GB2257372A

GB2257372A - Dehumidifiers

Info

Publication number: GB2257372A
Application number: GB9213171A
Authority: GB
Inventors: Ronald Leslie Adams; Roger Artindale Heron
Original assignee: GAST MANUFACTURING CO Ltd
Current assignee: GAST MANUFACTURING CO Ltd
Priority date: 1991-06-22
Filing date: 1992-06-22
Publication date: 1993-01-13
Anticipated expiration: 2012-06-22
Also published as: GB9113539D0; GB9213171D0; GB2257372B

Abstract

Comprise means for chilling input gas to precipitate moisture therefrom, and heat-exchanging means coupled to the chiling means to pre-cool the input gas by thermal transfer to the moisture-freed output gas. In an embodiment input air to an inlet 1 of the dehumidifier unit is supplied to a chiller assembly 6 via the outer tube 4 of a heat-exchanger coil 2, so as to pre-cool it by heat transfer to the contra-flowing chilled and dried air that leaves the assembly 6 via the inner tube 5 of the coil 2. The pre-cooled air is injected tangentially through a port 11 into a chamber 9 of the assembly 6 to impart swirling or vortex motion that increases its exposure to chilling from the cold junction of a Peltier-effect device 10 mounted on a cup-shape member 7 of the assembly 6. The chilled air passes from the chamber 9 through a coalescing filter 13. <IMAGE>

Description

Dehumidifiers This invention relates to dehumidifiers.

The invention is especially, though not exclusively, concerned with dehumidifiers for use, for example, in drying compressed air as supplied to run air bearings, or drive the turbines of dental drills. A dehumidifier suitable for such an application is known, this being of the kind in which air or other gas involved is chilled so that moisture precipitates out from it to an extent that leaves the gas sufficiently dry for the application in hand. Although this known kind of dehumidifier has been found to operate generally satisfactorily, there is a tendency for such operation to be inefficient. It is an object of the present invention to provide a form of dehumidifier of this know kind having enhanced efficiency of operation.

According to one aspect of the present invention a dehumidifier comprises means for chilling input gas to precipitate moisture therefrom, and heat-exchanging means coupled to the chilling means to pre-cool the input gas by thermal transfer to the chilled, moisture-freed gas output from the chilling means.

The heat-exchanging means may involve two elongate and thermally-intercoupled passageways that are located one within the other, the input gas being conveyed to the chilling means via a first of the passageways and the chilled, moisture-freed gas being conveyed from the chilling means via the second passageway. It may be found of advantage to arrange that the chilled, moisturefreed gas flows in the inner passageway, and that the directions of gas flow are opposite to one another in the two passageways.

The thermally-intercoupled passageways may be provided by substantially-coaxial tubes. Alternatively, the outer of the two passageways may be defined by a channel within a thermally-insulating member, and the inner by a tube located within the channel. In the latter case, the chilling assembly may with advantage be mounted within the thermally-insulating member.

According to another aspect of the present invention there is provided a dehumidifier in which input gas is chilled within a chamber to precipitate moisture therefrom, wherein the gas is caused to flow within the chamber with a swirling or vortex motion.

It has been found that the efficiency with which the input gas is chilled can be improved by causing the gas to flow in this way within the chamber. The swirling or vortex motion enhances the time and extent of exposure of the gas to chilling, and can be imparted simply and economically by directing the gas into the chamber substantially tangentially to a cylindrical wall of the chamber.

The gas may exit from the chamber via a centrally-located port into a filter for bringing about precipitation of the moisture from the chilled gas.

The chamber may be defined within thermally-conductive means that is in thermal contact with the cold junction of a Peltier-effect device. Moreover, the flow path for the chilled, moisture-freed gas from the chamber may extend via an elongate passageway that is thermally coupled to a heat-sink for the hot junction of the Peltier-effect device, such that the gas is warmed from the heat-sink.

A dehumidifier unit in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic, part sectioned, representation of the dehumidifier unit of the invention; Figure 2 is a sectional plan view of part of a chiller assembly of the dehumidifier unit of Figure 1, showing the chilling chamber of that assembly; and Figure 3 is a schematic, part sectioned, representation illustrating a modified form of the dehumidifier unit of Figure 1, in accordance with the present invention.

The dehumidifier unit to be described is for use in drying compressed air as supplied, for example, to run air bearings or to drive air turbines such as used in dental drills. The unit may also be used in the supply of air, or an air-oxygen mixture, to respiratory equipment.

Referring to Figure 1, the compressed air to be dried is supplied to an inlet 1 of the dehumidifier unit and within the unit passes to a heat-exchanger coil 2 via a pipe 3. The heat-exchanger coil 2 is wound from two elongate copper or aluminium tubes 4 and 5 that are mounted substantially-coaxially one within the other, and it is to the outer tube 4 of the coil 2 that the inlet air is supplied from the pipe 3. The air supplied from the pipe 3 flows through the tube 4 over the inner tube 5 and inwardly of the coil 2, to a chiller assembly 6.

After being chilled in the assembly 6, the air is supplied to flow in the inner tube 5 outwardly of the coil 2. In this way, the input air flowing through the outer tube 4 to the chiller assembly 6 is cooled by heat transfer through the wall of the tube 5 by the contraflowing chilled air in the tube 5.

The chiller assembly 6 comprises a cup-shape aluminium casing 7 and an aluminium insert 8 that seals into the casing 7 to define within it a domed, cylindrical chamber 9 for receiving the pre-cooled air from the tube 4. A Peltier-effect device 10 is mounted with its cold junction in direct thermal contact with the casing 7 to cool the assembly 6 and, thereby, the air in the chamber 9. Input air is in this respect injected into the chamber 9 from the tube 4 via a port 11 that opens substantially tangentially to the cylindrical wall of the chamber 9 (see Figure 2) so that a swirling or vortex motion is imparted to it within the chamber 9. This swirling or vortex motion enhances contact of the air with the cold walls of the chamber 9 and extends its path within the chamber 9 before it exits chilled, via a centrally-located port 12 of the insert 8.

The port 12 of the insert 8 opens into a coalescing filter 13 that is attached to the insert 8 within a separation vessel 14. The filter 13 brings about precipitation of moisture held in saturation in the chilled air flowing through it, and causes the precipitated water to coalesce into droplets that fall for collection to the bottom of the vessel 14. A float valve 15 responds to rise in the collected-water level in the vessel 14 to allow the water to drain off from the vessel 14 via a pipe 16 to a drain outlet 17.

The chilled and moisture-freed air passed by the filter 13 exits from the vessel 14 into the tube 5 of the heatexchanger coil 2 via a port 18 of the assembly 6. The heat transfer that takes place from the tube 4 through the wall of the tube 5 to pre-cool the input air to the chiller assembly 6, warms the exiting chilled air in the tube 5. The path of this air extends beyond the tube 5 of the heat-exchanger coil 2, by way of a tube 19 wound between the vanes 20 (only one of which is shown) of a heat-sink 21 that is mounted in direct thermal contact with the hot junction of the Peltier-effect device 10.

The dehumidified air in the tube 19 is thus warmed further, restoring it to about ambient room temperature, before it passes to an air outlet 22 of the unit.

Further heat dissipation from the sink 21 to ensure optimum operation of the device 10, is enhanced by air that is drawn between the vanes 20 from the ambient atmosphere by an electrically-driven fan 23. Electrical energisation of the device 10 itself, is made from a circuit (not shown in detail) that includes a transformer 24 and rectifier 25, and is regulated by a thermostat 26.

The thermostat 26 has a probe 27 (see Figure 2) that is mounted in the chiller assembly 6 close to the chamber 9, and is set to maintain a substantially-constant air temperature within the chamber 9. This temperature for a compressed-air pressure of 7 bar, may be about +5 degrees Celsius.

Instead of mounting the probe 27 within the casing 7 of the chiller assembly 6, it may be more economical in production costs, and as effective operationally, to wrap it and its connecting lead round the outside of the casing 7.

The efficiency of the dehumidifier unit described above is enhanced significantly by the pre-cooling of the input air to the chilling chamber 9 and the increased exposure of that air to chilling within that chamber 9 under the imparted swirling or vortex motion. Furthermore, the dried output air is supplied from the unit at an appropriate working temperature, the air having been restored to this by useful recovery of heat that otherwise would have to be dissipated in the chilling chamber 9 and through the forced air-cooling of the heatsink 18.

The degree of thermal insulation that can be achieved between the heat-sink 21 on the one hand, and the chiller assembly 6 and heat-exchanger coil 2, on the other, is important for efficiency of operation. To this end, the assembly 6 and the coil 2 may be encased within thermal insulating material, and a form of the unit modified in this way and incorporating further modification in relation to the chiller assembly and the heat exchangercoil, is illustrated in Figure 3 and will now be described.

Referring to Figures 3, the heat'exchanger coil 2 of Figure 1 is replaced in the modification by a heatexchanger that is formed in a square block 30 of heatinsulating plastics material. In this respect, the outer passageway of the heat-exchanger for conveying the input air from the inlet 1 to the chilling chamber 9, is formed by a spiral channel 31 within the block 30. A tube 32 extends along, and substantially coaxially with, the channel 31 to form the inner passageway for conveying the chilled, moisture-freed air to the tube 19 and thence to the unit outlet 22.

The chilling chamber 9 in the modification is defined within a cylindrical-cup member 33 that is pressuresealed into the block 30 with a port 34 for input air coupled to the channel 31 and an outlet port 35 for chilled air coupled into the tube 32. The mounting of the member 33 within the block 30 in this way insulates it to a substantial extent from the heat-sink 21, and together with the simplified construction of the heatexchanger, reduces costs of production.

Claims

Claims:

1. A dehumidifier comprising means for chilling input gas to precipitate moisture therefrom, and heatexchanging means coupled to the chilling means to precool the input gas by thermal transfer to the chilled, moisture-freed gads output from the chilling means.

2. A dehumidifier according to Claim 1 wherein the chilling means comprises thermally-conductive means through which the input gas flows, and a Peltier-effect device having its cold junction in thermal contact with said thermally-conductive means for chilling said thermally-conductive means and, thereby, the gas flowing through it.

3. A dehumidifier according to Claim 2 wherein a chamber is defined within said thermally-conductive means and the input gas is caused to flow within the chamber with a swirling or vortex motion.

4. A dehumidifier according to Claim 3 wherein the chamber has a substantially cylindrical wall, and the input gas is directed into the chamber substantially tangentially to said wall to impart said swirling or vortex motion to the gas.

5. A dehumidifier according to Claim 3 or Claim 4 wherein the gas exits from the chamber via a port centrally-located with respect to the chamber.

6. A dehumidifier according to any one of Claims 3 to 5 wherein the chilled gas flows from the chamber to the heat-exchanging means via a filter for bringing about precipitation of the moisture from the chilled gas.

7. A dehumidifier according to Claim 6 wherein the filter is mounted on said thermally-conductive means.

8. A dehumidifier according to any one of Claims 2 to 7 wherein the flow path for the moisture-freed gas extends from the heat-exchanging means via an elongate passageway that is thermally coupled to a heat-sink for the hot junction of the Peltier-effect device.

9. A dehumidifier according to Claim 8 wherein the heat-sink has cooling vanes and the passageway is provided by a tube that extends between the vanes.

10. A dehumidifier according to Claim 8 or Claim 9 including means for causing air of the ambient atmosphere to flow between the vanes to cool the heat-sink.

11. A dehumidifier according to any one of Claims 1 to 10 wherein the heat-exchanging means involves two elongate and thermally-intercoupled passageways that are located one within the other, the input gas being conveyed to the chilling means via a first of the passageways and the chilled, moisture-freed gas being conveyed from the chilling means via the second passageway.

12. A dehumidifier according to Claim 11 wherein the chilled, moisture-freed gas flows in the inner of the two passageways.

13. A dehumidifier according to Claim 11 or Claim 12 wherein the directions of gas flow in the two passageways are opposite to one- another..

14. A dehumidifier according to any one of Claims 11 to 13 wherein the thermally-intercoupled passageways are provided by substantially-coaxial tubes.

15. A dehumidifier according to any one of Claims 11 to 13 wherein the outer of the two thermally-intercoupled passageways is defined by a channel within a thermallyinsulating member and the inner passageway is provided by a tube located within the channel.

16. A dehumidifier according to Claim 15 wherein the chilling assembly is mounted within the thermallyinsulating member.

17. A dehumidifier in which input gas is chilled within a chamber to precipitate moisture therefrom, wherein the gas is caused to flow within the chamber with a swirling or vortex motion.

18. A dehumidifier according to Claim 17 wherein the chamber has a substantially cylindrical wall, and the input gas is directed into the chamber substantially tangentially to said wall to impart said swirling or vortex motion to the gas.

19. A dehumidifier according to Claim 17 or Claim 18 wherein the gas exits from the chamber via a port centrally-located with respect to the chamber.

20. A dehumidifier according to any one of Claims 17 to 19 wherein the chilled gas flows from the chamber to the heat-exchanging means via a filter for bringing about precipitation of the moisture from the chilled gas.

21. A dehumidifier according to any one of Claims 17 to 20 wherein the chamber is defined within thermallyconductive means that is in thermal contact with the cold junction of a Peltier-effect device for chilling said thermally-conductive means and, thereby, the gas flowing through it.

22. A dehumidifier according to Claim 21 wherein the flow path for the chilled, moisture-freed gas from the chamber extends via an elongate passageway that is thermally coupled to a heat-sink for the hot junction of the Peltier-effect device such that the gas is warmed from the heat-sink.

23. A dehumidifier according to Claim 22 wherein the heat-sink has cooling vanes and the passageway is provided by a tube that extends between the vanes.

24. A dehumidifier according to Claim 23 including means for causing air of the ambient atmosphere to flow between the vanes to cool the heat-sink.

25. A dehumidifier according to any one of Claims 17 to 24 wherein heat-exchanging means is arranged to cool the input gas prior to its entry to the chamber, by thermal transfer to the chilled, moisture-freed gas.

26. A dehumidifier according to Claim 25 wherein the heat-exchanging means comprises two elongate and thermally-intercoupled passageways that are located one within the other, the input gas flowing to the chamber in a first of the passageways and the chilled, moisturefreed gas flowing in the second passageway.

27. A dehumidifier according to Claim 26 wherein the chilled, moisture-freed gas flows in the inner of the two passageways.

28. A dehumidifier according to Claim 26 or Claim 27 wherein the directions of gas flow in the two passageways are opposite to one another.

29. A dehumidifier according to any one of Claims 26 to 28 wherein the thermally-intercoupled passageways are provided by substantially-coaxial tubes.

30. A dehumidifier according to any one of Claims 26 to 28 wherein the outer of the two thermally-intercoupled passageways is defined by a channel within a thermallyinsulating member and the other of the two passageways is provided by a tube located within the channel.

31. A dehumidifier according to Claim 30 wherein the chamber is defined within a thermally-conductive member mounted in the thermally-insulating member.

32. A dehumidifier substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

33. A dehumidifier according to Claim 32 modified substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.