FR3156490A1 - Pump for cryogenic fluid - Google Patents

Abstract

A pump for cryogenic fluid, comprising a compressor (31) configured to draw in an incoming flow (E) of cryogenic fluid arriving upstream and to discharge downstream a discharge flow having a pressure greater than the pressure of the incoming flow (E), a motor (41) configured to drive the compressor (31), and a service line (60) configured to take off a portion of the discharge flow, forming a service flow (R), and circulating in and/or along the motor (41) to cool the motor (41), wherein the service line (60) comprises at least one pressure drop device (64, 65) configured to reduce the pressure and/or increase the temperature of the service flow (R) so as to cause at least 50%, possibly at least 80%, possibly still at least 90%, of the service flow (R) to pass from the liquid state to the gaseous state. Fig. 1.

Description

Pump for cryogenic fluid

This disclosure relates to a pump for cryogenic fluid. Such a pump may in particular be used in a circulation circuit for liquid propellant in an engine, for example a rocket engine in the space sector. Such a pump may nevertheless also be used in the aeronautical sector for hydrogen aircraft engines or in the maritime sector or ground equipment.

Liquid hydrogen is a commonly used propellant in the space sector. However, using hydrogen in an engine such as a rocket engine poses numerous technical implementation challenges. In particular, this hydrogen is generally stored and distributed in a liquid state, and therefore at cryogenic temperatures, before possibly being reheated before being admitted into the engine's combustion chamber.

One of the difficulties encountered concerns the pump in this supply circuit. In particular, while the pump motor can be easily cooled by taking a portion of the pumped liquid propellant and circulating it in a service line, the presence of liquid in the motor air gap creates a significant loss of motor performance due to the significant torque consumption caused by the shearing of this liquid during motor rotation. Thus, to the first order, these shear losses are proportional to the density of the fluid and its coefficient of friction.

There is therefore a real need for a cryogenic fluid pump which is free, at least in part, from the drawbacks inherent in the aforementioned known configurations.

This disclosure relates to a cryogenic fluid pump, comprising
a compressor, configured to suck in an incoming flow of cryogenic fluid arriving upstream and to discharge downstream a discharge flow having a pressure greater than the pressure of the incoming flow,
a motor, configured to drive the compressor, and
a service line, configured to take a portion of the discharge flow, forming a service flow, and circulating in and/or along the engine to cool the engine,
wherein the service line comprises at least one pressure drop device configured to reduce the pressure and/or increase the temperature of the service flow so as to change from the liquid state to the gaseous state at least 50%, possibly at least 80%, possibly still at least 90%, of the service flow.

Thus, thanks to this specially dimensioned pressure drop device, the pressure of the service flow is reduced and/or its temperature is increased so that a significant part of the service flow passes into the gaseous state. As a result, its density and viscosity decrease drastically, which reduces the energy consumption by shear during engine rotation. For example, in the case of hydrogen, under cryogenic conditions, the density of gaseous hydrogen is approximately six times lower than that of liquid hydrogen while the viscosity of gaseous hydrogen is also approximately six times lower than that of liquid hydrogen.

It is thus possible to cool the pump motor without significantly penalizing its efficiency, which improves the pump's performance.

In this disclosure, cryogenic fluid is understood to mean a fluid whose temperature is less than 120 K, possibly less than 80 K, in particular less than 30 K.

In some embodiments, the cryogenic fluid is a liquid propellant, for example liquid hydrogen H2, liquid oxygen O2, liquid nitrogen N2, liquid helium He or liquid methane CH4.

In some embodiments, the compressor comprises a rotating impeller, for example a centrifugal impeller.

In some embodiments, the compressor includes an inducer. Such an inducer allows the incoming flow to be drawn in and accelerated before being compressed in the rotating impeller.

In some embodiments, the compressor is configured to increase the discharge flow rate to a pressure greater than 10 bar, possibly greater than 20 bar.

In some embodiments, the discharge rate is between 10 and 160 g/s.

In some embodiments, the motor is an electric motor. Such a configuration is particularly suitable for a fuel feed pump because it allows easy and precise control of the flow of fuel supplied. However, other types of drive are possible: for example, the pump could also be a turbopump.

In some embodiments, the service line begins at the rear of the compressor wheel.

In some embodiments, the service line runs in the air gap between the stator and rotor of the motor.

In some embodiments, the service flow rate is configured to assist in the lubrication of rotating components of the pump, for example one or more bearings.

In some embodiments, the service line passes through a bearing and/or roller of the pump. The service flow can thus lubricate and cool this bearing or roller.

In some embodiments, the service flow is configured to participate in axial balancing of the compressor.

In some embodiments, the service flow rate is between 8 and 20%, possibly between 10 and 15% of the discharge flow rate.

In some embodiments, at least one pressure drop device is a set of at least one fin provided on the back of the compressor wheel. Such fins, operating as a counter-pump, make it possible both to reduce the pressure of the service flow and to increase its temperature by shear. In addition, this transformation is progressive from the outside to the inside of the wheel.

In some embodiments, at least one pressure drop device is a local restriction of the service line. Such a restriction allows the pressure of the service flow to be reduced, substantially isothermally.

In some embodiments, said local constriction is a smooth seal.

In some embodiments, said local constriction is a labyrinth seal.

In some embodiments, said throttle is provided, in the service line, upstream of the first bearing supporting the rotating shaft of the compressor.

In some embodiments, said restriction is provided at an axial portion of the compressor extending rearward of the wheel.

In some embodiments, said restriction is provided along the outer edge of the compressor wheel. In this way, the pressure is suddenly dropped at the inlet of the service line.

In some embodiments, the service line terminates upstream of the compressor. Thus, the service flow is not lost.

In some embodiments, the service line is configured to open into a cryogenic fluid reservoir located upstream of the pump. In particular, the gaseous fraction of the service flow thus reinjected can contribute to pressurizing the cryogenic fluid reservoir.

In some embodiments, the service line opens into a reinjection cavity surrounding a pump inlet duct located upstream of the compressor.

In some embodiments, the service line passes through a liquefaction device before emerging upstream of the compressor. Such a liquefaction device allows only liquid to be reinjected upstream of the compressor. However, such a liquefaction device is not essential: indeed, if the service flow reinjected into the reinjection cavity includes a portion of gas, the latter may contribute to the pressurization of the cryogenic fluid reservoir.

In some embodiments, the liquefaction device comprises a heat exchanger.

In this presentation, the terms "axial", "radial", "tangential", "internal", "external" and their derivatives are defined in relation to the main axis of the pump; "axial plane" means a plane passing through the main axis of the pump and "radial plane" means a plane perpendicular to this main axis; the terms "upstream" and "downstream" are defined in relation to the circulation of the fluid in the pump; the terms "front" and "rear" are defined along the main axis, the front of the pump being located on the side of its inlet duct. In addition, when they relate to numerical values, the terms "lower", "upper", "between" and their derivatives are interpreted in the broad sense, that is to say, including the case where the value in question is equal to the announced limit.

The above-mentioned features and advantages, as well as others, will become apparent from the following detailed description of examples of embodiments of the proposed pump. This detailed description refers to the attached drawings.

The attached drawings are schematic and are intended primarily to illustrate the principles of the presentation.

In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different embodiments but having a similar function are identified in the figures by numerical references incremented by 100, 200, etc.

FIG. 1 There FIG. 1 is a sectional plan of a first example of a pump.

FIG. 2 There FIG. 2 is an enlargement of zone II of the FIG. 1 .

FIG. 3 There FIG. 3 is a pressure-temperature diagram of the service flow rate.

FIG. 4 There FIG. 4 is a partial sectional plan of a second example pump.

FIG. 5 There FIG. 5 is a partial sectional plan of a third example of a pump.

FIG. 6 There FIG. 6 is a partial sectional plan of a fourth example of a pump.

FIG. 7 There FIG. 7 is a sectional plan of a fifth example of a pump.

In order to make the disclosure more concrete, examples of pumps are described in detail below, with reference to the accompanying drawings. It is recalled that the invention is not limited to these examples.

There FIG. 1 represents, in section along a vertical plane passing through its main axis A, a pump 20 mounted on a main face 11 of a supply system, here a tank 10. Naturally, the pump 20 could be mounted on any other supply device, for example a propellant supply line.

In the present example, the tank 10 is a tank of liquid hydrogen stored at approximately 20 K and at approximately 1 bar. The tank 10 may also comprise a volume of gaseous hydrogen, this volume of gas having the main function of pressurizing the volume of liquid hydrogen.

The main face 11 of the tank 10 comprises a supply orifice 12 bordered by a fixing flange 13, this fixing flange 13 participating in the fixing of the pump 20, as will be described below.

The pump 20 comprises an intake duct 21, extending axially and open to the supply orifice 12 of the tank 10: this intake duct 21 allows the cryogenic fluid to enter the pump 20 and thus leads to a compressor 31.

In addition, the front end of the intake duct 21, forming part of a front part 53 of the casing 50 of the pump 20, has a fixing interface 57 allowing the pump 20 to be mounted against the reservoir 10. The fixing interface 57 comprises on the one hand a fixing flange 58, annular, applied and fixed against the fixing flange 13 of the reservoir 10. The fixing interface 57 comprises on the other hand a cylindrical end piece 59, projecting axially from the fixing flange 58 of the pump 20, engaged in the supply orifice 12 of the reservoir 10, the diameter of the cylindrical end piece 58 corresponding to the diameter of the supply orifice 12.

The compressor 31 comprises a rotor 32 rotating around the main axis A within a stator 35. The rotor 32 includes in a single piece an inductor 33 upstream followed by a centrifugal impeller 34 downstream. The stator 35 includes for its part a vein wall 36, extending the wall of the intake duct 21 downstream along the centrifugal impeller 34, and a volute 37, substantially annular, formed opposite the outlet of the centrifugal impeller 34 in a structural block 55 of the front part 53 of the casing 50.

The rotor 32 of the compressor 31 is driven in rotation by an electric motor 41 arranged at the rear of the compressor 31. The electric motor 41 thus comprises a rotor 42, driving the rotor 32 of the compressor 31 by means of a rotary shaft 43, and a stator 44, mounted in a main portion 51 of the casing 50 of the pump 20. The main portion 51 is attached against the structural block 55 of the front part 53 of the casing 50 and therefore integral with the latter. The rotary shaft 43 is supported by two bearings 45, 46, for example bearings. The front bearing 45 is carried to the stator 44 by a radial wall 47, fixed to the main portion 51 of the casing 50, delimiting within the casing 50 a space housing the compressor 31 and a space housing the motor 41. The rear bearing 46 is carried to the stator 44 by a rear cover 52 of the casing 50, attached against the main portion 51 of the casing 50 and therefore integral with the latter.

When the motor 41 drives the rotor 32 of the compressor 31, liquid hydrogen is sucked into the intake duct 21 and then into the compressor 31, thus constituting an inlet flow E. A main part of the discharge flow, obtained following the compression of the inlet flow E by the compressor 31, is directed towards an outlet duct (not shown) of the pump 20, thus constituting an outlet flow. In the present example, the compressor 31 brings the discharge flow to a pressure of the order of 10 bar.

However, a secondary portion of the discharge flow is diverted to a service line 60, thus constituting a service flow R. The service line 60 begins with a gap 61 separating the rear face of the centrifugal impeller 34 and the radial wall 47; the service flow R then passes through the front bearing 45, circulates in the air gap 41e between the rotor 42 and the stator 44 of the motor 41, passes through the rear bearing 46 and reaches a rear cavity 62 formed in the cover 52 of the casing 50. The service flow R then passes through a discharge conduit 63 extending from the cover 52 of the casing 50 to the reservoir 10 into which it opens.

The service flow rate R thus contributes to the axial balancing of the compressor 31, to the lubrication and cooling of the bearings 45, 46, and to the cooling of the electric motor 41.

More precisely, the service flow R is taken in the liquid state at the outer edge of the centrifugal impeller 34, at the inlet of the gap 61, then passes at least partially to the gaseous state before reaching the air gap 41e of the motor 41.

In this first example, as is best seen on the FIG. 2 , this passage to the gaseous state is driven by two pressure loss devices: fins 64 arranged at the rear of the hub 34a of the centrifugal impeller 34, in the gap 61, and a smooth bearing 65 forming a constriction between the radial wall 47 of the stator 44 and an axial extension 34b of the hub 34a of the centrifugal impeller 34.

The transformations caused by these pressure loss devices 64, 65 on the service flow rate R are visible on the pressure-temperature diagram of the FIG. 3 . On this diagram, curve 91 corresponds to the vaporization curve of the cryogenic fluid, here hydrogen, and trajectory 92 is that of the service flow rate R between points P1, P2, P3 and P4 of the service line 60.

The fins 64 rotating in solidarity with the centrifugal impeller 34, they slow down the service flow R in the gap 61 and heat it by shearing, which corresponds to the segment P1-P2 on the FIG. 3 , bringing the service flow rate R closer to the vaporization curve 91 both in pressure and temperature. Thus, in the present example, this first pressure loss device 64 increases the temperature of the propellant by 5 K and decreases its pressure until it is brought to less than 0.5 bar of the vaporization curve 91.

The constriction constituted by the plain bearing 65, represented by the segment P2-P3 on the FIG. 3 , for its part causes a reduction in the pressure of the service flow rate R, practically isothermally, resulting in crossing the hydrogen vaporization curve 91 and therefore in the transition to the gaseous state of the service flow rate R. A fraction of 50 to 100% of the propellant then passes to the gaseous state.

The passage through level 45, corresponding to segment P3-P4 of the FIG. 3 , for its part causes an increase in the temperature of the service flow R, the latter effectively cooling the bearing 45, as well as a small reduction in its pressure, thus moving it away from the vaporization curve 91 and ensuring that a significant part of the service flow R is in the gaseous state before circulating in the air gap 41e of the motor 41.

There FIG. 4 illustrates a second example of a pump 120 similar to that of the first example except that the plain bearing 165 provided between the axial extension 134b of the hub 134a of the centrifugal impeller 134 and the wall 147 of the stator is longer, which results in a greater pressure loss of the service flow rate R and therefore a greater reduction in pressure.

There FIG. 5 illustrates a third example of pump 220 similar to that of the first example except that a labyrinth bearing 266 is provided between the axial extension 234b of the hub 234a of the centrifugal impeller 234 and the wall 247, replacing the plain bearing of the previous examples. This labyrinth bearing 266 allows a greater pressure drop of the service flow rate R and therefore a greater pressure reduction.

There FIG. 6 illustrates a fourth example of a pump 320 similar to that of the first example except that the service line 360 comprises another type of pressure drop device. Indeed, in this example, a labyrinth bearing 367 is provided between the external edge of the hub 334a of the centrifugal impeller 334 and the annular surface of the structural block 355 located behind the volute 337; this labyrinth bearing is therefore located just upstream of the gap 361, at the inlet of the service line 360. Thus, in this example, the labyrinth seal 367 is sized to allow on its own the passage to the gaseous state of at least 50% of the service flow rate R.

On the other hand, in this fourth example, the centrifugal impeller 334 is devoid of vanes in the gap 361 and of a bearing, smooth or labyrinth, downstream of the gap 361.

There FIG. 7 illustrates a fifth example of a pump 420 similar to that of the first example except that the discharge conduit 463 is connected differently.

Indeed, in this fifth example, the front part 453 of the casing 450 comprises, in addition to the structural block 455, a structural wall 454, generally cylindrical and extending forward from the structural block 455, and a skirt 456, axisymmetric, extending from the structural block 455, first radially inwards then axially forwards, so as to form the vein wall and the wall 422 of the intake duct 421.

A reinjection cavity 471 extends concentrically between the intake duct 421 and a structural wall 454 of the front part 453 of the casing 450. The discharge duct 463 then opens at the bottom of this reinjection cavity 471. A convective circulation C in the reinjection cavity 471 makes it possible to take cryogenic fluid from the reservoir 410 and to circulate it from the internal side to the external side of the reinjection cavity 471, diluting in the process the service flow R reinjected into the reinjection cavity 471, and discharging the whole into the general volume of the reservoir 410.

In addition, before opening into the reinjection cavity 471, the discharge conduit 463 passes through a heat exchanger 468 which allows the reinjection flow R to be reliquefied before its reinjection upstream of the compressor 431.

Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated/mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims (12)

Pump for cryogenic fluid, including
a compressor (31), configured to suck in an incoming flow (E) of cryogenic fluid arriving upstream and to discharge downstream a discharge flow having a pressure greater than the pressure of the incoming flow (E),
a motor (41), configured to drive the compressor (31), and
a service line (60), configured to take a portion of the discharge flow, forming a service flow (R), and circulating in and/or along the engine (41) to cool the engine (41),
wherein the service line (60) comprises at least one pressure drop device (64, 65) configured to reduce the pressure and/or increase the temperature of the service flow rate (R) so as to change from the liquid state to the gaseous state at least 50%, possibly at least 80%, possibly still at least 90%, of the service flow rate (R). A pump according to claim 1, wherein the compressor (31) comprises a rotating impeller, for example a centrifugal impeller (34). A pump according to claim 1 or 2, wherein the motor is an electric motor (41), and
in which the service line (60) circulates in the air gap (41e) between the stator (44) and the rotor (42) of the motor (41). Pump according to any one of claims 1 to 3, in which the service flow rate (R) is between 8 and 20%, possibly between 10 and 15%, of the discharge flow rate. Pump according to any one of claims 1 to 4, in which at least one pressure loss device is a set of at least one vane (64) provided on the back of the wheel (34) of the compressor (31). Pump according to any one of claims 1 to 5, in which at least one pressure loss device is a local restriction (65) of the service line (60). A pump according to claim 6, wherein said local restriction is a smooth seal (65) or a labyrinth seal (266). Pump according to claim 6 or 7, wherein said constriction (65) is provided at an axial portion (34b) of the compressor (31) extending to the rear of the wheel (34). Pump according to claim 6 or 7, wherein said restriction (367) is provided along the outer edge of the wheel (334) of the compressor (331). Pump according to any one of claims 1 to 9, in which the service line (60) is configured to open into a cryogenic fluid reservoir (10) located upstream of the pump (20). Pump according to any one of claims 1 to 9, in which the service line (460) opens into a reinjection cavity (471) surrounding an intake duct (421) of the pump (420) located upstream of the compressor (431). Pump according to any one of claims 1 to 11, in which the service line (460) passes through a liquefaction device (468) before opening upstream of the compressor (431).