GB2363740A

GB2363740A - Ventilating dessicant chamber for container.

Info

Publication number: GB2363740A
Application number: GB0015373A
Authority: GB
Inventors: Geoff Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-06-23
Filing date: 2000-06-23
Publication date: 2002-01-09
Also published as: GB0015373D0

Abstract

A chamber 2 forming a regenerating dessicant vent is positioned in the wall 1 of a container and comprises a dessicant filling 3, an exterior ventilation opening 5, 5A which opens and closes to the exterior of the container and an interior ventilation opening 4, 4A which opens and closes to the interior of the container. The ventilation openings open and close in a synchronised manner so that only one is ever open. The opening and closing is dependant on the ambient temperature inside the chamber such that when it is below the equilibrium moisture point of the dessicant, the interior ventilation opening is open so that the dessicant adsorbs moisture from the container. When the temperature is above the equilibrium moisture point of the dessicant and the dessicant is expelling moisture, the interior ventilation opening is closed (Fig. 3) and the moisture is expelled to the atmosphere external to the container. The ventilation openings may be opened and closed by a thermally responsive material 7.

Description

2363740 Regenerating desiccant humidity vent The device relates to a

regenerating desiccant humidity vent, which can reduce moisture levels inside a closed container The device operates according to the temperature and humidity levels inside and outside the enclosure.

The background to the device is the dilemma faced by persons packaging goods susceptible to damage by humidity or moisture for shipment If the packaging enclosure is sealed, changes in temperature causes damaging condensation from humidity contained within the package This effect is commonly referred to as the "sweating" effect.

However, if the enclosure is permanently vented, air with high humidity can enter the enclosure and again cause damage This phenomenon can occur in plastic bags, wooden boxes, metal containers, mobile vehicles and mobile homes and such like.

Natural ventilation is often used to combat the "sweating" effect and is normally achieved through a grill or louver, which normally has no moving parts When there are moving parts these are normally only manually adjustable to give a set airflow rate over a long period of time To use natural ventilation as a means to control humidity requires that a sufficient area of duct is open to get a large enough air exchange If a traditional air vent is too large it will be detrimental, as there is little control if undesirable atmospheres are entering the enclosure.

Desiccants of both adsorptive and absorptive varieties have been used extensively for keeping air dry in a closed container These suffer from two main disadvantages.

1 Once the desiccant has reached its capacity to absorb moisture then no further air- drying is possible.

2 If high temperatures occur inside the container then adsorptive desiccant will expel moisture and raise the humidity inside the container There are desiccants which do not release moisture until the temperature is higher than might naturally occur but these are normally more expensive.

Thus, an objective of this device is to provide a method of drying the container with desiccants but having an automatic mechanism, which prevents moisture being re- released into the container, if the ambient temperatures rise Importantly, the desiccant is dried, giving it a new capability to dry the air inside the container again.

The device is designed to give users a low cost solution to the problem of condensation in containers With this in mind the initial cost of the device is very low in comparison to traditional electrically operated dehumidifiers and the desiccant can be automatically regenerated or dried without any human intervention given that certain ambient atmospheric temperature conditions prevail Studies have shown that the sweating effect is greatest when large daytime/night-time temperature swings take place driven by the heating and cooling caused by the sun It is in these situations that the device will be most effective in adsorbing and expelling humidity.

Accordingly, the device is a regenerating desiccant humidity vent comprising a chamber which is placed on the wall or surface of a closed container The chamber contains a desiccant or hygroscopic material The chamber has two vents, which can be opened and closed One vents to the outside of the enclosure and one vents to the inside of the enclosure These vents are mechanically linked so that when one vent opens the other shuts and vice versa It is important to note this simultaneous action as it means that the desiccant can only exchange moisture with either the air inside the container or outside the container but not both.

The key to the device is the actuation of the changeover from the chamber receiving air from the inside of the container to receiving air from the outside, given that adsorptive desiccants have an equilibrium point where dependent on the ambient conditions they change from absorbing moisture to expelling moisture The timing of the synchronised operation, in conjunction with the temperature controlled actuation to the ambient conditions, ensure that when the desiccant is absorbing moisture it is from the inside of the container and when it is expelling moisture it is to the exterior of the container If it was desirable to have high moisture levels inside the container then the device could be reversed so that moisture was adsorbed from the outside of the container and expelled inside the container.

The temperature level is the overriding factor in the equilibrium curve of when the desiccant absorbs or expels moisture Firstly it has by far the greatest impact on the drying capability of the desiccant and secondly as relative humidity is inversely proportional to temperature at a given specific g/M 3 the air will naturally accept more moisture at higher temperatures and vice versa.

Given these two considerations the device operates automatically using the thermal expansion of materials, which gives the necessary power and movement to operate the synchronised and connected air vents Thermally expanding actuators are commercially available and can easily give the motion of around 20 mm required to open and shut the vents By calibrating the movement of the vents, to the equilibrium point of the desiccant and with the expansion of the thermal material no other power sources such as batteries, kinetics, electrical supply is necessary.

This is seen as an advantage over devices, which require battery power for three reasons.

Firstly, batteries can fail in service and secondly they require periodic replacement with new batteries and finally batteries substantially increase running costs.

Devices, which use a fixed electrical power such as a mains supply or based on a ship or motor vehicles power source are not considered equivalent This is because the device is intended for use in containers used in shipping, storage and transit where portability, negligible human input and handling requirements limit the practicality for making electrical connections.

Given also that the device may be used in all weather conditions, materials are selected to withstand extremes of temperature and humidity.

An embodiment of the device will now be described with reference to the accompanying drawings in which:

Figure 1 shows a representation of a container in cross section with a regenerating desiccant humidity vent device positioned through the wall of the container.

Figure 2 shows a diagrammatic representation of an embodiment of the device drying the air inside the container.

Figure 3 shows a diagrammatic representation of an embodiment of the device expelling moisture from the desiccant material to the exterior of the container.

As shown in Figure 1 of the drawing, the chamber device ( 2) is positioned on the wall of an otherwise closed container ( 1) In Figure 2, The chamber device ( 2) is shown with the desiccant ( 3) adsorbing moisture from air which circulates from inside the container (I 1) through the air vents ( 4) which has its sliding vent ( 4 A) in the open position The exterior vent ( 5) is shown in the closed position The mechanical link ( 6) is connected to sliding vents ( 4 A) and ( 5 A) so that any movement of thermally expanding cylinder ( 7) applies equally and in the same direction.

The direction of the movements of the thermally expanding cylinder is shown by the adjacent arrow The position of the holes of the sliding vents ( 4 A) & ( 5 A) are staggered in relation to each other whereas the holes in the vents ( 4) & ( 5) are opposite each other.

This has the effect that movement in the thermally expanding cylinder ( 7) covers and uncovers the holes in vents ( 4) & ( 5).

The temperature at which the thermally expanding cylinder ( 7) expands and the movement that it expands is set according to the moisture equilibrium point of the desiccant ( 3) Figure 2 shows the thermally expanding cylinder ( 7) at a temperature below the moisture equilibrium point of the desiccant ( 3) so that it is in a contracted position The thermally expanding cylinder ( 7) is calibrated so that the holes in sliding vent ( 4 A) are open in relation to the holes in the vent ( 4), accordingly the sliding vent ( 5 A) is covering the holes in vent ( 5) The temperature that the desiccant stops adsorbing moisture is the temperature at which the thermally expanding cylinder ( 7) has been calibrated to expand.

Calibration is possible by adjusting a screwed knob ( 8) By adjusting the screwed knob ( 8) the volume in which the thermal material inside the can be increased or decreased.

This lowers or raises respectively the temperature at which the thermally expanding cylinder ( 7) operates allowing calibration to the moisture equilibrium point of the desiccant.

Thus if ambient temperatures rise above the equalibrium moisture point temperature of the desiccant ( 3) the thermally expanding cylinder ( 7) expands and through the mechanical link ( 6) moves the sliding vents ( 4 A) and 5 (A) so that they cover and uncover 7 the holes in vents ( 4) and ( 5) respectively When the temperature drops below the equilibrium point of the desiccant ( 3) the action described above reverses.

In Figure 3 the chamber is shown with the thermally expanding cylinder ( 7) in the expanded position showing the desiccant drying to the outside atmosphere The device is designed so that no airflow is possible directly from the outside of the container to the inside of the container and vice versa.

The action as described has the effect that at lower temperatures, below the equilibrium point the adsorbent will adsorb moisture from inside the container until it reaches its capacity but at temperatures above the equilibrium point it will expel moisture, drying and effectively regenerating the desiccant ready to adsorb further moisture.

It should be noted that a flexible breathable waterproof PTFE membrane ( 9) covers vent ( 5) to stop any ingress of rain or water form the exterior of the container This material is at its most breathable when temperatures are highest and moisture will move from the higher temperature area, the chamber ( 2) to the exterior of the chamber.

Claims

1 A chamber forming a regenerating desiccant humidity vent which is positioned on the wall of a closed container having A) a desiccant or hygroscopic filling in the chamber B) a ventilation opening positioned on outside of the container, which opens and closes to the exterior of the container and C) a ventilation opening positioned on the inside of the container, which opens and closes to the interior of the container where the two ventilation openings operate in a synchronised manner so that when one vent opens the other vent closes and vice versa and, Where the opening and closing of the vents is at a temperature equal or around the equilibrium point of the moisture adsorbing capability of the desiccant or hygroscopic material.

Such that when:

the ambient temperature inside the chamber is below the equilibrium moisture point of the desiccant, the desiccant is adsorbing moisture from the interior of the container as the interior ventilation opening is in the open position, and the exterior vent is in the closed position, so that moisture can only be adsorbed from the container into the desiccant.

and when the ambient temperature inside the chamber is above the equilibrium moisture point of the desiccant and the desiccant is expelling moisture, the interior ventilation opening is in the closed position and the exterior vent is in the open position so that moisture can only be expelled from the chamber into the atmosphere outside the closed container.

2 A chamber as claimed in claim 1, which uses the natural action of materials which expand and contract according to temperature changes to position the synchronised exterior and interior ventilation openings respectively open and shut or vice versa.

3 A chamber as claimed in 1 and 2 where the movement of the thermal material is calibrated according to temperature so that it provides the correct amount of movement to operate the synchronised vents open and shut at the point where the desiccant is at its moisture equilibrium point.

4 A chamber as claimed in 1 with a flexible membrane to prevent water entering the chamber, which improves its breathability with temperature allowing moisture to escape from the chamber but preventing water entering.

A chamber as claimed in 1,2, 3 and 4 which is self powered by naturally occurring energy requiring no external sources of energy such as electrical power, both battery or mains.