The present invention relates to a wall-mountable hand dryer of the type which uses an air-knife to wipe water from the surface of the user's hands.

Hand dryers are typically installed in public washrooms as an alternative to paper towels. There are three main types of hand dryer on the market: "warm-air" hand dryers, "high speed" hand dryers and "air-knife" hand dryers.

Warm air hand dryers are very well known. They are invariably low flow, low speed machines which rely on heating the air to promote an evaporative drying effect at the surface of the hand. Examples include the Model A Series of hand dryers manufactured and marketed by World Dryer Corporation. The heated airflow is typically discharged through a single nozzle and the drying action is a "hand-over-hand" action, requiring the user to rub the hands together under the nozzle with the aim of encouraging the evaporative drying effect.

High speed hand dryers, as the name suggests, use high speed airflow (>80 m/s) to provide a momentum-drying effect at the surface of the hands. Examples include the Xlerator® hand dryer manufactured and marketed by Excel Dryer Inc. Again the airflow is typically discharged through a single relatively large nozzle and the mode of use is somewhat similar to the "hand-over-hand" action of the warm air dryer, with the hands being held or cupped together underneath the nozzle to dry them. However, instead of being evaporated, the vast majority of the water on the surface of the hands is instead driven or blasted from the hands by the high-momentum airflow, with evaporation accounting for only a small proportion of water removal. The airflow tends not to be heated, though waste heat from the motor may in some cases be used to heat the airflow to a degree. The third general type of hand dryer is the air-knife hand dryer, examples of which include the Dyson Airblade range of Hand Dryers manufactured by Dyson (UK) Limited and the Jet Towel hand dryer manufactured by Mitsubishi Electric Corporation

These hand dryers use an air-knife - effectively a sheet or curtain of moving air - to remove the water from the user's hands. The mode of operation is analogous to the established use of air knives in industry to remove debris or liquid from the surface of a product (see e.g. EP2394123A1, which describes removal of debris from a glass sheet using air knives): the air-knife moves across the surface of the hand and, as it does so, wipes or scrapes the water from the surface of the hand.

In both the Dyson Airblade and the Mitsubishi Jet Towel, two opposing, stationary air- knives are used, one for each side of the user's hand. The hands are inserted between the air-knives and then withdrawn slowly to effect the required relative movement between the hands and the air knives.

In the Dyson arrangement - shown in Figure 1 - the air knives are discharged through narrow, continuous slots (only the rear slot a is visible in Figure 1), each less than 1mm wide. In the Mitsubishi machine - shown in Figure 2 - the air-knife is instead discharged through opposing rows of individual discharge apertures (only the rear row b is visible in Figure 2): here, the individual jets combine to produce the air knife downstream of the discharge apertures. In each case, the air knife is discharged at high speed (>80 m/s) to provide for an efficient wiping action across the surface of the hand.

The present invention is concerned with air-knife hand dryers, specifically.

According to the present invention there is provided a wall-mountable hand dryer of the type which uses an air-knife to wipe the water from a user's hand, the hand dryer being configured to have a maximum depth, front-to-back, of less than 150mm when it is surface-mounted on - rather than recessed within - the wall, the dryer having a projecting part which projects outwardly either from the wall or from a rear part of the dryer, the air-knife being directed downwardly onto the user's hand as it is passed lengthwise underneath the projecting part of the dryer, the air knife being discharged through one or more discharge apertures, the discharge apertures being positioned towards the front of the projecting part so that they are spaced at least 75mm from the wall or, as the case may be, the rear part of the dryer.

The hand dryer has the advantage that it is a low profile design. The maximum depth of 150mm when it is surface mounted on the wall is significantly less than the current range of Dyson Airblade hand dryers (depth front-to-back 250mm approx) or the

Mitsubishi Jet Towel hand dryer (depth front-to-back 220mm approx). In particular, the maximum depth of the dryer may be 4 inches (101.6mm) or less, allowing surface- mounting of the hand dryer in compliance with the Americans with Disabilities Act 1990 (ADA). This avoids the inconvenience and expense of having to recess the hand dryer into the wall in order to comply with the ADA: particularly advantageous when retro-fitting the hand dryer.

Despite the significant reduction in profile depth, the dryer nevertheless provides an effective air-knife drying action. The user dries the hands palm-open - moving the hands lengthwise front-to-back underneath the projecting part. The air knife is directed downwardly onto the hands and, as the hand is moved relative to the discharge slot, the air-knife mechanically wipes the water from the surface user's hands to dry them.

Because the drying action is a front-to-back action, the user can increase the effective depth of the dryer front-to-back by pitching the hands down. The most suitable pitch angle will vary according to the effective depth required by the user - users with larger hands will tend to pitch their hands at a steeper angle. By spacing the discharge apertures at least 75mm from the wall, however, the pitch angle is maintained within comfortable limits for most users. Consequently, the invention provides a shallow, low profile hand dryer which nevertheless offers an effective air knife drying action. The discharge apertures are preferably spaced the maximum depth from the wall. This maximises the effective depth of the dryer in use.

The discharge apertures may be provided on the underside of the projecting part, preferably along the front lower edge of the projecting part to maximize the spacing between the discharge apertures and the wall (or rear part of the dryer).

The projecting part itself may be an external casing of the dryer which projects from the wall in use, in which case the effective depth of the dryer can be maximised by arranging the discharge apertures along a front lower edge of the casing.

The discharge aperture(s) may be arranged in a V-configuration (viewed from the front of the dryer). This allows a user to bank his or her hands at a comfortable angle in use.

The discharge aperture(s) are preferably arranged to span the width of a user's hand, so that the air-knife provides a wiping action the full width of the user's hand. A lateral span of at least 80mm is considered preferable, though not essential. If it is intended to dry both hands at the same time, then the discharge aperture(s) may be arranged to span the width of both hands side-by-side underneath the discharge apertures(s). A lateral span of at least 200mm is considered preferable in this case, though again this is not essential - a shorter span may be suitable for certain countries, for example.

The discharge aperture(s) may be arranged to span the width of a user's hand, so that the air-knife provides a wiping action the full width of the user's hand. A lateral span of at least 80mm is considered sufficient in most cases. If it is intended to dry both hands at the same time, then the discharge aperture(s) may be arranged to span the width of both hands side-by-side underneath the discharge apertures(s). A lateral span of at least 200mm is considered preferable in this case, though again this is not essential - a shorter span may be suitable for certain countries, for example. The exit airspeed through the discharge aperture(s) is preferably in excess of 80 m/s to ensure that the air knife has an effective wiping action at the surface of the hands. A particularly effective wiping action can be obtained at airspeeds in excess of 150 m/s. The exit air speed is determined in accordance with general air knife principles by the discharge area and the pressure behind the discharge aperture(s). So, for example, increasing the discharge area will reduce the exit air speed at a given pressure.

Increasing the pressure for a given discharge area will increase the exit air speed.

The discharge aperture(s) may take the form of air holes arranged in a row or, alternatively, an elongate air slot. For example a single elongate air slot or row of air holes may be provided to discharge a single air-knife for drying the hands one after another; a pair of such slots or rows of holes may be provided for generating two separate air-knives which dry the hands simultaneously, or a single elongate slot or row of holes may be provided for generating a single air knife which is sufficiently long to dry the hands simultaneously side-by-side.

The slot, or air holes, may be less than 2mm wide, intended to provide a laminar, well- defined air knife with minimal wind shear. In one embodiment, the length of the slot - or length of the row of air holes - is at least 80mm.

In one embodiment, the discharge apertures are provided on the underside of an external casing of the hand dryer so that they face the floor, rather than a lower part of the hand dryer. This arrangement has the benefit of a large clearance underneath the discharge aperture for pitching the hands in use.

Embodiments of the invention will now be described with reference to the

accompanying drawings, in which: Figure 1 and 2 are schematic perspective views of conventional air-knife hand dryers; Figure 3 is a schematic perspective view of a wall-mountable hand dryer in accordance with a first embodiment of the present invention;

Figure 4 is a side view of the hand-dryer in Figure 3;

Figure 5 are schematic views looking down on the hand dryer shown in Figure 3, illustrating the mode of use of the hand dryer;

Figure 6 is a side view of the bottom part of the hand dryer of Figure 3;

Figure 7 is a schematic perspective view of a wall-mountable hand dryer in accordance with a second embodiment of the present invention;

Figure 8 is a side view corresponding to Figure 7;

Figure 9 is a schematic perspective view of a wall-mountable hand dryer in accordance with a third embodiment of the present invention;

Figure 10 is a side view corresponding to Figure 9;

Figure 11 is a schematic perspective view of a wall-mountable hand dryer in accordance with a fourth embodiment of the present invention;

Figure 12 is a schematic perspective view of a wall-mountable hand dryer in accordance with a fifth embodiment of the present invention;

Figure 13 is a schematic perspective view of a wall-mountable hand dryer in accordance with a sixth embodiment of the present invention; Figure 14 is a schematic perspective view of a wall-mountable hand dryer in accordance with a seventh embodiment of the present invention; and Figure 15 is a side view corresponding to Figure 14.

For simplicity, unless otherwise stated corresponding features have been given corresponding reference numerals in the following description.

Figures 3 and 4 illustrate a wall-mountable hand dryer 1 which works by using an air knife 3 - a curtain or sheet of moving air - to wipe the water from a user's hands. The hand dryer 1 is illustrated in its normal wall-mounted orientation.

The hand dryer 1 comprises an external box-like casing 5 which projects a maximum depth X from the wall 7. In this case X = 4 inches (101.6 mm) and thus the dryer is ADA-compliant, meaning that it complies with the Americans with Disabilities Act 1990:

"4.4.1 * General. Objects projecting from walls (for example, telephones) with their leading edges between 27 in and 80 in (685 mm and 2030 mm) above the finished floor shall protrude no more than 4 in (100 mm) into walks, halls, corridors, passageways, or aisles "

Source: ADA Accesibility Guidelines for Buildings and Facilities (ADAAG)

The air-knife 3 is discharged downwardly through a discharge aperture 9 on the underside of the casing 5.

The discharge aperture 9 is in the form of an elongate discharge slot, which extends laterally across the dryer 1 (in this case generally parallel with the wall 7). The user dries the hands palm-open, one side at a time, moving the hand lengthwise front-to-back underneath the discharge slot 9. This is illustrated in Figure 5, looking down on the dryer from above. The discharge slot 9 is 250mm long - intended to span both hands held side-by-side under the discharge slot. A shorter discharge slot may alternatively be used - say, 120mm in length - to dry first one hand and then the other in turn.

As the hands are moved relative to the discharge slot 9, the air-knife 3 mechanically wipes the water from the surface user's hands to dry them.

The shallow depth of the dryer 1 on the wall 7 means that a typical user's fingertips will tend to contact the wall 7 if the hands are held horizontal underneath the dryer 1.

However, the front-to-back drying action means that the user can avoid this by pitching the hand down at an angle Θ as it passes underneath the discharge slot 9, increasing the effective depth of the dryer (Figure 6).

If the discharge nozzles are spaced a distance, D, from the wall then the effective depth, d, is given by D = dcosQ. To provide for a comfortable pitch angle Θ in most cases, D is set at 75mm in accordance with the invention, so that the discharge slot 9 is spaced 75mm from the wall 5 in use.

The precise pitch angle Θ will vary from user to user for a given value of D. A user with relatively large hands, may prefer an effective depth d of, say, 150mm - equating to a pitch angle Θ of 60 degrees - whereas a user with small hands may only require an effective depth d of 120mm - equating to a pitch angle Θ of approximately 50 degrees.

If the maximum depth of the dryer exceeds 75mm, then shallower pitch angles Θ can be achieved by arranging the discharge apertures further towards the front of the dryer. The discharge slot 9 is fed via a ducted motor-driven fan housed inside the external casing 5 of the dryer 1, which fan draws air in through the intakes 11 on the side of the casing 5 and forces this air out through the discharge slot 9 to generate the air-knife 3. The discharge slot 9 is less than 2mm in width. The motor-driven fan is configured to provide an exit airspeed through the discharge slot 9 in excess of 80 m/s. This is intended to provide a well-defined, high speed, laminar air-knife which exhibits low wind shear. A particularly effective wiping action can be obtained at airspeeds in excess of 150 m/s.

Alternatively, a source of compressed air may be used to feed the discharge slot 9 via a plenum chamber behind the slot 9.

The discharge slot 9 is formed directly in the wall of the casing 5. This provides for easy-cleaning of the casing 5, and allows the casing 9 itself to be used as a duct or plenum for feeding the discharge slot 9.

Preferably, the slot 9 is machined into the wall of the casing 5- this provides good dimensional tolerance - but if the casing 5 is moulded then the slot 9 itself could be moulded as part of the casing 5.

Figure 7 shows an arrangement in which the dryer 10 is provided with two separate discharge slots 12, 13 - one for each hand - rather than a single "double-span" discharge slot. Here, the slots are provided along a front lower edge of the casing (see Figure 8), so that they are spaced the maximum depth X from the wall, which in this case is 4 inches (101.6mm) for ADA compliance.

In this arrangement, an effective depth of 150mm equates to a pitch angle Θ of 48 degrees and an effective depth of 120mm equates to a pitch angle Θ of 34 degrees. Figures 9 and 10 show an arrangement in which the dryer 100 is provided with discharge slots 15, 17 which are arranged in a V-configuration (viewed from the front of the dryer 100). This allows a user to bank the hands in use, making the drying action more comfortable for the user. The discharge slots 15, 17 are provided along a front, lower edge of the dryer 100, which edge is V-shaped to provide the required V-shaped configuration of the slots 15, 17.

A guide ramp 19 is additionally provided behind the slots 15, 17 in this arrangement. This is not essential, but it provides the benefit that it encourages a user to pitch the hands down in use.

The air-knife need not be directed vertically downwardly: it may project outwardly at an angle, for example. This is shown in Figure 11. Here, a single discharge slot 70 is configured to discharge an air-knife 30 forwardly towards the user, at a downward angle. The dryer Γ is similar in other respects to the dryer 1.

In the previous arrangements, the discharge apertures have been provided on the underside of an external casing of the dryer which projects from the wall. Figure 12 shows an arrangement in which the discharge aperture - again in the form of a single discharge slot 9 - is provided on a projecting part 21 forming the roof of a drying cavity 23 for collecting the waste water. The projecting part 21 in this case projects out from the rear wall 25 of the drying cavity 23, which rear wall 25 forms a rear part of the dryer 110. The discharge slot 9 is spaced 75mm from the rear wall 25 of the cavity 23.

In general, if the discharge aperture faces a lower part of the dryer - for example the base 27 drying cavity 23 in dryer 110 - then the discharge aperture is preferably spaced a distance C from the lower part of the dryer to provide sufficient clearance under the discharge slot to allow the majority of users to pitch the hand down without touching the lower part of the dryer. In the arrangement in Figure 12, this distance C is set at 120mm, so that the discharge slot 9 is spaced 120mm from the base 27 of the drying cavity 23.

Figure 13 shows an arrangement in which the discharge slot 9 is provided on a projecting part 29 which projects outwardly from a back-plate 31 forming a rear part of the dryer 1100. In this case the discharge slots face the floor, not a lower part of the hand dryer; this provides the benefit of a large clearance underneath the discharge aperture for pitching the hands in use. Figures 14 and 15 show a dryer 1000 which comprises discharge apertures in the form of a row of closely-spaced holes 700 formed in the wall of the casing 5.

ADA compliance is not an essential part of the invention. The depth X of the dryer may be up to 150mm when it is surface mounted on the wall: this is still a significantly shallower profile than the conventional air-knife hand dryers illustrated in Figures 1 and 2.

The invention provides a relatively shallow hand dryer which nevertheless provides an effective air-knife drying action which is comfortable to use.