GB2221527A - Heat exchanger - Google Patents

Abstract

The heat transfer efficiency of a heat exchanger is greatly increased by using a plurality of passageways of which the surface is embossed. The embossment interrupts the laminar boundary layer causing continuous generation and release of eddies. The passageways are defined by raised channel sections 4 abutting an adjacent plate. The height and pitch of the embossment may be varied to obtain optimum conditions for the fluid flowing through the respective passageways. <IMAGE>

Description

SPECIFICATION Heat Exchanger This invention relates generally to heat exchangers.

Heat exchangers are used to carry out the heat transfer function between two fluids. Examples of commercial heat transfer equipment, currently available, are as follows: - Shell and tube heat exchangers - Plate type heat exchangers - Run round coil systems - Recuperators - Regenerators - Heat wheels - Heat pipes - Heat pumps The invention is particularly applicable to systems, for example ventilation systems, or machines, for example air handling units, in which ambient air is drawn in to the system or machine, raised or lowered in temperature and discharged at an elevated or reduced temperature to waste.

According to the present invention, the heat transfer enhancement in a heat exchanger is obtained from an embossed surface within a flow passageway.

The laminar boundary sub-layer of the flow is interrupted causing a continuous generation and release of eddies.

The embossed surface also gives a relatively high condensing heat transfer coefficient compared to that of an unembossed surface.

The invention also provides a system or machine incorporating the heat exchanger.

In accordance with the present invention, there is provided a heat exchange recuperator unit comprising a plurality of spaced elongated flow passageways. Preferably the passageways are generally in rectangular section, through which ambient air can pass. Preferably the passageways are formed by raised channel means on a first plate abutting against a second plate such that the passageways are spaced apart by the raised channel means. The geometry of the passageway may be changed by altering the height and formation of the raised channel means. The said raised channel can be replaced by other mechanical means. The function of the raised channel means is to define the geometry of the flow passageways and to strengthen the heat transfer matrix in a recuperator unit.Warm air from a heating source may pass through a similar passageway arrangement at an angle to the ambient air passageways.

The components of the heat exchanger unit in accordance with the invention may be made of aluminium and steel and assembled by means of chemical sealants, welds, brazing, soldering or mechanical fastenings. The components may also consist of glass, paper, ceramics or other types of metals and non-metals depending on the actual application of the unit.

The type of embossed surface chosen for use in a heat exchanger is dependent on the application, particularly on the composition of the fluid passing through the passageways. The main factors affecting the performance of a heat exchanger are flow rate, viscosity, material in which the embossed surface is formed, the height and pitch of the embossment and the cross-section of the passageway.

The invention will now be described by way of example with reference to the accompanying drawings: Figure 1 shows in perspective the heat exchange recuperator unit with its frame work and heat transfer matrix in aluminium.

Figure 2 is an enlarged detail view of part of the heat exchange recuperator unit.

Figure 3 is the computer generated model of the embossed surface.

Figure 4 is the detail showing a form to build the heat transfer matrix.

Figure 5 is a sketch graph comparasion of composite condensing heat transfer coefficient for a heat exchanger in accordance with the invention and a heat exchanger incorporating smooth surface passageways.

Figure 1 and Figure 2 show a heat exchange recuperator unit embodying a preferred form of the invention in which waste air passes through the passageways in Face A of the recuperator unit and ambient air passes through the passageways in Face B of the recuperator unit. The waste air is leaving the recuperator unit from the bottom face of the recuperator unit and ambient air is leaving at the back of the recuperator.

The heat exchange recuperator unit comprises a plurality of passageways 1 and 2, each having a generally rectangular cross-section, adjacent passageways being spaced apart by raised channel sections 4. Each plate 5, 6, is formed from an embossed sheet which has been pressed to have raised channel sections of the desired formation. The first plate 5 is orientated such that the channels and passageway portions are vertical and communicate with face A whilst the second plate 6 is orientated so that the channels communicate with face B. The two plates are then forming an engagement between the raised channel formations of the first plate and the side of the second plate not having raised channel formations thus defining the passageways 1, 2. In the example, the passageways are orientated at 90 degree to each other.They may, however, be orientated at any angle which is preferable for the application. The L-sections 3 provide support for the heat transfer matrix.

The passageways of Face A are isolated from the passageways of Face B.

In a heat exchanger intended for use with air in passageways 1 and 2, a rectangular section was used. The embossed surface used was Stucco (Tradename), the height of the irregular embossment being 0.32mm and the pitch averaged 3.5mm.

It has been found that the above described heat exchange recuperator unit provides a worthwhile increase in heat transfer efficiency when compared with an unembossed receuperator unit. A comparison of composit condensing heat transfer coefficient for a heat exchanger utilising an embossed surface and a heat exchanger utilising a smooth surface is shown in Figure 5.

Although described above in a heat exchange recuperator unit, the interruption of boundary sub-layer by means of embossed surface could be used in other systems or machines where fluid is drawn in conditioned and discharged to waste. The size and shape of the exchanger can be altered to suit particular systems or machines. Example of possible uses of th eheat exchanger are in a laundry drying plant and ventilation systems for buildings such as hospitals, office blocks, shopping centres, or industrial premises.

The aboe described heat exchanger has the advantage over other appliances previously used that it has no moving parts, and waste air and ambient are isolated from each other. Furthermore the heat exchange recuperator unit is relatively easy and cheap to manufacture.

Claims (12)

1. A heat exchanger comprising a plurality of elongated passageways through which fluids may pass wherein at least part of the surface of the passageways are embossed.

2. A heat exchanger according to claim 1 wherein the embossed surface interrupts the laminar sub-layer fluid flow.

3. A heat exchanger according to any preceding claim wherein adjacent passageway portions on first and second plate are separated by raised channel sections.

4. A heat exchanger according to any preceding claim wherein first and second plates are abutted to each other defining the passageways.

5. A heat exchanger according to claim 4 wherein the cross-sections of the passageway may be altered by changing the raised channel section formation.

6. A heat exchanger according to claim 4 or claim 5 wherein the raised channel sections are formed by mechanical means.

7. A heat exchanger according to any preceding claim wherein the surface is metal.

8. A heat exchanger according to any preceding claim wherein all of the passageway surface is embossed.

9. A heat exchanger according to any preceding claim wherein the surface is regularly embossed.

10. A heat exchanger according to any one of claims 1 to 8 wherein the surface is irregularly embossed.

11. A heat exchanger substantially as hereinbefore described in accordance with the accompanying drawings.

12. A machine or system incorporated a heat exchanger in accordance with any one of the preceding claims.