EP1034029B1 - Method and device for increasing the pressure or enthalpy of a fluid flowing at supersonic speed - Google Patents

Abstract

The invention relates to a method and a device for increasing the pressure or enthalpy of a fluid flowing at supersonic speed, according to which steam is mixed with a liquid, said mixture is accelerated to a supersonic speed and a condensation shock is initiated. Before the condensation shock is initiated additional liquid is introduced into the mixture flowing at supersonic speed.

Description

The invention relates to a method for increasing the pressure or Increase in the enthalpy of a fluid flowing at supersonic speed, with steam mixed with liquid and this mixture to supersonic speed is accelerated, after which a condensation surge is triggered.

First of all, let's look at the basic problems of flowing mixtures of two-phase mixtures, e.g. Air / water or vapor liquid or the like.

In such mixtures the "speed of sound" can take small values, whereby "speed of sound" is to be understood as the size which is decisive for the formation of the Mach number (see VDI-Zeitung 99, 1957, No. 30, October 21, "Supersonic flows of high Mach number with small Flow velocities "by Carl Pfleiderer, pages 1535 and 1536; and "Basics for pumps from" em. Prof.Dipl.-Ing. W. Pohlenz, VEB Verlag Technik, Berlin 1975, pages 49 and 41).

Ostwatitsch also points out that in foam flows at "supersonic speeds" all appearances occur from single-phase supersonic flow are known (see "Gas Dynamics", Dr. Klaus Ostwatitsch, Vienna, Springer Verlag 1952, page 440). The analogy between two-phase flow and single-phase Flow of a compressible fluid is perfect. So you need for acceleration a two-phase flow from "subsonic" to "supersonic speed" also a convergent-divergent nozzle (Laval nozzle) or is the opposite process only by means of a shock or a series of Compression shocks possible. The processes in the surge are in the two-phase flow also extremely complex, the surprising thing being that the relationship between impact entry and exit velocity as well as Pressure increase is mediated by a heat flow (see "Technical Fluid Mechanics" by Herbert Sieglach, VDI Verlag 1982, pages 214 - 230, and W.Al-bring, "Applied Fluid Mechanics", 4th edition, published by Theodor Steinkopff, Dresden 1970, pages 183-194). Due to the amount of heat generated in the impact from If the subsonic flows to the supersonic, the impact intensity is determined.

Furthermore, compressible two-phase flows behave in such a way that the State variables - with the exception of entropy, temperature and the resting temperature - change opposite in the subsonic and supersonic range (see E.Truckenbrodt, "Fluid Mechanics", Volume 2, Springer Verlag 1980, page 68). It means e.g. the supply of heat to a supersonic flow is a delay, but to a Subsonic flow an acceleration.

The strength of the so-called condensation surge depends on the condensing surge Amount of water vapor (see Dr. Klaus Oswatitsch: Gasdynamik; Springer Verlag 1952, page 57).

The condensation surge occurs when a fluid flows that is oversaturated Contains water vapor, and is the result of a sudden condensation of the Steam, which takes place very quickly and in a narrow zone, which acts as a "condensation impact surface" referred to as. The stability of the condensation surge against small disturbances in the direction perpendicular to their surface depends on the thermodynamic Condition of the steam before the impact. This just has to correspond to the beginning of a rapid condensation of the steam. A detailed Derivation of this process can be found in L.D. Landau and E.M. Lifschitz: Hydrodynamics: Akademie publishing house, Berlin 1966.

The mechanism of the pressure increase is that condensation The vapor creates vacuum spaces from the speed of sound incoming fluid are filled up suddenly. The resulting kinetic Energy is converted into pressure.

The strength of the pressure increase due to the condensation depends on the temperature difference between steam and liquid or from the liquid temperature when mixed with the steam and depending on the location of the shock.

In experiments with water and steam, the full Condensation of the vapor over the compression shock measured a pressure that was large is enough to use the device as a feed pump.

In a known design of the type mentioned, such as, for example EP 0 555 498A1 shows, before the condensation surge is placed Stripped liquid to ensure that the condensation surge in the designated area takes place. You can also reach with the well-known Training that the liquid flowing in the diffuser is not so strong heated.

In the subject matter of the invention, before the condensation surge is triggered, additional liquid is introduced into the mixture flowing at supersonic speed. This ensures that the occurring in the condensation surge Pressure increased further, because of the higher fluid content, a higher flow energy is contained in the vapor / liquid mixture.

Advantageously, the supply of the additional liquid through the caused by the flowing mixture negative pressure, which causes there is no need for additional means for conveying the added liquid.

In an advantageous device for performing the invention Method in which a steam accelerating nozzle, a feed nip for a liquid medium, a converging mixing nozzle and a diffuser is provided, a parallel flow section being arranged between the mixing nozzle and the diffuser in which a gap dividing the parallel flow section is arranged the length of the gap measured in the direction of flow between the 0.5 to 0.9 times the diameter of the parallel flow section. Because of this gap size it is achieved that a sufficient amount of additional liquid automatically is sucked in without the flow of the vapor / liquid mixture affect.

In the drawing is an embodiment of the device according to the invention shown.

Fig. 1 shows schematically the structure of the device according to the invention.

Figs. 2 and 3 are diagrams in which the measurement results with those mentioned Device can be achieved, are shown graphically.

1 with a Laval nozzle is designated, the convergent part 2 an opening angle α of about 25 - 60 ° and their divergent part 3 an opening angle β of about 3 - 20 °. This Laval nozzle 1 is a mixing nozzle 4 from convergent and cylindrical areas downstream, the convergent area γ a Has angles of about 15 to 30 °. the length L1 of the cylindrical area is about 1 to 3 times its diameter. In this convergent area the diverging part of the Laval nozzle 1 projects into it, between the end of the Laval nozzle and the inner wall of the mixing nozzle a gap 5 is left open which mixes the liquid supplied via line 6 with the vapor becomes. At the convergent part 7 of the mixing nozzle 4, as already mentioned, a parallel flow part 8 to which a parallel flow part 9 of a diffuser 10 is connected downstream. The length L2 of the parallel flow part 9 is approximately 1 to 5 times its inner diameter D2. The opening angle of the divergent areas the diffuser 10 is approximately 15-45 °.

Between the parallel flow part 8 of the mixing nozzle 4 and the parallel flow part 9 of the diffuser 10, which parts are all arranged coaxially one behind the other are, a gap 11 is left, the gap width B about 0.5 times that Diameter D1 of the parallel flow part 8 of the mixing nozzle 4.

The gap 11 is connected to an annular space 12, via which an Line 13 secondary liquid can be introduced into the flowing gas / liquid mixture is.

1. Erzeugung eines Dampfflüssigkeitsgemisches, das sich mit Überschallgeschwindigkeit bewegt,

2. Erzeugung eines Gegendruckes, indem ein Verdichtungsstoß ausgelöst wird und der Dampfanteil des Gemisches vollständig kondensiert wird, wobei der Druck der Strömung schlagartig zunimmt,

3. um den Kondensationsvorgang zu beschleunigen und dadurch den Druck weiter zu vergrößern, wird eine Sekundärflüssigkeit niedriger Enthalpie in die Kondensationszone vor dem Verdichtungsschluß injiziert.

The process goes through the following steps:

1. generation of a vapor liquid mixture which moves at supersonic speed,

2. Generation of a back pressure by triggering a compression shock and the vapor portion of the mixture is completely condensed, the pressure of the flow suddenly increasing,

3. In order to accelerate the condensation process and thereby further increase the pressure, a secondary liquid of low enthalpy is injected into the condensation zone before the end of compression.

In the device according to the invention, these steps are triggered by that the steam passes through the Laval nozzle, the mixing nozzle and the diffuser. there the steam in the Laval nozzle is accelerated to supersonic speed, wherein in the supersonic portion of the nozzle, the steam is released to a pressure that is less than atmospheric pressure. The over the outer contour of the Laval nozzle in the liquid sucked in the mixing nozzle mixes with the steam and it is created a homogeneous mixture of vapor and liquid that has a much lower speed of sound has as pure liquid or pure vapor (see "Guide through the Fluid Dynamics ", 8th edition, Friedrich Viehweg & Sohn 1984, pages 390 - 395). Despite the braking effect caused by the liquid being sucked in, the mixture remains at supersonic speed. It is created in the gap between the mixing nozzle and the diffuser as a result of the acceleration of flow, a pressure that is less than atmospheric Pressure is. At the outlet of the diffuser is a throttle valve, not shown creates a back pressure, which is slowly increased until a vertical shock in the parallel flow part 9 of the diffuser, in which the Steam condensed completely via the shock. That leads to the desired one Pressure increase in the flow.

A secondary flow is created via the gap 11 between the mixing nozzle and the diffuser introduced from liquid into the condensation zone before the compression shock, which further accelerates the condensation process and increases the pressure. The condensation process is completely completed with the shock. The condensation of the steam is associated with thermal energy, about 600 cal / g become free. The heat is derived from the liquid flowing out of the diffuser added.

The magnitude of the pressure increase that can be achieved by the additionally supplied liquid is illustrated using an example in Table 1.

The data in Table 1 are graphical in the diagram connected as FIG. 2 played. This diagram clearly shows the increase in pressure as a result added secondary liquid is recognizable. When using 7 bar, 7.5 bar or 8 bar steam pressure, the pressure in the flowing liquid rises from 17 bar up to 21 bar at 16%, from 18 to 23 bar at 18% and from 19 to 25 bar with 18% addition of secondary fluid.

Claims (3)

1. A method for elevating pressure or increasing enthalpy of a fluid flowing at supersonic speed, wherein steam is mixed with the fluid and said mixture is accelerated to supersonic speed, whereupon a condensation shock is triggered, characterized in that before triggering of the condensation shock, additional fluid is introduced into the mixture flowing at supersonic speed.
2. A method according to Claim 1, wherein the introduction of the additional fluid is effected by the vacuum produced by the flowing mixture.
3. A device for carrying out the method according to Claim 1 or 2, wherein a steam accelerating nozzle, a feeder gap for fluid medium, a convergence mixing nozzle and a diffuser is provided, wherein a concurrent flow segment is arranged between the mixing nozzle and the diffuser, in which a gap is disposed dividing the concurrent flow segment, characterized in that the length (B) of the gap measured in the direction of flow is between 0.5 and 0.9 times the diameter (D1) of the parallel flow segment (8).

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