EP2865088A1

EP2865088A1 - Electrohydrodynamic generator

Info

Publication number: EP2865088A1
Application number: EP13808672.3A
Authority: EP
Inventors: Mose AKYUZ
Original assignee: Individual
Current assignee: MA GENERATOR AB
Priority date: 2012-06-25
Filing date: 2013-06-12
Publication date: 2015-04-29
Also published as: SE1200377A1; SE536557C2; EP2865088A4; WO2014003625A1

Abstract

The present invention relates to an electrohydrodynamic generator unit with a chamber. The chamber is provided with at least one hole electrode with at least one hole. The hole electrode is connected to a voltage source and is intended to generate a direct voltage field in the chamber. The chamber is further connected to at least one reservoir that contains a fluid such as water. The chamber further comprises at least one collecting electrode coupled to an electrical load. The elec trohydrodynamic generator unit functions in that said reservoir is coupled to an electrically earthed fluid feeding member arranged in the chamber, which member is intended, via at least one opening adapted to corresponding holes in the hole electrode, to eject drops of fluid from the reservoir towards the hole electrode, which fluid drops are charged by an electric direct voltage field generated by the hole electrode, to which a voltage has been applied, and are then accelerated through the chamber past the holes in the hole electrode and strike the collecting electrode, where the drops deposit their charge. The collecting electrode is intend¬ ed in turn to be coupled to an electrical load via the earthed fluid feeding member, wherein a closed circuit is formed, which is capable of driving the load with the charges that have been deposited on the collecting electrode.

Description

Electrohydrodynamic generator The present invention relates to an electrohydrodynamic generator (EHD). More specifically, the invention relates to an arrangement that converts kinetic energy of a fluid/liquid to electrical energy without using any moving parts. An advantage of an EHD according to the invention is that it is well adapted to micromanufacturing, which is a big advantage in many applications. Applications of the invention will be described at the end of this patent application after the background technology and a detailed description of the invention have been provided.

Background to the invention and prior art The invention relates to a method for generating electricity by exposing a fluid in motion to a high-voltage field. The principle is based on utilising the physics behind the interaction between a charged liquid/fluid and an applied electric field. The aim of the electric field that is used according to the arrangement is to polarise drops of fluid/liquid in order thereby to give the liquid a type of charge. By then let- ting these charged drops of liquid accelerate towards a cathode, an electric current will be generated, which current can be used to feed an electrical load linked to the cathode.

To provide an illuminative background to the invention, Lord Kelvin's electrostatic generator will be described. This arrangement has nothing in common with the invention with regard to construction, but basically the same physical principles lie behind both Lord Kelvin's electrostatic generator and the present invention. The principle of Lord Kelvin's electrostatic generator is that dripping water is used to create a voltage difference in an electrode system through electrostatic induction. Electrostatic induction is a phenomenon that causes a material to become polarised when it is exposed to an applied electric field. Schematically, Kelvin's generator can be depicted according to what is represented in figure 1. As is evident from the figure, the arrangement consists of a number of simple components. It mainly consists of a metal water container provided with two small holes for the water to drip down through. The water that drips down is collected in two metal beakers placed under the container. The beakers are electrically insulated from one another and from the environment. In addition, the generator is provided with two metal rings arranged between the water container and the beakers. The aim is for the water to pass through these rings when it drips from the container down into the different beakers. The rings are also electrically insulated from the environment and from each other. As is clear from the figure, the left ring is electrically coupled to the right beaker and the right ring to the left beaker. The entire system is initially electrically neutral. When the system is now activated, i.e. when the water begins to drip down through the holes and rings to the beakers, a phenomenon linked to electrostatic induction will occur. This is namely such that the water that drips down into the beakers will cause charges of opposed polarity to build up in the two beakers. The reason why a net polarisation is initially created between the beakers is not entirely known today, it could be due to the water drops picking up a small charge due to the so-called tribo-effect when they come into contact with the opening on the liquid container or with the air during the fall towards the beakers. In any case, a momentary imbalance will occur in the charge distribution between the beakers. The ingenious thing about the arrangement is that if the right ring (for example) receives a surplus of positive charges, these will be distributed on the ring so that the opening nearest this ring receives negatively charged drops of liquid. These negatively charged drops will then pass through the positively charged ring and land in the right beaker. This causes the right beaker to become negatively charged. The negatively charged beaker will in turn strengthen the effect in the positively charged beaker and this process continues as long as the dripping con- tinues. As the voltage difference between the beakers becomes greater and greater, this will eventually cause the water drops either to be repelled, meaning that the charging effect stagnates, or an electrical flashover occurs, which empties the beakers of their net charges. The prior art will be described further when a more detailed description of the invention and the physics behind it have been given.

Figures The embodiments will be described with the aid of the figures, in which:

Figure 1 schematically represents a possible variant of Lord Kelvin's arrangement.

Figure 2 represents an EHD according to the prior art.

Figure 3 schematically represents an embodiment of EHD according to the invention, where a chamber is represented with a single electrode set-up with an anode, called a hole electrode, a floating cathode, called a collecting electrode, and a fluid feeding structure. The designation z in the figure represents the impedance in the load.

Figure 4 shows a further embodiment of an EHD according to the invention, where the same hole electrode - collecting electrode set-up is represented as in figure 3, but the hole electrode here is provided with a plurality of holes adapted to a plurality of jets arranged on the fluid feeding member.

Figure 5 shows a further embodiment of an arrangement according to the invention, where instead two hole electrodes with corresponding cathodes are arranged symmetrically around a fluid feeding member. The fluid feeding member is provided with a plurality of jets arranged on the sides opposing the hole electrodes. The jets are adapted to corresponding holes on each of the hole electrodes.

Figure 6 represents an embodiment of the invention in cross section, where a closed fluid system is used in the electrohydrodynamic unit. Only the fluid system is represented in the figure.

Figure 7 shows in cross section how the water is led into the fluid feeding member from a reservoir. Since the duct in towards the jets only has one opening, the pressure differences will force the liquid out through the jets arranged on the fluid feeding member. Figure 8 shows in cross section how a plurality of fluid feeding members can be supplied with liquid from the same reservoir. Furthermore, it is shown how the fluid that runs off the collecting electrode is collected and returned for reuse.

Figure 9 shows the same principle as in figure 8, but in this figure the water is ejected in various directions with the aid of the jets arranged on each side of the fluid feeding member.

Detailed description of the invention and preferred embodiments

The invention will be described both functionally and component-wise with the support of the figures in the following. A number of different designations of components will be used, which is why we provide a fairly short list of terms with functional descriptions.

Chamber (1) refers to the complete enclosure for the arrangement. The chamber is provided with, or connected to, a reservoir (6) with a fluid. The aim is that the fluid shall be taken from this reservoir and led into the chamber via a jet. It is important that the fluid is divided up into particles, or small drops of liquid, when it leaves the jet. To achieve this particle division, mechanical or electrohydrodynamic atomisation of the fluid can be used. In the latter, the so-called Taylor angle is sought (which can be found by varying the high-voltage field in the chamber).

These techniques are well known in the technical field and will not be described in greater detail here.

Fluid feeding member (4) refers to an arrangement that can be earthed and ensures that the fluid/liquid, normally water, is taken from the aforesaid reservoir and ejected from the reservoir into the chamber via a jet (9). In one embodiment, this is achieved in that an excess pressure is present in the reservoir, i.e. the pressure in the reservoir is considerably higher than the pressure present in the chamber. The pressure of the chamber usually lies at normal atmospheric pressure. Since the jet creates an opening towards the chamber, the water will be injected into the chamber on account of the pressure equalisation. Another possibility is that the water is centrifuged and when a sufficiently high rotational speed has been obtained, cavi- ties are opened in the centrifuge. The water can be injected into the chamber in this way. It is clear here that the openings in the centrifuge are directed towards the chamber. If a centrifuge or similar arrangements are used to increase the velocity of the liquid, it is necessary for a motor to drive the centrifuge. In one embodiment, the arrangement for fluid feeding can consist of one nozzle.

Needle electrode refers to an electrode that is used to generate a corona discharge. This type of electrode is not used in the present invention, but is a substantial part of the prior art.

Hole electrode (2) refers to an electrode system through which the drops of liquid are to be pushed. Voltage should be applied to the hole electrode to a significant voltage by means of a DC voltage source, which is connected to the hole electrode. The aim of the arrangement is to charge the drops of liquid that are ejected from the nozzle via the induction effect. The hole electrode consists in principle of a structure manufactured from an electrically conductive material that is provided with one or more holes of sufficient diameter to let a charged water drop pass through.

The collecting electrode (3) is an electrode system which is arranged in one embodiment at the outer edge of the chamber, beyond the hole electrode when viewed from the fluid feeding member. Another cathode arrangement is represented in an embodiment that is shown schematically in figure 5. A collecting electrode is a cathode plate intended to receive charged drops of liquid. The cathode plate or collecting electrode is intended, furthermore, to be coupled to an electric load with an impedance z. The term collecting electrode is used to illuminate that its function is to collect up charged fluid drops that are first ejected from the fluid feeding member in order then to be charged and accelerated towards the collecting electrode, where they are collected. In a preferred embodiment, the collecting electrode consists of a floating cathode plate, i.e. a cathode plate with a potential that depends both on the collected charge on the plate and also on the background field, that is, the voltage at the hole electrode. In embodiments of this invention that are described below, the collecting electrode has an opposing polarity compared with the hole electrode. A possible electrode configuration according to the invention is now described with reference to figure (3). At one end of the chamber (1), a needle-shaped nozzle (4) is arranged. The nozzle has a length, a radius, and is also earthed. The nozzle is connected to a liquid container, not shown in the figure, and is disposed to take water from the liquid container and eject the water drops into the chamber at high velocity. Arranged at a certain distance from the nozzle is a hole electrode (2). The hole electrode is provided with a hole arranged directly in line with the jet of the nozzle. The aim of the hole is that it shall allow the water drops ejected by the nozzle to pass through. A high voltage is applied to the hole electrode by means of a DC voltage source. A collecting electrode (3) is arranged adjacent to the hole electrode towards the end of the chamber. This collecting electrode is a so-called electrically floating electrode. This means that the collecting electrode assumes a potential that is a function of the charge that is found at the electrode, but also of the surrounding field distribution. In contrast to the hole electrode, the collecting electrode has no hole. The collecting electrode is also connected to an electric load and to the earthed nozzle. A closed electric circuit is created between the nozzle, collecting electrode and load in this way.

When using an arrangement according to figure 3, the following will occur:

A quantity of liquid, the liquid can expediently be water, is taken from the container and led via the nozzle into the chamber. The quantity of water will be divided up into water drops, which are injected into the chamber at high velocity. If a positive voltage has now been applied to the hole electrode, the water drops will receive a negative charge when they leave the nozzle due to electrostatic induction. The resulting force on the drops when they are ejected from the nozzle will be substantially great, therefore, in the direction of the hole electrode. This is because the forces that eject the drops and the electric force on the drops from the hole electrode lie in the same direction. In the figure this has been symbolised by an arrow. Because of this, the water drops are given an even higher velocity when they leave the nozzle than would be the case if no electric fall were present. When the drops have travelled in the region between nozzle and hole electrode, as they approach the hole in the hole electrode they will curve towards the edge of the hole. Because they are given a considerable velocity when they are ejected from the jet, however, they will not curve too much, but will pass through the hole. Consequently, the distance between the opening of the jet and the hole in the hole electrode must not be too great, in order to avoid the drops being intercepted by the hole electrode and instead to permit them to pass through the hole. Another advantage of having a short distance is that the voltage at the hole electrode does not have to be so high to obtain atomisation and charging of the fluid.

When the drops have passed the hole in the hole electrode, they will experience an electric field that is opposed to the field on the opposite side of the hole electrode. This causes the water drops to be braked. In the figure this has been symbolised by two different arrows. By calibrating the ejection speed of the water drops and the voltage across the hole electrode, it is possible to ensure that all water drops that are ejected from the nozzle travel the entire path between the hole electrode and the collecting electrode in order to strike the latter.

When the drops hit the collecting electrode, they will automatically deposit their charge on the collecting electrode and then run off it. This leads to the charge of the collecting electrode being built up as more drops strike it. The charge that builds up on the collecting electrode can then be extracted by coupling the collecting electrode to a load via a coupling to the earthed nozzle. This creates a closed circuit in which electrical energy can be extracted from the mechanical energy from the motion of the water drops.

The main fact that must be observed when intending to convert a liquid's kinetic energy into electrical energy according to the present invention is that the liquid must be charged and atomised. The invention does not work with a continuous and neutral liquid. Thus the main problem is to obtain charging of a liquid in motion. We shall give some examples below of how a liquid in motion can be charged purely physically. A possible method is to allow the liquid to flow through a perforated hole electrode to which a voltage has been applied and which has been given a sufficiently high electric field in each cavity to create by this a so-called corona discharge. The corona discharge will deposit a portion of the emitted charge on the liquid flowing through the holes in the electrode. This is an alternative method of charging a liquid. To obtain an effective charging of the liquid, an effective corona discharge is required. According to Lord Kelvin's arrangement, the charging of the liquid takes place instead by polarisation of liquid drops through the induction effect. If a freely flowing liquid were used, this arrangement would not work, as the induction effect will not charge the liquid. Lord Kelvin's arrangement is consequently based wholly on the induction effect.

There are also possibilities for extracting energy from a continuously flowing liquid in an electric background field. An extremely high flow rate of the liquid is required, however, so that the convection current of the liquid is greater than the conduction current. Otherwise a net current is obtained through the liquid that discharges the electrode system.

The problems with the high velocities that are required for a liquid flow are overcome in that the arrangement according to the invention utilises drops of water (or of another suitable fluid). Compared with Lord Kelvin's arrangement, an arrangement according to the invention also provides a possibility of selecting the degree of polarisation of the water drops and thereby the amount of charging. This is done in that the external field that is placed over the hole electrode can be varied. The higher the voltage produced over the hole electrode, the higher the degree of charging of the drops. A higher power can ultimately be selected, therefore.

Before more embodiments are given, an EHD generator according to the prior art will be described briefly here. We refer to figure 2, which shows a sketch of a basic EHD set-up. The set-up consists of a needle-shaped electrode, an earthed attracting ring electrode at the narrowest area of the nozzle, and a collecting electrode. All these parts are placed along an insulating tube system (a de Laval nozzle here). High voltage is applied between the needle-shaped electrode and the attracting ring electrode to create thereby a corona discharge from the needle elec- trode, which releases free electrons. These electrons are assumed to bind to the flowing gas and drive in the direction of the collecting electrode. The shape of the tube system is disposed to provide cooling for the flowing gas when it passes the narrow hole in the nozzle and is thereby condensed into liquid particles (aerosols). These liquid particles will then be charged in that they collide with the charged gas particles and they will then be driven along in the background flow of gas. When the gas and the charged liquid particles have passed the narrow hole, the charged particles are allowed to move towards a braking electric field until they reach the collecting electrode, where they deposit the charge. The efficiency of an EHD ac- cording to the above has been estimated at a maximum of 10.8%. In reality, however, these dimensions are never attained, but the efficiency is usually in the order of 2% (for a power of 400 W and an excess pressure of 30 bar). The main reasons for losses are the electrical strength of the electrode system and the fact that the charge transfer between the corona electrode and the liquid particles is far from optimal. The latter is due to the fact that the free electrons that are created upon the corona discharge do not cover as great a volume, but are rather localised around the corona electrode. Another limiting factor is that energy is required to convert the driving gas (specifically steam) to liquid particles. This energy loss results in a reduction in the system's available kinetic energy. A further reduction in the kinetic energy in the system follows from the fact that it is collisions of the gas particles with the aerosols that creates the driving force of the same. This force transfer reduces the system's available kinetic energy.

Many of the problems related to conventional EHD technology are overcome ac- cording to the present invention. According to the invention, liquid drops are ejected from a nozzle via an externally arranged pressure force. Because liquid is shot out and gas is not used, a higher density of the flowing medium will automatically be obtained. This leads to a higher energy density and the disappearance of the energy losses that occur due to phase transformations. Since the flow of liquid particles in the chamber according to the present invention is also controlled by the external pressure, the system will not give any greater energy losses either on account of collisions between the driving gas and aerosols. According to the invention, the liquid drops are charged via electrical induction. This leads to each water drop being charged and able to travel through the system in order to deposit its charge on the collecting electrode. This is distinguished from conventional EHD technology with corona discharge, where the main charging takes place at the aerosols that are located in direct proximity to the corona discharge. Furthermore, it is possible according to the present invention also to control the degree of charging by varying the voltage that is applied between the jet or nozzle and the hole electrode. The charge transfer according to the invention is not time-dependent either, which is the case with arrangements dependent on corona discharge. This results in an on the whole momentary charge transfer that produces a continuous charge deposition at the collecting electrode.

According to both conventional EHD technology and the technology according to the present invention, an acceleration of the charged drops takes place in the intermediate space between holes and plate. Furthermore, a plate electrode also lies on the other side of the hole, which plate creates a field where the drops can be braked. In order not to give the collecting electrode too high a charge and in doing so to create such a large field that the drops are repelled, the velocity distribution of the incoming water particles must lie within a narrow range. The present invention provides an arrangement with just these options. EHD according to the prior art instead provides quite varying velocities since the area for phase transformations being rather elongated in a de Laval nozzle. It thus becomes difficult for an arrangement according to the prior art to select a potential that does not repel the particles before these hit the collecting electrode.

Another construction of an EHD generator is to be found in US patent no.

4677326, inventor Alvin Marks. This arrangement is based on extracting energy from the movement of aerosols by utilising a wind force that drives the aerosols in a background field. Charging of the aerosols takes place in that they are allowed to pass through needle-shaped nozzles and a perforated anode to which voltage is applied. The wind flow passes through perforations in the same electrode system as the aerosols are ejected from. A construction according to US patent no.

4677326 is quite large on account of the large distance that is required between hole electrode and collecting electrode in order for it to be possible to utilise the wind force effectively to move the charged aerosols past the hole electrode and towards the collecting electrode. The present invention consequently facilitates an improved arrangement which can be made considerably smaller by utilising ejection of the water drops.

Due to the fact that the arrangement can be made so small compared with the prior art, a possibility is also provided to design an electrohydrodynamic unit that consists of a large number of arrangements according to claim 1. This gives the opportunity of multiple power withdrawal, as several collecting electrodes will be impacted by a large number of water drops. Some variants of such constructions will be described below.

Before embodiments are provided, an estimate of different properties of an EHD generator according to the present invention will now be given. The aim is to pro- vide an estimate of the performance and the dimensions required for the arrangement to work. To maximise the values of the dimensions, experiments are necessary. Given what is depicted in this application, such experiments are routine and self-explanatory for a person skilled in the art. First an estimate of the available kinetic energy and power of the water drops is given. An important quantity here is the velocity of the water drops in the opening of the fluid feeding member. The higher the initial velocity the drops have, the more kinetic energy is available in the EHD system. Another important quantity is the electrically generated energy on the braking of the charged drops. This quanti- ty depends on how effectively the drops can be charged and how effective the braking is. Large drops will be charged more than small drops and consequently these larger drops will require particularly high electric fields to be braked. Extremely fast drops will also require high electric fields to be braked. In general it is not desirable to have electric fields that are too high due to the risk of electrical flashover. A balancing of the quantities is what is demanded for maximum performance, therefore. The parameter that is very probably the most important in the system, efficiency, is given by the quotient between kinetic energy and the electrical energy generated. An estimate of how much kinetic energy is available in an EHD generator with only one jet, see figure 3, can be obtained as follows. It generally applies to the kinetic energy that

„ nt ' V

E_k =

² (1) where v is the velocity and m is the mass of the flowing liquid. If the expression above is now differentiated with regard to time, the following is obtained,

P = -¾ = I-^._v ² +— ·— (ν²)=-·—

* dt 2 dt 2 dt 2 dt (2) an expression of the change in the kinetic energy, i.e. a mechanical effect, for a constant flow rate. Furthermore, it also applies that

dm _ dV_

dt ^{~ P '} dt (3) where dm/dt is the mass flow rate, p is the density and dV/dt is the volume flow rate (i.e. the quantity of liquid that passes an imaginary surface per unit of time). If this expression (3) is used in expression (2), a relationship is obtained for the mechanical effect that is available in an EHD according to the following:

₀ dE_k 1 dV 2

P_k =— ~ =—p v

dt 2 ^H dt (4)

The formulae above make it possible to estimate the available kinetic energy and power from a container that ejects liquid from a tube with the radius r and length /. We assume here that the velocity of the liquid is the same as the velocity of the drops that are ejected from the tube. Furthermore, these drops are presumed to have a density p, to be spherical and to have a size (i.e. a diameter) that corresponds on the whole to the diameter of the tube. For such a drop we obtain the following mass

m - p' V r/ = p ^π r 3

³ (5)

The flow rate v in equation (1) is provided in the stationary case by Poiseuille's equation: dV _ nr Ap

dt ^'Ί^ Τ' ₍₆₎ where η is the viscosity of the liquid. The volume flow rate dV/dt is provided in turn by

From a normal viewpoint there will not be a stationary flow in the tube, which is why experiments may be necessary to maximise the efficiency. Instead, the flow rate will vary along the length of the tube and depend on the exact geometry of the tube's attachment in the container and the tube's opening. If such complications are disregarded, it is possible by using Poiseuille's equation above to obtain an approximation of the velocity of drops at the opening of the fluid feeding member. We assume in the following numerical example that we have a water container with a pressure of 5 bar (5x10⁵ Pa), running from this container is a tube that opens in the chamber, through which tube liquid flows. We assume that the pressure in the chamber, i.e. on the outside of the tube, is normal atmospheric pressure of 1 bar. This produces a liquid pressure difference of 4 bar. Assume further that the tube has a radius of 5 microns and a length of 25 microns and that the liquid used is water. With a viscosity of 1.04x10^"3 Ns/m² for the water, the following can be obtained from expressions (6) and (7): i.e. v = 50 m/s. Since the flow rate is a quadratic function of the radius of the tube, we see that the velocity becomes higher if the tube's diameter is greater. The water drops also become bigger, however, which is not always desirable since, as stated earlier, substantial electric fields are required to brake large water drops. Furthermore, the velocity of the liquid at the opening is proportional to the inverse of the tube's length. This means that a shorter tube gives a higher velocity. This is advantageous as a shorter tube facilitates a more compact EHD arrangement well suited to miniaturisation. Thus to obtain suitable dimensions of an EHD arrangement that is to be miniaturised, the short tube length should be compensated for by a smaller radius of the tube. Finally, we can numerically determine the kinetic energy for a drop with a radius of 5 microns, a tube with a radius of 5 microns and length of 25 microns to E_k - 6.5 -10 ¹⁰ J p_or†h_e same construction the mechanical power is

P_¾ =4.9.1(T³ fr .

Now these estimates have been made, estimates shall now be made to provide a measurement of how much of the kinetic energy can be converted into electrical energy in an arrangement according to the present invention. An important parameter in this estimate is the degree of charge that the drops of liquid take with them when they leave the opening of the fluid feeding member. The amount of charge will depend on the strength of the electric field, the electrode configuration in the chamber and the exact geometry of the drops when they leave the opening. In principle it is impossible to calculate theoretically the induced charge for the general field, which is why numerical calculation methods and above all repeated trials are necessary to determine the optimum charge carried. It should be a straightforward job, however, for a skilled person to find more or less optimal degrees of efficiency via experiments by varying the field strength, tube geometry and electrode configurations. An extremely simplified calculation can be made, however, that demonstrates what velocity a known charge acquires when it is accelerated in a background field between an earthed nozzle and a hole electrode with a given positive potential Φ. The opening velocity of the drop is assumed to be given by equation (8) and it is assumed to start at the opening of the fluid feeding member. It is also assumed that the drop concludes its travel in the hole on the hole electrode. We assume as a first approximation that it moves straight forwards towards the hole in the hole electrode, i.e. it has no acceleration in any direction other than straight forwards, consequently a one-dimensional movement along the axis of the EHD arrangement is present.

By utilising the conservation of energy for the charged drop, the following velocity equation is obtained:

2 2 (9) where vi is the velocity of the drop when it reaches the centre of the hole electrode. From this it is possible to estimate the potential Φι that is required to brake a drop with a charge Q. By assuming that the starting point for the drop is the centre of the hole electrode and the finishing point is the collecting electrode and the beginning velocity is vi , the following equation is obtained:

2 * ^J (10)

By solving equation 10, the fact is obtained that the potential of the collecting electrode is negative, i.e. it brakes the charged drop. As is evident from equations (9) and (10), the only unknown variable is the induced charge. The potential Φ at the hole electrode is a quantity that should be assigned in such a way that no electrical flashover is obtained for a given distance between nozzle and hole electrode. This is a complex theoretical problem that must be iterated for each conceived electrode configuration. It is necessary, therefore, to apply a potential at the hole electrode for each assumed electrode configuration and then check that no flashover is received in the system with the drop placed precisely at the opening of the electrode tube. With such an iteratively found potential it is then possible to work out the induced charge Q of the imaginary drop. With the value obtained for the induced drop charge inserted into equation (9), the velocity of the drop in the gap between nozzle and hole electrode can then be estimated. To conclude, it is then possible using equation (10) to work out the potential Φι that causes the drop to be braked precisely when it reaches the collecting electrode. If this potential that has been worked out is applied to the collecting electrode, an optimally braking electric field is obtained.

Another embodiment of an electrohydrodynamic generator, in addition to the one described above in connection with figure 3, will now be described with reference to figure 4. In the figure, the electrohydrodynamic generator comprises a hole electrode (2) provided with a number of holes (5). It also comprises a plate provided with a number of fluid feeding members (4), here in the form of nozzles, in which each of these nozzles is provided with a jet or opening aligned with a corresponding hole in the hole electrode. As in the embodiment described previously, the intention is to place a high-voltage field over the hole electrode to charge the water drops that are ejected from the different fluid feeding members and to allow these drops to accelerate through corresponding holes in the hole electrode to strike the collecting electrode and deposit their charge there. Here too the collecting electrode is coupled to an electric load via a coupling to the electrically earthed fluid feeding members. The physical thing that occurs in this embodiment is the same as described in connection with figure 3, the only difference is that more water drops can be ejected per unit of time. Thus in the same way as previously, a closed circuit is created that can drive the load. In this embodiment, where a plurality of fluid feeding members is used, it can be arranged to collect its liquid from a common fluid reservoir, but it is also possible that each of the nozzles collects liquid from its own reservoir. The first-named is to be preferred if it is intended to create a closed fluid feeding system. This is to say that when the liquid runs off the collecting electrode, it is collected and returned via a water line to the different nozzles. More will be described later about such a closed system.

Yet another embodiment of an electrohydrodynamic generator is depicted in figure 5. In this figure, a plate with fluid feeding members as in the embodiment depicted above is arranged centrally in the middle of the chamber. In contrast to the previous embodiment, the plate in this case is provided with nozzles or openings and jets on both sides of the plate. It is thereby possible for the fluid feeding member to eject water drops in two directions into the chamber. Consequently, the chamber is also provided with two hole electrodes (2, 2') provided with holes (5, 5') linearly aligned with an opening of a corresponding nozzle on the fluid feeding member. Beyond each of these hole electrodes, towards the ends of the chamber, two collecting electrodes (3, 3') are arranged. These collecting electrodes are coupled to a load via the earthed fluid feeding member. Both the collecting electrodes and hole electrodes will be arranged mainly symmetrically around the plate with fluid feeding members. The physical thing that takes place in this embodiment is the same as described in connection with figure 3, the only difference is that more water drops can be ejected per unit of time. In use, a closed circuit that can drive the load will be created by this. It shall be noted that the electrical loads can be different, which makes it possible for one part, for example the left-hand part of the chamber, to drive a specific load while the right-hand part drives another load. In this case two different closed circuits are created. An embodiment according to the above is ideal for miniaturising the arrangement. One of the marked advantages of an electrohydrodynamic generator according to the present invention is that it can be miniaturised so easily. This makes it possible for a large number of drops to deposit their charge in an extremely short time. This leads in turn to the fact that a large energy withdrawal can be made per unit of time compared with the prior art. An expansion of the last embodiment yields an electrohydrodynamic generator provided with a number of fluid feeding plates with related and symmetrically arranged hole electrodes and collecting electrodes. The idea is that the chamber shall be provided with a large number of such subsystems in order in this way to optimise the performance when the generator is miniaturised. The power with- drawn per unit of time increases with the number of subsystems.

To understand the embodiment provided above, reference is made to figure 5 and figure 7 respectively. Figure 7 shows a variant of a fluid feeding member suitable for use together with symmetrically arranged hole electrodes (2, 2') and collecting electrodes (3, 3'), see the arrangement in figure 5. The fluid feeding member (4) in the figure consists of a hollow sheet or a hollow plate or a tube-like structure. The fluid feeding member is anchored in the walls of the chamber and has a closed end (4a) and an open end (4b). The open end is linked to the fluid reservoir (6) via a duct (21). Furthermore, the walls in the sheet, plate or the tube-like structure are provided with jets (9a) and (9b) arranged on each side of the sheet or the tube-like structure and opening into chamber (1). Even if the figure depicts the jets as tubelike nozzles that protrude from the wall, it is also possible to only use cavities in the wall. The jet can be preferred over cavities as it means that lower voltages are required over the hole electrodes to charge the water drops. In use, the water or another suitable fluid is now routed from the pressurised reservoir (6) to the hollow sheet, plate or tube-like structure (4) via duct (21). Because the end (4b) connected to the duct is open, the pressurised fluid enters the cavity at a high velocity. Since the opposite end (4a) is closed, the fluid will be pressed out via the jets (9, 9') due to the fact that the pressure in the chamber (1) is kept considerably lower than the pressure in the reservoir (6). In this way, a fluid feeding member is created that can spray fluid in two separate directions into the chamber. If two hole electrodes (2) and (2') respectively are now arranged on each side of the fluid feeding member (4), the jets 9 and 9' can eject fluid drops towards each hole electrode. If two collecting electrodes are also arranged outside of the corresponding hole electrodes, seen from the fluid feeding member, these will be fed with drops charged by the respective hole electrode, which in turn deposit their charge on their intended collecting electrode. One and the same fluid feeding member thereby feeds two separate hole-collecting electrode arrangements, which doubles the power withdrawal per unit of time. For this embodiment to work, a pressure difference is required to exist between the fluid reservoir or duct 21 that carries the liquid to the fluid feeding member and chamber (1). One method of ensuring this is for the reservoir or duct to have an excess pressure, while the chamber (1) is at atmospheric pressure. By letting the chamber have an opening to the environment, it can be seen to that the chamber is always at atmospheric pressure. The excess pressure in the reservoir or duct can be ensured by means of an externally connected pump. Alternatively, it goes without saying that external pumps can be connected to both the reservoir/duct and the chamber.

When it comes to the construction of the electrohydrodynamic generator, it is possible to attach the hole electrodes, fluid feeding member and collecting electrodes in the walls of the chamber so that they run along the entire chamber vertically. This requires fixed mounting of the constituent components and in the case of miniaturisation, where we speak of units in the order of millimetres or less, this becomes complicated. The alternative is to instead etch the components out of one piece of material in miniaturisations of the components. All parts will sit together in this way, hole electrodes and collecting electrodes thereby form material sheets that have not been etched away. The fluid feeding member will consist of a hollow and sheet-like structure which is provided with cavities or etched-out jets in the walls. The pressurised fluid will be pressed out through these cavities or jets upon use. This production method is extremely practical when using hole electrodes with many holes and fluid feeding members with many jets. Furthermore, the production method is also well suited for manufacturing a number of units in series. Then, as many units as required are quite simply etched out in the same piece of material. As the material is intended to conduct electricity, the material should either be conductive itself, or alternatively be coated with a conductive material on the sections where voltage is to be applied and currents go. For example, copper- plating of relevant sections is sufficient to achieve this aim. With reference to figure 6, an electrohydrodynamic arrangement with a closed fluid system is described below. The advantage of a closed fluid system is that the reservoir can be incorporated into the arrangement and frequent topping up of the liquid in the reservoir is not required, therefore. Because the liquid that has been charged and has deposited its charge is routed back to the fluid feeding member, the same liquid can be used time after time. In figure 6, we see a reservoir (6) partly filled with a fluid/compressed air. Because only parts of the reservoir are filled with liquid, the rest can be filled by compressed air. The reservoir is also provided with a valve at its lower edge. This is a control valve that can be arranged to regulate the time and the quantity of water that is to be released from the air-liquid tank. Connected to the valve is a duct (21) through which the liquid is supplied from the air-liquid tank to the jet or jets in the fluid feeding member. These jets are not depicted in the figure, but are represented by the chamber (1) in which they are arranged. The figure also shows the chamber (1) of the EHD generator in cross section. The air pressure in the generator chamber is considerably lower than the air pressure in the air-liquid chamber. It is advantageous for the pressure to be around normal atmospheric pressure. To obtain atmospheric pressure, the chamber can be provided with an opening to the environment. Alternatively, the chamber (1) and reservoir (6) or duct (21) are coupled to external pumps that en- sure that a pressure difference exists. How this is accomplished is not substantial to the function, as the relevant thing is that the pressure difference between the air-liquid reservoir and the generator chamber is sufficiently great for the liquid to attain the demanded velocity. When the liquid that has been injected into the chamber and deposited on the collecting electrode runs off the latter, the liquid is collected in the lower part of the generator chamber. Another duct runs from the lower part of the chamber, therefore, a return duct (22) where the liquid is intended to run out. This return duct (22) is then connected to the duct (21). Due to the large pressure difference between duct (21) and duct (22), the liquid will be returned through the latter to the duct (21) and be able to be injected into the generator chamber again. Initially, when the liquid is released from the air-liquid reservoir, it can be necessary for the duct (22) to contain liquid to ensure that the liquid from the reservoir goes directly to the generator chamber and not into duct (22). Alternatively, the return duct (22) can be provided with a valve that only permits a flow of liquid in one direction, i.e. in the direction from the return duct (22) to duct (21). The system has thus been provided with a virtually closed fluid feeding system in which the same quantity of liquid can be charged repeatedly. This system can be used for all the embodiments described above. It is especially suitable for use for the miniaturised system in which the components are etched from one piece of material. By using this system, the only work that needs to be done during the process is to pressurise the air-liquid reservoir. It goes without saying that it is also possible to provide such a closed system with a pump, wherein the liquid that runs out from the generator chamber is pumped back to duct (21). It would be normal to ensure that duct (21) continuously provides an excess pressure relative to both the generator chamber and the return duct (22).

An alternative to the closed fluid feeding system described above consists of a reservoir that only contains compressed air. This is to say that no fluid at all enters the container. The aim is that only the compressed air or gas shall be used to pressurise the duct between the generator and the reservoir. Initially, on start-up of the arrangement, duct (22) shall be provided with liquid. When the valve between duct (21) and the reservoir is opened, air will leave the reservoir under high pressure. This air movement will bring quantities of liquid with it from the duct, which can then be injected through the fluid feeding member. When the charged drops of liquid then run off the collecting electrode, they will run out into duct (22) to then be shot out again the next time the valve in the reservoir is opened. In this way it is possible by controlling the opening of the reservoir valve periodically in time to ensure that the same quantity of liquid can be used many times. In this embodiment, as in the previous ones, it can be preferable if all valves are check valves that only permit movement in one direction.

With reference to figures 8 and 9, a more detailed description will now be given of two different embodiments, which have been etched out of one piece of material and which are supplied with a common fluid feeding system that utilises recycling of the liquid.

Figure 8 shows an embodiment with a set-up of EHD units according to claim 2, arranged side by side. It makes sense for all fluid feeding members, hole electrodes and collecting electrodes included to be etched from one piece of material. Said piece of material has a border that has been designated (1), which corresponds to the chamber in previously described embodiments. According to the figure, three units are also depicted where each of these units consists of a fluid feeding member (4), a hole electrode (2) and a collecting electrode (3). At its up- per end the chamber is connected to a duct (21) that supplies water or fluid to the unit from a reservoir (6). As shown in the figure, the upper end of the chamber in the figure consists of three openings that correspond to end 4b in figure 7. That is to say they are inlets for water or fluid into the fluid feeding member. The fluid feeding member in this figure is provided with two jets (9), which are directed to- wards two opposing holes arranged in the hole electrode (2). Beyond the hole electrode, seen from the position of the fluid feeding member, the collecting electrode (3) is arranged. In use, fluid is now taken from the pressurised reservoir (6) and routed via duct (21) into each of the open ends (4b) in the fluid feeding member (4). Because the lower end (4a) of the fluid feeding member is closed, which is shown in figure 7, the water fed in will take the path through the jets (9), be atomised via the field in the chamber and be ejected into the open intermediate space in the chamber between the fluid feeding member (4) and hole electrode (2). Then the drops take the path through the hole in the electrode to finally deposit their charge on the collecting electrode (3). After the water drops have deposited their charge on the collecting electrodes (3), the water will run off the collecting electrode due to gravity. As is evident from figure 8, the lower section (11) of the region between hole electrode and collecting electrode is open. This is so that the water will run down from the electrode and be collected in a duct (22) arranged on the underside of the chamber. This duct corresponds to the return duct (22) de- scribed in connection with figure 6. The water is consequently led back thereafter to duct (21) to be used afresh to provide the fluid feeding member (4) with water. As this figure depicts three fluid feeding members and three collecting electrodes, the upper edge of the chamber (1) is provided with three cavities corresponding to the openings for the fluid feeding members, while the lower edge in the figure is provided with three openings to which the distance between the hole electrodes and collecting electrodes corresponds. This is a possibility for arranging a plurality of units according to the invention in line to create an EHD generator with high efficiency per unit of time. Another embodiment is provided in figure 9. This embodiment is substantially suggestive altogether of what was given above in connection with figure 8. What is different is that the fluid feeding member here is provided with jets that can eject liquid drops in separate directions in the chamber. The fluid feeding member is de- scribed above in connection with figure 7.

To provide an estimate of the magnitudes that give good results, a table is provided below with an estimate of effective values of the quantities involved. These are not the only possible values, however, but give only an estimate of the values in an effective dimensioning. To optimise the power of the arrangement, exact experiments are required where it is possible to start out from the approximations given above and then fine-tune the set-up. This is traditional experimental activity within the technological field and is straightforward for a skilled person. We give examples below, however, of a parameter family that can be used. These parameters are only by way of example. Since the parameters have a mutual dependency that is particularly complex, it can be necessary to carry out experiments if it is intended to change the parameters and optimise operation. The values of parameters given in the table are an example that results in drop velocities that lead to an acceptable power withdrawal from the arrangement.

Table 1

In the above table, a fluid pressure of 5 bar is envisaged over given tube dimen- sions, which gives a velocity of the drops of around 50 metres per second. Furthermore, the tube diameter relates to the diameter of the tube or of the jet in the fluid feeding member. The tube length relates to the length of the tube or the duct that leads to the jet in the fluid feeding member. Units/sheet relates to the number of units of the electrohydrodynamic generator that is used in each sheet according to the embodiment given above. In the same way, the number of sheets/square metre defines how many sheets shall be used in the three-dimensional construction. The voltage on hole electrode and voltage on collecting electrode relate to the voltages that are placed over the hole electrodes and collecting electrodes. Resistance load relates to the resistance of the load that is driven by means of the electrical energy that is formed in the electrohydrodynamic generator. Finally, electrical power indicates the power that can be withdrawn from a generator with these specific parameters. As stated, the complex dependency between the parameters requires that experiments are carried out to optimise the withdrawal of electrical power.

Applications and use of an EHD generator according to the invention An electrohydrodynamic generator according to the present invention can be used in many different fields. In principle it can be a complement to all types of current and voltage sources that are used to drive an electrical load. For example, an arrangement according to the invention can be used to generate high voltage. The quite low voltage that is used to apply voltage to the hole electrodes is converted to an output high voltage by utilising the conversion of the fluid's kinetic energy to electrical energy. It goes without saying that this applies also to currents.

A foreseeable application is use of the invention as a complement or replacement for today's turbine-driven technology.

Claims

Electrohydrodynamic generator unit comprising a chamber (1), which chamber is provided with at least one hole electrode (2, 2') with at least one hole (5, 5'), said hole electrode (2, 2') being connected to a voltage source (10) and being intended to generate a direct voltage field in the chamber, which chamber is also connected to at least one reservoir (6) containing a liquid such as water, the chamber further comprising at least one collecting electrode (3, 3') coupled to an electrical load (15'), which electrohydrodynamic generator is characterised by that said reservoir (6) is connected to an electrically earthed fluid feeding member (4) arranged in the chamber and provided with at least one jet (9, 9') adapted to corresponding holes (5, 5') in the hole electrode (2, 2'), wherein liquid can be routed from the reservoir (6) to the fluid feeding member (4) in order via the jet (9, 9') to eject drops of the liquid from the reservoir (6) towards said at least one hole electrode (2, 2'), which liquid drops are intended to be charged by an electric direct voltage field generated by said at least one hole electrode (2, 2'), to which voltage has been applied, and to be accelerated through the chamber past the holes (5, 5') in said at least one hole electrode (2, 2') and to strike the collecting electrode (3, 3') in order to deposit the charge there, which collecting electrode (3, 3') is intended to be coupled to an electrical load (15) via said fluid feeding member (4), wherein a closed circuit is formed that is capable of driving the load with the charges that have been deposited on the collecting electrode.

Electrohydrodynamic generator unit according to claim 1 , characterised by that it comprises an electrically earthed fluid feeding member (4) with a jet (9), which member is connected to a reservoir (6), a hole electrode (2) to which a voltage has been applied from a voltage source (10) and which is provided with a hole (5) adapted to the jet on the fluid feeding member (4), a collecting electrode (3) arranged beyond the hole electrode (2) and connected to an electrical load (15) via the earthed fluid feeding member (4), wherein liquid taken from the reservoir is ejected from the jet, charged by the electric field generated by the voltage over the hole electrode (2), accelerated through the hole (5) of the hole electrode to strike the collecting electrode (3) in order to deposit its charge there, wherein a closed circuit is created across the electrical load (15) and the earthed fluid feeding member (4).

Electrohydrodynamic generator unit according to claim 1 , characterised by that it comprises an electrically earthed fluid feeding member (4) with two jets (9, 9') directed in different directions, which member is connected to a reservoir (6), two hole electrodes (2) to which a voltage has been applied from a voltage source (10) and which are each provided with a hole (5, 5') adapted to each jet (9, 9') on the fluid feeding member (4), two collecting electrodes (3, 3') arranged beyond the corresponding hole electrode (2, 2') and each connected to an electrical load (10, 10') via the earthed fluid feeding member, wherein liquid taken from the reservoir is ejected from the jets (9, 9'), charged by the electric field generated by the voltage over the hole electrodes (2, 2'), and accelerated through the holes (5, 5') of the corresponding hole electrodes (2,

2') to strike the corresponding collecting electrode (3,

3') in order to deposit its charge there, whereby closed circuits are created across the electrical loads (15) and the earthed fluid feeding member

(4) .

4. Electrohydrodynamic generator unit according to claim 2, characterised by that said jet (9) consists of a set of jets (9), and that said hole

(5) consists of a set of holes (5), each of said holes being adapted to the corresponding jet (9) in the set of jets.

5. Electrohydrodynamic generator unit according to claim 3, characterised by that said jets (9, 9') consist of a set of jets (9, 9'), and that said holes (5, 5') consist of a set of holes (5, 5'), each of said holes (5, 5') being adapted to the corresponding jet (9, 9') in the set of jets.

Electrohydrodynamic generator unit according to one of claims 1-5, characterised by that the fluid feeding member (4) is provided with a closed end (4a) and an open end (4b) for the intake of liquid from a pressurised reservoir (6), the fluid feeding member further being fixedly arranged in the chamber (1) and provided with first and second jets (9, 9'), directed in different directions, wherein the liquid upon use is routed into the fluid feeding member (4) via the open end and is forced out through the jets (9, 9') via the pressure difference between the chamber and the reservoir.

Electrohydrodynamic generator unit according to claim 5 or 6, characterised by that both hole electrodes (2, 2') and the collecting electrodes (3, 3') are disposed to run through the whole chamber (1) on each side of the fluid feeding member (4), wherein the jets (9, 9') arranged on the fluid feeding member (4) are adapted to the holes in the corresponding hole electrode (2, 2').

Electrohydrodynamic generator unit according to claims 1-7, characterised by that the hole electrodes (2, 2'), collecting electrodes (3, 3') and the hollow tube structure that constitutes the fluid feeding arrangement (4) are etched out of a homogeneous piece of material.

Electrohydrodynamic generator, characterised by that it consists of a number of generator units according to any of claims 1-7, arranged side by side.