[0001] The invention concerns a cooling device for a mixer for operation in viscous liquids
where amounts of solid bodies are frequent.
[0002] Mixers of this type comprise a driving unit such as an electric motor, a propeller
and a driving shaft there between. The propeller may be designed with two or more
vanes and to be driven with various speeds depending on type of use.
[0003] Mixers are used within different fields for homogenizing and to keep particles in
suspension in liquids for different industrial processes, in farming, for treatment
of sewage water etc. The mixer may be arranged horizontally or vertically or in different
angle positions there between. It can also be arranged to move in such a way that
the flow from the mixer is caused to sweep over larger areas or being directed towards
certain spots within the liquid tank.
[0004] In order to obtain an effective mixing or flow a jet ring is often arranged around
the propeller having a diameter somewhat exceeding that of the propeller and a normally
relatively limited axial extension. With no jet ring present a dominating radial flow
is obtained which means that the axial flow through the machine becomes very limited
as the same amount of liquid is rapidly sucked back to the propeller. In addition
there is a leakage between the pressure and the suction side of the propeller which
further decreases the axial flow. According to known practice the jet ring is normally
designed as a cylinder having a somewhat expanding collar at its inlet to facilitate
the inflow. Such jet rings are shown in the Swedish Design Registrations No:s 34601
and 39392.
[0005] The electric motor is cooled by the surrounding medium which calls for a certain
flow around the motor, which flow normally is obtained by the mixer itself. When mixing
liquids that demand a certain shear stress to be exceeded before any movement is created,
Bingham liquids, problems may occur to obtain a flow strong enough. This might cause
the motor to be overheated.
[0006] The invention concerns a device for solving the problem mentioned above. The invention
is described more clearly below with reference to the enclosed drawings.
[0007] Fig 1 shows a mixer provided with a cooling device according to the invention, while
Figs 2 and 3 show flows around a mixer not provided with a cooling device, Fig 2,
and with a cooling device, Fig 3.
[0008] In the drawings 1 stand for a mixer with a driving unit, electric motor 2 and a propeller
3. 4 stands for a jet ring and 5 an extension of this.
[0009] With reference to Fig 2 the conditions when mixing Bingham liquids are discussed.
The mixer here creates a flow symbolized by the arrows in the light part of the drawing.
The area close to the electric motor is not included in the flow which means an insufficient
heat exchange between the motor housing and the surroundings.
[0010] In Fig 3 is shown the flow increase or the extension of the area where flow takes
place, which is obtained by help of the invention. The propeller creates an under
pressure at its inlet side, inside of the jet ring, which means that critical shear
stress is exceeded and a flow is obtained through the jet ring along the wall of the
motor housing which thus is given an effective cooling.
[0011] In the example above an extended jet ring has been used to obtain an effective cooling
of the motor housing. It is however possible, according to the inventor, to arrange
one or several means around the motor, parted from the jet ring, which obtain the
necessary flow.
1 A cooling device for mixers comprising an electric motor and a propeller with a driving
shaft there between, said mixer, including the electric motor, being meant to operate
submersed in the mixed medium, characterized in that the mantel surface of the electric
motor (2) is partly or entirely surrounded by a cylindrical wall (5) for intensifying
the media exchange at said surface.
2 A cooling device according to claim 1, characterized in that the wall (5) is an extended
part of a jet ring (4, 5) surrounding the propeller.
