Device and method for generating electroplasmic heat

Description

[0001] Description

[0002] Title: Device and method for generating electro-plasmic heat.

[0003] Technical field

[0004] The present invention relates to the fields of thermal engineering, calorimetry and medium and high voltage electrical circuits. It relates more particularly to a device and a related method for generating heat.

[0005] The invention also relates to an installation for heating a fluid using the heat generation device.

[0006] Prior art

[0007] Heating a liquid, such as water, is commonly achieved by ohmic heating. To do this, an electrical resistor is subjected to a direct or alternating voltage U in an electrical circuit in which a current I flows. The resistor then releases a power P = UI = RI 2which can be used to heat the liquid.

[0008] The inventors have, however, shown that it is possible to generate thermal energy greater than the electrical energy supplied, as described in the article [1].

[0009] As shown in Figures 1 to 3, the device 1 described in this article [1] comprises two electrodes 2, 3 immersed in pure water, the water having an electrical conductivity of less than a few microsiemens per centimeter. One of the electrodes 2 is in the form of a point and arranged in a so-called point-plane configuration with the other of the two electrodes 3 being planar. The two electrodes 2, 3 are arranged at a distance of the order of 0.1 mm from each other. The pure water between the two electrodes constitutes an electrical resistance 4 between them.

[0010] Applying a voltage between the electrodes generates discharges in the following way. Initially and as shown in Figures 1 and 2, a water vapor channel (streamer in English) is formed and progresses from a first electrode to the second electrode. This channel is created by the intense electric field between the two electrodes which allows the ionization of the generated water vapor. During this phase, which can last several tens of microseconds, the voltage between the electrodes remains high and the current low. An ohmic type heating of the liquid water takes place between the end of the vapor channel and the second electrode.

[0011] In a second step and as shown in Figure 3, the water vapor channel 5 reaches the second electrode. Due to its ionization, the vapor channel has a very low electrical resistance, which causes the resistance between the electrodes 2, 3 to drop. The voltage across the electrodes drops and the current intensity increases, causing an electrical discharge. The measured generated energy is greater than the supplied energy at least under certain conditions.

[0012] Figure 4 shows the typical time course of current I and voltage U across electrodes 2, 3 as a function of time t. In the example of Figure 4, a voltage of about 900 V is applied at t = 0 s. The voltage remains substantially constant during the first phase of creation of a vapor channel by ohmic heating and the current remains low at about 10 A, corresponding to a resistance R = U / I = 110 ohms. When the electrical discharge between the electrodes occurs, the voltage drops and the current intensity increases due to the flow of current in the vapor channel. During this phase, the voltage drops to about 80 V and the current reaches 200 A, corresponding to a resistance R = U / I = 0.4 ohms.

[0013] The device 1 described in the article [1], as illustrated in figures 1 to 3, is however difficult to implement in the context of industrial use for heating liquid or generating steam.

[0014] First, obtaining discharges in pure water requires very precise geometry of the electrodes. At least one of the electrodes must have a very small radius of curvature, of the order of 0.1 mm, to benefit from the tip effect. In addition, the distance between the electrodes must be small, of the order of 0.1 mm, and maintained very precisely. However, electrical discharges generate pressure capable of moving the electrodes. To avoid this, sufficiently massive electrodes with a diameter of the order of several millimeters must be used: this therefore prevents the use of wire electrodes, i.e. with a small diameter, for example less than or equal to 2 mm. The tip of the electrode must then be sharpened precisely to obtain a sufficiently small radius of curvature. Furthermore, the passage of electric current during a discharge wears down the electrodes, in particular by ablation and hollowing.This limits the number of discharges to a few thousand and would therefore require a frequency of electrode changes that would be prohibitive for industrial use.

[0015] In addition, electrode wear pollutes the water in which the discharges are carried out due to particle ablation. This pollution can make the water sufficiently conductive to prevent the formation of a plasma necessary for obtaining energy gains. When the conductivity of the water becomes too high, the passage of current between the electrodes produces only ohmic heating.

[0016] Figure 5 illustrates the evolution of current I and voltage U as a function of time t for the same device as a function of a number of discharges N. More precisely, a number of 1352 discharges were carried out at a frequency of 2.7 discharges per second. It is clear from Figure 5 that the average time to create the vapor channel increases with the repetition of discharges, which reflects the wear of the electrodes.

[0017] Figure 5 also shows the unstable nature of the discharges: in fact, in parallel with the average increase in the time to create the steam channel, we observe a significant and random variation in this time, highlighting the instability of the phenomenon.

[0018] There is therefore a need to improve existing heating devices capable of generating thermal energy greater than the electrical energy that powers them, in particular to improve their predictability and lifespan.

[0019] The aim of the invention is to meet at least part of this need.

[0020] Statement of the invention

[0021] To do this, the invention relates, according to one of its aspects, to a heat generation device, comprising:

[0022] - an enclosure containing a liquid electrolyte,

[0023] - a first electrode in the form of a wire and a second electrode which extends along a surface, preferably flat, and is arranged in a so-called wire-surface configuration with the first electrode, the first and second electrodes being immersed at least partially in the liquid electrolyte, - a power supply configured to generate an electrical voltage, preferably in the form of pulses, between the first and second electrodes so as to generate a plasma around the first electrode.

[0024] By "liquid electrolyte" is meant here and within the framework of the invention, the usual meaning, namely a liquid which allows the passage of electric current, due to the presence of mobile ions within it.

[0025] Advantageously, the invention makes it possible to obtain high-efficiency heating. Indeed, the inventors have observed following several hundred experiments that the thermal energy generated by the device according to the invention can be greater than 1.5 times the electrical energy supplied to the device, reaching up to 4 to 8 times this value.

[0026] The invention therefore allows significant energy savings.

[0027] Without being bound by a theory, the inventors observe that this energy gain is linked to the formation of a plasma around the first electrode in the form of a wire. This hot and dense plasma is confined by the liquid electrolyte and seems to be the location of the observed amplification phenomenon.

[0028] To create a plasma around the first electrode, the density of the electrical energy deposit in the liquid electrolyte must be sufficient to create a volume of water vapor. The electric field must also be strong enough to ionize the water vapor.

[0029] Without being bound by this theory, the inventors believe that plasma is formed by the corona effect.

[0030] As will be seen in more detail later, the device according to the invention makes it possible to form a plasma in a stable manner and without significant wear of the electrodes, unlike the device according to the state of the art, described in relation to figures 1 to 5.

[0031] According to an advantageous embodiment, the first electrode has a diameter of between 0.1 mm and 2 mm.

[0032] Preferably, the distance between the first and second electrodes is greater than 1 mm, preferably 2 mm, 5 mm or 10 mm. It may be less than 50 cm, 10 cm or 5 cm. According to a preferred embodiment, the conductivity of the liquid electrolyte and the distance between the first and second electrodes are chosen so that the resistance of the liquid electrolyte between the latter is less than or equal to 20 ohms, preferably 10 ohms or 5 ohms.

[0033] Advantageously, the liquid electrolyte is a mixture of water and a base or an acid, in particular a mixture of water and soda.

[0034] Preferably, the enclosure includes a system for draining the liquid electrolyte to allow its replacement. The draining system may be configured to allow continuous replacement of the liquid electrolyte and / or to allow complete draining and replacement of the volume of liquid electrolyte in the enclosure.

[0035] According to an advantageous characteristic, a wall of the enclosure forms the second electrode.

[0036] The enclosure preferably has a volume of between 0.1 liters and 10 liters. More preferably, the enclosure is hermetically sealed.

[0037] The invention also relates to an installation for heating a fluid, comprising:

[0038] - a container containing the fluid and,

[0039] - a heat generation device according to the invention, the enclosure of the device being hermetically sealed and arranged in the container and in contact with the fluid.

[0040] The invention finally relates to a method of operating the heat generation device according to the invention, comprising a step consisting of applying, by pulses, an electrical voltage, preferably between 100 V and 10,000 V, between the electrodes by means of the electrical power supply so as to generate a plasma around the first electrode.

[0041] According to an advantageous characteristic, the voltage is applied in pulses of duration between 1 ps and 10 ms.

[0042] Preferably, the sign of the applied voltage alternates between positive and negative between two consecutive pulses.

[0043] Other advantages and characteristics of the invention will become more apparent upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0044] [Fig 1] [Fig 2] [Fig 3] Figures 1 to 3 represent the different stages of operation of a heating device according to the prior art.

[0045] [Fig 4] Figure 4 is a graph representing the typical time evolution of the voltage and current across the electrodes of the device according to Figures 1 to 3.

[0046] [Fig 5] Figure 5 is a graph representing the evolution of the voltage and current as a function of the number of discharges carried out on the same device according to the prior art.

[0047] [Fig 6] Figure 6 represents a heat generating device according to the invention.

[0048] [Fig 7] Figure 7 is a side view of a subassembly of the device of Figure 6.

[0049] [Fig 8] Figure 8 is a front view of the subassembly of Figure 7.

[0050] [Fig 9] Figure 9 is a graph showing the typical time course of the voltage and current across the electrodes of the device in Figures 6 to 8.

[0051] [Fig 10] Figure 10 is a graph representing the evolution of the voltage and current as a function of the number of discharges carried out on the same device according to the invention.

[0052] [Fig 11] Figure 11 represents a device according to the invention in a configuration allowing the measurement of the thermal energy generated.

[0053] [Fig 12] Figure 12 illustrates a fluid heating installation comprising a heat generation device according to the invention.

[0054] Detailed description

[0055] Figures 1 to 5 have already been detailed in the preamble, so they will not be commented on below.

[0056] Figures 6 to 8 illustrate a heat generation device 100 according to the invention.

[0057] In the illustrated example, the device 100 comprises a subassembly 10 which comprises an enclosure 11 containing a liquid electrolyte 14.

[0058] A first electrode 12 and a second electrode 13 are immersed in the liquid electrolyte 14.

[0059] The first electrode 12 is in the form of a wire, i.e. a solid cylinder of small diameter. The second electrode 13 extends along a surface and is arranged in a wire-surface configuration with the first electrode 12. The second electrode 13 is preferably a planar electrode. But it can also be curved. Preferably, the surface of the second electrode 13 is greater than 1 cm 2 , at 10 cm 2 , at 50 cm 2 or 100 cm 2 and / or less than 1000 cm 2 .

[0060] The first electrode and the second electrode are connected to a power supply 16 configured to generate an electrical voltage across the terminals of the electrodes. The power supply 16 may in particular be a generator or may come from an electrical network.

[0061] In the illustrated embodiment, a switch 17 makes it possible to selectively connect the power supply 16 to the second electrode 13 and a capacitor 18 is arranged between the terminals of the power supply 16. The electrodes 12, 13 are also each connected to a terminal of the capacitor 18.

[0062] Functioning

[0063] In operation, the power supply charges the capacitor 18 until a defined voltage is reached, with the switch 17 remaining open. Once the capacitor is charged, the switch 17 can be closed, which causes the capacitor 18 to partially discharge. A current of up to several tens to several hundred amperes flows in the circuit for a short time, typically between a few microseconds and a few milliseconds.

[0064] This generates a plasma 15 around the first electrode 12 in the liquid electrolyte. The plasma 15 is obtained by ionization of the water vapor generated around the first electrode.

[0065] Switch 17 is then opened and capacitor 18 is recharged. After recharging, a new discharge can take place to continue heating the electrolyte.

[0066] Advantageously, the capacitor can be chosen so that its capacity is sufficient so that at each discharge, the electric charge it releases into the circuit is small compared to its total charge. This makes it possible to maintain a quasi-constant voltage during the discharge of the capacitor.

[0067] The inventors found that the generation of plasma 15 leads to excess energy, the thermal energy generated being greater than the electrical energy supplied to the device. Figure 9 shows the typical evolution of the voltage across the electrodes and the intensity of the current flowing through the circuit during a discharge. It is observed that the voltage U is substantially constant at 900 V during its application time of approximately 200 ps. The current is intense from the start of the discharge and then decreases until it becomes substantially zero. The plasma is created from the start of the discharge.

[0068] Compared with the typical voltage and current evolution shown in Figure 4, it is noted that the voltage and current profiles are of a very different nature. There is in fact no creation of an ionized vapor channel followed by the creation of a plasma with passage of an intense current under a low voltage. Due to the conductivity of the electrolyte 14, the current intensity is significant from the start of the discharge.

[0069] Advantageously, the electrodes of the device according to the invention are therefore not subjected to a violent shock corresponding to dielectric breakdown when the ionized vapor channel connects the two electrodes in the device according to the prior art: the integrity of the electrodes is preserved and their wear is much less significant. This makes it possible in particular to use an electrode 12 with a small diameter wire and to improve the service life of the device.

[0070] Sizing

[0071] The generation of the plasma around the first electrode 12 can be obtained with different configurations of the device. The conductivity of the liquid electrolyte, the diameter of the first electrode 12 and the voltage applied to the terminals of the electrodes 12, 13 are in particular chosen to achieve the desired generation of the plasma.

[0072] To create a plasma around the first electrode, the density of the electrical energy deposit in the liquid electrolyte must be sufficient to create a volume of water vapor. The electric field must also be strong enough to ionize the water vapor.

[0073] The distance between the electrodes is therefore not a major factor in obtaining a plasma. However, care is preferably taken to ensure that the distance between the electrodes is greater than the spatial extension of the plasma formed, i.e. a distance typically greater than 1 mm, 2 mm, 5 mm or 10 millimeters. More preferably, the distance between the electrodes is large enough to avoid direct breakdowns by creating a vapor channel between the electrodes. This distance depends on the voltage used and is typically of the order of 1 mm to 10 mm. Preferably, the conductivity of the liquid electrolyte is chosen so that it has an electrical resistance between the first and second electrodes that is less than or equal to 20 ohms, preferably 10 ohms or 5 ohms. However, a lower conductivity is possible if the applied voltage is sufficiently high.

[0074] Alternatively or in combination, the conductivity of the liquid electrolyte is preferably greater than 1 S / m, 2 S / m, 4 S / m or 10 S / m.

[0075] The liquid electrolyte is preferably water mixed with a base or an acid. In particular, the liquid electrolyte may be a mixture of water and sodium hydroxide at a concentration of between 0.05 mol / l and 1 mol / l.

[0076] The first electrode is a wire-shaped electrode, i.e., a cylinder with a circular cross-section. Its diameter is chosen to allow plasma generation depending on the applied voltage. Plasma formation is facilitated when the diameter of the first electrode is small. A cylinder with a diameter between 0.1 mm and 2 mm is preferably chosen. A larger diameter is possible if it allows plasma to be produced.

[0077] The length of the first electrode is preferably greater than or equal to 1 cm and less than or equal to 10 m, 5 m or 10 cm. In particular, a length of around one meter is well suited in a heating installation such as a large hot water tank. In this case, a significant current flows in the circuit and the capacitor and power supply can be sized accordingly.

[0078] Preferably, the first electrode is metallic, in particular made of copper, iron, nickel, palladium, tantalum or tungsten,

[0079] The higher the voltage applied between the electrodes, the stronger the electric field, promoting the ionization of the water vapor. However, the use of high voltages requires suitable electrical equipment and stricter safety conditions. The choice of voltage used will therefore depend on the conditions of implementation of the invention. Voltages between 100 V and 4000 V are preferably used.

[0080] Advantageously, the voltage applied between the electrodes is applied in short pulses, preferably between 1 ps and 10 ms. The applied voltage may be constant during a pulse. It may be identical for each of the pulses. Alternatively, the sign of the applied voltage may be changed after a certain number of pulses have been delivered, in particular after each pulse. In this case, an alternation of positive and negative voltage pulses is obtained.

[0081] Alternatively or in combination, the frequency of the pulses may be variable. In particular, a first series of pulses may be carried out at a high frequency, followed by a pause of a duration preferably between 1 s and 10 s, then a new series of pulses may be carried out at a high frequency, with a voltage of the same sign or of the opposite sign to that used during the first series of pulses.

[0082] Other voltage time profiles can also be used.

[0083] In an exemplary implementation of the invention illustrated in Figure 11, the enclosure 11 is made of steel and has a cylindrical shape with a diameter of 13 cm and a length of 15 cm. The enclosure is open on an upper face and contains a mixture of water and soda forming a liquid electrolyte.

[0084] A first electrode 12 is immersed in the liquid electrolyte to a depth of between 0.5 cm and 3 cm. The first electrode extends along the central axis of the enclosure, at a distance of 6.5 cm from its wall. The first electrode 12 is metallic, preferably made of copper, iron, nickel, palladium, tantalum or tungsten, and is a straight cylinder with a diameter of between 0.1 mm and 2 mm.

[0085] The cylindrical wall of the enclosure 11, connected to the electrical ground, constitutes the second electrode 13.

[0086] Table 1 details the measurement results obtained for a discharge with the device described as a function of the sodium hydroxide concentration of the conductive liquid and the voltage imposed between the electrodes.

[0087] [Table 1]

[0088] For a zero concentration of sodium hydroxide, i.e. using pure water, it is found that the thermal energy generated is modest and less than the electrical energy supplied. The inventors found that no plasma forms under these experimental conditions with the configuration of the device used.

[0089] For sodium hydroxide concentrations greater than or equal to 0.1 mol / l, the inventors were able to obtain the formation of a plasma and noted that the thermal energy generated is significant, greater than the electrical energy supplied.

[0090] It is also clear from Table 1 that the current flowing in the circuit increases significantly with the sodium hydroxide concentration. Under these conditions, it may be preferable to lower the imposed voltage in order to limit the current intensity.

[0091] Figure 10 represents the evolution of current I and voltage U as a function of time t for the same device as a function of the number of discharges N.

[0092] Contrary to what is observed in Figure 5, the duration of the discharges obtained with the device according to the invention does not show any significant variation from one discharge to another: the phenomenon is stable.

[0093] Furthermore, no wear of the electrodes is observed: the performance of the device remains constant with the number of discharges. Visually, the inventors also noted that no wear is apparent on the electrodes, even after several tens of thousands of discharges.

[0094] Measurement of the thermal energy obtained To measure the thermal energy released by a discharge of the device according to the invention, the following measuring method can be used.

[0095] The principle of the measuring process consists of heating the conductive liquid to the boiling point and measuring the decrease in mass in the enclosure during discharges, which corresponds to the evaporation of part of the liquid contained in the enclosure.

[0096] Thus, the measuring method makes it possible to obtain the evaporation rate with and without discharges of the heat generating device according to the invention, which leads to the thermal energy generated by the discharges.

[0097] As illustrated in Figure 11, the measuring method uses a scale 30 on which the enclosure 11 of the heat generating device is arranged. The scale makes it possible to measure the reduction in the mass of the liquid contained in the enclosure.

[0098] The first electrode 12 is connected to the power supply 16. An insulated gate bipolar transistor acts as a switch 17 between the first electrode 12 and the power supply 16. The heat generating device also comprises a capacitor 18 arranged between the power supply and the electrical ground.

[0099] The wall of the enclosure 11 acts as a second electrode and is connected to ground.

[0100] The voltage between the first electrode 12 and the substantially cylindrical wall of the enclosure 11 acting as a second electrode is measured by a voltage measuring device 20. The current between the wall of the enclosure and the electrical ground is measured by an intensity measuring device 21.

[0101] The heat generating device according to the invention makes it possible to heat the liquid electrolyte in which the electrodes are immersed. The heat generated can be transmitted by conduction to a medium external to the device.

[0102] The enclosure 11 can thus replace the resistance of a cumulus to heat water in a water heater. Similarly, the heat generating device can be used to heat water for heating a building by replacing an electric or gas boiler. Figure 12 shows a heating installation 40 of a fluid 42 comprising a container 41 containing the fluid 42. The enclosure 11 of the heat generating device is hermetically sealed and is arranged in the container 41 in contact with the fluid, so that the heat generated in the enclosure 11 is communicated to the fluid.

[0103] The heat generated by the device can also be used to produce water vapor, either by heating a separate water tank or by directly using the water vapor produced in the enclosure 11.

[0104] Advantageously, the enclosure 11 has a volume of between 0.1 and 10 liters.

[0105] Preferably, when using a fluid heating installation, the heat generating device generates discharges of a duration of between 1 ps and 10 ms at a frequency of 0.1 Hz to 100 kHz until the fluid reaches the desired temperature.

[0106] The water vapor generated can be used in particular to cook food, to carry out vulcanization processes, to produce energy by turning a turbine, to carry out steam cracking, to hydrate a medium such as paper during production or even for cleaning and / or sterilization processes (floors, boilers, medical devices, etc.).

[0107] The inventors also observed the production of hydrogen in the hot plasma created during the discharge: the device according to the invention can therefore also enable the generation of hydrogen.

[0108] Other variations and improvements may be provided without departing from the scope of the invention.

[0109] List of cited references

[0110] [1]: “Electric discharges in water: energy balances”, Clauzon et al., Annals of the Louis de Broglie Foundation, Volume 43, number 1, pages 91-101, 2018.

Claims

Claims 1. Heat generating device (100), comprising: - an enclosure (11) containing a liquid electrolyte (14), - a first electrode (12) in the form of a wire and a second electrode (13) which extends along a surface, preferably flat, and is arranged in a so-called wire-surface configuration with the first electrode, the first and second electrodes being immersed at least partially in the liquid electrolyte, - a power supply (16) configured to generate an electrical voltage, preferably in the form of pulses, between the first and second electrodes so as to generate a plasma around the first electrode.

2. Device according to claim 1, the first electrode having a diameter between 0.1 mm and 2 mm.

3. Device according to one of the preceding claims, the distance between the first and second electrodes being greater than 1 mm, preferably 2 mm, 5 mm or 10 mm.

4. Device according to one of the preceding claims, the conductivity of the liquid electrolyte and the distance between the first and second electrodes being chosen so that the resistance of the liquid electrolyte between the latter is less than or equal to 20 ohms, preferably 10 ohms or 5 ohms.

5. Device according to one of the preceding claims, the liquid electrolyte being a mixture of water and a base or an acid, in particular a mixture of water and soda.

6. Device according to one of the preceding claims, the enclosure comprising a system for draining the liquid electrolyte in order to allow its replacement.

7. Device according to one of the preceding claims, a wall of the enclosure forming the second electrode.

8. Device according to one of the preceding claims, the enclosure having a volume of between 0.1 liters and 10 liters.

9. Installation (40) for heating a fluid (42), comprising: - a container (41) containing the fluid and - a device according to one of the preceding claims, the enclosure of the device being hermetically sealed and arranged inside the container and in contact with the fluid.

10. Method of operating the device according to one of claims 1 to 8, comprising a step consisting of applying by pulses, an electrical voltage, preferably between 100 V and 10000 V, between the first and second electrodes by means of the electrical power supply so as to generate a plasma around the first electrode.

11. Method according to the preceding claim, the voltage being applied by pulses of duration between 1 ps and 10 ms.

12. Method according to the preceding claim, the sign of the applied voltage alternating between positive and negative between two consecutive pulses.

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