This invention relates to evaporative air-cooling apparatus .

Known evaporative air-cooling apparatus generally comprises either water sprays, flowing water films or sheets of air permeable absorbent material wetted from above to obtain the necessary contact between air and water for evaporation to take place. With all of these known evaporative air coolers there is some "carry-over" of water droplets into the atmosphere and it has been proved that spray eliminators and the like do not achieve total elimination of the problem of water droplet "carry¬ over". It it also now known that certain viruses can be carried on minute droplets of water and that water droplet "carry-over" can lead to the transmission of diseases such as Legionnaires disease.

The present invention has as its object to provide evaporative air-cooling apparatus which overcomes the problem of ^" carry-over" of water droplets.

The present. invention provides evaporative air- cooling apparatus comprising, in its position 01 use, a water container open at its top, means defining an air passage through said apparatus, and an array of discrete lengths of capillary material arranged in said air

passage above said water container and with their lower ends depending into said .water container, whereby, in use, said lengths of capillary material will become wet with water from said water container by surface tension alone and air passing through said passage will flow over the surfaces of said lengths of capillary material to evaporate water therefrom and cool the air.

The capillary material may be any material, such as cotton, synthetic fibres or sponge-like material, having an internal capillary or pore structure such that the surface tension of water will cause the water to rise in the material in the manner of a wick. With a properly selected capillary material it is possible to achieve water lift heights in excess of 300 mm.

Air flowing over the surfaces of the lengths of capillary material evaporates water therefrom, e.g. , from the pores thereof. The uptake of latent heat necessary for evaporation to take place chills both the air a d the water remaining in, and still to be evaporated from, the capillary material- Since the rate of flow of water in the capillary material is relatively slow, this residual water is progressively chilled by the evaporative heat demand and provides an additional amount of contact cooling to the air flowing over the surfaces of the

lengths of capillary material, resulting in a cooling factor greater than the humidi ication chilling factor alone .

The apparatus of the invention may comprise means for maintaining a predetermined level of water in said water container.

According to one embodiment, the means for maintaining a predetermined level of water in said water container comprises an air-tight water reservoir arranged above said water container and a pipe or tube depending from said reservoir and communicating said reservoir and said water container, said pipe or tube being open at its lower end and terminating substantially at said predetermined water level. Said reservoir may have an opening therein, e.g. in a top portion thereof, through which it can be filled with water and closure means may be provided for closing said opening in an air-tight manner. Valve means may be provided for closing said depending pipe or tube wliilst said reservoir is being filled with water.- Low-level indicator means may be provided for indicating when the water in said reservoir has fallen to a prede ermined level and the reservoir requires refilling.

According to another embodiment of the invention, said means for maintaining a predetermined level of water in said water container comprises means for connecting said water container to a source of water, e.g. to a mains water supply, and valve means for controlling the supply of water to said container whereby to maintain said predetermined level. Said valve means may be a loat-controlled valve or ballcock.

An alternative means for maintaining a predetermined level of water in said water container comprises simple overflow means, e.g. an overflow pipe.

The apparatus of the invention may comprise a housing having an air inlet and air outlet and said air passage may extend between said air inlet and said air outlet and be at least partially defined by said housing.

Said array may comprise a plurality of closely- spaced substantially parallel discrete lengths of capillary material. Said discrete lengths of capillary material may be arranged in a plurality of substantially parallel rows or substantially concentric rings with the lengths of capillary material in one row or ring offset from the lengths of capillary material in the or each adjacent row or ring, whereby air passing through said passage is caused to follow a labyrinthine path through said array. The lengths of capillary material in each

said rot- ^* or ring may be mounted in or on a frame and said frames may be mounted in a housing of the apparatus or in an outer frame. Each said discrete length of capillary material may be in the form of a strip or cord.

Fan means may be provided for passing air through said passage and may be located either downstream or upstream of said array.

Where large volumes of air are required to be cooled, the apparatus of the invention may comprise two or more said arrays arranged one above the other and each having a said water container associated therewith.

If desired, the apparatus may comprise a first air passage having a said array therein and a second air passage having heat exchanger means therein, the evaporation of water from said array serving to remove heat from said heat exchanger means to cool air passing through said second air passage. In this way air passing through said secotid passage can be cooled without increasing the humidity thereof. Said first air passage may be directly beneath said second air passage, a plurality o f tubes may extend vertically through said air passages, that part of each said tube in said first passage may have capillary material therearound, whereby to provide said array, and that part of each said tube in said second passage may have one or more fins thereon to

increase the surface area thereof, whereby to provide said heat exchanger. Preferably each of said tubes comprises a heat pipe, i.e. , a sealed length of pipe or tube containing a heat exchange or heat transfer medium, usually a fluid which is in a liquid state below a particular temperature and in a gaseous state when at a temperature above said particular temperature.

The invention will be more particularly described with reference to the accompanying drawings in which: -

Figure 1 is a sectional elevation of one embodiment of evaporative air-cooling apparatus according to the invention.

Figures 2 and 3 are .a front elevation and fragmentary plan view respectively of an array of lengths of capillary material used in the apparatus of Figure 1,

Figure 4 is a sectional elevation of another embodiment of evaporative air-cooling apparatus according to the invention,

Figure 5 is a sectional elevation of another embodiment of apparatus according to the invention,

Figure 6 is a sectional elevation of another embodiment of apparatus according to the invention,

Figure 7 is a sectional elevation of yet another embodiment of apparatus - according to the present invention,

Figure 8 is a sectional elevation of a further embodiment of apparatus according to the present invention, and

Figure 9 is a sectional plan view on the line Y-Y of Figure 8.

Referring to Figures 1 to 3 of the drawings, it will be seen that the evaporative air-cooling apparatus illustrated therein comprises a housing 1 having an air inlet 2a or 2b, an air outlet or outlets 3 and defining an air passage 4 extending between the air inlet 2a or 2b and the air outlet or outlets 3. Mounted within the air passage 4 is an array 5 of discrete lengths 6 of capillary material the lower ends of which depend into a water container 7 mounted in the housing 1 below the level of the array 5. Also mounted within the housing 1 above the water container 7 is a water reservoir 8 connected to the water container 7 by means of a pipe or tube 9. The water reservoir 3 is air-tight and the pipe or tube 9 terminates at subs an ially the level within the water container 7 at which a predetermined level of water is to be maintained in the water container 7.

Thus, when the water level in the water container 7 has risen to the point where it closes the lower end of the pipe or tube 9 air t-'ill be prevented from entering the reservoir 8 and no further ^' water will pass from the reservoir 8 into the water container 7 until the level of water in the water container 7 has fallen below the lower end of the pipe or tube 9. Low-level indicator means 8a is provided for indicating when the water in reservoir 8 has fallen to a predetermined level and the reservoir 8 requires refilling. A valve 10 is provided for closing the pipe or tube 9 whilst the reservoir 8 is being filled through a filler opening 11 normally closed by a sealed closure 12. A fan 13 driven by a motor (not shown) is provided for passing air through the passage 4.

As will be seen from Figures 2 and 3 the lengths 6 of capillary material in the array 5 are in substantial spaced parallel relationship and are arranged in parallel rows with the lengths 6 in one row offset from the lengths 6 in an adjacent row or rows so that air passing through the array 5 is caused to follow a labyrinthine path. The lengths ^" 6 of capillary material in each row- are mounted on or in a frame 14.

If desired the water container 7 may be provided with an overflow pipe 15, although with the arrangement shown in this embodiment this should not be required.

The apparatus illustrated in Figure -_ , in which like parts have been given , like reference numerals, is suitable for use with conventional air ducting and comprises a housing 1 of sheet metal the outlet end 3 of which has a peripheral flange 16 whereby the housing can be connected to sheet metal air ducting. In this embodiment the water container 7 is supplied with water from a supply thereof, e.g. , a mains supply or an external water tank, by way of a water pipe 17. A predetermined water level is maintained in the water container 7 using any suitable valve means (not shown) such as a float-controlled valve or a ballcock or simply the overflow pipe 15.

The embodiment of Figure 5, in which again like parts have been given like reference numerals, is suitable for handling large volumes of air and comprises three arrays 5 arranged one above the other and each having a water container 7 associated therewith as shown. The upper water container 7 may be supplied with water through a water pipe 18 and the lower water containers 7 may be supplied -with water through overflow pipes 19 wliich serve to maintain a required predetermined level of water in each of the water containers 7. As many arrays 5 as required may be arranged one above the other according to the volume of air to be cooled.

The embodiment of Figure 6 is for use in situations where height is a consideration and comprises an annular water container 7 and an annular array 5. The annular array 5 depends from a top plate 20 which also carries a motor 21 for the fan 13. The embodiment also comprises a bottom plate 22 spaced from the top plate 20 by spacers 23 and a deflector plate 24 for directing air into the fan 13 and which also supports the water container 7. In this embodiment the fan 13 is downstream of the array 5.

The embodiment shown in Figure 7 is similar to the embodiment of Figure 6 except that the motor 21 and fan 13 are mounted on the bottom plate 22, the fan 13 is upstream of the array 5, the deflector plate 24 is omitted and the top plate 20 acts as a deflector to direct air into the fan 13.

In the embodiment of Figures 8 and 9, the apparatus comprises a first air passage 4a and a second air passage 4b, with the second air passage 4b being arranged directly above the first air passage 4a. An array of heat pipes 25 extend vertically through the first and second passages. That part of each heat pipe 25 in the first passage 4a has capillary material 26 therearound to form the array 5 whilst that part of each heat pipe 25 in the second passage 4b has one or more fins 27 thereon whereby the assembly forms a heat exchanger 28. In this way, the evaporation of water from ^' the surfaces of the

capillary material 26 due to the flow of air through the first passage 4a serves not only to cool the air flowing through the first passage 4a but also to extract heat from the heat exchanger 28 which in turn cools the air flowing through the second passage 4b. In this way the air flowing through the second passage 4b is cooled without increasing the humidity thereof. By suitable baffle or other arrangements (not shown) a space to be supplied with cooled air can be supplied either from the first passage 4a or from the second passage 4b or even with a required mixture of air from the passages 4a and 4b according to the humidity requirements in the space receiving the cooled air.

It will be understood that the evaporating air- cooling apparatus of the present invention is completely self-regulating in that water will only be evaporated from the surfaces of the lengths of capillary material at the rate at which it can be absorbed by the air in increasing the relative humidity of the air and reducing the dry-bulb temperature. Water will only be supplied to the capillary material at the same rate as that at which it is evaporated, since it is the evaporation of water from the surface pores of the lengths of capillary material which enables the surface tension in the water to induce its replacement. Consequently, if no evaporation takes place, then no water will be supplied to the capillary material and the system will remain in a

static balanced condition until air is cause t«. f lot- over the surfaces of the lengths of capillary material and so induce evaporation.

The cross-section of the lengths of capillary material is an important parameter in the design of air- cooling apparatus according to the present invention, since it is the cross-sectional area which is the controlling factor in the water handling capability of the capillary material, and is proportional to the square of the effective diameter of the lengths of capillary material, whilst the surface area of the lengths of capillary material is the controlling factor in the rate of evaporation capability and is proportional to the effective diameter of the lengths of capillary material. Thus, the cross-section of * the lengths of capillary material can be selected according to the required height of the array or the required rate of evaporation having regard to the material selected as the capillary material. Likewise, the number of lengths of capillary material and the arrangement thereof i the arrav is to some extent determined by the overall temperature reduction required of a particu r ai flow.

If air-cooling app.-tratu.s according to the invention is !.o be used in a mobile situation, sucli as in a motor vehicle or trailer vehicle, then the spaces between the lengths of capillary material where they depend into the

water container can be filled with an absorbent material, e.g. , a natural or synthetic sponge material, to depress any water movement and so prevent undue spillage.

Because the apparatus of the present invention relies totally upon the surface tension of water to wet the capillary material, no water droplets are produced which can "carry-over" into the atmosphere and which might carry viruses or the like which could constitute a health risk.