GB2105159A

GB2105159A - Induction heating apparatus

Info

Publication number: GB2105159A
Application number: GB08223832A
Authority: GB
Inventors: Robert Stanley Ellis
Original assignee: Cheltenham Induction Heating L
Current assignee: Cheltenham Induction Heating L
Priority date: 1981-08-28
Filing date: 1982-08-18
Publication date: 1983-03-16

Abstract

This invention relates to fluid heating apparatus and comprises an induction heating system having a primary input coil (10), and a secondary output coil (11) and a linking laminated magnetic core loop (12). The secondary coil (11) is formed of a hollow tube and its two ends are short circuited by a strap (17). A coil (11) is coupled to the fluid input and output conduits (18, 19); the framework includes a fluid pump (20). When current is fed through the primary coil (10) fluid flowing through the secondary coil (11) is heated. <IMAGE>

Description

SPECIFICATION Induction heating apparatus This invention relates to apparatus for heating a fluid using electrical power supply.

Existing electrical fluid heaters usually incorporate electrical resistance heating elements or fluid contacting electrodes, and suffer from a number of disadvantages. For example, they usually require considerable expenditure on maintenance. They are somewhat inefficient and create heat losses, they are slow in operation, and are not effective for generating steam from water or for providing instantaneous heating of a moving fluid stream. It is an object of the invention to overcome some of the existing limitations and disadvantages.

Broadly stated the invention consists in a fluid heater comprising an electrical induction heating system having a primary input coil and a secondary output coil, and including means defining a fluid loop in thermal conducting relationship with the secondary coil.

According to a preferred feature of the invention the secondary coil is short circuited and the fluid loop is an open loop with a fluid input and output connection. It is particularly advantageous for the secondary coil to be in the form of a hollow tube or conduit which also forms the fluid loop.

The apparatus preferably also includes a pump or impeller for creating flow of the fluid through the conduit. The pump is conveniently located on the low temperature input side of the heating conduit.

According to another preferred feature of the invention the secondary coil is formed of a mterial of greater electrical resistivity than the primary coil.

This allows the secondary coil to be formed of a smaller number of turns, and of shorter length, than would otherwise be the case.

The primary and secondary coils may be linked by an air core, but preferably by a magnetic core, such as a laminated magnetic loop threading the two coils.

In any case the apparatus preferably includes means for varying the heating effect on the fluid, comprising a variable voltage regulator or wave shape modulator on the power input supply to the primary coil. Alternatively the apparatus may include means for varying the magnetic coupling between the primary and secondary coils, for example by adjusting their relative positions or by altering the properties of the magnetic core.

The invention may be performed in various ways and one specific embodiment with some possible modification will now be described with reference to the accompanying drawings, in which: Figure lisa diagrammatic plan view of a fluid heater according to the invention, and Figure2 is a cross section therethrough.

In this example the appartus comprises an induction heating system having a primary input coil 10, a secondary output heating coil 11, and a linking laminated magnetic core loop 12. The primary winding may consist of from one hundred to one thousand turns of copper conductor, electrically insulated and is usually mounted on a hollow bobbin surrounding a limb of the core. The power input to the primary winding in this example is at mains frequency 50 Hertz, though other frequencies may be used. The secondary coil 11 in this example is formed of a hollow tube of a high resistance, high temperature material such as stainless steel. This has three turns and the two ends 15, 16 are cross connected by a welded stainless steel strap 17 which acts as a short circuiting link.The two ends 15, 16 are provided with couplings for connection to fluid input and output conduits 18,19 and the input conduit includes a fluid pump or inpeller 20 located on the cool input side of the fluid circuit.

Thus it will be seen that the alternating current supplied to the primary coil 10 induces a heavy current in the short circuited secondary winding 11 and the resulting heat generated in the hollow tube is transmitted directly to the fluid flowing through the tube. Very high temperatures can be achieved almost instantaneously and the equipment is extremely simple to manufacture and requires minimal maintenance. It can be used for heating many varieties of gases or liquids, or as a boiler for generating steam from water.

There may be an automatic control including a temperature sensor in the output 19 from the heating coil connected to a control on the input supply to the primary coil. This may, for example, be a variable voltage regulator or a thyristor with a closed loop feedback system. Alternatively, the control may be applied to the impeller 20 to vary the fluid flow rate such as to maintain the required output temperature. Another possibility is to vary the magnetic coupling between the primary and secondary windings. If an air cored system is used this can be achieved by placing the two coils concentrically one within the other and moving one axially relative to the other.

The core 12 may be a permanent closed loop, or it may be split and provided with a temporary closure.

Instead of running the fluid through a hollow tube, which acts as the secondary coil 11, the fluid may be caused to pass around an annular passage or chamber, which is in heat conducting relationship with the secondary coil. Thus, it is not essential that the walls of the fluid conduit should be of electrically conducting material provided that there is thermal contact between the fluid and the secondary coil.

1. A fluid heater comprises an electrical induction heating system having a primary input coil and a secondary output coil, and including means defining a fluid loop in thermal conducting relationship with the secondary coil.

2. Apparatus according to Claim 1, in which the secondary coil is short circuited and the fluid loop is an open loop with a fluid input and output connection.

3. Apparatus according to Claim 1 or Claim 2, in which the secondary coil is in the form of a hollow tube or conduit which also forms the loop.

4. Apparatus according to any of the preceding

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Induction heating apparatus This invention relates to apparatus for heating a fluid using electrical power supply. Existing electrical fluid heaters usually incorporate electrical resistance heating elements or fluid contacting electrodes, and suffer from a number of disadvantages. For example, they usually require considerable expenditure on maintenance. They are somewhat inefficient and create heat losses, they are slow in operation, and are not effective for generating steam from water or for providing instantaneous heating of a moving fluid stream. It is an object of the invention to overcome some of the existing limitations and disadvantages. Broadly stated the invention consists in a fluid heater comprising an electrical induction heating system having a primary input coil and a secondary output coil, and including means defining a fluid loop in thermal conducting relationship with the secondary coil. According to a preferred feature of the invention the secondary coil is short circuited and the fluid loop is an open loop with a fluid input and output connection. It is particularly advantageous for the secondary coil to be in the form of a hollow tube or conduit which also forms the fluid loop. The apparatus preferably also includes a pump or impeller for creating flow of the fluid through the conduit. The pump is conveniently located on the low temperature input side of the heating conduit. According to another preferred feature of the invention the secondary coil is formed of a mterial of greater electrical resistivity than the primary coil. This allows the secondary coil to be formed of a smaller number of turns, and of shorter length, than would otherwise be the case. The primary and secondary coils may be linked by an air core, but preferably by a magnetic core, such as a laminated magnetic loop threading the two coils. In any case the apparatus preferably includes means for varying the heating effect on the fluid, comprising a variable voltage regulator or wave shape modulator on the power input supply to the primary coil. Alternatively the apparatus may include means for varying the magnetic coupling between the primary and secondary coils, for example by adjusting their relative positions or by altering the properties of the magnetic core. The invention may be performed in various ways and one specific embodiment with some possible modification will now be described with reference to the accompanying drawings, in which: Figure lisa diagrammatic plan view of a fluid heater according to the invention, and Figure2 is a cross section therethrough. In this example the appartus comprises an induction heating system having a primary input coil 10, a secondary output heating coil 11, and a linking laminated magnetic core loop 12. The primary winding may consist of from one hundred to one thousand turns of copper conductor, electrically insulated and is usually mounted on a hollow bobbin surrounding a limb of the core. The power input to the primary winding in this example is at mains frequency 50 Hertz, though other frequencies may be used. The secondary coil 11 in this example is formed of a hollow tube of a high resistance, high temperature material such as stainless steel. This has three turns and the two ends 15, 16 are cross connected by a welded stainless steel strap 17 which acts as a short circuiting link.The two ends 15, 16 are provided with couplings for connection to fluid input and output conduits 18,19 and the input conduit includes a fluid pump or inpeller 20 located on the cool input side of the fluid circuit. Thus it will be seen that the alternating current supplied to the primary coil 10 induces a heavy current in the short circuited secondary winding 11 and the resulting heat generated in the hollow tube is transmitted directly to the fluid flowing through the tube. Very high temperatures can be achieved almost instantaneously and the equipment is extremely simple to manufacture and requires minimal maintenance. It can be used for heating many varieties of gases or liquids, or as a boiler for generating steam from water. There may be an automatic control including a temperature sensor in the output 19 from the heating coil connected to a control on the input supply to the primary coil. This may, for example, be a variable voltage regulator or a thyristor with a closed loop feedback system. Alternatively, the control may be applied to the impeller 20 to vary the fluid flow rate such as to maintain the required output temperature. Another possibility is to vary the magnetic coupling between the primary and secondary windings. If an air cored system is used this can be achieved by placing the two coils concentrically one within the other and moving one axially relative to the other. The core 12 may be a permanent closed loop, or it may be split and provided with a temporary closure. Instead of running the fluid through a hollow tube, which acts as the secondary coil 11, the fluid may be caused to pass around an annular passage or chamber, which is in heat conducting relationship with the secondary coil. Thus, it is not essential that the walls of the fluid conduit should be of electrically conducting material provided that there is thermal contact between the fluid and the secondary coil. CLAIMS

4. Apparatus according to any of the preceding claims, including a pump or impeller for creating flow of the fluid through the conduit.

5. Apparatus according to Claim 4, in which the pump or impeller is located on the low temperature input side of the heating conduit.

6. Apparatus according to any of the preceding claims, in which the secondary coil is formed of a material of greater electrical resistivity than the primary coil.

7. Apparatus according to any of the preceding claims, in which the primary and secondary coils are linked by a magnetic core.

8. Apparatus according to Claim 7, in which the magnetic core is a closed loop threading the two coils.

9. Apparatus according to any of the preceding claims, including means for varying the heating effect on the fluid, comprising a variable voltage regulator or wave sharp modulator on the power input supply to the primary coil.

10. Apparatus according to any of the preceding claims, including means for varying the magnetic coupling between the primary and secondary coils, for example by adjusting their relative positions or by altering the properties of the magnetic core.

11. Afluid heater substantially as hereinbefore described with reference to the accompanying drawings.