C417S472000, C417S534000

Reexamination Certificate

active

06345963

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a pump with positive displacement for pumping and entrainment of a fluid in piping.
It extends to a device for thermal control of the components of a space system, such as an artificial satellite or a space station with a long service life.
Use of space systems with a long service life such as unmanned commercial satellites (for telecommunications, scientific or observation purposes etc.) or space stations, and in particular orbital stations, is tending to become considerably more frequent. As a consequence, the constraints of industrial production and cost are becoming increasingly important, as opposed to technical performance alone.
In particular, these space systems incorporate components, and in particular electronic components, which emit heat and have to be cooled, and dissipate increasingly high levels of power (with power densities which develop accordingly), and which must be kept within ever narrower temperature ranges. The distances of transport between the hot source and the cold source are also increasing. The conventional passive thermal control means (in particular by conduction or radiation) are thus insufficient.
When use of thermal conduction and radiation is insufficient, the known thermal control devices on board the satellites consist in general of heat pipes. In fact, heat pipes have the advantage of greater reliability and a longer service life than those of mechanical pumps. In fact, it should be noted that in a satellite, the service life of the equipment must be assured for several years, before launching takes place. Conventionally, this service life must be approximately ten to fifteen years.
However, heat pipes have disadvantages: in order to test them on the ground, they need to be placed on a low gradient which does not necessarily correspond to the configuration of flight, which detracts from the representativity of the tests; their dimensions need to be made to measure for integration in each space system; their rigidity is a constraint which causes problems during integration, which is sometimes difficult, or even impossible; they are very sensitive to the non-condensable gases which they produce, and their efficiency and characteristics are considerably affected by these non-condensable gases; and they have a low capacity for transporting thermal power.
In addition to heat pipes, thermal control devices have also been proposed which comprise one or a plurality of loops of heat-transfer fluid, associated with a pumping device of the capillary or mechanical type.
Pumping devices of a capillary type have a low transport capacity (limited flow rate and manometric height), in particular for tests on the ground in the presence of gravity; they are complex to start; and their tolerance for extreme operating modes is low (when the power to be transported becomes very low, or in the presence of non-condensable gases).
Mechanical pumping devices in the form of a centrifugal pump have been used in practice in certain manned missions (shuttles, capsules, stations etc) for operation of loops which use monophasic heat-transfer fluid.
In the very rare cases of unmanned missions where mechanical pumping has been selected, there has also been option for a centrifugal pump. Thus, the publication “Integrated Pump Assembly—An Active Cooling System for Mars Pathfinder Thermal Control” Gajanana C. Birar et al, SAE TECHNICAL PAPER SERIES 961489 pp1-8, 26th International Conference on Environmental Systems, Monterey, Calif., Jul. 8-11, 1996, explains that use of a positive displacement pump was rejected, in favour of a centrifugal pump, for the thermal control loop of the Mars “Pathfinder” probe. This probe was qualified for a service life of a few months.
In addition, a centrifugal pump is not appropriate in the case of a diphasic fluid loop for a space system such as a commercial satellite, since pumps of this type have high electrical consumption, a large size, and a high cost.
Pumps with positive displacement (U.S. Pat. No. 2,797,646, U.S. Pat. No. 4,585,397, U.S. Pat. No. 4,421,464) incorporate many moving parts in dynamic contact (pumps with a reciprocal displacement pumping unit, such as a piston or deformable unit) which are subject to wear, in particular the intake and output valves of the manifold and the parts for transmission of movement to the pumping unit, the service life of which cannot be determined on the ground other than by service life duration tests, which in general are statistical. The performance levels of this type of pump also vary considerably according to the wear, and thus deteriorate over a period of time. In addition, these pumps generate significant stresses on the materials, as well as vibrations and unbalanced forces.
In particular, U.S. Pat. No. 4,421,464 describes a pump pumping liquid helium, comprising bellows which are actuated by an electromagnetic motor, which is totally immersed in the liquid helium. Since the mobile part of the pump and of the motor are connected by flexible electrical connections, and the valves are diaphragm valves, a pump of this type cannot be qualified for space applications with a long service life. In addition, it is not applicable to pumping of fluids such as heat-transfer fluids (for example ammonia) of the diphasic fluid thermal control loops for space systems, with which the components of the motor are not compatible.
Thus, hitherto, it has been considered that pumps with positive displacement cannot be qualified for space applications with a long service life.
In addition, pumping of a thermal control heat-transfer fluid, in particular in a loop with a diphasic fluid, of a space system, requires particularly stringent performance levels, including: a pumping height of several metres, high resistance to static pressure (which can be as much as 160.10
5
Pa, with permanent deformation, and 80.10
5
Pa without permanent deformation), a flow rate of several grammes per second, and a reduced energy consumption and size. In addition, it must be possible to vary the power to be transported within an extensive range, and to regulate the flow rate easily (i.e. using an electronic system which is simple, reliable and has a small size).
Thus, the hydrostatic pressure generator described by U.S. Pat. No. 3,657,930, the pumping unit of which consists of a piezoelectric crystal, does not fulfil these criteria, since the amplitude of displacement of a pumping unit of this type is not sufficient. In addition, in this case also, flexible electrical connections must be provided in order to supply the crystal with electrical energy through the wall of the cylinder, thus causing problems of service life. Also, U.S. Pat. No. 3,508,848 describes a single-effect diaphragm pump, with vortex fluid diodes, which is actuated by a pneumatic oscillator. This solution therefore requires a pneumatic external alternative pressure source, to which the aforementioned problems of suitability and service life apply, and which does not make it possible to achieve the above-described performance levels.
In practice therefore, no mechanical pump exists which can be qualified for a long service life, and is designed to be able to be integrated in a space system, and in particular an unmanned commercial satellite or a space station, for pumping of a thermal control heat-transfer fluid, in particular in a diphasic fluid loop.
In particular, even if use of diphasic fluid thermal control loops is theoretically possible in unmanned commercial satellites, practical implementation of these loops is impeded by the fact that there is no corresponding qualified pump.
SUMMARY OF THE INVENTION
The object of the invention is thus to eliminate these disadvantages, and to provide a pump with positive displacement which can be integrated in a space system such as a satellite or a space station, and the service life of which in space can be guaranteed on the ground for several years, and in particular for at least ten years.
The object of the invention is also to provide a pump of this type, whic

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