EP0534082A1 - Pump system for delivering liquid or gaseous media - Google Patents

Abstract

The invention relates to a pump system for delivering liquid or gaseous media in a pressure vessel (DG) which is sealed with respect to the receiver (13) by means of a diaphragm (16) whose work output is based on a foil (10) which is made of piezoelectric material and is coated on both sides in an electrically conductive manner. Illustrative embodiments are described and drawn. <IMAGE>

Description

The invention relates to a pump system for conveying liquid or gaseous media according to the preamble of claim 1.

Pump systems of this type are state of the art in a wide variety of embodiments and for a wide variety of purposes. Each of these systems has proven itself for the purpose assigned to it, but also has disadvantages. In one case you have to work very low frequency, in the other case the inertia of the drive is too great or in the third case the power losses are too high etc.

The present invention is based on the object of demonstrating a pump system of the type mentioned at the outset, the pump frequencies of which extend into the kHz range and higher, have rapid controllability, are almost free of power loss and are hardly subject to wear.

Fig. 1

einen Querschnitt durch ein Ausführungsbeispiel in schematischer Darstellung,

Fig. 2

eine perspektivische Skizze für ein Ausführungsbeispiel mit gerollter Piezofolie in schematischer Darstellung,

Fig. 3

eine perspektivische Skizze für ein Ausführungsbeispiel mit gefalteter Piezofolie in schematischer Darstellung.

This combination of tasks is solved in a surprisingly simple, reliable manner by the measures indicated in claim 1. Further developments and refinements are specified in the subclaims and exemplary embodiments are explained in the following description. The figures in the drawing complete these explanations. Show it:

Fig. 1

3 shows a cross section through an exemplary embodiment in a schematic illustration,

Fig. 2

1 shows a perspective sketch for an exemplary embodiment with rolled piezo film in a schematic illustration,

Fig. 3

a perspective sketch of an embodiment with folded piezo film in a schematic representation.

As can be seen from FIG. 1 of the drawing, the pump system shown there is based on an electrically conductive coating on both sides Film 10 made of a piezoelectric material - for example PVDF (polyvinylidene difluoride). This piezo film 10 is now folded (FIG. 3) or rolled in two layers (FIG. 2) in a pressure vessel DG filled with liquid 15 with low compressibility, which is closed with a membrane 16 towards the recipient 13. An inlet valve 14a and an outlet valve 14b are assigned to the recipient 13. An electrical control voltage 12 is applied to the piezo film 10 via electrical connections 11, which causes polarization and thus a change in the film thickness. The resulting change in pressure in the pressure vessel DG now moves the membrane 16, which in turn varies the volume of the recipient 13.

A periodic change in voltage now produces a pumping effect in connection with the two valves 14a, 14b. However, this creates a pump system that operates at a very high frequency (kHz range and higher), has a quick controllability due to the low inertia of the drive, and since the piezoelectrics can in principle be controlled without power, only very low power losses occur because of ohmic and inductive There are no losses whatsoever. It is also essential that this pump system is almost wear-free.

The change in tension and thus the change in thickness must take place so quickly that, due to the inertia of the film and the liquid (in the case of the folded film), the transverse contraction cannot follow the change in thickness. This results in the change in volume of the film.

For quasi-static or slowly changing operation, the transverse contraction must be prevented by the thickness and by the elastic properties of at least one of the electrically conductive coatings (electrodes), for example by an Al foil con bonded to the piezoelectric foil with approx Thickness of the PVDF piezoelectric film.

In a further exemplary embodiment it is proposed that the pressure vessel DG be replaced by a cylinder with a piston (not shown) complete, the diameter of the cylinder must be adapted to the desired piston stroke. This can be easily implemented by any specialist who has become familiar with the present pump system.

An exemplary embodiment is to be arithmetically shown below. This is based on a cylindrical pressure vessel DG with a diameter D = 30 mm, a height H = 50 mm and thus with a volume V = 35 cm³. The thickness dimensioning of the piezo film 10 should be 100 µm. As already explained above, the film 10 must be folded or rolled in two layers in the pressure vessel DG so that no contact can occur between the two contact surfaces.

The maximum film area that is accommodated in the volume V of the pressure vessel DG is A _F = 3,500 cm². Based on a fill factor F _f = 0.6, A _Feff = 2,000 cm².

Das Druckgefäß 10 ist mit einer inkompressiblen Flüssigkeit - beispielsweise Glyzerin mit K = 4.7 x 10³ MPa - gefüllt.The change in the thickness D of the piezo film 10 at an electrical voltage of 1,000 V is 1 per mille: ΔD = 0.1 μm. This results on the assumption that the change in the thickness D cannot be compensated for by changing the length or width of the film 10 in opposite directions:

$\text{ΔV = 20mm³}$

The pressure vessel 10 is filled with an incompressible liquid - for example glycerol with K = 4.7 x 10³ MPa.

dies entspricht ungefähr 27 bar.The change in pressure due to volume change is calculated from:

$\text{Δp = K AV / V = 4.7 x 10³ MPa 20mm³ / 35,000mm³ = 2.7 MPa}$

this corresponds to approximately 27 bar.

If not a membrane but a cylinder with a piston is connected to the pressure vessel 10, then a diameter of D _K = 2 mm and an area of A _K = 3 mm² are assumed. The calculation of this embodiment shows that the piston is moved with a force of 8.1 N and a stroke of 6 mm.

Claims (5)

Pump system for the conveyance of liquid or gaseous media in a pressure vessel, which is closed off to the recipient by means of a membrane, characterized in that films (10) with an electrically conductive coating on both sides are folded or rolled in a double layer with a certain space between them in a corresponding manner formed pressure vessel (DG) in a liquid (15) with low compressibility and are connected via electrical connections (11) to a voltage source (12), the periodic electrical voltages of which cause a change in the film thickness, the volume via the membrane (16) of the recipient (13) vary, the recipient (13) being assigned an inlet (14a) and an outlet valve (14b). Pump system according to claim 1, characterized in that the pressure vessel (DG) instead of a membrane (16) has a cylinder with a piston at the end, the cylinder diameter being dimensioned in accordance with the desired piston stroke. Pump system according to one of claims 1 or 2, characterized in that PVDF (polyvinylidene difluoride) is used as the piezoelectric film material. Pump system according to claims 1 to 3, characterized in that the piezo foils (10) in the pressure vessel (DG) are arranged so as to be folded or double-rolled such that contact between the foil surfaces is impossible. Pump system according to claims 1 to 4, characterized in that the incompressible liquid (15) in the pressure vessel (DG) is glycerine.

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