Method And Apparatus For Distributing Fluids

Abstract

A method and apparatus are disclosed for discharging fluid in a sheetlike flow made up of contiguous flow zones extending across the width of the sheetlike flow. The fluid flow rate in each flow zone is individually controllable and is virtually unaffected by the fluid flow in the adjacent flow zones. The method consists of expanding the widths of a plurality of spaced-apart, individually flow-rate-controlled streams until all streams are contiguous and thus form an uninterrupted sheetlike flow, while maintaining substantially uniform flow rate distribution profile across the width of each stream. The apparatus consists of a plurality of diffusion chambers arranged in a line and with the flow direction of each chamber parallel to each other. The widths of the chambers widen downstream in the chambers until all chambers adjoin each other. Fluid enters the upstream end of each chamber from its individual, valve-controlled conduit. The invention has particular value in applying fluid to a wide surface where the amount of fluid desired to be applied varies for different areas across the width of the surface. A particular use for the invention is to aid uniform drying of a wet paper web on a papermaking machine by controlling the flow rate distribution profile across the width of a sheetlike flow of steam discharged against the paper web.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements in distributing fluid against a surface to be treated by the fluid where it is desired to form a sheetlike flow of the fluid having an incrementally variable flow rate across the width of the sheetlike flow.

2. Description of the Prior Art

In many manufacturing operations it is desirable to apply with controlled distribution a fluid against a surface to be treated. For example, it may be desired to heat or cool a surface by spraying a fluid, such as air, water, or steam, against a surface which requires more heating or cooling at some points across its area than at others. It may also be desirable to apply a fluid under controlled distribution to a surface for coating, impregnating, or other similar purposes.

A particular application where it is desirable to apply a fluid against a surface with controlled distribution is found in the manufacturing of paper. In one method of papermaking, it is a common practice to dry wet paper webs by carrying them on a traveling felt through a driving nip in which they are pressed into engagement with the heated surface of a Yankee dryer by a pressure roll. Moisture in the web is heated and evaporated by heat supplied to the Yankee dryer from steam circulated through the interior of the dryer.

In recent years, limitations on drying capacity have caused serious restrictions upon the operating speeds of papermaking machines. To overcome these restrictions, manufacturers have made extensive efforts to increase the drying capacity of papermaking machines in a wide variety of ways. For example, Yankee dryer drums of larger diameter, on the order of 15 feet and more have been employed. In addition, attempts have been made to supply a greater amount of heat to the wet paper web by transferring more heat through the Yankee dryer shell. Pressure limitations of the material forming the dryer shell and the corresponding saturation temperature of the steam contained therein have been pushed upwards to the limits permitted by safety regulations.

One of the problems experienced in the operation of the papermaking machines has been the loss of heat from the outer surface of a Yankee dryer in the drying nips formed by the pressure rolls and the Yankee dryer. It is believed that this loss is chiefly caused by contact of the relatively cold wet paper web and its carrying felt with the surface of the Yankee dryer. Heat removed from the dryer shell at these points is inefficiently used as it is unavailable for drying the web in the remaining portion of the dryer circumference, where the greatest amount of evaporative drying preferably takes place. A number of attempts have been made to reduce this heat loss, but most have been rather ineffective.

One solution to this heat loss problem is to apply steam to the surface of the wet paper web to be dried in the region immediately preceding the point where the paper web contacts the surface of the Yankee dryer. This solution is disclosed in U.S. Pat. No. 3,560,333. In the apparatus of this patent the steam is discharged against the paper web from a cylindrical header having a plurality of holes cut along its length through a portion of its sidewall generally facing the drying nip. The plurality of holes are arranged generally in one or more lines along the header. Extending from the sidewall of the header on each side of the line of holes is a seal plate. One seal plate extends from the header to a point adjacent the surface of the Yankee dryer and spaced therefrom by a small incremental distance or clearance so that it is just out of contact with the Yankee dryer. Similarly, the other seal plate extends from the header toward the suction pressure roll to a point adjacent to, but spaced by a small clearance from the surface of the web carried on the felt wrapping the suction pressure roll. The holes are adapted to emit steam from the interior of the header into the space between seal plates in a manner whereby the steam impinges upon the seal plates and is uniformly diffused. This prevents damage to the wet paper web due to jetting of steam against it. Baffles are sometimes employed to control uniformity of steam flow and temperature at various points across the paper web being dried. With use of the apparatus described above, it has been found that substantial increases in the speed of operation of papermaking machines are achieved without any sacrifice or reduction in the dryness level of the paper sheet produced.

While the apparatus disclosed in U.S. Pat. No. 3,560,333 enables papermaking machines to be operated at a faster speed, it does not enable fine control of the sheet moisture content profile across the width of the sheet as the sheet leaves the Yankee dryer. Control of the sheet moisture content is of major importance, because uniformity of the end product is affected by the dryness of the sheet coming off the Yankee dryer. The sheet moisture content has been found to vary as much as 10 percent across the width of the paper web when the above apparatus is used.

Consideration of the problem readily suggests that it can be corrected by controlling the amount of heat, or steam flow rate, which is directed to any particular location across the width of the paper web. For example, if the middle two feet of the paper web is coming off the Yankee dryer wetter than the rest of the web, the amount of steam applied to the middle 2 feet is increased in proportion to the amount of steam applied to the rest of the web. In order to accomplish this selective control, the flow of steam must be controlled at various increments across the width of the paper web. In other words, the flow rate distribution profile of the steam being discharged against the paper web must be controlled.

One apparatus for distributing steam against a paper web which offers control of the flow rate distribution profile is disclosed in U.S. Pat. No. 3,574,338. The apparatus disclosed in this patent consists of a long chamber extending across the width of the paper web and having numerous distribution outlets facing the paper webs. The outlets are small (one-eighth to three-sixteenths inch in diameter) and are spaced apart from each other in rows, the distance between rows and between outlets being between one-half and three-fourths inch apart. The sum of the open areas defined by the outlets equals approximately 4 percent of the area of the plate required to support the outlets. Steam enters the chamber through a plurality of valved ports spaced equally along the width of the chamber. Individual adjustment of each valve controls the flow rate distribution profile of the steam discharging from the chamber.

Although the apparatus disclosed in U.S. Pat. No. 3,574,338 might offer some control of the flow rate distribution profile, it is readily apparent that the apparatus will not accomplish fine control. All of the port valves discharge steam into the common chamber, and from the chamber the steam passes through the numerous small outlets. It is easy to see that shutting one valve would not prevent steam from coming out of the outlets closest to that valve, because the steam from the other valves would merely move along the width of the chamber to fill the void in front of that valve and, thus, supply steam to its outlets. This occurrence is further assured because the chamber outlets are small compared to the chamber size, thus causing pressure build-up inside the chamber. The resulting steam distribution profile would be one with desired high flow rates in some locations, desired low flow rates in other locations, and gradual flow rate change from the high flow rate locations to the low flow rate locations.

Another obvious shortcoming of this apparatus is the fact that the steam is discharged in discrete, spaced-apart streams. Thus, if the discharge plate is close to the paper web, the steam distribution profile consists of spaced-apart streams of high flow rate and areas of practically no flow rate between the streams. The farther from the discharge plate, the more the tendency is for the streams to spread and fill the voids in between and perhaps even form a flow of steam uninterrupted across its width. But at the distance required to accomplish this, the flow rate distribution profile would deteriorate substantially and the velocity of the steam would have diminished greatly, probably to the degree of being unable to penetrate air barriers following the moving paper web in a papermaking machine.

Another apparatus for distributing steam against a paper web which offers control of the flow rate distribution profile is disclosed in U.S. Pat. No. 3,516,607. This patent discloses an apparatus consisting of a long, high-pressure chamber extending across the width of the paper web and a series of low-pressure chambers communicating with the common, high-pressure chamber. Each low-pressure chamber has a group of spaced-apart nozzles extending from the chamber and directed toward the paper web. Steam is passed from the high-pressure chamber through individually valved ports into the low-pressure chambers, and from there, it is discharged through the groups of nozzles and against the paper web.

This apparatus offers fine control of the steam flow rate from each group of nozzles, unaffected by the steam flow from the other groups of nozzles. But the steam distribution profile within each group is far from being uniform. Rather, it consists of spaced-apart, high-flow-rate streams with practically no steam flow between each stream. Like the apparatus of U.S. Pat. No. 3,574,338, this apparatus has the discussed disadvantages of spaced-apart discrete streams.

In addition to the other disadvantages of flowing the steam in numerous spaced-apart discrete streams, concentrations of high flow velocity in each stream could be deleterious to the paper web. Therefore, the velocity of each stream must be kept low enough to prevent harm to the paper web. Limitations on the stream velocity limits the amount of steam which can be applied to the paper web in a given flow area. It is readily apparent where all streams flow at the same velocity, that the larger the percent of flow area filled with streams, the greater the amount of steam being applied to the paper web. And, of course, the greatest amount of steam can be applied when the flow area is completely filled with one large stream having a uniform, maximum flow rate over the entire flow area. Therefore, maximum steam flow, and resulting heat energy transfer, cannot be obtained by flowing the steam in numerous spaced-apart discrete streams.

In a papermaking operation, it is frequently desirable for several reasons to apply the steam to an area of the paper web which forms a narrow continuous band across the width of the paper web. For example, the distance along the length of the paper web available for applying steam may be very short. Also, uniform flow rate of steam within the flow area is easiest accomplished if the area is as small as possible. The width of the flow area must, of course, be equal to the width of the paper web, and therefore, only the thickness of the flow area can be varied. Furthermore, there may be a minimum desirable flow velocity as well as a maximum, in which case the most efficient method of applying the steam is in a wide sheetlike flow.

One such case where it is desirable to apply the steam in a sheetlike flow occurs where a suction pressure roll forms the driving nip with the Yankee dryer. The suction pressure roll has a suction box on the interior of the roll to draw moisture from the paper web through the felt and perforated shell. The suction box is positioned to extend somewhat upstream of the driving nip. It is at this upstream portion of the suction box that it is best to direct the steam. Farther downstream the paper web disappears into the driving nip, and farther upstream the solid shell of the roll impedes penetration of the steam through the paper web. With a suction pressure roll, as well as with solid pressure rolls, air follows the moving paper web and Yankee dryer and accumulates into a high pressure barrier of air at the driving nip. In order to penetrate this barrier of air, the steam must be applied with at least a minimum velocity.

Thus, it is an object of the present invention to discharge fluid against a surface to be treated in a wide sheetlike flow, uninterrupted across its width.

It is a further object of the present invention to control the fluid flow rate distribution profile across the width of a wide sheetlike flow.

It is yet another object of the present invention to finely control the fluid flow rate distribution profile across the width of a wide sheetlike flow by individually varying the flow rate of each zone of a series of contiguous flow zones making up the sheetlike flow.

It is still a further object of the present invention to maintain uniform flow rate within each individual flow zone.

It is another object of the present invention to discharge fluid against a surface to be treated in a wide sheetlike flow, uninterrupted across its width and with the velocity of the fluid contacting the surface being controlled and within a range of desirable maximum and minimum velocities.

SUMMARY OF THE INVENTION

In order to fully appreciate the invention, certain terms must be clearly understood, and therefore, throughout this application and claims the following definitions apply:

"fluid" includes both liquids and gases;

"sheetlike flow" is a thin, wide stream of flowing fluid;

"flow rate distribution profile" is the profile formed by the quantitative flow rates of fluid at each location across the width of the stream;

"contiguous" is having contact on all or most of one side;

"adjacent" is to be near with the absence of anything of the same kind in between;

"adjoin" is to meet or touch at some point or line.

The objects of the invention are accomplished by providing an apparatus for flowing the fluid in a plurality of flow-rate controllable streams through a plurality of diffusing chambers adjacent to each other in a line and all aligned toward the surface to be treated. The width of each stream is gradually expanded in its respective flow chamber until all of the streams adjoin to form a sheetlike flow uninterrupted across its width. The sheetlike flow then consists of a plurality of contiguous flow zones, with each zone being formed from a different flow stream. Each flow stream width is expanded in such a manner that the flow rate distribution profile across the width of each individual flow zone is uniform so that the maximum amount of fluid can be discharged in each zone for any given maximum flow velocity, and also so that the treating effect of the fluid on the surface to be treated will be uniform within each zone. The flow rate of each stream is controlled by its associated valve to assure the desired flow rate distribution profile of the combination of streams. Further assurance of flow rate uniformity in each flow zone is acomplished by extending the upper and lower walls of the diffusing chamber beyond the stream width controlling walls of the diffusing chamber to form a common conduit for all of the flow zones and, thus, to assure that the slight width expansion of each zone necessary to completely meet its adjacent zones after flowing past the stream width controlling walls is controlled. Improvement of uniform dispersion of the fluid as it flows through the diffusing chambers is accomplished by initially flowing the fluid into the chamber at an abrupt angle to one of the walls of the chamber.

In the preferred embodiment and use for the invention, the apparatus is used to apply heating steam to a wet paper web on a papermaking machine. In this embodiment steam is flowed from a steam header extending across the width of the paper web, through a plurality of valved conduits, and into the ends of diffusing chambers. As the widths of the diffusing chambers are increased in the flow direction, the heights of the chambers are decreased to prevent a loss of flow velocity which could reslut in the steam condensing in the chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially broken away elevation view of the fluid distribution apparatus of the invention in use with a paper-making machine.

FIG. 2 is a cross-sectional view taken along lines 2--2 of FIG. 1 showing the internal structure of the diffusing chambers of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The fluid distribution apparatus of the invention is illustrated in FIG. 1 in its preferred use of discharging a sheetlike flow of steam against a wet paper web 3 passing through the drive nip 4 formed by a pressure roll 5 and a Yankee dryer 6 just before being transferred to the Yankee dryer 6. The pressure roll 5 shown here is of the suction type. The suction box, illustrated by suction box walls 7, draws moisture and steam through the paper web 3, felt 8, and perforated shell 9 of the suction pressure roll 5. The steam is supplied through conventional piping 10 to the steam header 11 which extends parallel to and along the full length of the surface of the paper web 3. Extending from the steam header 11 in a straight line along one side are a number of outlet conduits 12 which conduct steam from the header 11 in individual discrete streams through throttling valves 13, pipes 14, and through diffusing chamber entrances 15 into the diffusing chambers 16. The diffusing chambers 16, also shown in cross-section view in FIG. 2, consist of sidewalls 17 which diverge downstream from the diffusing chamber entrances 15 and top and bottom walls 18 which converge downstream from the chamber entrance 15. The top and bottom walls 18 extend slightly beyond the termination 19 of the sidewalls 17.

The diffusing chambers 16 are arranged so that the sidewalls 17 of each chamber adjoin the nearest sidewall 17 of its adjacent diffusing chamber 16 at the termination 19 of the sidewalls 17. Downstream of the termination 19 of the sidewalls 17, the top and bottom walls 18 of all of the diffusing chambers 16 join into two continuous strips forming a common flow conduit 20 for all of the diffusing chambers 16. The common outlet 21 of the diffusing chambers 16 is positioned close to the paper web 3 so the steam will be impinged against the paper web 3 with the desired velocity and before its flow rate distribution profile bgins to deteriorate.

Referring back to FIG. 1, the steam header 11 is illustrated by conventional steam piping, however, it could be of different design. For example, it could have a square or rectangular cross-section. Baffle plates (not shown) mounted inside of the header between the steam inlet 10 and the outlet conduits 12 could also be included to reduce condensate carryover into the conduits 12. The preferred embodiment of the invention uses conventional circular pipe as shown in FIG. 1. The use of pipe offers advantages in that it is readily available and is capable of withstanding internal pressure with minimum wall thickness.

The size selected for the steam header 11 is dependent upon the amount of steam to be flowed through the apparatus. It is preferable that the steam pressure is substantially uniform across the width of the header, and this goal is best attained by using a header 11 which is very large in comparison to the size of the outlet conduits 12. It is also helpful to centrally position the steam inlet 10 in the header 11. A satisfactory arrangement has been found to be the use of two steam inlets 10, each positioned about one-quarter of the header length from each end of the header 11.

In order to aid in preventing the passage of steam condensate into the diffusing chambers 16, it is desirable to remove as much condensate as possible from the steam while in the header 11. This can be done by use of a condensate drain 22 mounted in a low spot on the header 11 and leading to a steam trap (not shown).

The number of outlet conduits 12 from the steam header 11 is determined by balancing the economic advantage of using as few as possible with the process advantage of more precise control of the flow rate distribution profile obtained by using as many as possible. When using the apparatus with a paper machine having a width of the order of 18 feet, it has been found that 36 outlet conduits spaced 6 inches apart is quite satisfactory. Of course, this means that steam flow rate variations in the sheetlike flow can be made in increments of 6 inch widths. If smaller increments are desired, the number of outlet conduits 12 can be increased. The number of diffusing chambers 16 in the apparatus is, of course, equal to the number of outlet conduits 12.

Throttling valves 13 can be provided by any type of conventional steam valve. However, it is preferable that they be of a type which enables fine flow control, such as needle valves, globe valves, or angle valves. The size of the valves 13 is dependent upon the maximum amount of steam desired to pass through each diffusion chamber 16 and the amount of pressure drop desired through the valve. In keeping with good engineering design, the smallest valve size which will meet these requirements should be selected. Of course, each outlet conduit 12 is provided with a throttling valve.

The dimensions of the diffusing chambers 16 are selected upon consideration of desired flow quantities as well as physical positioning requirements of the apparatus. For example, the steam header 11 must be positioned far enough away from the pressure roll to prevent interference with the operation of the papermaking machine. And convenient operator access requires that the throttling valves 13 be located on the side of the steam header 11 away from the pressure roll 5. Thus, in order to take advantage of the compact, well supported design configuration of the apparatus as shown in FIG. 1, where the diffusing chambers 16 extend over the top of the steam header 11, the minimum length L of the diffusing chambers 16 must be equal to the sum of the diameter of the steam header 11, the spacing required for the throttling valves 13, and the spacing required to prevent interference between the steam header 11 and the pressure roll 5. An example of a satisfactory length for a diffusing chamber 16 is approximately 2 feet, where the steam header 11 is 10 inches in diameter, and the throttling valves 13 are 11/2 inches screwed-end angle valves. Longer diffusing chambers 16 would be unnecessary under the same circumstances. Shorter diffusing chambers 16 could be used where the physical positioning requirements of the apparatus would permit it. However, the chambers 16 should not be shortened to the point where the stream width expansion accomplished in the chambers 16 is produced so abruptly that the uniform flow rate across the width of each chamber 16 is not maintained.

The width w of each diffusing chamber 16 at the outlet 21 is, of course, determined by the total width of the paper web 3 (which equals the total width W of all diffusing chambers) divided by the number of chambers 16. At the inlet ends of the diffusing chambers 16, the width is somewhat less than at the outlet ends, but at least as large as the chamber entrances 15. The function of the diffusing chamber 16 is to expand the width of the stream while maintaining uniform flow rate across the width of the stream. This function is best accomplished by gradually increasing the stream width from chamber width at the chamber entrance 15 to the chamber width at the chamber outlet 21.

The height of the diffusing chamber 16 is dependent upon the desired flow rate and velocity of the steam. The chamber width, as already stated, is determined by the width of the paper web 3 divided by the desired number of diffusing chambers 16 and is, therefore, determined independently of the flow rate and velocity of the steam. Thus, the height of the diffusing chamber 16 becomes a controlling dimension for the flow rate and velocity. The desired flow rate is based upon the amount of heat desired to be added to the paper web and the available thermal energy in the steam. The velocity is limited to a range which is sufficient to penetrate the moving paper web 3 and the air currents that surround it, yet not so great as to harm the paper web. Once the desired flow rate, velocity and the condition of the steam to be supplied to the steam header 11 have been determined, the height of the diffusing chambers 16 is calculated by standard methods.

It is very desirable that the height of the diffusing chambers 16 be less at the outlet 21 than at the engrance 15, in order to compensate for the chamber width increase. It is preferable that the cross-sectional flow area in each diffusing chamber 16 decreases, or at least remains the same size, downstream in the chamber 16. This is because decrease in flow velocity could cause the steam to condense in the chamber 15, resulting in several deleterious effects, including an upset of the uniform flow rate of the steam across the width of the chamber.

The length dimension X of the common flow conduit 20 may be varied somewhat, but is preferably short, on the order of 4 inches. If it is long, the seaprate flow streams coming from the diffusing chambers 16 will begin to merge with each other before they reach the paper web 3 and will interfere with the flow rate of each other. That is, steam flowing in a particular stream at a high flow rate will tend to expand into a second, adjoining stream flowing at a lower rate and increase the flow rate of the second stream beyond the desired rate, while decreasing the flow rate of the first stream below its desired rate. The result is a loss of fine control of the steam flow rate distribution profile. On the other hand, if the common flow conduit 20 is too short the individual streams flowing from the diffusing chambers 16 will be discharged into the atmosphere before they have completely expanded laterally sufficiently to meet each other and form an uninterrupted sheetlike flow. Once the streams have left the vertical confines of the common flow conduit 20, the stream will expand laterally only at the expense of disrupting the uniform flow rate profile in each individual stream. However, it should be noted that much of the advantage of the invention can still be retained even without the common flow conduit 20 because the amount of lateral stream expansion is small after leaving the confines of the sidewalls 17.

In the preferred embodiments of this invention, the diffusing chamber entrance 15 faces the top wall 18 of the diffusing chamber 16 at an abrupt angle. This is a desirable arrangement because it is preferable for the steam flow to be disrupted in the inlet end of the chamber 16 before flowing through the chamber. If the chamber entrance 15 points in the direction of the outlet 21, the steam may be jetted through the chamber 16 uninfluenced by the chamber walls for at least a portion of the length of the chamber. The result would be that the walls of the chamber would have less opportunity to control the width expansion of the stream, and the flow rate profile across the width of each stream may not be uniform at the outlet 21 of the chamber 16. Therefore, for purposes of describing the invention, an abrupt angle for entry of the stream into the chamber 16 is one which causes the stream to disrupt against one of the walls of the chamber 16 at an effective distance from the chamber outlet 21.

The selection of materials for the apparatus of the invention is dependent upon the steam temperatures and pressures desired. For example, if low pressure steam is supplied to the steam header 11, standard carbon steel materials may be used. Of course, in positions of high wear, such as the valve seat and plug, harder materials may be desired. The diffusing chambers 16 may be best manufactured in two pieces. The first piece is a bottom plate with integral sidewalls 17 of the chambers 16, and the second piece is a flat top plate forming the top walls 18 of the chambers. This two-piece construction is illustrated in FIGS. 1 and 2. In FIG. 1, the two pieces are shown having opposite cross-hatching, and in FIG. 2, the diffusing chambers 16 are shown in plan view with the top plate removed. The two pieces may be attached to each other in any of several well-known methods, such as with bolts.

Selection of the pressure and condition of the steam to be supplied to the steam header 11 will depend upon the desired temperature and velocity of the steam applied to the paper web. For application with the preferred use of the invention, saturated steam of from 5 to 15 psig has been found satisfactory for the steam supplied to the steam header 11. For best results in penetrating the paper web and the air barriers which surround it, the steam discharge velocity should be on the order of about 15,000 to 25,000 feet per minute.

It is to be recognized that the invention can be used to apply heat to paper webs at locations in the papermaking operation other than at the nip between the pressure roll and Yankee dryer. The invention also could be used to apply sream, as well as other fluids, to surfaces in other manufacturing operations. It is also to be recoginzed that the flow rate of each discrete stream flowing to its respective diffusion chamber 16 can be controlled by means other than a valve. For example, where the desired flow rate does not fluctuate, an orifice or other fixed flow control means can be employed. In fact, properly sized outlet conduits 12 can be used to control the flow. And individually controlling the flow rate of each stream also includes flowing all streams at the same rate, if such is desired. Accordingly, the invention is not intended to be limited in use other than by the appended claims.

Claims

What is claimed is:

1. Method of forming a sheetlike flow of fluid having an incrementally variable flow rate distribution profile across its width, said method comprising the steps of:

flowing the fluid in a plurality of streams spaced-apart in a line and all flowing in the same direction;

expanding the width of each stream to bring it into contiguity with adjacent streams to form a sheetlike flow uninterrupted across its width;

insulating each stream from the influence of flow from adjacent streams while expanding the width of the stream;

flowing each stream with a substantially uniform flow rate across the width of the stream where it has become contiguous with adjacent streams; and

individually controlling the flow rate of fluid in each stream.

2. Method as recited in claim 1, including the step of decreasing the thickness of each stream as the width is expanded at a ratio of thickness decrease to width increase of at least 1, whereby the fluid velocity at the end of the width expanding step is at least as fast as at the beginning of the width expanding step.

3. Apparatus for forming a sheetlike flow of fluid having an incrementally variable flow rate distribution profile across its width, comprising:

means for flowing the fluid in a plurality of streams spaced apart in a line and all flowing in the same direction;

means for expanding the width of each stream to bring it into contiguity with adjacent streams to form a sheetlike flow uninterrupted across its width;

means for insulating each stream from the influence of flow from adjacent streams while expanding the width of the stream;

means for flowing each stream with a substantially uniform flow rate across the width of the stream where it has become contiguous with adjacent streams; and

means for individually controlling the flow rate of fluid in each stream.

4. Apparatus as recited in claim 3, including means for decreasing the thickness of each stream as the width is expanded at a ratio of thickness decrease to width increase of at least 1, whereby the fluid velocity is at least maintained while the stream width is expanded.

5. Apparatus for distributing steam across the width of a paper web with a controllably variable flow rate distribution profile, comprising:

means for supplying steam in a plurality of discrete streams;

valve means for individually controlling the flow rate of each stream;

a plurality of steam diffusing chambers spaced apart in a line extending across the width of the paper web, each of the chambers being open at the chamber end facing the paper web, closed at the opposite end, and further comprising first and second pairs of opposing flow-control walls, the first pair of flow-control walls gradually converging toward the open end of the chamber and the second pair of flow-control walls gradually diverging toward the open end of the chamber, and adjacent steam diffusing chambers being substantially adjoining at the open ends of the chambers; and

means for conducting each of the plurality of discrete streams into a separate diffusing chamber at a location spaced from the open end of the chamber.

6. Apparatus as recited in claim 5, wherein the second pair of flow-control walls terminates at the open end of the chamber a relatively short distance before the termination of the first pair of walls.

7. Apparatus as recited in claim 6, wherein the cross-sectional flow area in each diffusing chamber is at least as large at the location where the stream is conducted into the chamber as at the open end of the chamber.

8. Apparatus as recited in claim 6, wherein the means for conducting each of the pluralities of discrete streams into its respective diffusing chamber enters the diffusing chamber at an abrupt angle to one wall of the first pair of opposing flow-control walls.