US3262276A

US3262276A - Method and apparatus for reducing the temperature of pressurized liquids at near saturation temperature

Info

Publication number: US3262276A
Application number: US380998A
Authority: US
Inventors: Robert A Fisher
Original assignee: Martin Marietta Corp
Current assignee: Martin Marietta Corp
Priority date: 1964-07-08
Filing date: 1964-07-08
Publication date: 1966-07-26
Anticipated expiration: 1983-07-26

Description

July 26, 1966 R. A. FISHER 3,262,276

METHOD AND APPARATUS FOR REDUCING THE TEMPERATURE OF PRESSURIZED uqums AI' NEAR SATURATION TEMPERATURE Filed July 8. 1964 FIGZ l2 l4 l6 I8 20 INVENTOR.

ROBERT A. FISHER BY 471% W, I a MW .4 TTOR NE Y6 United States Patent 3,262,276 METHOD AND APPARATUS FOR REDUCING THE TEMPERATURE OF PRESSURIZED LIQUIDS AT NEAR SATURATION TEMPERATURE Robert A. Fisher, Canoga Park, Califi, assignor to Martin- Marietta Corporation, New York, N.Y., a corporation of Maryland Filed July 8, 1964, Ser. No. 380,998 8 Claims. (Cl. 62--5) This invention relates to an apparatus for reducing the temperature of pressurized liquids, and more particularly to a vortex evaporator sub-cooler used most advantageously in cooling liquids of the cryogenic type.

Handling cryogenic liquids during missile loading operations is complicated by product-ion of vapor during transport, mass measurement, and tank loading. The liquid temperature in the storage tank is usually equal to or slightly above its normal boiling point. Heat transferred to the pressurized liquid as it flows through lines and fittings adds to the problem. The resultant vapor produced when the liquid is depressurized upon entering the missile tank where the pressure is close to the barometric value, may be prohibitive. Any vapor production in the transport lines leads to excess friction effects through phase interaction. Additional release of vapor in the missile tank not only interferes with the mass loading measurements but also limits the mass of the cryogenic liquid which can be loaded. These effects may be greatly reduced by sub-cooling the liquid prior to tank entry.

The sub-cooling of cryogenic liquids may be effected by two methods; heat exchange with a substantially colder medium, and heat removal by evaporation.

The first method requires a heat exchanger with either liquid nitrogen or liquid helium as the heat transfer medium. The second method entails reducing either the total pressure over the liquid or the partial pressure of the vapor in contact with the liquid. The partial pressure may be reduced :by sweeping the ullage region of the tank with helium. While both of these methods are successful, they are subject to the disadvantage of high cost and/ or cumbersome equipment. The second method generally results in large losses of liquid. Also, helium is a natural resource which is subject to reserve limitations.

It is therefore, a primary object of this invention to provide means for sub-cooling pressurized liquids near saturation temperature which is simple, of relatively low cost, is completely passive in operation and has a high rate of separation of gas from the sub-cooled liquid.

It is a further object of this invention to provide a device of this type which automatically acts to re-pressurize the low temperature, high-pressure liquid after subcooling.

Further objects and advantages of this invention will become apparent as the following description proceeds, and the features of novelty which characterize this invention will be pointed out with particularity in the following detailed description and claims and illustrated in the accompanying drawing which discloses, by way of example, the principle of this invention and the best mode which has been contemplated of applying that principle.

In the drawing:

FIGURE 1 is a side elevational view, partially in section of one embodiment of the vortex evaporative subcooler.

FIGURE 2 is a vertical sectional view of the device shown in FIGURE 1 taken along lines 2-2.

FIGURE 3 is a reverse side elevational view of the device shown in FIGURE 1 with the outer plate re moved showing the fluid discharge arrangement.

FIGURE 4 is an exploded, perspective view of the elements forming the assembly shown in FIGURES 1 through 3 inclusive.

FIGURE 5 is a semi-schematic view similar to FIG- URE 2 of the device shown in FIGURES 1 through 4 inclusive, illustrating the principles of operation of the vortex evaporative sub-cooler.

In general, the present invention is directed to a method of lowering the temperature of a body of pressurized liquid at near saturation temperature comprising the steps of reducing the pressure of said liquid body, moving said body in a circular path to evaporate a portion of the superheated liquid body adjacent the inner surface of said moving body whereby the temperature of the remaining portion of said moving liquid body is reduced, and repressurizing said remaining liquid body at reduced velocity.

The apparatus of this invention comprises a completely passive vortex evaporator sub-cooler for reducing the temperature of cryogenic liquids and the like and includes a circular vortex chamber with an inlet nozzle positioned tangentially of and opening into said chamber. Means are provided for directing high pressure liquid at near saturation temperature through said nozzle for tangential delivery within said chamber against the annular chamber wall to form a moving liquid annulus in contact with said chamber Wall and a vapor core centrally thereof. A diffuser outlet is positioned tangentially of the circular chamber spaced axially of said inlet nozzle, in position to receive the high velocity fluid for discharge therefrom at increased pressure and low velocity. At least one opening is formed co-axially of the circular chamber within the region occupied by the vapor core whereby vapor evaporated from the surface of the high velocity cryogenic liquid may be freely vented from the chamber while the liquid body is sub-cooled thereby.

Referring to the drawing, there is shown in FIGURES 1 through 4 inclusive, a preferred embodiment of the completely passive, vortex evaporator sub-cooler for cooling cryogenic liquids and the like. The assembly 10 forming a housing or cell consists of a series of

plates

12, 14, 16, 18, and 20, which are held together in sealed, abutting relationship. A series of through bolts indicated at 22 pass through respective bores 24 of each of the plates, the bores being aligned and suitably spaced to produce a permanently sealed assembly regardless of the high pressure of the fluids passing through the vortex evaporator sub-cooler. The three

inner plates

14, 16 and 18 act to form an annular vortex chamber indicated at 26 in FIG. 2. It is important to note that the annular opening 28 formed within plate 18 is of lesser diameter than the annular opening 30 formed within plate 14, with both of these openings being larger in diameter than opening 32 formed within the central baffle plate 16. Reference to FIGURE 1 shows plate 18 having a tapered inlet nozzle 34 in the form of a tapered duct of rectangular cross sectional configuration having an opening 36 tangent to the annular opening 28. A small section or rim of the plate 16 acts as a liquid baflle as can be seen in FIGURE 1. The pressurized liquid is delivered to the assembly through conventional high pressure fluid inlet coupling member 38 which includes a threaded connector portion 40 for attachment to an inlet conduit (not shown), thereby receiving high pressure fluid as indicated by the arrow in FIGURE 1. Since the duct 34 is tapered, high pressure liquid entering the duct 34 has its pressure head transformed to velocity head. Therefore, the pressurized fluid discharging from inlet nozzle 34 tangentially to the annular opening 28 moves at high velocity about the surface wall formed by opening 28 within the plate member 18 in an annular path. The liquid is charged as a thin stream which, as a result of centrifugal force, hugs the wall 28 and rotates at high velocity. It tends to move over the lip or rim of plate 16 into the portion of chamber 26 formed by the much larger diameter opening 30.

The vortex evaporator sub-cooler is basically a refrigeration device which produces a vortex of superheated liquid in an enclosed cell or chamber in much the same manner as the cyclone separator. The liquid which is near saturation temperature is effectively superheated by the low pressure existing in the vortex and boils thus producing a vapor. As a result of centrifugal force, the high artificial gravity field of the vortex readily separates this vapor from the liquid phase. The liquid is injected tangentially to the chamber wall opening 28, through the relatively high velocity nozzle 34. As the velocity increases in the nozzle 34, the pressure decreases, creating a super heated condition in the liquid and inducing boiling. The process continues into the vortex chamber 26 where the two phases are separated as a result of centrifugal force acting upon the phases of different density. The evolved vapor moves outwardly from the chamber walls leaving a liquid annulus or body which hugs the wall and a co-axial vapor core within the liquid annulus. As a result of evaporation, the liquid annulus hugging the chamber wall has its temperature reduced and is therefore sub-cooled prior to discharge through the diffuser outlet best seen in FIGURE 3. FIGURE 3 shows the larger diameter opening 30, eccentrically positioned, which terminates in a rearwardly directed diffuser outlet 42. Appropriate fluid connection is made through an outlet coupling 44 similar to coupling 38, including a threaded connecting means 46. The coupling 38 may be connected to a fluid discharge conduit (not shown). The discharge is shown by the lower arrow of FIGURE 3. The middle or central plate 16 acts as a barrier or baffle allowing a thin film of high velocity liquid which is moving in a circular path about wall 28 to move over the lip of opening 32 into the larger diameter opening 30 for discharge through diffuser outlet 42. The high velocity, low pressure fluid is converted into high pressure, low velocity fluid as a result of movement through diffuser 42 for discharge from the vortex-evaporator-cooler at reduced temperature.

During movement of the high velocity fluid through the vortex chamber 26, the induced boiling produces vapor which evolves from the surface of the liquid body. The evolved vapor is vented to the atmosphere through vents co-axial to the circular vortex chamber 26. The

outer plates

12 and 20 carry, respectively,

vent pipes

48 and 50 which extend through openings 54 within the

respective plates

12 and 20, the vent pipes having their inner ends positioned within the vortex chamber 26. To facilitate mountnig of the pipes on

respective plates

12 and 20, annular members 52 are welded to the

pipes

48 or 50 and extend perpendicular thereto and are fixed to the outer surface of the

respective plates

12 and 20 in sealed relation thereto.

The principles utilized by the vortex cell asserts that a liquid element, at saturation temperature and migrating toward a free surface through a negative pressure gradient, evolves vapor. This assumes that heat transfer by conduction and radiation between the liquid element and its environment is incapable of maintaining an unsaturated condition in the element.

The ability of the unit to separate the vapor from the boiling liquid is limited by (l) the viscosity of the twophase mixture, (2.) the effect of gravity field, and (3) the liquid surface area through which the escaping vapor must pass. Viscosity of the mixture is a function of the liquid-vapor mixture ratio, the temperature, and pressure. In the free vortex produced by the cell, the artificial gravity field due to centrifugal force decreases with increasing distance from the center of rotation. Since faster separation of the two phases occurs in a higher gravity field, .a small gaseous core produces the best separating conditions. However, the surface of the interface between the boiling liquid annulus and the vapor core, through which the generated vapor must pass, increases with increasing core diameter. The most efficient overall system, therefore, is a compromise between these two features.

An experimental vortex evaporator sub-cooler which operates satisfactorily includes a vortex unit having a chamber 2" in diameter and 1%" long. The injector head of the nozzle is in width by /2 in length and the vent ports are /8 in diameter. Reference to FIG- URE 5 shows a cross section of the device and its method of operation. The liquid is introduced into inlet nozzle 34 of the cell 10 forming a liquid annulus 60 which hugs the inner wall opening 30' adjacent the inlet end of the chamber 26. The liquid annulus 60 moving at high velocity and at reduced pressure allows superheated liquid to boil as indicated by the bubbles 62 adjacent the gaseous core, producing a net cooling effect on the remaining liquid body. The evolved vapor is vented to the atmosphere through the vapor vents 48' and 50'. The test unit indicates that separation of vapor from the boiling liquid annulus is rapid enough to allow high cool ing rates without experiencing appreciable losses of the residual liquid passing through diffuser outlet 42' after passing over the baflle formed by opening 32'. In a device of this type, a loss of approximately 7% of the liquid through the vents is considered appreciable.

It is to be noted that most of the boiling occurs just prior to and after the pressurized fluid is injected into the vortex chamber from the inlet nozzle and that most of the boiling occurs at the interface existing between the liquid phase, that is, annulus '60, and the gaseous phase or core located centrally thereof.

An analysis of the device of the size indicated operating on water flowing at 0.4 pound per second in superheated 13 F., in a unit 2" in diameter and 1%" long provided a temperature drop as high as 6 F. as set forth later.

Several tests were made using water as the fluid near its saturation temperature. The following table shows the results of 27 runs with the various columns indicating the flow rate of liquid in gallons per minute, the vent loss of liquid in percentage of total flow, the inlet temperature of the saturated water in degrees Fahrenheit, the outlet temperature of the sub'cool water and the temperature drops in degrees Fahrenheit.

Vent Flow Loss, Inlet Outlet Run Rate, Percent Temp, Temp., 'I., F.

g.p.m. of Total F. F.

Flow

To prove that the cooling effect measured was due to boiling heat transfer only, the vent ports were periodically closed to stop the boiling process. The outlet temperature was observed to return to the value of the inlet temperature except for very high temperature runs. For these runs, the temperature was slightly less than the inlet temperature, one or two degrees Fahrenheit, and equal to the saturation temperature at the pressure in the volute. The temperature apparently developed a super-heated condition in the water and boiled as the pressure decreased in the cell due to frictional losses.

The present invention has great application to cryogenic liquids because of the need in the missile industry to reduce the temperature of a liquid from its boiling by only a few degrees. The proposed method repressurizes the cool liquid and disposes of the vapor in a compact system as contrasted to the prior art methods which retain the gas in the stream or if the gas is vented, the stream must be repressurized. In the present system initial pressure energy is converted to kinetic energy, most of which may be recovered as pressure after evaporation has occurred. Furthermore, the separation of vapor from liquid may take place at high rates in a confined space because the effects of density difference are magnified by centrifugal action.

Variations may occur in vortex cylinder diameter, height, bafiling, vapor venting and stream introduction and removal. These variations may take the form of changes in size, shape and location of the components Without departing from the spirit of this invention. For instance, the vortex chamber may include a series of annular sections separated by annular bafiies having openings of less diameter thereby insuring that all of the high velocity fluid emanating from the nozzles reaches the portion of the liquid phase annulus adjacent the interface to allow boiling of the superheated portion of the liquid to inherently cool the remaining liquid body. Further, while the invention in a preferred form is shown as an assembly formed of a series of stacked plates, the unit may be formed as a single casing or housing in integral form as suggested by the schematic teaching of FIGURE 5. It is to be noted that the present invention provides an extremely simple evaporation method for cooling pressurized cryogenic liquid and the like. A free vortex of liquid is used to convert the pressure head to velocity head and, after evaporation of some liquid, to reconvert velocity head to pressure head. The system operates on a steady flow basis. The process is accomplished continuously without the use of moving parts by the method including the steps of decompression, evaporation and recompression of the liquid. The process is confined to a cylinder and its inlet and exit sections and is carried on wholly within a single unit assembly.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment and method of operation, it will be understood that various omissions and substitutions and changes in the form and detail of the device illustrated and its method of operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A method of temperature reduction of a body of pressurized liquid at near saturation temperature comprising the steps of: depressurizing said liquid body to cause superheating thereof, moving said liquid body in a vortex path, evaporating a portion of the superheated moving liquid body in said vortex path whereby the temperature of the remaining portion of said moving liquid body is inherently reduced, and repressurizing said remaining liquid body.

2. A method of temperature reduction of a body of pressurized liquid at near saturation temperature comprising the steps of: depressurizing said liquid body to cause superheating thereof, whirling said depressurized liquid body to form a vortex, evaporating a portion of the superheated whirling liquid body whereby the temperature of the remaining portion of said liquid body is inherently reduced, and repressurizing said remaining liquid body.

3. The method of lowering the temperature of a body of pressurized liquid at near saturation temperature, comprising the steps of: reducing the pressure of said liquid by changing pressure head to velocity head to cause superheating of said liquid body causing said depressurized body of liquid to move in a vortex path to allow a portion of the superheated moving liquid body to evaporate therefrom and to inherently cool the remaining portion of said moving liquid body, and directing the remaining portion of said liquid body from said vortex path into a diffusing area to effect repressurization at reduced velocity.

4. The method of lowering the temperature of a body of pressurized liquid at near saturation temperature comprising the steps of: depressurizing said pressurized liquid body to cause superheating thereof, causing said depressurized liquid body to move in a vortex path whereby, as a result of centrifugal action, a portion of the superheated liquid body evaporates therefrom to inherently cool the remaining portion of said moving depressurized liquid body, removing the vapor produced by evaporation centrally of said vortex path and repressurizing the remaining liquid body at reduced velocity.

5. A completely passive, vortex evaporator sub-cooler for pressurized liquids at near saturation temperature comprising: a circular vortex chamber including first and second annular openings separated by a baflie having a circular opening of less diameter than said other openings, an inlet nozzle positioned tangentially to and opening into said first opening, means for directing said liquid through said nozzle for tangential delivery within said chamber to form a moving annulus of liquid in contact with said chamber wall and a vapor core centrally thereof, diffuser means positioned tangentially of said second opening spaced circumferentially from said first opening, in position to receive the high velocity fluid for discharge therefrom at increased pressure and reduced velocity, and at least one vapor vent formed coaxially of said vortex chamber within the region occupied by the vapor core whereby vapor evaporated from the surface of said high velocity liquid may be freely vented from said chamber while said remaining liquid is sub-cooled thereby.

6. A completely passive, vortex evaporator sub'cooler for lowering the temperature of a body of pressurized liquid at near saturation temperature, comprising a circular vortex chamber, an inlet nozzle positioned tangentially to and opening into said chamber, means for directing high pressure liquid through said nozzle to form a moving liquid annulus in contact with said chamber wall and a vapor core centrally thereof, a diffuser outlet positioned tangentially of said circular chamber, spaced circumferent-ially in said circular chamber from said inlet nozzle, and in position to receive the high velocity fluid for discharge therefrom at increased pressure and reduced velocity, and at least one vapor vent in fluid communication with said vapor core whereby vapor evaporated from the surface of said high velocity liquid annulus may be freely vented from said chamber while said remaining liquid body is sub-cooled thereby.

7. The apparatus as claimed in claim 6 further including an annular bafile member positioned centrally of said vortex chamber, between said inlet nozzle and said diffuser outlet and having an opening of less diameter than the diameter of the remaining portions of said circular vortex chamber whereby said moving body of liquid passes over said baffle from said inlet nozzle to said diffuser outlet to enhance separation of vapor from the superheated liquid.

8. A completely passive, vortex evaporator sub-cooler for lowering the temperature of a body of pressurized liquid at near saturation temperature, said apparatus com- 'bly including a first central plate having a first circular opening therein, a second plate positioned on one side thereof having an opening of slightly greater diameter, coaxial to said first opening, an inlet nozzle formed in said second plate tangential to, and tapering inwardly toward, said second opening, a third plate positioned on the opposite side of said first plate from said second plate having a third opening of a diameter larger than the opening of said second plate and positioned eccentrically with respect to said first and second openings, said third plate including a diffuser outlet extending away from said third opening tangential with respect thereto and spaced circumferentially with respect to said inlet nozzle, said assembly further including a pair of end plates, vents formed in respective end plates, means for directing said pressurized liquid through said inlet nozzle, and means for receiving repressurized liquid from said diffuser outlet, whereby gas evolved from the free surface of said high velocity liquid moving within the free vortex passes outward through said vents, and means for clamping said plates together to form a sealed assembly.

References Cited by the Examiner UNITED STATES PATENTS 2,893,216 7/1959 Seefeldt 625 3,044,270 7/1962 Biever 62-55 3,129,075 4/1964 Anliot 625 3,160,490 12/1964 Fabre 62-5 WILLIAM J. WYE, Primary Examiner.

Claims

1. A METHOD OF TEMPERATURE REDUCTION OF A BODY OF PRESSURIZED LIQUID AT NEAR SATURATION TEMPERATURLE COMPRISING THE STEPS OF: DEPRESSURIZING SAID LIQUID BODY TO CAUSE SUPERHEATING THEREOF, MOVING SAID LIQUID BODY IN A VORTEX PATH, EVAPORATING A PORTION OF THE SUPERHEATED MOVING LIQUID BODY IN SAID VORTEX PATH WHEREBY THE TEMPERATURE OF THE REMAINING PORTION OF SAID MOVING LIQUID BODY IS INHERENTLY REDUCED, AND REPRESSURIZING SAID REMAINTAINING LIQUID BODY.