US3409470A - Cyclic water hammer method - Google Patents

Description

1968 J. KARPOVICH CYCLIC WATERv HAMMER METHOD 2 Sheets-Sheet 1 Filed June 27, 1966 INVENTOR. Ja/nv kar oaw'c/i United States Patent Oflice 3,409,470 CYCLIC WATER HAMMER METHOD John Karpovich, Caro, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Continuation-impart of application Ser. No. 195,660, May 11, 1962. This application June 27, 1966, Ser. No. 563,626

4 Claims. (Cl. 134-1) This application is a continuation-in-part of my copending application Ser. No. 195,660, filed May 11, 1962, for Cyclic Water Hammer Apparatus, now abandoned.

This invention relates to a method for generating socalled cavities in a liquid system in an enclosed vessel to facilitate mixing, cleaning or the like within the said vessel.

The use of ultrasonic means for generating cavities in a liquid system and using the cavities in a number of operations such as cleaning and mixing, for example, are well known.

However, the generation of cavities by ultrasonic means usually involves the use of an electronic oscillator and an associated transducer, and such apparatus is by its nature somewhat complicated and expensive.

Accordingly, a principal object of this invention is to provide an improved method for cleaning enclosed vessels.

Another object of this invention is to provide an improved, simpler and more economical method for removing adherent materials from surface of enclosed vessels.

A further object of this invention is to provide an improved method of cleaning surfaces of elements contacted by a liquid system in an enclosed vessel.

Still .another object of this invention is an improved method for cleaning surfaces of heat exchanger apparatus.

In accordance with one embodiment of this invention there is provided apparatus for generating cavities in a liquid medium, usually in a cyclically recurring manner, comprising a quick opening and closing valve having an input flow bore, a pair of output florw bores, this valve being adapted to alternately bl ock flow through each of the output flow b'ores. The input to the valve is coupled to a line having liquid therein which is pumped through the valve while at least one of the output flow bore-s is coupled to the interior of a vessel to be cleaned. As liquid base material is pumped through the valve, the rapid opening and closing of the valve output bore results in the liquid beyond the shutoff point being placed in tension, generating cavities in the liquid. At the same time, the vessel surface to be cleaned is heated to a temperature at which surface boiling occurs under the conditions present when the liquid base material is under tension.

With the collapse of the thus generated cavities due to the stoppage of flow of the liquid base material beyond the valve, surface boiling occurs .at and along the heated surface or surfaces of the vessel. The combination of the cavitation plus surface boiling results in the loosening and removal of adherent materials from the surface being cleaned.

The surface being cleaned may be .a tube, of a heat exchanger, for example, or any inner surface of an enclosed, pressurizable vessel.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of cyclic water hammer apparatus in accordance with this invention;

FIG. 2 is a side elevational view, partly broken away 3,409,470 Patented Nov. 5, 1968 and in section, of one form of flutter valve which is adapted for use in this invention;

FIG. 3 is a schematic illustration of a multiple valved cyclic water hammer apparatus in accordance with this invention; and

FIG. 4 is a schematic view of a heat exchanger apparatus made in accordance with this invention.

Referring to the drawing, and particularly to FIG. 1, there is shown apparatus for generating cavities in a liquid system comprising a pump 10, usually of the centrifugal or continuous flow type, which is coupled to a flow loop, indicated generally by the numeral 12, which along a substantial part of its length is divided by .a partition 14 into two flow channels 16, 18. A flutter valve 20, pivotally coupled to the end 22 of the partition 14 which faces the oncoming flow from the pump 10, is adapted to seat and close, in turn, each of the flow channels 16, 18, for example.

A pressure release reservoir or compliance element 24 is coupled to the flow loop 12 ahead of the pump 10 in the direct-ion of liquid flow from the pump.

In operation, the flow loop and part of the pressure release reservoir or vessel 24 is filled with a pumpable liquid base medium such as oil and water, for example. The pump is then started, pumping the liquid base medium in the direction of the arrow 26 towards the end 22 of the partition 14. The flutter valve 20 is easily swung to close one or the other of the channels 16, 18. Assuming, for example, that the flutter valve suddenly closes the channel 18, a Water hammer occurs and the liquid base medium beyond the closed valve is placed in tension until the tensile strength of the liquid is overcome, causing the liquid to fracture and produce cavities. The produced cavities are unstable, bearing under pressure from the surrounding liquid, and will collapse suddenly, resulting in the generation of shock waves inn the liquid. The formation and collapse of such cavities is often referred to as cavitation.

The function of the pressure release vessel is to act as a de-surger to isolate the pump from the flutter valve and to accommodate excess liquid when cavities are formed in the closed system. After the cavities are formed, the liquid in the flow channel which is closed off at one end by the flutter valve 20 changes its direction of flow as the cavities collapse and hammer back, opening the valve 20 and causing it to close the flow channel 16. This cyclic closure behavior of the flutter valve continues in a repetitive manner, resulting in a cyclic water hammer and shock wave generation.

The arrangement of FIG. 1 can be regarded as a mechanical oscillator. The apparatus shown in FIG. 1 is used to make an oil and water emulsion or may be used, for example, in the mixing or treating of liquids which may or may not be subjected to external influences while in the apparatus. Examples of external influences are heat and radiation.

Referring now to FIG. 3, it may be seen that the apparatus of this invention is useful in systems where the liquid base medium passes through the device only a single time and is not recirculated as with the apparatus shown in FIG. 1.

In the apparatus shown in FIG. 3, the liquid base medium is pumped by means of a pump 28 from a first vessel 30 to a second vessel 32. A flow line, indicated generally by the numeral 34, is coupled through the pump 28 and extends from the vessel 30 into the vessel 32. The line 34 is divided into two separate flow channels at a plurality of places along its length by means of partitions 36, 38, 40, for example.

A flutter valve 42, similar to the valve 20 in FIG. 1, is pivotally mounted at the end of partition 36 where the liquid base flow medium enters the flow channels 43,

. 3 a 44 and is adapted to close either of the channels 43, 44, depending on the conditions of operation existing in the apparatus.

Similarly, the valves 46, 48 are pivotally mounted at the fluid entry end of each of the partitions 38, 40 to alternately close the flow paths 50, 52 and 54, 56.

In operation, the apparatus acts similarly to the apparatus shown in FIG. 1, except that each separate flutter valve and its associated flow path acts to sequentially generate cavities in the respective flow path, as does the valve and flow paths 16, 18, to provide a much larger population of cavities in the liquid flowing from the vessel to the vessel 32 than would occur if only a single valve and flow path arrangement were to be used.

Referring now to FIG. 2, there is shown a flutter valve assembly, indicated generally by the numeral having a T shaped body section 62 which has a liquid input line 64 and liquidoutput lines 66, 68 which communicate with each other. The transverse diameter of the input line 64 is preferably, but not necessarily, larger than the transverse diameter of each of the output lines 66, 68. The inner or body ends 70, 72 of the output lines 66, 68 are each shaped to form a seat for a ball valve 74 which is disposed within the body 62 of the valve 60. The wall part 76 of the body 62 lying between the valve seat ends 70, 72 is curved slightly so that when no liquid medium is being pumped through the device the ball valve 74 tends to lie away from both of the valve seats 70, 72 and slightly off center with respect to the path of fluid flow from the input line to the output lines.

In operation, the slightly off center at rest position of the ball valve 74 assures that when liquid is pumped or passed through the inlet line 64 and out the outlet lines 66, 68 that the ball will be carried along by liquid and seat against one of the seats 70, 72. The sudden seating of the ball causes a water hammer to occur in the Output line ahead of the seated ball and in that output line the liquid goes into tension and forms cavities. As the cavities collapse, the surge of force resulting therefrom forces the valve off its seat and towards the other valve seat. The valve is then carried towards the other seat by the flow of liquid after it passes the midpoint between the two valve seats. Again, the seating of the ball valve 74 causes a water hammer, the production of cavities in the liquid in the closed output line, and the subsequent unseating of the ball valve -by the collapse of the cavities as before.

The mechanical oscillator arrangement shown in FIG. 2 may be used as are the flutter valves 20, 42, 46, or 48 in FIGS. 1 and 3 where the larger, full diameter part of the flow line 12 or 34 is the input line 64 to the device 60 and the flow channels 16-18, 4344, 50-52, and 54-56 are the output lines 66, 68 of the device.

Another embodiment of this invention is shown in FIG. 4.

In the apparatus of FIG. 4, a liquid is driven through the line 80 by the pump 82 (or other driving means not shown). A compliance element 84, illustrated as a surge tank, for example, is coupled to the line 80 between the pump 82 and a flutter valve 20 illustrated in FIG. 1. The valve assembly 86 comprises the flutter element (or valve) 88 and valve seats 90, 92 which communicate with the input end of the hollow tubes 94, 96. Alternatively, other types of quick opening and closing valves may be used across the tubes 94, 96 to place the pressurized liquid in the tubes in tension and produce a water hammer.

The tubes 94, 96 terminate at their output end in a common header 98 and are then coupled to some utilization means, not shown. The tubes 94, 96 are surrounded by and enclosed in an enclosed vessel such as a heat exchanger jacket 100 having an inlet 102 and an outlet 104 by means of which a heat exchanger fluid, such as steam, for example, is circulated through the jacket 100' and around the tubes 94, 96.

4 As liquid, e.g., water, is pumped through the apparatus, the valve element 88 of the flutter valve assembly suddenly closes against one of the valve seats or 92, placing the liquid behind the valve (i.e., in the direction in which liquid normally flows) in tension and causing the production of cavities in the liquid. As stated previously, the formation and collapse of such cavities is often referred to as cavitation.

On collapse of the so-produced cavities, the liquid in the flow channel or tube whose end has been closed by the flutter valve 88 hammers 'back and knocks the flutter valve across so that the end of the other channel (94 or 96) is closed. Cavities then form in the newly closed tube, collapse, flip the flutter valve to close the other tube, and the repetitive process continues.

The heat exchange fluid applied to the heat exchange jacket may be either hotter or cooler than the liquid in the line 80, but should be at a temperature wherein boiling of liquid at the heated surface occurs when the liquid is placed under tension and cavitation occurs.

Further, if the temperature of the tube walls (or of any surface to be cleaned in accordance with this invention) is, under treating conditions, above the boiling temperature of the liquid base flow material, the flow rate of the liquid base material is maintained at such a rate that the liquid base flow material does not reach boiling temperature as it passes through or along the surface to be cleaned except when the liquid base material is under tension.

When the liquid pumped or flowing under pressure through the tubes 94, 96 of the heat exchanger is of a type which tends to form a coating or deposit, such as water deposited scale, on the walls of the tube during usage of the device, it has been found that the heat transfer characteristics of a heat exchanger in which periodical placing the flow liquid under tension momentarily was done are much better than for identical tubes in a heat exchanger wherein no cavity generating means was incorporated. Measurements of these characteristics were made at intervals over an extended time period.

Thus, while this invention has particular merit as a method of cleaning adherent materials from surfaces of an enclosed element or vessel, the periodic placing of the liquid flow material under tension and the consequent momentary production of surface boiling constitutes a method of preventing or greatly slowing of the buildup of adherent materials on such surfaces (assuming surface temperatures during normal operation of the element or vessel are sufficient to cause surface boiling).

Usually the flutter valve assembly (or its equivalent) is placed close to (about a foot away from) the input end of the tubes to be cleaned (or kept clean). The length of the tubes 94, 96 is, for best results many times their diameter.

It is also practical to use one flutter valve assembly to operate two heat exchangers.

If the tubes of each exchanger are coupled to a common header, the tubes 94, 96 each may be coupled to a separate header of a heat exchanger. In event the fluid (liquid) in the heat exchanger jacket of each exchanger is to be cavitated to produce a cleaning or scale (deposit) removing action, the connections to the tubes 94, 96 could instead be made to the input (102 in the illustration) of the heat exchanger jackets. With such a setup, the outer surfaces of the heat exchanger tubes and the wall surfaces of the heat exchangers would be cleaned.

If the liquid contacting the part of the exchanger which is to be cleaned is inexpensive, such as water, for example, it is, of course, practical to use only the tube connected to one valve of the flutter valve assembly in the cleaning operation while the other tube or leg of the device is a line through which the liquid is conducted to waste or to a tank for re-use. The leg or line which is not coupled to the heat exchanger should preferably be as long or longer than the other line which is coupled to the heat exchanger in order to avoid wasting unduly large amounts of liquid.

Because the method of this invention is equally applicable to the cleaning of enclosed pressurizable vessels in general, the outer walls of the tubes 94, 96, as well as the walls of the heat exchanger jacket, may be cleaned (or kept clean) by coupling one of the output lines from the valve 88 to the input 102 of the heat exchanger jacket, for example. In such a setup, the output 104 of the heat exchanger jacket may be coupled to a return line to a liquid base material source, or to waste.

The cyclic closing of the flutter valve if such a 'valve is used, is a function of the characteristics of the system in which it works, but cyclic rates of from 1 cycle per minute to somewhat over 400 cycles per minute have been used.

Excellent cleaning of (or the prevention of a buildup of a deposit on)heat exchanger tubes and surface parts of other enclosed pressurizable vessels has been accomplished when the flutter valve assembly is in operation only one-half hour in a 24 hour period of operation at a flutter valve cyclic opening and closing rate of about 1.5 cycles per second.

Although not shown in the drawing, the test setup used had valving means whereby the flutter valve assembly could be bypassed during the time the valve was not in operation.

The pressure of the liquid in the line 80 may vary from 5 p.s.i. to 4,000 p.s.i., for example, but a pressure of 65 pounds per square inch on the liquid base flow material (which was readily available) has operated the heat exchanger device of FIG. 4 very well during tests.

While a flutter valve has been described in connection with the operation of the invention, the ball valve of FIG. 2 or other type of quick opening and closing, double or single acting mechanical valves(s), of course, may be used as a substitute. The ball valve may be made of metal, a solid state plastic, wood, or any suitable material.

While pressure limits approaching one pound/sq. inch to several hundred pounds/sq. inch have been tested, the upper pressure limit is, in practice, apparently limited only by the ability of the apparatus to withstand the pressure.

The heating of the surface to be cleaned may be accomplished by steam, as mentioned, or by flame, resistance heating, induction heating or any suitable means.

What is claimed is:

1. A method of removing material adhering to a surface part of an enclosed vessel which is adapted to be pressurized, said vessel having spaced apart inlet and outlet means for passing liquid base flow material over said surface part, comprising flowing liquid which is under pressure along said surface part, heating said surface part to be cleaned to above the boiling temperature of said flowing liquid under tensile stress conditions, and then suddenly interrupting the flow of liquid at said inlet means thus placing said liquid under tension whereby boiling occurs at said surface part.

2. A method in accordance with claim 1, wherein said liquid base flow material is flowed past said surface part at a volumetric rate such that general boiling does not occur while said material is flowing.

3. A method in accordance with claim 1, wherein the flow of said flowing liquid base material is interrupted at a rate of between 5 cycles/minute and 250 cycles/minute.

4. A method of removing material adhering to a wall surface of a heat exchanger having tubes which have inner and outer walls, and which has spaced apart inlet and outlet means for passing liquids over said wall surface, comprising flowing liquid which is under pressure along said wall surface between said inlet and outlet means, heating said surface to be cleaned to above the boiling temperature of said flowing liquid under tensile stress conditions, and then suddenly interrupting the flow of liquid at said inlet means thus placing said liquid under tension whereby boiling occurs at said wall surfaces.

References Cited UNITED STATES PATENTS 1,628,530 5/1927 Burnett 13422 1,840,834 l/1932 Davis -84 2,089,317 8/1937 Wilder 134--22 2,123,434 7/1938 Paulson et al 13422 2,514,797 7/1950 Robinson 165-84 2,664,274 12/1953 Worn et a1. 16584 MORRIS O. WOLK, Primary Examiner.

I. T. ZATARGA, Assistant Examiner.

Claims (1)

1. A METHOD OF REMOVING MATERIAL ADHERING TO A SURFACE PART OF AN ENCLOSED VESSEL WHICH IS ADAPTED TO BE PRESSURIZED, SAID VESSEL HAVING SPACED APART INLET AND OUTLET MEANS FOR PASSING LIQUID BASE FLOW MATERIAL OVER SAID SURFACE PART, COMPRISING FLOWING LIQUID WHICH IS UNDER PRESSURE ALONG SAID SURFACE PART, HEATING SAID SURFACE PART TO BE CLEANED TO ABOVE THE BOILING TEMPERATURE OF SAID FLOWING LIQUID UNDER TENSILE STRESS CONDITIONS, AND THEN SUDDENLY INTERRUPTING THE FLOW OF LIQUID AT SAID INLET MEANS THUS PLACING SAID LIQUID UNDER TENSION WHEREBY BOILING OCCURS AT SAID SURFACE PART.

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