CN102007814A - Heater for fluids - Google Patents

Abstract

To improve environmental protection from hydrocarbon emissions particularly from vehicles a heater (1) for fluids comprising heating elements (2, 2') of an electrically conductive monolith, wherein the heater (1) comprises a passageway for the fluid to be heated with a defined flow direction of the fluid during heating operation, the heater (1) comprising at least two heating elements (2, 21) arranged side by side inside the passageway, so that they are arranged in parallel with respect to the fluid flow, is proposed improved in that one of the at least two heating elements is a controlled heating element (21), which has a slightly larger heating power, and a temperature sensor (19) is provided at or close to the downstream end (23) of the controlled heating element (2'), and wherein the temperature sensor (19) is connected to a control means (11) for temperature control during heating operation of the heater (1); and a method of operating such a heater (1).

Description

heater for fluid

technical field

The present invention relates to a heater for a fluid, a fuel vapor storage and recovery apparatus comprising such a heater, and a method of operating such a heater comprising an electrically conductive monolithic heating element, wherein , the heater comprises a passage for the fluid to be heated, the fluid having a defined fluid flow direction during heating operation, the heater comprising at least two heating elements arranged side by side within the passage such that they are arranged in parallel with respect to the fluid flow .

Background technique

A heater of this kind is known from US 2007/0056954 A1. In particular, the use of such a heater is described therein in relation to purge heaters for fuel vapor storage and recovery equipment intended to reduce evaporative emissions from motor vehicles. The disclosed washer heater may comprise a plurality of electrical heating elements connected to a power source, such as, for example, the battery of a car. The cleaning heater may, for example, comprise electrically conductive ceramics as heating elements.

Alternatively, the purge heater may comprise conductive carbon, preferably porous monolithic carbon. Such porous monolithic carbons are disclosed, for example, in US 2007/0056954 A1. These monolithic carbon heating elements have a channel structure that allows air to flow through the heating element and thus allows enhanced heat transfer directly to purge air drawn in from the atmosphere.

An important use of such heaters is in fuel vapor storage and recovery equipment to reduce evaporative emissions from motor vehicles. Fuel vapor storage and recovery facilities including fuel vapor storage tanks have been known in the art for many years. Gasoline fuel used in many internal combustion engines is extremely volatile. The evaporative emission of fuel vapors from vehicles with internal combustion engines occurs mainly due to the venting of the vehicle's fuel tank. When the vehicle is parked, changes in temperature or pressure cause air laden with hydrocarbons to escape from the fuel tank. A part of the fuel inevitably evaporates into the air inside the tank and thus assumes the form of vapor. If the air emanating from the fuel tank is allowed to flow undisposed into the atmosphere, it will inevitably carry this fuel vapor with it. There are some government regulations regarding how much fuel vapor can escape from a vehicle's fuel system.

Typically, to prevent the loss of fuel vapors into the atmosphere, the fuel tank of an automobile is vented through a duct to a canister that contains a suitable fuel absorbing material, such as activated carbon. High surface area activated carbon particles are widely used and temporarily absorb fuel vapors.

Fuel vapor storage and recovery including fuel vapor storage tanks (so-called canisters) when the vehicle is parked for extended periods of time and when the vehicle is being refueled and vapor-laden air is being expelled from the fuel tank (refueling emissions) The system must cope with fuel vapor emissions.

In fuel recovery systems for the European market, refueling emissions are usually not a significant issue because these refueling emissions are generally not vented through the canister. However, in integrated fuel vapor storage and recovery systems for the North American market, these refueling emissions are also vented through the canister.

Due to the nature of the absorbent in the carbon canister, it is clear that the canister has a limited filling capacity. It is generally desirable for canisters to have a high carbon working capacity, however, it is also desirable for canisters to be relatively small for design purposes. In order to ensure that the canister always has sufficient carbon working capacity under typical operation of an internal combustion engine, a certain negative pressure is applied to the interior of the canister from the engine's air intake system through the canister's fuel vapor discharge port. By this, ambient air is let into the canister from the ambient air intake port to pick up the trapped fuel vapors and carry them through the fuel vapor exhaust port to the intake manifold of the engine's air intake system. During this canister purge mode, fuel vapors stored in the canister are burned in the internal combustion engine.

Despite the effectiveness of current fuel vapor storage and recovery systems, there is still residual emission of hydrocarbons that are directed into the atmosphere. These so-called "leakage emissions" (Diurnal Breathing Loss, DBL) are driven by diffusion, especially when high hydrocarbon concentration gradients exist between the atmospheric vent port of the canister and the absorbent. When it is possible to reduce the hydrocarbon concentration gradient, see-through emission can be significantly reduced. Clearly, this can be achieved by increasing the working capacity of the canister.

However, it should also be clear that only a certain percentage of the hydrocarbons stored in the canister can be effectively purged or vented during the purge mode. This can be a problem for cars with limited cleaning time, such as in electric hybrid cars, where the operating mode of the internal combustion engine is relatively short.

Another problem arises with regard to so-called flexi fuels, which include significant amounts of ethanol. Ethanol is a highly volatile fuel with a relatively high vapor pressure. For example, so-called E10 fuel (10% ethanol) currently has the highest steam production on the market. This means that the canister draws in extremely high levels of fuel vapors from the fuel tank. On the other hand, during the normal purge mode of a conventional canister, only a certain percentage of the inhaled fuel vapors can be expelled. As a result, the fuel vapor capacity of ordinary canisters is depleted relatively quickly. Thus, the leakage emissions of a fully loaded canister usually increase to a point beyond the emission values given by law.

In order to improve the cleaning removal rate during cleaning mode, several vapor storage and recovery devices have been proposed which use so-called cleaning heaters. By heating the ambient air directed into the tank through the ambient air inlet ports, the removal efficiency of hydrocarbons trapped in the micropores of the absorbent is significantly improved.

For example, US 6,230,693 B1 discloses an evaporative emission control system which reduces the amount of fuel vapor emitted from a vehicle by providing an auxiliary tank which operates together with a storage tank of the evaporative emission control system. The storage tank contains the first adsorbent material and has a vent port in communication therewith. The auxiliary tank includes a housing, first and second channels, heaters and connectors. Inside the housing, the second adsorbent material is in full contact with the heater. During the regeneration phase of operation of the control system, the heater may be used to heat the second sorbent material and passing purge air. This enables the second and first adsorbent materials to more easily release the fuel vapors they adsorbed during the previous storage phase of operation so that they can be burned out during internal combustion.

Furthermore, the storage tank of the evaporative emission control system according to US 6,230,693 comprises two side-by-side fuel vapor chambers connected by a flow channel. Specifically, tank separation actually implies flow restriction. Because the driving pressure through the tank is very low, keeping flow restrictions to a minimum was an important design consideration.

Contents of the invention

It is an object of the present invention to provide a heater for a fluid, and a fuel vapor storage and recovery device, the heater comprising a conductive monolithic heating element, wherein the heater comprises passages for the fluid to be heated, The fluid has a defined direction of fluid flow during the heating operation, the heater comprises at least two heating elements arranged side by side in the channel so that they are arranged in parallel with respect to the fluid flow, the heater is simple, compact and reliable in design , and allows for easy and efficient controlled operation, the fuel vapor storage and recovery device has improved fuel recovery efficiency. Yet another object is to provide a method for operating such a heater which allows easy and efficient controlled operation.

These and other objects are achieved by a heater for fluids comprising an electrically conductive monolithic heating element, wherein the heater comprises passages for a fluid to be heated having a defined direction of fluid flow during heating operation , the heater comprises at least two heating elements arranged side by side in the passage such that they are arranged parallel to the fluid flow, characterized in that one of the at least two heating elements is a controlled heating element having Slightly larger heating power, and a temperature sensor is provided at or near the downstream end of the controlled heating element, and wherein the temperature sensor is connected to the control device for temperature control during heating operation of the heater.

The arrangement according to the invention ensures both improved safety and improved efficiency of such a heater. The arrangement of the temperature sensor with the heating element (which has a slightly greater heating power) ensures that the heater is effectively controllable for the maximum temperature, thus preventing overheating of the heater, on the one hand preventing the risk of fire, and on the other hand allowing control close to the maximum temperature, thus increasing the efficiency of the heater. A temperature sensor located at or near the downstream end of the heating element minimizes the effect of changing flow rates of the fluid, ie significantly reduces the adverse effect of flow changes on the heating performance of the heater.

A fuel vapor storage and recovery device comprising a heater according to the invention, with the advantages of the invention described above, is particularly effective for motor vehicles with cyclic operation of the engine (e.g. gasoline/electric hybrid drive) . It is typical for this type of drive that when switching to electric drive, the engine is shut down and the purge air flow through the fuel vapor storage and recovery device exhibits a rapid change from high to low. For conventionally designed heaters, this rapid change in purge air flow creates a high risk of overheating the fuel vapor storage and recovery equipment, which creates a significant fire hazard, or the heater needs to be controlled to temperatures well below the critical temperature, thus providing poor recovery performance. For this application, however, recovery performance is critical due to the reduced operating time of gasoline engines.

A particularly useful, fail-safe embodiment of the invention is characterized in that at least two heating elements are electrically connected in series with each other, and that the controlled heating element has a greater electrical resistance than the other heating elements.

An alternative embodiment is characterized in that at least two of the heating elements are electrically connected in parallel to each other, and that the controlled heating element has a lower electrical resistance than the other heating elements.

A further useful embodiment of the invention is characterized in that the heater comprises more than two heating elements and that the heating elements are grouped together, wherein the heating elements of a group are electrically connected to each other in series, and the groups of heating elements are mutually connected to each other. Electrically connected in parallel, wherein the group comprising the controlled heating element has a lower resistance than the other group of heating elements, and the controlled heating element has a greater resistance than the other heating elements of the same group, or is characterized in that the heater comprises More than two heating elements, and the heating elements are grouped together, wherein the heating elements of a group are electrically connected in parallel to each other, and the groups of heating elements are electrically connected to each other in series, wherein the groups comprising the controlled heating elements has a greater resistance than the other set of heating elements, and the controlled heating element has a lower resistance than the other heating elements of the same set.

A preferred embodiment of the heater according to the invention is characterized in that the heating element comprises a conductive carbon monolith which is a porous carbon monolith having a honeycomb structure, when the porous carbon monolith has channels When the channel size is between 100 μm and 2000 μm, more specifically when the porous carbon monolith has an open area (open area) between 30% and 60% in the cross-section perpendicular to the flow path in the channel In particular, the honeycomb structure allows a substantial portion of the fluid flow to pass through the monoliths within the channels.

Particularly good performance of the heater according to the invention in a typical automotive environment with a conventional 12V DC power supply is obtained if the heating element is arranged with a total resistance of not more than 2.5 ohms, preferably not more than 1 ohm, more preferably about 0.8 ohms .

When the temperature sensor is a thermistor, the heater according to the invention is especially able to prevent the risk of fire in the event of a short-circuit of the temperature sensor connections.

The above and other objects are achieved by a fuel vapor storage and recovery device comprising a heater as described above, and by a method for operating a heater or a fuel vapor storage and recovery device as described above in a vehicular environment, the method comprising the steps of: obtaining a refueling signal indicating that a vehicle fuel tank in fluid communication with the heater has been refueled; and powering the heater for no more than 45 minutes/24 hours, preferably about 30 minutes/24 hours, from engine start after refueling 24 hours while controlling power to the heater in response to a temperature signal from a temperature sensor.

In a preferred embodiment of the method according to the invention, the method further comprises the steps of: obtaining a fuel level signal from a fuel gauge; Power supply, wherein the predetermined reading is 1/3 of the fuel tank capacity, preferably 1/4 of the fuel tank capacity. At such low fuel levels, the fuel vapors generated do not cause a significant increase in tank pressure. Accordingly, the vapor load of the fuel vapor storage and recovery plant is low, and the recovery efficiency is sufficient without the aid of heating at any ambient temperature. Also, when the fuel tank is fueled and fuel vapors flow through the canister at high flow rates in an integrated system, the efficiency of the canister reduces emissions due to the exothermic effect during adsorption, using a cold carbon bed in the canister much better.

Energy savings can also be achieved by stopping power to the heater under all operating conditions if the ambient temperature is below a predetermined value, preferably below -7°C, more preferably below -10°C. At such low temperatures, less fuel vapor is generated within the fuel tank, and the fuel vapor storage and recovery device will be sufficiently efficient even without heating.

When the control of the power supplied to the heater includes pulse width modulation of the power supplied to the heater, energy loss through the heat sink can be minimized and power can thus be saved.

In a particularly preferred embodiment, the method further comprises the steps of: performing at least one test cycle; and, if one or more of the following conditions are met, stopping power to the heater and sending a fault signal to the vehicle Diagnostic system: Malfunction detected in temperature sensor circuit; heater control self-test failure; detection of increase in resistance of individual heater element arrangement beyond a predetermined value; and supply voltage exceeding a predetermined maximum value, or falling to a predetermined minimum value below. More preferably, the fault detected in the temperature sensor circuit includes one of: an open circuit in the thermistor circuit; a short circuit in the thermistor circuit; and a bad thermistor contact. This embodiment enables improved fail-safe operation, taking into account the fact that improper handling (in particular uncontrolled heating) may cause a fire hazard.

Detection of an increase in resistance of a monolithic heater element arrangement is an indication that one of the heater elements has failed or is disconnected. It is also an indication of impending operational failure of the expected heater and fuel vapor storage and recovery equipment (if such equipment uses said heater). With this embodiment of the method according to the invention, the legal requirements for on-board diagnostics of emission control devices can be met.

Best recovery performance and safe operation are obtained when the electrical power to the heater is controlled such that the temperature at the temperature sensor is from about 132°C to about 145°C, preferably to about 140°C.

Description of drawings

The invention is described below by way of non-limiting examples with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a heater according to the invention, including a simplified wiring scheme;

Figure 2 shows an enlarged cross-sectional view of two adjacent heater element end sections;

Figure 3 represents a cross-sectional view in the plane indicated in Figure 2; and

Figure 4 shows a sectional view through a carbon canister comprising a heater according to the invention.

Detailed ways

Figure 1 schematically depicts a heater for a fluid, generally designated by the numeral 1, according to one embodiment of the present invention. The heater 1 comprises a conductive monolithic heating element 2 . The heater 1 according to the invention can well be used with a fuel vapor storage and recovery device 3 shown in FIG. 4 . Such a fuel vapor storage and recovery device 3 is commonly called a canister, and is typically used as part of the emission control system of motor vehicles with gasoline-powered engines. The illustration is schematic and elements have not been drawn to scale.

A fuel vapor storage and recovery device or canister 3 includes a vapor inlet port 4 connected to a fuel tank (not shown), and a vent port 5 to communicate with the atmosphere, and to an internal combustion engine of a motor vehicle (also not shown) Clean port 6. The canister 3 is filled with absorbent in the form of granular activated carbon.

During shutdown of the motor vehicle's engine, the canister 3 is connected to the fuel tank of the motor vehicle via the vapor inlet port 4 and to the atmosphere via the vent port 5 . During the engine running cycle of the car, a flow path will be established between the vent port 5 and the purge port 6 . The internal combustion engine sucks a certain amount of air to be combusted in the combustion chamber of the internal combustion engine from the atmosphere through the canister 3 through the vent port 5 into the purge port 6, thereby cleaning the absorbent of the canister 3 and supplying the hydrocarbons removed from the canister into the combustion chamber of the engine. In the drawing, arrows indicate air flow paths during cleaning of the canister 3 . The terms "downstream" and "upstream" in the context of this description always refer to the gas flow during the cleaning of the canister 3, which is defined by the flow direction of the fluid during the heating operation.

The carbon canister 3 includes a first vapor storage chamber 7 , a second vapor storage chamber 8 and a third vapor storage chamber 9 . The first vapor storage chamber 7 is the vapor storage chamber immediately after the vapor inlet port 4 and is also the largest vapor storage chamber in terms of gas flow during hydrocarbon loading to the carbon canister 3 .

It is evident from Fig. 4 that the vapor storage chambers 7, 8, 9 have a circular cross-section and are arranged in concentric relation to each other. The first vapor storage chamber 7 surrounds the vapor storage chambers 8 and 9 . Immediately after the vent port 5, at the upstream side of the third vapor storage chamber 9, a purge heater chamber 10 is arranged, which is also cylindrical in shape, ie circular in cross section.

The wash heater chamber 10 has at its upstream face two inlet openings 12 which allow ambient air to be drawn into the wash heater chamber 10 . The cleaning heater chamber 10 has a relatively thin-walled surrounding wall 13 which is designed such that heat radiation from the heater 1 can be transferred into the surrounding carbon bed of the first vapor storage chamber 7 . The surrounding wall 13 of the heater 1 defines a passage for the fluid, which is the air flow through the heater 1 .

As can be easily seen from Figures 1 and 4, the heater 1 preferably comprises four heating elements 2 arranged side by side in a heater chamber 10 forming a passage. The individual heating elements 2 are arranged in parallel with respect to the air flow through the heater chamber 10 .

The heating element 2 may be cylindrical in shape and comprise an electrically conductive porous carbon monolith, like for example a synthetic carbon monolith. A method of manufacturing such a carbon monolithic heating element 2 is generally disclosed in document US 2007/0056954 A1 and in more detail in paragraphs [0013] to [0024], which document is hereby incorporated by reference. The carbon monolith is a porous carbon monolith having a cell structure that allows the majority of fluid flow to pass through the monolith. Each heating element 2 provides a continuous longitudinal channel (not shown) allowing gaseous fluid flow through each heating element 2 in the longitudinal direction. The channels within the porous carbon monolith may have dimensions between 100 μm and 2000 μm. The porous carbon monolithic heating element has an open area of between 30% and 60% in a cross-section perpendicular to the flow path in the channel.

A suitably typical heating element 2 may have a diameter of about 10mm and a typical length of about 50mm. Each heating element 2 operates as a resistive heating element. In a preferred embodiment shown in the figures, four electric heating elements 7 are electrically connected in series and to a control and switching device 11 which in turn is connected to the As a power source for the vehicle's generator and battery.

The heating element 2 is connected to a control and switching device 11 via a power cord 16 and a copper connector 17 . The interconnection of the individual heating elements 2 is provided by connectors 18 . The arrangement of the individual heating elements 2 provides a total resistance of not more than 2.5 ohms, preferably about 0.8 ohms. In order to provide approximately 75 watts of heating power at a supply voltage of 13.7V, some sort of power regulation is required.

A suitable method of controlling the supplied power is pulse width modulation (PWM). The main advantage of this approach is the low power losses in the control and switching means 11 . The control and switching arrangement 11 itself may be less expensive, although PWM operation requires certain auxiliary electrical components to minimize adverse feedback in the vehicle power grid and to provide electromagnetic compatibility (EMC). In addition, space and possible ventilation for otherwise large heat sinks that would otherwise be required can be saved, with an overall advantage in terms of cost and space required.

However, conventional current regulator circuits can also be used, but cooling is required. Conventional current regulation is also advantageous if the dissipated heat can be used for some other purpose.

One of the heating elements 2 has a slightly higher heating power than the other heating elements 2 . This heating element defines the controlled heating element 2'. A temperature sensor in the form of a thermistor 19 is arranged at or near the downstream end 23 of the controlled heating element 2'. A temperature sensor 19 is connected to the control device 11 via wires 20 and 21 for temperature control during the heating operation of the heater 1 . In the illustrated embodiment of four heating elements 2, 2' connected in series, the controlled heating element 2' has a slightly greater length than the other heating elements 2, eg 53 mm. The controlled heating element 2' has a slightly higher electrical resistance than the other heating elements 2 due to the same diameter and thus the same cross-sectional area. Preferably, the thermistor 19 is mounted approximately 50 mm from the upstream end 22 of the controlled heating element 2', corresponding to the location of the downstream end 23 of the other heating element 2, at the downstream end of the controlled heating element 2' In the opening in the section, as shown in more detail in FIGS. 2 and 3 . This arrangement only ensures that the thermistor 19 detects the temperature at the hottest part of the heater.

The control and switching device 11 is also connected via a data line 24 to an on-board diagnostic system and via, for example, a CAN bus 25 to other devices of the vehicle. Of course, it will be apparent to those skilled in the art that other suitable wiring is also possible.

The heating element 2 will only be activated during the cleaning operation of the fuel vapor storage and recovery device 3, as described in more detail below. As explained above, during a standstill of the vehicle, the fuel in the fuel tank evaporates into the air space above the maximum fill level of the fuel tank. This steam-laden air flows into the carbon canister 3 through the steam inlet port 4 . During the refueling of a car, where usually the internal combustion engine is also shut down, in so-called integrated systems, the fuel being pumped into the fuel tank causes an air flow through the vapor inlet port 4, the flow of which air flow is equal to the flow of refueling Corresponding. Correspondingly, hydrocarbon-laden air is pumped into the carbon bed of the carbon canister 3 at a flow rate of up to 60 liters/minute. The activated carbon inside the canister absorbs hydrocarbons, and the hydrocarbon molecules are trapped within the carbon's internal microporous structure. More or less cleaned air will be expelled from the vent port 5 . The efficiency of absorption at such high flow rates is better if the carbon bed is cold due to the exothermic effect that accompanies absorption. Therefore, it is advantageous to suppress the heating operation of the heater 1 at low fuel levels in the fuel tank for refueling requirements.

During the operating cycle of the internal combustion engine of the vehicle, the fuel vapor storage and recovery device 3 according to the invention is set into a purge mode. Ambient air is drawn by the internal combustion engine of the vehicle from the ventilation port 5 through the inlet opening 12 into the washer heater chamber 10 . During washing, the heating element 2 is supplied with electrical energy by the vehicle's generator or battery. The air flows through and around the heating element 2, thereby being heated to a temperature below 150°C but in no case exceeding 150°C. At the same time, the radiant heat emitted by the heating element 2 heats the surrounding carbon bed of the first vapor storage chamber 7 . The heated air flows through the third vapor storage chamber 9 . On its way, the ambient air will be loaded with hydrocarbons stored in the carbon bed. This air flow, as indicated by the arrows in Figure 4, flows into and through the carbon bed of the first vapor storage chamber 7 and is finally drawn through the purge port 6 to the purging line, This purge line leads to the internal combustion engine.

A method of operating a heater 1 used in a fuel vapor storage and recovery device 3 in a vehicular environment comprises the steps of obtaining a refueling signal via the CAN bus 25 indicating that the vehicle tank has been refueled. Such a signal may be obtained from a fuel cap switch that detects a closed fuel cap. If the signal is present, the heater 1 will be energized for no more than 45 minutes in 24 hours from the start of the engine, preferably about 30 minutes every 24 hours, while being controlled to the heater 1 in response to the temperature signal from the temperature sensor 19 electricity. With regard to the embodiment described above, the thermistor 19 is calibrated to a temperature of 140° C. to provide the best compromise between recovery efficiency and safety.

Also, the fuel level signal will also be obtained from the fuel gauge via the CAN bus 25, and if the fuel level signal indicates that the fuel level has dropped to a predetermined reading, preferably 1/4 of the fuel tank capacity, as described above for refueling , the heater 1 will not be powered.

Energy savings can be achieved by stopping power to the heater 1 under all operating conditions if the ambient temperature is below a predetermined value, eg below -10°C. An external temperature signal may also be provided via the CAN bus 25, or otherwise obtained from the motor management system. The control and switching device 11 preferably performs at least one test cycle, for example, before supplying power to the heater 1, and if one or more of the following conditions occur, then stop supplying the power to the heater 1, and send a fault signal via the data line 24 to On-Board Diagnostic System: Malfunction detected in the circuit of thermistor 19 and wires 20 and 21; self-test of heater controller 11 failed, or increase in resistance of monoblock heater element 2 beyond a predetermined value detected, A failure in one of the heater elements 2 is thus indicated, such as a broken single piece or a disconnection; etc. A damaged or disconnected heater element 2 will disable the canister 3 which is part of the emission control system and the fault condition needs to be indicated to the driver. Preferably, a limp-home mode will be activated to allow the driver to go home and take the car to a repair shop.

Faults detected in the temperature sensor circuits 19, 20, 21 include one of the following: an open circuit in the wiring 20, 21; a short circuit in the thermistor 19; and a bad thermistor 19 contact. This embodiment ensures an improved fail-safe operation, taking into account the fact that improper handling (especially uncontrolled heating) may cause a fire hazard.

In addition, when the power supply voltage exceeds a predetermined maximum voltage value, or falls below a predetermined minimum voltage value, the control and switching device 11 will stop supplying power to the heater 1 to avoid damage or failure such as overheating.

The best recovery performance and safe operation are obtained when the electric power to the heater 1 is controlled by the control and switching device 11 such that the temperature at the temperature sensor 19 is from about 132° C. to about 145° C., preferably to about 140° C., thereby preventing Any part of the heater 1 that is in contact with the air/gasoline vapor mixture continuously exceeds 150°C.

Claims (21)

1. A heater (1) for a fluid comprising a conductive monolithic heating element (2, 2'), wherein said heater (1) comprises a passage for a fluid to be heated, the fluid Having a defined direction of fluid flow during heating operation, said heater (1) comprises at least two heating elements (2, 2') arranged side by side within said passage such that they are arranged parallel with respect to the fluid flow, which It is characterized in that one of the at least two heating elements is a controlled heating element (2'), which has a slightly larger heating power, and in which the controlled heating element ( 2′) at or near the downstream end (23) is provided with a temperature sensor (19), and wherein the temperature sensor (19) is connected to the control device (11), at the heater (1) Used for temperature control during heating operations. 2. The heater (1) according to claim 1, characterized in that said at least two heating elements (2, 2') are electrically connected to each other in series, and said controlled heating element (2') has Greater resistance than other heating elements (2). 3. The heater (1) according to claim 1, characterized in that said at least two heating elements (2, 2') are electrically connected in parallel to each other, and said controlled heating element (2') has Lower resistance than other heating elements (2). 4. The heater (1) according to any one of the preceding claims, characterized in that the heater (1) comprises more than two heating elements (2, 2') and that the heating The elements are grouped together, wherein the heating elements in a group are electrically connected to each other in series, and the groups of heating elements are electrically connected to each other in parallel, wherein the group comprising the controlled heating elements has a higher small resistance, and said controlled heating element (2') has a larger resistance than other heating elements in the same group. 5. The heater (1) according to any one of claims 1 to 3, characterized in that the heater (1) comprises more than two heating elements (2, 2'), and the heating The elements are grouped together, wherein the heating elements in a group are electrically connected to each other in parallel, and the groups of heating elements are electrically connected to each other in series, wherein the group comprising said controlled heating element (2') has a specific heating The other set of elements has a larger resistance, and the controlled heating element has a lower resistance than the other heating elements in the same set. 6. The heater (1) according to any one of the preceding claims, characterized in that the heating element (2, 2') comprises a conductive carbon monolith which is a porous carbon monolith , the porous carbon monolith has a honeycomb structure that allows a substantial portion of fluid flow to pass through the monolith within the passageways. 7. The heater (1) according to claim 6, characterized in that the porous carbon monolith has channels with a channel size between 100 μm and 2000 μm. 8. The heater (1) according to claim 6 or 7, characterized in that the porous carbon monolith has a cross-section between 30% and 60% in a cross-section perpendicular to the flow path in the passage. open area between. 9. The heater (1) according to any one of the preceding claims, characterized in that the heating elements (2, 2') are arranged such that the total resistance does not exceed 2.5 ohms, preferably not more than 1 ohms, More preferably about 0.8 ohms. 10. The heater (1 ) according to any one of the preceding claims, characterized in that the temperature sensor is a thermistor (19). 11. A fuel vapor storage and recovery device (3) comprising a heater (1) according to any one of the preceding claims and a control device (11). 12. A method for operating a heater (1) according to any one of claims 1 to 10 or a fuel vapor storage and recovery device (3) according to claim 11 in a vehicular environment comprising the following step: i) obtaining a refueling signal indicating that a vehicle fuel tank in fluid communication with said heater (1) has been refueled, and ii) power is supplied to said heater (1) for no more than 45 minutes/24 hours from engine start after refueling, Simultaneously, the power supplied to the heater (1) is controlled in response to a temperature signal from a temperature sensor (19). 13. The method according to claim 12, characterized in that the power supply of step ii) is about 30 minutes/24 hours. 14. The method according to claim 12 or 13, further comprising the step of: iii) obtain a fuel level signal from the fuel gauge, and iv) preventing power to the heater (1) if the fuel level signal indicates that the fuel level has dropped to a predetermined reading. 15. The method according to claim 14, characterized in that the predetermined reading of step iv) is 1/3, preferably 1/4. 16. The method according to any one of claims 12 to 15, further comprising the step of v) Stopping power to said heater (1) under all operating conditions if the ambient temperature is below a predetermined value. 17. The method according to claim 16, characterized in that the temperature of step v) is -7°C, preferably -10°C. 18. A method according to any one of claims 12 to 17, further comprising the steps of: performing at least one test cycle; and stopping power to the heater (1) if one or more of the following conditions are met, and Send fault signal to OBD: a) a fault is detected in the temperature sensor circuit, b) the self-test of the heater control device (11) failed, c) an increase in the resistance of the monolithic heater element (2, 2') arrangement beyond a predetermined value is detected, and d) The supply voltage exceeds a predetermined maximum value, or falls below a predetermined minimum value. 19. The method of claim 18, wherein the fault detected in the temperature sensor circuit comprises one of the following: - open circuit of the thermistor circuit, - a short circuit in the thermistor circuit, and - Bad thermistor contact. 20. The method according to any one of claims 12 to 19, wherein the power supplied to the heater (1) is controlled such that the temperature at the temperature sensor (19) is from about 132°C to about 145°C, preferably to about 140°C. 21. A method according to any one of claims 12 to 20, wherein the controlling of the power supplied to the heater (1) comprises pulse width modulation of the power supplied to the heater (1).

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