GB2050779A

GB2050779A - Electrical Heating Apparatus

Info

Publication number: GB2050779A
Application number: GB7920987A
Authority: GB
Original assignee: Electrothermal Engineering Ltd
Current assignee: Electrothermal Engineering Ltd
Priority date: 1979-06-15
Filing date: 1979-06-15
Publication date: 1981-01-07

Abstract

Electrical heating apparatus comprises a closed vessel (1) having an external surface (5) which provides a recess for receiving a flask to be heated, the vessel containing a substance in a liquid phase (4) and a vapour phase, being substantially free from gaseous impurities, and there being an electrical heater (3) in the liquid phase for heating it when supplied with electrical power. The heater is within an inner tube (2) which is immersed in the liquid phase. The vessel may be a tubular vessel having end plates; in an example there is a plurality of such external surfaces along the tubular vessel which provide recesses for receiving flasks to be heated and the inner tube extends in the axial direction of the tubular vessel between the end plates and is attached at its ends in openings of the end plates, the heater being received in the inner tube in a sealed manner. Power supply control equipment for the heater (3) is contained in a housing (6), the temperature of the heater being set by adjusting a slidable magnet (16) which cooperates with reed switches to switch resistors into circuit with a solid state energy regulator. <IMAGE>

Description

SPECIFICATION Electrical Heating Apparatus The present invention relates to electrical heating apparatus.

According to the present invention there is provided electrical flask-heating apparatus comprising a closed vessel having an external surface which provides a recess for receiving a flask to be heated, the vessel containing a substance in a liquid and vapour phase, being substantially free from gaseous impurities and there being an electrical heater in the liquid phase for heating it when supplied with electrical power.

The heater could be within an inner tube which is immersed in the liquid phase.

The vessel could comprise a tubular vessel having end plates, there being a plurality of such external surfaces along the tubular vessel which provide recesses for receiving flasks to be heated.

The present invention also comprises a combination of apparatus according to the invention and electrical equipment for controlling it, the equipment including regulating means for regulating electrical power supplied to the said heater, which means includes a movable member comprising magnetic material and a device sensitive to the position of the said member, the regulating means being such that in use it regulates such electrical power in dependence on the position of the said member.

The said member could be a magnet.

The said device could comprise a reed switch.

In this case, the regulating means could further include a solid state energy regulator connected with the heater and a plurality of such switches connected with the regulator, the magnet being movable for closing a selected one at a time of the switches and the regulating means being such that, in use, the regulator regulates electrical power supplied to the heater to a level which depends upon which of the switches is closed.

The or each switch could be encapsulated in a manner for substantially preventing electrical arcs produced by the switch or switches from igniting flammable liquids or vapours in use of the combination.

The regulating means could further include a thermostat switch connected for switching off electrical power to the heater in use of the combination in response to sensing a predetermined temperature, the thermostat switch being such that it resets in response to sensing that the temperature drops below the predetermined temperature, the thermostat switch being encapsulated in a manner for substantially preventing electrical arcs produced by it from igniting flammable liquids or vapours in use of the combination.In this case, the regulating means could further include a further thermostat switch connected for switching off electrical power to the heater in use of the combination in response to sensing a predetermined temperature greater than the firstmentioned predetermined temperature, the further thermostat switch being such that it does not reset in response to sensing that the temperature drops below the second-mentioned predetermined temperature, the further thermostat switch being encapsulated with the first-mentioned thermostat switch in a manner for substantially preventing electrical arcs produced by it from igniting flammable liquids or vapours in use of the combination.

Instead of being a reed switch, the said device or each of a plurality of such devices could be a Halieffect device or a saturable reactor or a circuit sensitive to the position of a member comprising magnetic material.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an electrical heating system comprising an electrically heated boiler and control equipment for the boiler, Figure 2 shows part of a practical embodiment of the boiler, Figure 3 shows an interior view of a housing of the control equipment, and Figure 4 is a circuit diagram of the electrical circuitry of the control equipment and the boiler.

Referring first to Figure 1, a boiler comprises a stainless steel vessel 1 through which extends a stainless steel tube 2 containing a mineralinsulated electrical heater 3. The tube 2 is immersed in a liquid 4, in particular Thermex (Registered Trade Mark), the use of this liquid in a yarn heater being described in British Patent Specification No. 1,513,735. The vessel lisa closed vessel, containing as well as the liquid 4, vapour of the liquid but substantially no air or other gaseous impurities. Also, the vessel 1 has a bowl-shaped surface 5 to provide a recess for receiving a flask containing liquid to be heated.

A practical form of such a boiler is shown (except for the heater 3) in Figure 2. It comprises a stainless steel tube about 76 cm long and about 5 cm in diameter having stainless steel end plates welded to it, in apertures of which plates the stainless steel tube 2 is welded. The heater 3 is welded in the tube 2 and the open ends of the latter sealed with an epoxy resin. A plurality of such surfaces 5 (namely surfaces 5a to 5t) are provided by cutting apertures in the tube and welding in place bowl-shaped stainless steel portions.Thereafter, a hole is drilled in the tube, a copper pipe is attached via the hole, liquid 4 is poured into the vessel 1 via the pipe, the liquid is brought to the boil at normal atmospheric pressure so that air is driven off, the vessel is closed by crimping the copper pipe and the vessel with the liquid in it is allowed to cool.

Control equipment for the boiler includes a housing 6 containing electronic circuitry described below, the housing 6 having a mains input comprising a polyvinyl chloride insulated cable 7 communicating with the housing 6 via a sealing gland 8. Electrical power is supplied to the heater 3 via a mineral insulated cable 9 which communicates with the housing 6 via a sealing gland 10. The equipment also includes, attached to the side of the boiler, a self-resetting thermostat switch 11 and a non-resetting thermostat switch 12 which opens at-a higher predetermined temperature than the thermostat switch 11. The thermostat switches 11 and 12 are connected in series with each other (see below) and are connected with electronic circuitry in the housing 6 via a mineral insulated cable 13 which communicates with the housing 6 via a sealing gland 14.The housing 6 has a slide 15 along which, in the directions of the double arrow, can be slid a magnet 16.

An interior view of the housing 6 is shown in Figure 3. The cables 7, 9 and 13 communicate with a six-way terminal block 1 7. Also a module 18 is fixed in the housing 6 by fixing tabs 19 and 20, the module containing six reed switches 21 a to 21f, a solid state energy regulator 22 and five resistors (see below). Reference numeral 23 indicates internal wiring.

A circuit diagram showing the electronic circuitry in the housing 6, the heater 3 and the thermostat switches 11 and 12 is shown in Figure 4. In this schematically shown cable 7, the terminal N is the neutral terminal and the terminal L is the live terminal, the system being designed to operate from 230 volts alternating current mains. The solid state energy regulator 22 is a standard energy regulator chip, in this example one made by Ling Dynamic Systems under No.

PC1-8. The reed switches 21 a to 21 fare connected between the terminals 1 and 2 of the regulator 22 in the manner shown, switches 21 b to 21fbeing connected via respective resistors of the values shown. The regulator 22, the switches 21 a to 21 f and the five resistors are encapsulated in the module containing them, the module being tilled with an epoxy resin encapsulant as indicated by a dot-dash line. Also, the thermostat switches 11 and 12 are contained in a module filled with an epoxy resin encapsulant, as indicated by reference numeral 24 in Figures 1 and 4.

Moreover, the housing 6 is designed as a safety enclosure to meet British Standard No. BS 5501 and European Standard No. EN 50018.

The system comprising the control equipment and the electrically heated boiler is used in the following manner. Flasks containing liquid are placed in the recesses provided by the bowlshaped surfaces 5a to Sf and power is supplied to the heater 3 via the cable 9. The power supplied is regulated to a desired level by sliding the magnet 9 so that a particular one of the reed switches 21 a to 21 fis closed so that the regulator 22 causes regulation of the power supplied to a particular level. Liquid 4 within the boiler is boiled off and condenses on internal surfaces of the vessel 1, the boiling and condensing action ensuring that all surfaces of the boiler are substantially at the same temperature.

Thus, flasks received by the recess will be heated according to the amount of power supplied to the heater 3, the temperature of the internal surfaces of the boiler balancing at the point at which the heat lost to the flasks equals the heat supplied by the heater 3. If the power input is increased to a point such that a hazardous temperature could arise, thermostat switch 11 opens to switch off the input power. When the temperature has fallen again to a safe value, the power is restored by this thermostat switch closing. If this thermostat switch fails then, at a predetermined temperature above the predetermined temperature at which it should have opened, the thermostat switch 12 will open and as this is a non-resetting thermostat switch, the system is rendered permanently off.

The system comprising the control equipment and the boiler is especially suitable for heating flasks either containing flammable liquids or in areas where flammable liquids or vapours may be present, for example such a system could be used for boiling off petrol or ether. Flammable liquids and vapours may be ignited by electrical arcs from electrical apparatus, sparks from impacts of certain materials, or surface temperatures which are above the spontaneous ignition temperature.

In the above-described control equipment, arcs from any of the switches 21 a to 21 fand arcs from either of the thermostat switches 11 and 12 are substantially prevented from igniting flammable liquids or vapours by virtue of the thermostat switches 11 and 12 being encapsulated in a module filled with an epoxy resin encapsulant and the switches 21a to 21fbeing encapsulated with the resistors and the regulator 22 in a module encapsulated with an epoxy resin encapsulant.

Also, the thermostat switch 12 opens in the event of failure of the thermostat switch 11 and the housing 6 is designed as a safety enclosure as referred to above. Moreover, in the boiler, the heater 3 is isolated from flammable liquids or vapours.

Claims

1. Electrical flask-heating apparatus comprising a closed vessel having an external surface which provides a recess for receiving a flask to be heated, the vessel containing a substance in a liquid and vapour phase, being substantially free from gaseous impurities and there being an electrical heater in the liquid phase for heating it when supplied with electrical power.

2. Apparatus according to claim 1, wherein the heater is within an inner tube which is immersed in the liquid phase.

3. Apparatus according to claim 1 or 2, wherein the vessel comprises a tubular vessel having end plates, there being a plurality of such external surfaces along the tubular vessel which provide recesses for receiving flasks to be heated.

4. Apparatus according to claims 2 and 3, wherein the said inner tube extends in the axial direction of the tubular vessel between the said end plates and attached at its ends in openings of the end plates, the heater being received in the inner tube in a sealed manner.

5. Apparatus according to any preceding claim, wherein the or each recess is a bowl-shaped recess.

6. Apparatus according to any preceding claim wherein the vessel is made of stainless steel.

7. Apparatus according to claim 2 or any of claims 3 to 6 as dependent on claim 2, wherein the inner tube is made of stainless steel.

8. A combination of apparatus according to any preceding claim and electrical equipment for controlling it, the equipment including regulating means for regulating electrical power supplied to the said heater, which means includes a movable member comprising magnetic material and a device sensitive to the position of the said member, the regulating means being such that in use it regulates such electrical power in dependence on the position of the said member.

9. A combination according to claim 8, wherein the said member is a magnet.

10. A combination according to claim 8 or 9, wherein the said device comprises a reed switch.

11. A combination according to claim 9, wherein the regulating means further includes a solid state energy regulator connected with the heater and a plurality of such switches connected with the regulator, the said member being movable for closing a selected one at a time of the switches and the regulating means being such that, in use, the regulator regulates electrical power supplied to the heater to a level which depends upon which of the switches is ciosed.

1 2. A combination according to claim 10 or 11, wherein the or each switch is encapsulated in a manner for substantially preventing electrical arcs produced by the switch or switches from ignition flammable liquids or vapours in use of the combination.

13. A combination according to claim 12, wherein the or each switch is encapsulated in an epoxy resin encapsulant.

14. A combination according to any of claims 8 to 13, wherein the regulating means further includes a thermostat switch connected for switching off electrical power to the heater in use of the combination in response to sensing a predetermined temperature, the thermostat switch being such that it resets in response to sensing that the temperature drops below the predetermined temperature, the thermostat switch being encapsulated in a manner for substantially preventing electrical arcs produced by it from igniting flammable liquids or vapours in use of the combination.

15. A combination according to claim 14, wherein the regulating means further includes a further thermostat switch connected for switching off electrical power to the heater in use of the combination in response to sensing a predetermined temperature greater than the firstmentioned predetermined temperature, the further thermostat switch being such that it does not reset in response to sensing that the temperature drops below the second-mentioned predetermined temperature, the further thermostat switch being encapsulated with the first-mentioned thermostat switch in a manner for substantially preventing electrical arcs produced by it from igniting flammable liquids or vapours in use of the combination.

16. A combination according to claim 15, wherein the thermostat switches are electrically connected in series.

1 7. A combination according to any of claims 14 to 16, wherein the or each thermostat switch is encapsulated in an epoxy resin encapsulant.

1 8. Electrical heating apparatus, substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

1 9. A combination of electrical heating apparatus and electrical equipment for controlling the apparatus, substantially as herein described with reference to the accompanying drawings.