阅读说明：本技术 热管理方法和设备 (Thermal management method and apparatus ) 是由 L.M.菲利普 于 2018-12-04 设计创作，主要内容包括：本公开涉及热管理系统(2),所述热管理系统(2)被配置为加热由金属构成的导管(4)。热管理系统(2)包括发电机(16),用于以高频率生成交流电流。提供第一和第二电连接件(19、20),用于将发电机(16)连接到导管(4)。在使用中,发电机(16)以高频率将交流电流输出到第一和第二电连接件(19、20),交流电流被引入到导管(4)中,并且导致导管(4)的直接加热。本公开还涉及包括热管理系统(2)的排放系统(1),并且涉及加热导管(4)的相关方法。(The present disclosure relates to a thermal management system (2), the thermal management system (2) being configured to heat a conduit (4) composed of metal. The thermal management system (2) comprises a generator (16) for generating an alternating current at a high frequency. First and second electrical connections (19, 20) are provided for connecting the generator (16) to the conduit (4). In use, the generator (16) outputs alternating current at high frequency to the first and second electrical connections (19, 20), which alternating current is introduced into the conduit (4) and causes direct heating of the conduit (4). The disclosure also relates to an exhaust system (1) comprising the thermal management system (2), and to a related method of heating a conduit (4).)

1. Thermal management system (2) for heating a conduit (4) made of metal, comprising:

a generator (16) for generating an alternating current at a high frequency; and

-first and second electrical connections (19, 20) for connecting said generator (16) to said conduit (4);

wherein, in use, the generator (16) outputs an alternating current at a high frequency to the first and second electrical connections (19, 20), the alternating current being introduced into the conduit (4) and causing direct heating of the conduit (4).

2. The thermal management system (2) of claim 1, wherein the generator (16) is configured to output an alternating current at a frequency greater than or equal to 100 hertz (Hz).

3. The thermal management system (2) of claim 1, wherein the generator (16) is configured to output an alternating current at a frequency greater than or equal to 1 kilohertz (kHz).

4. The thermal management system (2) of claim 1, wherein the generator (16) is configured to output an alternating current at a frequency greater than or equal to 10 kilohertz (kHz).

5. The thermal management system (2) of claim 1, wherein the generator (16) is configured to output an alternating current at a frequency greater than or equal to 100 kilohertz (kHz).

6. The thermal management system (2) of any of the preceding claims, wherein the motor (16) is reconfigurable for outputting alternating current at different frequencies.

7. The thermal management system (2) of any of the preceding claims, wherein the generator (16) is configured to output an alternating current having a magnitude less than or equal to one of: 50 amps or 20 amps.

8. The thermal management system (2) of any of the preceding claims, wherein, in use, the voltage in the conduit (4) is less than or equal to 60 volts, or less than or equal to 48 volts.

9. The thermal management system (2) of any of the preceding claims, wherein the first and second electrical connectors (19, 20) each comprise a cable comprising a plurality of strands of individually insulated electrical wires.

10. The thermal management system (2) of any of the preceding claims, comprising a fault detection module for identifying when the resistance exceeds a predetermined threshold or is outside a predetermined operating range.

11. Exhaust system (1) comprising a thermal management system according to any of the preceding claims and at least one conduit (4) to which said first and second electrical connections are connected.

12. The exhaust system (1) according to claim 11, wherein said at least one conduit (4) is electrically isolated.

13. The exhaust system (1) according to claim 12, wherein said at least one conduit (4) is supported by one or more supports (6), said one or more supports (6) each comprising an electrical insulator for electrically isolating said conduit (4).

14. The discharge system (1) according to any one of claims 11, 12 or 13, comprising a first and a second coupling (9, 11) provided at respective ends of said at least one conduit (4), said first and second couplings (9, 11) each comprising an electrically insulating coupling.

15. The discharge system according to any one of claims 11 to 14, wherein said at least one conduit (4) is made of stainless steel.

16. The discharge system according to any one of claims 11 to 14, wherein said at least one conduit (4) is constituted by a magnetic material.

17. A method of heating a conduit comprised of metal, the method comprising:

-using an electric generator (15) to introduce an alternating current into the conduit (4), said alternating current being introduced directly into the conduit at a high frequency to heat the conduit (4) by joule effect.

18. The method of claim 17, wherein the alternating current is at a frequency greater than or equal to 100 hertz (Hz).

19. The method of claim 17, wherein the alternating current is at a frequency greater than or equal to 1 kilohertz (kHz).

20. The method of claim 17, wherein the alternating current is at a frequency greater than or equal to 10 kilohertz (kHz).

21. The method of claim 17, wherein the alternating current is at a frequency greater than or equal to 100 kilohertz (kHz).

22. The method of any of claims 17-21, wherein the alternating current has a magnitude less than or equal to one of: 50 amps or 20 amps.

23. The method of any one of claims 17 to 22, wherein the voltage in the conduit is less than or equal to 60 volts, or less than or equal to 48 volts.

24. The method of any of claims 17 to 23, comprising: modifying the frequency of the alternating current in accordance with one or more parameters of the catheter (4).

25. The method of any of claims 17 to 24, comprising: monitoring the electrical resistance of the conduit (4) to detect a fault.

26. The method of claim 25, comprising: detecting a fault when the resistance exceeds a predetermined threshold or is outside a predetermined operating range.

27. A non-transitory computer readable medium having stored therein a set of instructions that, when executed, cause a processor to perform the method of any of claims 19 to 26.

Technical Field

The present disclosure relates to thermal management methods and apparatus. In particular, but not exclusively, the present disclosure relates to a thermal management system for a conduit, an exhaust system comprising a thermal management system and a method of heating a conduit.

Background

An exhaust system 101 including a known Thermal Management System (TMS) 102 is shown in fig. 1. TMS 102 is operable to control the temperature of conduit 104, which conduit 104 is used to deliver process gas for use in an industrial process. For example, an exhaust system 101 may be provided to transport deposition gases and associated powders exhausted from a Chemical Vapor Deposition (CVD) process. TMS 102 includes controller 115 and a plurality of resistive heater pads 123. The controller 115 is configured to supply current to each of the resistive heater pads 123. The resistive heater pads 123 are spaced apart from each other and are disposed along the length of the conduit 104. The resistive heater mats 123 may each be one (1) meter in length, so for a conduit 104 that is ten (10) meters in length, it may be necessary to provide ten (10) of said resistive heater mats 123. If the conduit 104 has a complex geometry, for example, including one or more bends or valves, it may be necessary to provide additional resistive heater mats 123. In use, the resistive heater mat 123 is heated and the conduit 104 is heated by thermal conduction. However, heat transfer from the resistive heater pad 123 to the conduit 104 may be poor, particularly on stainless steel, which is a poor thermal conductor. The resistive heater mat 123 may be difficult to install, particularly if the conduit 104 has a complex geometry. In addition, the heat transfer from the resistive heater mat 123 depends on the quality of the fit onto the conduit 104, which depends on the operator. The resistive heater mat 123 may also be susceptible to failure and defects.

The present invention seeks to overcome or ameliorate at least some of the problems associated with prior art systems.

Disclosure of Invention

Aspects of the invention relate to a thermal management system, an exhaust system comprising a thermal management system, a method of heating a conduit, and a non-transitory computer readable medium, as claimed in the appended claims.

According to an aspect of the invention, there is provided a thermal management system for heating a conduit composed of metal, the thermal management system comprising:

a generator for generating an alternating current at a high frequency; and

first and second electrical connections for connecting the generator to the conduit;

wherein, in use, the generator outputs alternating current at a high frequency to the first and second electrical connections, the alternating current being introduced into the conduit and causing direct heating of the conduit. In use, an alternating current is introduced directly into the conduit. The supply of alternating current results in direct heating of the catheter by joule effect. Thus, heat is generated in the core of the conduit. By heating the conduit itself (rather than a resistive heater mat positioned against its outer surface), heat transfer can be improved. By supplying alternating current at a high frequency, the effective resistance of the conductor is increased. Thus, there may be a greater power dissipation into the conduit (also referred to as I2R losses), which may result in increased heating, at least in certain embodiments, as compared to prior art systems. In at least some embodiments, the magnitude of the alternating current is lower than the direct current required to provide equivalent heating.

The same current flows through the conduit between the connections established by the first and second connectors. Thus, the temperature may be at least substantially uniform along the length of the conduit. A single temperature measurement located somewhere along the conduit (e.g., by a thermocouple or other temperature sensor) may be sufficient to monitor the temperature within that section. The first electrical connector may be connected at or near a first end of the conduit and the second electrical connector may be connected at or near a second end of the conduit. In this arrangement, the conduit may be heated along its length.

The thermal management system may be used to provide heating of conduits having complex shapes (e.g., including check valves, bends, etc.). The need to provide a separate resistive heater mat is reduced or eliminated.

The generator may comprise an Electrical Control Unit (ECU) for controlling the frequency and/or magnitude of the generated alternating current. The ECU may include one or more processors.

In at least some embodiments, the alternating current introduced into the conduit has a frequency sufficiently high to cause the current to flow primarily in the outer region of the conductor (commonly referred to as the "skin" of the conductor). The skin may have a depth equal to or less than the thickness of the conductor. The term "high frequency" as used herein may be understood to refer to frequencies greater than or equal to 100 hertz.

The generator may be configured to output an alternating current at a frequency greater than or equal to 100 hertz (Hz).

The generator may be configured to output an alternating current at a frequency greater than or equal to 1 kilohertz (kHz).

The generator may be configured to output an alternating current at a frequency greater than or equal to 10 kilohertz (kHz).

The generator may be configured to output an alternating current at a frequency greater than or equal to 50 kilohertz (kHz).

The generator may be configured to output an alternating current at a frequency greater than or equal to 100 kilohertz (kHz).

The generator may be configured to output an alternating current at a frequency of less than or equal to 500 kilohertz (kHz). In certain embodiments, the generator may be configured to output an alternating current at a frequency greater than 500 kilohertz (kHz).

The motor may be reconfigurable for outputting alternating current at different frequencies.

The generator may be configured to output an alternating current having a magnitude less than or equal to one of: 50 amps or 20 amps.

In use, the voltage in the conduit may be less than or equal to 60 volts, or less than or equal to 48V.

For example, the first and second electrical connectors may each include L itz wires.

In at least some embodiments, monitoring the intensity of the current flowing through the conduit will indicate whether there is a fault. The presence of a current flowing through the conduit ensures continuity and, therefore, good heating of the conduit.

The thermal management system may include a fault detection module. The fault detection module may be configured to identify when the resistance exceeds a predetermined threshold or is outside a predetermined operating range. The fault detection module may calculate the resistance based on the current and voltage output by the generator. If the resistance exceeds a predetermined threshold, the fault detection module may determine that there is a poor or faulty electrical connection, for example, between sub-sections of the conduit, and/or between the first and second electrical connections and the conduit. The fault detection module may operate continuously. Alternatively, the fault detection module may operate periodically, for example, in a fault detection mode.

The first electrical connector may be connected to the conduit at or near an inlet of the conduit. The second electrical connector may be connected to the conduit at or near the outlet of the conduit.

The first and second electrical connections may be configured to connect to first and second electrical contacts provided on the conduit. For example, the electrical contacts may be fastened to the conduit by mechanical fasteners. For example, the electrical contacts may be permanently attached to the conduit by welding.

The conduit may be a discharge conduit. The exhaust conduit may be adapted to convey a process gas, for example, a process gas from a Chemical Vapor Deposition (CVD) process. For example, in an industrial process, the exhaust conduit may form part of an exhaust system.

Alternatively, the conduit may be a foreline. The conduit may be configured to supply gas for use in an industrial process.

Alternatively, or in addition, the thermal management system may be adapted to heat the valve. For example, the valve may be connected to a conduit. The thermal management system may be adapted to heat both the conduit and the valve. By way of example, the thermal management system may be adapted to heat an isolation valve present on the exhaust conduit or foreline.

According to a further aspect of the invention, there is provided an exhaust system comprising a thermal management system as described herein and at least one conduit to which first and second electrical connections are connected.

The exhaust system may optionally include at least one valve, such as an isolation valve. In use, the thermal management system may heat at least the conduit and the at least one valve.

At least one conduit may be electrically isolated. At least one conduit may be supported by one or more supports, each of the one or more supports including an electrical insulator for electrically isolating the conduit. The electrical insulator may comprise an electrically insulating coating, such as a teflon (RTM) coating. Alternatively, or in addition, the electrical insulator may comprise an electrically insulating member for contacting the conduit. Alternatively, or in addition, each support may be constructed of an electrically insulating material.

The exhaust system may include first and second couplings disposed at respective ends of the at least one conduit. The first and second couplings may be arranged to form a fluid tight seal, for example to seal an inlet and an outlet of a conduit. The first and second couplings may each include an O-ring, for example, an O-ring constructed of an elastomeric material or rubber. The first and second couplings may each comprise an electrically insulating coupling. Thus, the first and second couplings may be adapted to electrically isolate the conduits.

The exhaust system may include a thermal insulator for thermally insulating the conduit. For example, the exhaust system may include insulation disposed around the conduit.

The at least one conduit may be constructed of stainless steel. At least one of the conduits may be constructed of other materials, for example, having a greater electrical resistance.

At least one of the conduits may be constructed of a magnetic material. For example, the at least one conduit may comprise magnetized stainless steel. At least one conduit may be constructed of a magnetic material having a relative magnetic permeability greater than one (> 1). By forming at least one conduit from a magnetic material, the effective resistance of the material will increase, thereby facilitating thermal heating. At least one of the conduits may be constructed of a ferromagnetic material.

According to other aspects of the invention, there is provided a method of heating a conduit composed of metal, the method comprising:

an electrical generator is used to introduce an alternating current into the conduit, which is introduced directly into the conduit at a high frequency to heat the conduit by joule effect.

The alternating current may be at a frequency greater than or equal to 100 hertz (Hz).

The alternating current may be at a frequency greater than or equal to 1 kilohertz (kHz).

The alternating current may be at a frequency greater than or equal to 10 kilohertz (kHz).

The alternating current may be at a frequency greater than or equal to 50 kilohertz (kHz).

The alternating current may be at a frequency greater than or equal to 100 kilohertz (kHz).

The alternating current may be at a frequency of less than or equal to 500 kilohertz (kHz). In certain embodiments, the alternating current may be at a frequency greater than 500 kilohertz (kHz).

The alternating current may have a magnitude less than or equal to one of: 50 amps or 20 amps.

The voltage in the conduit is less than or equal to 60 volts, or less than or equal to 48 volts.

The method may include modifying the frequency of the alternating current in accordance with one or more parameters of the conduit. For example, the frequency of the alternating current may be modified according to one or more of the following parameters: the length of the conduit, the diameter of the conduit, the wall thickness of the conduit, the conductivity of the material from which the conduit is formed, and the material from which the conduit is formed.

The method may include monitoring the electrical resistance of the conduit to detect a fault. The method may include detecting a fault when the resistance exceeds a predetermined threshold or is outside a predetermined operating range. The resistance can be calculated from the current and voltage output to the catheter. If the resistance exceeds a predetermined threshold, the fault detection module may determine that there is a poor or faulty electrical connection, for example, between sub-sections of the conduit, and/or between the conduit and one or more electrical connections. The method may include continuously monitoring the resistance. Optionally, the method may include periodically monitoring the resistance, for example, in a fault detection mode.

According to other aspects of the invention, there is provided a non-transitory computer readable medium having stored therein a set of instructions that, when executed, cause a processor to perform the method described herein.

Any of the control units or controllers described herein may suitably comprise a computing device having one or more electronic processors. The system may comprise a single control unit or electronic controller, or alternatively, different functions of the controller may be implemented or stored in different control units or controllers. As used herein, the term "controller" or "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers operating together to provide any of the described control functions. To configure a controller or control unit, an appropriate set of instructions may be provided that, when executed, cause the control unit or computing device to implement the control techniques specified herein. The set of instructions may suitably be embedded in the one or more electronic processors. Optionally, the set of instructions may be provided as software stored on one or more memories associated with the controller for execution on the computing device. The control unit or controller may be implemented in software running on one or more processors. One or more other control units or controllers may be implemented in software running on one or more processors (optionally the same one or more processors as the first controller). Other suitable arrangements may also be used.

Within the scope of the present application, it is expressly intended that the various aspects, embodiments, examples and alternatives set forth in the preceding paragraphs, in the claims and/or in the following description and drawings and in particular in the individual features thereof, may be employed individually or in any combination. That is, features of all embodiments and/or any embodiments may be combined in any manner and/or combination unless such features are incompatible. The applicant reserves the right to change any originally filed claim or to file any new claim accordingly, including amending the right of any originally filed claim to depend from and/or incorporate any feature of any other claim (although not originally claimed in that respect).

Drawings

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic representation of a prior art thermal management system for an exhaust system;

FIG. 2 shows a schematic representation of a thermal management system according to an embodiment of the invention; and

FIG. 3 is a graph showing the relationship between current and frequency to dissipate a fixed amount of power for a given section of conduit.

Detailed Description

An exhaust system 1 comprising a Thermal Management System (TMS) 2 according to an embodiment of the invention will now be described with reference to the accompanying drawings. The exhaust system 1 is adapted to convey a process gas comprising condensable solids to an abatement device 3, said abatement device 3 being connected to the exhaust system 1. For example, an exhaust system 1 may be provided to transport deposition gases and associated powders exhausted from a Chemical Vapor Deposition (CVD) process. The TMS 2 is configured to control the temperature of the exhaust system 1 to ensure that the compounds remain volatile, thereby preventing or inhibiting the build up of solids that may partially or completely clog the exhaust system 2. It will be appreciated that the TMS 2 and exhaust system 1 may be used in other industrial processes.

As shown in fig. 2, the exhaust system 1 comprises a conduit 4. The conduit 4 is in the form of a tube constructed of metal, such as stainless steel. For example, the catheter 4 may comprise a DN40 tube having an inner diameter of 40 mm. The conduit 4 may have a wall thickness of about 1mm or in some embodiments up to 2 mm. For example, the catheter 4 may be 10 meters or more in length and may follow a coiled path. The conduit 4 forms a substantially continuous fluid path for conveying the exhaust gas to the abatement device 3. The catheter 4 may comprise a single length of tubing. However, the conduit 4 typically comprises a plurality of sub-sections 5-1, 5-2 joined together in a fluid tight manner. The conduit 4 may include one or more bends to provide the required connection to the abatement device 3. The conduit 4 is supported along its length by a plurality of supports 6. In the present embodiment, the support 6 is configured to electrically isolate the conduit 4. In the present embodiment, the supports 6 each comprise a clamp 7, said clamp 7 having an electrically insulating coating 8, such as teflon (RTM), for contacting the outer surface of the catheter 4. In a variant, an electrically insulating insert (not shown) may be provided between the clamp 7 and the conduit 4. In one variant, the support 6 may be formed of an electrically insulating material.

An inlet coupling 9 is provided at an inlet 10 of the exhaust system 1 and an outlet coupling 11 is provided at an outlet 12 of the exhaust system 1. In the present embodiment, an outlet coupling 11 is provided to connect the exhaust system 1 to the emission abatement device 3. The inlet and outlet couplings 9, 11 each comprise an O-ring for forming a fluid tight seal with the associated component. Furthermore, according to an aspect of the invention, the inlet and outlet couplings 9, 11 are electrical insulators. The inlet and outlet couplings 9, 11 may be formed of a suitable electrically insulating material and may comprise electrically insulating members.

A gate valve 13 is provided at the outlet 12 of the exhaust system 1. The gate valve 13 is operable to selectively open and close the outlet 12. The gate valve 13 may be heated to reduce the build up of solids. Insulation 14 is provided around the exterior of the duct 4 to thermally insulate the duct 4.

The TMS 2 includes an Electronic Control Unit (ECU) 15 and a generator 16. the ECU 15 includes at least one processor 17 configured to control operation of the generator 16. A Human Machine Interface (HMI) 18 is provided to control operation of the TMS 2. the generator 16 is for generating Alternating Current (AC) at a high frequency As described herein, the generator 16 may be configured to generate AC at a frequency greater than or equal to 100 Hertz.TMS 2 includes first and second electrical connections 19, 20 for connecting the generator 16 to the conduit 4. the first electrical connection 19 is connected at or near the inlet 10 of the exhaust system 1 and the second electrical connection 20 is connected at or near the outlet 12 of the exhaust system 1. in this embodiment, the first and second electrical connections 19, 20 each include a cable comprising a plurality of individual insulated wires that may be twisted or braided together (e.g., L itz wires).

In use, the generator 16 injects a high frequency electrical current into the conduit 4 via the first and second electrical connections 19, 20. The introduction of an alternating current into the catheter 4 causes heating due to joule effect. When AC is supplied to the conduit 4, the current density is greatest near the surface of the conductor, since the current flows primarily in the "skin" of the conductor. Thus, heating at or near the surface may be more pronounced due to the increased current density. This is due to the so-called "skin effect" whereby the current flows mainly at the "skin" of the conductor. "epidermal depth" () is determined by the following equation:

wherein: = the depth of the epidermis,

p = the resistance of the resistor, and,

ω = angular velocity, and

μ = magnetic permeability.

As the frequency of the AC increases, the skin depth decreases. Due to the reduction in skin depth (which reduces the effective cross section of the conductor), the effective resistance of the conductor increases at higher frequencies. Thus, by increasing the frequency of the AC introduced by the generator 16, the heating of the conduit 4 may be increased. In at least some embodiments, introducing AC at a frequency greater than or equal to 100 Hz provides sufficient heating of the conduit 4. However, the generator 16 may be configured to generate AC at a higher frequency, for example, to reduce the magnitude (amplitude) of the current.

According to aspects of the invention, the TMS 2 generates heat directly inside the catheter 4. Thus, the TMS 2 performs indirect heating using the catheter 4 as a heating element, rather than using an external heating element. The operation of TMS 2 will now be described. The power dissipated is proportional to the square of the current applied to the resistance. This relationship is defined by the following equation:

P=I ² R

wherein: p = power (watts),

i = current (ampere), and

r = resistance (Ω).

The relationship between current and frequency is shown in the graph 21 shown in fig. 3 to dissipate 280 watts of power in a DN40 tube that is one (1) meter in length. Graph 21 shows that increasing the frequency of the AC allows a reduction in the magnitude of the current necessary to achieve the same power dissipation. By way of example, only a current of 18A (compared to the equivalent 300A in DC) is required, considering a supply frequency of 500 kHz. Furthermore, current injection involves a low voltage (less than 48V) across the length of the tube, which improves safety. The generator 16 may optionally also provide double insulation by implementing a small HF transformer in order to make TMS 2 compliant with SEMI and EN 61010.

By way of comparison, it will be appreciated that equivalent heating by supplying Direct Current (DC) to the conduit 4 is not practical as very large currents will have to be used. A conventional DN40 conduit formed from stainless steel has a typical resistance of 2.7 milliohms/meter. Considering that the power density along the conduit (4) is 0.2W/cm²(equivalent to 280W for a tube DN40 of 1 meter in length, as according to the example shown in fig. 3), it would be necessary to supply more than 300 amps of current. By forming the conduit (4) from a metal with a higher electrical resistance, the required current can be reduced, but this will likely result in higher costs and may present additional challenges such as chemical compatibility with compounds in the process gas.

The TMS 2 may optionally include one or more temperature sensors 22. Because a substantially uniform temperature is generated along the catheter 4, in certain embodiments, the TMS 2 may include a single temperature sensor 22. The temperature sensor 22 may output a temperature signal S1 to the ECU 15 to provide feedback. The ECU 15 may thereby control the current supplied by the generator 16 to the conduit 4 to maintain the conduit 4 at a desired operating temperature or within a desired temperature range.

According to another aspect of the invention, TMS 2 may be configured to implement a fault detection mode. In particular, the TMS 2 may be configured to check the integrity of the electrical circuit comprising the catheter 4. A predetermined voltage (V) may be applied and a current (I) may be measured. The resistance (R) of the conduit 4 may be calculated to determine whether there is a poor electrical connection, for example between sub-sections of the conduit 4, or between the conduit 4 and the first and second electrical connectors 19, 20 respectively. TMS 2 may indicate a fault condition if the resistance (R) is greater than or equal to a predetermined threshold or outside a predetermined operating range.

In at least certain embodiments, the TMS 2 described herein may provide for effective heating of the catheter 4 over its useful life. TMS has particular application in integrated systems because access to the catheter 4 is no longer required to replace the TMS 2. In certain embodiments, TMS 2 may be considered maintenance free.

TMS 2 has been described herein with particular reference to an exhaust system 1. However, it will be understood that TMS 2 may be used in other applications where heating of a catheter is required. For example, TMS 2 may be used to provide controlled heating of a foreline or valve (such as an isolation valve).

It will be understood that various changes and modifications may be made to TMS 2 described herein without departing from the scope of the invention. For example, the catheter 4 may be made of a magnetic material. By using magnetic material (with a relative permeability > 1) for the conduit 4, the skin effect can be enhanced, thereby increasing the effective resistance of the conduit 4 and facilitating heating.