US3157105A

US3157105A - Apparatus for producing an air curtain

Info

Publication number: US3157105A
Application number: US128592A
Authority: US
Inventors: Tamm Walter; Knapp Werner
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-08-01
Filing date: 1961-08-01
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 1 Filed Aug. 1, 1961 FIG'J WALTER TAMM WERNER KNAPP INVENTORJ .Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 2 Filed Aug. 1. 1961 WALTER TAMM WERNER KNAPP INVENTORS m9 o m: H wow or mu Nov. 17, 1964 I W. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 3 Filed Aug. 1. 1961 WALTER TAMM WERNER KNAPP INVENTORS O O O O 0 0 0 0 0 0 0 O O O O OOOOOOOOO Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 4 Filed Aug- 1. 1961 WEI TER TQM/t7 wERA EZ K HP Nov. 17, 1964 w. TAMM ETAL APPARATUS FOR PRODUCING AN AIR CURTAIN 9 Sheets-Sheet 5 Filed Aug. 1, 1961 4 7- TaQA/E/ Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet 6 I ll M/ VENTQQS Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet 7 WALTER TAMM WERNER KNAPP INV EN TORS Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet 8 WERNER KNA PP WALTER TAMM INVENTORS Nov. 17, 1964 w. TAMM ETAL 3,157,105

APPARATUS FOR PRODUCING AN AIR CURTAIN Filed Aug. 1, 1961 9 Sheets-Sheet 9 W444 122 7 7mm fi WEZA/EZ 41/4 9 ,q 7- ramusy out its range of adjustability.

United States Patent 3,157,105 APPARATUfi FQR PRQDUCENG AN Am CURTAEN Walter Tarnm, Georgenstrassefiai, Munich, Germany, and Werner Knapp, Fcderburgstrasse 59, Ravensburg, Germany Filed Aug. 1, 1961, Ser. No. 128,592 12 (Claims. (til. as-se) The present invention relates to an apparatus for restricting air convection between two spaces interconnected by a wall opening, eg. the interior and the exterior of a building, by screening such opening with the aid of a curtain of air passing across the opening.

It is the object of our invention to provide improved means for producing air curtains of the character described to screen openings communicating between regions of chambers of air at markedly different temperatures whereby cool air may be prevented from entering a eated chamber and warm air from entering a cooled chamber. We have found that conventional air curtains are defiectedat least at the lower portion of the opening by a convection current of cool air moving toward the region of higher temperature and rising from the higher density of the cool air. Thus, the air in a cold chamber at C. is about 13% more dense thanthe external air, which is at a temperature of, say, +20 C., and consequently the pressure exerted by a column of cold air 2.5 meters high in the chamber exceeds by about 6.53 kg./ m. that of a column of the warmer air of the same height. It is, accordingly, a feature of our invention to provide an air-curtain-producing apparatus adapted to screen such openings with a curtain of air directed preferably downwardly thereacross at an adjustable slight angle of, say, 15 to thereby deflecting a preferably minor portion of the stream in counter-curreut to the aforementioned convection current of cool air and counterbalancing the normal pressure gradient across the opening. An air curtain so oriented will deflect a stream or entering air to produce a secondary circulation in the region of the opening between two transverse limiting surfaces such as, for example, the ground and a ledge forming a seal between the wall and the source of air flow supported thereon. This source, in turn, should include a plenum chamber, supplied with air from one or more blowers, and an elongated nozzle communicating with it, the nozzle having as its outlet an elongated slot extending along an edge of the usually rectangular wall opening. In order to insure the existence of the aforementioned ant ls, the nozzle is advantageously defined, along the major sides of the slot, by two panels having the desired inclination with respect to the adjacent wall surface. A system of this description has been disclosed in our copending application Ser. No. 706,171, filed December 30, i957, and now abandoned, of which the present application is a continuation-'in-p art; 1

Devices of this character have proved themselves use ful not only at building doors and windows but also, to an ever-increasing extent, on mobile equipment such as refrigerated trucks. In many instances a. highly compact arrangement is called for along with some mechanism for effectively controlling the flow of air under different operating conditions. It is, therefore,,a furt er object of the present invention to provide simple and dependable means for maintaining an optimum rate of air flow in such devices and, preferably, for enabling adjustment of this r ate witlL'n wide limits. A more particular object of the inevntion is to provide means for equalizing the flow rate over the entire length ofthe nozzle through Advantageously, the apparatus according to our invention has not only means for controllins the quantity of air Q and the velocity V thereof in forming the air curtain, out also means for adjusting the angle ,8 between the plane of the screened opening and the nozzle of the apparatus and, consequently, for setting the complementary impact angle 0: between the impinging air curtain and ground or ledge. The. air curtain, upon impact, divides into a forward stream generally directed toward the warm region and a rearward stream which establishes the secondary circulation to counterbalance the effect of the cold-air convection current. We have found that optimum screening results, for openings between regions having the usual temperature differentials (e.g. 20 to 50 C.) therebetween, may be obtained when the ratio of the flow rates Q and Q of the rearward and forward streams is equal to about 1/2. Since the fiow-rate ratio may be given by the expression the angle or will be found to have a value of about 20 although the optimum angle for each installation may have to be determined by the particular conditions preseat at the screened opening. in general, We have found that the angle or should be equal to about 20i5.

Although the optimum selection of the other air-curtain parameters, eg. nozzle width and flow rate, may also be determined individually for each installation, highly satisfactory air curtains were obtained with nozzles 20 to 30 mm. in width and flow rates from 8 to 12 meters per second to screen out cold air; with nozzles up to 60 mm. in width and how rates from 12 to 18 meters per second to screen out Warm air, breezes and, occasionally, high winds; and with nozzle widths from to mm. and flow rates of 15 to 20 meters per second for air curtains adapted to repel insects from an opening.

It should be noted further that the lower the speed at which the air-curtain stream impinges upon the opposite Wall or ledge, the smaller is the quantity of air which constitutes the rearward stream. When the air-curtain flow rate is reduced below a predetermined value, determined by the conditions (e.g. temperature) present at the opening, no rearward stream is able to flow countercurrent to the convection-current stream at the base of the opening and to provide a balancing effect therefor. There are, however, limits to the'maximum and minimum values of the impact an le and to the flow rate of the aircurtain stream. For example, the smaller the impact angle or is made, the larger will be the unprotected triangular area between the main air-curtain stream and the plane of the opening, thereby decreasing the effectiveness of the curtain since screened-out air tends to penetrate the air curtain via this unprotected region.

It is, therefore, another feature of the invention to provide means for setting the nozzles of the air-curtain-producing apparatus at the correct angle and to control the flow of air therethrough, thereby enabling the apparatus to be used equally well for openings of relatively low height where relatively low flow rates are desirable and for relatively high openings where high flow rate are required. Generally, an opening of reduced height will require an apparatus having a smaller nozzle angle than an apparatus employed for air-curtain screening of higher openings.

A further feature of the invention resides in the provision of means for screening the lateral portions of the aforementioned triangular region, included between the main air-curtain stream and the plane of the opening, by secondary air curtains, thereby preventing the penetration of screened-out air through the air curtain via this region.

in order to reinforce the secondary stream of the air curtain, which generally flows toward the cooler region,

a the air-curtain-produciug apparatus may be provided with Venturi-type aspirating means, e.g. a tube communicating with the interior of the nozzle and the space defined by the latter, the building-wall portions adjacent the opening and the sealing or baffle means in the gap between the nozzle and the wall, adapted to accelerate the secondary stream. While it is usually preferable to dispose the air-curtain apparatus above the opening to be screened within the warm region, we have found that space-saving considerations, especially for screened openings of refrigerated vehicles, often require the positioning of the apparatus within the cooled area in which case the primary air-curtain stream is directed in counter-current to the convention current of cool air toward the opening. To minimize the excess of the primary stream over the convention current, the impact angle of the main aircurtain flow is set as close to 90 as is practical. More over, it frequently is desirable to position a pair of such air-curtain-producing devices along each vertical edge of a generally rectangular opening whereby the nozzles of the two devices direct opposing air-curtain streams toward the median plane of the opening. While the opposing streams may be designed to merge at a straight angle (i.e. 180) whereby substantially equal forward and rearward streams may be established, it is preferable that the two air-curtain streams include an angle less than 180 whose vertex is directed toward the warmer region, thereby resulting in a forward stream whose flow rate may be in the aforementioned desirable ratio of 2:1 to the flow rate of the rearward stream.

In accordance with another aspect of this invention there is provided, in an air-curtain-producing apparatus of the character hereinabove described, a tubular element open at one or both ends, defining a plenum chamher, which is formed on one side with a longitudinal slot extending over a major part of its length, this slot terminating in a nozzle extending substantially tangentially of the tubular element whereby air admitted under pressure from the open end or ends is deflected sideways and then outwardly through the nozzle; between the source of air and the plenum chamber proper, i.e. the region defined by the longitudinal slot, there is formed within the tubular element a generally cylindrical space or antichamber free from internal obstructions whose axial length is sufficient to enable the turbulent incoming air to revert to laminar flow. This axial length is advantageously of the order of the width of the element, or at least as large as its radius, and may in practice range between about 10 and 25 cm. with tubes of 20 to 40 cm. in diameter. The plenum chamber beyond this space is preferably provided, according to a further feature of the invention, with guide means partly obstructing the air flow through the slot whereby a substantial part of the air is deflected further along the tube so as to pass through the nozzle at locations remote from the inlet; in this manner the velocity of the outflowing air can be substantially equalized over the length of the plenum chamber. The guide means may comprise a set of axially spaced, laterally offset baflies within the tube or, in simpler cases, a perforated screen spanning the slot.

We have found, in this connection, that the velocity of the outflowing air can be substantially equalized over the length of the nozzle in the absence of such bafiies under certain conditions although, even under such circumstances, it is advisable to use the battles to insure a minimum velocity gradient from the portion of the nozzle proximal to the inlet of the plenum chamber to the portions of the nozzle remote therefrom. More specifically, we have determined that the ratio V /V of the velocity V of the outlet air at a location of the elongated nozzle remote from the closed end of the plenum chamber to the velocity V of the outlet air at a location proximal thereto is proportional to \/1+ (cl/A) where ((1/11) is the ratio of the outlet cross-sectional area a to the cross-sectional area A of the inlet to the plenum chamber. Thus, the maximum gradient between the velocities V and V may be maintained below any desired value by a suitable dimensioning of the inlet and outlet cross-sectional areas; for instance, if, as is generally the case, the velocity V ranges from V V to V =l.l V the ratio (a/A) will be found to range from a/A=0 to about a/A==0.48.

Advantageously, a plurality of angularly adjustable transverse plates, which function as dampers, may be spacedly positioned along the elongated mouth of the nozzle to provide a final means for adjusting the velocity of the outlet air therealong and for correcting the direction of flow of the outlet air. These dampers may be independently adjusta he or provided with common actuating means for regulating the air outflow. The outlet tip of the nozzle may, according to a more specific feature of the invention, be angularly displaceable about an axis parallel to its major dimension to permit correction of the angle of impact. We have also found that, when nozzles extending substantially tangentially from a plenum chamber are employed, air turbulence in the region wherein the tangential nozzle opens into the cylindrical plenum chamber may be obviated by the provision of a deflecting strip extending from the common inner wall of nozzle and plenum chamber into the latter and including with the plane of the nozzle an angle of about 20 to 40.

The above and other objects, features and advantages of the invention will become more fully apparent from the following detailed description, reference being made to the accompanying drawing in which:

FIG. 1 is a perspective view of an air-curtain-producing apparatus embodying the invention;

FIG. 2 is a side view of the apparatus (parts broken away) taken on the line II-II of FIG. 3;

FIG. 3 is a cross-sectional view taken on the line llilii of FIG. 2;

FIG. 4 is a view (parts broken away) of the left-hand portion of FIG. 2, drawn to a larger scale and illustrated in a ditferent position of adjustment of its inlet-control mechanism;

FIG. 5 is a cross-sectional view taken on the line VV of FIG. 4;

FIG. 6 is a view similar to FIG. 2, showing a modified embodiment;

PEG. 7 is a cross-sectional view taken on the line VlIVlI of FIG. 6;

FIG. 8 is a side-elevational view, partly in section, of the nozzle of an air-curtain-producing apparatus provided with aspirating means according to the invention;

FIG. 8A is a front-elevational view, partly in section, of the apparatus shown in FIG. 8;

FIG. 9 is a view similar to FIG. 8 of a nozzle according to another embodiment of the invention;

FIG. 10 is a side-elevational view of an air-curtainproducing apparatus illustrating means for adjusting the angle included between its air curtain and the plane of the screened opening;

FIG. 11 is a view similar to FIG. 10 of an apparatus having a register disposed at the base of the opening below its nozzle for deflecting the air stream;

FIG. 12 is a perspective front view of an apparatus whose air intake has an axis parallel to the nozzle;

FIG. 13 is a front-elevational view of an apparatus Whose air intake has an axis extending transversely to the elongated nozzle;

FIG. 14 is a cross-sectional view taken along the line XIVX1V of FIG. 13;

FIG. 15 is a front-elevational view, partly in section, of an apparatus whose plenum chamber is supplied with air via two tangential blowers;

FIG. 16 is a view similar to FIG. 15 of another apparatus in which the blower means are disposed within the plenum chamber;

FIG. 17 is a cross-sectional view taken along the line XVII-XV1I of FIG. 16;

FIGS. 18-21 are side-elevational views of air-curtainproducing devices according to further embodiments of the invention, illustrating the operation thereof somewhat schematically;

FIG. 22 is a view similar to FIG. 7 of a plenum chamber and its tangential nozzle, showing additional means for suppressing turbulence;

FIG. 23 is a cross-sectional view taken along line XXIII-XXIII of FIG. 22;

FIG. 24 is a front-elevational view of a wall opening provided with lateral air-curtain-producing devices;

FIG. 25 is a cross-sectional view taken along the line XXVXXV of FIG. 24;

FIG. 26 is a view similar to FIG. 24 of an opening having an air-curtain-producing apparatus thereabove and provided with supplemental means for preventing the flow of air between the chambers interconnected by the opening according to another embodiment of the invention;

PEG. 27 is a cross-sectional view taken along line XXVIL-XXVII of FIG. 26;

FIG. 28 is a perspective front view of an air-curtainproducing apparatus whose inlet axis extends transversely to the nozzle;

FIG. 29 is a front-elevational view of a slightly modified apparatus; and

FIG. 30 is a side View of the apparatus of FIG. 29.

As shown in FIG. 1, an air-curtain-producing apparatus 101 is fastened upon a vertical wall 131, above an opening 132 therein, by means of brackets (not shown) engaging

lugs

130, 130" of which several pairs are provided at diiierent peripheral locations to afford a choice of mountings. The apparatus 101, of generally tubular elongated shape, is provided on one end with an adjustable air intake 105 having a port screened by a mesh guard 106 for the admission of an air flow at a rate controlled by an adjusting mechanism 120. An elongated nozzle 127 has an outlet slot 137 and slants downwardly from the cylindrical main part 102 of the apparatus. Air issues from the nozzle 127 at high speed, the main air stream forming an angle 13 with the wall 131. Depending upon various conditions, such as the dimensions of nozzle 127 and the temperature gradient in opening 132, the optimum angle of incidence u. for achieving the best screening effect may vary between approximately and 25 as previously noted, the complementary impact angle ,8 between the impinging air stream and ground being therefore about 65 to 75. The space between wall 131 and the diverging lower end of nozzle 127 is sealed by a packing 129.

The air intake 105 of the apparatus 101 comprises, as shown in FIGS. 2, 4 and 5, in a head 111 restrictedly rotatable on the hollow cylinder 102 whose interior defines a plenum chamber 103 and an antechamber 128. A plurality of vanes 107 made of mild steel or other convenient material, e.g. sheet aluminum, are spot-welded to sleeves 109 swingable around arms 110, the latter extending radially from a central boss 103. Any convenient number of vanes may be provided, eight being shown in the illustrated embodiment. The inner end of each sleeve 109 has welded to it a bent lug 112 which extends through a slot 113 in a disk 114 rigidly attached (e.g. by welding) to a central support shaft 115 traversing the boss 103. The shaft 115 is carried by a spider 116 having a plurality of bars whose outer ends are welded to cylinder 102 from the inside. On its end remote from disk 114 the shaft 115 supports a fan constituted by an electric motor 117 baring blades 118 (FIG. 4).

The arms 110 extend radially to the intake head 111 to which the outer ends of the arms are attached by bolts 119. On its circular edge embracing cylinder 102, head 111 supports a rack 121 bearing a graduated scale. A worm 122 mounted on a shaft 123 engages the rack 121, and a pointer 124 registers the relative angular displacement of head 111 and cylinder 102 on the scale, thereby also indicatingthe degree of opening of the air intake 105. Shaft 123, journaled in bearings 1Z5, terminates at one end in a milled knob 134. The mesh guard 106 is fastened to the air intake by means of cleats 126.

The fan forces air from the entrance port of intake 105 into the plenum chamber 103 and expels it through the nozzle 127. As shown in FIG. 3, the nozzle 127 is tapered to provide a constriction which concentrates the air flow to produce a downwardly directed jet. The air on the downstream side of the fan 118 is turbulent, hence the antechamber 128 is formed as a free space devoid of bafiles and projections so that the air flow is smoothened when passing through this section. The plenum chamber 103, on the other hand, is provided with axially spaced and laterally ofiset bafiles 133a, 1331), 133a, 133d which direct the outlet air into the nozzle 127. In order to insure an equal exit velocity along the whole length of the duct 127, the plenum chamber 103 is divided by the battles 133a to 133d into compartments of equal crosssectional areas; for this purpose the centrally located bafiies 133b, 1330 are nearer to each other than to the outer bafdes 133a, 133d. As a result of this arrangement the air velocity prevailing in the compartments defined by the bafiles is substantially uniform.

As shown in FIG. 3, the upstream edges of the baffles 133a to 133d are inclined to the vertical; each bafile comprises a curved downstream portion which directs the air from plenum chamber 103 into the nozzle 127 and merges with an upstream portion extending longitudinally of the plenum chamber. Advantageously, the proximal edge of at least one baffie lies at the junction of antechamber 123 and plenum chamber 103 as here shown for the battle 133a.

It has been found that with plenum chambers arranged in this manner it is possible to minimize any variations in the velocity of the air leaving the plenum chamber at different points, the maximum velocity variation being 5% of the mean velocity.

In FIG. 2 the vanes 107 are shown in a fully closed position, thereby obstructing the flow of air into the plenum chamber 103. The vanes 107 can be moved in unison from this position toward a partly or fully open position, as shown in FIGS. 4 and 5, by causing a relative rotational movement between the intake head 111 and the cylindrical chamber housing 102 by means of the adjusting mechanism operated by knob 134. Rotation of the arms 110 connected to the head 111 causes the lugs 112 to co-operate with the slots 113 in disk 114 to rotate the vanes 107 on their sleeves 100 around the arms 110 into the open position. The disk 114 does not move because it is rigidly fixed to shaft 115. Advantageously, the disk is somewhat resilient or covered by a. soft elastic layer to cushion the impact of the vanes 107 upon closure. 7

It is, therefore, possible to move the vanes 107 from their coplanar closure position (FIG. 2) through a continuity of intermediate positions (FIGS. 4 and 5) into a fully open position, in which the air flow through the intake is substantially unimpeded, and vice versa.

In the modification illustrated in FIGS. 6 and 7 the baffles are dispensed with, and in their place there is arranged a perforated partition 133' located between the plenum-chamber housing 1 3. and the nozzle 127 while extending along the entire length of the nozzle. The partition has the effect of distributing the air pressure so that throughout the length of the duct 127 the air velocity will again be substantially uniform. The device 101' shown in FIG. 6, centrally subdivided by a partition 1 11, has two oppositely positioned air intakes 105', 105" Whose heads 111, 111" are jointly controlled by a thermostatic device to regulate the rate of inflow. Evidently, a symmetrical arrangement such as that shown in FIG. 6 may also be used for the type of device illustrated in FIGS. 1-5, particularly with plenum chambers of great length.

In FIG. 8 we show an air-curtain-producing apparatus whose plenum chamber feeds air to a nozzle 4, mounted upon a wall 7 above an opening 1 therein. A suitable sealing means in the form of a resilient packing is disposed between the nozzle 4 and the wall 7 and forms therewith a downwardly open space as illustrated, for example, in FIG. 20. As clearly though somewhat diagrammatically shown in the latter figure and in FIGS. 18, 19 and 21, the nozzles 4 and 4 (FIG. 19) include angles {3 with the plane of the opening 1 whereby the air-curtain streams 5, issuing from the nozzles, includes a complementary impact angle a with the floor 6 and, upon impact, forms the aforementioned primary stream and a secondary circulation 9 of air. The latter comprises a stream extending along the floor 6 in counter-current to any cool air fiow along the latter from the cooler chamber A (FIG. 18) toward the warmer chamber B. The circulating stream 9 is deflected upwardly within the cooler chamber A whence it returns to the nozzle 4, 4' to become entrained by the downwardly flowing air curtain.

Whereas in the embodiment illustrated in FIG. 18 the apparatus including its fan 2, plenum chamber 3 and nozzle 4 is mounted directly upon the wall without any gap therebetween whereby the nozzle-forming plates serve to direct the circulating stream 9 back into the main aircurtain flow, in the embodiment of FIG. 19, which is shown to have a nozzle 4' formed with two parallel mouths adapted to produce a double-layer curtain of particular effectiveness, a resilient packing 10' is disposed between the nozzle and the wall 7 to prevent the accumulation of non-circulating air therein. Depending upon the specific operating conditions, the packing 10' may completely fill the gap of triangular cross-section between the nozzles 4 (FIG. 19) to prevent the formation of a dead space therein or may leave therein a recess 1011 (FIG. 20), swept by the secondary circulation 9, adjacent the outlet end of the nozzle. Frequently, the air-curtain apparatus must be disposed at some distance from the plane of the opening (FIG. 21) to, say, permit the passage of a sliding door or the like between the nozzle 4 of the apparatus and the opening. In this case, we prefer to dispose a sealing plate 11 between the nozzle 4 and the wall 7. This plate functions fully as effectively as the packings 1G and 16' described above.

Although the sealing means 10, 10' and 11, illustrated in FIGS. 1821, effectively prevent the accumulation of stagnant air between the

nozzles

4, 4 and the wall 7, we have found that the use of such sealing means along the elongated mouth of the nozzle, liable to encumber the apparatus and to prevent needed adjustment of the angle 5, may be dispensed with if suction or Venturi means are provided on the nozzle to draw any air present in the gap into the main air-curtain streams. Thus, the nozzle 4 of the apparatus illustrated in FIG. 8 is provided with a suction tube whose upper extremity 12 terminates in the gap between the nozzle 4 and the Wall 7 while its lower extremity 13 opens downwardly in the nozzle 4. At least part of the secondary circulation 9 is, as a consequence of the Venturi effect at the extremity 13 of the tube, drawn into the other end 12 of this tube, thereby preventing stagnation of any air in the gap.

In FIG. 9 we show another air-curtain apparatus wherein the nozzle 4" is swivelable about a longitudinal axis on its ball-and-socket joint 15 relatively to the plenum chamber 3 whereby the angle ,8 included between the nozzle and the wall 7 (FIGS. 18-21) may be adjusted to provide optimum results as previously noted. To lock the nozzle in its optimum angular position, it is formed with a link 16 having an arcuate slot engaged by a locking screw afiixed to the Wall 7. In this embodiment the nozzle 4 has an Opening at its upper end communicating with the gap between the nozzle and the wall 7 and is formed internally with a plate 14' terminating at the upper nozzle opening whereby air is sucked by a Venturi effect from the gap into the nozzle as indicated by the brokenline arrows.

A more convenient method of mounting the air-curtainproducing apparatus so that its nozzle angle is adjustable is shown in FIG. 10. The plenum chamber 3 and its nozzle portion 4 are pivoted at a hinge 17 to the wall 7 while a turnbuckle 18, interconnecting the apparatus and the wall, is disposed above the hinge 17 so that the angle {3 may be increased by decreasing the effective length of the turnbuckle 13 and vice versa.

FIG. 11 illustrates an apparatus mounted in accordance with another embodiment of the invention wherein the angle [3 between the wall 7 and the nozzle 4 of the apparatus is substantially 0 and the complementary angle or is substantially 90. The impact-receiving surface 6 directly below the nozzle 4 is formed with a slotted or otherwise apertured plate 19 which covers a depression 21 in the surface 6. In this depression, which is formed with upwardly diverging walls, there is disposed an airguiding cylinder with its axis substantially parallel to the nozzle 4- whereby the air-curtain stream entering the depression is deflected slopingly upwardly and outwardly from the substantially planar curtain.

In FIG. 12 we show an air-curtain-producing arrangement wherein an axial blower 2 feeds a plenum chamber which, in contradistinction to the plenum-chamber housing 162 (FIG. 1) of cylindrical configuration throughout its length, has a turbulence-suppressing cylindrical antechamber 22 flanged at 25 to the angularly adjustable flared distributing portion 23 of the plenum chamber 3. The distributing portion 23 is formed with a generally C-shaped nozzle outlet whose elongated intermediate portion extends parallel to the plane of the opening 1 and emits a downwardly directed main air-curtain stream of the type shown at 5 in FIGS. 18-21. The side portions 4a, 4b of the outlet extend transversely to the elongated main portion dc thereof and form lateral air curtains which enclose the sides of the space of triangular crosssection between the main air-curtain stream and the plane of the opening. The width of the lateral air curtains may be adjusted with the aid of a pair of lateral regulators 8 hinged to the plenum-chamber housing.

Instead of having axial blowers or fans disposed at one or both longitudinal extremities of the apparatus as shown in FIGS. l-7 and 12, the cylindrical plenum-chamber housing 28 in FIGS. 13 and 14 is equipped with a centrifugal blower 26 whose outlet communicates with the plenum chamber 3 at a central location, the chamber 3 being provided with deflecting guides 27 to direct the incoming air stream toward each end of the chamber, thereby equalizing the outlet flow velocity along the nozzle 4 of the chamber.

FIG. 15 shows two centrifugal blowers 26 axially supplying air to the cylindrical housing 28 whose plenum chamber 3 contains a plurality of laterally offset baflles 27, generally similar to the bafiles 133a to 133d of FIGS. 2 and 3, at each side of the chamber to render the velocity of the outgoing air substantially uniform over the length of the nozzle.

In FIGS. 16 and 17 we show another embodiment wherein a centrifugal impeller 29, driven by a motor 31, is journaled in the housing 28 with its axis parallel to that of the housing but oifset therefrom whereby air may be sucked into the plenum chamber 3 thereof via the longitudinal slot 30 in housing 28 and expelled via the longitudinally extending nozzle 4 parallel to that slot.

A particularly advantageous construction of the generally cylindrical plenum chamber described above is shown in FIGS. 22 and 23. The cylindrical housing 58, surrounding a plenum chamber 53, merges into a tangential nozzle 54 which extends substantially parallel to the axis of housing 58 and is formed by a pair of spaced longitudinal panels 54', 54". At the junction between the inner panel 54' and the housing 58 we provide a relatively narrow longitudinally extending flap 55 (e.g.

of a width equal to about that of the spacing between the

plates

54, 54") which is bent inwardly and includes an angle between substantially 20 and 40 with the plane of panel 54. The flap 55 has been found to reduce turbulence in the nozzle 54 as the air, under the high, substantially static pressure in the. chamber, enters the nozzle. 1

In order to adjust the outflow from nozzle 54 to eliminate any substantial deviation of the flowfrom a portion of the nozzle rout of the main air-curtain sheet of air and to reduce, any remaining variation in the velocity of the air at diiferent locations along the nozzle, we provide an array of relatively closely spaced, individually adjustable dampers 56 extending between the main panels 5d, 54" tranversely to the latter at the mouth of the nozzle. The dampers, of a length equal to a fraction (preferably about one quarter) of the effective height of p the nozzle as seen in FIG. 23, may be frictionally engaged by the panels or, as shown in FIGS. 22 and 23, pivoted on their pins 57. The latter carry ratchet wheels 58' respectively engaged by manually retractable pawls 59 to hold the bafiles 56 in the positions to which they are set. The dampers 56 are, advantageously, spaced apart by distances approximately equal to their length.

In FIGS. 24 and 25 we show two air-curtain-producing

units

201 and 201", each generally similar to the apparatus 101 illustrated in FIG. 1, whose nozzles extend longitudinally along opposite lateral edges of an opening 1 and direct respective air-curtain streams 265', 205 toward the median plane of the opening. The major portion 266 of the air stream merging at the median plane flows away from the cold chamber 207 while secondary circulations 2%99 (similar to the circulation 9 previously described) are established between the opening 1 and the nozzles which are inclined, as before, at the angles 5 to the plane of the opening. Since the air curtain shielding the opening 1 must withstand larger cold-air currents at the base of the opening than at its top, we design the baffles (which are generally similar to the bafiles 133a-133d) of the units 201', 201 so that the velocity V of the air curtain at the base of the opening 1 is from 10 to greater than the velocity V of the air curtain at the top of the opening.

FIGS. 26 and 27 illustrate another air-curtain-pro ducing arrangement according to our invention wherein an intake head 305 containing an axial blower of the type housed in the head 195 (FIG. l) is flanged to an intermediate plenum-chamber housing 320' which, together with another housing 320" flanged to the main cylindrical housing 328, produces lateral air curtains at each side of the principal air curtain as previously described. For this purpose, the housings 3219' 320" enclose extensions of the main plenum chamber and have nozzles 3521', 321 which extend perpendicularly to the longitudinal nozzle 354 that lies parallel to the upper edge of the doorway 1. We have found that it is possible to increase the efficiency of the air-curtain screen, especially for relatively high openings, by providing a mechanical barrier, at least at the lower part of the opening, between the cool-air chamber and the secondary circulation balancing the convection-current outflow from this chamber. Advantageously, the mechanical barrier may comprise resiliently defiectable sheet means, e.g., of rubber, interposed between the main air curtain and the cold chamber and extending over a substantial portion of the doorway from its base. The sheet means may comprise a pair of swinging rubber doors 33d, 33%" mounted along the lateral edges of the doorway (FIGS. 26 and 27) upon vertical rods 331', 331 so as to be defiectable by a cart or the like thrust through the doorway into th dot-dash position and, upon passage of the cart therethrough, to swing back to their solid-line position.

In FIG. 28 we show another air-curtaim-producing apparatus having an axial fan 2, of the type shown in FIGS. 8-11, which feeds a downwardly flared plenum chamber 3 and its elongated nozzle 4. The latter is adjustable, e.g. as illustrated in FIG. 9, about a longitudinal pivot and is bracketed by a pair of lateral air-curtain nozzles 8' Which are adjustable about respective transverse pivots. The nozzles 8 produce lateral air screens which enclose, together with the main air screen, the space of triangular cross-section between the latter and the plane of the open ing 1 as described hereinabove. A plurality of velocityequalizing and distributing batlles 27a are spacedly positioned in the plenum chamber 3 to direct the air stream substantially uniformly to the nozzles 4 and 8'.

FIGS. 29 and 30 of the drawing show another apparatus, generally similar to the one illustrated in FIG. 28 but with the curved baliies 27a of the latter replaced by the planar 'bafiles 27b.

The construction of the apparatus may of course be modified without departing from the scope of the invention as defined by the appended claims. Thus, for example, some of the features herein disclosed will also be useful where the air leaves the plenum chamber by a plurality of axially spaced lateral outlets rather than by a continuous slot.

What is claimed is:

l.'An apparatus for producing an air curtain to screen a generally rectangular door opening in an enclosure wall against penetration by convection currents, comprising an elongated plenum chamber extending substantially horizontally above said opening, lower means coupled with said plenum chamber for supplying air thereto,van elongated nozzle on said plenum chamber communicating with the interior therewith, said nozzle having a pair of longitudinally extending parallel panels inclined with respect to said wall at an angle between substantially l5 and 25 for producing an air current across said opening downwardly diverging from said wall at said angle, said panels forming between them an air-outlet slot extending substantially over the full width of said opening and tacing a floor surface near the bottom of said opening, one of said panels lying closer than the other to said wall, and sealing means between said one of said panels and said wall above the lower edge of said one or said panels forming a reflecting surface for upwardly circulating air branched off said air current at said floor surface, said one of said panels being provided with air-entrance means below said reflecting surface for aspir'ating part of said upwardly circulating air into said nozzle.

' 2. An apparatus for producing an air curtain to screen a generally rectangular door opening in an enclosure wall against penetration by convection currents, comprising an elongated plenum chamber extending substantially horizontally above said opening, a source of air under pressure in said chamber, an elongated main nozzle on said plenum chamber communicating with the interior therewith, said nozzle having a pair of longitudinally extending parallel panels inclined with respect to said Wall at an angle between substantially 15 and 25 for producing a primary air current across said opening downwardly diverging from said wall at said angle, said panels forming between them an air-outlet slot extending substantially over the full width of said opening and facing a floor sur face, and a pair of auxiliary nozzles disposed near the ends of said main nozfle and bridging the space between said panels and said wall, said auxiliary nozzles communicating with said source for producing downwardly directed secondary air currents substantially transverse to said primary air current, thereby screening off three sides of a region of generally triangular cross-section adjacent said opening.

3. A device for screening an opening in an enclosure Wall by an air curtain, comprising a body of generally cylindrical configuration open on at least one of its ends, said body including a peripherally closed first section forming an antechamber next to said open end and a second section axially adjoining said first section, said second section forming a plenum chamber communicating with said antechamber and being provided along its side with nozzle means forming an outlet slot, said slot communicating with the interior of said plenum chamber and extending over substantially its entire length, and a source of air under pressure having a discharge end within said body ahead of said open end, said antechamber constituting a free space of sufiicient length in axial direction to convert the stream of air entering said plenum chamber from a turbulent state to substantially laminar flow.

4. A device according to claim 3, further comprising air-distributing means in said plenum chamber extending generally longitudinally thereof adjacent said nozzle for substantially equalizing the velocity of the outgoing air flow along said slot.

5. A device according to claim 4 wherein said air-distributing means comprises a series of bafiles having transveresly spaced upstream portions and laterally curved downstream portions directed toward said nozzle, said upstream portions extending in longitudinal direction of said plenum chamber, said downstream portions being relatively staggered in longitudinal direction.

6. A device according to claim 5 wherein at least one of said bafiles terminates substantially at the junction of said plenum chamber with said free space.

7. A device for preventing the flow of air from a colder region to a warmer region through a door opening in a wall separating said regions, comprising a body on said wall above said door within said warmer region, said body forming a generally cylindrical plenum chamber extending substantially horizontally across the width of said opening, and air-circulating means on said body having an intake in said warmer region and a discharge end communieating with said plenum chamber; said body being provided with a slot forming a lateral air outlet for said plenum chamber over substantially its entire length, said outlet being trained upon an opposite floor surfaced at a downward angle of inclination relative to said wall at which the air current issuing from said slot is split, upon impinging upon said floor surface, into a major component directed toward said warmer region and an oppositely directed minor component sufiicient to prevent the intrusion of air from said colder region along said floor surface, said major and minor components being related in substantially the ratio of 2: 1.

8. In a door-screening system comprising, in combination, a device for preventing the fiow of air from a colder region to a Warmer region through a door opening in a wall separating said regions, comprising a body on said wall above said door within said warmer region, said body forming a generally cylindrical plenum chamber extending substantially horizontally across the width of said opening, and air-circulating means on said body having an intake in said warmer region and a discharge end communicating with said plenum chamber; said body being provided with a slot forming a lateral outlet for said plenum chamber over substantially its entire length, said outlet being trained upon an opposite floor surface at a downward angle of inclination relative to said wall at which the air current issuing from said slot is split upon impinging upon said floor surface, into a major component directed toward said warmer region and an oppositely directed minor component sufficient to prevent the intrusion of air from said colder region along said floor surface, and swingable gate means at a lower portion of said door opening extending over substantially less than the full height thereof.

9. A method of preventing the flow of air from a colder region to a warmer region through a door opening in a wall separating said regions, comprising the steps of creating a downwardly directed air curtain across said opening toward a floor surface at the bottom thereof, said air curtain diverging downwardly from said wall at an angle so chosen as to split said air curtain, upon its impingement on said floor surface, into a major component directed toward said warmer region and an oppositely dit2 rected minor component suflicient to prevent the intrusion of air from said colder region along said floor surface; and compensating for changes in the temperature difference between said regions by varying said angle to an extent maintaining the ratio of said major and minor components at a value of substantially 2: 1.

10. A device for preventing the flow of air from a colder region to a warmer region through a door opening in a wall separating said regions, comprising a body on said wall above said door Within said warmer region, said body forming a plenum chamber extending substantially horizontally across the width of said opening, and aircirculating means on said body having an intake in said Warmer region and a discharge end communicating with said plenum chamber; said body being provided with a slot forming a lateral air outlet for said plenum chamber over substantially its entire length, said outlet being trained upon an opposite floor surface at a downward angle of inclination relative to said wall at which the air current issuing from said slot is split, upon impinging upon said floor surface, into a major component directed toward said warmer region and an oppositely directed minor component sufficient to prevent the intrusion of air from said colder region along said floor surface, said major and minor components being related in substantially the ratio of 2:1.

11. In a door-screening system, in combination, a device for preventing the flow of air from a colder region to a warmer region through a door opening in a wall separating said regions, comprising a body on said wall above said door within said warmer region, said body forming a plenum chamber extending substantially horizontally across the width of said opening, and air-circulating means on said body having an intake in said warmer region and a discharge end communicating with said plenum chamber; said body being provided with a slot forming a lateral outlet for said plenum chamber over substantially its entire length, said outlet being trained upon an opposite floor surface at a downward angle of inclination relative to said wall at which the air current issuing from said slot is split, upon impinging upon said fioor surface, into a first component directed toward said warmer region and an oppositely directed second component opposing the intrusion of air from said colder region along said fioor surface, said major and minor components being related in substantially the ratio of 2: 1, and swingable gate means at a lower portion of said door opening extending over substantially less than the full height thereof.

12. A device for screening an opening in an enclosure wall by an air curtain, comprising a body forming an elongated plenum chamber of generally cylindrical configuration open on at least one of its ends and being provided along its side with nozzle means forming an outlet slot, said slot communicating with the interior of said plenum chamber and extending over substantially its entire length, and a source of air under pressure having a discharge end within said body ahead of said open end, said discharge end being separated within said body from said chamber by a free space of sufiicient length in axial direction to convert the stream of air entering said plenum chamber from a turbulent state to substantially laminar flow.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. AN APPARATUS FOR PRODUCING AN AIR CURTAIN TO SCREEN A GENERALLY RECTANGULAR DOOR OPENING IN AN ENCLOSURE WALL AGAINST PENETRATION BY CONVECTION CURRENTS, COMPRISING AN ELONGATED PLENUM CHAMBER EXTENDING SUBSTANTIALLY HORIZONTALLY ABOVE SAID OPENING, BLOWER MEANS COUPLED WITH SAID PLENUM CHAMBER FOR SUPPLYING AIR THERETO, AN ELONGATED NOZZLE ON SAID PLENUM CHAMBER COMMUNICATING WITH THE INTERIOR THEREWITH, SAID NOZZLE HAVING A PAIR OF LONGITUDINALLY EXTENDING PARALLEL PANELS INCLINED WITH RESPECT TO SAID WALL AT AN ANGLE BETWEEN SUBSTANTIALLY 15 AND 25* FOR PRODUCING AN AIR CURRENT ACROSS SAID OPENING DOWNWARDLY DIVERGING FROM SAID WALL AT SAID ANGLE, SAID