EP2926892B1 - Stirring device - Google Patents

Description

The present invention relates to a stirring mobile comprising at least two blades and capable of being fixed to a rotation shaft.

The manufacture of many products requires an operation of homogenization, dilution, dissolution, reheating ...

For this, mechanical stirrers with a rotating shaft are most often used, provided with a drive most often by an electric motor, with a shaft and a mobile agitation or stirrer. The set therefore consists of a container, a product and a stirrer.

The present invention relates to the design of agitators which are generally propellers or turbines comprising a so-called agitation mobile mounted on a rotation shaft.

A turbine is provided with straight blades at 90 ° relative to the vertical, it is however customary to call an entirely mobile turbine made up of straight blades, even positioned inclined.

A turbine generates a radial flow, which generates shear and dissipates energy.

A helix is preferably formed from a pitch portion of a helical, strongly inclined, of a bent or bent sheet metal.

A propeller develops an axial and methodical flow.

The rotation of the agitation mobile causes a displacement of the liquid which makes it possible to carry out the desired operation, more or less efficiently depending on the shape of the mobile, 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, for the formation of an emulsion.

The invention deals more specifically with the case where it is sought to minimize the energy losses by shearing 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 which gives the best result. Indeed, these operations only require setting in motion of the product, that is to say a pumping rate.

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

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

We can distinguish two main families of propellers represented by the 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 proving difficult.

Such a use is in fact often considered too expensive because the high yield is not appreciated at its fair value, only the cost of the investment being really considered. High efficiency is only considered interesting 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 time consuming, therefore expensive and can only be carried out by special machines. Indeed the technical problems are numerous due in particular to the thickness of the sheet and the 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.

Folded propellers already exist on the market, but they have a very specific shape with a blade wedge fold to limit radial leaks. Improving performance was not the technical problem its designers sought to address.

EP 0 771 586 A1 described in Fig. 13 a stirring mobile comprising three blades and able to be fixed on a rotation shaft, each blade comprising a leading edge facing the fluid to be stirred and a trailing edge opposite the leading edge, in which each blade is obtained by bending a flat sheet, where each blade has two substantially longitudinal folds over the major part of the blade and intersecting at the distal end of the blade, and in which the leading edge has an angle of incidence positive in its proximal part and a negative angle of incidence in its distal part. US 2005/243646 A1 also describes another motive for agitation. There is therefore a need for a propeller that is easy to build, that is to say without special equipment or particular skill, providing a good flow rate which is the essential factor in determining the agitation, without however consuming too much power, as would a single blade with a flat, inclined shape, which would de facto lead to high power, a large shaft and a high thickness of the blade and ultimately to a non-competitive manufacturing cost.

According to the invention a stirring wheel with features of claim 1 is provided.

The length of each ply may be greater than 75% of the maximum radius of the blade. 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 is between 6 and 15 °.

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

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 can 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 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 the angle of flight.

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

Preferably, for each blade, the angle of attack a between the side comprising the leading edge and the central side 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 d'un hélice qui n'est pas un 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 characteristics and advantages of the invention will appear in the following description of a preferred embodiment with reference to the accompanying drawings but which is in no way limiting. On these drawings:

• Fig. 1 is a side elevational view of a stirrer 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 wheel set 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 Fig. 6 are perspective views illustrating the introduction of stirring propellers with three and two blades in 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 propeller of Fig. 7 ,
• Fig. 9 is a view similar to Fig. 7 of a third embodiment of a propeller according to the invention, comprising three blades,
• Fig. 10 is a top view of the propeller of Fig. 9 ,
• Fig. 11 is a view similar to Fig. 7 of a fourth embodiment of a propeller according to the invention, comprising three blades,
• Fig. 12 is a top view of a propeller which is not an embodiment of a propeller according to the invention, and
• Fig. 13 is a diagram illustrating the linear speeds at different points of the propellers.

Throughout the following description of various embodiments of propellers according to the invention, the relative terms such as “upper”, “lower”, “front”, “rear”, “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, produced with 2 plies, an inexpensive solution that can be produced using tools available to most mechanical-boiler workshops.

Insofar as each blade of the propeller has two folds, each blade therefore has three sides 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 side comprising the leading edge and the central side. The angle d is the positioning angle between the pan center of the blade and horizontal, when the axis of rotation is vertical. The angle of flight f is the angle between the side comprising the trailing edge and the central side.

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

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

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

If we denote by l the width of the blade at its end and L the width of the blade at its base at the level of the axis, the sizes l and L are very similar and l> 0.5 L and preferably l> 0.75 L.

This element was privileged even if it goes against the usual practice. In fact, most propellers have a narrow end, in the shape of a trapezoid, in order to limit the torque by thinning the blade at its end.

Studies have shown that taking into account the combination of the angles chosen, the bends of the blade and its shape, the performance compared to 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
• ρ = 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 = speed of rotation of the mobile
• ρ = density
• v = fluid velocity
• S = area of the mobile
• k = constant

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

With Nq, adimensional number characterizing the propeller (its shape, the number of blades etc ...).

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

With Np, adimensional number characterizing the propeller (its shape, the number of blades etc ...).

The efficiency is the ratio of the energy providing the pumping flow rate and the energy required to turn 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 $$\begin{array}{l}v=\mathrm{Q}/\mathrm{S}=\\ \begin{array}{cc}\nu =\frac{\mathit{<figure-callout\; id="3"\; label="Nq\; ND"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Nq</figure-callout>}{\mathit{ND}}^{}{\mathit{}}^3}{\pi \frac{D^2}{4}}=\mathit{kND}& \frac{P2}{\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}3}=\mathrm{<figure-callout\; id="3"\; label="k\; Nq"\; filenames="imgf0001.png"\; state="\{\{state\}\}">k</figure-callout>}\frac{{\mathit{Nq}}^{}}{}\frac{{\mathit{}}^3}{\mathit{Np}}\end{array}\end{array}$$
  

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

• General relation of fluid mechanics: P1 = ρΔPQ (1)
• Pumping rate: Qp = Nq ND ³ (2)
• Power necessary for the rotation of the mobile: P2 = Np ρ N ³ D ⁵ (3)
• Simplified Bernoulli relation: ΔP = 1/2 ρ v ² $$\begin{array}{l}v=\mathrm{Q}/\mathrm{S}=\\ \begin{array}{cc}\nu =\frac{\mathit{<figure-callout\; id="3"\; label="Nq\; ND"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Nq</figure-callout>}{\mathit{ND}}^{}{\mathit{}}^3}{\pi \frac{D^2}{4}}=\mathit{kND}& \frac{P2}{\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="imgf0001.png"\; state="\{\{state\}\}">P</figure-callout>}3}=\mathrm{<figure-callout\; id="3"\; label="k\; Nq"\; filenames="imgf0001.png"\; state="\{\{state\}\}">k</figure-callout>}\frac{{\mathit{Nq}}^{}}{}\frac{{\mathit{}}^3}{\mathit{Np}}\end{array}\end{array}$$
  

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 2-blade propeller 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 Impeller 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 yields of the propellers proposed are particularly good with regard to the state of the art and conventional propellers and turbines such as the marine propeller or the turbine with blades inclined at 45 °.

The number of propeller blades increases the quantity of liquid displaced but also the power consumed.

Without being entirely 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 taking into account the surface and the angles, the average fluid speeds show that with 2 blades, the power decreases by 31% compared to a three-blade propeller while the flow only decreases 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 saving of 33% in terms of material, labor to form the blade and weld it on a hub.

The installation of the propeller is easier. Indeed, depending on the diameter of the shaft, it is sometimes not possible to install three blades around it.

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

Finally, the propeller can be made in one part for various reasons, for example welded to the drive shaft to allow its possible coating in a corrosive or abrasive medium or when it is not possible to fix it subsequently. The three-bladed propeller is particularly difficult to introduce in a pipe when the mobile exceeds 500 mm, but a two-blade propeller of the same diameter is easily inserted 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 proposed propellers, thanks to the surface of the blade, the folds and the angles combined, it is possible to maintain a frankly identical axial profile.

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

“Simple” propellers composed of inclined blades or even formed of a fold do not allow a predominantly axial flow to be provided because of the “radial and tangential leaks, for the invention, a predominantly axial flow is noted.

The manufacture of the prior art propellers is complex.

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

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

The manufacture of the proposed propellers is relatively easy using a folding machine, so we can talk about a better competitive subcontractors, a greater choice of them.

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

The gain in power for the same pumping rate, an essential element of calculation of agitation to perform a mixture, allows a gain on the engine, the speed reducer transmitting the torque, on the guidance system and on the sealing, the mobile carrier shaft and the thickness of the mobile. For example, there is a gain of 20% in power between the proposed propeller and a marine propeller.

It is easy to imagine the economic gain made from an investment point of view for the user as well as from the competitive interest for the manufacturer.

Claims (12)

1. Stirring member (M) that comprises at least two blades and is able to be fastened to a rotation shaft,
   each blade comprising a leading edge facing the fluid to be stirred and a trailing edge facing away from the leading edge,
   each blade being obtained by bending a flat sheet,
   each blade having two longitudinal bends,
   the length of each bend being greater than 60% of the maximum radius of the blade,
   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, referred to as the angle of incidence, being positive, in the sense that the distal end of the outer edge, remote from the shaft, could meet the fluid before the proximal end when the member is in rotation,
   wherein the two bends are parallel and the angle of incidence is comprised between 6 and 15°.
2. Stirring member (M) as claimed in claim 1, characterized in that the length of each bend is greater than 75% of the maximum radius of the blade.
3. Stirring member (M) as claimed in any one of claims 1 to 2, characterized in that at least one of the bends is perpendicular to the outer edge of the propeller.
4. Stirring member (M) as claimed in any one of the preceding claims, characterized in that it comprises only two blades.
5. Stirring member (M) as claimed in any one of claims 1 to 4, characterized in that each blade has, on account of the presence of the two bends, a substantially U-shaped cross section in a plane parallel to the axis of rotation of the member and parallel to the outer edge of the blade.
6. Stirring member (M) as claimed in any one of claims 1 to 4, characterized in that each blade has, on account of the presence of the two bends, a substantially Z-shaped cross section in a plane parallel to the axis of rotation of the member and parallel to the outer edge of the blade.
7. Stirring member (M) as claimed in any one of the preceding claims, characterized in that the trailing edge is at an angle of between 30 and 70° to the intersection with the section plane of a plane orthogonal to the axis of rotation of the member, this angle being referred to as the departure angle.
8. Stirring member (M) as claimed in any one of the preceding claims, characterized in that, if the width of the blade at its distal end is denoted I and the width of the blade at its base at the level of the axis is denoted L, l > 0.5 L.
9. Stirring member (M) as claimed in any one of the preceding claims, characterized in that, for each blade, the angle of attack a between the face containing the leading edge and the central face is between 13 and 25°.
10. Stirring member (M) as claimed in any one of the preceding claims, characterized in that, if the width of the blade at its distal end is denoted I and the width of the blade at its base at the level of the axis is denoted L, I > 0.75 L.
11. Stirring member (M) as claimed in any one of the preceding claims, characterized in that the first bend (A), that is to say the one which will meet the fluid first, is made along an axis passing through the center of rotation of said member.
12. Stirring member (M) as claimed in any one of the preceding claims, characterized in that the distal end of the trailing edge is situated forward of the proximal end of this same trailing edge with respect to the direction of rotation of the propeller, the distal end will thus meeting the fluid first.

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