GB1599395A

GB1599395A - Heat exchanger

Info

Publication number: GB1599395A
Application number: GB1822277A
Authority: GB
Original assignee: IMI MARSTON RADIATORS Ltd
Current assignee: IMI MARSTON RADIATORS Ltd
Priority date: 1978-05-12
Filing date: 1978-05-12
Publication date: 1981-09-30

Description

(54) HEAT EXCHANGER (71) We, IMI MARSTON RADIA TORS LIMITED (formerly Marston Radiators Limited), a British Company, of Sovereign House, Seacroft, Leeds, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to heat exchangers and has particular, but not exclusive, reference to heat exchangers for relatively viscous fluids such as oil. A particular form of heat exchanger, usually used as an oil cooler, comprises a flat tube which contains the oil to be cooled over which is passed air. Located within the tube is a corrugated splitter which is normally in the form of a square-wave corrugation which splits the quasi rectangular oval tube into a number of smaller rectangular section passageways.The corrugated splitter is soldered to the tube utilising molten solder which has the effect of increasing the heat transfer to the outside of the tube and increasing the mechanical strength of the assembly, particularly in respect of internal hydraulic pressure, when the "legs" of the corrugation and the soldered joints are under tcnsile stress.

Normaliy there is no interchange of fluid passing through the heat exchanger between the rectangular passageways defined by the splitter and the walls of the tube.

It has been proposed, see for example British Patent 1,184,125, to provide slots in the corrugations along the length of the corrugations to permit intercommunication between the passageways in the tube.

It has now been discovered that by means of the present invention improved heat exchanger turbulence can be provided, which in turn improves the heat exchanging characteristics of the heat exchanger.

By the present invention there is provided a flat tube heat exchanger comprising at least one flat tube having in its bore an elongate, longitudinally corrugated member which, together with walls of the tube, define a plurality of substantially parallel passageways within the tube and a plurality of projections extending into the passageways from the corrugated member and/or the walls of the tube to cause or enhance turbulence of fluid passing, in use, through the passageways. At least some, and preferably all, of the projections preferably extend from, and are integral with, the corrugated member. The projections are preferably tags pierced in the corrugations.

Preferably the corrugated member is bonded to the tube, for example it may be soldered or brazed to the tube. The corrugated member may, for example, be in the form of a square wave or a rectangular wave. Preferably the base and tops of the wave are provided with the tags.

The tags may be punched into the corrugations. The punching may be by means of a nail punch to provide a plurality of ears, typically four ears. Alternatively the tags may be punched out by a die. The tags may each be in the form of a narrow rectangle attached by one of the short edges to the corrugations.

The tube may, for example, be formed of steel, copper or copper alloy such as brass in which case the corrugated member is preferably formed of a steel, copper or copper alloy which may be coated with solder before or after forming if the joining medium is solder or be coated with copper if the joining process is copper brazing. Alternatively, the tube may, for example, be formed of an aluminium alloy in which case the corrugation is preferably also formed of aluminium of an aluminium alloy.

By way of example embodiments of the present invention will now be described with reference to the drawings accompanying the provisional specification of which: Figure 1 is a cross-sectional view of a prior art flat tube and splitter; Figure 2 is a cross-sectional view of a flat tube and splitter in accordance with the invention; Fig. 3 is a perspective view of an alternative form of splitter; Figure 4 is an enlarged cross-sectional view of a tag formed in the splitter of Figure 3; Figure 5 is a graph of oil pressure drop against oil flow; and Figure 6 is a graph of air side heat dissipation against air approach velocity.

Referring first to Figure 1 this shows a flat tube oil cooler duct comprising a flat tube 1, normally formed by rolling and seam welding a flat sheet of metal, containing a corrugated member ("splitter") 2.

After insertion of the splitter 2 into the flat tube 1, the tube 1 is then rolled or pressed flat onto the splitter to provide sufficient contact for the soldering or brazing operation which normally joins these two components together metallurgically. The corrugated splitter provides a series of so-called "fins" and splits the tube into a series of smaller passageways.

There is no connection between the passageways. The splitter 2 is normally soldered to the inside of the tube 1 to increase heat transfer and to resist the effect of internal hydraulic pressure. Referring to Figure 2 this shows a flat tube heat exchanger in accordance with the invention in which within the flat tube 3 there is a corrugated splitter 4 which has a series of tags 5 which are punched out of the top and base of the corrugations and make an angle of about 30 therewith. These tags are directed inwardly into the concave portion of the corrugation. The tags interrupt the oil flow along the length of the passageway thereby breaking up laminar flow to provide turbulence which results in increased heat transfer rates between the oil and the inside of the tube wall.The holes left by the tags also provide access for molten solder to flow between the channel base and the tube wall to increase the area of the soldered joint. This again increases heat transfer and also improves mechanical strength. The nail punch piercing results in two or more, usually four, ears without loss of metal.

An alternative arrangement is shown in Figure 3 in which the tags 6 are die cut and formed as is shown more clearly in Figure 4 to increase the turbulence within the ducts. The tags are in the form of rectangles which are relatively thin and which are integral with the top and base of the corrugation at one end only.

Although the turbulators could be put into the transverse legs such as 7 of the corrugations this would be difficult to do although it would form an effective heat transfer. It would not, however, improve the solderability of the assembly in the same way as do the holes in the top and base of the corrugation.

Figure 5 is a graph of oil pressure drop in psi of oil at 70"C passing through 18 tubes 12" long each incorporating a splitter which forms 10 small subsidiary ducts. The oil flow in gall/min is given along the bottom line of the graph. It will be seen that the line 8 which corresponds to the invention is higher than line 9 which corresponds to conventional unperforated splitters of the type shown in Figure 1. The increased turbulence results in the improved heat exchange characteristics shown in Figure 6.

In Figure 6 there is drawn a graph of heat dissipation through the air, KW/m2/0C MTD (mean temperature difference) against approach air velocity in m/s. Line 10 corresponds to the heat dissipation by a heat exchanger tube in accordance with the invention having 18 fins per inch in which the oil flow is 330 litres/ min/m (22 gall/min/ft) as compared to line 11 which shows a prior art heat exchanger of the type shown in Figure 1, again with an oil flow of 330 litres/min/m. In the arrangement tested to produce the results of line 11 there were only 14 fins per inch. Line 12 is the results obtained on the same heat exchanger as for line 10 but in this case using an oil flow of 220 litres/min/m (14.8 gall/min/ft). Line 13 corresponds to the prior art heat exchangers the same as that tested to produce the results of line 11 but this time using an oil flow of 220 litres/min/m.

It can be quite clearly seen from Figures 5 and 6, particularly Figure 6, that the invention provides a significant improvement in heat exchange characteristics over the prior art heat exchanger as exemplified by Figure 1. Generally, the heat dissipation properties of a heat exchanger of the invention may be improved by increasing the number of fins per inch and/or by providing tags having a steeper angle of inclination, for example 45" rather than 30 and/or by increasing the number of tags by reducing the distance between adjacent tags.

The heat exchangers which were tested to produce the results illustrated in Figures 5 and 6 were manufactured from steel tubes and turbulators with solder bonded external copper fins.

WHAT WE CLAIM IS:- 1. A flat tube heat exchanger comprising at least one flat tube having in its bore an elongate, longitudinally corrugated member which, together with walls of the tube, define a plurality of substantially parallel passageways within the tube and a plurality of projections extending into the passageways from the corrugated member and/or the walls of the tube to cause or enhance turbulence of fluid passing, in use, through the passageways.

2. A heat exchanger as claimed in claim 1 wherein at least some of the projections extend from the corrugated member.

3. A heat exchanger as claimed in claim 2 wherein said projections are integral with the corrugated member.

4. A heat exchanger as claimed in claim 3 wherein said projections comprise tags punched or pressed out of the corrugated member.

5. A heat exchanger as claimed in any one of claims 1 to 4 wherein the corrugated member comprises rectangular corrugations.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of a tag formed in the splitter of Figure 3; Figure 5 is a graph of oil pressure drop against oil flow; and Figure 6 is a graph of air side heat dissipation against air approach velocity. Referring first to Figure 1 this shows a flat tube oil cooler duct comprising a flat tube 1, normally formed by rolling and seam welding a flat sheet of metal, containing a corrugated member ("splitter") 2. After insertion of the splitter 2 into the flat tube 1, the tube 1 is then rolled or pressed flat onto the splitter to provide sufficient contact for the soldering or brazing operation which normally joins these two components together metallurgically. The corrugated splitter provides a series of so-called "fins" and splits the tube into a series of smaller passageways. There is no connection between the passageways. The splitter 2 is normally soldered to the inside of the tube 1 to increase heat transfer and to resist the effect of internal hydraulic pressure. Referring to Figure 2 this shows a flat tube heat exchanger in accordance with the invention in which within the flat tube 3 there is a corrugated splitter 4 which has a series of tags 5 which are punched out of the top and base of the corrugations and make an angle of about 30 therewith. These tags are directed inwardly into the concave portion of the corrugation. The tags interrupt the oil flow along the length of the passageway thereby breaking up laminar flow to provide turbulence which results in increased heat transfer rates between the oil and the inside of the tube wall.The holes left by the tags also provide access for molten solder to flow between the channel base and the tube wall to increase the area of the soldered joint. This again increases heat transfer and also improves mechanical strength. The nail punch piercing results in two or more, usually four, ears without loss of metal. An alternative arrangement is shown in Figure 3 in which the tags 6 are die cut and formed as is shown more clearly in Figure 4 to increase the turbulence within the ducts. The tags are in the form of rectangles which are relatively thin and which are integral with the top and base of the corrugation at one end only. Although the turbulators could be put into the transverse legs such as 7 of the corrugations this would be difficult to do although it would form an effective heat transfer. It would not, however, improve the solderability of the assembly in the same way as do the holes in the top and base of the corrugation. Figure 5 is a graph of oil pressure drop in psi of oil at 70"C passing through 18 tubes 12" long each incorporating a splitter which forms 10 small subsidiary ducts. The oil flow in gall/min is given along the bottom line of the graph. It will be seen that the line 8 which corresponds to the invention is higher than line 9 which corresponds to conventional unperforated splitters of the type shown in Figure 1. The increased turbulence results in the improved heat exchange characteristics shown in Figure 6. In Figure 6 there is drawn a graph of heat dissipation through the air, KW/m2/0C MTD (mean temperature difference) against approach air velocity in m/s. Line 10 corresponds to the heat dissipation by a heat exchanger tube in accordance with the invention having 18 fins per inch in which the oil flow is 330 litres/ min/m (22 gall/min/ft) as compared to line 11 which shows a prior art heat exchanger of the type shown in Figure 1, again with an oil flow of 330 litres/min/m. In the arrangement tested to produce the results of line 11 there were only 14 fins per inch. Line 12 is the results obtained on the same heat exchanger as for line 10 but in this case using an oil flow of 220 litres/min/m (14.8 gall/min/ft). Line 13 corresponds to the prior art heat exchangers the same as that tested to produce the results of line 11 but this time using an oil flow of 220 litres/min/m. It can be quite clearly seen from Figures 5 and 6, particularly Figure 6, that the invention provides a significant improvement in heat exchange characteristics over the prior art heat exchanger as exemplified by Figure 1. Generally, the heat dissipation properties of a heat exchanger of the invention may be improved by increasing the number of fins per inch and/or by providing tags having a steeper angle of inclination, for example 45" rather than 30 and/or by increasing the number of tags by reducing the distance between adjacent tags. The heat exchangers which were tested to produce the results illustrated in Figures 5 and 6 were manufactured from steel tubes and turbulators with solder bonded external copper fins. WHAT WE CLAIM IS:-

1. A flat tube heat exchanger comprising at least one flat tube having in its bore an elongate, longitudinally corrugated member which, together with walls of the tube, define a plurality of substantially parallel passageways within the tube and a plurality of projections extending into the passageways from the corrugated member and/or the walls of the tube to cause or enhance turbulence of fluid passing, in use, through the passageways.

6. A heat exchanger as claimed in claim 5

wherein the corrugations are substantially square.

7. A heat exchanger as claimed in any one of claims 1 to 6 wherein the crests and/or the troughs of the corrugated member are provided with said projections.

8. A heat exchanger as claimed in any one of claims 1 to 7 wherein at least some of said projections are substantially rectangular.

9. A heat exchanger as claimed in claim 8 wherein the two major faces of said substantially rectangular projections lie transversely to the longitudinal axes of said passageways.

10. A heat exchanger as claimed in any one of claims 1 to 9 wherein the corrugated member is attached to the walls of the tube.

11. A heat exchanger substantially as described hereinbefore with reference to, and as shown in, Figure 2 of the drawings filed with the provisional specification.

12. A heat exchanger substantially as described hereinbefore with reference to, and as shown in, Figures 3 and 4 of the drawings filed with the provisional specification.

13. An engine comprising at least one heat exchanger as claimed in any one of claims 1 to 12 for cooling water or oil circulating, in use, in the engine.