GB2136705A

GB2136705A - Producing a vapour/gas mixture

Info

Publication number: GB2136705A
Application number: GB08328860A
Authority: GB
Inventors: James Francis Pollock; John Malcolm North; Roy Frederick Preston
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1983-01-18
Filing date: 1983-10-28
Publication date: 1984-09-26
Also published as: GB2136705B; GB8328860D0

Abstract

A vapour/gas mixture is produced by passing a liquid through a permeable porous electric heating element 65 so as to heat the liquid, and directing a gas to mix with vapour of the heated liquid so as to form a mixture of the vapour and the gas. The gas may be passed through the heating element 65 with the liquid, or be directed into the liquid after the liquid has passed through the heating element 65, or be directed into the vapour from the heated liquid. The vapour/gas mixture may provide a breathable oxygen- containing gas for a diver, or be used as a fuel for a heat engine. <IMAGE>

Description

SPECIFICATION A method of and an apparatus for producing a vapor/gas mixture This invention relates to a method of and to an apparatus for producing a vapour/gas mixture, and more particularly but not exclusively, for producing a vapour/gas mixture at a predetermined vapour pressure of the liquid.

According to one aspect of the present invention, there is provided a method of forming a mixture of a gas and a vapour, the method comprises heating a liquid with a fluid permeable porous electic heating element, and directing a gas to mix with vapour of the heated liquid.

According to another aspect of the present invention, an apparatus for mixing a vapour with a gas comprises, a chamber adapted to contain a liquid, a fluid permeable porous electric heating element disposed in the chamber so as to heat said liquid, and means for directing a gas to mix with vapour of the heated liquid.

Preferably, the liquid is arranged to pass through the heating element, which heating element may be at an inletforthe liquid into the chamber, although if desired the heating element may be arranged to be immersed in a quantity of the liquid in the chamber so as to heat the liquid. The gas may be passed through the porous heating element, or be directed through the heated liquid, or be directed into the vapour evaporated from the heated liquid, so as to mix with said vapour of the heated liquid.

The gas may be directed at a pressure above ambient pressure through the heated liquid or into the vapour. Alternatively, the gas may be directed through the heated liquid or into the vapour by the effect of a sequential negative pressure applied to the heated liquid, and said sequential negative pressure might be applied for example, by a heat engine, or by the respiratory cycle of a human body, for example that of a diver.

Means may be provided for sensing the temperature of the heated liquid or the vapour, and controlling the temperature of the porous heating element thereby.

The gas might comprise a gaseous mixture such as air or a mixture of oxygen with an inert gas such as helium, or a mixture of air or oxygen with a hydrocarbon for use as a fuel for a heat engine.

In yet a further aspect, the invention includes a vapour/gas mixture produced by the method of the invention.

The porous heating element might comprise carbon or silicon carbide, or a mixture of silicon and silicon carbide, or silicon, carbon and silicon carbide, for example as disclosed in British Patent Specification Nos 2056829A, 2083330A and 1600253, and co-pending application No 8234714 (United States Serial Nos 159187 filed 13th June 1980,309795 filed 8th October 1981, and 330827 filed 15th December 1981, and Patent No 4257157) which are incorporated by reference herein and to which reference is directed for further detailed information. A suitable porous heating element might have a voidage of 50-98% and a bulk density of 50-750 kg/m3 and comprise individual heating elements consisting of fine fibres of a diameter in the range 5-300 microns.

Athermal barrier/dispenser may be used in conjunction with the porous heating element to produce a uniform fluid flow through the porous heating element as described in British Patent Specification No 1466240 (United States Patent No 3943330) to which reference is directed and which is incorporated by reference herein.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic side representation in medial section of a respiratory unit, and Figure 2 shows a diagrammatic side representation in medial section of a gas/vapour mixer unit.

Referring now to Figure 1, a respiratory unit 10 is shown for installation inside a diving bell (not shown) to supply a heated and humidified, oxygen containing gas mixture. The respiratory unit 10 comprises a chamber 11 having an inlet 12 at the bottom of the chamber 11, and an outlet 13 at the top of the chamber 11. A permeable porous electric heating element 15 of annularform is mounted on an annular electrode 14 which is seated on an annular electrically insulating member 16 atthe bottom of the chamber 11 about the inlet 12.The heating element 15 has an impermeable end cap which also serves as an electrode 17 mounted on the top of the heating element 15, and the electrodes 14, 17 are connected to an electric circuit 18 controlled by a switch 19 which is responsive to a thermocouple 23, extending through the side of the chamber 11.

A 'U' tube 20 has a limb 21 which extends from the inlet 12, and a limb 22 which extends to a holding vessel 24 disposed above the chamber 11. A riser tube 26 extends upwardly from the outlet 13 and terminates at one end of a manifold 28, a return tube 30 extending from the riser tube 26 to the top of the holding vessel 24 to which a vent tube 32 extends from the manifold 28, A thermocouple 34 is installed in a branch 36 and a humidity measuring probe 38 installed in a branch 40 of the manifold 28, the other end of the manifold 28 forming an outlet 42 for the discharge of a heated and humidified oxygen-containing gas mixture into the diving bell.

An inlet pipe 44 for the oxygen-containing gas mixture is connected to the riser tube 26 to discharge the gas mixture into an annular space 46 defined between the riser tube 26 and a perforated tube 49 concentrically disposed in the riser tube 26, end caps 51 at each end of the perforated tube 49 closing the ends of the annular space 46.

In operation, with the chamber 11 containing water delivered from the holding vessel 24, the heating element 15 is energised by the electric circuit 18 (e.g. 200 watts). An oxygen-containing gas mixture (e.g. oxygen/helium) is supplied through the inlet pipe 44 from a cylinder (not shown) or a pump (not shown) into the annular space 46 at a pressure slightly above ambient pressure. The gas mixture from the annular space 46 penetrates the perforated tube 49 to mix with the water in the perforated tube 49 and thus becomes saturated with water vapour and also gives rise to a gas lift effect on the water in the riser tube 26 as the gas mixture flows upwardly from the perforated tube 49 into the riser tube 26.

This gas lift effect promotes circulation of the water in the respiratory unit 10 as the level of the aerated water in the riser tube 26 rises to the level of the return tube 30 so that water flows through the return tube 30 into the holding vessel 24, any of the gas mixture entrapped with the water in the return tube 30 and reaching the holding vessel 24 venting through the vent tube 32 into the manifold 28. The circulation of the water in the respiratory unit 10 entails flow of the water through the heating element 15 thereby heating the water, and when a predetermined temperature of the water in the chamber 11 has been detected by the thermocouple 34 the electric supply to the heating element 15 is broken by the switch 19 but is subsequently energised by the switch 19 as and when necessary to maintain the temperature of the water in the champ ber 11 at the predetermined temperature.The heated water from the chamber 11 in passing through the perforated tube 49, heats the gas mixture that penetrates the perforated tube 49 in addition to saturating the heated gas mixture with water vapour. The heated vapour/gas mixture that emerges from the water in the riser tube 26 flows through the manifold 28 and out of the outlet 42.

The rate of flow of the gas mixture through the inlet pipe 44, and the temperature of the water in the chamber 11, affect the temperature and the humidity of the heated vapour/gas mixture flowing through the manifold 28 as detected by the thermocouple 34 and the humidity measuring probe 38 respectively, and can be altered to provide required values of the temperature and humidity of the heated vapour/gas mixture.

The perforated tube 49 may comprise a metal mesh or gauze, and the permeable porous electric heating element may be as described in the afore said Patent Specifications Nos 2056829A, 2083330A, and 1600253, and co-pending application No 8234714 to which reference is directed for further detailed information.

Referring now to Figure 2 a vapour/gas mixer unit 60 is shown, and comprises a chamber 61 having an inlet 62 at the bottom of the chamber 61 and an outlet 63 at the top of the chamber 61. A permeable porous electric heating element 65 of annular form and similar to the heating element 15 of Figure 1 is mounted on an annular electrode 64 which is seated on an annular electrically insulating member 66 at the bottom of the chamber 61 about the inlet 62, and has an impermeable end cap which serves as an electrode 67 mounted on the top of the heating element 65. The electrodes 64, 67 are connected to an electric circuit 68 controlled by a switch 69.

A 'U' tube 70 has a limb 71 extending downwardly from the inlet 62 and a limb 72 that rises above the chamber 61, a horizontally disposed limb 73 con necting the limbs 71 and 72 together. A riser tube 76 extends upwardly from the outlet 63 to a source 77 for applying a partial vacuum sequentially to the riser tube 76.

In operation, the mixer unit 60 is partially filled with a liquid to the static levels shown by broken lines 78 and 79 in the chamber 61 and the limb 72 respectively, and the porous electric heating element 65 is energised (e.g. 200 watts). When a partial vacuum is applied by the source 77 to the riser tube 76, the level 78 of the liquid in the chamber 61 rises and the liquid flows through the heating element 65 into the chamber 61 to such an extent that the level 79 of liquid in the limb 72 falls below the top of the horizontal limb 73 to the level shown by broken line 81 in the horizontal limb 73.Thus air flows through the horizontal limb 73 and through the heating element 65 with the liquid where it is heated together with the liquid and saturated with vapour of the liquid, the vapour saturated heated air then flowing through the riser tube 76 to the partial vacuum source 77. On the air pressure in the riser tube 76 being restored to ambient pressure, the level of the liquid in the chamber 61 and the limb 72 returns to the static levels 78,79 respectively. A partial vacuum when applied sequentially by the source 77 to the riser tube 76 results in a repeated sequence of vapour saturated air rising in the riser tube 76 to the source 77, followed by the restoration of the liquid in the mixture unit 60 to the static levels 78,79.

The source 77 might be provided by a human body (e.g. a diver) inhaling a heated and humidified air supply from the mixer unit 60 containing water as the liquid to saturate the air. Alternatively when the mixer unit 60 is used in carburation, the source 77 might be provided by a heat engine, the partial vacuum being applied sequentially to the riser tube 76 by the induction portion of the heat engine cycle and the liquid in the mixer unit 60 comprising a liquid hydrocarbon fuel for supplying a vaporised hydrocarbon fuel to the heat engine.

The temperature to which the heating element 65 is arranged to heat the liquid to determine the saturation vapour pressure of the liquid depends on the application of the mixer unit 60, and can be varied by adjustment of the current supplied to the heating element 65, or the rate of flow of the liquid and the airthrough the heating element 65.

If desired, the limb 72 might be connected to a supply of a liquid hydrocarbon fuel instead of being open to the environment, a float operated valve (not shown) being provided in the limb 72 to control the supply of the liquid hydrocarbon fuel into the limb 72 to maintain the heated liquid level 78 in the chamber 61 substantially at a predetermined level. As the level of the liquid hydrocarbon fuel in the chamber 61 and the limb 72 would therefore fluctuate only to a small extent, a supply of air or oxygen would need to be provided to mix with the vaporised hydrocarbon fuel so as to allow a combustible gas mixture to be formed and supplied to the source 77.

Alternatively, the limb 72 might be supplied with a gas from a pressurised source (not shown), and such a gas might comprise a gaseous fuel for a heat engine providing the source 77.

It will be understood that air or oxygen may be mixed with vaporised liquid issuing from the heating element 65, or evaporated from the heated liquid.

Although the invention has been described in relation to the liquid to be vaporised being constrained to flow through the heating element 15 or 65, for some applications this may not be necessary.

For example, in an alternative vapour/gas mixer unit (not shown), the fluid permeable heating element may be immersed in a static quantity of liquid in a chamber so as to heat the liquid, and gas bubbled directly through the liquid so as to become saturated with vapour of the liquid.

Claims

1. A method of forming a mixture of a gas and a vapour, the method comprising heating a liquid with a fluid permeable porous electric heating element, and directing a gas to mix with vapour of the heated liquid.

2. A method as claimed in Claim 1, wherein the liquid is directed so as to pass through the heating element.

3. A method as claimed in Claim 1 or Claim 2, wherein the gas is directed to pass through the heating element.

4. A method as claimed in Claim 1, wherein the gas is directed into the vapour evaporated from the heated liquid.

5. A method as claimed in Claim 1 or Claim 2, wherein the liquid is contained in a circulatory system, the system having an upwardly extending portion thereof and an exhaust outlet for the gas/ vapour mixture, and the gas is directed into the liquid in the upwardly extending portion to produce a gas lift effect therein and thereby promote circulation of the liquid in the system.

6. A method as claimed in any one of the preceding Claims, wherein the gas is directed at a pressure above ambient pressure.

7. A method as claimed in any one of Claims 1 to 3, wherein the gas is directed by the effect of a negative pressure applied to the heated liquid.

8. A method as claimed in Claim 6 or Claim 7, wherein the pressure is applied sequentially.

9. A method as claimed in any one of the preceding Claims, including sensing the temperature of the heated liquid or vapour, and controlling the temperature of the porous heating element thereby.

10. A method as claimed in any one of the preceding Claims, including sensing the humidity of the gas vapour mixture, and controlling the rate of flow of the gas so as to produce a required humidity of the gas/vapour mixture.

11. A method as claimed in any one of the preceding Claims, wherein the gas includes oxygen.

12. A method as claimed in any one of the preceding Claims, wherein the gas includes a hydrocarbon fuel.

13. Apparatus for mixing a vapourwith a gas, and comprising a chamber adapted to contain a liquid, a fluid permeable porous electric heating element disposed in the chamber so as to heat said liquid, and means for directing a gas to mix with vapour of the heated liquid.

14. Apparatus as claimed in Claim 13, including an inlet for the liquid into the chamber, and the heating element being located at said inlet so that the liquid flows through the heating element into the chamber.

15. Apparatus as claimed in Claim 13 or Claim 14, including a duct upwardly extending from the chamber, and the gas directing means comprising a branch duct at the upwardly extending duct for directing the gas into the liquid in the upwardly extending duct.

16. Apparatus as claimed in Claim 15, wherein the upwardly extending duct comprises a portion of a circulatory system for the liquid, the system being connected to the inlet of the chamber.

17. Apparatus as claimed in Claim 15 or Claim 16, including a relatively narrow, perforated tubular wall in the upwardly extending duct at the branch duct, and a closure between the tubular wall and the side of the upwardly extending duct one at each end of the tubular wall.

18. Apparatus as claimed in Claim 14, wherein a liquid su.pply duct is connected at one end to the inlet and at the other end thereof extends above the heating element.

19. Apparatus as claimed in Claim 18, wherein a portion of the liquid supplu duct extends below the heating element, and the other end of the liquid supply duct is open to the atmosphere.

20. Apparatus as claimed in any one of Claims 13, 14 or 18, wherein the chamber is connected to means for applying a negative pressure to the chamber.

21. Apparatus as claimed in any one of Claims 13 to 20, including means at the chamber for sensing the temperature of the heated liquid, and for controlling the temperature of the heating element thereby.

22. Apparatus as claimed in any one of Claims 13 to 21, including means for sensing the humidity of the gas/vapour mixture.

23. A method of forming a mixture of a gas and a vapour, substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

24. A gas/vapour mixture produced by the method as claimed in any one of Claims 1 to 12, or Claim 21.

25. Apparatus for mixing a vapour with a gas substantially as herein before described with reference to Figure 1 or Figure 2 of the accompanying drawings.