GB2049147A - Spine fin tube heat exchangers - Google Patents

Abstract

A spine fin tube heat exchanger wherein the density of spine fins (11) is greater along portions of passes of tube (10) within a pattern (33) of high flow of air or the like across the heat exchanger. Those portions of the tubing at the bends (12 to 18) and outside the pattern (33) are formed with a lower density of spine fins (11). Such lower density outside the pattern (33) and at the bends does not materially reduce the overall heat exchange capacity of the heat exchanger, and results in a heat exchanger where less material and time are required to form the heat exchanger without any significant loss in its capacity. The fins are preferably applied to the tube by changing the rate of feed of the tube (10) as it feeds through a head wrapping said tube with spine fins, in order to increase the amount of stretch of the spine fin strip along the zones of low density compared to the amount of stretch in the strip along the zone of high density. Consequently, the same mount of material is required for each wrap along both kinds of zones. <IMAGE>

Description

SPECIFICATION Spine fin tube heat exchangers The invention relates to heat exchanger systems and particularly to spine fin tube heat exchangers and to a method and apparatus for producing such heat exchangers.

It has been previously proposed to combine heat exchangers with fans to move a stream of fluid such as air over the heat exchanger in order to cause heat to be transferred between the fluid and the heat exchanger. Such systems are often used, for example, in heat pumps in air conditioning units.

It has also been proposed to provide such heat exchangers with tubes helically wrapped with spine fins, as disclosed in the specifications of United States Patent Nos 3 005 253; 3 134 166; 3 160 129; and 3 688 375, and such specifications are incorporated herein by reference.

Such spine fin tube heat exchangers are formed by wrapping a substantially straight tube with one or more strips of helically arranged spine fins wherein the helix angle of the strips and the axial spacing of the spine fins are uniform. Such spine fins greatly increase the heat exchange capacity for a given length of tube. After wrapping, such tube is bent back and forth to form multiple pass heat exchangers, which are usually installed in systems with a fan that forces fluid across the passes.

In the past, such heat exchanger tubes have been wrapped with a uniform helix angle even though the spine fins at the bends are likely to be damaged during the bending operation and therefore do not contribute to the transfer of heat as efficiently as the undamaged portions along the length of the passes. Further, such uniformly wrapped passes do not uniformly contribute to the heat exchange capacity in most instances, since the fans do not move uniform amounts of fluid across the entire length of such passes.

According to the invention there is provided a spine fin tube heat exchanger comprising a tube helically wrapped with spine fins, the tube being formed with a plurality of reverse bends joined by substantially straight passes to be positioned in a stream of fluid for heat exchange therewith, the spine fins along at least a portion of the straight passes having one density and along the bends having a lesser density than said one density.

The tube of such a heat exchanger is helically wound with spine fins which have a smaller helix angle and smaller spacing along the passes of the heat exchanger where the greatest amounts of fluid pass and have a greater helix angle and larger spacing along the portions of the tube at the bends and along the portions of the tube over which lesser amounts of fluid pass. Consequently, a heat exchanger for a given capacity requires less material and time to produce.

The tube is wrapped with the helically wound spine fins while the tube is substantially straight. In order to provide the portions with a greater helix angle, the apparatus for manufacturing of the wrapped tube can vary the relative speed between the axial feeding of the tube and the speed of rotation of a wrapping head to produce first spaced zones with a relatively small helix angle and small fin spacing and intermediate second zones spaced along the length of the tube with the greater helix angles and greater fin spacing.

Preferably, the variation in helix angle is accomplished by changing the rate at which the tube is fed axially into the wrapping head and the machine is programmed to produce the zone of greater helix angle at appropriate locations along the length of the tube so that when the tube is bent into the finished heat exchanger, such zones extend along the bends in the tube and along the portions of the tube over which lesser amounts of fluid pass.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a side elevation of a spine fin tube heat exchanger according to the invention, with portions of the spine fins removed for purposes of illustration and schematically illustrating a fan to blow a stream of air over the heat exchanger; and Figure 2 is a schematic, perspective view of a machine for producing the spine fin tubing for the heat exchanger illustrated in Fig. 1.

Fig. 1 illustrates an assembled heat exchanger of a kind which may be used, for example, in an air conditioning unit and comprises a piece of tube 10 helically wound with spine fins 11. For purposes of illustration, such spine fins 11 are only illustrated as straight lines extending radially with respect to the tube, but it should be understood that the spine fins extend the helical pattern completely around the tubes and that the spine fins are formed generally in the manner disclosed in the United States Patent specifications referred to above.

Fig. 1 illustrates the spine fins directly opposite each other; however, it should be understood that the strips of spine fins may or may not provide diametrically opposite fins or, for that matter, the spines may not be radial with respect to the tube 10 but, instead, may be inclined to some extent. Further, the tube may be single-wrapped with a single strip or multiple-wrapped with two or more spine fin strips. Still further, the strips may be L-shaped as illustrated in United States Patent specification No 3 005 253 or may be generally Ushaped as illustrated in United States Patent specification No 3 134 166.

The tube 10, with the spine fins 11 thereon, is reversely bent at seven locations, 1 2 to 18, to provide a plurality of parallel, substantially straight passes. In the illustrated embodiment, the heat exchanger has eight passes 21 to 28, which connect between the adjacent bends and through which a refrigerant fluid or other fluid flows back and forth when the heat exchanger is in use.

A fan 31, illustrated in chain dotted lines, is mounted adjacent to the heat exchanger and operates to blow a stream of air or the like across the fin tube passes. In the illustrated embodiment, the fan 31 is a rotary, axial flow blade-type fan which rotates about an axis 32 and moves air across the heat exchanger with a substantially circular pattern illustrated by the chain dotted line 33. With such a fan, the air velocity is greatest within the circular pattern 33, the lower air velocity is provided across the heat exchanger outside of such circle.

In order to provide a high rate of heat exchange between the air passing over the heat exchanger and the fluid flowing through the tube 10, the spine fins 11 are disposed along the pass 22 with a high density provided by a small helix angle between the positions 34 and 35, and a lesser density provided by a larger helix angle around the bends 1 2 and 1 3 and along the pass 22 from the bend 1 2 to the position 34 and between the bend 1 3 and the position 35. Consequently, a relatively high density of spine fins is provided along the pass 22 in the pattern of high air flow and a relatively low density of spine fins is provided along the bends and the portions of the pass which are outside of such pattern of high air flow.

In a similar manner, the pass 23 is provided with a relatively high and substantially constant density between the positions 36 and 37 and a lower density beyond such positions and around the adjacent bends 1 3 and 14. Similarly, the spine fins along the pass 24 are provided with a high density or maximum heat exchange between the positions 38 and 39, and lower density around the bends 14 and 15.

In a symmetrical type of heat exchanger, as illustrated in Fig. 1, the length of high density wrapping on the pass 25 is the same as the high density wrapping along the pass 24, the length of the high density wrapping along the pass 26 is the same as that along the pass 23, the length of high density wrapping along the pass 27 is the same as that along the pass 22, and the length of high density wrapping along the pass 21 is the same as that along the pass 28, with the high density wrapping existing on the pass 21 between positions 41 and 42.

With this heat exchanger, the entire portion of the heat exchanger within the circular pattern of highest flow produced by the fan 31 is wrapped with high density spine fins for a maximum amount of heat exchange between the air and the fluid flowing through the tube, but the portions of the heat exchanger outside of such circular pattern are wrapped with lower density, resulting from the use of a larger helix angle in the wrapping operation.

Therefore, less material is required to produce the heat exchanger than heretofore without any appreciable loss in heat exchange capacity for a given size heat exchanger. Also, in the preferred embodiment, the tube is advanced at a greater rate when wrapping at larger helix angles so the time for producing the tubing for the heat exchanger is also reduced in accordance with the present method.

It should be understood further that in the bending process in which the various bends are formed in the wound tubing, the spine fins along the bend are also bent and damaged to some extent so that they cannot contribute to the heat exchange with the same efficiency as the undamaged fins along the straight portions of the tube. In the drawings, however, no attempt has been made to illustrate the manner in which the damage occurs at the bends, since the damage is random in character and cannot be effectively represented in the drawing.

Fig. 2 schematically illustrates a machine for producing spine fin tubes for heat exchangers according to the invention. Such a machine has feed rolls 50 which engage opposite sides of the tube 10, are connected by gearing 51, and are powered to feed the tube 10 in the direction indicated by an arrow by a suitable drive motor 52. A wrapping head 53 rotates, in the direction of an arrow shown thereon around the tube 10 and wraps the tube 10 with spine fins as the tube feeds axially through the head. The wrapping head 53 is supplied with strips of material 54 for the spine fins, which strips have been cut and shaped with suitable rotary cutters and form ing rollers, to be wrapped on the tube 10 under tension.

The spacing betwen adjacent fins is deter mined by the helix angle of winding, which is determined by the relationship between the speed of rotation of the head 53 and the axial speed at which the tube 10 is fed through the head. When the speed of the feed of the tube 10 is increased, the helix angle increases and gives a greater spacing between adjacent fins, resulting in a lower density of wrapping.

When the speed of the feed is reduced while the speed of the head 53 remains constant, the helix angle is reduced and a higher den sity wrap is achieved. In the illustrated ma chine, a programmed speed control 56 is connected to control the operating speed of the motor 52, thereby to control the rate of feeding of the tube. The speed control 56 is also connectd to the head 53 through a suitable electrical connection, schematicaliy il lustrated by 57, so that it can respond to a given number of revolutions of the head to change the speed of the motor 52 and feed to provide the desired pattern of wrapping.The speed control is programmed to produce a slow feed of the tube 10 for the appropriate periods to produce each of the spaced zones of high density wrapping and to produce higher feed speeds for appropriate periods to produce the intermediate zones of low density wrapping required to produce the finished heat exchanger.

Then after the tubing is wound, it is bent along the intermediate zones of relatively low density wrapping to provide the heat exchanger illustrated and described in connection with Fig. 1. In such heat exchanger, the lengths of the zones of high density are not uniform, nor are the lengths of the zones of low density, since each pass is arranged to provide high density only within the circular pattern 33. Therefore, the cotrol 56 is programmed to produce the various zone lengths required.

Preferably the rate of feed of the strip material 54 to the tube 10 and the rotational speed of the wrapping head 53 are maintained substantially constant during the entire winding operation so that the same amount of strip material is used to form each turn or wrap along the entire length of the tube. Such strip material is stretched a greater amount when winding the intermediate zones of low density than the stretch along the high density zones to accommodate the greater helix angle.

The stretching or elongation of the strip, however, must be within the limits to which it can stretch without rupture or breaking. In practice, the stretch along the zones of low density is maintained at about one per cent and along the zones of low density the stretch is maintained at about three per cent. With such difference in stretch or elongation of the strips, substantial increases in the helix angle or spacing can be achieved without causing breakage of the typical aluminum spine fin material used to form the fins of the heat exchanger.

Claims (14)

1. A spine fin tube heat exchanger comprising a tube helically wrapped with spine fins, the tube being formed with a plurality of reverse bends joined by substantially straight passes to be positioned in a stream of fluid for heat exchange therewith, the spine fins along at least a portion of the straight passes having one density and along the bends having a lesser density than said one density.

2. A spine fin heat exchanger according to claim 1, wherein the spine fins along the straight passes are provided with said one density along the portions thereof to be positioned within said stream and provided with said lesser density along the portions thereof which are to be positioned outside said stream.

3. A spine fin heat exchanger according to claim 1 or claim 2, wherein a substantially uniform amount of material is provided in each wrap of the spine fin along the entire length of the tube.

4. A heat exchanger system comprising a heat exchanger operable to transfer heat between two fluids and means to cause a flow of one of said fluids over said heat exchanger as a stream of said one fluid having a substantially predetermined pattern wherein the flow rate over first portions of said heat exchanger in alignment with said pattern is substantially greater than the flow rate over second portions of said heat exchanger outside of said pattern, said heat exchanger comprising a tube wrapped with helically wound spine fins and a plurality of bends to provide a plurality of separate passes through said stream of said one fluid, said spine fins being wrapped with a smaller helix angle and providing a higher spine density along said first portions of said heat exchanger and with a greater helix angle providing a lower spine density along at least part of said second portions of said heat exchanger.

5. A heat exchanger system according to claim 4, wherein said bends are located outside said pattern and are provided with said lower density.

6. A method of producing helically wound spine fin tube heat exchangers comprising helically wrapping a substantially straight tube with spine fins having a first helix angle and a first spine fin density along a plurality of spaced first portions and with a second helix angle greater than said first helix angle and a lower spine fin density along intermediate second portions between said first portions, and thereafter bending said tube along said second portions to provide a plurality of substantially straight passes formed at least in part by said first portions.

7. A method or producing heat exchangers according to claim 6, wherein said spine fins are formed of a strip of material which is stretched as it is wound onto said tube, said strip being stretched a greater amount along said second portions than along said first portions.

8. A method of producing heat exchangers according to claim 7, wherein substantially the same length of strip is used for each wrap along both of said portions.

9. Apparatus for forming spine fin tube heat exchanger tubing comprising feed means for axially feeding a tube, and a spine fin wrapping head through which said tube is axially fed by said feed means, means for producing relative rotation between said tube and said head, and means for intermittently changing the relationship of the rate of feed of said tube and the relative rotation of said head with respect to said tube to produce spaced first zones of tubing having a first density of spine fins thereon and intermediate second zones of tubing between said first zones having a lower density of spine fins thereon.

10. Apparatus according to claim 9, wherein said head is rotated at a uniform speed, and said feed means feeds said tube with a first axial speed when producing said first zones and with a greater speed than said first axial speed when producing said second zones.

11. Apparatus according to claim 9 or claim 1 0, wherein said wrapping head wraps said tube with a strip of stretchable spine fins and supplies a uniform amount of said strip for each turn thereof.

1 2. A heat exchanger system comprising a heat exchanger operable to transfer heat between two fluids and means to cause flow of one of said fluids over said heat exchanger as a stream of said one fluid having a substantially predetermined flow pattern, said flow pattern providing zones of relatively high flow rates over first portions of said heat exchanger and zones of lower flow rates over other portions of said heat exchanger, said heat exchanger comprising a tube wrapped with helically wound spine fins, said tube being wrapped with a smaller helix angle and providing a higher spine density along at least part of said first portions and with a greater helix angle providing a lower spine density along at least parts of said other portions.

1 3. A spine fin tube heat exchanger substantially as hereinbefore described and illustrated with reference to the accompanying drawings.

14. A method of producing helically wound spine fin tube heat exchangers as claimed in claim 6 and substantially as hereinbefore described.