WO2003065143A1

WO2003065143A1 - Humidity control device

Info

Publication number: WO2003065143A1
Application number: PCT/GB2003/000397
Authority: WO
Inventors: Geoffrey Russell-Smith
Original assignee: Geoffrey Russell-Smith
Priority date: 2002-01-31
Filing date: 2003-01-30
Publication date: 2003-08-07
Also published as: GB0202211D0; GB2384727A

Abstract

The invention provides a humidity control device (1) comprising an outer container (2) and an inner container (3). The outer container (2) has a plurality of ventilation holes (4). The inner container (3), containing a desiccant (10), is suspended inside the outer container (2) by a spring (7). When the desiccant (10) is dry, the spring (7) retracts and the inner container (3) is supported near the top (2c) of the outer container (2). As the desiccant (10) adsorbs moisture it increases in weight, causing the spring (7) to extend and the inner container (3) to move downwards. If the desiccant (10) is then exposed to a drier atmosphere, moisture is desorbed and the inner container (3) will move up again. A scale (12) is fixed on the inner container (3) and can be viewed through a window (11). As the inner container (3) moves up and down within the outer container (2) the scale (12) moves relative to the window (11), providing an indication of the degree of hydration of the desiccant (10).

Description

HUMIDITY CONTROL DEVICE

The invention relates to a humidity control device, particularly, though not exclusively, to a humidity control device for controlling the humidity in an enclosed area or storage container.

It may be desirable to control the humidity in storage containers for dry goods or in enclosed areas such as caravans or wardrobes. For example, when goods are transported from one location to another, they are often packed into a packaging container. If the packaging container is sealed, changes in ambient temperature can lead to the creation of condensation within the container from moisture present in the air surrounding the goods. This effect is commonly referred to as "sweating", and can occur in, for example, plastic bags, wooden boxes or metal containers. It can also be a problem in mobile vehicles, mobile homes, caravans and the like.

The creation of condensation within a packaging container is undesirable since it can damage goods packed within the container, particularly those goods which are susceptible to, for example, rust or rot.

Ventilation is often used in an attempt to combat "sweating". Such ventilation may be provided by means of a grille or louver. Such ventilation may having no moving parts or may have moving parts that are adjustable to provide a set airflow rate over a long period of time.

Permanent ventilation does not, however, eliminate the problems caused by unwanted moisture. This is because in the event that the air surrounding the packaging container has a higher humidity than the air within the container, the humidity within the container will increase in order to reach equilibrium with the environment outside the container.

It is known to provide desiccant materials to control moisture in small containers. A number of devices include a desiccant held within a porous bag or mesh, for example, which may be placed directly within the container or which may be supported in a wall of the container. Control means using desiccants have been primarily used for substantially sealed containers and have not been practicable for only partly enclosed areas or areas that are sometimes enclosed and sometimes open to changes in atmosphere.

Adsorptive and absorptive desiccants have been used extensively to control moisture in closed containers. There are, however, two particular disadvantages associated with using desiccants. These disadvantages are: (i) a desiccant medium can only absorb or adsorb a predetermined amount of moisture such that once the desiccant medium has absorbed or adsorbed this amount, it cannot absorb or adsorb any more moisture; and

(ii) in the event that the temperature within the container increases, adsorptive desiccants will expel moisture contained therein, which in turn increases the humidity within the container.

The use of desiccants to control humidity in enclosed areas presents a number of problems due to the slow response of the desiccant and the limits on the reusability of the devices.

An object of the invention is to provide an improved humidity control device. Further objects of the invention are to provide a humidity control device that can control humidity within an enclosed area and which can provide an indication of the long-term storage conditions within such an enclosed area.

The invention provides a humidity control device comprising: an outer container having at least one ventilation hole providing access to the interior of said outer container; an inner container supported within said outer container and movable relative to said outer container, said inner container containing a desiccant material, the inner container being supported within the outer container by deformable means mounted on an upper face of the inner container and attached to the inside of an upper face of the outer container such that the inner container is movable up and down within the outer container in response to changes in the weight of the desiccant within the inner container, the weight of the desiccant depending on its degree of adsorption of moisture; and indicator means to indicate the degree of moisture adsorbed by the desiccant, said indicator means comprising an indicator means mounted on the inner container and said outer container further comprising a window means for viewing the indicator means, the indicator means as viewed through the window means thus providing an indication of movement of the inner container relative to the outer container and a consequent indication of the degree of moisture adsorbed by the desiccant.

The inner container is supported within the outer container by deformable means, preferably spring means, mounted on an upper face of the inner container and attached to the inside of an upper face of the outer container such that the inner container moves up or down within the outer container in response to changes in the weight of the desiccant within the inner container, the weight of the desiccant depending on its degree of adsorption of moisture, and hence in response to changes in the force exerted by the inner container on the spring means.

The outer container comprises a window means for viewing the indicator means and the indicator means advantageously comprises a scale visible through the window means. Preferably the scale is attached to or printed on the inner container and comprises an elongate scale extending along the inner container in a vertical direction such that the scale moves up and down in response to changes in the weight of the desiccant in the inner container depending on its degree of hydration.

Preferably the indicator means is provided with calibration means such as a knob or screw adjustment to adjust the position of the indicator means relative to the window in the outer container.

Preferably the shape of the inner container substantially matches the profile of the interior of the outer container, and in particular the sides of the inner container are advantageously parallel to the sides of the outer container so that the inner container can move in a vertical direction within the outer container but cannot move much in a lateral direction.

Advantageously the outer container has a plurality of faces and comprises ventilation holes in more than one of the faces.

Preferably the outer container is of a substantially flat configuration having a substantially planar front face, a substantially planar back face and relatively narrow side, top and bottom faces. Advantageously the inner container is also of a substantially flat configuration having a substantially planar front face, a substantially planar back face and narrow side, top and bottom faces and is sized such that it fits within the outer container with a small clearance along the sides to allow for movement of the inner container up and down within the outer container as the degree of hydration of the desiccant changes.

Preferably the outer container has a plurality of ventilation holes to provide an optimum area of contact of the surface of the inner container to a surrounding environment. Advantageously the ventilation holes may comprise louver type vents such that the holes have a degree of protection against ingress of, for example, water by splashing.

Preferably the outer container comprises ventilation holes on both the front face and the back face of the outer container.

In a particularly advantageous embodiment of the invention, the outer container further comprises feet means on an outer surface of the outer container to maintain the outer container at a distance from a surface against which the device may be positioned. For a device having a substantially flat configuration, preferably the outer container comprises feet on at least one of the planar front and back faces to maintain the surface of the planar face at a distance from a surface against which the device may be positioned. The provision of the feet means enables ventilation holes in both the front and back faces of the device to be accessible to ambient air, effectively doubling the surface area of the inner container, and hence the desiccant, that is in contact with the air entering the device. The arrangement in which the outer container has ventilation holes on both sides further enables air to circulate through the device, further increasing the contact area and time of the air with the desiccant. In particular, by having holes on both sides the flow through of air through the device can greatly increase its effectiveness. The feet prevent the device being placed flat against any surface and hence ensure that air can reach both sides of the device.

The outer container also provides protection against damage to the inner container and desiccant.

Advantageously support feet may be provided to enable the device to be freestanding and/or hanging means may be provided for the device to be hung adjacent to a wall for example.

The inner container needs to be formed from a material that is impermeable to the desiccant so that the desiccant is retained within the container, but that is porous to any moisture in the ambient air.

In a preferred embodiment the inner container comprises a porous rigid plastics material. A particularly advantageous material is a porous sintered plastics material such as a sintered high-density polyethylene material.

In an alternative arrangement the inner container comprises a holder means having a plurality of holes or slots and a porous liner of porous fabric, paper or similar within the holder means in which the desiccant material is retained. The holder means itself may be of a porous or non-porous material.

The preferred desiccant medium for the device is a quick response desiccant that can rapidly adsorb and desorb moisture. Preferably the desiccant medium has a relatively quick response, compared to generally used desiccants, to changes in humidity in ambient air to adsorb moisture from air of relatively high humidity and to desorb moisture to air of relatively low humidity. Preferably the response time of the desiccant to bring the desiccant into equilibrium with the surrounding atmosphere is of the order of a few hours, compared to most presently used desiccants which have a response time of days or longer.

When a hygroscopic desiccant medium is exposed to air, at a constant temperature, it will adsorb or desorb moisture from the air until it attains equilibrium with the air. If the ambient conditions of the air change, then the desiccant medium will seek to move to a new equilibrium. Equilibrium is achieved when the vapour pressure of moisture in the desiccant medium and the surrounding air are equal.

The vapour pressure of moisture present in a desiccant medium relative to the vapour pressure of moisture present in the air determines whether the desiccant medium will adsorb or desorb when it is exposed to the air.

If the vapour pressure of moisture present in the desiccant is greater than the vapour pressure of moisture in the air, the desiccant will expel moisture until the vapour pressure of moisture in the desiccant and in the air is equal, and vice versa.

For the humidity control device to provide an effective performance in terms of the amount of moisture that it can remove from or introduce to the container, the characteristics of the desiccant medium are paramount.

The desiccant medium is preferably chosen to have as high a capacity for moisture as possible. The desiccant device is also preferably quick at responding to changes in humidity. In a preferred embodiment, the desorption characteristic of the desiccant medium closely follows the adsorption characteristic of the desiccant medium as can be depicted in terms of a hysteresis curve. For better performance of the desiccant, the second, or desorption, part of the curve should follow the first, or adsorption, part of the curve as closely as possible. This helps to ensure that the performance of the desiccant medium does not deteriorate over time by gradually retaining more and more moisture through repeated use of the device. It also assists in maximising the ability of the desiccant medium to desorb moisture, and therefore regenerate, during favourable ambient temperature and humidity conditions.

As an indication of a good desiccant medium, the maximum difference between the change in mass of the desiccant medium when it is adsorbing moisture compared to when it is desorbing moisture, at any value of relative humidity, is 12% or less of the initial mass of the desiccant.

A particularly preferred desiccant medium comprises a processed silica gel having a very high surface area, with a microporous structure to maximise its porosity. A preferred type of silica gel is of the type that has a pore structure between macro-pored and fine-pored silica gel and combines good adsorption characteristics with good desorption characteristics. This type of silica gel is often referred to as Type B silica gel, for example that produced under the trade name Fuji® Silica Gel B-type.

The invention will now be described, by way of example only, by reference to the accompanying drawings, of which: Figure 1 shows front view of a humidity control device in accordance with the invention;

Figure 2 shows a side view of the device of Figure 1; Figure 3 shows a rear view of the device of Figure 1 ; Figure 4 shows a cross-sectional view of a preferred embodiment of the device; and

Figure 5 shows a front view of an alternative embodiment of the invention, cut away to show the inner container.

As shown in the Figures 1 to 4, a humidity control device 1 comprises an outer container 2 and an inner container 3. The outer container 2 as shown comprises cuboid shape with rounded corners and edges and is moulded from plastics material. This shape is only exemplary as many other shapes are possible such a cylinder of round, oval or complex cross-section or various box shapes.

The outer container 2 has a plurality of ventilation holes 4 on the front 2a and back 2b of the container 2. The ventilation holes 4 are of a louver type arrangement to protect the interior of the device from accidental splashes of water. Feet 5 are provided on the rear face 2b of the outer container 2. Suspension means 6 may be provided to enable the device to be hung from a hook if desired.

The inner container 3 is formed from a porous sintered plastics material.

The inner container 3 is suspended inside the outer container 2 by a spring means 7. The spring means 7 is attached to the inside of the top face 2c of the outer container 2 and to a fixing point 8 at the base of a recess 9 in the inner container 3. A desiccant 10 is supported inside the inner container 3. The desiccant preferably comprises a processed silica gel having a very high surface area, with a microporous structure to maximise its porosity. The desiccant 10 is loosely packed within the inner container 3 so that it substantially fills the inner container 3 but is not tightly packed.

When the desiccant 10 is dry, the spring 7 retracts and the inner container 3 is supported near the top 2c of the outer container 2 (as shown in Figure 4). As the desiccant 10 adsorbs moisture it increases in weight and the downward force on the spring 7 increases causing the spring 7 to extend and the inner container 3 to move downwards. As the desiccant 10 becomes saturated the inner container 3 will move down to a lower position. If the desiccant 10 is then exposed to a drier atmosphere so that moisture can be desorbed, the inner container 3 will move up again.

A window 11 is provided in the one face of the outer container 2, shown here as the front face 2a. A scale 12 is fixed to the front face 3a of the inner container and can be viewed through the window 11. A marker 11a indicates the position of the scale 12 relative to the window 11. As the desiccant 10 adsorbs and desorbs moisture the inner container 3 moves up and down within the outer container 2 and the scale 12 moves relative to the window 11, providing an indication of the degree of hydration of the desiccant 10.

Calibration means 13, such as an adjustment knob, is provided at the top of the spring 7 to adjust the position of the scale 12 with respect to the window 11. • In use, the device 1 is placed in a storage container or substantially closed area such as a caravan (not shown). Air flows around the device 1 and flows through the ventilation holes 4 and around and through the inner container 3. If the air has a relatively high humidity, the desiccant 10 will adsorb moisture, thus removing the moisture from the air and drying the air. If the atmosphere in the storage container is very damp, the desiccant 10 will continue adsorbing moisture until it is fully saturated. This can be seen from the scale 12. If the atmosphere in the storage container remains very humid, the device 1 can be removed to a drier atmosphere to enable the desiccant 10 to dry out and thus recharge the device 1 ready for reuse. The type of desiccant 10 that is used means that the desiccant 10 responds very quickly to changes in relative humidity thus adsorbing moisture quickly from a damp atmosphere and desorbing it quickly when exposed to a drier atmosphere.

The scale 12 and marker 11a provide an indication of the long-term storage conditions within a storage container, enabling a user to see what the state of the humidity in the container is during use.

The humidity in an enclosed area such as a storage container may vary in the short term due to temperature changes but in the long term, for example over a number of days or weeks, the desiccant 10 in the device 1 will come into equilibrium with the long term trend in the humidity in the container.

Figure 5 shows an alternative embodiment of the invention in which the inner container 3 comprises a holder 3' which may be of a non-porous material, for example of moulded plastics material, having a plurality of holes or slots 14 and a porous liner 15 of porous fabric, paper or similar within the holder 3' in which the desiccant material 10 is retained. The device 1 provides a compact and simple means for controlling humidity in a wide variety of applications. The indicator means 11,12 showing the degree of hydration of the desiccant 10 in the device 1 enables a user to know how damp the atmosphere in an area is, such that the humidity conditions can be monitored, and further provides an indication of when it would be advantageous to remove the device 1 to enable the desiccant 10 to dry out so that the device 1 can be reused.

Claims

1. Humidity control device comprising: an outer container having at least one ventilation hole providing access to the interior of said outer container; an inner container supported within said outer container and movable relative to said outer container, said inner container containing a desiccant material, the inner container being supported within the outer container by deformable means mounted on an upper face of the inner container and attached to the inside of an upper face of the outer container such that the inner container is movable up and down within the outer container in response to changes in the weight of the desiccant within the inner container, the weight of the desiccant depending on its degree of adsorption of moisture; and indicator means to indicate the degree of moisture adsorbed by the desiccant, said indicator means comprising an indicator means mounted on the inner container and said outer container further comprising a window means for viewing the indicator means, the indicator means as viewed through the window means thus providing an indication of movement of the inner container relative to the outer container and a consequent indication of the degree of moisture adsorbed by the desiccant.

2. Humidity control device according to claim 1 wherein the deformable means comprises a spring means.

3. Humidity control device according to claim 1 or claim 2 wherein the indicator means comprises a scale visible through the window means.

4. Humidity control device according to claim 3 wherein the scale is attached to the inner container.

5. Humidity control device according to claim 4 wherein the scale comprises an elongate scale extending along the inner container in a vertical direction such that the scale moves up and down in response to changes in the weight of the desiccant in the inner container depending on its degree of hydration.

6. Humidity control device according to any one of the preceding claims wherein the indicator means is provided with calibration means.

7. Humidity control device according to claim 6 wherein the calibration means comprises a knob or screw adjustment to adjust the position of the indicator means.

8. Humidity control device according to any one of the preceding claims wherein the outer container has a plurality of ventilation holes to provide an optimum area of contact of the surface of the inner container to a surrounding environment.

9. Humidity control device according to claim 8 wherein the ventilation holes comprise louver type vents.

10. Humidity control device according to any one of the preceding claims wherein shape of the inner container substantially matches the profile of the outer container.

11. Humidity control device according to claim 10 wherein the sides of the inner container are parallel to the sides of the outer container.

12. Humidity control device according to any one of the preceding claims wherein the outer container has a plurality of faces and comprises ventilation holes in more than one of the faces.

13. Humidity control device according to claim 12 wherein the outer container further comprises feet means on at least one of the faces to maintain the face at a distance from a surface against which the device may be positioned.

14. Humidity control device according to any one of the preceding claims wherein the outer container is of a substantially flat configuration having a substantially planar front face, a substantially planar back face and narrow side, top and bottom faces.

15. Humidity control device according to claim 14 wherein the inner container is of a substantially flat configuration having a substantially planar front face, a substantially planar back face and narrow side, top and bottom faces.

16. Humidity control device according to claim 14 or claim 15 wherein the outer container comprises ventilation holes on both the front face and the back face of the outer container.

17. Humidity control device according to any one of claims 14 to 16 wherein the outer container further comprises feet means on at least one of the planar front and back faces to maintain the surface of the planar face at a distance from a surface against which the device may be positioned.

18. Humidity control device according to any one of the preceding claims wherein the inner container comprises a porous rigid plastics material.

19. Humidity control device according to claim 18 wherein the inner container comprises a porous sintered plastics material.

20. Humidity control device according to any one of claims 1 to 17 wherein the inner container comprises a holder means having a plurality of holes or slots and a porous liner of porous fabric, paper or similar within the holder means in which the desiccant material is retained.

21. Humidity control device according to any one of the preceding claims wherein the desiccant comprises a quick response desiccant medium that can rapidly adsorb and desorb moisture.

22. Humidity control device according to claim 21 wherein the desorption characteristic of the desiccant medium closely follows the adsorption characteristic of the desiccant medium.

23. Humidity control device according to claim 21 or claim 22 wherein the desiccant comprises a processed silica gel having a very high surface area, with a microporous structure to maximise its porosity.