EP2421657A1 - Nozzle capable of maximizing the quantity of movement produced by a two-phase flow through the relief of a saturating flow - Google Patents

Abstract

The invention relates to a nozzle (10) capable of relieving a saturated flow (D), comprising a convergent (2), a throat (3), a tube (4) and a mixing element (5) downstream from said throat (3) capable of mixing the vapor and liquid phases of the saturating flow.

Description

 Nozzle capable of maximizing the amount of movement produced by a two-phase flow coming from the expansion of a saturating flow

Background of the invention

The invention lies in the field of ejectors and nozzles used as expansion members in turbines.

In general, these devices are designed to convert the energy of pressure into kinetic energy, this kinetic energy being used to produce a work, for example to rotate augers, turbine blades or, in the case of ejectors , to suck a flow.

These devices are commonly used to relax steam or very subcooled liquids. However the use of ejectors or nozzles to relax saturating liquids remains marginal, the appearance of a vapor phase significantly limiting the amount of movement of the two-phase liquid / vapor after expansion.

Figures 1 to 4 illustrate this phenomenon. Figure 1 shows a nozzle 1 according to the state of the art. This nozzle 1 comprises a convergent 2, a neck 3, and a moderate angle divergent 4. A saturating liquid flow D enters the nozzle 1 through the convergent 2, and travels this nozzle from right to left through the neck 3 then the moderate divergence 4. FIG. 2 shows the abscissa of the measured pressure of the flow rate D during its course in the nozzle 1 of FIG. 1, and the ordinate the mass velocity pV, product of the density p by the velocity V. Note that this mass velocity is maximum at the neck 3, (marked by the vertical line). FIG. 3 represents the evolution of the homogeneous liquid-vapor density (p, expressed in kg / m ³ ) of the flow rate D as a function of the pressure (P, expressed in MPa) during its course in the nozzle i. These results, obtained by calculation, teach that the density p decreases with the appearance of the vapor phase during the pressure decrease along the nozzle.

FIG. 4 represents the evolution of the speed (V, expressed in m / s) of the flow rate D as a function of the pressure (P, expressed in MPa) during its course in the nozzle 1.

These results, obtained by tests, show that the real increase in the speed of the two-phase mixture resulting from the drop in density due to the partial vaporization of the liquid (dashed curve) deviates significantly from the theoretical evolution (curve in full line).

These poor performances have severely limited the development of two-phase turbines, some even thinking that these are not of industrial interest. The invention aims to overcome the disadvantages of that of the prior art by proposing, in a first aspect, a nozzle capable of maximizing the amount of movement produced by a two-phase liquid / vapor flow from the expansion of a saturating liquid.

Furthermore, it is known that ejectors such as two-phase turbines can achieve higher energy performance especially for refrigeration systems or heat pumps with isenthalpe expansion valves.

To date, turbines and ejectors are widely used to relax liquids that remain liquid or vapors that remain mainly vapor; these thermodynamic evolutions of relaxation approach the ideal isentropic relaxation. This isentropic expansion fixes, for a given pressure difference and for the expansion of a liquid, the minimum fraction of vapor that can be generated from the expansion of this high pressure saturating liquid. FIG. 5 illustrates a vapor compression refrigeration cycle, in the form of a T / S diagram, in which the mass entropy S

(expressed in kJ / kg.K) and the temperature T (expressed in Kelvin) are respectively represented on the abscissa and on the ordinate. This diagram illustrates:

between the states 101 and 102, a compression of the refrigerant in the vapor phase, from the low evaporation pressure to the high condensation pressure; and between the states 102 and 103, a desuperheating phase of the steam followed by a condensation in which the refrigerant becomes a saturating liquid.

The transition between point 103 (high condensing pressure) and point 104 _ith (low evaporation pressure) illustrates the isenthalpe expansion of the current state of the art. The amount of steam generated during this expansion is maximum.

Such isenthalpe expansion is far from achieving the performance of the ideal isentropic expansion, illustrated in FIG. 5 by the transition between the high condensation pressure (point 103) and the theoretical point (point 1O4 _IS ). In the case of isentropic expansion, the amount of steam generated is minimal and the difference in the evaporation entropy of the saturating liquid is much greater than in the case of the isenthalpe expansion.

It is recalled that an isenthalpe expansion is typically done in an orifice whose upstream and downstream sections are much greater than the size of the orifice, the sudden narrowing and the sudden enlargement on either side of the orifice allowing create a significant loss of charge complementarily to that of the orifice.

In a turbine or in an ejector, it is known to limit the pressure drop by bringing the fluid to the neck by a convergent. Tests and some scientific articles show that the relaxation is almost isentropic in the convergent, up to the neck.

It is then fundamental to note that the speed of the liquid downstream of the neck remains substantially identical to that it was at the neck, in other words that the pressure energy is not converted into kinetic energy.

This phenomenon is illustrated by FIGS. 6A to 6C which will now be described. Figure SA shows an ejector 60 of the prior art. This ejector mainly comprises a nozzle i as described with reference to FIG. 1 and a hollow body 62. The role of the nozzle 1 is to relax a high-pressure flushing liquid flow PFISI up to a theoretical low pressure Pth_ _F is3 by increasing its speed, in order to cause a flow rate of fluid F2 at pressure PF2S2 significantly lower than PFISI . This fluid flow rate _F 2 is usually a steam flow rate from the evaporation of a fluid at evaporation pressure PF2S2 less than the pressure P _F isi and the pressure Pτh_Meiss of the mixture after ejection.

The hollow body 62 has a convergent 63, a mixing chamber 64 of constant section S4 and a conical divergent 65 of maximum section S5.

The flow Fl enters the nozzle 1 at the section S1 and expands into a two-phase primary flow until it leaves the section S3.

We notice :

VFISI: the speed of the primary flow Fl at section S1; - PFISI: the pressure of the primary flow Fl at the section S1;

- Vτ _h _Fis3: the theoretical speed of the primary flow Fl at section S3;

- Pτ _{h ^} Fis3: the theoretical pressure of the primary flow Fl at section S3. The flow F2 enters the ejector 60 by a section S2. It is driven and accelerated in a flow called "secondary" by the primary flow Fl because of the pressure difference between sections S3 and S2.

We notice ; - V _F 2S2; The speed of the secondary flow F2 at section S2;

Pp2 _S 2: the pressure of the secondary flow F2 at section S2; and

- Vτh _^ F2S3: the theoretical speed of the secondary flow F2 at section S3. The primary flow Fl and secondary flow F2 begin to mix in the convergent 63 at constant pressure and then enter the mixing chamber 64 in which a biphasic mixture is formed at theoretical velocity Vτh_Meis4 and theoretical pressure Pτhj "s4- The divergent 65 forms a diffuser for decelerating the two-phase mixing of fluid flows Fl and F2 up to a speed Vτh_Meiss and transforming the kinetic energy into potential energy pressure. The pressure of the mixture increases in the divergent 65 to a theoretical outlet pressure Pm _. Meiss-

But in reality, it is found that the actual velocity VBusei_Fis3 of the primary flow Fl measured at the outlet of the neck 3 is much lower than the theoretical velocity VVh_Fis3-

Consequently: the drive of the secondary flow F2 is less than in theory;

- The actual pressure P ususeoieis * of the mixture at the outlet of the mixing chamber 64 is less than the theoretical pressure Ptn_Meis4; thereby :

- The actual output pressure Pβuseijieiss is less than the theoretical output pressure Pnoieiss.

This state of affairs is represented in FIGS. 6B and 6C on which the pressures and speeds defined above are respectively represented, the theory being represented in solid line, and the performance of the prior art in bold dashed line. The invention also relates to an ejector which does not have the disadvantages of the current state of the art.

Object and summary of the invention

More specifically, the invention relates to a nozzle capable of relaxing a saturating flow. This nozzle comprises a convergent, a neck, a tube, and a mixing element located in the tube, downstream of the neck, the mixing element being able to split the saturating liquid phase to mix with the vapor phase.

Thus, and in a general manner, the nozzle according to the invention aims to mix the vapor and liquid phases of the saturating liquid downstream of the neck, whereas in the current state of the art, it is sought to treat these two phases separately However, the Applicant has found that in the nozzles of the prior art, the liquid and the vapor are separated at the outlet of the neck, at the level of enlargement. Downstream of the neck, she noted a slippage between the liquid phase and the vapor phase: the vapor phase seeking to occupy the entire volume allotted to it spreads around the periphery of the central liquid flow. Therefore, the liquid jet at the outlet of the convergent is not accelerated by the steam formed by the trigger, the latter being placed at the periphery of the liquid jet.

The invention therefore proposes mixing the vapor and liquid phases, which, as will be demonstrated later, considerably increases the amount of movement produced by the two-phase liquid / vapor flow coming from the expansion of the saturating liquid.

In a particular embodiment, the tube is a divergent section increasing, for example conical. The opening of this cone may be chosen to maintain the constant mass flow rate during the acceleration of the two-phase flow rate.

Alternatively, the moderate conical divergent 4 may be replaced by a cylindrical tube.

In a particular embodiment, the convergent nozzle according to the invention comprises a needle to vary the neck section.

In a particular embodiment, the aforementioned mixing element is a fixed helix.

In a variant, this helix can be mobile.

In another embodiment of the invention, the mixing element may comprise forms of revolution of increasing sections.

The nozzle according to the invention can be used in many devices, and in particular in an ejector, in a Hero turbine, in a Pelton turbine, or in a Francis turbine. More specifically, the invention also relates to an ejector comprising a body crβux _r this hollow body having a convergent, a mixing chamber and a divergent, this ejector comprising, in the convergent, an expansion nozzle as mentioned above, the nozzle being adapted to to relax a primary flow of saturating liquid, in order to cause a secondary flow introduced into the convergent around this nozzle.

The invention thus makes it possible to satisfactorily mix the vapor and liquid phases of the primary flow, and to drive the secondary flow much more efficiently than in the ejectors of the state of the art. This gives a real output pressure very close to the theoretical output pressure.

The invention also relates to a Hero turbine comprising one or more hollow arms movable in rotation about an axis, this axis supplying the hollow arm (s) with a saturating liquid, this turbine comprising an expansion nozzle as mentioned above in FIG. end of each of the hollow arms.

The invention also relates to a Pelton turbine comprising at least two buckets integral with a wheel that is rotatable about an axis, this turbine comprising at least one expansion nozzle as mentioned above, capable of projecting a two-phase jet in direction of the buckets.

The invention also relates to a Francis-type turbine comprising at least one expansion nozzle as mentioned above and capable of projecting a two-phase jet towards the inside of a rotor of said turbine. In a particular embodiment, the ejector according to the invention comprises a second mixing element, partly in the mixing chamber and partly in the diverging portion. This characteristic favors the mixing of the two-phase flow of the primary flow at the outlet of the nozzle with the secondary flow. Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character, in the figures: - Figure 1 shows a nozzle of the prior art; Figures 2 to 4 show pressure and velocity values of a saturating flow flowing in the nozzle of Figure 1; Fig. 5 is a T / S diagram illustrating a vapor compression refrigeration cycle; Figure 6 shows an ejector of the prior art; FIGS. 6B and 6C show pressure and velocity values of the primary and secondary flows flowing in the ejector of FIG. 6A; Figures 7A and 7B show a nozzle according to a particular embodiment of the invention;

FIG. 8 represents a mixing element that can be used in the invention;

FIG. 9 shows pressure and velocity values of a saturating flow flowing in the nozzle of FIGS. 7A and 7B; FIGS. 10A and 10B show a Hero turbine according to a first particular embodiment of the invention; FIG. 10C schematically represents a Hero turbine according to a second particular embodiment of the invention;

FIG. 11 represents a Pelton turbine according to a particular embodiment of the invention; - Figure 12 shows a Francis turbine according to a particular embodiment of the invention; Figure 13A shows an ejector according to a particular embodiment of the invention; and

FIGS. 13B and 13C show pressure and velocity values of the primary and secondary flows flowing in the ejector of FIG. 13A,

Detailed description of an embodiment

Figures 7A and 7B show a nozzle 10 according to the invention. It is distinguished from the nozzle 1 of Figure 1 in that it comprises a mixing element 5 downstream of the neck 3, able to create a homogeneous mixture of vapor and liquid phases in the moderate divergent 4, this having the consequence of considerably increase the amount of movement of the phase flow at the output of the divergent 4. In the embodiment described herein, the moderate divergent 4 of the nozzle 10 according to the invention has a slightly flared conical shape to keep the mass flow rate constant during the acceleration of the two-phase flow rate. In the embodiment described here, the mixing element 5 is constituted by a fixed helix shown in FIG.

FIG. 9 represents, in solid bold line, the evolution of the speed V of the flow rate D as a function of the pressure during its course in the nozzle 10. This figure repeats the curves of FIG. 4 for comparison purposes. It makes it possible to demonstrate that the introduction of the mixing element 5, in the form of a helix, downstream of the neck 3 makes it possible to approach the theoretical curve (in solid line).

Returning to FIGS. 7A and 7B, the speed of the flow D at the outlet of the nozzle 10 can be adjusted by varying the outlet diameter δ 6 of this nozzle. In the example of FIG. 9, the flow rate at the outlet of the nozzle 10 according to the invention is equal to 110 m / s, much greater than the speed of 20 m / s obtained in the absence of mixer 5.

It is known that the energy available in the nozzle is given by the relation V ^2/2. Consequently, the available kinetic energy (6050 J / kg) at the outlet of the nozzle 10 according to the invention is approximately 30 times greater than that obtained at the outlet of the nozzle 1 of the prior art (200 J / kg).

The nozzle 10 according to the invention may in particular be integrated in a turbine or in a two-phase ejector. FIGS. 10A and 10B respectively show, in front view and in plan view, a two-phase turbine 20 of the Hero type according to the invention.

In the embodiment described here, this turbine 20 comprises two hollow arms 21, each of these arms having at its end, a nozzle 10 according to the invention.

The hollow arms 21 are rotatable about a hollow axis 22 adapted to supply these hollow arms with a saturating liquid. It will be recalled that in a Hero-type turbine, the work is recovered directly on the axis 22 thanks to the impetus of the jets that start tangentially from the arms 21.

FIG. 10C shows another turbine 20 'of the Hero type according to the invention, with eight hollow arms 21' distributed around an axis 22 'for supplying saturating liquid, each arm 21' comprising a nozzle 10 conforming to FIG. invention, not shown.

FIG. 11 represents a two-phase turbine 30 of the Pelton type according to the invention. This turbine 30 comprises two nozzles 10 according to the invention, the two-phase jets at the outlet of these nozzles coming to hit buckets 31 integral with a movable wheel 32 to set it in motion.

FIG. 12 represents a two-phase turbine 40 of the Francis type according to the invention. This turbine 40 comprises eight nozzles 10 according to the invention, the two-phase jets at the outlet of these nozzles being directed towards the inside of a rotor 42.

FIG. 13 shows an ejector 70 according to the invention.

It is distinguished from the ejector 60 of the state of the art, in that it comprises, in replacement of the nozzle 1, a nozzle 10 according to the invention, the helix 5 generates a vortex for mixing the vapor and liquid phases of the primary flow Fl.

The pressures and speeds obtained in the ejector 70 according to the invention are respectively represented in FIGS. 13B and 13 C. In particular, it can be seen that by using the nozzle 10, the actual velocity V _BuS eio _^ Fis3 of the primary flow Fl at section S3 of this nozzle 10 is very close to the theoretical velocity Vτ _h _ _F is ₃ -

Moreover, in the embodiment described here, the ejector 70 according to the invention comprises a second fixed helix 5 that can be placed in or out of the mixing chamber 64.

This second helix favors the mixing of the phases of the two-phase flow of the primary flow Fl with the secondary flow F2.

Claims

REVENDICAΉQNS 1. Nozzle (10) capable of relaxing a saturating flow (D), said nozzle comprising a convergent (2), a neck (3) and a tube (4), characterized in that it comprises, in said tube, a mixing element (5) downstream of said neck (3) capable of splitting the saturating liquid phase to mix with the vapor phase. 2. Expansion nozzle (10) according to claim 1, characterized in that said tube (4) is a divergent section increasing. 3. Expansion nozzle (10) according to claim 1 or 2, characterized in that said mixing element (5) is a fixed helix. 4. Expansion nozzle (10) according to claim 1 or 2, characterized in that said mixing element (5) has forms of revolution of increasing sections. 5. Expansion nozzle (10) according to any one of the claims 1 to 4, characterized in that said convergent (2) comprises a needle for varying the section of said neck (3). An ejector (70) having a hollow body (62), said hollow body (62) having a convergent (63), a mixing chamber (64) and a diverging portion (65), said ejector (70) being characterized in that it comprises, in said convergent (63), an expansion nozzle (10) according to any one of claims 1 to 5, said nozzle (10) being able to relax a primary flow (Fl) of saturating liquid, so driving a secondary flow (F2) introduced into said convergent (63) around said nozzle (10). 7. Ejector (70) according to claim 6, characterized in that it comprises a second mixing element (5) partly in said mixing chamber (64) and partly in said divergent (65), suitable for promoting mixing the two-phase flow of said primary flow (F1) at the outlet of said nozzle (10) with said secondary flow (F2). 8. Hero turbine (20, 200 comprising at least one hollow arm (21, 210 rotatable about an axis (22), said axis (22) supplying said hollow arm (21) of saturating liquid, characterized in that it comprises an expansion nozzle (10) according to any one of claims 1 to 5 at the end of said at least one hollow arm (21). 9. Pelton turbine (30) having at least two buckets (31) integral with a wheel (32) rotatable about an axis, characterized in that it comprises at least one expansion nozzle (10) according to the invention. any of claims 1 to 5 adapted to project a two-phase jet towards said buckets (31). 10. Francis type turbine (40) comprising at least one expansion nozzle (10) according to any one of claims 1 to 5 adapted to project a two-phase jet inwardly of a rotor (42) of said turbine.