US3445093A - Cooling towers - Google Patents

Description

J REDER COOLING TOWERS May 20, 1969' Sheet of 5 Filed Oct. 23, 1985 1 NVEN TOR. .705 cf Peder,

J. REDER COOLING TOWERS May 20', 1969 Sheet Filed Oct 23, 1965 FIG. 2

me W1 E e mw U y 0, 1969 J. REDER 3,445,093

COOLING TOWERS Filed Oct. 23, 1965 Sheet '3 of s INVENTOR.

se Peder J. REDER May 20, 1969 COOLING TOWERS Sheet Filed Oct. 25, 1965 INVENTOR. jsefPdfl I 0 May 20, 1969 J. REDER COOLING TOWERS Filed Oct. 23, 1965 Sheet I 015 O a N s ll/ i m,

MOTOR FIG. 6

f////////////////l //l//////// INVENTOR.

Dose Peder FIG-7 United States Patent 3,445,093 COOLING TOWERS Josef Reder, Heidelberg, Germany, assignor of one-third to Bernard Olcott, New York, N.Y. Filed Oct. 23, 1965, Ser. No. 503,498 Int. Cl. F28c 1/00 US. Cl. 261-24 21 Claims ABSTRACT OF THE DISCLOSURE A packingless cooling tower (a cooling tower without internal packing or fill) in which the ambient air together with droplets of hot liquid to be cooled are moved in vertical whirling arcs in a plurality of horizontally disposed doughnut-shaped rings. Such vertical whirling arcs are formed at ambient air inlet passages which have an inwardly curved lip along the inside of which is moved a stream of the hot liquid.

This invention relates to cooling towers as used in air conditioning and refrigeration systems and particularly to a new and improved type of forced draft or induced draft cooling tower.

It is an object of the invention to provide a more compact and lighter weight cooling tower as compared to the prior art cooling towers.

Another object of the invention is to provide a cooling tower having higher over-all efficiency than the prior art cooling towers.

Another object of the invention is to provide a low cost cooling tower having components which are in themselves simple to manufacture in mass production and assemble to make up the cooling tower structure.

Another object of the invention is to provide a cooling tower which can operate over long periods of time with little maintenance expense.

Another object of the invention is to provide a cooling tower which reduces loss of the coolant, which advantageously may be water, by evaporation.

Another object of the invention is to eliminate all or at least some of the inlet air louvres as used in big and small cooling tower plants to prevent water loss from wind drift.

Another object of the invention is to eliminate splash bars, closely spaced wetted surfaces or fill and large water collection basins thereunder as commonly used in conventional cooling tower designs.

Another object of the invention is to avoid dead air regions within the interior of the cooling tower where normally no useful heat transfer is effected. Such fault of prior art cross-flow or counter-flow towers has been caused by sharp-edged splash bars or narrow-spaced filmpacking surfaces. The rough absorbent surfaces in such packing devices are quite well suited when new for keeping up a thin water film, good for evaporation, but this is very soon made ineffective by algae, dirt and all sorts of micro-organism growth.

In accordance with the invention there is provided a process for cooling a coolant which comprises the steps of moving the coolant as drops or droplets in a plurality of whirling vertical arcs through a mechanically powered upwardly moving gaseous medium, the whirling arcs forming a hollow torus or doughnut-shaped ring about a vertical axis.

3,445,093 Patented May 20, 1969 'ice The process of the invention may be implemented in a cooling tower which comprises a plurality of hollow deflector members each having arcuate cross sectional shapes at lower portions thereof which extend inwardly, means vertically supporting the plurality of deflector members at different distances relative to a common vertical axis and spacing them to form gaseous medium inlet passages between selected adjacent deflector members, means moving a coolant downwardly along the inside arcuate surface of the deflector members, and mechanically powered means upwardly moving the gaseous medium through the interior of the deflector members.

As applied to a preferred type of mechanical-draft, mixed-flow and evaporation type of cooling tower plants, air and water drops and droplets are moved in the interior thereof as a plurality of concentric toroids having difierent relative velocities, which can be visualized as an upwardly moving group of torus or doughnut-shaped air whirls similar to smoke rings, for producing the necessary water evaporation surfaces as well as to increase contact time of water to air particles without the need for splash-packing bars or narrow spaced film-packing surfaces.

Particularly, this invention is directed to simplify small and big tower plant installation by utilizing the well known Karman-Street phenomenon of trailing edge vortices behind sharp cornered slots in conical shaped (tapered) deflector shells, for breaking up big water drops of a down and inward rushing water film (blanketing effect) into many tiny droplets with a high water surface-volume ratio to speed up the heat transfer rate from the hot water to the cooling air particles in a parachute or umbrella effect.

A feature of this invention is to use air for repeated uplifting of water droplets right to the top of the cooling zone in the cooling tower, namely near and under the drift eliminating level (biggest cell diameter) thus minimizing water pump-head and increasing the contact time of water and air without the need to increase the amount of wetted surfaces, tower height or floor area.

Another feature of the invention is to use the centrifugal forces of the torus whirls, rotating with high speed around their whirl centers, to splash Water droplets against the smooth and highly polished wetted surfaces of the deflector shells in order to contribute to the heat transfer rate by mixing already cooled water particles with still warmer water flow near or on the deflector walls of each cooling cell.

Another feature of the invention is that only one (or a relative few) standardized multi-slotted, conical (tapered) shaped deflector, developed for optimum performances at minimum material demands for the casing, is needed to satisfy a plurality of demands for cooling range, inlet and outlet water conditions, ambient temperature and capacity. Thus, true mass production of such deflectors is achievable and only the size of the fan housing needs alterations according to power, desired performance, size and plant situations.

Also, the pumping head is the same for all power demands of such cooling plants, because any amount of similar cells can be clustered around an optimum fan casing and any amount of fan casing units can be put into rows of cooling tower units without effecting each other in performances if the units are properly positioned with respect to prevailing wind directions to prevent recirculation effects.

A particularly outstanding feature of this invention is that the cooling tower tapers downwardly so that the size of the water collecting basin is very much less in diameter than the maximum diameter of the cooling tower. Accordingly, the normal large and expensive concrete water basin is eliminated.

Another feature of the invention is that the pump head is not controlled by the height of the fan casing above ground level and how much free-space is needed to get cooling air into the shell-units without undue loss in static pressure. The pumping head is governed only by the difference of the water level in the collecting cups and the free outlet of the spray nozzles or water outlet slots in the water distribution top levels.

Another feature of the invention is to avoid heavy supporting structures for splash-bars or heavy asbestoscement sheets as used in other cooling tower systems. All deflector shells are self-supporting and hung from fancasing with a minimum of bolts or even only hung on nylon-ropes or reinforced glass-fibre rods. All piping for water inlets and outlets are made independent of the cell structures, so no stress, due to heat-expansion forces, can be loaded on the light-weight deflector shells.

Another feature of the invention is that all wetted surfaces can be made of highly polished, non-corrosive materials, preferably from resin bonded glass-fibre or any other inexpensive hard plastics of low heat resisting materials as used in modern households all over the world. The high polishing, avoided in all other film-packing devices of the prior art, is of particular advantage to take advantage of the surface-tension forces in the thin water film on the deflector interior surface. The building up of dirt or algae patches is nearly impossible because of the smooth surfaces and any unwanted formation of rivulets is prevented by the constant bombardments of splashing droplets thrown out of the whirling torus vortexes.

Also, a rough absorbent well wetting water surface is not needed in this invention. The wetting surfaces in the invention are provided by the rotating torus vortexes and the deflector shell casing in itself is only a fraction of the exposed surfaces of millions and millions of tiny droplets exploding in the parachute stage of the whirls.

Another object of the invention is that each deflector cell unit of the entire cooling plant can be adjusted for proper and even flow of air and water by adjusting slot dimensions from outside of any water-spray filled chambers. Thus, freedom of any channeling of either air or water is secured and the sizable draw-backs of large counterflow coolers is avoided. In such coolers, velocity through the tower filling, especially in narrow spaced film-packing towers, is always greatly uneven. Very little air movements near walls and bottom centers of big towers minimize overall cooling efliciency considerably, because the air always rushes through where no or little water opposes the air stream. Thus, any hole in the water distribution increases at once the rush of air streams where less air resistance is met and where practically no contribution to the heat transfer is achieved. Most conventional counterflow cooling systems have such unstable stream pattern. This is avoided in the present invention because the rotating whirls are very in the moving pattern and cannot alter the direction of movement of the maximum speed nucleus which is always in the center of the deflector cell unit.

Another feature of the invention is that all the standardized conical (tapered) shaped shell casings of one diameter are interchangeable and each single shell (beginning with the smallest water collecting cup) can be placed into the next bigger one. Hence, all the deflector units can be stored inside the largest single shell housing. This is most important for reducing transportation costs and space requirements in the manufacturing plants.

Also, the erection of such shell units is easy and can be done by any inexperienced labor forces without the need for heavy lifting tools. Just the erection of the fan housing will need some supervising of a technician in the cooling tower art.

The water distribution system in such deflector units is conventional and might be done by spray nozzles in the center line, or ring-pipes around the biggest deflector shell or simply by letting the water 'fall out of a central pipe and be blown up by the strong upward current of the inrushing air stream. Also, a rotating disk or a rotating slotted pipe can assist the water distribution.

An advantage of all systems of this invention is the easy maintenance of all tower components, because there arent any narrowly spaced bars or sheets and everything is accessible without the mechanic getting wet. All components can be inspected from the outside through the slots.

Other objects and features of the present invention will be set forth or apparent in the following description and claims and illustrated in the accompanying drawings, which disclose by way of example and not by way of limitation, in a limited number of embodiments, the principle of the invention and structural implementations of the inventive concept.

In the drawings, in which like reference numbers designate like components in the several views:

FIG. 1 is a vertical cross sectional view of an embodiment of the cooling tower according to the invention;

FIG. 1a is a prospective view, partly in cross section, of an alternate structure for the cluster of deflector shells of FIG. 1;

FIGS. 1b, 1c, 1d and 1e illustrate in cross section, various arrangements of the air intake slot for the deflector shell of FIGS. 1 and 111;

FIG. 2 is a diagram illustrating the theory of the water cciring action within the cluster of deflector shells in F 1;

FIGS. 3 and 3a to 3d and 3 illustrate by plan views, elevation views and cross sectional views embodiments of the invention employing a plurality of clusters of deflector cells similar to those in FIG. 1;

FIG. 3e illustrates how the component deflectors of FIGS. 1, 3, 3a to 3d and 3f nest together in their disassembled condition for convenience in shipment.

FIG. 4 illustrates a number of variations and modifications of cooling tower embodiments according to the invention;

FIGS. 5 and 5a illustrate another embodiment and modification of the cooling tower employing rotary intake water distribution according to the invention;

FIG. 6 illustrates in cross sectional view another embodirnent of the cooling tower employing mass produced staidardized deflector shells according to the invention; an

FIG. 7 illustrates still another modification, partly in cross section and partly in elevation, of a cooling tower temploying rotary deflector shells according to the inven- In the cooling tower of FIG. 1, there are provided a plurality of deflectors 10a, 10b, 10c, 10d and 102, each being a thin-walled cylinder having a cross sectional shape with an upper outwardly turning lip, a central straight portion sloping inwardly and a lower inwardly turning lip. The plurality of deflector members 10a to 102 are positioned and supported so that they are all concentric with a common vertical center line and so as to provide an annular air inlet passage between adjacent deflectors to permit passage of an air stream 12 therebetween and into the interior of the deflector units. The structure for supporting and positioning the deflectors 10a to 10c are not shown on FIG. 1 for the sake of more clearly illustrating only components and features which are important in the invention. A water inlet pipe 14 carrying coolant water to be cooled terminates in an annular or torus shaped header 16 which has an annular water outlet slot 18 positioned to discharge the inlet water upon the interior surface of deflector 10a as a moving thin water film 19. Below the lowermost deflector member 102, there is positioned a water collecting cup 20 having an upstanding outwardly turning lip which cooperates with the lower most lip of deflector c to form an air inlet passage similar to the ones between the adjacent deflectors 10a to 102. A water outlet pipe 22 is connected to the water collecting cup 20 for providing cooled water to an air-conditioning or refrigeration system (not shown). Another plurality of deflector members 10a, 10b, 10c, 10d and 10e' can optionally be positioned over another water collecting cup 20 connected to Water collecting cup 20 by a pipe 22 for doubling the cooling capacity of the tower. The cooling tower casing 24 supports a conventional motor driven fan (not shown) and a conventional eliminator 26 between the fan and header 16.

The operation of the cooling tower according to the invention will be explained with the aid of FIG. 2 with the assumption that the fan produces a velocity of 1, 0 feet per minute at the common vertical axis 17 and the water film velocity at a central point A on the deflector 10a is 200 feet per minute. As shown, the lower edge of each deflector has a sharpened edge 11. When the water film 19 reaches the edge 11 at point B, it has an increased velocity of say, 600 feet per minute, and is altered to form elongated tear drops under the influence of the sharp edge at B and the velocity of the air stream at that region. All the drops will not be exactly the same size. As determined by the direction and strength of the drafts produced by the fan and the inlet air as shown at the bottom of FIG. 2 and the size of the water drops formed at point B, heavy drops will take the path of 21 where the draft is nearly zero and lighter drops will take the path of 23 into the region of upward drafts. However, most of the larger drops along path 21 may not reach the collecting cup 20 because they may fall into the upward draft region of a lower deflector 10b to 10e which have whirls closer to the common vertical axis 17. The smaller water drop gains velocity and at point C begins to experience a rather large upward draft, thereafter, it moves upwardly with increasing velocity to points D and E while assuming more and more the shape of a parachute or umbrella. After the water drop assumes such a parachute shape as at point B, the further influence of the updraft is to explode it into very many small water droplets as shown at point F where the velocity is 1,000 feet per minute. The continuing arcuate movement of the water drops and droplets at an increased speed of 1,200 feet per minute are partly turned sidewise towards the interior deflector surface and thereafter whirl around again to form toms path 30a. As shown in FIG. 2a, the vortex centers of the torus whirls 30a, 30b, 30a, 30a, etc. associated with the deflectors 10a, 10b, 10c, 10d, etc. have a progressively smaller toroidal diameter so that there is formed within the interior of the tower a plurality'of concentric toroidal whirling rings of air, water spray water droplets and water drops whirling relative to each other and thereby large heat transfer surfaces are effectively provided as water droplets are split up repeatedly into many smaller droplets.

The concentric deflectors 10a, 10b, etc. shown to be cylinders of revolution in FIG. 1 may alternatively be formed in a V-shaped structure 40 with straight side walls as shown in FIG. 1a where the air intake passages are formed by stamping staggered slots 41a, 41b, 41c, etc. in the flat sidewalls. The water distribution headers 16, 16' and the discharge orifices 18, 18' can then be straight instead of circular as in FIG. 1. The apex of the V-shaped walls provide the desired water collecting cups 20, 20. The arrangement shown in FIG. 1a is particularly useful for converting a conventional rectangular cooling tower to the present invention by replacing the interior cubic fill with the deflector 40.

FIGS. 1b to 1e illustrate alternate shapes of the air inlet passages useful for the structure of FIG. 1. FIGS. 1b and le are also particularly useful for the structure of FIG. la since the adjacent slotted walls are aligned. In FIGS. 10 and 1d, the adjacent walls are offset to take advantage of prevailing winds to induce and assist the draft within the tower and to minimize water drift losses.

FIGS. 3, 3a to 3h illustrate cluster arrangements of a plurality of concentric deflectors to increase the tower capacity while maintaining the lower height. FIGS. 3d, 3c and 3 f show cluster arrangements for three, four and seven basic deflector assemblies. As shown in such figures, the upper portion 9 of deflector 10a is octagonal in shape While the lower portion thereof and the other deflectors 10b, 10c etc. are circular in cross section. Also, in FIG. 3, the air intake passage appearing in FIG. 1 between deflectors 10a and 10b is closed as shown in FIGS. 3a and 3b because it is more eflicient to admit the intake air at a lower position in the cooling tower. FIG. 3e illustrates how the progressively smaller concentric deflector shells in one of the cluster assemblies can nest one within the other to reduce shipping expense by reducing the overall bulk of the package to be moved to the cooling tower site. Construction details are shown in FIGS. 3g and 3h.

FIG. 4 illustrates variations in the intake water distribution system according to the invention. In FIG. 4, the water inlet pipe 14 terminates in a vertical water riser 50 which raises the column of intake water into an upper portion of the cooling tower. Two different arrangements of discharging the inlet water at the top end of riser 50' are illustrated in the left and right sides of the center line C respectively. On the left side pipe 50 is open ended and intake water spills over the lip 51 and into the interior of the tower. Under the influence of the upwardly moving intake air 12 as powered by fan 51, some of the discharged water follows the path 19' while other portions of the incoming water dribbles over lip 52 and tends to cling to the circumference of pipe 50 until is reaches a water deflector 54 positioned around the circumference of 50. With the increased water velocity obtained on the trip down towards 54, the dribbling water then can take a path 19" under the influence of the up-rushing incoming air stream 12.

Alternatively, as shown to the right side of C an apertured shower head fitting 56 may be secured over the top end of pipe 50 so that the inlet water enters the interior of the cooling tower as a plurality of fine streams 19". Also the vertical pipe 50 may have apertures 58 uniformly distributed around its circumference at selected levels to spray a plurality of streams of inlet water 19"" at various levels within the interior of cooling tower. It is to be understood that the few representations of elements 54, 56 and 58 are for illustrative purposes only and that the number and the shape of such elements in FIG. 4 are not intended to be limiting or to limit the scope of the inventive concept.

Another modification of the invention is shown in FIG. 5 wherein the top of the water distributions stand-pipe 50 has a rotary slinger 59 as driven by fan 52 and shaft 53. Under the influence of the water pressure in pipe 50 and the rotation of the slinger 59, inlet water is sprayed in a plurality of thin sheets or fine streams 55 within the interior of the two concentric arrangements of deflector assemblies.

It is to be understood that the vertical doughnut-shaped whirls may also be given a horizontal rotation about the vertical axis of the tower by curving the vanes in the water drift eliminator 26 and/or modifying the fan 52.

In a modification of the invention as shown in FIG. 6, the cooling tower comprises a plurality of assemblies of mass produced standardized concentric deflectors each having relatively small overall dimensions and similar in shape to the deflectors 10a, 10b, etc. of FIG. 1. The lowermost deflector in each assembly acts as a water collecting cup 20 which discharges its accumulated water through a bottom orifice 60 upon a splash platform 62 for distribution within the interior of the next lower cluster of deflectors. Different from the forced air arrangement in the other illustrated embodiments, the fans 52 are placed below the plurality of deflector clusters and a plurality of louvers 64 placed above the deflector clusters act as a simple and efliflicient water drift eliminator which under the influence of a prevailing wind also acts to aid the fans 52 to force air through the interior of the cooling tower. As in FIG. 4, water deflectors 54 assist in the formation of doughnut-shaped whirls within the interior of the cooling tower.

Still another modification of the invention is shown in FIG. 7 wherein a slotted inverted rotary cone 70 acts not only like a series or cluster of deflector shells it also acts as an impeller to force air into the interior of the cooling tower when driven by motor 52 and shaft 53. As in FIG. 6, louvers 66 are placed above the cooling tower to act as wind deflectors so that the prevailing Wind 66 acts to induce air 12 into the interior of the cooling tower and thereby assist the action of motor 52 and the inverted deflector-impeller 70.

In all illustrated embodiments, the deflector shells and other portions of the cooling tower are preferably made of smooth plastics materials and the velocities indicated in and discussed with FIG. 2 are approximate for illustrative purposes only.

While the only fluid to be cooled herein above referred to has been water, other fluids may be also used such as steam and liquid chemicals.

Another embodiment of the invention is one wherein the deflectors are made of metal each with a hollow interior and piping interconnecting the interiors of a series of deflectors. By such an arrangement, steam passing through the piping and the interiors of the metal deflectors will condense in heat transfer with the water film 19 passing over the inside surface of the deflectors as in FIGS. 1 and 2. Alternatively, in cold environments, only the doughnut-shaped air whirls, without intake water, may be sufficient to condense the steam.

As can be observed from FIGS. 1, 4, 5, the pump head H is considerably reduced from that required in conventional cooling towers which lifts the intake water to an elevation approximately that of the drift eliminator 26.

While there has been described and pointed out the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated and its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What I claim is:

1. A packingless cooling tower which comprises a plurality of cylindrical deflector members having different diameters and an inwardly directed arcuate surface at one end thereof, means vertically supporting the plurality of cylindrical deflector members in a downwardly tapering arrangement with the inwardly directed arcuate surface of each cylindrical deflector disposed at the bottom thereof so that vertically adjacent cylindrical deflectors are spaced to form gaseous medium inlet passages therebetween, means moving a fluid stream downwardly along the inside surface of the uppermost cylindrical deflector and then along its inwardly and upwardly directed arcuate surface, and mechanically powered means upwardly moving the gaseous medium through said inlet passages and into the interior of the deflector members in vertical whirling arcs within a horizontally disposed doughnut-shaped ring pattern.

2. A cooling tower according to claim 1 wherein said fluid moving means includes an inlet fluid pipe discharging fluid upon an upper inside surface of the upper-most deflector member.

3. A cooling tower according to claim 1 including a vertical fluid riser disposed along the concentric axes of such cylindrical deflectors with orifices at the top end thereof for spraying the fluid onto the interior wall of the top deflector member.

4. A cooling tower according to claim 1 including a vertical fluid riser with an open top end.

5. A cooling tower according to claim 1 including a vertical fluid riser with orifices in the periphery thereof at selected locations therealong.

6. A cooling tower according to claim 1. including a vertical fluid riser and water deflectors disposed around the periphery of said riser at selected vertical locations thereof.

7. A cooling tower according to claim 1 wherein said fluid moving means includes a vertical fluid riser and a rotary slinger positioned at the upper open end thereof.

8. A cooling tower according to claim 1 wherein said mechanically powered means include motor driven fans positioned near a bottom portion of the cooling tower and 'Wherein there are included louvers at a top portion of the tower and near the periphery of the upper-most deflector member.

9. A cooling tower according to claim 1 wherein said plurality of deflector members are formed along a pair of flat walls arranged in a V-shaped manner.

10. A cooling tower according to claim 1 wherein said fluid moving means includes in each deflector cluster a vertical fluid riser with orifices at the top end thereof for spraying the fluid into the interior of the deflector members of each cluster.

11. A cooling tower according to claim 1 including a sharp edge along the innermost edge of the arcuate surface of said cylindrical deflector surfaces.

12. A cooling tower according to claim '1 wherein said cylindrical deflectors have an outwardly directed arcuate surface at the top ends thereof.

.13. A cooling tower according to claim 1 wherein said deflector members are tapered cylinders with lower portions thereof of smaller inside diameter than upper portions thereof.

14. A cooling tower according to claim 13 wherein the lower deflector member of adjacent deflector members has a smaller diameter and the adjacent deflector members are concentric relative to a common axis.

15. A cooling tower according to claim 1 including means for rotatably mounting said deflector members and means for driving said rotatably mounted deflector members.

16. A cooling tower according to claim 15 wherein said rotatably mounted deflector members are shaped as an impeller so that when turned it forces said gaseous medium into the interior of said deflector members.

17. A cooling tower which comprises a plurality of deflector clusters, each deflector cluster having a plurality of deflector members each having an inside arcuate surface, means vertically supporting the plurality of deflector members in each deflector cluster to form gaseous medium inlet passages between selected adjacent deflector members, means moving a fluid in each deflector cluster downwardly along the inside arcuate surface of the deflector members, and mechanically powered means upwardly moving the gaseous medium through the interior of all deflector clusters.

18. A cooling tower according to claim 17 wherein said fluid moving means includes an inlet fluid pipe in each cluster discharging fluid upon an upper inside surface of the upper-most deflector member in each deflector cluster.

19. A cooling tower according to claim 17 wherein said fluid moving means includes a vertical fluid riser with an open top end in each cluster, each fluid riser having orifices in the periphery thereof at selected locations therealong and water deflectors disposed around the periphery of said riser at selected vertical locations thereof.

20. A packingless cooling tower which comprises at least one wall tapering inwardly in a downward direction, vertically spaced rectangular openings along said wall, said wall at each of said openings having a contiguous portion thereto which curves inwardly and upwardly with a horizontal innermost edge, means flowing a stream of water along the inside top edge of said wall, and mechanically powered means moving ambient gas through said openings and upwardly past the inwardly curved portions of the Wall to form vertically whirling arcs in horizontally disposed cylindrical patterns near said openings.

21. A cooling tower according to claim 20 including a sharp edge along the horizontal innermost edge of the contiguous portion of said wall.

References Cited UNITED STATES PATENTS Swift.

Umbricht et al.

Collins.

Steger.

De Flon et a1.

Freneau et a1. 261-77 XR 10 2,872,167 2/1959 Pratt 261-77 XR 2,872,168 2/1959 Mart. 3,018,847 1/1962 Stanly 261-111XR 3,081,987 3/1963 Meek 6123.1. 5 3,084,918 4/1963 K0131 et al. 3,099,696 7/1963 Meek. 3,150,934 9/1964 Hazard 26188 XR FOREIGN PATENTS 693,844 9/1964 Canada. 10 109,580 3/1900 Germany.

340,127 12/1930 Great Britain.

TIM R. MILES, Primary Examiner.

15 U.S. 01. x11.

Images