US2159856A - Mixing or dissolving apparatus, etc - Google Patents

Description

May 23, 1939.

G. M LEAN 2,159,856

MIXING OR DISSOLVLNG APPARATUS, ETC

Filed July 31, 1937 INVENTOR.

M ATTORNEYS Patented May 23, 1939 PATENT OFFICE 2,159,856 MIXING B DISSOLVING APPARATUS, ETC

Gordon Macbean,

Flushing, N. Y., minor to The Turbo-Mixer Corporation, New York, N. Y., a corporation of New York Application July 31, 1937, Serial No. 156,864

2 Claim.

This invention relates to mixing apparatus and to dissolving apparatus. It is particularly applicable to mixing or dissolving tanks in which liquid is repeatedly recirculated by one or more rotating impellers, each of which discharges the liquid outwardly in tangential or quasi-tangential directions.

When such a rotating impeller acts on liquid of low viscosity in a plain cylindrical tank, the

i0 rotary motion of the impeller is imparted to the mass oi liquid. The liquid swirls and a vortex forms over the impeller. Thus, the mixing action is poor, since the whole mass of liquid tends to move as a unit, with the elemental volumes l5 travelling in nearly circular paths.

With a very viscous liquid the drag of the tank wall on the liquid largely counteracts the tendency of the entire mass to swirl. The vortex is relatively small. The elemental volumes of the 20 liquid are drawn inwardly by the impeller, in pronounced spiral paths, and the mixing action is satisfactory. To obtain similar mixing action with a liquid 01' low viscosity, it is usual to place bailles on the tank wall for the purpose of estab- 25 lishing the necessary drag between the tank and lthe mass of liquid. As the viscosity of the liquid increases, the bailllng required decreases until a point is reached beyond which baflling is detrimental to the mixing action. With very high 30 viscosity material, the battles have the effect of forming pockets adjacent to the tank wall. Such parts of the mix as are in these pockets, tend to stay there and are not effectively recirculated and intermixed with the rest of the material in 3 the tank. Additionally, the power required to rotate the impeller under such conditions is undesirably large.

From the foregoing, it will be seen that satisfactory mixing with the prior art apparatus, re-

quires different installations for materials of high and low viscosity. Often this necessitates extra installations .which cannot be used to capacity. But an even more serious drawback exists in processes that cause the material to undergo a 45 great change in viscosity during the mixing or dissolving treatment. Some examples of such processes are paint pigmentation, the manufacture of clay slurries and asphalt emulsions, and the dissolving of materials used in making rayon,

50 acetate silk, and lacquers, e. g., dissolving xanthate materials in a solution of caustic soda. For such processes, the prior art mixing apparatus can be no more than a compromise which will function efflciently only at an intervening 55 viscosity. The time and the energy required to carry out the process are increased accordingly.

A general object of the present invention is to provide mixing or dissolving apparatus which functions efiiciently with material of either high or low viscosity. 5

Another object of the invention is to provide mixing or dissolving apparatus which functions efficiently as the mix progressively increases in viscosity.

More specific objects of the invention are to equip mixing or dissolving apparatus with bodies which have diminishing effect as the viscosity of the mix increases, and to provide a suitable method of determining the best placement of such bafiles.

Other specific objects are to provide a baille which has full effect at low viscosity and virtually no eiiect at high viscosity, and to provide a method of placement for such a baflle.

Various additional objects and advantages will be apparent to those skilled in the art from a consideration of the following disclosure.

In general, the circulation in the tank is along paths outwardly of the impeller toward the side of the tank, along the tank wall in a helical path, inwardly of the tank wall toward the axis of the impeller, and lengthwise of such axis back to the impeller ior recirculation. This is a complex path of movement involving vertical and horizontal components of motion. For convenience and clarity the path of flow will be discussed hereinafter in terms of the vertical and horizpntal components oi motion.

Two suitable forms of construction are shown. by way of example, in the accompanying drawmg, wherein:

Fig. l is a largely diagrammatic vertical section through a two-impeller mixer embodying the present invention, the view being taken approximately on line I-l of Fig. 2; Fig. 2 is a largely diagrammatic plan view of the same; Fig. 3 is a diagram indicating the horizontal component of the flow in the case of a liquid 01 low viscosity;

Fig. 4 is a diagram indicating the horizontal component of, the flow in the case of a liquid of high viscosity; and

Fig. 5 is a largely diagrammatic vertical section through a single-impeller mixer.

In Figs. 1 and 2 a tank designated as a whole by 5 has a cylindrical side wall I, and has a top flange 8 to receive a cover (not shown). Depending coaxially into the tank is a vertical shalt 9 that is rotated by any suitable source 0! power I (not shown). Mounted on the shaft are spaced involute impellers Ill and II which may be of convenional form but which are preferably of the "tilted variety disclosed in United States Patent 1,908,002. In a zone above impeller Ill there is affixed to tank wall I a series of baffles I2 (four shown). In the zone between impellers III and II there is afiixed to tank wall I a second series of baiiles I3 (four shown).

The bailles I2 and [3 may be mounted with the aid of any suitable means. the drawing merely showing supporting rods II to illustrate the mounting in a diagrammatic manner. Each of the baiiies I2 and i3 extends in a generally vertical direction and is spaced inwardly from the tank wall I, as shown in the drawing. Additionally, each of the baflles I2 and I3 is positioned at an angle to the tank radius, with its trailing longitudinal edge if farther from the tank wall than its leading edge 1. Each of bailies I2 is also inclined from bottom to top circumferentially of the tank in the direction of impeller rotation. Baiiies I3 are positioned vertically.

The action of the baiiles in opposing swirling of the liquid is illustrated in Fig. 3. The spiral line I indicates the horizontal component of the path which an elemental volume of relatively low viscosity liquid would follow in the absence of baflles. With the baffles present, the liquid moving in the same direction at Ill strikes a bailie (I! or l3) and is projected at H toward the axial zone of the tank.

As the viscosity of the mix increases, the path l5 becomes a more and more pronounced spiral, with the result that the bailles present less and less effective surface to the spiral flow. Thus the effect of the bailies decreases as the viscosity increases. With very high viscosity the horizontal component of flow without baffles wouldbe as indicated by line I5 in Fig. 4. It will be apparent that this path is such that the baffles I2 and I3 are positioned edgewise to the flow and hence offer only skin friction resistance.

With regard to the vertical component of flow, the tank may be considered as divided into superimposed flow zones. roughly indicated in Fig. 1 by dotted flow lines. Each of the impellers is in a zone of outward flow. Adjacent each side of each zone of outward flow is a zone of flow axially of the tank. And the zones of axial flow merge into zones of inward flow.

This vertical component of flow is very effective in promoting the mixing or dissolving, and hence it should be impeded as little as possible. As an elemental volume of liquid moves upwardly (e. g., along circuit d) it also moves circumferentially of the tank in the direction of impeller rotation (see Fig. 3). Thus, the resultant path is on an incline, upwardly and circumferentially in the direction of impeller rotation. As the longitudinal axes of baflies I2 are also correspondingly inclined these bailles oiier only skin friction resistance to the vertical component of flow.

As the flow in circuit b baflles I3 should theoretically be circumferentially inclined the same as bailies I2. However, these bailles also handle the downward flow in circuit c, for which baiiies I3 should theoretically be circumferentially inclined in the opposite direction. As a compromise the longitudinal axes of bailies I3 are positioned vertically; and the variation from the theoretically desirable inclination is small enough to be permissible.

The form of the invention shown in Fig. 5 is generally similar in arrangement and action to the first form of the invention. The shaft 20 carries a single impeller 2|, which is positioned near the bottom of tank 22. A series of baiiies 23 (three shown) are supported from the tank wall 24. These baffles are spaced from the tank wall, inclined to the tank radius, and have their axes circumferentially inclined, all in correspondence with baiiies I2 in Figs. 1 and 2.

The spacing of the baiiles from the tank wall eliminates pocket formations which tend to trap and localize portions of the mix. Furthermore, such spacing prevents the baffles from inter-fer ing with the flow adjacent to the wall, where it has a tendency to be a minimum. In the forms shown in the drawing the bailles do not extend in alignment with the impellers, which leaves a perfectly free flow path from the impeller to thetank wall. With liquids of low viscosity, Part of the horizontal flow component passes between the baffles and the tank wall. This produces eddies at the restrictions, and these eddies augment the retarding eil'ect of the battles and also enhance the mixing action.

The range of viscosities to be handled determines the optimum inclinations of the battle. In determining the placement of the baflies, I prefer to do it by trial. The tank, or a substantial duplicate thereof, is filled with a transparent material of the maximum viscosity to be handled. Dark beads or other suitable objects are also placed in the tank, so that the lines of flow can be seen. A bailie is then temporarily inserted and adjusted into such position that it is edgewise to the path of flow. In this way the optimum inclinations of the baille, can be predetermined for both the horizontal and vertical components of flow. In an installation which I have used for viscosities up to 60,000 centipoise, the angle alpha in Fig. 3 was 55. This angle is the angle which the horizontal center line of the bame makes with the horizontal tank tangent intersected by the center line. The higher the maximum viscosity, the greater the baiile inclinations will be, and vice versa.

The amount of space between the baille and the tank wall which I have found desirable is from one-half inch to one inch, per foot of tank diameter. While the bailies may be given a curved form to correspond exactly with the flow lines at maximum viscosity, they are conveniently made oi fiat sheet metal and with the proper placement serve adequately. The mounting of the bailles may provide for adjustment of the baffle inclinations after the installation is made, with means to lock the baffles at the desired setting. However, it is usually simpler and more satisfactory to predetermine the battle placement and use baiile mountings which do not provide for adjustment of the inclinations.

In compliance with the patent statutes, I have disclosed the best forms in which I have contemplated applying my invention, but the disclosure should be considered as illustrative, not limiting.

What is claimed is:

1. In mixing apparatus of the type in which the mix is circulated by a pair of vertically spaced rotating impellers mounted on a substantially vertical shaft, the improvement which comprises: two series of upwardly extending bailies each adjacent to and spaced from the tank wall, the first series being located above the level of the upper impeller and the second series being located between the levels of the two impellers, the batfies of both series having their deflecting faces inclined with respect to the intersecting tank radii, the baifles oi the first series being also incomprises: upwardly extending bailies adjacent to and spaced from the tank wall, the baffies being located along said inclined upward flow path and being themselves inclined upwardly and circumferentially in the direction of impeller rotation, said baflle inclination being approximately equal to said inclination of the flow path, and the baiiies also being inclined with respect to the intersecting tank radii and having the trailing edges of the baffles closer to the center of the 10 tank than the leading edges of the battles.

GORDON MACLEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,856.

G-ORDON HacLEAN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 6h, for the words As the flow" read As to flow; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of June, A. o. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

inclined with respect to the intersecting tank radii, the baifles oi the first series being also incomprises: upwardly extending bailies adjacent to and spaced from the tank wall, the baffies being located along said inclined upward flow path and being themselves inclined upwardly and circumferentially in the direction of impeller rotation, said baflle inclination being approximately equal to said inclination of the flow path, and the baiiies also being inclined with respect to the intersecting tank radii and having the trailing edges of the baffles closer to the center of the 10 tank than the leading edges of the battles.

GORDON MACLEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,856.

G-ORDON HacLEAN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 6h, for the words As the flow" read As to flow; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of June, A. o. 1959.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

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