GB2308883A - Heat exchanger with concertina plate - Google Patents

Abstract

A heat exchanger may be built of three components The main part is made of a sheet of material corrugated into panels (1), the corrugations running at an angle of about 30 to 60 degrees to the long edge of the sheet. This sheet is then folded alternately over and under into a concertina shape and the two parts of the outer casing (2) assembled to it as shown in figures 2 and 3 then sealed using a suitable method. The heat exchanger now comprises two separate chambers with the full area of the original corrugated sheet in common, and fluid moving through one chamber will be constrained to run in multiple spirals, thus exchanging heat effectively with fluid moving in the opposite direction in the other chamber.

Description

HEAT EXCHANGER This invention relates to a heat exchanger.

A heat exchanger allows two substances, normally fluids, to come into thermal contact so that the colder fluid is heated by the hotter one, and the hotter fluid is cooled by the colder one. The two fluids are kept separate from each other. Common examples are car radiators, central-heating radiators and refrigerators.

Heat exchangers are used in many machines, either to lose unwanted heat as in car radiators to gain it as in refrigeration systems. They are generally based on tubes joined by various junctions and usually have fins added to the tubes to increase the effective surface area and thus increase the amount of heat energy transferred for a given temperature difference. This finning involves many parts which must be made and assembled to a high degree of accuracy in order to make the final assembly efficient for its size. Joints are often made internal to the structure, making subsequent repair of faults difficult as welds or solder joints must be undone in order to access the matrix.

The present invention provides a method whereby a compact and efficient heat exchanger may be manufactured from just three parts with all joints being accessible from outside the assembly. A sheet (1) of thin material is formed into an odd number of panels of corrugations where the corrugations run at an angle of about 45 degrees to the edge of the sheet. This angle may be varied depending upon the exact use of the final assembly. The panels are then folded together in a concertina shape so that adjacent corrugations now run at about 90 degrees to each other.

The folded sheet is now compressed lightly into a block so that the adjacent peaks of corrugation are touching and the block is rectangular as viewed from the end.

Two L-shaped pieces of material (2) are then clamped onto the sides of the block with the free ends of the corrugated sheet protruding from the joints between the L-shaped pieces (see Fig 3). The block ends are not covered by the L-shaped pieces, and the concertina end of the corrugated sheet shows here. All joints are now suitably sealed, depending upon the temperature and the pressure the assembly will experience.

The heat exchanger now has two separate chambers which have the full area of the corrugated sheet in common. A fluid passed in one direction in chamber 1 will follow a multiple spiral path from one end to the other, thereby exchanging heat quickly and efficiently with a fluid in chamber 2 flowing in the opposite direction.

Since the sheet is corrugated, a high differential pressure can exist between the two chambers and between the chambers and the outside world.

Two specific examples of implementation of the invention will now be discussed, showing use at high temperatures and pressures and at low temperatures and pressures.

As the first example of implementation of this idea, a sheet of 0.2mm copper foil 8.12 metres long and 32cm wide is corrugated into 101 8cm by 32cm panels. The depth of the corrugation is 0.6mm and there is 2mm between peaks giving an uncompressed thickness of the sheet of 0.8mm.

A lcm by 32cm uncorrugated margin at either end of the sheet allows for jointing. A lcm by 8cm margin at the top and bottom of each panel is folded twice to give a quadthickness (0.8mm) section 2.5mm wide at the top and bottom of each panel. This makes clamping and subsequent joining by electroplating more reliable.

When this is folded into the concertina shape it gives a block that is 30.5cm long by 8cm by 8cm. Two pieces of 30.5cm by 16.2cm copper sheet 1.6mm thick are folded to L-shapes 8cm by 8.2cm and 30.5cm long.

These are assembled to the block as shown in the drawing.

The assembly is sealed by electroplating copper onto the side joints and over the entire ends since it is difficult to weld such thin material reliably.

The resultant heat exchanger will transmit about 200W per degree Celsius difference between the chambers with a flow of 7 litres per second of air.

The free cross-sectional area of each chamber is 24 sqcm, and this is equivalent to about a 5.5cm diameter tube. It is made up of tubelets of effective diameter 1.5mm and effective length a bit less than 1.4 times the length of the heat-exchanger, in this case about 37cm. There are about 1400 of these tubelets.

For a normal situation of 50 degrees Celsius difference, this will exchange 10 Kilowatts of heat. One twice this size would be adequate to act as the radiator for most family cars, and regulating the airflow to give constant coolant output temperature would eliminate the need for a thermostat. A small centrifugal fan and air filter would be needed, thus increasing the size, but the space required would be easier to find in todays cramped engine bays since it takes up less space than the current rubber hosing.

The output airstream would be clean, hot air which could be diverted to heating the car interior thus avoiding the extra expense of a separate heater matrix and fan.

A heat exchanger of about one third this size could be used with a room-temperature controlled fan as the radiators in a central heating system for buildings. The radiator would be much smaller than current versions and could be easily hidden in trunking or skirting. Appropriate filtering would stop the matrix from clogging whilst supplying cleaner air back into the room. By using the heat exchanger in centralheating boilers the size of these could be substantially reduced, though in this case extra care would need to be taken with exhaust gases as they would be much cooler than current systems and would need fan-assist to ensure safe dispersal.

A second example of this invention may be built by taking a 1 metre wide roll of thermoplastic 0.5mm thick and 20.25 metres long. This is corrugated by vacuum-forming to a depth of 1.5mm in panels 20cm wide and then folded and sealed into a block 20cm square and 1 metre long. The side joints and ends would be sealed with adhesive. The internal area of this block is about 23 square metres and the useable surface area is about 21 square metres after allowing for end effects. The heat transfer capability is over 2 Kilowatts per degree Celsius with a 50 litre per second airflow.

Modern buildings are well-sealed and thus build up stale air which is not healthy. Air-conditioning recirculates air after adjusting the temperature and humidity, but dqes not remove the increased pollution levels associated with human occupation. Frequently windows are opened in order to gain breathable air, thus negating the benefits of the heating system.

Using this plastic heat exchanger the air could be extracted from a building through the heat exchanger and the air coming in through the other chamber would be heated almost to the same temperature. Fresh air would thus be introduced into the building for a very low heat loss. If the fans to drive the system were on the inside, then the fan energy alone should be enough to make up for the heat lost through heat-exchanger inefficiency. The air-conditioning, if used, would then be able to work as designed because people would have no need to open windows. By adding fresh air from outside the building and removing stale air, the problems of Legionnaire's disease would also be reduced.

Claims (1)

1: A heat exchanger that may be built using only three components: a sheet corrugated into panels (1) which is folded into a concertina-shape block and two side pieces (2) suitably sealed onto the block. The completed assembly has two separate chambers that share the area of the corrugated sheet in common thus fluids running in opposite directions in each chamber will quickly transfer heat from the hotter fluid to the cooler fluid.

2: A heat exchanger as claimed in Claim 1 which will hold pressure or vacuum in either or both chambers and has a high heat transfer for its size.

3: A heat exchanger as claimed in Claim 1 or Claim 2 that may be manufactured from alternate materials and in different sizes to fit the device to the intended use as regards temperature, pressure and fluids to be used.

4: A heat exchanger substantially as described herein.

Amendments to the claims have been filed as follows 1: A heat exchanger that may be built using only three components: a sheet corrugated into panels (1) which is folded into a concertina-shape block and two identical side pieces (2) suitably sealed onto the block. The completed assembly has two separate chambers that share the area of the corrugated sheet in common thus fluids running in opposite directions in each chamber will quickly transfer heat from the hotter fluid to the cooler fluid.. All joints and seals are externally accessible thus reducing manufacturing errors.