US3538933A

US3538933A - Fluid mixing device

Info

Publication number: US3538933A
Authority: US
Inventors: Robert E Miller
Original assignee: British Oxigen Ltd
Current assignee: BOC Group Ltd
Priority date: 1967-08-07
Filing date: 1968-08-05
Publication date: 1970-11-10
Anticipated expiration: 1987-11-10
Also published as: NL6811211A; SE340936B; DE1773997A1; FR1575410A

Description

United States Patent [72] Inventor Robert E. Miller [56] Ref r n Cited Welwyn Garden City, England UNITED STATES PATENTS [2U P 75mm 3,080,886 3/1963 Severson 137/816 [22] Flled Aug. 5, 1968 1 3,122,165 2/1964 Horton 137/815 [45] Patented Nov. 10, 1970 73 A The British 0, en Com an Limited 3,272,214 9/1966 Warren 137/815 1 p y 3,366,130 1/1968 Reader 137/815 :1 British Company 1 [32] Priority Aug. 7, 1967, Sept. 14, 1967 Primary Examiner-William R. Cline [33] Great Britain AttorneyTownshend & Meserole [31] 36.163/67 and 41,938/67 [54] FLUID MIXING DEVICE 4 Claims 2 Drawing Figs ABfiTlRACT: A fluid-mixing device comprises two inlet chan- [52] 11.8. CI 137/815 nels. one for each of the fluids to be i nv rg ng [51] lm,C| Fls 1/14 towards an interaction zone, an outlet channel leading from [50] Field of Search 137/815, the zone, n w n ing channels one on either side of the 1 88(Consulted) outlet channel.

. 1- FLUIIiMlXING Davies In operation, the two fluids" to be madam passed along separate supply, lines into'the inlet channels, and themass flow rates of the twofluids are adjusted untilthe pressuresin the sensing channels are equal. When this pressure equalisation has been attained, the fluidmixtu'repasses out of the interaction zone through the putlet-tehannel.

A number ofthese fluid mixing devices may be corineetedin cascade so that an inlet channel of the seconddevice and each of the subsequent devices is coupledto the outlet channel'of the immediately. precedingdevice.

FIEIJDZQF THE'INVENTION This inventionrelat es'to a fluid=mixing deviceforenabling at least two fluids front-separate suppliesto be mixed in a preselected mass flowra'tio.

osscmrrlosor THE PRIOR ART.

One particular applicationoftheinvention is inithe mixing of gases for; in;f1aine-cuttingarid fgasshielded electric arc welding. In flame-cutting processes the constituent gases have previously beenmixcdiin'the correct flow ratio bythe operator-observing the flame, and then adjusting the gas supplies accordingly. Thisis :fairly straightforward when us'ingan city-acetylene flame becauseithe flame provides a' clear visual indicationwhenthe oxygenand acetylene are present in the required ratioh I-Ioweverg the flamesof other gas rnixtures, such-as oxygenpropane and oxygemnatuial gas donot all provide this clear visual indication, and, itfis extremely difficult to obtain the required mass flow-ratio by observing the flame;

SUMMARYOFJTHE INVENTION The present invention aims at providing a fluid-mixing device adapted to; give a simple indication of correct or incorrect mixing of the' two fluids.

Accordingly the present invention provid'es a fluid-mixing device which, in its broadest aspect, is asdeiined inclaim l o'f the appended claims. v p

Fluid mixing devices of this type willbe referred to as fluid mixingdeviees of the typeidescribed. The pressuredifi'erehce may be indicated by any suitable dcvicesuchas amanometer; and the fluid mixing device may be arranged sorthat the pressure difference-between the sensing channels'is'zero when the required mass flow ratio is obtained.

Accordingly'the present invention also providesiaplurality of fluid mixing devices of the type described connected in cascade so that an inlet channel of these'conddevice and each of the subsequentdevices iscoupled to theo'utlet channelof the immediately precedingdevice.

The invention will now. be particularly described with reference to theaccompanying drawingsinwhich:

FIG. 1 is adiagrammatiesectiohal elevation of a mixing device for twoagases tobe usedina'flame cutting process; and

FIG. 2 is a diagrammatic sectional. elevation ofa cascade mixing device for mixing two' fluids' in apres'el'ected'mass flow ratio.

tion through thecentre of the blockl perpendicular to the sides 2 andl 3of the block.

Supply lines 4 and'S, ene foreaeh of the two gases-lead into the divergent ends of two inclihedinlet channels 6 and 7;and the convergent ends of these channels'comr nunicate through nozzles8 and 9 to aninteracti on zone 10. Ari outlet 11 extends from the zone to the forward face 12 of the block 1, and twosensing channels l3and '14leadfro'm the zone 10 one on either side 'enhepunet 11 Referring to FIG; mixing device Jis'madeout of a block] of rectangular crosssectidn, and the drawing isa-sec-.

required ratio, the mixed gases pass out of the zone through the outlet 11, and thestatic pressures in the

channels

13 and 14 are equal. If the-mass 'flow ratio of the two gases deviates from the required value' then the output jet of the mixed gases is deflected to one side of the zone 10, and the pressurerises in the sensing channel on that particular side.

The outlets from the

channels

13 and 14 are connected to any suitable pressure difference measuring device, such as a manometer, and theoperator adjusts the flow in the supply lines 4 and 5 to bring the differential pressure reading of the manometer to zero. This is a simple method of maintaining a gas mixture of a required constituency which is independent of the visual appearance of the mixture flame.

1f itisdesired to mix two gases in avery large mass flow ratio such as for example 100:2 the problem arises that firstly, there is a lower limit to the physical size of the smaller nozzle, and secondly, with two gas streams differing in magnitude by a largearnount the smaller streamtends to be swamped by the larger. These measuring devices operate most accurately whenthe mass flow ratio has a value in the range from 1:1 to l :10 which is regarded as-a low mass flow ratio.

One way-of solving this problem is to modify the mixing device by having a shunt line flowing from the larger supply line to its appropriate inlet channel; this shunt line being arranged to take 2 percent of the larger constituent gas. This 2 percent is then mixed with the smaller constituent gas to provide a 1:1 mass flow ratio which is indicated by the pressure difference measuring device, and the mixed gases are then directed-to join the'larger supply line downstream from the mixing device. In this way a 100:2 mass flow ratio is obtained although the actual ratio to be measured is 1:1 thereby enabling an accurate pressure differential reading to be obtained. V

The mixing device may be made-of any suitable material such as metal, epoxy resin, ceramic orplastic.

The supply lines 4 and 5, and the outlets from the

channels

13 and 14 may be passed through the block 1 at right angles to the inlet channels 6 and 7, and the

channels

13 and 14 respectively'.

Referring to FIG. 2,,

fluid mixing devices

15, 16, 17 and 18 l of th'e'type described have

inlet channels

19 and 20, 21 and V 22, 23 (and 24, and'25 and 26 respectively. These mixing The mixing devices are made out of a block 31 of rectangular cross section, and the drawing shows a section through the centre of the block 31 parallel to the major faces of the block.

The outlet channel 30 extends to the side 32, and the

inlet channels

19, 20, 22, 24 and 26 extend to the side 33.

'Ihe'mixingdevices have

sensing channels

34, 35, 36, 37, 38, 39,40 and 41 and the outlets from the sensing channels in any one fluid mixing device are connected to any suitable pressure difference measuring device, such as a manometer.

The operationof this device is basically similar to the operation of the fluid mixing device illustrated in FIG. 1. The operatoradjusts the 'flow intoboth'inlet channels of the first mixing device to bring the differential pressure reading of the appropriate manometer to zero. Thereafter headjusts the flow into only'tha tirilet channel of each succeeding device which is notconnected to the outlet cha'nneiof the preceding device.

"A cascade mixing device such as this has certain important advantages. For example, it is particularly suitable for carrying out thecontinuous mixing of fluids in preselected mass flow ratios. When carrying out continuous mixing it was previously necessary to have flow meters in each fluid line, and the accurate determination of the mixture constituency was deter- ."mine'd by the accuracy of each of these'meter's. The meters are frequently sensitive to-pressure and temperature fluctuations,

particularly when mixing gases, and the appropriate corrections have to be made from these fluctuations. With this invention it is only necessary to have one flowmeter in either one of the

inlet channels

19 and 20 to give the correctflow reading in that channel. Thereafter the mass flow rates in the

other inlet channels

22, 24 and 26 are adjusted in that sequence using the respective manometers for indicating when balancing has been achieved, to provide a fluid mixture of the required composition in the outlet channel 30. The composition of the final mixture is determined by mass flow ratios of all the stages, which are calibrated beforehand.

Another advantage of this cascade configuration is that it enables a large mass flow ratio to be obtained with a high degree of accuracy. Normally if it is desired to mix fluids in a large mass flow ratio the problem arises that it is extremely difficult to produce a pressure difference measuring device which reads accurately at these large ratios. These measuring devices operate most accurately when the mass flow ratio is small, such as for example 1:1. In our arrangement a large mass flow ratio can be produced by using several fluid mixing devices in cascade, with each device operating at a small mass flow ratio. For example in the illustrated device suppose each fluid mixing device had a mass flow ratio of 1:1. Then it would be seen that the ratios in the

outlet channels

27, 28, 29 and 30 are 1:1, 1:3, 1:7 and 1:15 respectively. To take the most general case, the final ratio will be given by the expression (R, 1) (R l) (R,,+ 1) 1:1 where R R R, are the mass flow ratios of successive mixing stages. In this way a very large mass flow ratio may be accurately obtained although the actual ratio being measured in each stage is small, thereby enabling an accurate differential pressure reading to be obtained.

In the illustrated example one fluid is fed into

inlets

19 and 20, and the other'fluid is fed into all the other inlets, so that the first fluid is successively diluted as it passes through the various stages.

Another advantage of this cascade configuration is that any suitable combination of fluids can be mixed by feeding in each fluid at the appropriate inlet. The resulting product will be thoroughly mixed because the process is one of successive dilution and mixing.

Although the device as illustrated is formed in one block, it would be quite simple to use separate plug-in elements so that as many extra stages can be added as required to give the desired dilution.

1 claim:

1. A fluid-mixing device for mixing fluids in a predetermined ratio comprising at least two inlet channels, one for each of the fluids to be mixed, arranged to direct jets of fluid which impinge on each other to form a combined jet of which the direction of flow is a function of properties of the constituent jets, and which is adapted to flow towards an outlet channel, the respective positions and flow capacities of the inlet channels and outlet channel being so configured that essentially all flow of the combined jet will pass through and essentially along the axis of the outlet channel when the predetermined ratio is present, two sensing channels located one on each side of the axis of the outlet channel so that the differential pressure between the two sensing channels is dependent upon the divergence if any between the direction of flow of the combined jet and the axis of the outlet channel.

2. A fluid-mixing device according to claim 1 in which the pressure difference between the sensing channels is substantially zero when the required mass flow ratio is obtained.

3. A fluid-mixing device according to claim 1 including means for directing a fraction of one of the fluids to be mixed to its appropriate inlet channel, the fraction being chosen to provide a low mass flow ratio in the inlet channels.

4. A plurality of fluid-mixing devices according to claim 1 connected in cascade so that an inlet channel of the second device and each subsequent device is coupled to the outlet channel of the immediately preceding device.