Agitating – With heating or cooling – Medium in stirrer or mixing chamber
Reexamination Certificate
1999-03-30
2001-10-02
Soohoo, Tony G. (Department: 1723)
Agitating
With heating or cooling
Medium in stirrer or mixing chamber
C366S270000, C366S325920, C366S329200, C366S249000
Reexamination Certificate
active
06296384
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an agitating apparatus for agitating various kinds of fluids, semisolid fluids, powders or the like in a tank, and in particular to a vertical agitating apparatus adapted to be used in an agitating tank of an acute conical bottom type.
RELATED ART
In an agitating apparatus of this kind, in general, a rotary shaft which incorporates agitating blades and which is journalled in an agitating tank at the center of the latter, the rotary shaft being projected from the tank, and is rotated by a drive located outside of the tank so as to rotate the agitating blades which therefore produce swirling flows and vertically circulating flows in a substance to be processed (substance to be agitated), within the tank in order to agitate and mix the substance. Discharge type swept-back blades such as turbine blades, paddles, propellers and the like, and shearing type agitating blades such as gates, helical ribbon blades, screws or anchors and the like have been conventionally known as the agitating blades.
Referring to
FIG. 7
, which is a sectional view illustrating an agitating apparatus using conventional two-stage turbine blades as an example, an agitating tank
20
has a bottom part in a conical bottom shape having an apex angle &agr;, a rotary shaft
21
adapted to be rotated by a drive outside of the tank, which is incorporated being extended over the overall length of the tank, and one or more agitating blades
23
which are attached to an intermediate part of the rotary shaft
21
. The agitating blades
23
discharges liquid toward the peripheral part of the tank through the rotation of the rotary shaft
21
, and accordingly, thus obtained discharge flows circulate the liquid within the tank. Coils
24
may be arranged in the inner peripheral part of the tank.
(1) Conventional agitating blades cannot attain vertically uniform mixing in the case of a high depth agitating tank (having a ratio L/D>1.5 where L is a depth from the liquid surface to the bottom of the tank, and D is an inner diameter of the tank). (2) Further, in an agitating tank of an acute-angle conical bottom type having an apex angle less than 60 deg., only a pair of crossarm-like blades
30
similar to agitating blades
23
in a straight barrel part of the tank are provided to the lower part of the rotary shaft
21
, as shown in
FIG. 7
, and a stagnant part
27
of liquid is inevitably generated in the tip end part of the conical bottom part in which no mixing is effected. In particular, in the case of the provision of coils in the peripheral part of the inside of the tank, the above-mentioned deficiencies (1) and (2) become highly remarkable.
Referring to
FIGS. 7
to
11
, the above-mentioned deficiencies will be explained in detail. If the above-mentioned discharge type agitating blades
23
are used in a single stage, the agitating blades
23
being located normally in the vicinity of TL (a joint line between a cylindrical part and a conical bottom part of the tank), as shown in
FIG. 8
, and the flowing speed of discharged liquid is retarded on the way of displacement of the discharged liquid in a deep liquid condition (as shown in a part A of
FIG. 8
) since the distance of displacement from the bottom part
20
a
of the tank to a liquid surface
25
is long. Thus, stagnation occurs in a part B of FIG.
8
and accordingly, vertically uniform mixing cannot be achieved.
In order to eliminate this nonuniform condition, a multistage configuration having agitating blades of more than two stages may be used as shown in FIG.
9
. However, discharge flows impinge upon one another between blades
23
a
and
23
b
so that the fluid in the tank exhibits as if a partition wall is present in the vertically intermediate part of the tank, as indicated by reference numeral
26
, and as a result, the vertical uniform mixing would be rather hindered by this partition wall-like liquid phase.
In the agitating tank
2
of a conical bottom type having an apex angle of less than 60 deg. as shown in
FIGS. 7
,
10
and
11
, the shorter the distance to the conical bottom, the smaller the cross-sectional area, the fluid resistance is likely to occur in flowing fluid. Thus, precisely, the fluid can not reach the tip end of the conical bottom, but it goes in a direction in which the fluid resistance is less. Thus, the so-called flow separation occurs. As a result, the stagnation part
27
of the liquid occurs in the tip end part of the conical bottom, the higher the viscosity of the liquid, the higher this tendency. This stagnation in that part cannot be overcome even by using paddle-like agitating blades
30
in the tank bottom part. It is noted that the hatched parts shown in
FIG. 7
exhibits those parts where inferior flow occurs in the liquid.
Further, in an agitating tank using shearing type blades such as gates, helical ribbon blades, screws or anchors, it is said the blades are in general rotated at a low speed for raising and scraping liquid in order to promote mixing of the same. However, in this case, the Reynolds number of liquid flow should be less than Re=100 in order that the shearing blades can exhibit their nominal performance, that is, the liquid flow must fall in a region of laminar flow. Out of this region, the capability of creation of vertical circulation becomes excessively low. That is, if the Reynolds Number exceeds 100, the mixing can hardly occur in the vertical direction. It is noted that the Reynolds number, that is, Re number is exhibited by d
2
n&rgr;/&mgr;, where d (m) is a diameter of an agitating blade, n (1/s) is a rotational speed of blades, &rgr; (kg/m
3
) is a density of liquid, and &mgr; (kg/m·s) is a viscosity of the same.
Further, most of conventional agitating blade shapes and combinations thereof cause fluid to flow upward in the vicinity of the wall surface of a tank (refer to reference numerals
28
,
29
in FIG.
7
), and accordingly, such conventional blade shapes cannot create an ascending flow at the center of an acute conical bottom of a tank. Further, since the flow speed becomes lower on the way, in the case of deep liquid or a conical bottom, and accordingly, not only one flow but several side flows
28
,
29
(isolated from the main stream) would occurs in the tank, and accordingly, the overall uniform mixing in the tank becomes remarkably inferior.
SUMMARY OF THE INVENTION
The present invention is devised in order to eliminate the above-mentioned conventional deficiencies, and accordingly, one object of the present invention is to provide a vertical agitating apparatus which can shorten the time required for vertically uniform mixing, allows the flow rates in the vertical direction to be uniform in an agitating tank such as a deep liquid agitating tank, and can shorten the time of heat transmission, and which can prevent stagnation from occurring in liquid in an agitating tank of a conical bottom type having an apex angle of less than 60 deg. or the like.
According to the first aspect of the present invention, there is provided a vertical agitating apparatus comprising an agitating tank having a center and having a bottom part formed in a conical shape having an apex angle of less than 60 deg., and a rotary shaft attached at the center of the agitating tank, and adapted to be rotated by a drive located outside of the tank, and agitating blades attached to the rotary shaft and having a conical bottom paddle part which are located in the bottom part of the agitating tank and which has a shape along the half apex angle of the conical bottom part of the agitating tank.
According to the second aspect of the present invention, there is provided a vertical agitating apparatus comprising an agitating tank having a center, a rotary shaft having a lower part, arranged at the center of the tank and rotated by a drive located outside of the agitating tank, conical bottom paddle blades and attached to the lower part of the rotary shaft, lattice blades in combination of vertical grids each having an outer edge, and horizontal a
Kuratsu Masafumi
Nakano Mineo
Yamaoka Masao
Yatomi Ryuichi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Soohoo Tony G.
Sorkin David
Sumitomo Heavy Industrie's, Ltd.
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