Abstract:
Disclosed is a tower packing for vapor-liquid contact whichincludes a plurality of sheets of corrugated material, the sheetsbeing arranged generally vertically and parallel to one anotherwith the corrugations of adjacent sheets criss-crossing oneanother. The sheets are provided with a plurality of holes foreffecting both liquid and vapor distribution in said packing, andthe holes are arranged on the sheets with the horizontal spacingbetween adjacent holes being no greater than about five times thehorizontal extent of a hole, and in no event greater than about 5millimeters. The horizontal extent of the holes is no greater thanabout 2 millimeters.
In one form the packing isconstructed so that the angle said corrugations strike to thevertical axis of the packing and the fold-to-fold dimension of thecorrugations are so selected with respect to the horizontal andvertical extent of a hole and the horizontal and vertical spacingbetween adjacent holes that a plurlity of said holes fall on agiven corrugation fold of a sheet.
Description:
FIELD OF THE INVENTION
The present invention relatesto tower packing, and, more particularly, to structured towerpacking for columns incorporating counter-current vapor-liquid flowtherethrough.
BACKGROUND OF THEINVENTION
In the chemical engineeringarts, structured tower packings are a known class of devices usedto effect heat and mass transfer between vapor and liquid streamsin a tower for the purposes of distillation, rectification,fractionation, stripping, splitting, absorption, desorption,cooling, heating, and similar unit operations. Towers containingstructured tower packing are a form of packed towers, and are mostoften operated with the vapor and liquid streams in counter-currentflow.
The primary design object in astructured tower packing is to provide ample opportunity for theliquid and vapor which are typically flowing in counter-currentrelation through the tower to come into intimate and extendedreactions with one another so that the mass and energy exchangereactions between the vapor and liquid may proceed. These reactionsare in most instances gas film coefficient controlled, ultimately,and in this circumstance means that care must be taken to obtaingood gas distribution, and such turbulence and mixing in the gas ascan be readily had, so that the vapor or gas film at the interfaceis as thin as possible.
These reactions are alsostrongly dependent on the area of contact between the vapor and theliquid, and this circumstance means that care should be taken toobtain very good liquid distribution over the surface of thepacking so that the area of contact is as large as can beobtained.
Structured tower packings arepassive devices in the sense that they have no moving parts, and noexternal power is input directly to them. As a consequence, theobjects of obtaining good vapor and liquid distribution and goodintimate contact between the vapor and the liquid must be obtained,if at all, by configuring the structure of the packing and itssurface and through-the-surface features to maximize the liquid andvapor distribution in a passive manner.
Within the field of structuredtower packing, one type which has been of technical and commercialimportance in recent times is that which is formed of a pluralityof sheets or lamellae of one or another kinds of material, with thesheets being corrugated and arranged generally parallel to the axisof the tower in which they are installed. The sheets are corrugatedand provided with holes or apertures. The holes or apertures areknown to facilitate gas or vapor distribution within the packing,particularly laterally of the packing, and also to act as liquiddistributing devices affecting the flow pattern of liquid movingacross the sheets. The sheets are preferably corrugated, with thecorrugations arranged at angles to the tower axis so that thecorrugations of adjacent strips criss-cross. This latterconstruction makes it unnecessary to use various spacers or othersupplementary devices to position the sheets with respect to oneanother, unless that is especially desired, since thecriss-crossing ridges of the plates provide sufficient mechanicalstrength to maintain the plates in the desired position, especiallyif they are wrapped with binding material, or are spot welded orotherwise connected at their points ofcontact.
Early examples of this class ofstructured tower packing are taught in Stedman U.S. Pat. No.2,047,444 and Huber British Patent No. 1,004,046. More recently,efforts have been made to improve the performance of this kind ofpacking by various sorts of surface or through-the-surfacetreatments. Examples of tower packing within this class having suchtreatments include: U.S. Pat. No. 4,296,050 to Meier; U.S. Pat. No.4,604,247 to Chen et al., West German application No. 3,414,267.3to Raschig.
The performance of towerpackings and other vapor liquid separation devices such as trays iscommonly evaluated by a parameter defined as Height Equivalent to aTheoretical Plate (H.E.T.P.), as first proposed in an article by W.A. Peters appearing in the June 1922 issue of Journal of Industrialand Engineering Chemistry. The H.E.T.P. is expressed in lineardimensions, such as, feet, inches, meters or centimeters, and thelower or smaller the H.E.T.P., the better the efficiency of thevapor-liquid contact device under consideration. H.E.T.P. is oftenplotted against parameters which are indicative of vapor and liquidflow rates such as F-factor (defined as V s [Dv ] 0 .5, (lbs/ft 3 ) 0.5 ft/sec.) and C-Factor (defined as V s [D v/(D 1 -D v )] 0 .5, ft/sec.).Where V s =Superficial velocity, ft./sec.; Dv =Vapor density lbs./ft 3 ; and D1 =Liquid Density, lbs/ft 3 . It is generallypreferred that plots of H.E.T.P. against such parameters producecurves which are as flat as can be had, over as broad a range ofthe flow rate parameter as possible. Such flat curves areindicative of good performance over a wide range of operatingconditions, including the region near flooding at high flow ratesand at very low liquid rates, where the volumetric flow rate ofliquid may be so low that not enough liquid is available to wet outthe entire plate surface of the packing.
SUMMARY OF THEINVENTION
The present invention relatesto an improved structured tower packing of the corrugatedplate-type in which the corrugation angles are such that thecorrugations of adjacent plates criss-cross and wherein the platesare apertured or provided with holes which are specially sized andpositioned upon the plates.
More particulary, one aspect ofthe present invention includes a tower packing for vapor-liquidcontact made up of a plurality of sheets of corrugated material.The sheets are arranged generally vertically and parallel to oneanother with the corrugations of adjacent sheets criss-crossing oneanother. The sheets are provided with a plurality of holes foraffecting both liquid and vapor distribution in the packing. Theholes are arranged on the sheets with the horizontal spacingbetween adjacent holes being no greater than about five times thehorizontal extent of a given hole and in any event no greater thanabout 5 millimeters. As used herein, "horizontal extent of a givenhole" means the largest dimension of the hole measured in ahorizontal direction (in the case of a round hole, its diameter)and "horizontal spacing between adjacent holes" means the closesthorizontal edge-to-edge distance between adjacent holes. Thehorizontal extent of the holes is no greater than about 2millimeters. A practical lower limit on hole size is about 1millimeter in horiztonal extent, since tooling for smaller holestends to be fragile and troublesome.
It is also preferred that theholes be arranged generally orthogonally on said sheets. The termorthoganol is used herein to denote that vertical rows of holes aregenerally parallel to the axis of a vertically arranged tower, andhorizontal rows of holes extend generally at right angles to thetower axis and thus orthogonal to the vertical rows. The term isalso used to denote an arrangement of holes which is generallyrectangular in appearance, as distinguished from a triangularpattern of holes. It is also preferred that a vertical spacingbetween adjacent holes is no greater than about 5millimeters.
In accordance with anotheraspect of the invention, there are also certain relationshipsestablished between hole size, hole spacing, preferably holepattern, corrugation angle, and the fold-to-fold dimension of thecorrugations in order to maximize the gas and liquid distribution,while minimizing pressure drop in the gas phase, and enhancing theoverall performance of the packing.
Holes perform several functionsin packings of this kind. They act as liquid dividers, which divertthe flow of liquid on a packing sheet around them, thus aiding inthe horizontal or lateral spread of the liquid. They also act asgas distributors, enabling gas to flow laterally through thepacking from one corrugation channel to another. Holes also enableliquid to flow from one side of a packing sheet to the other sideof the same sheet, thus exposing a fresh surface of a liquid filmto gas contact, a particularly efficient step, and otherwisestirring and mixing the liquid film. Finally, some holes sheet overwith liquid and thus provide gas access to both sides of a thinliquid film, again enhancing mass and energy transfer. A given holemay perform any or all of these functions sequentially andrepeatedly during the operation of a vapor liquid contacttower.
With respect to thecorrugations, the fold-to-fold dimension of such corrugations has alarge influence on the vapor phase pressure drop through thepacking, since it is the fold-to-fold dimension which defines thesize of the generally triangularly-shaped angles gas flow passagesthrough the packing. This dimension also determines the amount ofsheet area in a sheet of nominal rectangular dimensions; thesmaller the fold-to-fold corrugation dimension, the larger thesurface area of the plate is. It is also known that in a corrugatedtower packing of the criss-crossed type, the downwardly flowingliquid tends to concentrate in the troughs and/or valleys of thecorrugations.
The foregoing considerationsmake it desirable to size the holes so that all of the above listedeffects on liquid flow are obtained or are obtainable in view ofthe surface tension properties of the liquid being treated. It isalso desirable to position many of the holes in a sheet in thefolds occurring at the valleys of the corrugations. It should, ofcourse, be noted that a valley on one side of a sheet is a peak orridge on the other side of the sheet. In this manner, the holeshave the maximum opportunity to advantageously effect the flow anddistribution of the liquid on the sheet.
To this end, it is desirable inaccordance with the present invention to have the tower packingarranged so that the angle which the corrugations strike to thevertical axis of the packing and the fold-to-fold dimension of thecorrugations are so selected with respect to the horizontal andvertical extent of a hole and the horizontal and vertical spacingbetween adjacent holes that a plurality of the holes and preferablymany of them fall on corrugation folds of thesheet.
In a preferred form theforegoing considerations produce a tower packing in which thespacing of the holes is substantially equal in the horizontal andvertical directions and further in which the corrugations strike anangle of about 45° to the vertical axis of the packing. Theseconsiderations also lead to a preference for a tower packing inwhich the horizontal projection of the fold-to-fold dimension ofthe corrugations is substantially a multiple of the horizontalspacing between holes of the packing. More preferably, thatmultiple is two or more and in any event should fall between 2 and20.
It its preferred form, thetower packing of the invention is one in which the holes are round,inasmuch as this is an easy hole shape to tool for and produce.Nonetheless, the invention contemplates inclusion of holes that areother than round in which event it is preferred that theirhydraulic radius be no greater than about 1 millimeter. Examples onnon-round holes include ovals, oblongs, elliptical holes,triangular holes, rectangular holes, narrow slit-type holes, andthe like.
It has been found that theliquid dividing function of the holes mentioned above is enhancedif the holes are provided with small ridges or burrs at leastaround their upper rims, and it is accordingly preferred that thisconstruction be used in accordance with the invention. The burrsproject outwardly and provide small dams which divert the liquidlaterally at the edge of a hole. It is further preferred that burrsproject from opposite sides of a tower packing sheet so that theirliquid division enhancing function is obtained on both sides of thesheet.
If the burr occurs at thebottom of a hole, instead of at the top, its predominant functionis to divert liquid through the hole to the other side of the sheetinstead of dividing it. This, too, is a desirable function andpromotes mass and heat transfer.
It has been found that in theoperation of perforating sheet materials, particularly metalsheets, there is an important and strong relationship between holesize and both the relative and absolute sizes of the burraccompanying a given hole in terms of burr length and height andthe amount of "puckering" or distortion along the hole edgeresulting from the frictional forces involved in the hole punchingoperation. It has further been found in accordance with theinvention that when holes of a diameter no greater than about 2millimeters are compared with holes only moderately larger, such asthe 4 millimeter diameter holes common in tower packings of theprior art, the burrs associated with the smaller holes show notonly greater size variances, but also averaged values for burrlength and height which are an order of magnitude greater thanthose for the larger holes. As is pointed out above, theseprominent burrs aid in the liquid division and diversion functionsof the holes.
In the discussion above,several different effects of the holes were listed and discussed,several of them acting primarily on the liquid flowing down thesheet. It has been found that in order to maximize the obtaining ofsuch effects, the size of the holes in the sheet should not be toolarge, and hence the maximum holes size of about 2 millimetershorizontal extent is specified in accordance with the invention. Atthe same time, the total open area on a sheet established by theholes should be no greater than by about 20 percent of the area ofthe sheet. If it is greater, efficiency falls off to the pointwhere greater tower height is needed to provide adequate surfacearea for the liquid and gas to interact.
Various materials ofconstruction may be employed in accordance with the invention. Thepreferred material is sheet metal of a type having adequatecorrosion resistance and inertness to the liquids and vapors beingtreated in the particular tower under consideration. Alternatematerials include plastic, paper, particularly resin-impregnatedpaper, or ceramics. The material may be of the expanded type, suchas expanded metal or plastic, or it may be a woven or knittedmaterial, such as woven wire cloth or knitted wire mesh, orcorresponding materials formed of plastic resins or textiles.Various through-the-surface features such as slits may be employedin addition to the holes, and various kinds of surface featuressuch as grooves and fluting or embossing may be utilized. All thesespecial structures or surface treatments are for the purpose ofenhancing the spread of liquid on the sheet to enlarge and maintainits area of contact with the vapor.
From the foregoing it can beseen that the principal object of this invention is the provisionof an improved tower packing of the corrugated criss-crossedapertured sheet type which has improved efficiency and performanceas compared with prior packings.
The manner in which thisobject, together with other objects and purposes is obtained inaccordance with the invention may best be understood by aconsideration of the detailed description which follows, togetherwith the accompanying drawings.
BRIEF DESCRIPTION OF THEDRAWINGS
FIG. 1 is a somewhat simplifieddiagrammatic isometric view of a packed tower utilizing a towerpacking constructed in accordance with the principles of thepresent invention.
FIG. 2 is a fragmentary,isometric view on an enlarged scale of a portion of a tower packingconstructed in accordance with the principles of the presentinvention;
FIG. 3 is an enlarged,fragmentary isometric view of a portion of a single sheet of thetower packing material of FIG. 2;
FIG. 4 is a fragmentary planview of a portion of a sheet of tower packing material constructedin accordance with the invention;
FIG. 5 is a diagrammatic layoutof a hole pattern utilized in accordance with the invention, with ahole pattern of the prior art superimposed in dashed lines forcomparison;
FIG. 6 is a diagram of a holepattern utilized in accordance with the invention for the purposeof showing certain geometric relations having a bearing on liquiddistribution considerations.
FIG. 7 is an enlargedfragmentary plan view of a single hole through a sheet, with theburr associated with the hole being located across the top of thehole
FIG. 8 is an enlargedfragmentary plan view of a single hole through a sheet, with theburr associated with the hole being located across the bottom ofthe hole;
FIG. 9 is a diagrammaticcross-sectional elevational view of a portion of a sheet of packingwith the burrs thereon being positioned at the tops of the holesand all projecting to one side of thesheet;
FIG. 10 is a diagrammaticcross-sectional elevational view of a portion of a sheet of packingwith the burrs thereon being positioned at the tops of the holesand projecting to both sides of thesheet;
FIG. 11 is a diagrammaticcross-sectional elevational view of a portion of a sheet of packingwith the burrs thereon being positioned at the bottoms of the holesand projecting to one side of a sheet;
FIG. 12 is an enlargedcross-sectional view copied from a micro-photograph of a sheethaving a hole with a burr associatedtherewith;
FIGS. 13A-13G are plan views ofholes of a variety of shapes for use in a tower packing sheet;and
FIG. 14 is a diagrammaticisometric view on a reduced scale of a tower packing cartridgeconstructed in accordance with theinvention.
DETAILED DESCRIPTION PREFERREDEMBODIMENTS
Referring first to FIG. 1,there is illustrated a process tower designated generally as 10.The tower has a metal shell 11 and has piping for various streamsprovided thereon. Thus there is an overhead line 12, and a bottomstream take-off 13. There is also a side stream draw-off line 14, aside feed line for liquid 15, and a side stream vapor feed line orreboiler return line 16 for vapor. Also provided is a reflux returninput line 18. Manways 17 are provided at various points in thetower for access during shut down or turn around for maintenanceand construction purposes.
The tower 10 illustrated inFIG. 1 has three packing beds in it designated from top to bottom19, 20 and 21. Vapor enters the tower through reboiler return line16 and courses upwardly through the tower and packing beds 19, 20,21 to leave through overhead line 12. In doing so, the vapor streamis enriched by material evaporated into it as it passes through thepacking beds, and is depleted by material condensed from it as itpasses through said beds.
In operation, liquid is alsofed into the tower through reflux return line 18 and side streamfeed input line 15. The liquid flows downwardly through the towerand ultimately leaves the tower either as side stream draw offthrough line 14, or at bottom stream draw off through line 13. Inits downward flow, the liquid is depleted of some material whichevaporates from it as it passes through the packing beds 19, 20 and21, and is enriched or added to by material which condenses into itout of the vapor stream.
Associated with the refluxinput line 18 is a distributor 22 for distributing the liquidacross the top of packing bed 19. Associated with side stream inputline 15 is another distributor 23 which serves the same functionwith respect to liquid entering the bottom packing bed 21. A liquiddistributor 24 is also provided above packing bed 20 forredistributing liquid flowing downwardly out of collector tray 25.Collector tray 25 is positioned below the top packing bed 19 and afraction of the liquid so collected is drawn off through sidestream draw off line 14.
Although many variations intower arrangement are possible, that shown in FIG. 1 forillustrative purposes may be taken as typical. The specialstructured tower packing material of the present invention isutilized in packing beds 19, 20, 21 is described in more detailbelow.
Referring now to FIGS. 2 and 3in combination it can be seen that the tower packing of the presentinvention designated generally as 30, includes a plurality ofsheets 31, 32, 33 and 34 which are corrugated along fold linesindicated at 35 and provided with holes or perforations orapertures 36. The corrugation fold lines are arranged at angles sothat they criss-cross when adjacent plates are considered. In thisway there are formed a number of troughs or generally triangularlycross-sectioned passages which are angled upwardly so far as qasflow in concerned and which are angled downwardly so far as liquidflow is concerned, the passages being open topped and intersectingrepeatedly other passages of oppositeangulation.
In FIG. 14 a single towerpacking element or cartridge 51 is shown in isolation. It isgenerally cylindrical in shape to fit in a round column, and ismade up of a plurality of corrugated and perforated sheets 52arranged in parallel relation with the corrugations of adjacentsheets criss-crossing. The sheets are preferably held in positionby bands 53 which also help to seal against the inner wall of thecolumn. The packing beds 19, 20 and 21 of FIG. 1 are each formed ofa plurality of cartridges or elements 51 stacked in the column withadjacent elements rotated so that sheets thereofcross.
Referring to FIG. 4, there isshown a sheet 37 before corrugating, the holes 36 are preferablyarranged in an orthogonal pattern. In the case of the orthogonalpattern shown in FIG. 4 there are horizontal rows 38A and verticalrows 38B and all of the holes 36 fall both in a horizontal row anda vertical row. In addition, in the particular orthogonal patternshown in FIG. 4, the vertical spacing on ahole-center-to-hole-center distance 39 is preferably the same asthe horizontal hole-center-to-hole-center distance 40. As has beenmentioned above, it is preferred that the hole diameter of roundholes 36 be no greater than about 2 millimeters. If holes which areother than round employed it is preferred that they be dimensionedfirst, so that their horizontal extent is no greater than about 2millimeters, and secondly that their hydraulic radius be no greaterthan about 1 millimeter. Some of the reasons for these preferencescan be seen from a consideration of FIG. 6 to which attention isnow directed. In FIG. 6 a group of holes 41, 42, 43, 44 are shownarranged in an orthogonal and basically square pattern in dashedlines. If a liquid stream is visualized as flowing in two strandsdown the plate on which holes 41-44 are located in two streams eachbasically of the same width as said holes, it can then be seen thatthe stream widths are indicated by the arrows 45 and 46. When suchhypothetical streams encounter holes 41 and 42, it is known fromobservation that the streams split and tend to flow around theholes. If holes 41 and 42 are located a distance apart such thattheir horizontal spacing is no greater than about the horizontalextent of holes 41 and 42, in the case of round holes, theirdiameter, then the split streams will occupy basically all of thespacing between holes 41 and 42. The size of the split streams isindicated by arrows 47 and 48, and the stream dividing effect isindicated diagrammatically by the arcuate arrows 49 and 50. Arrow48A thus illustrates the total stream area between holes 41 and 42which is filled by stream 47 and 48 asshown.
If, instead of flowing aroundholes 41 and/or 42 the holes are sized so that the liquid may flowacross the holes, then the stream proceeds across the holes 41and/or 42 and eventually these streams encounter holes 43 and 44where they may be split as just described or again flow across theholes. In addition to flow across the holes, there will be, in someinstances, flow through the holes so that the liquid is transferredto the backside of the sheet down which it isflowing.
FIGS. 13A-13G illustrates somepossible variations of hole shape, 54 being triangular with the topside horizontal, although other orientations can be used; 55 is anoblong or oval hole; 56 is a horizontally oriented rectangularhole; 57 is an octangonal hole; 58 is a square hole; 59 is atear-drop shaped hole: and 60 is a cross-shaped hole. It should benoted that the various shapes of holes of FIGS. 13A-13G will alsocreate a variety of burr configurations which affect fluid flow inthe manner discussed herein.
Attention is directed to FIG. 5which illustrated an advantage obtained by limiting the hole sizeto less than about 2 millimeters, as compared to the largerapproximately 4 millimeter holes encountered in various parts ofthe prior art. In FIG. 5 holes of approximately 2 millimeter sizeare indicated at 45 in full lines, while in dashed lines, largerholes approximately twice the diameter or 4 millimeters areindicated in dashed lines at 46. The pattern of both the prior artholes 46 and the holes of the invention in FIG. 5 is orthogonal andon a square pattern, basically. The hole sizes and spacings arealso selected so that there is substantially the same amount orpercentage of open space on the plate as FIG. 5 is drawn. If FIG. 5is considered with the foregoing in mind it can be seen that in theupper left-hand quadrant of FIG. 5 there are a total of five smallholes which interrupt a diagonal 47 drawn at 45° to represent afold line of a corrugation, while only three of the prior art holesinterrupt that diagonal. This means that a stream of liquid flowingdown a fold of a corrugation in the valley of the corrugation so tospeak will engage five small holes for every three large holes itencounters. Thus, it will be divided five times instead of threetimes, and in addition, the smaller holes are more likely to filmover with liquid and are more likely to pass the liquid from oneside to the other side of the plate.
The magnitude of theimprovement obtained in accordance with the invention is striking.For example, a 4 millimeter triangular hole pattern in a towerpacking of selected crimp height or corrugation fold-to-folddimension with a standard test system (ortho-para-xylene at totalreflux) produced an H.E.T.P. in one series of tests of about 19inches. The hole pattern arranged in accordance with the inventionin tower packing otherwise the same (2 millimeter holes spaced 5millimeters apart) produced an H.E.T.P. with the same test systemof approximately 11-13 inches. This improved efficiency can beexploited through reduced tower height and reduced energy costs foroperating the tower.
From the foregoing discussionit can be seen that in one sense an ideal structure would have acorrugation fold at every interval (considered on a horizontalprojection basis) of the spacing (hole-center-to-hole-center) ofthe holes, since this would mean that basically every hole wouldfall in a fold or crease of the corrugations. However, otherconsiderations, such as the desired pressure drop and the desiredmaximum area of open space on a plate, as well as the desiredmaximum hole size, considered as diameter, horizontal extent, orhydraulic radius, mean that not all tower packings are desirablybuilt in this ideal manner.
In the prior art there areteachings that a triangular hole pattern is to be consideredpreferable to the orthogonal hole pattern of the preferredembodiments of the present invention (See U.S. Pat. No. 3,918,688and Canadian Patent No. 1,095,827 and Japanese Utility Model No.44-4761). However, triangular hole patterns are more awkward toform as a matter of stamping tooling, particularly if a progressivedie press is employed, and if the hole size and spacing constraintstaught in accordance with the present invention are followed, theorthogonal pattern of hole spacing produces just as favorableresults as the triangular hole pattern taught by the prior art.There is, in accordance with the invention, thus no undesirabletrade-off between ease of manufacturing and tower packingperformance such as is implicit in the teachings of the priorart.
On FIGS. 7 through 12 there areillustrated various aspects of the burr feature of the presentinvention. In FIG. 7, hole 61 in sheet 62 has a burr 63 formedaround its upper margin. As flow lines 64 indicatesdiagrammatically, burr 63 tends to aid in diverting liquid flowaround the hole.
FIG. 8 is similar to FIG. 7,and illustrates a hole 65 in sheet 66 with a burr 67 formed aroundits lower margin. Burr 67 tends to aid in diverting liquid flowthrough hole 65, as is indicated diagrammatically be flow lines68.
FIGS. 9, 10, and 11 are similarcross-sectional elevational views showing diagrammatically how theholes and burrs appear from the side. In FIG. 9 the burrs 70 are atthe tops of holes 71 in sheet 72, and will tend to divert flow ofliquid around the holes. All of the burrs 70 project to one side ofsheet 72 and their effect on liquid flow will be confined to thatside of the sheet.
In FIG. 10 the burrs 73 and 74are also at the tops of holes 75 in sheet 76 and will tend todivert flow of liquid around the holes. However burrs 73 project toone side of the sheet 76 and burrs 74 project to the other, so theywill affect liquid flow on both sides of thesheet.
FIG. 11 shows burrs 77 locatedat the bottoms of holes 78 in sheet 79. These burrs will tend todivert liquid flow through holes 78 as is indicated by flow line80.
In FIGS. 7 through 11, thelength of a burr may be taken to be its horizontal or arcuateextent; its width or thickness may be regarded as its verticalextent; and its height may be taken to be the distance it projectsabove the sheet.
FIG. 12 is copied from amicro-photograph showing a hole in a 0.005 inch thick sheet ofstainless steel edge-on at a magnification of about 100x. The burr81 is concentrated on one side of hole 82 in sheet83.
In the table produced justbelow, size measurements on burrs found on 2 millimeter and 4millimeter round holes are reported. From this table the effect ofhole size on burr size described above may be seen quantitatively.The small holes produce the more formidable holes which act as moreeffective liquid dividers and diverters.
From the foregoing it can beseen that there is provided in accordance with the presentinvention a superior tower packing which is easily constructed andvery efficient in operation.