US3921915A - Nozzle means producing a high-speed liquid jet - Google Patents

Abstract

A nozzle device producing a high-speed liquid jet, to be used for example in an apparatus to cut, break, deform, clean or otherwise treat materials, is characterized in that its internal cavity to receive a liquid column has a continuously converging contour lying within the limits defined by the following two equations: A. A/Ao (1 + (X/L) ((Ae/Ao) 1 -1)) 1 B. A/Ao ( 1 + (X/L) ((Ae/Ao) 1/5 -1) ) 5 WHERE A is the variable internal cross section of the nozzle cavity; Ao is the value of A at the nozzle entrance; Ae is the value of A at the nozzle exit; L is the nozzle length from entrance to exit; and X is the variable coordinate along the axis of the jet nozzle.

Description

Glenn et al.

[ Nov. 25, 1975 NOZZLE MEANS PRODUCING A HIGH-SPEED LIQUID JET Inventors: Lewis A. Glenn; Bo Lemcke, both of Lausanne; Inge Ryhming, Mollie-Margot, all of Switzerland lnstitut Cerac SA, Ecublens, Switzerland Filed: July 17, 1973 Appl. No.: 380,014

Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. B 380,014.

Assignee:

Foreign Application Priority Data July 19, 1972 Sweden 9464/72 U.S. Cl..l 239/589; 239/602 Int. Cl. B05B 1/00 Field of Search 239/101, 102, 601, 602,

References Cited UNITED STATES PATENTS 7/1970 Cooley 239/101 3/1972 Naydan 239/102 Primary Exarr lnerM. Henson Wood, Jr Assistant Exarrlin er-Andres Kashnikow Attorney, Agerit, 0r Firm-Flynn & Frishauf [57] ABSTRACT A nozzle device producing a high-speed liquid jet, to be used for example in an apparatus to cut, break, deform, clean or otherwise treat materials, is characterized in that its internal cavity to receive a liquid column has a continuously converging contour lying within the limits defined by the following two equations: a. A/A, {,1 (X/L) 1e/A0) 1]} b. A/A,,= {1 (X/L) [(Ae/A0)"" 1 where A is the variable internal cross section of the nozzle cavity; A, is the value of A at the nozzle entrance; A is the value of A at the nozzle exit; L is the nozzle length from entrance to exit; and X is the variable coordinate along the axis of the jet nozzle.

7 Claims, 5 Drawing Figures US. Patent Nov. 25, 1975 Sheet 1 of3 3,921,915

mGX/ mClX.

1 FIG. 2 n) US. Patent Nov. 25, 1975 Sheet2 of3 3,921,915

Pm-(kb) F|G.3

US. Patent Nov. 25, 1975 Sheet30f3 3,921,915

X FIG. 4 /L NOZZLE MEANS PRODUCING A HIGH-SPEED LIQUID .IET

2 L is the nozzle length from entrance to exit; and X is the variable coordinate along the axis of the jet nozzle. The internal cavity of the nozzle of the present inven- This invention relates to a nozzle means producing a 5 tion is approximately hyperbolic in shape. its relative high-speed liquid jet to be used for example in an apparatus to cut, break, deform, clean or otherwise treat materials.

Specifically, in such an apparatus a column of liquid is accelerated to moderate velocity, preferably by direct application of gas pressure to one end or, via the action of an intermediate free piston, and is then directed into a converging nozzle of appropriate design. The function of the nozzle is to redistribute the initially more or less uniform energy content of the column such that a small mass fraction at the forward or leading end contains, at discharge, essentially all the energy. The jet stagnation pressure thus derived can be many times the strength e.g. of even the hardest rock materials and can thus serve as a useful tool for excavation, tunneling, mining and a variety of other industrial applications.

The prior art contour of the internal cavity of a nozzle, schematically illustrated as the upper curve 4 in FIG. 1, has a radius that exponentially decreases with distance from the nozzle entrance. With this nozzle, the relative rate of area change (l/A) (SA/8X) is invariant over the entire contour.

It was stated as prior art that the nozzle with exponential shaped internal cavity would produce a pressure in the impact chamber that sharply increases to the maximum active pressure and is then maintained constant. Further, according to the prior art, such a nozzle was thought desirable in that it would ensure a multiple increase in energy transferred by a piston to liquid as compared with other known constructions of jet nozzles.

As will be apparent from a consideration of the accompanying drawings and graphs, the attainment of maximum pressure in the impact chamber as rapidly as possible, thereafter to be maintained thus, is neither required for high performance, nor does it in fact occur as described in the prior art.

It is an object of the present invention to provide a new and improved nozzle means to produce a highvelocity liquid jet, to be used in an apparatus for hydraulic treatment of different materials.

It is a further object of this invention to provide, in a single pulse discharge, containing the highest possible percentage of input (kinetic) energy, the maximum possible stagnation pressure subject to the constraint that the maximum static pressure attained within the nozzle is less than a predetermined value that which would cause rupture or yield failure.

SUMMARY OF THE INVENTION a b A/A,= {l (X/L)[(Ae/A0) n -1 where A is the variable internal cross section of the nozzle cavity;

A,, is the value of A at the nozzle entrance; A. is-the value of A at the nozzle exit;

change in cross-section decreasing much more rapidly at the nozzle entrance than at the exit plane.

BRIEF DESCRIPTION OF THE DRAWINGS apparatus, with a fluid piston.

DETAILED DESCRIPTION OF THE DRAWINGS The basic apparatus is shown in FIG. 1. A free piston l strikes an initially motionless column of liquid 2 with initial velocity U,,. The liquid column 2 has length I and cross-sectional area A The internal nozzle cavity of the present invention has a surface contour 5 beginning at point 6 and leads to an exit point 7. Contour 4 represents the prior art nozzle contour. Assuming the impedance of the piston l is many times that. of the fluid 2, as is the case for example when steel strikes water, the initial velocity of the liquid 2 atthe piston interface will be approximately U,,. As a result ofthe impact, a shock wave will be driven into the liquid with minimum velocity C the sound speed in the undisturbed fluid, and the pressure behind this shock will be at least P p C, U where p,, is the density of the undisturbed fluid. When the shock wave has traversed the liquid column 2 it will reflect from the front surface 3 thereof as a rarefaction. As a result of this action, the front surface will be accelerated to a velocity of approximately 2U,,. The rarefaction will travel back towards the piston 1, increasing the velocity of the fluid behind. However, there is also a rarefaction emanating from the piston end since the ambient pressure on the back side of the piston is much lower than the shock induced value P,,. This latter rarefaction will act to reduce the fluid velocity behind it so that the net effect will be a monotonically increasing velocity profile as the liquid packet is viewed from rear to front. The velocity gradient will become even steeper as the liquid column traverses the converging nozzle contour 4 or 5. Two different shapes (prior art 4 and present invention 5) are shown to distinguish the importance of proper nozzle shape on system performance.

The family of nozzle contours to which both the prior art and the present invention belong can be represented by the equation:

A/A. {1 (X/Lxue/Aov'" 1]l," 8(X/L) where A is the variable internal nozzle cross section;

A is the value of A at the nozzle entrance 6; A. is the value of A at the nozzleexit 7; L is the nozzle length from entrance to exit;

4 contrast with those of the prior art and of FIG. I are discussed hereinbelow.

In the following table, and in FIGS. 3 and 4 are compared the performance of an apparatus employing the teachings and concepts of the present invention with those of the prior art; the effects of compressibility are included.

DESCRIPTION EXPONENTIAL WITH METALLIC PISTON (PRIOR ART) HYPERBOLIC WITH M ETALLIC PISTON HYPERBOLIC WITH FLUID PISTON familyof possible nozzle configurations. In particular, it can be shown via well established mathematical theorems that as n grows without bound, in either the negative or positive direction, equation (1) above reduces to the prior art exponential contour, i.e.,

if n 1 Moreover, with n 2, the nozzle radius will be a hyperbolic function of the running coordinate (X/L).

In accordance with the present invention, the internal cavity'of the nozzle has an approximately hyperbolic shape, the continuously converging contour of the internal cavity of the nozzle lying within the limits defined by the following two equations:

a. A/ {l +(X/L)[(Ae /Ao) *"1 b. A/A,,= 1 (X/L)[(Ae/A0)' 1 where v A is the variable internal cross-section of the nozzle cavity;

A,, is the value of A at the nozzle entrance;

A}. is the value of A at the nozzle exit;

L is the nozzle length from entrance to exit; and

X is the variable coordinate along the axis of the jet nozzle. The advantages and improved performance characteristics of the nozzles of the present invention over the teachings of the prior art will become more apparent from'the discussions hereinbelow.

FIG. 2 depicts some of the results of analysis of the various nozzle contours, based on incompressible flow theory. The ratio of the maximum static pressure attained anywhere within the nozzle, 6 to the maximum discharge stagnation pressure, $0, is shown as a function of n. According to the objectives of the present'invention, this ratio should be as low as possible. A value of 0.25 is noted for the exponential design, whereas the value for n -2 is only 0.108. Even lower values are observed for n 2 but in order to take advantage of these lower values (when compressibility is considered), exceedingly long and perhaps impractical nozzles would be required.

FIG. 5 illustrates a nozzle configuration which eliminates altogether the piston l of FIG. 1. In FIG. 5, the fluid itself functions as a piston. In FIGS. 1 and 5, like elements are designated by like reference numerals. The characteristics of the embodiment of FIG. 5 in In the above table are tabulated the maximum discharge stagnation pressure Po the maximum static pressure ttained anywhere within the nozzle fi the ratio of employs a metallic piston with a nozzle of exponential contour or shape (A). In the second prior art exponential nozzle is replaced by a nozzle with hyperbolic con+ tour (B). The third, represented schematically in FIG. 5, eliminates altogether the intermediate metal piston (C), the fluid itself serving the function of the pistonpln all three cases, (A), (B), (C), the system energy, over-1 all area ratio, ratio of initial water package to nozzle length, and initial system velocity (or Mach numer.= Un/C'o) are invariant and the fluid considered iswaters sure will then also be reduced, perhaps to the,70 kbar level claimed as the maximum attained with the prior art. Replacing the exponential nozzle contour (A) with a hyperbolic nozzle contour (B) decreases the ratio P /P0, from 0.537 to O.l7 and increases the efficiency by 13% while. however, reducing the maximum stagnation pressure by about a third. The stagnation pressure loss can be mainly regained, without the detrimental effect of increased static wall pressure, by eliminating the intermediate piston [third configuration (C), FIG. 5]. In this case, there results a stagnation pressure of I09 kb (more than 50 times the cornpressive strength I of conventional granite) with a manageable maximum static wall pressure of only 15.4 kb and a further jump in efficiency to FIG. 3 shows the maximum static pressure distribution in each nozzle as a function of axial position. Contrary to the earlier disclosures, of the prior art, it is seen that nozzles designed according to the prior art (A) do /P0, and the energy conversion effi ciency, 'n, for each of three possible configurations. The first configuration, representative ofthe prior art,

not attain pressures in the impact chamber that sharply increase to the maximum active pressure and are thereafter constant. In fact. after the initial rarefaction from the forward surface of the water packet. at X. =0. the pressure in the impact chamber is small in comparison to that developed behind the leading edge of the water by the nozzle convergence. This latter pressure, moreover, increases continually until slightly after the initial discharge from the exit, thereafter dropping rapidly. Since the exponential nozzle has a constant relative rate of change of cross-section, the initial rate of increase of the pressure gradient acting on the front sur face of the fluid is less than for the corresponding hyperbolic nozzle (B) or (C). Hence less acceleration is accomplished in the upstream end of the nozzle. Not until the leading edge of the water packet is half way through the nozzle is the pressure gradient for the exponential nozzle equal to that of the hyperbolic nozzle of the present invention.

FIG. 4 shows the ratio of fluid velocity to initial velocity as a function of the axial coordinate at the instant of discharge. The prior art design (A) is seen to have a much steeper gradient at the discharge end, the result of the steep pressure gradient within the nozzle shown in FIG. 3. The velocity gradients derived with the nozzle configuration of the present invention are much less severe, although the maximum discharge velocity obtained with design (C) differs by only 7% from that of design (A). At the same time P,,,, for design (C) is reduced to 0.25 of that obtained with design (A). The elimination of the piston in design (C) of FIG. 5, aside from the practical advantage gained by simplifying the machine fabrication, serves to increase the efficiency of the energy conversion process by eliminating the impedance mismatch between piston and fluid. An added advantage is that at the instant the front surface of the liquid packet begins to accelerate into the nozzle, the fluid piston design (C) results in a compression wave moving into the fluid from the leading edge rather than 6 a rarefaction as is the case with designs (A) and (B). This allows the front surface to initially accelerate more rapidly and makes more efficient use of the nozzle.

We claim:

1. A nozzle means producing a high-speed liquid jet. said nozzle means having an internal cavity to receive a liquid column and leading to a nozzle exit. characterized in that the internal cavity has a continuously converging contour lying within the limits defined by the following two equations:

A is the variable internal cross-section of the nozzle cavity;

A is the value of A at the nozzle entrance;

A,. is the value of A at the nozzle exit;

L is the nozzle length from entrance to exit; and

X is the variable coordinate along the axis of the jet nozzle.

2. A nozzle means according to claim 1 comprising means rearward of said continuously converging contour of said cavity for retaining a liquid column therein.

3. A nozzle means according to claim 2 comprising a piston located rearward of said liquid column.

4. A nozzle means according to claim 3 wherein said piston is of a hard metal.

5. A nozzle means according to claim 2 wherein said means rearward of said continuously converging eontour of said cavity retains therein a liquid column of substantially constant cross-section along the length thereof.

6. A nozzle means according to claim 1 wherein said continuously converging contour is approximately hyperbolic in shape.

7. A nozzle means according to claim 3 wherein said piston is a fluid piston.

Claims (7)

1. A nozzle means producing a high-speed liquid jet, said nozzle means having an internal cavity to receive a liquid column and leading to a nozzle exit, characterized in that the internal cavity has a continuously converging contour lying within the limits defined by the following two equations: a) A/Ao ( 1 + (X/L)((Ae/Ao) 1 -1)) 1 b) A/Ao ( 1 + (X/L)((Ae/Ao) 1/5-1)) 5 where A is the variable internal cross-section of the nozzle cavity; Ao is the value of A at the nozzle entrance; Ae is the value of A at the nozzle exit; L is the nozzle length from entrance to exit; and X is the variable coordinate along the axis of the jet nozzle.

2. A nozzle means according to claim 1 comprising means rearward of said continuously converging contour of said cavity for retaining a liquid column therein.

3. A nozzle means according to claim 2 comprising a piston located rearward of said liquid column.

4. A nozzle means according to claim 3 wherein said piston is of a hard metal.

5. A nozzle means according to claim 2 wherein said means rearward of said continuously converging contour of said cavity retains therein a liquid column of substantially constant cross-section along the length thereof.

6. A nozzle means according to claim 1 wherein said continuously converging contour is approximately hyperbolic in shape.

7. A nozzle means according to claim 3 wherein said piston is a fluid piston.

Images