US2882240A - Smoke generator - Google Patents

Description

April 14, 1959 A. F. cHARwAT SMOKE GENERATOR 2 Sheets-Sheet I 1 Fi-led Feb. 27, 1956 April 14, 1959 A. F. CHARWAT SMOKE GENERATOR Filed Feb. 27. 1956 2 sheets-shea 2 eser-ral',-

lited States Patent `2,882,240 SMOKE `GElJERTAOR Andrew F. Charwat, Los Angeles, Calif., fassignor to INorthrop Aircraft,` Inc., Hawthorne, Calif., a corporation of California ApplicatonFebruary 27, "1956, vSerial No. 567 ,786

yt Claims. (CL-252-359) The present invention relates to smoke generators for 'use in examining the-dow of a gaseous lluild over airfoils or 'other bodies positioned in` a 'stream of said huid, and is of :the type producing a visible vapor condensation or fog as distinguished from the use of fumes or clouds of dust.

The usual use of such generators is to introduce smoke into a wind tunnel in whichfan' a'irfoil is suspended, in order to 'examine through windows "in the wall of 'the tunnel, `the character Yof the air ilow 'over the airfoil surface. Such apparatus are of increasing importance as the speed of airplanes increases and vintensive study is beingmade of means to maintain a close adherence ofthe airstream to the" surface of the 'airfoil at the high speeds. y l

The ""smoke should be dense and v'clearlyvisible,uniform in` quality during extended'runs, have good permanence in the airstrea'm, 4benoncorrosive, nontoxic, and 'be free from depositsfwhich" clog narrow passages.

.The apparatus by which the `smoke is produced should bersimpl'e and reliable, automatic in action, capable of wide variation in the amount ofsatisfactory smoke produced as may be required, from a thin-filament to' the large quantity required to make visible an eXtend'edeld of dow. Y

The' design of a satisfactory smoke generator to meet the requirements 'mentioned provides severall problems. The most suitable material has been found to be a heavy mineral oil which .is heated to Ydrive off vapor which is mixed with air to produce smoke by condensing the oil vapor into minute `droplets of about inneren in diameter. f

In known types of smoke `generators A'using he'avy'oil vapor the 'oil was boiledk and the vapor exhausted through a small oriiice'before being 'mixed withjet's of air, but resultant condensation of' the hot` oil at the orilice was a source of trouble. l A v e The rate of production of the oil vaporshould be con-y stant, requiring' a constant level of the oil in the heater, a constant rate of heating the oil and avoidance `of variation of conditions in the heater. In previously suge gested apparatus variation in the heater is` caused by injecting vapor from a` jet into a stream of air, which yis the only adjustable element with resultant variation of the smoke produced. e

Inorder to meet the requirements above outlined of a satisfactory smoke generator, itis an object of theinven'- tion'toprovide a heating vessel `in which oil is heatedat a, constant rate' to' a temperature well below the boiling point of the oil and to keep allparts of the generator below that temperature. Y

lt is a further object'of thel invention to lprovide for removing the vapor produced by heating'th'e o-il by playing cool air on the heated surface of the oil in the heater, to condense the vapor and remove the 'resulting 'sinoke through tubes of relatively large diameter, thus avr'idingV the use of narrow oriiices through which the vapor is ejected.

. loe

2 A'further object of the invention is to provide a smoke generator capable of as wide variation in the amount of smoke fproduced` as may be required without variation in the quality, of the smoke.

A`Another Vobject of the invention is to provide a smoke generator which is lexible in adjustment,l enabling the economical working of the device yat good elliciency under a variety of conditions.

-A `still further object of the invention is to provide a smoke Ygenerator capable of prolonged use without the need of disassembly for cleaning, thus reducing the idle time ofthe device.

Ano'ther object of the invention is to provide a method for producing smoke from heated loils maintained below their boiling point. A

Still further objects and Afeatures of the invention will appear ifromthe following speciiication read with reference to the accompanying illustrative drawings.

In the drawings: l e

"Figure 1 is a front elevation of the device of the invention; x

Figure `2 is across section, drawn on a reduced scale, on the line "2 2 in Figure `l; and l Figure 3 isY a schematic diagram majking clear the arrangement of 4the various components of the device.

It should be noted that in the form illustrated the `device is intended to supply smoke to a small wind tunnel i'n which ininiature models of Vair foils and the like are tested. e

"Referring no'v'v lto Figure yl, the vnumeral 10 indicates a case containing thesmoke generator, this case comprises side walls 11 and 12, a base 13, top 14, and a front panel 1S carrying control valves and switches, 'but` both "front and 'back ''f 'the ease 10 'are apen to facuitate access to various components of the device for reasons which will'later appear. i

The components of the device comprise a 'reservoir 16 for the `oilused to supply the smoke, the reservoir being provided with an imper'forate filler cap `17 and oil shut-off valve 18 operated by handle 18a, which controls the oil supply to a constant level control means 1'9. The means 19 vcomprise a transparent, tubular, valve housing body 20, ofy'mol'ded' Pyrenfor example, formed with'ilanges 21 Vand 22. rnnge 21 is' clamped by end plate 23 to plate Y2.4 'on which the lvalve '|18 is mounted, and vilange 22`iscla'n'1ped between 'plate 25 arid plate 2:6 to which an oil' delivery tube is braz'ed. The oil in housing 20 is maintained at a constant level by'iloat 28 acting on a spring loaded 4oil inlet vvalve 29. The levelofthe oil is indicated bythe `dashed line 30.

Tube 27 delivers; the oil tothe heating unit generally metal wan 3'2, the oilbei'ng towed in a thin Sheet through the heating unit, in the embodiment shown, by arranging the cylindrical body 33 of a thermo-switch coakially in the heater and supplying 'the 'oil ytol the relatively narrow spacei34 between the outer surface of the body 33 and inner wall lof the'heater. The housing Z0, yheater 31 and connecting conduit form a U`shaped container so that if the pressure on keach end 4is equal, the level of the liquid inthe housing will be the same as that of the liquid in the heater. e e i Heating coils 35 andV 36 arewound around the outer periphery ofthe heater, these coils having equal values of resistance and being arranged so that they may be connected in series or parallel, as indicated 'in Figure 3, by

' switch 37. Thermo-switch 33 is of the make or break type and may be adjusted to operate at any value between and 400 F.' by settingwheel 38. The electrical elements will be further referred to later.

`Aii'e'at retaining jacket 39 is placed over the heating coils. A jet ring 40 or vapor condensing' chainber mounted above the heater 31, and heat transfer to it from the heater is reduced by an asbestos washer (not shown) or the like and by a wire screen 42 mounted in the heater at the level 30 of the top of the oil therein. The jet ring 40 is covered by a cap 43, a second screen 44 being mounted between the top of the jet ring 40 and the cap 43. A smoke unrestricted outlet 'conduit 45. leads from the cap to a collector vessel later decribed.

Air under low pressure is supplied to the jet ring 40 through air inlet 46, shut-olf valve 47 and pipe 48 to a valve body 50, which is manually adjusted by knurled wheel 51 to control ow to a series of jets supplied by small diameter tubes, for instance 2 as shown at 52, 53, which inject the air into the jet ring above the top of the oil. A second valve 54 is arranged to enable one jet or both jets to be supplied with air, or both jets shut ofI.

The remainder of the air flows through tubes 55 leading air from the outer shell of the valve and over the length of the tubes 52, 53 of the jets and exhausting into the space around the jet ring 44, thus aiding in keeping it cool.

A further path for air entering valve S is provided by a tube 56 leading to the collector vessel above referred to and for a purpose later described.

It is to be noted at this point that the oil heated in the heater is not boiled but that the vapor given olf by the heated air is condensed to smoke by the cool low pressure air delivered by the jets, the construction being such as to keep the smoke cool.

The oil reservoir 16, oil valve housing 19 and the jet ring 40 are maintained at a common pressure by tubing' 57 and a small condensate trap 58 is provided to trap any vapor condensed in the tubing.

The smoke owing through outlet 45 is led to the collector and settling vessel 59 from which it is discharged through the unrestricted discharge tube 60 for use.

A regenerator or feed-back arrangement is preferably provided to improve the quality of the smoke especially at very low ilow rates. The regenerative arrangement comprises the tube 56, the air flowing through which is controlled by the on-oi valve 61, and delivers air from its nozzle end 62 into the belled end 63 of feed-back tube 64, with an injector elect which pulls some of the smoke out of the collector vessel 59. The smoke flow in tube 64 is also controlled by valve 61 and is delivered into valve 54 through jet 65 and mixes with the air passing to the jets and into the jet ring 40, the recirculated air and smoke being a considerablefraction of the pure air injected into the jet ring.

The regenerative action improves the quality of the smoke particularly at low ow rates both by maintaining circulation even at minimum rates of smoke production and also is believed to increase the amount ofsmoke formation by providing already formed particles of condensed vapor as nuclei for facilitating the formation of smoke particles.

The circuit by which electric current is supplied to both the thermoswitch 33 and the heating coils comprise a plug in socket (not shown) and to which a cable shown at 67 is connected. Lead 68 is connected through the make-or-break thermoswitch 33 to contact arm 69 of movable contact operating bar 70 of insulating materialy positionl which may be moved to either high or low from off position by the small handle 71. Lead 72 is connected between contact 73 and a connection at the mid point of heating coils 35, 36. Contact 74l is connected by lead 75 to the lower end of coil 35. Switch arm 69 may be brought into engagement with either contacts 73 or 74. A second contact 76 is connected by lead 77 to lead 75. A lead 78 is connected to the upper end of heating coil 36 and to the opposite side of the line. A second contact arm 79 is mounted on contact operating bar 70 and thus moves in unison with contact yarm 69. l

perature which will be below boiling point of the oil,

Arm 79 is connected to lead 78 and engages contact 76 when contact arm 69 engages contact 73 thus completing parallel circuits for coil halves 35 and 36. When arm 69 engages contact 74 a circuit is established in the coil halves 35, 36 which then are in series. The circuit arrangement enables a greater amount of heat to be supplied to the oil heater when heating the oil to start the device thus cutting down starting time and, after generation of smoke has been stabilized, enables the apparatus to continue in operation with lesser amount of heat. A manually operated master switch 80 enables electric current to be cut olf or supplied to the apparatus, and a pilot light 81 indicates when the electric current is turned on by the switch.

A satisfactory oil for use in the device is a paraiin boiling at 460 F., the thermoswitch being set at about 400 F. so that boiling of the oil cannot occur. The small smoke generator described which measures about 15 inches in width, 18 inches in height and 8 inchesin depth, and is therefore readily transportable, can produce a density of about 10g smoke particles per cubic inchl and can be adjusted to deliver from .25 cubic inch to 2 cubic inches of smoke with an input of some 250 watts at lower power.

The cool smoke produced and the relatively large diameter tubes through which it is conducted reduce condensation of the smoke to a minimum and such as occurs causes no clogging of the passages.

The use of air at a constant low pressure and the equalization of the pressures in the oil supply tank, float valve housing and oil vapor or jet chamber, with the maintenance of the oil at a substantially constant temensures steadiness of the smoke generation and freedom from interference from variations of pressure either within the apparatus or due to outside causes. I I

The flexibility of output without variation 1n quality of smoke or instability in rate of smoke generation is believed to be much better than that obtained by previ ously proposed devices.

While in order to comply with the statute, the lnvention has been described in language more or less specificl as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into eifect, and the invention is therefore claimed in any of its forms' or modifications within the legitimate and valid scope of the appended claims.

What is claimed is: 14. In vapor or smoke generating apparatus, the combination comprising: a liquid heating chamber; means adapted to supply liquid and heat to said heating cham-. v` ber; a thermostat in said heating chamber adapted toI maintain the temperature of liquid in the latter below the boiling temperature of said liquid; a vapor receiving. chamber contiguous with and arranged above said heat-i ing chamber; unrestricted conduit means adapted to con# vey vapor from said vapor receiving chamber; a first, metal screen positioned at the top of said heating chamber to provide a perforated partition between the latter and said vapor receiving chamber; tubes adapted to deliver a cool gaseous medium into said vapor receiving chamber in a direction to impinge on said first screen;

first conduit means adapted to deliver al gaseous mediumto said apparatus; second conduit means communicatingv with said rst conduit means and staid tubes; and valve.A

. means adapted to direct a portion of said gaseous medium owing through said second conduit means to said tubes andthe remainder against the outside walls of said vapor collecting chamber.

2. Apparatus as set forth in claim 1 and in addition in `cluding a second wire screen arranged in said vapor collecting chamber between the area of introduction of, cool gaseous medium thereinto and the unrestricted l.

conduit means leading condensed vapor or smoke out of the apparatus.

3. Visible vapor or steam generating apparatus comprising: a liquid heating unit; means supplying liquid and heat to said unit; said unit including a chamber receiving vapor from said unit; a thermostat mounted in said unit and adapted to maintain the heat of said liquid below the boiling point thereof; means maintaining said vapor receiving chamber at a relatively low temperature; means injecting a gaseous medium under pressure and at a lower temperature than said vapor into said vapor receiving chamber; unrestricted conduit means leading the vapor condensed in said vapor receiving chamber out of the unit for usc; a settling vessel into which the coudensed vapor or smoke from the vapor receiving cham ber is led; unrestricted conduit means leading the condensed vapors or smoke from said settling chamber out of the apparatus for use; and means for recycling a portion of the condensed vapor or smoke from the settling chamber into the gaseous medium introduced into the 20 vapor receiving chamber.

4. Apparatus as set forth in claim 3 in which said means for recycling a portion of the condensed vapors or smoke comprise: an injector positioned in said settling chamber; a conduit leading gaseous medium under pressure to said injector; conduit means leading from said injector to lead smoke injected therein to the conduit leading gaseous medium into said vapor receiving chamber; and valve means controlling the conduits for recycling a portion of the smoke Treating Oil Field Emulsions, Petroleum Industry Series (Voc. Training Course), 1949, Amer. Petrol. Inst., Austin, Tex., page 86.

Claims (1)

1. IN VAPOR OR "SMOKE" GENERATING APPATATUS, THE COMBINATION COMPRISING: A LIQUID HEATING CHAMBER; MEANS ADAPTED TO SUPPLY LIQUID AND HEAT TO SAID HEATING CHAMBER; A THERMOSTAT IN SAID HEATING CHAMBER ADAPTED TO MAINTAIN THE TEMPERATURE OF LIQUID IN THE LATTER BELOW THE BOILINAG TEMPERATURE OF SAID LIQUID; A VAPOR RECEIVING CHAMBER CONTIGUOUS WITH AND ARRANGED ABOVE SAID HEATING CHAMBER; UNRESTRICTED CONDUIT MEANS ADAPTED TO CONVERY VAPOR FROM SAID VAPOR RECEIVING CHAMBER; A FIRST METAL SCREEN POSITIONED AT THE TOP OF SAID HEATING CHAMBER TO PROVIDE A PERFORATED PARTITION BETWEEN THE LATTER AND SAID VAPOAR RECEIVING CHAMBER; TUBES ADAPTED TO DELIVER A COOL GASEOUS MEDIUM INTO SAID VAPOR RECEIVING CHAMBER IN A DIRECTION TO IMPINGE ON SAID FIRST SCREEN FIRST CONDUIT MEANS ADAPTED TO DELIVER A GASEOUS MEDIUM TO SAID APPARATUS; SECOND CONDUIT MEANS COMMUNICATING WITH SAID FIRST CONDUIT MEANS AND STAID TUBES; AND VALVE MEANS ADAPTED TO DIRECT A PORTION OF SAID GASEOUS MEDIUM FLOWING THROUGH SAID SECOND CONDUIT MEANS TO SAID TUBES AND THE REMAINDER AGAINST THE OUTSIDE WALLS OF SAID VAPOAR COLLECTING CHAMBER.

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