EP2926892A1 - Stirring helix - Google Patents

Abstract

Mobile stirrer comprising at least two blades and adapted to be fixed on a rotating shaft, characterized in that each blade has a leading edge facing the fluid to be agitated and a trailing edge opposite the leading edge, characterized in that each blade is obtained by folding a flat sheet, each blade having two longitudinal folds (A, B), the length of each fold (A, B) being greater than 60% of the maximum radius of the blade.

Description

The present invention relates to a mobile stirrer comprising at least two blades and adapted to be fixed on a rotating shaft.

The manufacture of many products requires a process of homogenization, dilution, dissolution, reheating ....

For this purpose it is most often used mechanical stirrers rotating shaft, provided with a drive usually by electric motor, a shaft and a mobile stirrer or agitator. The set consists of a container, a product and an agitator.

The present invention relates to the design of stirrers which are generally propellers or turbines comprising a stirring mobile mounted on a rotating shaft.

A turbine is provided with straight blades at 90 ° with respect to the vertical, however, it is customary to call any mobile turbine consisting of straight blades, even positioned inclined.

A turbine generates a radial flow, generating shear, energy dissipation.

A helix is preferably formed of a pitch portion of a helicoid, strongly inclined, a curved or folded sheet.

A propeller develops an axial and methodical flow.

The rotation of the stirring wheel causes a displacement of the liquid which makes it possible to perform the desired operation, more or less efficiently depending on the shape of the wheel, its size and the speed of rotation.

Rotation can also cause shear and dissipate energy in the liquid to be mixed.

Sometimes these two phenomena are necessary, during a reaction, the formation of an emulsion.

The invention deals more specifically with the case where it is sought to minimize shear energy losses in order to obtain a displacement of the liquid and its mixing with low losses, which implies a high efficiency.

In such a case it is the use of a propeller that gives the best result. Indeed, these operations only require a setting in motion of the product, ie a pumping rate.

We will seek to develop this flow with the least energy possible and it is known that the propellers consume less energy than the turbines for an equivalent flow.

In ancient times, we used only turbines, not requiring special design, and then a century ago, marine propellers appeared, more efficient and less energy consuming.

There are two main families of propellers represented by patents US 4,147,437 and FR 1 578 991 .

These two families of propellers are still used today, given their performance compared to marine propellers.

However, for some markets, the use of turbines, because of the high power required and therefore the cost, or high efficiency propellers is difficult.

Such use is often considered too expensive because the high yield is not appreciated at its fair value, only the cost of the investment is really considered. High efficiency is considered interesting only for large machines, or when the cost of energy is high or at least taken into account.

The manufacture of high efficiency propellers is difficult and / or long, so expensive and can only be performed by special machines. Indeed, the technical problems are numerous due in particular to the thickness of the sheet and delicate curvatures to obtain. It is not possible to have these propellers manufactured in another workshop or on another continent, for example, which entails a high transport cost.

There are already folded propellers on the market, but they have a very specific shape with a blade corner fold to limit radial leakage. Performance improvement was not the technical problem that its designers were trying to deal with.

There is therefore a need for a propeller easy to build, that is to say without special equipment or skill, providing a good flow which is the essential factor for determining the agitation, without however consuming too much power as would a simple blade of flat and inclined shape, which would lead de facto to high power, a large shaft and a large blade thickness and ultimately at a non-competitive manufacturing cost.

According to the invention, a stirring disc comprising at least two blades and capable of being fixed on a rotation shaft, is characterized in that each blade has a leading edge facing the fluid to be agitated and a trailing edge opposite the leading edge, characterized in that each blade is obtained by folding a flat sheet, each blade having two longitudinal folds, length of each fold being greater than 60% of the maximum radius of the blade.

The length of each fold may be greater than 75% of the maximum radius of the blade.

Advantageously, the two folds are parallel.

At least one of the folds may be perpendicular to the outer edge of the helix.

The angle between the leading edge and the radial axis of the blade passing through the center of rotation and perpendicular to the outer edge, called the angle of incidence, is positive, the distal end of the outer edge, away from the shaft, attacking the fluid before the proximal end, when the mobile is rotating.

The angle of incidence may be between 4 and 20 °, preferably between 6 and 15 °.

Advantageously, the stirring mobile comprises only two blades so as to facilitate its introduction through the opening of the fluid container to be agitated.

Each blade may have, due to the presence of the two folds, a cross section substantially U-shaped in a plane parallel to the axis of rotation of the mobile and parallel to the outer edge of the blade.

The section of each blade may also be substantially Z-shaped in a plane parallel to the axis of rotation of the mobile and parallel to the outer edge of the blade.

The trailing edge may have an angle between 30 and 70 ° with the intersection with the plane of section of a plane orthogonal to the axis of rotation of the mobile, this angle being called leakage angle.

Preferably if we note the width of the blade at its distal end and L the width of the blade at its base at the axis, then l> 0.5 L.

Preferably, for each blade, the angle of attack α between the pan comprising the leading edge and the central panel is between 13 and 25 °.

• Fig. 1 est une vue en élévation latérale d'un agitateur selon l'invention,
• Fig. 2 est une vue en perspective schématique, à plus grande échelle, d'un premier mode de réalisation d'une pale d'un mobile d'agitation selon l'invention,
• Fig. 3 est une vue de dessus de la pale de Fig. 2,
• Fig. 4 est une vue en bout de la pale de Fig. 2,
• Fig. 5 et Fig. 6 sont des vues en perspective illustrant l'introduction d'hélices d'agitation à trois et deux pales dans un contenant,
• Fig. 7 est une vue schématique en perspective d'un second mode de réalisation d'une hélice d'agitation selon l'invention,
• Fig. 8 est une vue de dessus de l'hélice de Fig. 7,
• Fig. 9 est une vue similaire à Fig. 7 d'un troisième mode de réalisation d'une hélice selon l'invention, comportant trois pales,
• Fig. 10 est une vue de dessus de l'hélice de Fig. 9,
• Fig. 11 est une vue similaire à Fig. 7 d'un quatrième mode de réalisation d'une hélice selon l'invention, comportant trois pales,
• Fig. 12 est une vue de dessus de l'hélice d'un autre mode de réalisation d'une hélice selon l'invention, et
• Fig. 13 est un schéma illustrant les vitesses linéaires en différents points des hélices.

Other features and advantages of the invention will appear in the following description of a preferred embodiment with reference to the accompanying drawings but which has no limiting character. On these drawings:

• Fig. 1 is a side elevational view of an agitator according to the invention,
• Fig. 2 is a schematic perspective view, on a larger scale, of a first embodiment of a blade of a stirring machine according to the invention,
• Fig. 3 is a top view of the blade of Fig. 2 ,
• Fig. 4 is an end view of the blade of Fig. 2 ,
• Fig. 5 and 6 are perspective views illustrating the introduction of three and two-blade stirring propellers into a container,
• Fig. 7 is a schematic perspective view of a second embodiment of a stirring propeller according to the invention,
• Fig. 8 is a top view of the helix of Fig. 7 ,
• Fig. 9 is a view similar to Fig. 7 a third embodiment of a propeller according to the invention, comprising three blades,
• Fig. 10 is a top view of the helix of Fig. 9 ,
• Fig. 11 is a view similar to Fig. 7 a fourth embodiment of a propeller according to the invention, comprising three blades,
• Fig. 12 is a top view of the propeller of another embodiment of a propeller according to the invention, and
• Fig. 13 is a diagram illustrating the linear velocities at different points of the propellers.

Throughout the following description of different embodiments of propellers according to the invention, the relative terms such as "upper", "lower", "front", "back", "horizontal" and "vertical" are to be interpreted when the propeller according to the invention is installed in an operating situation.

We can see on Fig. 2 to 4 a first embodiment of a propeller according to the invention, made with 2 folds, inexpensive and achievable solution with the help of tools that have most workshops mechanical-boiler.

Since each blade of the helix has two folds, each blade thus has three faces and in a sectional view, it is necessary to define three angles to define the profile of the blade. These angles are more particularly visible Fig. 4 .

The angle of attack is the angle a between the pan with the leading edge and the central pan. The angle d is the angle of positioning between the pan central to the blade and the horizontal, when the axis of rotation is vertical. The leakage angle f is the angle between the pan with the trailing edge and the central panel.

This propeller has an angle of attack α and a leakage angle f of 21 °. The first fold A, that is to say the one that will attack the fluid first, is made along an axis passing through the axis of rotation of the helix. The second fold is noted B. It may be noted that the distal end of the trailing edge is located forward with respect to the proximal end of the same trailing edge and the direction of rotation of the helix. The distal end will attack the fluid first.

The blades are folded so as to obtain a cambering coefficient of less than 12%, so as to improve the energy efficiency. The angle of attack is between 13 and 22 ° in order to have a suitable Cx. Indeed beyond 30 ° the radial forces generated will be very important. Then we approach the case of the turbine.

The blade area is generous and almost quadrilateral in order to obtain a high pumping rate because the displaced volume is a function of the surface of the blade.

If we note the width of the blade at its end and L the width of the blade at its base at the axis, the magnitude l and L are very close and l> 0.5 L and preferably l> 0.75 L.

This element has been privileged even if it goes against the usual practice. Indeed most propellers have a narrow end, trapezoidal shape, to limit the torque by refining the blade at its end.

Studies have shown that given the combination of chosen angles, blade bends and shape, the performance over known propellers is quite acceptable.

• P : puissance hydraulique
• ΔP = pression différentielle entre l'entré et la sortie du mobile
• Q = débit
• D= diamètre du mobile
• N= vitesse de rotation du mobile
• p = densité
• v= vitesse du fluide
• S = aire du mobile
• k =constante

If we note respectively:

• P: hydraulic power
• ΔP = differential pressure between the input and the output of the mobile
• Q = flow
• D = diameter of the mobile
• N = rotation speed of the mobile
• p = density
• v = fluid velocity
• S = mobile area
• k = constant

The flow of a helix is given by the following simple relation: $$\mathrm{Qp}=\mathrm{nq}{\mathrm{<figure-callout\; id="3"\; label="ND"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ND</figure-callout>}}^3$$

With Nq, dimensionless number characterizing the helix (its shape, the number of blades etc ...).

The power consumed is calculated as follows: P = Np ρ N ³ D ⁵

With Np, dimensionless number characterizing the helix (its shape, the number of blades etc ...).

The efficiency is the ratio of the energy supplying the pumping rate and the energy required to rotate the mobile.

• Relation générale de mécanique des fluides : P1 = ρΔPQ (1)
• Débit de pompage :Qp = Nq ND³ (2)
• Puissance nécessaire à la rotation du mobile :P2 = Np ρ N³ D⁵ (3)
• Relation de Bernoulli simplifiée :ΔP = 1/2 ρ v²
• v = Q/S = $$v=\frac{{\mathit{<figure-callout\; id="3"\; label="NqND"\; filenames="imgf0001.png"\; state="\{\{state\}\}">NqND</figure-callout>}}^3}{\pi \frac{D^2}{4}}=\mathit{kND}$$
  
  $$\frac{P2}{P3}=k\frac{{\mathit{<figure-callout\; id="3"\; label="Nq"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Nq</figure-callout>}}^3}{\mathit{Np}}$$
  

The yield can be expressed simply with the general relation of fluid mechanics and the simplified Bernoulli relation:

• General relationship of fluid mechanics: P1 = ρΔPQ (1)
• Pump flow: Qp = Nq ND ³ (2)
• Power required for mobile rotation: P2 = Np ρ N ³ D ⁵ (3)
• Simplified Bernoulli relationship: ΔP = 1/2 ρ v ²
• v = Q / S = $$v=\frac{{\mathit{<figure-callout\; id="3"\; label="NqND"\; filenames="imgf0001.png"\; state="\{\{state\}\}">NqND</figure-callout>}}^3}{\pi \frac{D^2}{4}}=\mathit{KND}$$
  
  $$\frac{P2}{P3}=k\frac{{\mathit{nq}}^3}{\mathit{np}}$$
  

Note that the calculation is identical by looking for the power consumed to generate 1 m3 / h for example.

We note, for example: Mobile type nq np yield New 3 blade propeller 0.68 0.58 0.54 New propeller with 2 blades 0.59 0.40 0.50 State of the art 1 0.60 0.41 0.53 State of the art 2 0.61 0.49 0.46 Turbine with blades inclined at 45 ° 0.75 1.20 0.37 Turbine with 6 straight blades 0.85 5.5 0.12

It can be seen that the propeller yields proposed are particularly good with regard to the state of the art and conventional propellers and turbines such as the marine propeller or the impeller with blades inclined at 45 °.

The number of propeller blades increases the amount of fluid displaced but also the power consumed.

Without being quite proportional, it is often noted that the power consumed increases proportionally to the number of blades by a factor of 0.8.

But in this case considering the surface and the angles, the average fluid speeds show that with 2 blades, the power decreases by 31% compared to a propeller with three blades whereas the flow decreases only by 13% only.

The interest of using a propeller with two blades is therefore multiple.

From an economic point of view, manufacturing two blades instead of three allows a gain of 33% in terms of material, manpower to form the blade and weld on a hub.

The implantation of the propeller is easier. Indeed according to the diameter of the tree it is sometimes not possible to implant three blades around it.

In addition some products are partially destroyed by the shear provided by the blades. Indeed at each rotation the blade "cut" the product to break (flocs, emulsion, polymers ...) and a mobile equipped with two blades will shear only twice per rotation and not three times.

Finally the propeller can be made in one part for different reasons, for example welded to the drive shaft to allow its possible coating in corrosive or abrasive medium or when it is not possible to fix it later. The three blade propeller is particularly difficult to introduce in a tubing when the mobile exceeds 500 mm, but a propeller with two blades, of the same diameter is easily introduced as illustrated Fig. 5 and 6 .

We observe in particular on the Fig. 13 a profile of the speed field leaving the blade almost identical for the three propellers proposed, thanks to the surface of the blade, folds and angles combined, we manage to maintain a profile frankly axial identical.

The propeller is sought for its flow leaving the blade rather axial to blow towards the bottom in the axis and back to the wall, to sweep the bottom of any deposited particles.

"Simple" propellers composed of blades inclined or formed of a fold do not provide a predominantly axial flow because of "radial and tangential leaks, for the invention there is a predominantly axial flow.

The manufacture of propellers of the state of the art is complex.

In some cases it requires a complex machine that can twist blades for propellers of 10 m diameter, single machine, still in production.

Saber-type propellers given their curvature require a template for each diameter and shape hence a combination of more than one hundred templates.

The manufacture of propellers proposed is relatively easy with the help of a folder, so we can evoke a better competitive subcontractors, a greater choice of these.

The mechanical determination of an agitator is dictated by its diameter and speed of rotation for a given operation and therefore the power generated for the rotation of the mobile.

The power gain for the same pumping rate, the essential computation element of stirring to effect mixing, allows a gain on the motor, the speed reducer transmitting the torque, on the guide system and on the seal, the movable shaft and the thickness of the mobile. For example, there is a gain of 20% in power between the propeller proposed and a marine propeller.

One can easily imagine the economic gain realized from the investment point of view for the user as the competitive interest for the builder.

Claims (13)

Mobile (M) agitator comprising at least two blades and adapted to be fixed on a rotating shaft, characterized in that each blade has a leading edge facing the fluid to be agitated and a trailing edge opposite the edge of the blade. etching, characterized in that each blade is obtained by folding a flat sheet, each blade having two longitudinal folds, the length of each fold being greater than 60% of the maximum radius of the blade. Mobile agitation (M) according to claim 1, characterized in that the length of each fold being greater than 75% of the maximum radius of the blade. Mobile agitation (M) according to claim 1 or 2, characterized in that the two folds are parallel. Mobile agitation (M) according to any one of claims 1 to 3, characterized in that at least folds is perpendicular to the outer edge of the propeller. Stirring machine (M) according to one of the preceding claims, characterized in that the angle between the leading edge and the radial axis of the blade passing through the center of rotation and perpendicular to the outer edge, called angle of incidence, is positive, the distal end of the outer edge, away from the shaft, attacking the fluid before the proximal end, when the mobile is rotating. Mobile agitation (M) according to claim 5, characterized in that the angle of incidence is between 4 and 20 °. Mobile agitation (M) according to claim 5, characterized in that the angle of incidence is between 6 and 15 °. Stirring device (M) according to one of the preceding claims, characterized in that it comprises only two blades Mobile. stirrer (M) according to any one of claims 1 to 8, characterized in that each blade has, due to the presence of two folds, a substantially U-shaped cross section in a plane parallel to the axis of rotation of the mobile and parallel to the outer edge of the blade. Mobile agitation (M) according to any one of claims 1 to 8, characterized in that each blade has, due to the presence of the two folds, a cross section substantially Z-shaped in a plane parallel to the axis of rotation of the mobile and parallel to the outer edge of the blade. Stirring device (M) according to any one of the preceding claims, characterized in that the trailing edge has an angle of between 30 and 70 ° with the intersection with the section plane of a plane orthogonal to the axis of rotation of the mobile, this angle being called leakage angle. Stirring device (M) according to one of the preceding claims, characterized in that if the width of the blade is noted at its distal end and L is the width of the blade at its base at the level of the blade. axis, l> 0.5 L. Stirring device (M) according to any one of the preceding claims, characterized in that for each blade, the angle of attack α between the pan comprising the leading edge and the central panel is between 13 and 25 °.

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