GB2151504A - Moisture extractor and air purifier - Google Patents

Abstract

Adiabatic expansion of air is used to cool the air and condense out water vapour. The water vapour is extracted, together with other impurities, such as dust and bacteria. Devices which embody the principle of adiabatic expansion as a means for purification are described. As shown, air from fan N is blown through chamber A, valves E and F being open. Lever C is operated to move diaphragm B, and valves E and F are closed. Water condenses in the chamber. Lever C is released followed by the opening of valve E and then valve F to prevent recompression of the air in chamber C. Water collects in exit pipe R and is drained through valve V. <IMAGE>

Description

SPECIFICATION Moisture extractor and air purifier This invention relates to an air purifier.

All presently available moisture extractors (dehumidifiers) and air purifiers are based on one of the following: a) moisture condensation by heat exchange with a cooling coil containing a refrigerant b) adsorption or absorption by compounds such as silica gel or activated alumina.

In addition dust is extracted by passing the dirty air through a filter system which may or may not include an electrostatic precipitator.

The present invention does not use the above methods but uses the well known principle of the adiabatic expansion of air and the cooling effect caused by such an expansion. Moisture in the air condenses with nucleation taking place on dust particles or other impurities in the air.

Thus by suitable design of a device such as that to be described the moisture is extracted from the air using a water collection system and the dust and other impurities contained in the air are extracted at the same time. Dust particles down to molecular sizes can be extracted, thus the potentially harmful respirable dust can be removed.

The expansion is arranged to take place in the presence of a wire matrix and even in the total absence of dust nucleation can take place. Indeed it is known' that if the volumetric expansion ratio is in excess of approximately 1.4:1 nucleation will even take place around the nitrogen molecules in the air.

The adiabatic expansion of air has been used previously in the Wilson cloud chamber for the detection of ionising radiation and to liquefy air or its constituents, but not for the removal of impurities or water vapour from the air. To liquify gases, adiabatic expansion is often used in conjunction with a Joule-Kelvin expansion. The invention could be used to extract certain other gaseous impurities, in the absence of dust, nucleation taking place on these impurity molecules.

For this use it may be necessary to add water vapour before expansion. Further, the invention could also be used to extract harmful bacteria or viruses from air.

Examples of the advantages of the invention over present systems: 1) simultaneous extraction of dust, water vapour and other impurities.

2) Extraction of molecular sized species.

3) Absence of filters which can clog and lose efficiency.

4) Elimination of refrigerant systems.

5) Adaption to manual operation of a suitable device.

6) Adaption to field use for, for example, obtaining drinking water from air.

THEORY An approximately reversible adiabatic expansion of a gas against a piston or a turbine blade, with the performance of external work, always produces a decrease in temperature, no matter what the original temperature. The fall in temperature of the gas, for example air, upon expansion can be calculated from the following equation:"

where T, is the original temperature, V, the original volume, V2 and T2 the new volume and temperature respectively and y the ratio of the principal specific heats of air.

Thus, if T1 = 20 C (293 K) and V, - = 0.5, T2 = 223 K or - 50"C.

V2 Similarly, a volume expansion ratio of 1.2:1 will reduce the air temperature to - 3"C.

In practice, a volume expansion ratio of between 1.2 and 1.5:1 is chosen for convenience.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which; Figure 1 shows an expansion chanber and means for causing the expansion Figure 2 shows a spring mechanism allowing lever movement to continue to bring about expansion after that same lever movement has closed the inlet and outlet valves.

Figure 3 shows a concentric arrangement of the inlet and outlet air pipes.

Figure 4 shows a modification to the air inlet and outlet of the expansion chamber "The results calculated are a close approximation to those actually observed-the degree of approximation results from the non ideal behaviour of air and deviation from truly adiabatic expansion.

Construction of the Device Refering to Fig. 1, a circular chamber A has one wall constructed from a moveable diaphragm B supported between steel plates. The diaphragm is moved by a lever mechanism C, the lever being operated on by a solenoid D. The solenoid is activated via a variable timer which can in turn be varied by a signal from a moisture detector, via suitable circuitry. Alternatively the solenoid could be replaced by a motor driven cam, or the lever C operated entirely manually.

The entire chamber A is insulated externally as shown. A matrix consisting of wire gauze or mesh or other suitable nucleating surface is contained in the chamber-this acts as a water collection surface.

Air enters the chamber A via a valve E which may be linked to the diaphragm lever C and leaves via valve F, which again may be linked to the lever C.

The chamber A can be of non uniform cross section such that the cooling effect can be different in different parts of A. This can aid the flow of air through the device and aid nucleation.

The air inlet and outlet from chamber A can be formed by two concentric tubes, as shown in Fig. 3-the exiting cold air then serves to reduce the temperature of the incoming air.

The chamber A may be constructed from metal but in this event the internal surface may be insulated to reduce the thermal mass of the chamber walls in contact with the expanding air. It is desirable in general to have a containing chamber of low thermal mass-similarly the matrix in A must be of very thin section metal to reduce its thermal mass-the matrix must have poor thermal contact with the containing chamber.

Operation of the Device Again with reference to Fig. 1, with atmospheric pressure on both sides of the diaphragm B the inlet valves E and F are both open and a fan B blows air through the chamber". On applying a force to the lever C to move the diaphragm to expand the air in the chamber A, valves E and F are caused to close-this can in its simplest form be by levers operated from C and shown in Fig.

1. E and F are caused to close upon only slight movement of C. Further movement of C in the same direction causes the air in A to expand. This futher movement can be achieved by the spring mechanism shown in the enlarged section in Fig. 2. The air on the other side of the diaphragm B is free to flow to atmosphere through aperture S.

On the maximum movement of C the expansion in A is at its greatest. The air cools, nucleation takes place and the matrix in A is cooled-some drops of water condense on the matrix. The lever C is then released to return to its original position, this is aided by the low pressure in A and by the spring T. As soon as C starts to move, valve E is caused to open followed with a slight delay, by valve F. This delay can be achieved by adjusting the relative length of levers P and Q. Opening valves E and F prevents the air, previously expanded, from being recompressed. Air enters through E, being opened in advance of F, because of the higher pressure outside chamber A-the flow of air into A is aided by the fan N.

Repetition of the above cycle lowers the temperature in A to the point where droplet formation and condensation on the matrix in A is optimised with the flow through A. Water collects in the exit pipe R and drains through tap V. If the removal of dust or other impurities is not the prime use at a given time then the temperature of the matrix may be lowered to an extent where the expansion cycles may be intermittently stopped and air allowed to flow continuously through the chamber A.

"A fan could also be arranged to pull air through the chamber.

The device may be controlled through a variable timer operating on the solenoid U which in turn may be fed from a moisture detector. Further control could be incorporated whereby the expansion ratio is varied to, for example, provide a greater cooling effect when the device is first operated.

In a further embodiment of the device the air inlet and outlet of Fig. 1 are replaced by the inlet and outlet shown in Fig. 4. Here the action of the piston moving back is arranged to force air into the expansion chamber A through pipe Y- fan N is eliminated. Further movement of the piston expands the air in A. A seal Z seals the expansion chamber A from chamber X. The seal Z is flexible. K acts as a three way valve.

Consider the piston moving back to expand the air in A, the valve H is arranged to close, again possibly and most simply by levers connected to lever C of Fig. 1. Valve K is in a position such that A is open to X but A is closed in atmospheric air through J. The air in chamber X flows into A through opening I post valve K. K is then arranged to close sealing A from X, H is arranged to open and further movement of the piston back expands the air in A. At the end of the expansion valve K is arranged to open to connect A with X and air is drawn in through S, aided by the low pressure in A, past H and ultimately into A through I. Pressures are equalised at atmospheric pressure in chambers A and X. Movement of the piston forward is arranged to close K to seal the inlet I and to open chamber A to atmosphere through J. As the piston moves forward the air in A is forced out through J.The cycles repeats as the piston completes its forward movement and starts to move back to expand the air in A once more.

In this embodiment it is not essential to insulate the piston as shown in Fig. 1 as any cooling of the piston will aid in cooling the incoming air passing through chamber X into chamber A.

In yet a further embodiment of the invention the movement of the piston could be achieved by connecting chamber X to a small vacuum pump instead of using a lever such as C. By suitable operation of a valve the pressure in chamber X could be suddenly reduced causing the piston to move back and expand the air in A.

It should be noted that in the embodiments of the invention described above where the air is caused to expand into chamber A upon first entering A the air may be expected to undergo a very small reduction in temperature due to the Joule Kelvin effect-this will aid the overall cooling effect.

It should also be noted that the device could be operated in such a manner that a given volume of air could be made to undergo more than one expansion to achieve a more thorough removal of impurities.

Claims (1)

1. An air or gas purifier which uses the principle of the adiabatic expansion of a gas in the purifuication and/or dehumidification of a gas such as air by the removal of water vapour and/or dust or other impurities.

2. The automatic operation of a device according to claim 1 by for example a solenoid or cam operated diaphgram linked or otherwise to a valve controlling the air inlet to the expansion chamber and to a valve controlling the air outlet from the expansion chamber to provide a continuous cyclical operation of the device.

3. A device according to any one of claims 1 to 2 whereby the air inlet and outlet valves are remotely operated in synchronisation with the diaphragm bringing about the expansion to provide a continuous cyclical operation of the device.

4. A device according to any one of the claims 1 to 3 whereby a specific quantity of water is used to dose relatively dry air for the purposes of purification by removal of dust and or other impurities.

5. A device according to any one of the claims 1 to 4 whereby the movement of the diaphragm is used both to force air into the expansion chamber in one part of the cycle and to expand the air on another part of the cycle. The air upon first entering the expansion chamber undergoing a Joule Kelvin cooling.

6. The use of a vacuum pump with a device according to any one of the claims 1 to 4 to bring about movement of the diaphragm and the consequent expansion of the air to be purified.

7. A device according to any one of the claims 1 to 4 whereby a positive pressure from, for example, a fan is used to drive air through the expansion chamber or a negative pressure is used to draw air through the expansion chamber. The air upon first entering the expansion chamber undergoing a Joule Kelvin cooling.

8. A device according to any one of the claims 1 to 3 whereby a linkage system is used to operate on the gas inlet and outlet valves to change the lead/lag relationship between them and/or the diaphragm movement.

9. Operation of a device according to any one of the claims 1 to 8 in an intermittent way whereby a cycle of expansion is caused to take place for a sufficient time to cool the heat exchange matrix in the expansion chamber-operation of the device is then a constant volume flow followed by a cycle of expansions.

10. A device according to claim 1 whereby a conversion or dual function is used to operate the device automatically or manually in a cyclical and/or intermittent way.

11. A device according to any one of the claims 1 to 10 wherein the use of a matrix or other device is used to collect and or facilitate the collection of water droplets in the expansion chamber.

12. A device according to claim 1 wherein the expansion chamber is of non uniform cross section.

13. A device according to claim 1 in which the expansion ratio can be varied to provide a varying cooling effect at different times.

14. A device according to claim 1 wherein concentric tubes are used for the air inlet and outlet to provide a counter flow between the cool outgoing air and the warm incoming air.

15. A device substantially as herein described with reference to and as illustrated in the accompanying drawings.

16. Any novel feature or novel combination of features disclosed herein and/or the accompanying drawings.

References

1. Yarwood, J. Atomic Physics University Tutorial Press 1 965