US2231088A - Cooling tower - Google Patents

Description

" Feb.11,1941. A smcHARbsolg 2,231,088 COOLING TowER` Filed March 12. 195s @l y /4 3376973, (f (3" .64 l Il;

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" 1/5/ 10 if Pl l INVENTOR ZZQ@ fZzb/ardlsalz BY y " ATTORNEYS Patented Feb. 11, 1941 u UNITED STATES PATENT OFFICE y y f COOLING Towna w Allan Shakespeare Richardson, Butte, Mont.

Application Marchiz, 193s, serial No. 195,536

s claims. (creci- 112) Thisinventlon relates to cooling towerspartic ularly of the forced draft type for cooling liquids. and aims yto provide certain new and useful improvements in apparatus of this character. y

In liquid cooling towers ofthe forced. draft type it is customary to permit the liquid to fall in drops from a distributing system at .the top of the tower. Passage of the liquid` through .the towerV is retarded by numerous filling piecesof various shapes which catch the drops of `liquid from above, and, after the liquid has flowed downward over the surfaces of` these Vfilling pieces, it falls in drops onto similar filling pieces below. Such towers may be operated more or less satisfactorily at gas velocities up to'about 500 feet per minute, butat higher gas velocitieslthe efliciency of heat transference decreases and. liq,

uid is' caughtby the gaseou'sdraft and blown out of the tower. The efficiency of such towers depends to a large extent upon the'fallingliquid to secure a high `ratio of contact betweenliquid and gas resulting in a high efficiency of heat` transference. 'I'his is accomplished, in part; by rtheprogvision of a large number of lclosely-spaced corrugated metal sheets, preferably vof special configuration, downwhich the liquid to be cooled flows in thin films countercurrently withthe` n'sing draft of cooling gas. 'I'he corrugated sheets have substantially identicallyl but reversely curved surfaces forming ridges andfurrows, the reverses in the curvature of the curved surfaces occurring` closely adjacent the peaks of the ridges and the depths of the vfurrows and are spaced from the mid-point therebetween; The ratio of depth of corrugation topitch of the corrugated sheets is relatively high, preferably about l to 3. Preferably, the specially-shaped sheets are of uniform pitch with respect to each pair of reverse curves, with about two-thirds of each curve of uniform curvature and radius." The `close spacing of the sheets and their special configuration provide narrow and sinuous channels through which the gaseous cooling medium flows, under forced draft, in a turbulent manner, thereby exercising a scouring-like action that breaks up stagnant liquid films and promotes the rate of heat transference.` The liquid to be cooled is delivered separately to each surface of each sheet near but at least several `sinuatlons below' the tops thereof, and preferably at a'pointbelow a valley or furrow but slightly above the adjacent peak or ridge of the sinuous surface of each sheet, in such a manner as not to be caught by lthe gaseousl draft and carried out of the tower. In this manner liquid may be delivered to the sheets during passage of gas at high velocity through l the tower without substantial loss of unevaporated liquid by blow-over. Such high velocity of gas passing through the tower may be of the order of at least about 1000 feet per minute.

The foregoing and other novel features of the invention will be better understood from the following description'taken in connection with the accompanying drawing, inwhich Fig. lis a sectional elevation of a cooling towerembodying .the invention, l

Fig. 2 is `an enlarged sectional view through theassembly of reverse curve sheets, and Fig. 3 is a further enlarged sectional view illustrating the special configuration of the sheets.

The tower or chimney illustrated in the drawing comprises a lower portion 5 of concrete, or the like, and a superimposed upper portion 6 of steel, or the like, both rectangular in section.` It

will of course be understood that the tower may be built of other materials and may be of any appropriate dimensions. The tower has, a lateral opening 1 near its bottom for the introduction of the gaseous cooling medium, and a sump 8 at its base for thecollection of .the cooled liquid. Liquid is `withdrawn from the sump through a dis; charge pipe 9.

Suspended within thetower is the assembly of closely spaced metal sheets I0 of thepreferred special configuration. These sheets are in the form of continuous reverse curves, best shown in Fig. 3 of the drawing. The pitch (cz-J7)A of each pair of reverse curves is uniform and the two reverse curves (a-c and c--b) of each pair are of thesame form. For approximately two-thirds of its` length (a-d and c-e) each curve is the varc of a circle, and the remainder of the length (d-c and e-b) of each curve is of varying radii. The space between the assembled sheets is approximately the depth of the furrow or corruga- -tion,(o-c, Fig. 3).

l The vertical edges or ends of each strip I0 are secured to flat strips I I, as for example by soldering or welding the strip to the peaks or ridges on one side of the sheet (Fig. 2). The upper ends of the Vstrips II are angularly bent outwardly (I2) and rest on brackets I3 secured to opposite sides of the upper portion B of the tower. 'Ihe strips II may if desired serve as spacing members for the sheets. The closely-spaced sheets extend 55 vertically from near the gas inlet 1 to near the top of the tower and provide a multiplicity of narrow sinuouschannels for the draft of cooling gas. While the horizontal distance between the sheets is uniform, the distance between lthe sheets perpendicular or normal to the direction of gas flow is not uniform, but repeatedly contracts and expands. Thus, for each pitch-distance, the area. of the channel between .the sheets perpendicular to the direction of air flow twice contracts and then expands, thereby providing a succession of Venturi-like passages for the gas flow.

A tank or reservoir I4 is mounted on top of the tower for holding the liquid to be cooled. Pipes I5 and I6 deliver the liquid to a pair of upper headers I'I and a pair of lower headers I8, respectively, the two headers of each pair being on opposite sides of the tower. Liquid distributing tubes I9 and 2D are connected between the pairs of upper and lower headers I'I and I8, respectively. The liquid distributing tubes (within the assembly of sheets) are perforated to deliver the liquid to be cooled onto the surfaces of the sheets I0. The tubes are positioned above the peak of the curve of the surface of the sheet to which it delivers liquid so asto be out of the gas stream. The upper two sets of tubes I9 deliver liquid to the opposite surfaces of the sheets below the tops thereof, preferably two or three corrugations below the tops, sothatsuch liquid as is caught by the gaseous draft before it reaches the surface of the sheet is blown against the sheet at a higher elevation by reversals in the direction of gas flow because of its greater momentum due to its greater density. Theliquid then adheres to the sheets andflows downwardly over .the surface thereof by gravity. The lower two sets of tubes, 20 similarly deliver liquid to the opposite surfaces of the sheets at an appropriate distance below the upper tubes. i

The cooling tower of the invention is particularly applicable for cooling water or brine in connection with air-conditioning equipment. Air isthe most available gas for cooling. By way of example, the operation of the tower will be described as applied to coolingwater by a forced draft of air.

The water (or brine) to be cooled is delivered from the storage tank I4 to the tubes I9 and 20 s o that uniform films of water cover both sides of the sheets I0 and iiow by gravity countercurrent to the air fiow. 'I'he liquid lm is held to the metal surfaces by surface tension and practically no'liquid is carried from the tower by the cooling air. The special vconfiguration of the narrow channels between the sheets causes va considerableturbulence in the air ow which eliminates all so-called channeling effect with its consequent dead airv films. The cooling air is blown into the tower by an appropriate fan or blower (not shown) through the opening I near its base, an'd is unifornrly distributed to the channels between the sheets by deflecting plates 2|. 'I'he top of the tower is open for the free discharge of the air. 'I'he cooled liquid collects in the sump 8, from which it may be withdrawn asdesired through the outlet 9.

The considerations affecting pitch, depth of corrugation, and curvature of corrugation of the sheets I0 Vof the cooling tower of the invention are brieiiy as follows:

There is a certain minimum quantity of liquid per minute per horizontal linear foot of sheet surface that is necessary to maintain a uniformly wetted surface, or continuous downwardly moving film of water. This may vary for different materials used in fabricating the sheets and for different liquids. With galvanized iron sheets in a tower for cooling water or brine, this quantity is approximately 0.15 gallons per minute per horizontal foot of surface, or double that quantity per horizontal foot of sheet since both sides of the sheet are utilized.

Assuming that a given quantity of water is to be cooled through a definite temperature range, and to within a definite temperature difference between it and the air entering and leaving the tower, the quantity of air required must be sufficient to satisfy the heat balance. Transference of heat from Water to air increases with increase in the velocity of air motion, and in an approximately straight line relationship as far as can be determined experimentally. However, the

`resistance to air flow varies as the square of the velocity and hence it follows that there is an economic limit below which it is not possible to decrease the space between the sheets.` Nevertheless, the space between the sheets should be of insufficient width to permit a straight line flow therethrough of any appreciable volume of gas.

I have determined that the transference of heat is increased by increasing the number of corrugations perfoot of vertical distance, and by increasing the ratio of depth of corrugation to pitch. Inthis case also, the resistance -to air flow is increased by increasing the number of corrugations and by increasing the ratio of. depth of corrugation to pitch.

With other conditions constant, efficiency commences to decrease when the sheets are separated .beyond the vtangent position, and the most eiiicient arrangement is based upon the best balance of all ofthe foregoing factors. Obviously, the proportions of corrugations and spacing of sheets may vary widely with different requirements. In a water cooling tower utilizing air as the gaseous lcooling medium, ythe ratio of depth of corrugationv to pitch may advantageously be about 1 to 3 and the space between the sheets may be approximately the depth of corrugation. I have obtained very' satisfactory results, in a water cooling tower, with galvanized metal sheets having a depth of corrugation of 11/2 inches and a pitch of i1/inches thearc section (a-d) of the curve having a radius of about 1H inches for Yapproximately one third (l1/2 inches) of the pitch. In a water cooling'tower with such specially-shaped sheets spaced at about 1% inch centers the coefficient of heat transference at an air velocity of about 650 feet per minute is approximately twice as high as with ordinary corrugated sheets of the same pitch and depth of corrugation. In the ordinary corrugated sheet the adjoining reverse curves are symmetrical about a line normal to their junction at the peak of each corrugation. At an air velocity of about 1000 feet per minute the coefficient of heat transference'of the specially-shaped sheets of the invention-is about 60% higher than with ordinary corrugated sheets. u

The improvement in performance of the specially-shaped sheets of the invention is due in part to the fact that two-thirds of the surface ofthe sheet is available for impingement of the air against the water iilm as compared withonehalf in the case of the ordinary corrugated sheet. However, the actual improvement in performance is considerably greater than the ratio of surfaces exposed to impingement. This, I believe, is due to turbulence in the air flow induced by the fact that althoughthe horizontal distance between the sheets is constant, the area normal orperpendicular to the lines of air flow is not constant. In other words, there are alternate restrictions and enlargements of the area normal to the lines of air flow, thus imparting to the air flow repeated Venturi-like effects.

In a cooling tower of the invention approximately 40 feet in height, utilizing the speciallyshaped sheets of about the dimensions hereinbefore recited and about 29 feet long, I have cooled water from about '75 F. to 50 F. with air entering at a wet bulb temperature of 49 F. In l5 other words, the water was cooled to within 1 F. of the wet bulb temperature of the air entering the tower. At the same time the temperature of the air leaving the tower was up to within 7 F. of the water entering the tower, that is a wet bulb temperature of 68 F. Such a performance would be practically impossible with the heretofore known types of forced draft cooling towers. The estimated height of a conventional cooling tower of the prior art to cool water down to within 4 F. of thewet bulb temperature of the air entering the tower, with a temperature difference of about 7i F. between the air leaving the tower and the water entering the tower, is approximately 200 feet.

I claim:

1. In a cooling tower, a series of `closely-spaced straight line flow therethrough of any appreciable volume of gas, means `for inducing an upwardV current of gas through the spaces between said sheets, and means for delivering a liquid sepa- 40 rately to each surface of each sheet near but at least several sinuations below the upper end thereof, whereby liquid may be delivered to said sheets during passage of `gas at high velocity through the tower without substantial loss of un- 45 evaporated vliquid by blow-over.

2. In a cooling tower, a series of closely-spaced sinuous sheets having successive substantially identical but reverscly curved surfaces forming ridges and furrows, the reverses in the `curvature 50 of said curved surfaces occurring closely adjacent the peaks of said ridges and the depths of said furrows and being spaced from the mid-point therebetween, said sheets being operatively positioned within the tower to provide a, plurality of 55 generally upright and relatively narrow sinuous channels for the flow of gas, the area of said channels perpendicularl to the direction of gas flow repeatedly contracting and expanding, means for inducing an upward current of gas 60 through said channels, andmeans for delivering a liquidto the surfaces of said sheets.

3. In a cooling tower, a series of closely-spaced sinuous sheets operatively positioned within the and size and of insuiiicient width to permit a a tower and providing a plurality of generally upright and relatively narrow sinuous channels for the flow of gas, means for inducing an upward current of gas at high velocity of the order of at least about 1000 feet per minute through said channels, and means for delivering a liquid separately to each surface of each sheet near but at least several sinuations below the upper end thereof and at a point below a valley but slightly above the adjacent peak of the sinuous surface to which the liquid is delivered, whereby liquid may be delivered to said sheets during passage of gas at high velocity through the tower without substantial loss of unevaporated liquid by blowover. i

4. In a cooling tower, a series of closely-spaced sinuous sheets operatively positioned within the tower to provide a plurality of generally upright and relatively narrow sinuous channels for the iiow of gas, said sheets being in the form of continuous pairs of substantially identical but reverse curves forming ridges and furrows, the reverses of said curves occurring closely adjacent the peaks of said ridges and the depths of said furrows and being spaced`from the mid-point therebetween, the depth of the furrow of each curve being approximately one-third of the pitch of a pair of reverse curves and the spacing of the sheetsbeing such that said channels are of insuilicient width to permit a straight line iiow therethrough of any appreciable volume of gas, means for inducing an upward current of gas `through said channels, and means for causing films of liquid to flow by gravity over the surfaces of said sheets.

5. In a liquid cooling tower, a series of closelyspaced sinuous sheets operatively positioned Within the tower to provide a plurality of generally upright and relatively narrow sinuous channels for the flow of cooling gas, said sheets being in the form of continuous pairs of reverse curves forming ridges and furrows, the reverses of said curves occurring closely adjacent the i peaks of said ridges and the depths of said furrows and being spaced from the mid-point therebetween, the depth of the furrow of each curve approximately one-third the pitch of a pair of reverse curves and approximately two-thirds of each curve being the arc of a circle, the horizontal width of said channels being substantially uniform and approximately equal to the aforesaid depth of furrow andthe width of said channels perpendicular to the direction of gas ow alternately decreasing and increasing throughout the length thereof, means for inducing an upward current of cooling gas through said channels, and separate delivery means for delivering the liquid to be cooled separately to each surface of each sheet near but at least several sinuations below the upper end thereof and at a point slightly above the peak of the sinuous surface to which the liquid is delivered.

ALLAN SHAKESPEARE RICHARDSON.

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