US2356757A - Air conditioning apparatus - Google Patents

Description

g W. L. FLEISHER AIR CONDITIONING APPARATUS Filed we.

lNVENfOR 3 Wu TEI? FZE/SHER BY 56 V72 ATTORNEYS I ran STATES FFKIE AIR CONDITIONING APPARATUS Walter L. Fleisher, New City, N. Y.

Application December 10, 1941, Serial No. 422,319

2 Claims.

This invention relates to apparatus for use in the conditioning of air for human comfort, and, primarily to apparatus designed to clean air eniciently without, however, completely saturating it with moisture. For household or theatre use, it is desirable, as long as thorough cleaning of the air is obtained, to use a conditioner having only about thirty per cent saturation efiiciency because it is undesirable to put too much moisture into theatres or rooms. This is true especially in the winter time because of the likelihood of moisture condensation on windows or other cold surfaces and of other objectionable features. Also,

it is undesirable because with increased saturation eiliciency the temperature of the air leaving the conditioner is lowered, and air too cool for comfort is introduced into the room or chamber. For instance, if air enters a highly eflicient saturating device at 70 F. and 30% relative humidity, it has a wet bulb temperature of approximately 53 F. If it becomes saturated in the device, the air leaving the latter, unless reheated, will have a temperature of 53 F. On the other hand, if the air enters a low saturation efilciency device at 70 and 30% relative humidity and only becomes 50% saturated, it will emerge from such a device at 62 or 63 R, which is a satisfactory temperature. A device having only saturation efilciency will produce this desirable result.

It is an object of this invention to provide a construction having low saturation efiiciency and high cleansing efliciency such as will produce this desirable result. 7

A further object of this invention is to provide a novel form of conditioning cell construction for use in the device which by its construction and arrangement in the device will contribute I to the production of high cleaning efilciency and low saturation efllciency.

In such a cell construction long strands preferably of glass filaments are used: These strands are all oriented, that is, arranged in substantial parallelism as will be presently described and are all of substantially the same length. They are arranged in the'cell so as to extend at an angle with the horizontal which for reasons which will presently appear should not be less than 40 nor more than 55. It is necessary with such arrangement to so support these strands as to substantiaily eliminate either sagging or any likelihood of slipping or other displacement incidental to movement of the device and the passage of air and conditioning medium through the cell.

It is, therefore, an object of this invention to provide means in the cell construction to effect the required type of support which at the same time will not cause clogging of the cell, and in effect permit it to be self-cleaning during operation.

In conjunction with such cell construction, it i essential to provide highly eflicient and inexpensive means for properly flushing and wetting the cell with small quantities at a time of conditioning medium. While small. it must be in sufilcient amount to secure proper humidification and at the same time effect a flushing action on the filaments of the cell to remove the dirt therefrom and'make the device self-clean ing. This is accomplished by delivering measured small quantities of water intermittently in a solid thin sheet-like stream across the cell in a narrow area at its top. Such thin sheet-like stream has enough momentum and cohesion to run down along the strands like a cross-section of the stream, and every inch of the narrow strip or area of the surface has approximately the full measured quantity of the water passing over it at each delivery, less, of course, the small amount of water that remains behind as a film on the strands and the small amount that falls through the cell. The solid mass of water moving over and through the strands is what is so I effective in flushing the strands of dirt and dust and carrying it to the bottom of the cell where it is washed OK with the water falling off the cell. Another way of describing the effect of the delivery of a solid thin sheet-like stream of con-' ditioning medium along the top of the cell is that somuch water at a time of the measured small quantity is delivered on a narrow strip or area across the top of the cell that it has no time to fall or run vertically through the cell but has to run down as a mass along the surface of the cell much like water running down a sliding board in a swimming pool. This mass of water is what effectively flushes the cell strands of dirtand carries it to the bottom and away from the cell. In its travel a thin film is left on the strands for cleaning and humidifying action on air passin through the cell. The orientation of the filaments, the angular arrangement of the cell as specified and the manner of delivery of the water or other conditioning fluid is what effectually produces satisfactory flushing action with small amounts of water delivered intermittently. Without such features, it would be necessary to utilize a pump to recirculate the conditioning medium to save water particularly in a small house having a metered supply.

It is another object of this invention, therefore, to provide means for delivering small quantitles of water in a thin stream on a narrow area extending across the cell at its top in such a way as to effect the desired flushing action just described.

These means are in contrast with sprays for moistening humidifiers. Sprays wouldbe ineffective for any flushing action on the cells. For example, if three gallons per minute of conditioning medium is divided into a minute spray and delivered as such to a cell, no fiushing effect would be produced. On the other hand, if this same quantity of fluid is released in a thin sheetlike stream across a narrow band at the top of the cell, it has enough momentum and cohesion to run down the strands and produce the flushing effect described. In other words,'by proper delivery, a small quantity of water can be utilized to secure the necessary flushing effect and thus produce a great economy as to water use and as to necessary structure for proper humidifica'tion.

The provision of cell structure and wetting means in the manner described has important advantages. The wet clean filter or cell saves considerably on the annual cost of fuel. This is true because there is no clogging with dirt to reduce air flow through the cell. For example, in fan-operated systems, automatic fuel feed control is effected by the temperature of a room or house. If the filter of such a system becomes clogged, the controls always call for more heat and consequently fuel. Most of this heat and fuel is wasted as it goes up the chimney. If, on the other hand, the wet self-cleaning, flushed cell filter embodying the invention herein is used, no dirt clogging occurs. A uniform quantity of air passes through the filter at all times and neither heat nor fuel is wasted.

The wet clean or self-cleaning cells do not clog or require replacement. The expense for new filters is thus eliminated.

A further object of this invention is to provide air conditioning structure which may be manufactured at low cost, easilyassembled and which will have a minimum of operating parts.

Still another object is to provide novel means for supplying conditioning medium or fluid intei'lmittently to the novel air conditioning cell or ce s.,

To the accomplishment of the foregoing and such other objects as may hereinafter appear, this invention consists in the novel construction and arrangement of parts hereinafter described in detail and then sought to be defined in the appended claims, reference being had to the accompanying drawing which forms a part hereof, and which illustrates, merely for the purpose of illustrative disclosure, preferred embodiments of the invention, it being expressly understood, however, that various changes may be made in practice without digressing from the inventive idea.

In the drawing in which similar reference characters denote corresponding parts:

Fig. 1 is a perspective view partially in section of a conditioning cell utilized in carrying out the invention;

Fig. 2- is a vertical elevation of one form of conditioning device embodying the cell of Fig. 1;

Fig. 3 is a vertical section of another form of 7 conditioning device embodying cells of the type shown in Fig. 1;

Fig. 4 is a vertical section of a detail of the wetting system employed with the devices of Figs. 2 or 3;

Fig. 5 is a vertical section elevation taken along line 5-5 of Fig. 4, illustrating a detail of the conditioning medium distributor of the wetting system;

Fig. 6 is a view similar to Fig. 4 of a modified form of the same detail;

Fig. 7 is a view similar to Fig. 5 of said modified form; and

Fig. 8 is a diagrammatic elevation of both a modified form of wetting system and a modified type of conditioner.

Referring to the drawing, l0 denotes a cell unit for use, for example, in conditioning devices ll, Ha or Ilb, shown respectively in Figs. I

2, 3 and 8. This cell unit It! comprises a peripheral casing or open frame l2 of metal or other suitable material. Each of the sides In of this frame is substantially U-shaped in cross' section forming a continuous inner groove around the inner periphery of the frame. Other suitably channelled frame constructions may be used. At the bottom of the casing, and spanning its bottom face is a heavy, substantial grating H of wire or other suitable material, having suflicient strength when mounted on the frame to reinforce the frame against distortion. In practice, this grating may be of wire having openings 2 to 3 inches square which are large enough to eliminate substantial resistance to air flow by the screen or grating. The screen, for example, may be made of heavy material such as galvanized iron wire of about diameter. It should be 'sufliciently strong to support the frame against distortion and to carry the parts supported thereon hereinafter described. The peripheral edges of this screen or grating lie adjacent the channel of the frame being supported on a side wall of of said channel.

A layer l5 of oriented strands I6 is supported directly on the grating or screening l3. 'The strands are preferably of glass but may be of other suitable material. They are each continuous in length and span the breadth of the frame l2, their opposite ends lying respectively within the channels at opposite sides 12a of the frame. Each of the strands I6 is preferably about 250 microns in diameter and is about 20 inches long.

These strands have been oriented from a mass of strands, i. e. made to all extend in substantial parallelism byorientation with a method and in a machine such as that described in U. S. Patent No. 2,132,457 issued to J. L. Blackshaw, October 11, 1938. If the strands are so oriented and a thickness of a inch layer is built up on the screening l3, experience has shown that with the size of strands noted there are about seven to eight strands depth in inch of layer thickness. This number of strands which are only approximately $4 in diameter assume, because of irregularities and a certain number of accidental diagonal strands, a position which occupies this inch of thickness. While a few of the strands in the layer are out of alignment, the major number lie in substantial parallelism on the screening l3, spanning the frame breadth 11 between a pair of its opposed edges I21; and with the opposite ends of the strands lying in the respective channels at said opposed edges.

. the frame l2, by angle bar A corrugated wire screen ll of approximately inch mesh is placed over the layer l5. This screen spans the full length x and breadth y of the frame. It is made of comparatively thin wire, so that notwithstanding its mesh it presents practically all clear area and will not materially interfere with air passage through the cell as will be presently described. This screen I1 is corrugated so as to be approximately inch thick over the corrugations. The upper and lower crests A of the corrugations extend in a direction substantially perpendicular. to the longitudinal axes of the strands IS in layer l5, and the distance between any adjacent pair of crests A is approximately 1 inch. By so corrugating this wire screen I! and by having its upper and lower crests A extend across the oriented glass strands, resilient support is given to the parallel strands at every inch.

A second layer 20 of oriented strands i6 is placed on the top of the screen IT. The oriented strands l6 of layer 20 extend in substantial parallelism with those in layer i having been oriented in the same way and being of the same dimensional characteristics. The layer also is approximately inch thick and the opposite ends of its strand is he in the same grooves of the respective opposite sides i2a of the frame l2. A coarse screen 2| of the same construction as the screen I3 is placed over the top of layer 20 with its marginal edges spanning the frame l2 and secured suitably thereon. For convenience, both the screenings l3 and 2! may be held to auxiliary frames 22, 22' which fit over the frame i2 and clamp the peripheral ends of said screenings to said frame i2. These angle bar frames may be suitably held in position by screws S or the like. The material between the screens l3 and 22 is thus maintained under slight compression with supporting cross members every inch on both internal faces between the layers l5 and 20 effected by the upper and lower crests A of the corrugated screen H. The latter acts so that any movement that would tend to disturb the position of the strands is counteracted by the spring action of its corrugations. Thus friction at every inch along the length of the strands has the tendency to keep the strands from slipping. The corrugatiors also prevent sagging. With this construction thus. no other support is required to keep the strands from sagging or moving out of position, or when the cell It! is mounted at an acut an l to s ip or tend to slip from top to bottom of the cell to create voids through which air or water could pass without being acted upon The construction of the cell In just described is in contrast to mats wherein the strands are not oriented. In such, it is necessary to fix with latex or other means the entire mass to make the individual fibres hold their position and prevent their settling into a mass. Such latex or other method of fixing fibres in position prevents cleaning, holds dirt part cles tightly to the fibres, fills up the interstices with dirt and soon makes such a filter inoperative, does not allow air to pass through and does not direct liquid in a continuous stream. The novel cell In does not have these defects. It is in fact self-cleaning.

Cells ID are adapted for use in conditioning devices such as shown in Figures 2, 3 and 6. Refer ring first to Fig. 2, the conditioning device ll thereof comprises a container which is provided at opposite side walls with aligned openfin by capillarity,

ings SI, 32 serving respectively as an air inlet and-an air outlet. The cell I0 is supported from the bottom 33 of the container by a suitable bracket 36 and similarly from the top 35 by a suitable bracket 36 in such manner that the cell and the axes of its filamentary strands l8 extend at an acute angle of preferably 45 and not less than 40 nor more than 55 with the horizontal. This angular range is essential with this type of oriented cell ill in order to get continuous wetting with water or liquid from the top to the bottom of the filaments or strands. If the cell and consequently its strands are placed at an angle other than within this critical range, the tendency of the conditioning medium such as water supplied, as will be presently described, falling on the top strands, particularly during the flushing period, also to be presently described, is to fall through the 'cell in and leave the lower parts of the strands dry. However, when the cell in is positioned within the angular, range required herein, the water runs down along the length of the strands It as in a runway, wetting them from top to bottom and leavingsufflcient liquid film on the strands to catch the air-contairted dust and hold it so that it does not follow the air stream B. Then, when the flushing period occurs, these solid dust particles are washed ofi the strands, leaving a clear film of medium on them. for repeated collection of dust.

Also, because of the strand position in relation to the flow of thewater and the length of the strands, about 20 inches, water or liquid is dropped only across the upper in a solid thin sheet-like stream. Enough of the water as it runs down along the continuous strands to their bottom ends is held to the strands to form a film the entire length of the strands and thus maintains a continuous contact between water film surface and air passing through the cell i0. Excess liquid or water over that which remains attached as a film to the top strands drop to those directly below, and in turn the unattached excesses drop through the balance of oriented strands below. This liquid follows also along the lengths 'of the strand to their bottom ends. Some water, of course, at the time of wetting falls through the cell It! before reaching the bottom ends of the strands. This water carries dirt and falls toward the bottom 33 of the container which may act as a sump.

The water may be recirculated suitably for weting the complete saturation with moisture of air passing therethrough the cell It and its position in the apparatus II is purposely designed for, and can only effect partial saturation. In the apparatus II, the air fiowing in the direction of arrows B is in contact with the moisture film on the strand l5 of layers l5 and 2B for only approximately 2 inches (the approximate thickness 2 inches of the cell l0) because of the slope of the strands with respect to the incidence of the air denoted by the arrows B. This is a sufficiently long path to break the air film and do satisfactory clearing but is not long, enough to complete saturation. From exper ment, about 30% saturation efficiency is all that can be obtained. This is very desirable for household and theatre use so long as thorough-mleaning of the air is obtained because it is undesirable to put too much moisture into such closures in the winends of the strands temperature Hi can be. effected.

. discharge rate can be altered to meet efllciency the temperature of the air leaving such cool for comfort. For example, if air enters an F. and 30% rel- 70 ative humidity, it has a wet bulb of approximately 53 F. If it becomes saturated in such device, the air leaving, unless reheated, has a of about 53 F.'which is too cool. On the other hand, if the air enters the device I I at 70 F. and 30% relative humidity it becomes only about 50% saturated and emerges at 62 to 63 E, which is a satisfactory and comfortable temperature.

Another advantage of the particular cell struc- 1 ture and the angular mounting thereof in the device H, is that the conditioning liquid film adheres to the individual strands IS in the layers i5 and 2 for a considerable length of time, i. e.

This attribute of remaining moist because of capillary attraction allows of the feeding of water or other conditioning fluid to the upper part of of medium, titles, and not flow too rapidly so that flushing will reoccur before the strand surfaces are completely dry at which time they are incapable of performing the duties of partial air humidiilcation and dust or dirt arrestance. The intermittent feeding meansmay comprise a tank 40' adapted to be supported suitably above the conditioner container 30. This tank holds Just sufficient medium meeting the requirements just noted. In practice with a cell I 8 having dimensions of 20 inches x 20 inches x 2 inches sloped at an angle of 45, for flushing and cleaning and\ wetting, a discharge of 2V: or other medium per minute at approximately 10 minute intervals is required. If tank 40 has a 3 gallon capacity, thiscan be made to empty in about 1 minute through a syphon 4| by supplementing one ogits ilegs 42 with a 1 inch .pipe 48, long enough to give a head of about 18 inches. 11' the tank is supplied with medium as water at one-tenth of this rate, from a suitable source (not shown) through the control valve 44, the syphon action will start each time the tank is filled above the syphon level and discontinue (break) upon each complete emptying of the'tank 40. It will not restart once the tank has been emptied until the latter has been completely refilled. Since the filling rate is 3 gallons in 10 minutes and the emptying rate is 3 gallons in one minute, an intermittent flow of water to'the cell The relationship of tank capacity and syphon any required set of conditions by change in tank capacto 3 /2 gallons of water phon action.

scribed herein,

ity, or rate of filling or rate of syphon discharge. The particular dimensions and flow rates are by way of example. Also, the syphon means for effecting intermittent flow is optional. able control for intermittent flowjnay be used.

The water or other medium discharged by the pipe 48 must be uniformly distributed in a thin sheet-like stream at the top of cell Ill throughout the length :n 01' the'latter, or if cells in end alignment are employed, the water must be distributed throughout'the lengths a: of the aligned cells as a thin sheet-like stream. To this end,- suitable distributing means are employed. These means may comprise a trough 48 supported suitably from the top 35 of the device III. This trough extends parallel to the length a: of cell l0 and prefthe upper side so that the rims-of the slot form a type of nozzle. If necessary, other nozzling may be employed. A retarding screen M is supported suitably in the trough 48. This screen is prefers ably #10 mesh or other suitable mesh and delays flow of water to the slot 58. With this construction, the medium emerging from the pipe 43, through a T head 52 empties as a thin sheet-from the trough 48 slowly because of the screen BI and the small-sized slot 58. The trough fills substantially completely before thereof through said.slot 50 occurs. This trough 48 has a capacity only slightly in excess of tank 40.

tank at a single emptying is distributed evenly in the trough 48 and is retarded there before discharge through the slot 50 until the trough 48 is substantially filled by the discharge from the tank 40, at which time the trough empties itself through the slot 58 as a narrow sheet-like stream extending completely across the top of the cell l0. The thin sheet-like streams of water emerging from the slot fall onto the top portion of the cell Hi. This thin stream 8, as previously dehesion to run down along the strands like a crosssection of the stream, and every inch of narrow strips or area of the cell surface has approximately the full measured quantity (in this instance 3 gallons) passing over it ateach delivery less, of course, the small amount of water that remains behind as a film on the strands and the small amount that falls completely through the cell. The 3 gallon mass of water moving over and through the cell flushes the cell strands and carries it to the bottom of the cell. Thus a small amount of water at a time is effective to accomplish both flushing and wetting of the cell.

When the water in tank "has been syphoned out to a level below the lower end of leg 4| of the vacuum is broken, stopping sy- The latter will not restart until the tank 481s completely filled to above the level of the syphon from the source through the valve 44. In this way, a very simple inexpensive means for producing intermittent flushing and wetting with small quantities of conditioning medium is achieved. This is an integral part of the general idea of cheap humidification and cleaning.

The action each time the tank 4| is filled comthe syphon,

material emptyingv has enough momentum and copletely is as follows: Syphoning begins and the medium in the tank empties rapidly into trough 48 from which its discharge is sufilciently retarded bythe action of screen until the trough has filled. From the latter the medium is uniformly distributed through outlet 60 over the top of the cell Hi. This medium runs down alon the lengths of the strands flushing retained du'st thereon which is carried with the stream to the bottom of the cell and drops off with it, Also, medium falling completely through the cell carries some of the dust with it. As the medium passes through the cell, by capillarity, the filaments retain a tenacious film of conditioning medium. The film, as pointed out, remains for to provide an additional retarder 54. This latter comprises a V-shaped baflle plate having perforations 5'5 and extending parallel to the slot 50a. The bafiie plate is suitably supported, for example, on screen 5la. It and said screen retard the flow or water through slot 50a long enough for trough 48a to fill. The water emerges through slot 50a in the thin stream S designed to fall along a narrow strip across the top of the aligned cells: The stream S functions there in the same way as when only one cell is used to flush and moisten the strands.

Since some of the water distributed on the cell It will drop right through, and, also since as a general rule a large excess of water is carried to the bottom of cell ill by capillarity of the strands, and then falls of! in one solid stream, a second cell can be used in series with the first cell. Such construction is shown in Fig. 3.

In this figure the same general construction utilized in Fig. 2 is employed, like parts being characterized by primed similar reference numerals. A first cell H3 is supported by the bracket 36' from the top 35' of the container 30'. The lower end of cell I0 is attached to the upper end of a series connected cell illa, whose lower end in turn is supported by the bracket 36 from the bottom 33' of the container 30'.

The two cells l0 and Illa extend in. opposite angular direction and each makes an acute angle, preferably of 45 with the horizontal and within the critical range of not less than 40 nor more than 53. Construction of the cells l0 and lila is identical with that of cell It.

Intermittent feeding device for supplying water to cell l0 may be identical with that of Fig. 2. Excess medium falling from the bottom or cell Hl' falls directly onto the top end of the top layer of cell Illa. This medium acts in cell Illa in similar manner as the water distributed initially to cell It or As with the modification of Fig. 2, the number of cells Hl' arranged end to end, and, likewise, the number of cells lDa arranged end to end may be multiplied to meet any given set of conditions. Moreover, it is possible with enlarged wetting arrangements to multiply the number of angularly arranged banks of cells, each succeeding bank being arranged at an opposite acute angle to its predecessor and each bank making an acute 7:;

angle with the horizontal within the range spec- I ifled for cells l0, III or Illa. Troughs 48a are used in such instances.

The cells Iii of Fig. 1 may rectly with a hot air furnace as shown in Fig. 8. Therein the cell lfib is shown as mounted within the air conduit of a furnace lib near the air inlet B. The cell or cells lilb are arranged at an acute angle with the horizontal within the angular range specified for cells l0, ill or Illa. In-

shape and ornamentation may be made to con form or fit harmoniously with the decorations of the room in which it is placed. It has a capacity suitable to supply sufficient water or other conditioning medium at the required intermittent rate necessary to properly activate cell- Mb. This may be that of tank 40. The tank is supplied with water, for example, from the sink faucet (not shown) or other sources at'a controlled rate through a control valve 62. A syphon 63 is supported in the tank with its emptying leg 84 connected to a pipe 65 passing through the flooring 66 and terminating in a trough 61 like trough 48 located within the furnace Hb in a position to deposit water on the cell Nib therein in the manner specified as to cells Hi, It and Illa. The vertical, length of pipe 65 should be sumcient to give adequate head to the water leaving the trough, and preferably sumcient to give at least an 8 foot head to the water. Intermittent feeding as before is 'con-' trolled by the relative speed of feed of water to the tank and the speedoi drainage therefrom through the syphon'tii. II the latter is faster,

intermittent water feed is' efiecteda These speeds can be adjusted as desired. An advantageous result of locating the tank 61 in they kitchen where it is visibly accessible is that the.

rooms occupant can determine by observation whether or'not the feed trough 81 is clogged. If the water level in the tank does not fall intermittently, the trough is then known to be clogged. Where it is not possible to utilize a filter cell in the furnace, the trough 61 may be replaced by a spray head (not shown) directed to discharge a spray against the hot bonnet (not shown) of the furnace for convenient controlled humidification of the air.

The syphon arrangement for intermittently supplying fluid may be replaced by any other suitable means for intermittently supplying the distributing troughs 48, 48a, 6'! with conditioning fluid. The chief requirement is that the latter distribute the said fluid as thin sheet-like streams across a narrow width on the top of the cells 10 so that the hereindescribed flushing and wetting may be effected simply and cheaply with small quantities of water. Another arrangement for intermittently supplying the fluid could. for example, be a tiltable trough arranged above the top of the width of cells In that becomes unbalanced each time it is full, then tipping and discharging its contents over its lip in a thin sheet-like stream to achieve the flushing and wetting previously "described. When empty the trough returns to original position and does not re-tilt until again filled. 1

be associated di- Q If tanks II and SI are closed, such is provided with a suitable air relief valve V.

While specific embodiments have been disclosed, there is no intention of limitation to the exact details shown and described. Variations within the scope oi the claims is contemplated.

What is claimed is:

i. In a device of the character described a unit cell adapted for support at an angle with the horizontal and comprlsing'a frame, an apertured retaining member spanning the open area of one face of said frame, a layer consisting of a plurality of elongated oriented filamentary members, each spanning said frame between its upper and lower edges, a corrugated, apertured, resilient member overlying said layer, a second layer consisting of a plurality of oriented filamentary members, each spanning said frame between its upper and lower edges, an apertured retaining member overlying said last-named layer and spanning the open area of said frame, the thicknesses of said layers and said dimensions of said resilient member being so admeasured as to maintain the members of said layers under compression between said apertured retaining members.

2. In a device of the character described a unit cell adapted for support at an angle with the horizontal and comprising an open frame having an inner peripheralchannel, a coarse-mesh retaining screen spanning the open area of one face of said frame with its peripheral edges lying at said channel, a layer consisting of a plurality of oriented filamentary members overlying said retaining screen, each of said filamentary members extending in substantial parallelism with the others and the full distance between a pair of opposite sides of said frame, a corrugated screen overlying said layer and arranged so that its corrugations extend transversely of the lengths of said filamentary members, a second layer of filamentary material substantially similarly arranged as said first named layer and a second coarse-mesh retaining screen overlying said second layer with its peripheral edges lying at said chan- I nel, the dimensioning of said channel, of the layer thickness and of said corrugated screen being so admeasured as to maintain the filamentary members of said layers under compression between said coarse retaining screens. I

' WALTER L. FLEISHER.

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