FI54955C - BAERYTETORKARE. - Google Patents

Description

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B 11 UTLÄGGNINGSSKRIFT 54955 • (45) ^ ^ '(51) Kv.ik. * / Int.ci. » D 21 F 5/18 F 26 B 15/20 SUOMI - FINLAND (21) Patenttlhikemu * - Patencanaökning 3239/71 (22) Hakemlipllvl —An * ökninj * d * | 12.11.71 (E | \ '' '' (23) Initial cloud - Glltighetsdag 12.11.71 (41) Become public - Bllvlt offentlig .05.72

Patent and Registration Offices ... (44) Date of publication and date of publication. -

Patent and Registration Office Ansökan utlagd och utUkrtften publkerad 29.12.78 (32) (33) (31) Requested Privilege — Begird Priority 16.H.70 26.O8.7i USA (US) 897 ^, I75052 (71) Overly, Inc ., 209 Jackson Street, Neenah, Wisconsin 5 ^ 956, USA (US) ^ (72) Frederick Overly, Winneconne, Wisconsin, Kenneth John Pagel, Neenah,

The present invention relates to a membrane-based web dryer in which a nozzle generating a web of mucus directs the flow of air to the contact of the stream of air flow into the air flow contact of the Wisconsin, USA (US) (7 * 0 Leitzinger Oy (5 * +).

In the paper industry, and also in the printing industry, efforts have been made in practice to prevent wet paper webs or fresh ink from coming into physical contact with anything other than drying air. As the web thus moves several thousand meters per minute, the web of drying air directed at it must stabilize the web and at the same time generate sufficient heat transfer to achieve the desired moisture removal from the web.

It is generally assumed that the laminar air flow along the web stabilizes the web best. Thus, the nozzles are generally designed to generate a laminar air flow parallel to the movement of the web.

Mucosal nozzles which are particularly suitable for this purpose are described in U.S. Pat. No. 3,587,177.

However, this patent states that in certain cases a turbulent air flow is required to achieve the desired drying. According to this patent, this turbulent flow is provided in a system in which the air supply velocities are above 1000 m / min and in which the flow is improved by using either cut-off surfaces or additional nozzles.

However, it has now been found that by extending the air membrane surface substantially evenly over a distance proportional to the dimensions of the nozzle, a better turbulent air flow can be experienced to experience the rust and at the same time improve heat transfer without increasing the power requirement.

When using mucosal generating nozzles on opposite sides of the web in a drying zone where the nozzles support and guide the moving web between them, it has been difficult to keep the web flat and prevent it from passing through the dryer along a tortuous or wavy path.

It is generally considered necessary to remove spent air from the drying zone from re-contact with the web as soon as possible.

However, if the chamber of each air membrane nozzle has a rounded outlet corner which produces a Coanda effect, it has been found that the air follows the curved shape of the corner and leaves the web abruptly and thus generates wave motion in the web, which is detrimental.

However, if the nozzles are placed directly opposite each other on both sides of the web, a much more favorable vibration of the web is obtained, leaving a space between the nozzles, whereby, however, due to the unevenness of the applied forces, harmful undulating movement of the web is not prevented.

If the nozzles are placed close to each other on both sides of the web, or if adjacent nozzles are used, the jets of which are directed in opposite directions along the web, it has not been possible to prevent the formation of a web wave in this way either, but rather has increased.

The present invention is based on the finding that maximum drying efficiencies with a given power supply can be achieved by using 3,54595 one or more air film nozzles disposed on at least one side of the moving web and having nozzle openings arranged to supply air at speeds greater than 1000 m / min at a Reynolds * number of about 4000 to 3,000, and having a nozzle having a substantially flat surface substantially parallel to the web to generate a turbulent air flow between the nozzle surface and the web, in a ratio L / D, where L is the length of the flat surface in the air flow direction and D is the nozzle gap width of 40 to 90, the width of the nozzle gap is more than about 1.52 mm.

If a plurality of such air film nozzles are located on opposite sides of the web, they should be arranged alternately and their planar nozzle surfaces should sharply terminate to prevent possible Coanda effect, which may interfere with web control by a nozzle on the opposite side of the web.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a dryer with the nozzles positioned above and below the web to be dried.

Figure 2 is a schematic side view of the dryer of Figure 1.

Figure 3 is a graphical representation of power requirements at different Reynolds numbers and different L / D ratios.

Fig. 4 is an enlarged sectional view of the nozzle taken along line 4-4 of Fig. 1, further showing air flow between the nozzle and the web.

Fig. 5 is a sectional view according to Fig. 4 showing a preferred embodiment of the nozzle to the dryer according to Fig. 1.

As shown in Figures 1 and 2 of the drawings, the web 1 passes horizontally through the drying zone from the roll 2 to the roll 3, whereby a plurality of air film nozzles 4 are arranged above and below the web in the drying zone.

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Each nozzle 4 has a nozzle chamber 5 extending over the entire length of the web 1, the ends of which are closed and in the middle of which an air supply pipe 6 leads.

Several nozzles 4 extend over the entire width of the web. The nozzles can be arranged relative to each other in any way. In the figure, the distance between each of the two adjacent nozzles is greater than the width of the nozzle, so that by placing the nozzles alternately under and on the web, it is possible to control the web movement and prevent direct airflows on opposite sides of the web.

The nozzle chamber 5 of each nozzle 4 has a substantially rectangular cross-section and its outlet opening is in the form of a slot 7 extending over the entire width of the chamber along one corner thereof. -

A gap 7 is formed between the inwardly turned flange 8 of the flat portion 9 of the nozzle chamber 5 facing the web and the inwardly turned edge plate 10, which plate forms from the edge portion of the respective side 11 of the nozzle chamber 5.

The plate 10 is arranged substantially tangential to the curved surface of the flange 8, defining a gap 7 therebetween.

The side of each nozzle chamber 5 facing the web is flat and extends parallel to the web 1, the distance 12 between the nozzle and the web substantially corresponding to the width of the gap 7 of the nozzle.

The optimum ratio of the total length of the nozzle surface 9 in the direction of web movement to the width of the gap in order to achieve the best drying of the web with the lowest power requirement and air speeds of 4500 m / min is ~ generally about 60.

Preferably, the width of the slot 7, which is also approximately the same as the distance 12, is between 1.0 and 3.2 mm.

The power required to achieve the required airflow is best between 2 and 3.3 to 10 hp / m web in the drying zone.

In practice, the higher the temperature of the air coming from the nozzle, the lower the power required to bring the air into contact with the web at a given speed, but the greater the power required to achieve the desired drying effect.

In general, when operating in the area of use of the system, it is also true that the greater the length of the distance 9 in the direction of movement of the web in a given slot width, the less power is required to achieve a given drying effect.

The air discharged from the nozzle slot 7 flows in a laminar flow along the corner flange 8 following its curved surface until it reaches the flat surface 9 of the nozzle chamber 5. The air then flows in a turbulent flow between the surface 9 and the web 1 in the opposite direction as the web moves. When the air reaches the edge opposite the flange 8 of the lower surface 9 of the nozzle chamber, it flows away from the web 1 and can be removed from the dryer by any suitable means.

If the edge of the surface 9 is sufficiently rounded to produce the Coanda effect, the air tends to follow the rounding as shown in Fig. 4 and tends to pull the web upwardly wavy, with multiple nozzles on each side of the web tending to interfere with the desired smooth flow of the web. .

This disadvantage can be avoided by using a sharp corner 13 at the end edge of the flat surface 9 as shown in Fig. 5, thus essentially avoiding the Coanda effect.

When the end edge 13 is sharp, air follows the web 1, leaving a space 12 between the lower surface 9 and the web 1.

The next adjacent nozzle chamber 5 with its nozzle openings 7 is located at a distance from this end edge 13 which is substantially greater than the width of the nozzle chamber so as to leave a space 14 through which air discharged from the adjacent end edge 13 at high speed can be removed from the drying zone.

The passage of the web 1 as it passes through the space 14 between two adjacent nozzles 4 is controlled by a nozzle 4 on the opposite side of the web, the nozzles being arranged alternately against the web.

54955

Air is discharged from the space 14 next to the end edge 13 and releases the web 1 so that the web is then guided by a second nozzle on the opposite side. The turbulent air flow flowing in the space 14 touching the web 1 and the nozzle side 9 improves the heat transfer to the web, causing the moisture to evaporate rapidly from the dough. In general, the power corresponding to a given heat transfer or drying effect depends on the Reynolds number, which indicates the magnitude of the turbulence, and on the L / D ratio, where L is the length of the surface 9 in the web motion and D is the distance between the surface 9 and the web 1. To determine these quantities, formulas have been presented from which they can be calculated (R. Byron Bird, Warren E. Stewart, and Edwin N. Lightfoot, "Transport Phenomena," John Wiley & Sons, 1960.),

The curves in Figure 3 show the ratio L / D and the ordinate mass flow rate or power demand, and curves A and B are shown for two Reynolds __ numbers, giving values within the most appropriate limits in practice. Curve A corresponds to a Reynolds number of 10,000 and curve B to a Reynolds number of 5,000.

• · - 5 it

The power figure reported by 10 X P is a suitable measure of the power requirement obtained from the energy balance according to paragraph 13 of the above book and the force function expressed as a function of air velocity and density, nozzle and web dimensions, and thermal conductivity.

This power number has the following equation: P * = (L / D) 2/1-e ~ Φ / 3

In the equation, L is the length of the surface 9 in the direction of web movement, D is the width of the nozzle gap 7 and / 1-e φ / is a logarithmic function, where Φ represents the heat transfer per nozzle and e is the logarithmic base number.

From the curves, it can be determined that the most advantageous power requirement is achieved when the L / D ratio is between about 40 and 100 and the Reynolds number is less than 10,000. When the Reynolds number is 4000, the minimum power requirement is achieved with an L / D ratio of about 65.

The power figure is best kept below 3.00 because the drying efficiency drops rapidly as the power requirement increases. The power requirement is thus 2 best 3.3 to 10 hp / m.

In the nozzle shown in the figures, the decrease in air velocity immediately after leaving the slot 7 is about 330 m / min for each 1.6 mm distance along the curved flange until the air reaches the space 12 between the web and the surface 9, where the vent becomes turbulent and continues to the nozzle chamber 5. on the opposite side. The turbulent air flow then encounters the web 1 and releases heat as it removes moisture from the web. In this method, the air cools and loses some of its velocity as it passes through space 12.

The optimum air flow velocity in the nozzle gap 7 is generally above 4200 m / min, under favorable conditions an air velocity as low as 1100 m / min can be used. The exact width of the gap 7 depends to a large extent on the required L / D ratio and the air velocities used.

When constructing a dryer, certain factors are determined in advance, such as web travel speed, approximate amount of moisture to be removed, space available for the dryer, available power, air speeds, and the ability to heat the air to the desired operating temperature.

By making the above initial assumptions, it is possible to determine by a suitable formula the number and size of nozzles required, the most preferred Reynolds number, the distance L from the surface 9 and the width D of the gap.

Claims (3)

8 54955 An air film web dryer, wherein one or more air film nozzles (4) are arranged on at least one side of the moving web (1) and the nozzle slot (7) of each nozzle is arranged to supply air at a speed of more than 1000 m / min, characterized in that each nozzle has a flat surface (9) approximately parallel to the web, the ratio L / D of which L is the length of the flat surface (9) in the direction of air flow and D is the width of the nozzle gap (7) of about 40 to 90, the Reynolds number of the nozzle being about 4000 to 8000, wherein a turbulent air flow flows between the nozzle surface (9) and the web (1) to create a drying effect. Dryer according to claim 1, characterized in that the ratio L / D is about 60 and the air flow rate is about 4200 m / min as it enters the space (12) between the nozzle (9) and the web (1) with a Reynolds number of about 5000 to 7000 . Dryer according to claim 1, wherein a plurality of air membrane nozzles (4) are arranged alternately in series on the opposite side of the moving web (1) in the drying zone, characterized in that the mucosal delimiting surface (9) of each nozzle (4) extends approximately parallel to the web (1). with the same distance from it and terminates at a sharp edge (13) to direct the flow of air discharged from the intermediate space (12) along the web.