US2878744A - Flue control devices adapted for combustion heaters - Google Patents

Description

arch 1959 D. SILVERMAN FLUE CONTROL DEVICES ADAPTED FOR COMBUSTION HEATERS Filed Oct. 10, 1956 INVENTOR.

United s Pat n FLUE CONTROL DEVICES ADAPTED FOR COMBUSTION HEATERS Thi'sinvention relates to stationary, omnidirectional flue or ventilator pipe. cowls or terminations, particularly adapted to generate a positive suction, due to the action of the wind flowing over their surfaces.

- This application is a continuation-in-part of my prior application Serial No. 175,249, filed July 21, 1950 now Patent No. 2,766,677, issued October 16, 1956.

Numerous occasions arise when it is necessary to provide a flue, ventilator pipe or conduit leading from, the inside of a closed structure, such as a house, to the outside of that structure, where such a pipe is in the path of the wind. In blowing around and over'the end of the vent pipe projecting from the structure, the wind may induce a suctionor a pressure-generative effect, dependent upon the design of the termination or cowl. In most cases a suction-generative effect is desired, as when the structure is to be ventilated and a circulation of air through the structure and out through'the vent pipe is desired. Such is the case also when the pipe is the termination of a gas or oil burning appliance, and the vent pipe is provided to carry to the out-of-doors the products of combustion of the appliance.

-In cases where a suction effect is desired it may be particularly objectional, or even dangerous to have a pressureefiect. For example, when there is a pressure or blow back efiect of the wind, the flame of a gas burning appliance may be extinguished, with resulting danger to the occupants of the structure in which the appliance is installed.

A general object of my invention, therefore, is a novel and improved method and apparatus for control of the suction-generative eifect on the vent pipe from a chamber due to a flow of wind over the vent pipe. A specific object of this invention is to provide a high suctiongenerative effect on the exhaust pipe of a combustion chamber, due to the flow of air over the pipe. Another object of my invention is a rigid omnidirectional flue or ventilator pipe termination or cowl, in which a high suction-generative effect is provided by wind blowing across it, without the possibility of back pressure, no matter what the magnitude or direction of the wind may be.

Other objects, uses and advantages of my invention will become apparent as the description proceeds.

Stated generally, my invention for control of the suc tion-generative effect induced by a flow of air across an exhaust conduit, flue or vent pipe comprises the provision of a substantially spherically shaped housing completely surrounding the open end of the vent pipe, with at least a portion of the surface of the housing perforated with openings. The perforated openings should be small enough in diameterflthat there'will. be a. minimum" of turbulence in the flow of air overthe surface of the housing, and thus a maximum of suction-generative eflect'. This will be better understood by reference tothe accompanying drawings forming a part of this application, and illustrating certain embodiments of'my inven* tion. In these drawings:

i ce Figure l is an elevation view in section of one embodiment of my invention.

Figure 2 is a plan view in section of the embodiment of Figure 1 taken along section line 2--2.

Figures 3 and 4 are elevation views in section, of two other embodiments of my invention.

Referring now to the drawings and particularly to Figure 1, which illustrates one embodiment of my invention for a high suction-generative cowl for a vent pipe, the cowl is shown mounted on top of a vent pipe 11. It is fastened thereto by means of screws 12 or other type of fastening. The cowl itself comprises a tubular element 13, which may be a part of or an extension of the vent pipe 11. The tubular element is attached to and made part of a transverse circular member 14 which forms the base of the cowl and carries the downward tubular extension 15 by means of which the cowl is fastened to the pipe 11. Parts 13, 14 and 15 of the cowl can be cast or molded as an integral unit, of metal or plastic, or can be formed of sheet material, as is well known in the art. A circular cover 16 of sheet material is supported above the top opening of the tubular element 13 by means of brackets 17 which can be fastened by screws or other means (not shown) to the tubular element 13. The cover 16 acts as a shield to prevent direct ingress of rain into the top opening of the tubular element 13 while permitting free flow of gases out of the vent pipe. Y

A housing of sheet material 18 is formed in a substantially hemispherical shape and of the same diameter as the base 14. It is.placed over 'the 'top end of and completely encloses the tubular element'13, and is fastened to the base 14 by means of screws 19, or other means. The housing 18 is perforated by a multiplicity of small holes 20 over at least a portion of its surface. The pinpose of the holes is to permit the outflow of gases from the-vent pipe, and also to create a suction, due to the flow of the wind over the surface of the housing, to assist in this outflow of gases. For simple outflow of gases, the total cross-sectional area of the holes need not be appreciably greater than the cross-sectional area of the vent pipe. However, the magnitude of the suction-generative effect due to the flow of air over the surface is a fum tion of the size 'of the housing with respect to the pipe, and of the total area and number of holes in the surface. If less than the total area of the housing is perfo rated, I prefer that the perforations. be placed in a hori zontal band along the lower portion of the housing for two reasons: First, if the top housing 18 is not perforated over the top center portion then it acts as a rain shield, and the parts 16 and 17 can be dispensed'with. Second, if the perforations are arranged in a horizontal band about the base of housing 18, then the cowl will provide a higher suction-generative effect when the wind flows diagonally upward or downward across the cowl, as it does when the cowl is mounted on a sloping roof.

In Figure 2 I show a cross-section of the embodiment of Figure 1 taken along the line 22. This is shown to illustrate the type of action that takes place when wind blows over an obstacle and to show the importance, in

the design of a'cowl, of the size of the housing, the number and size of the perforations, and the importanceof a spherical shape.

In Figure 2 the housing 18 is shown perforated with large diameter holes 24, 25, 26, 27, etc. spaced around, they periphery. Typical flow lines of the wind 21, 2-2, and 23, etc. are shown flowing toward the cowl. In the abs nce of thejcowl structure, these flow lines would contime as straight parallel lines. Because of the obstrucf tion of the housing 18, the flow lines are deflectedand crowded outwardly. The fiow of air builds up a pressure at the point of impingement on the surface, for example,

in the region of the opening 24, where the flow line 21 intersects normal to the surface. The two lines 30 and 31, shown dotted, are drawn to show the extent (of the order of 60 degrees) of the angle within which a pressure effect is generated. Outside of this region the flow of air is tangential to the surface of the housing. If this is a smooth flow the velocity of the air will be the greatest, and will thus generate the greatest suction effect. Where the surface is perforated, if the holes are of small enough diameter, the flow of air will be only slightly disturbed, and the effect will be essentially the same as for a smooth surface. However, when the holes are large, as shown in Figure 2, the crowding of the flow lines along the surface forces the air to flow into the holes in the form of vortexes, as indicated. This disturbs the smooth flow of air along the surface of the housing, and thus reduces the suction-generative effect.

The larger the diameter of the housing the larger the diameter of the holes before they seriously disturb the smooth flow pattern of air over the surface. And since the diameter of the cowl is generally limited in size with respect to the vent pipe, the preferred hole diameter can be expressed in terms of the vent pipe diameter. I prefer to have the maximum dimension of the holes less than about A the diameter of the vent pipe, and with a maximum upper limit of 1 inch for a high suction-generative cowl. On the other hand I prefer not to go to too small a size, since such small diameter holes may be closed off by dust, dirt, ice or snow, or other foreign matter. Also, I prefer not to go to too small openings since they create a throttling action to the flow of air through the openings. For these reasons I prefer to make the dimensions of the perforations in the range of about 0.2 to 1 inch. They may be round, rectangular or polygonal in shape. The round shape is to be preferred since the same dimension of opening is presented to the flow of air no matter what the direction of flow over the surface of the cowl.

The magnitude of the suction-generative effect is determined by the velocity of flow of the air over the surface of the cowl. The larger the diameter of the housing 18, the greater the crowding of the flow lines and the greater the velocity of the air along the streamline 22 flowing close to the surface, and thus the higher the suction generation. I prefer a housing of diameter in the range of 1.5 to 2.5 times that of pipe 11.

In connection with Figure 2 I have shown how a pressure-generative effect is created at the leading edge of an obstruction when the wind blows against it. For a cylinder, the angle through which the pressure effect exists is about 30 degrees each side of center. It is greatest head-on to the wind, and falls off on each side, reaching zero at about 30 degrees. At angles greater than about 30 degrees the effect of the air flow is suction-generative. If the cylindrical object is of considerable axial length, that is, in a direction perpendicular to the plane of the drawing of Figure 2, this pressure region exists for the length of the object. There is air flow into the cowl in the pressure region, as shown by arrows 35 and 36. In the suction-generative region, there is outflow of air or gases, as shown by the arrows 32, 33 and 34. The overall effect on the flow of gases in pipe 11 is determined by the resultant of the pressureand suction-generative effects. Thus the overall suction-generative effect can be increased by increasing the suction generation (such as by the use of small openings) or it can be increased by reducing the pressure generation. One way of reducing the pressure-generative effect is to change from a cylindrical shape to a spherical or spheroidal shape of housing. In this case the extent of the pressure region is limited in all directions from the direct point of air impingement. In other words, the air pressure built up on the leading face is bled off by flow of air in all directions away from the point of impingement, instead of only in the circumferential direction. Therefore, for a high suction cowl, I

prefer one in which the shape of 'the housing is substantially spherical or spheroidal. Although the shell portion of the housing of Figure 1 is only a hemisphere, the overall action of this cowl will be substantially that of a spheroidal housing since the extent of any cylindrical portion is quite small, and because the perforations are in the portion which is part of a spherical surface.

The embodiment shown in Figure 3 illustrates another type of high suction-generative termination or cowl. It consists of an essentially spherical or spheroidal housing with perforations 20. As in Figure 1, a rain shield 16 is mounted over the end of the tubular element 13 by means of brackets 17. The element 13 is fastened to the vent pipe 11 by means of screws 12. The spherical housing can be constructed in two parts; an upper half 37 and a lower half 38, the latter being securely fastened to element 13 by means such as screws 39. The two hemispheres may be joined together along one equatorial seam 40 by means of a thin strap 41, which may be riveted, welded or screwed to the parts 37 and 38.

If the upper half of the housing is not perforated over its entire surface I prefer that the perforations be symmetrically arranged around the lower edge, leaving the top central part unperforated. In this case the cap 16 and brackets 17 are not required for rain protection. Also, in that case the tubular extension 13 of the vent pipe 11 can be dispensed with and the lower half of the housing 38 can be supported directly by the vent pipe. in this case the cowl comprises simply a spherical or spheroidal housing of sheet material entirely enclosed except for a circular opening in the bottom substantially of the same diameter as the vent pipe, with means for fastening the housing to the vent pipe.

The spherical or spheroidal shape of the housing 37-38 creates a streamline flow of air over the surface no matter what the direction or attitude of the wind. Furthermore, due to the spherical shape, a minimum area of the surface is pressure-generative. This type of structure provides a high suction-generative capacity.

Another embodiment, adaptable to simpler manufacture is shown in Figure 4. This comprises 3 parts; a base portion 42, an intermediate portion 43 and a top portion 44. In this embodiment a separate tubular element 13 is not used. Instead, the vent pipe 11 is inserted directly into the cowl. This feature could of course be used in the other embodiments as well. The base portion 42 is an annular dish adapted to be placed over and to surround the end of the pipe 11, and to be rigidly fastened thereto by means, such as screws 12. The central portion 43 is a shallow thin-walled circular cylinder. This may be formed from a strip of sheet material which can be perforated in proper pattern and then rolled into a cylindrical form and riveted, welded or otherwise fastened to form a cylinder of the same diameter as that of the base 42. The top cap 44 is dished in a manner similar to the base 42 except that it has no central opening. The three parts can be fitted together and fastened into a rigid, substantially spherical assembly, by means well known in the art. This cowl completely encloses the end of the vent pipe 11.

Since all the perforations in this embodiment are in the central shallow cylinder, the top cap serves not only to control the air flow over the cowl, but also serves as a rain shield and nothing further is required for that purpose. This also eliminates the need for the tubular element 13 of Figures 1 and 3, since it is no longer needed to support the rain shield 16. Thus the housing can be fastened directly to the vent pipe.

In all the embodiments shown, the same preferences hold for (l) a substantially spherical or spheroidal shape of housing, (2) for a diameter of housing substantially greater than that of the vent pipe, (3) for perforations of. a size small compared with the diameter of the vent pipe, and (4) perforations placed either over the entire surface of the housing, or at least in a circumferential band arranged perpendicular to the axis of the vent pipe.

While I have described my invention in terms of the foregoing specific embodiments and modifications, it is obvious that many further embodiments and modifications are possible and will occur to those skilled in the art. For example, the part 38 of Figure 3 could be attached directly to the vent pipe 11 in a manner similar to that of part 42 of Figure 4. The invention therefore should not be considered as limited to systems with the exact details described, but is rather to be ascertained from the scope of the appended claims.

Having described my invention, what I claim as new, and desire to secure by Letters Patent is:

l. A high suction-generative cowl for a vertical vent pipe comprising a housing adapted to be placed over the top of, rigidly fastened to and completely enclosing the open end of said vent pipe, said housing having circular symmetry about a vertical axis coincident with the axis of said vent pipe, at least a major part of the outer surface of said housing conforming to a substantially spheroidal surface, the diameterof said housing being substantially larger than that of said vent pipe, a multiplicity of perforations arranged in a circumferential band around said housing, said openings having dimensions in the range of 0.2 to 1.0 inch, whereby said vent pipe will be rain free and when the wind blows over the surface of said housing from any direction there will be a minimum of turbulence and a maximum suction generated in said vent pipe.

2. A cowl as in claim 1 in which said housing comprises a base, an intermediate and a top portion, said base portion comprising a circular annular dish of spheroidal shape convex downward whose outer diameter is equal to that of said housing and Whose central opening is adapted to encircle said vent pipe, and to be rigidly fastened thereto, said intermediate portion comprising a shallow thin walled cylinder whose diameter is equal to the outer diameter of said base portion, said cylinder being perforated with a multiplicity of small holes, said top portion comprising a circular spheroidal convex cap of diameter equal to that of said cylinder, and means to fasten together into a rigid spheroidal housing said base, said intermediate and said top portions.

3. A cowl as in claim 1 in which said housing is made in two parts, a "base portion and a cap portion, said base portion exposing to the outside an annular spheroidal surface with a central opening adapted to encircle said vent pipe, said base portion adapted to be rigidly fastened to said vent pipe, said cap portion comprising a substantially hemispherical surface of diameter equal to the outer diameter of said base portion, the lower portion of said cap perforated with a multiplicity of small holes around the complete circumference and means for fastening into a rigid assembly said base and cap portions.

4. A high suction-generative cowl for a vent pipe comprising a substantially spheroidal shaped housing adapted to be placed over, to completely surround the end of and to be rigidly fastened to said vent pipe, said housing being substantially larger in diameter than said vent pipe and comprising a base portion, an intermediate portion, and a top portion, said base portion comprising a spheroidal shaped annular dish with inner diameter substantially equal to that of said vent pipe and outer diameter equal to the diameter of said housing, means for fastening said base portion to said vent pipe, said intermediate portion comprising a shallow thin walled cylinder of substantially the same diameter as the outer diameter of said base portion, said cylinder being perforated with a multiplicity of small holes around the complete circumference, said upper portion comprising a convex circular spheroidal cap of the same diameter as the outer diameter of said base portion, and means for fastening together to form a rigid assembly said base, said intermediate and said top portions.

5. A cowl as in claim 4 in which said intermediate portion comprises a strip of perforated sheet material rolled longitudinally and fastened to form a shallow cylinder.

6. A cowl as in claim 4 in which said perforations have dimensions in the range of 0.2 to 1.0 inch.

7. A high suction-generative cowl for a vent pipe comprising a base portion, an intermediate portion, and a top portion, said base portion comprising a circular annular dish, the annular surface of said dish being part of a spheroidal surface, a central opening in said dish, a short cylindrical tube inserted in said opening and extending below the annular surface, and adapted to encircle and to be fastened to said vent pipe, said intermediate portion comprising a strip of perforated sheet material rolled and fastened in the form of a shallow cylinder of diameter equal to the outer diameter of said base portion, said top portion comprising a circular convex spheroidal cap of diameter equal to the outer diameter of said base portion, means for fastening together into a rigid assembly said base, intermediate and top portions whereby a substantially spheroidal rigid housing is provided which can be placed over and completely enclose the top of said vent pipe.

References Cited in the file of this patent UNITED STATES PATENTS 363,236 Hodel May 17, 1887 1,036,352 Senter et a1 Aug. 20, 1912 2,656,833 Moran Oct. 27, 1953 2,701,999 Moran Feb. 15, 1955 FOREIGN PATENTS 550,159 France Dec. 7, 1922 310,993 Great Britain May 6, 1929

Images