EP0355082A1

EP0355082A1 - Jet ring

Info

Publication number: EP0355082A1
Application number: EP89850233A
Authority: EP
Inventors: Ingvar Karlsson; Martin Mohammar; Ulf Arbeus
Original assignee: Flygt AB; ITT Flygt AB
Current assignee: Xylem Water Solutions AB
Priority date: 1988-08-16
Filing date: 1989-07-19
Publication date: 1990-02-21
Anticipated expiration: 2009-07-19
Also published as: SE8802902D0; DE68906484T2; AU614630B2; DE68906484D1; SE8802902L; EP0355082B1; JPH0275333A; AU3643689A

Abstract

The mixer includes a driving motor (1) and a propeller (3) surrounded by a jet ring (5). The latter is formed like a funnel having its wider part turned towards the motor (1).

Description

The invention concerns a jet ring of the type designed to surround the propeller in a so-called propeller mixer.
Mixers of the above mentioned type include a driving unit, an electric motor, a propeller and a driving shaft between those two. The propeller may have two or more blades and can be arranged to be driven with varying speeds, all depending on the use.
Mixers are used within various fields for homogenizing and suspension maintenance of liquids for different industrial processes, for liquid manure, for waste water etc. The mixer can be arranged horizontally or vertically or with different angles therebetween. It can also be arranged movable so that the flow from the mixer is brought to sweep over bigger areas or directed towards certain spots within the liquid tank.
Another field where a mixer may be used is for creation of currents in a lake to prevent formation of ice.
In order to create an effective mixing or flow it is normally a condition that the propeller must be surrounded by a jet ring with a diameter somewhat bigger than the diameter of the propeller and with a normally limited axial extension. If the jet ring is eliminated, a radial flow would accur limiting the axial flow through the machine as a part of the liquid amount would be sucked back into the propeller and as a certain leakage would accur between the pressure and the suction side of the propeller.
According to known technique the jet ring is cylindrically formed and provided with a somewhat outwards bent collar to make the inflow easier. Such jet rings are shown in the Swedish Design Registration No:s 34601 and 39392.
A disadvantage with these known designs is that the flow close to the ring may be turbulent depending on a too sharp alteration. This causes so-called discontinuance of the boundary layer with an often unstable blocking as a result. The flow through the machine and thus the mixing ability then decreases.
Another disadvantage with an unsteady or failing flow (blocking) close to the ring is that vibrations are easily amplified as the tips of the propeller blades will operate under conditions for which they are not designed. If in addition the cylindric part of the ring after the propeller is extended, there is a relatively large area that is exposed to pressure pulsations causing strain in the material.
According to the invention the disadvantages mentioned above are reduced by help of a specific design of the jet ring as specified in the claims.
The invention is described more closely below with reference to the enclosed drawings. Fig 1 shows a side view of a mixer provided with a jet ring according to the invention. Fig 2 shows the jet ring seen in axial direction and Fig 3 shows a diagram over the fluid losses as a function of the ratio between the radius and the diameter of the jet ring.
In the drawings 1 stands for an electric motor, 2 a driving shaft, 3 a propeller with blades 4, 5 a jet ring with inlet and outlet rims 6 and 7 respectively.
In order to obtain an effective mixing a jet ring 5 must thus be arranged around the propeller 3. In this way an axially directed jet is obtained which in its turn brings parts of the surrounding fluid mass. The flow towards and into the propeller has mainly a direction perpendicular to the axis of rotation.
In order to secure a good flow near the inside of the jet ring, the ring is designed in a special way according to the invention.
The conventional, mainly cylindric ring is replaced by a funnel shaped ring having a significant radial extension. The transition between its inlet rim, which in principle is perpendicular to the axis of rotation and its outlet rim, which is axially directed, takes place along an even curve having a relatively big radius.
The ratio betwen the axial and radial extensions of the jet ring may vary somewhat depending on number of revolutions, type of mixer, the qualities of the liquid to be mixed etc. It is important however, that the inlet rim is directed mainly radially and that the transition from inlet to inlet takes place along an even curve having a relatively big radius. The latter is of course dependant on the diameter of the ring. The bigger the ratio is between the transition radius and the ring diameter, the smaller the flow losses will be and thereby the disturbances (within certain limits). A ratio between 0.1 and 0.3 is normally sufficient. Bigger ratios may cause manufacturing problems.
According to the invention there is obtained a jet ring for mixers of different types which in a simple and effective way increases the efficiency of the mixer and simultanously adds to a diminishing of the vibration problems. The latter is further diminished as the funnel formed ring is more rigid than the previously used tube form.

Claims

1 A device for mixers comprising a driving motor, a rotating driving shaft and a propeller, the periphery of which is surrounded by a jet ring having a short axial extention, characterized in that the jet ring (5) is funnel shaped having its bigger diameter at its inlet rim (6) and its smaller at the outlet rim (7), the transition between inlet and outlet rims (5) and (6) respectively, taking place along a smooth curve with a radius (r) not being less than 10 % of the diameter (D) of the jet ring (5).

2 A device according to claim 1, characterized in that the inlet part of the jet ring (5) is so designed that its inlet rim (6) is directed mainly perpendicular to the direction of the axis of rotation (2).