GB2327148A

GB2327148A - Thermoelectric cooling systems

Info

Publication number: GB2327148A
Application number: GB9808872A
Authority: GB
Inventors: Barry John Coles
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-26
Filing date: 1998-04-27
Publication date: 1999-01-13
Also published as: GB2327148A8; GB9808872D0

Abstract

The cooling system comprises a Peltier effect electrothermal device 12 coupled to a heat sink assembly 14 and a cooling element assembly 16, a fan 23 for passing through the cooling element assembly 16 an air stream which is directed towards the user, and a fan 33 for passing through the heat sink 14 an air stream which is directed away from the user. Alternatively, a single fan can be used whose air stream is split into two portions. The fan(s) may be switched independently to the electrothermal device. The heat sink 14 and cooling assembly 16 are both configured as a plurality of parallel plates fixed longitudinally to the direction of the air streams.

Description

Cooling Fazes The present invention relates to cooling fans, in particular to fans used to cool domestic and office premises.

During warm weather, the occupants of a room in a house or office may become uncomfortably hot. The usual method of relief is to use an electric fan.

However, the fan does not actively cool the air; it simply moves the warm air around the room, and any cooling effect felt by the room's occupants is mainly due to the increased evaporation of moisture from the skin. When there is little moisture on the skin, or when the ambient air humidity is high, cooling is much less effective.

Some types of fan rely on the endothermic effect of evaporation to actively cool the air. The air is blown over a reservoir of water, and by encouraging evaporation, the air is cooled. Apart from the inconvenience of having to ensure that there is always watcr in the reservoir, this device becomes less effective with increasing ambient air humidity. As the air's relative humidity approaches saturation, little evaporation from the reservoir, and therefore little cooling, will occur.

The object of the present invention is to provide a fan capable of cooling air, irrespective of its humidity, and which is portable and simple to use.

According to the invention there is provided an electrothermal device coupled to a heat sink assembly and a cooling element assembly, fan means for passing air streams through the heat sink and cooling element assemblies, and outlet means for directing the emergent air streams in different directions. An "electrothermal device", as used herein, is a device which generates a temperature difference between its operative faces in response to an electric current being applied to it; the electrothermal device can conveniently be a device utilizing the Peltier effect.

The fan means may comprise a single fan the outlet of which is split into the two air streams, or may comprise two fans, one for each air stream. The fan means may be upstream or downstream of the heat and cooling element assem blies (or one upstream and one downstream if separate fans are used for the two air streams).

The electrothermal device cools the cooling element, which in turn cools the air stream directed over it by the fan. and by moving the device, this cool air may be directed as required by the user. Unavoidably, the electrothermal device also produces heat; this is dissipated by the heat sink into the second air stream, which is blown in any direction other than that of the cool air stream.

A cooling fan embodying the invention will now be described, by way of example, with reference to the drawings, in which: Fig. l is a vertical longitudinal section of the fan; Fig. 2 is a simplified perspective view of the fan; and Fig. 3 is a simplified perspective view of the cooling element.

The cooling fan utilizes a Peltier effect device, this being a well-known electrothermal device. The Peltier effect occurs at a junction of dissimilar conductors to which a voltage is applied, and causes the junction to be heated or cooled. The magnitude of heating or cooling depends on the voltage and the characteristics of the conductors. A Peltier device uses conductors selected to maximize the cooling occurring at the junction of the conductors.

Referring to the drawings, the fan comprises a Peltier device 12, a heat sink assembly 18, and a cooling element assembly 20, with the heat sink assembly being mounted in a roughly rectangular casing and the cooling element assembly being mounted on top of that casing. The Peltier device is in thermal contact with the cooling element 16. Air is drawn into inlet 21 of the cooling element assembly by a fan 23 and is cooled as it passes over the cooling element's fins.

The cool air is expelled from an outlet 22. This cool air may then be directed to wherever it is required by the user.

The other junction or junctions in a circuit exhibiting the Peltier effect will produce heat, the amount of which will be equal to the heat deficit at the cooling junction, plus the joule heating produced by the circuit. A Peltier device for this application conveniently has a power rating of around 50 W.

The junction producing heat is in thermal contact with the heat sink 1 4. An insulating layer 13 may be provided between the two heat sinks and air streams.

Air drawn in through the heat sink assembly's inlet 31 by the fan 33 is warmed as it passes through the heat sink's fins and is expelled through the heat sink assembly's outlet 32. The outlet is directed away from the cooling element assembly's outlet (roughly at right angles).

The efficiency of the system for cooling air is dependent not only on the Peltier device itself, but on the heat exchange characteristics for both junctions, that is, the shape, size and material of the heat sink and the cooling element, and the air flow over each. The heat sink and the cooling element are both made of materials with a high thermal conductivity, and are shaped to maximize the surface area in contact with the air, both being constructed from parallel fins running longitudinally along the device. Typically, they may be made from aluminium or copper. The heat sink can conveniently have a flattened roughly square form overlapping the cooling air channel, compared to the roughly cubical form of the cooling element in the cooling air channel. The heat sink comprises a flat plate with the fins attached to it; the fan 33 blows its air edgewise onto the fans. The cooling element, shown in Fig. 3, comprises a roughly square channel of thick material with the fins forming a parallel stack across the channel as shown.

In a closed cycle system, that is where the area to be cooled is finite and in thermal isolation from the outside environment, a heat sink area to cooling element area ratio of 2:1 is often used, but for this system, a larger ratio of 4:1 or 5:1 is desirable. For effective cooling in this system, the cooling element should conveniently reduce an ambient air temperature of 25 C by 3 C and have an air flow of 15 L/s or more.

The whole system is mounted on a stand 30, which may be pivoted to allow the cool air to be directed more easily. An adjustable louvre may be provided over the fan 23, as an alternative means of directing the cool air. The warm air outlet from fan 33 may similarly be provided with direction adjustment means; it may occasionally be desirable to direct the warm air stream to a particular object. Grilles may be provided over the inlets 21 and/or 31 if desired.

In its simplest form, the two fans and the Peltier device will all be connected together and controlled by a single switch. A separate switch may however be provided for the fan 23, so that that fan may be operated to give a stream of air at ambient temperature if desired.

The Peltier device has to be driven by DC, and it is convenient to drive the fans with DC at the same voltage as well. The system can therefore be driven from a battery, or from the AC mains via a rectifier (and preferably also a transformer, as a relatively low voltage is convenient for the Peltier device).

The system described above has separate air streams, each with its own fan, for the heat sink and cooling element assemblies. [t will be evident however that a single fan at the inlet of the system, with the its outlet being separated into the two air streams between the fan and the heat and cooling elements. The division can be set to give a desired ratio between the two streams.

Although the system described here is for a portable air cooler, the prin ciples may of course be incorporated into a window mounted ventilation system or a fully inbuilt air conditioning system, with the unwanted warm air being vented out of the building.

In summary, there is provided a cooling system comprising a Peltier effect electrothermal device coupled to a heat sink assembly and a cooling element assembly, a fan for passing through the cooling element assembly an air stream which is then directed towards the user, and a fan for passing through the heat sink an air stream which is then directed away from the user. Alternatively, a single fan can be used whose air stream is them split into two portions. The fan s may be switched independently to the electrothermal device. The heat sink and cooling assembly are both configured as a plurality of parallel plates fixed longitudinally to the direction of the air streams.

Claims

Claims

A A cooling system comprising an electrothermal device coupled to a heat sink assembly and a cooling element assembly, fan means for passing air streams through the heat sink and cooling element assemblies, and outlet means for directing the emergent air streams in different directions.
2 A cooling system according to claim 1 wherein the fan means comprise a single fan, whose air stream is them split into two portions, one portion being directed to the cooling element assembly, and the other portion being directed to the heat sink assembly.
3 A cooling system according to claim I wherein the fan means comprise two separate fans, the air stream from one passing through the cooling element assembly, and the air stream from the other passing through the heat sink assembly.
4 A cooling system according to any previous claim, wherein the fan means may be switched independently to the electrothermal device.
5 A cooling system according to any previous claim, wherein the heat sink is configured as a plurality of parallel plates fixed longitudinally to the direction of the air stream.
6 A cooling system according to any previous claim, wherein the cooling element is configured as a plurality of parallel plates fixed longitudinally to the direction of the air stream.
7 A cooling system according to any previous claim, wherein the electrothermal device is a Peltier device.
8 A cooling system substantially as herein described.
9 Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).