This invention relates to a hand drier of the kind that propels air onto a user's hands. Particularly, but not exclusively, the invention relates to a hand drier that is suitable for use in washrooms.

Various kinds of hand drier are well-known and they are generally considered to be a more hygienic way of drying a person's hands than using roller towels or paper tissues. However, some conventional hand driers do not heat air to an effective temperature in a sufficiently short amount of time to enable satisfactory drying of a person's hands.

Overcoming this problem has tended to be addressed by using a more powerful motor to propel the air through the drier and/or by using a higher capacity heating element. An unfortunate side-effect of this is a commensurate increase in power consumption, thereby leading to elevated cost and wasted energy.

The present invention sets out to provide a hand drier that can deliver a properly effective hand drying experience, yet reduce power consumption, thereby conserving energy and saving operating costs.

Accordingly, the invention provides a hand drier comprising:

a blower which operates to compress air in order to heat the air, and which blows the heated air in order to cause the heated air to move;

an air inlet for introducing air to the blower; and

an air outlet duct for directing the heated air along an air flow path within the air outlet duct;

wherein the air outlet duct is situated within the air inlet such that, during drying of a hand, heated air from the air outlet duct is re-circulated via the air inlet to the blower; and

wherein a first portion of the air outlet duct is shaped such that the air flow path slopes towards the front of the drier within the air inlet.

The re-circulated heated air is able to mix with other, generally colder, air being drawn into the blower. The re-circulated heated air is able to pass again through the blower in order to be further compressed and therefore heated in order to increase the temperature of the air exiting the air outlet duct. This thereby reduces the energy needed to give effective drying of the hands.

The blower may itself provide a further reduction of the energy needed to give effective drying of the hands. More specifically, where there is air leakage within the blower, then this air leakage may create a back-flow which is subjected to further compression within the blower, thereby further heating the air and helping to reduce the energy needed to dry hands effectively.

The apparatus of the present invention will normally be such that the air is heated only by the compression of the air. No other heating means need be provided.

The above effects are further enhanced by the shape of the outlet duct, which accelerates the air, thereby causing it to exit the hand drier at a faster speed relative to an outlet duct that extends straight downwards, for example, without a need to increase the power supplied to the blower. This increased speed enhances the drying effect due to the increased force applied by the air to the water on the user's hands.

The high air speed also causes an enhanced back rush of air as it comes into contact with a user's hands. This back rush returns a higher volume of air to the blower as compared to an outlet duct that extends straight downwards, thereby increasing the compression heating effect delivered by the blower. The shape of the outlet duct, and its location relative to the inlet duct, further combine to offer an optimized circular air flow from the outlet duct back to the inlet duct during drying operations.

The regenerative heating afforded by locating the outlet duct within the housing saves further energy. More specifically, a proportion of the air is heated and drawn back into the blower in order to recover energy. This enables the apparatus of the present invention to operate in a heat regenerative manner, which is especially energy-saving.

The air outlet duct and the air inlet may share a common wall whereby the air outlet duct is a tubular formation, the air inlet is a doughnut formation, and the tubular formation is positioned within the doughnut formation. In such a case, the tubular formation may have a curved longitudinal axis in the said first portion. The longitudinal axis may have a radius of curvature of from 100mm to 200mm, preferably 120mm to 180mm, and more preferably 130mm to 160mm.

The said first portion may extend over substantially the entire length of the air outlet duct. Alternatively, the said first portion may be situated in a distal end region of the air outlet duct.

The walls of the first portion may have a straight incline. In such a case, when the drier is oriented for use, the central longitudinal axis of the first portion may be inclined at an angle of between 45 to 55 degrees to the horizontal plane. Preferably, the central longitudinal axis is inclined at an angle of between 50 to 55 degrees to the horizontal plane.

In addition to the first portion, the air outlet duct may have a second portion that is curved along its length. The second portion may be positioned upstream of and feed into said first portion.

At least a portion of the internal diameter of the air outlet duct may taper along the air flow path.

The air outlet duct may have an air outlet mouth and the air inlet may have an air inlet mouth; the air outlet mouth may be situated within the air inlet, so that expelled air is propelled from the air outlet mouth to a user's hands via the air inlet mouth.

The air outlet duct may be curved towards a front portion of the air inlet mouth.

The hand drier may comprise a plurality of said air outlet ducts, such as two said air outlet ducts. Alternatively, the hand drier may comprise just a single said air outlet duct.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 schematically illustrates the general principle of operation of the invention;

Figure 2 is a section through an embodiment of the invention and shows individual components of the apparatus in more detail;

Figure 3 is a view of the inside of part of the apparatus shown in Figure 2, as seen from the front;

Figure 4 is a view of the inside of part of the apparatus shown in Figure 2, as seen from the side;

Figure 5 is a view of part of the apparatus shown in Figure 2, as seen from the side;

Figure 6 is a view of part of the apparatus shown in Figure 2, as seen from beneath;

Figure 7 is another view of part of the apparatus shown in Figure 2;

Figure 8 is a cross section taken along the line A-A shown in Figure 7;

Figure 9 shows the distal portion of the air outlet duct of Figure 8 in isolation;

Figure 10 shows cross sections taken along the lines A-A and B-B of Figure 9;

Figure 1 1 shows another view of a hand drier according to an embodiment of the invention; and

Figure 12 shows a cutaway of the hand drier shown in Figure 1 1 .

Figure 1 illustrates a hand drier 2. The drier 2 comprises a blower 6, which operates to compress air in order to heat it, and which blows the heated air in order to cause the heated air to move. A blower inlet 8 is provided for introducing air to the blower 6. The drier 2 further comprises an air outlet duct 10 for directing the air that has been heated and propelled by the blower 6 onto an object 4 that is to be dried, such as a user's hand.

The air inlet 8 is operatively connected to the air outlet duct 10 such that, during drying, heated air from the air outlet duct 10 is re-circulated via the air inlet 8 to the blower 6. This re-circulation is shown in Figure 1 by arrows 12, 14, with the re-circulated air passing along ducting 16. Thus, as shown schematically in Figure 1 , the air inlet 8 provides air to the blower 6 via an air inlet port 1 1 and also via the ducting 16.

As shown by arrows 18, 20, the re-cycled heated air from the air outlet duct 10 is able to mix with other, generally colder, air being drawn into the blower 6. The recycled heated air is used to further increase the temperature of the air exiting the air outlet duct 10. This reduces the energy needed to give effective drying of the object 4. Also, if the blower 6 is such that air leakage occurs within the blower 6, then air leakage backflows and again is subject to re-circulation and multiple compressions as indicated by the arrows 18, 20. This provides a further heat recirculating feature which increases the temperature of the air exiting the air outlet duct 10, thereby further reducing the energy needed to give effective drying of the objects 4. The re-circulation of the heated air during the drying of the objects 4 is caused by the objects 4 deflecting the heated air from the air outlet duct 10 to the air inlet 8.

Referring now to Figures 2 to 12, there is shown a hand drier 22 according to an embodiment of the invention. Similar parts to those of the apparatus 2 have been given the same reference numerals for ease of comparison and understanding.

As can be seen from the figures, the hand drier 22 is such that the air outlet duct 10 is positioned within the air inlet 8. More specifically, the air outlet duct 10 and the air inlet 8 share a common wall 24. This causes the air outlet duct 10 to have a tubular formation, and the air inlet 8 to have a doughnut formation. The tubular formation is positioned within the doughnut formation, so as to define the inner perimeter of the doughnut formation as shown. It should be noted that the common wall is not an essential feature of the invention. In other embodiments, the air outlet duct cold be formed in a larger structure that was situated within the air inlet, possibly with some other intermediate component or components situated in between.

The air outlet duct 10 has an air outlet mouth 26. The air inlet 8 has an air inlet mouth 28. The air inlet mouth 28 receives heated air that has been deflected from the user's hand 4 and also cooler air from the environment. It will be noted from the figures that the air outlet duct 10 slopes towards the front of the drier as it extends downwardly within the air inlet 8 towards the air inlet mouth 28. The shape of this portion means that the exiting air is directed along a sloped trajectory as it is propelled towards the air outlet mouth 26. The transition to the sloped trajectory causes a pressure gradient to develop in a direction perpendicular to the air flow path, with lower pressure on one side of the outlet duct. As a consequence of Bernoulli's Principle, this decrease in pressure causes an increase in flow speed that causes the air to exit the air outlet mouth 26 at a faster speed without a need to increase the power supplied to the blower 6. This increased speed enhances the drying effect due to the increased force applied by the air to the water on the user's hands 4.

In some embodiments, the sloping portion may itself be curved i.e. the air outlet duct may curve towards the front of the drier as it extends downwardly within the air inlet 8 towards the air inlet mouth 28. In such cases, the exiting air will be directed along an arcuate air flow path as it is propelled towards the air outlet mouth 26. In this instance, the continuing passage of the air along a curved path can help to enhance the effects described above, whereby air is forced to exit the air outlet mouth at faster speed.

It has been found that the air expelled from the outlet duct 10 is particularly suitable for drying hands if the air exits the outlet duct 10 at a flow rate of 25 - 35 litres per second (more preferably 28 - 32 litres per second) with a fluid pressure of 5 - 6 kPa (more preferably, 5.2 - 5.5 kPa)..

It will also be noted that the internal diameter of the air outlet duct 10 tapers as it extends downwardly within the air inlet 8 towards the air inlet mouth 28. Due to the Venturi effect, this reduction in the diameter of the air outlet duct 10 causes a further acceleration of the air as it is propelled towards the air outlet mouth 26, with the consequence that the air exits the air outlet duct 10 at a higher speed than it would have done from a duct of constant diameter.

Although the internal diameter of the air outlet duct 10 reduces over substantially its entire length in this embodiment, the reduction in diameter may occur over just a portion of the length in other embodiments. Typically, but not essentially, this may be a distal portion of the air outlet duct 10. In other embodiments, the air outlet duct 10 may have a substantially constant internal diameter over its entire length.

In the illustrated embodiment, it will be noted that the air outlet duct 10 terminates inside the air inlet 8, so that the air outlet mouth 26 is contained within the air inlet 8. This enables the returning air to be drawn into the air inlet 8 more efficiently, thereby resulting in an increased delivery of recycled air to the blower 6 and improving operating efficiency. In other embodiments, the air outlet duct 10 may project outside the air inlet mouth 28.

The relatively higher air speed of the exiting air offered by the above described effects causes an enhanced back rush of air as it comes into contact with a user's hands 4. This back rush returns a higher volume of air to the blower 6 as compared to a prior art outlet duct, thereby increasing the compression heating effect delivered by the blower 6.

The shape of the air outlet duct 10, and its location relative to the air inlet 8, further combine to offer an optimized circular air flow from the air outlet duct 10 back to the air inlet 8 during drying operations.

The apparatus 22 further includes ducting 30 for directing the re-circulated air to the blower 6. The ducting 30 is comparable to the ducting 16 shown in Figure 1 . The ducting 30 directs the re-circulated air to an inlet formation 32 on the blower 6.

As shown in Figure 2, the blower 6 comprises a rotor 34 and an electric motor 36 for causing the rotor 34 to rotate. The rotor 34 comprises a plurality of vanes 38 mounted on a central shaft 40.

The blower 6 can be any type of positive displacement apparatus and/or of aerodynamic form. The blower 6 can be a bypass type of apparatus, where the air moved does not pass through the electric motor 36. Alternatively, the blower 6 can be of a type where the air does pass through the electric motor 36.

During operation, air is drawn into the air inlet 8 and compressed within the blower 6. This increases the temperature of the air. A proportion of the air is recirculated within the blower 6. This re-circulated air is inside the overall recycling path formed by air deflected off the object 4 which is in close proximity to the air outlet duct 10. The recirculation of the air enables the heated air to be further heated, and thereby to reduce the overall energy required by the electric motor 36 to get the air to the required temperature. Figure 3 shows in detail how the air outlet duct 10 is mounted in the air inlet 8 in such a way that air that is deflected from the objects 4 is drawn back into the blower 6. Re-circulation of the heated air to the blower 6 is able to be controlled such that the air does not overheat and does not impair the required velocity of the exiting air.

Figure 7 shows another view of the air inlet of Figure 2. As can be seen, the air outlet duct 10 extends inside the air inlet. In this example, the walls of the air inlet extend downwards past the point at which the air outlet duct terminates.

Figure 8 shows a cross section along the line A-A of Figure 7. As seen in Figure 8, the distal portion of the air outlet duct slopes towards the front of the drier, with the walls of that portion following a straight incline. Since the outlet duct is tapered, the opposing walls of the outlet duct have different angles of incline. Here, it is possible to define a central longitudinal axis 50 of the duct that forms an angle with the horizontal plane, which in this example is 52.5 degrees.

Located immediately upstream of the first portion is a second portion 52 that is curved and which serves to enhance the acceleration of the air as it passes into the sloped portion of the air outlet duct 10.

The flow of air inside the drier can be further understood with reference to Figures 1 1 and 12. Figure 1 1 shows a drier according to an embodiment, whilst Figure 12 shows a cutaway of that drier. Referring to Figure 12, air enters the drier through the air inlet mouth 28 positioned at the base of the drier and is channeled towards the blower 6, as shown by arrow 54. The blower 6 compresses the air in order to heat it and propels it back towards the user's hands through the air outlet duct 10 (as shown by arrow 56). As can be seen, the air outlet duct emerges within the air inlet, such that air being expelled from the outlet duct mixes with the air that is entering the drier and which is to be circulated towards the blower.

Together, the positioning of the air outlet duct 10 within the air inlet and the sloped geometry of the air outlet duct act to increase the efficiency of the drier. Locating the air outlet duct within the air inlet means that the outgoing air is mixed with the incoming air, helping to ensure that heat from the air is recaptured and recirculated through the device. The shape of the air outlet duct meanwhile serves to accelerate the outgoing air as it leaves the outlet duct; this has the dual effect that it facilitates better mixing of the outgoing air with the incoming air (so retaining heat inside the drier), whilst at the same time providing an enhanced drying effect as the outgoing air applies an increased force to the water on the user's hands.

By way of example and in order to show the advantages of a hand drier according to the present invention, it may be assumed that the apparatus of the present invention has a minimum product lifetime of one million drying cycles. Over such a standard life, known apparatus for drying objects with warm air would emit 8600Kg of carbon dioxide from electricity consumption. Similarly, if paper towels were to be used for drying objects such for example as hands, then 29600 paper towels would be used, requiring subsequent disposal, for example in landfill or by burning. In advantageous contrast, the apparatus of the present invention would generate only 657Kg of carbon dioxide. This equates to the apparatus of the present invention paying for itself more than 2.5 times on electricity saving compared to the mentioned known hand drier, and 43 times compared with paper towels. The apparatus of the present invention is doubly advantageous in use in that firstly it benefits the environment, and secondly it saves operating costs.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, both the apparatus 2 and the apparatus 22 have only one of the air inlet 8 and one of the air outlet duct 10. More than one air inlet 3 and/or more than one air outlet duct 10 may be employed. The apparatus 2, 22 may have control means (not shown) for causing the apparatus to stop and start. The control means may be a sensor operative in response to the proximity of the objects 4 to be dried, or the control means may be a push button. Other types of control means may be employed. The apparatus 2, 22 may be contained within a housing of an appropriate commercially desired shape.

Individual components shown in the drawings are not limited to use in their drawings and they may be used in other drawings and in all aspects of the invention.