WO1988009910A1

WO1988009910A1 - A spiral tube heat exchanger and a method for its manufacture

Info

Publication number: WO1988009910A1
Application number: PCT/DK1988/000087
Authority: WO
Inventors: Hans Fuglede
Original assignee: Hans Fuglede
Priority date: 1987-06-04
Filing date: 1988-06-03
Publication date: 1988-12-15
Also published as: DE3877369D1; EP0424369B1; ATE84364T1; DK156315B; DK286787A; AU1950088A; DK286787D0; DK156315C; EP0424369A1; DE3877369T2

Abstract

By a spiral tube heat exchanger with a spiral tube (3) wound around the external wall of a vessel (9), with an external shell (6) which envelopes the spiral tube (3) tightly, and the internal surface of which may be provided with an insulating layer of a solid-hardening expanded elastomeric foam (7), a high efficiency is to be ensured, together with low production and maintenance costs and with low cleaning costs. These objectives are achieved with a spiral tube heat exchanger by welding or glueing the individual turns on to the adjacent turns either directly or by spacers, by filling the spiral tube itself (3) with a solid-hardening expanded elastomeric foam (8) such as polyurethane or similar, or expanded mineral silicates such as fibre gypsum or similar ceramic materials and composites.

Description

A SPIRAL TUBE HEAT EXCHANGER AND A METHOD FOR ITS MANUFACTURE .

- 1 -

This invention relates to a spiral tube heat exchanger with a spiral tube wound around the external wall of a vessel, with an exter¬ nal shell, which is fitted tightly around the spiral tube, and whose internal surface may be provided with an insulating layer of a solid- hardening expanded elastomeric foam.

Such spiral tube heat exchangers are known from for instance DE- patent specification 956 050, in which the individual turns are wound around the wall of a vessel with some spacing between the turns with a view to allowing a fluid to flow along the spiral tube. In order to prevent the fluid flowing around the spiral tube from passing freely from turn to turn in a sort of "short circuit", it is proposed in this patent specification to manufacture the external shell of an elastic material, which fits tightly around the spiral tube. In this spiral tube heat exchanger, heat is transmitted both through the wall of the vessel and through the tube wall of the spiral tube heat exchanger, which results in a reduction of the efficiency as, depending on the material chosen, both walls have a relatively poor thermal conduc¬ tivity. The fluid which encloses the spiral tube itself on the external surface of the vessel will also have a low thermal conductivity across the flow, depending on its flow conditions, for instance at a laminar flow.

From US-patent specification 4,196,772 it is a known method to envelope a spiral tube-like plastics body of a deformable material with an insulating layer sited externally on the spiral tube formed by the body. Here it is also the intention to provide a soft spiral tube, which may be deformed during heating by the effect of the pressure from the fluid flowing in the spiral tube, so that the spiral tube will adapt to the external surface of the enveloped vessel with a view to making the heat transmission between the fluids more efficient. Here, heat is also transmitted both through the wall of the vessel and the wall of the spiral tube, which does not, as stated above, provide an optimal transmission of heat.

From DE-patent publication 26 45 059 a method and a foil is known for the manufacture of a heat exchanger wall, where the heat exchanger tubes are glued upon the wall of the vessel and enveloped externally by a shell with a heat insulating material. This patent application shows a siting of the spiral tubes with some spacing between them, where an insulating material is furthermore filled into the space bet¬ ween the spiral tubes. The space which will invariably occur between the filled-in insulation material, the spiral tube and the wall of the vessel is not mentioned, and it may then at most contribute to reducing the heat transmission from the spiral tube to the fluid contained with¬ in the wall of the vessel. It is not indicated whether a fluid is to be able to flow in the space existing between the spiral tube and the wall of the vessel.

From DE-patent publication 28 54 450 a heat exchanger is known, which consists of a process tank with a spiral tube heat exchanger, which is placed on the internal surface of the process tank. It is em¬ phasized that the spiral tube heat exchanger is manufactured of half- tubes sited closely against each other. Such a siting of the spiral tube heat exchanger, whereby the internal surface of the process tank will be corrugated, will, however, offer problems both with respect to pressure resistance and to for instance cleaning and maintenance, as such a corrugated surface is very likely to be deformed if subjected to pressure differences, and it has several inaccessible points, where dirt may accumulate. Moreover, the manufacture of such a heat exchanger surface is very costly, and the tube wall material will still have a limited thermal conductivity, especially if the spiral tube is thick- walled in order to increase the pressure resistance, or if it is manu- factured of a plastics material.

It is therefore the object of the present invention to provide a spiral tube heat exchanger which has a high efficiency, is economical both in manufacture and in use, and which is easy to maintain and clean. This task is solved according to the present invention by welding or glueing each turn to the adjacent turns, either directly or via spa¬ cers, by filling the spiral tube itself with a solid-hardening, expand¬ ed elastomeric foam, such as polyurethane or similar, or expanded mineral silicates, such as fibre gypsum or similar ceramic materials and composites. With the spiral tube heat exchanger according to the present in¬ vention, a sectional area of flow is provided, which is approximated to a triangular shape, with the wall of the vessel forming one side and the two other sides of the cross-section being formed by the spiral tube walls of two adjacent tubes, i.e. two quarter-circle arcs. With this cross-section and even at relatively low flow velocities tur¬ bulence will be generated, which will ensure that the passing fluid has good possibilities of exchanging heat energy with the fluid contained in the vessel. Furthermore the cylindrical wall of the vessel will be the only barrier between the two fluids, which ensures an optimal heat transmission.

In all spiral tube heat exchangers known at present the fluids are contained either in the vessel, or they flow in the spiral tube, which has obviously not contributed to an optimal joint surface through which heat can be transmitted. With the spiral tube heat exchanger according to the present invention the joint heat exchanger surface has been max¬ imized at the same time as a controlled exchange of energy is obtained between the fluids. As a consequence of the nonuniform sectional area of flow in which especially the spiral tube walls with their convex shape offer a large friction surface relative to the sectional area of flow, the passing fluid has to be driven through the spiral tube heat exchanger under friction, with a consequent loss of pressure, which will then result in a generation of turbulence. This turbulence contri¬ butes to ensuring that the flow in the spiral tube heat exchanger pas- ses not only in a type of coil, but also that strong cross-flows will be generated, which will have the result that the passing fluid can efficiently exchange heat energy with the fluid contained in the ves¬ sel. The pressure loss resulting from the turbulent flow has to be com¬ pensated by a higher entry pressure for the flowing fluid. According to a further embodiment of the invention it is proposed to equip the spiral tube which is wound around the vessel with at least one fin, with e.g. a rectangular cross-section. If two fins are used, these will be placed with one fin diametrically opposite the other. These embodiments will serve to increase the sectional flow area, with- out increasing the diameter of the spiral tube, at the same time as the surface designed for glueing or welding is easily accessible. These embodiments are of special interest where a process tank or a spiral tube heat exchanger has to be built in at narrow sites, and at the same time a higher pitch of the winding is obtained. This is of importance where a brief flow time is intended .for the fluid passing around the vessel.

According to the present invention it is proposed to place spacers between the individual turns of the spiral tube. Like the fins, the spacers will result in a widening of the space between the individual turns of the spiral tube. This will allow manufacture of process tanks with relatively small external dimensions, with the only necessary re¬ quirement for the plastic tube being that it has to be circular.

A similar effect is obtained according to the present invention by fitting from outside, between the individual turns of the primary spi- ral tube, a further secondary spiral tube, whose diameter is smaller than the diameter of the primary spiral tube, but wider than the space between the individual turns of the primary spiral tube, and by filling also this secondary spiral tube with a material corresponding to the filler in the primary spiral tube. Hereby the further advantage is ob- tained that the glueing pressure during fastening is provided by the winding of the secondary spiral tube in the space between the turns of the primary spiral tube. It should be stated here, that the diameter of the secondary tube should primarily be adjusted to the distance to the external shell, so that this shell can be rectilinear parallel with an axial line on the cylindrical surface of the shell.

A further essential advantage is obtained in the spiral tube heat exchanger according to this invention, by placing along the internal surface of the vessel, a spiral tube corresponding to the spiral tube of the external surface, with a filler and an internal shell. Thereby an extremely efficient counter-flow heat exchanger is provided, which, depending on the length of the spiral tube heat exchanger, can heat or cool any volume of fluid per time unit with a very high efficiency.

A spiral tube heat exchanger according to the present invention is manufactured by the following method steps: 1) A spiral tube is wound and fixed tightly around the vessel designed as a process tank, on which spacers may be placed between the individual turns of the tube,

2) in the spiral tube is filled a solid-hardening, expanding elasto- meric foam, such as polyurethane, which will foam up and harden, to ensure hardness and solidity of the spiral tube, and

3) a solid-hardening expanding elastomeric foam is applied around the external part of the spiral tube, whereon a shell is fitted.

By this method a mechanically extremely stable spiral tube will be ob¬ tained, which is secured externally by the further application of e.g. a fibre filler in the elastomeric foam, which all in all serves to re¬ inforce the vessel, which will thereby obtain a very high pressure re¬ sistance. Below the invention will be described in more detail by means of the embodiments shown by way of example in the drawing, in which:

fig. 1 shows a lateral view of a spiral tube heat exchanger with inlet and outlet sockets, and a spiral tube sited under an external shell, fig. 2 shows an enlarged section through part of the spiral tube heat exchanger according to the invention, where the spiral tube is sited between the wall of the vessel and the external shell, fig. 3 shows a spiral tube heat exchanger as in fig. 2, where the spiral tube is equipped with rectangular diametri¬ cally opposed fins, fig. 4 shows a spiral tube heat exchanger as in fig. 3, where spacers are placed between the turns of the spiral tube, fig. 5 shows a spiral tube heat exchanger as in fig. 4, where the spacers are replaced by a secondary spiral tube with a smaller diameter than the primary spiral tube, and fig. 6 shows a spiral tube heat exchanger, embodied as a counter-flow heat exchanger with a symmetrical con- ^" struction around a cylinder wall of the flow canal for In fig. 1 a spiral tube heat exchanger is indicated by 1, and the vessel itself is indicated by 2. The vessel 2 is provided with an inlet socket 4 and an outlet socket 5. Tightly wound around the vessel is a spiral tube 3, which is covered externally by a shell 6. Between the spiral tube 3 and the shell 6 an insulating foam material 7 has been filled in.

It appears in greater detail from fig. 2 how the spiral tube wind¬ ing according the the invention is filled with a filler 8, and that it is sited closely adjacent to the wall of the vessel 9, to which it is attached either by glueing or e.g. by ultrasonic welding. Between the spiral tube 3 and the vessel wall 9 is an approximately triangular sec¬ tional area of flow 10, the area of which A appears from the equation:

A = JsD²(1 - L) k

where D is the diameter of the spiral tube 3. It appears clearly from fig. 2 that the convex walls of the spiral tube suspend the two sides of the cavity whereby, jointly with the vessel wall 9, they generate a friction of a certain final level, which can ensure that even at^" low flow velocities, turbulence may be generated in the passing fluid.

Fig. 3 shows a spiral tube heat exchanger according to the present invention, in which the spiral tube 3 is provided with two fins 11, placed diametrically opposite each other. The fins 11 are assembled either by glueing or e.g. by ultrasonic welding. For control of the fins 11 ^"during assembly, these may be provided with suitable control features 12, for instance, as shown, in the form of concave/convex mouldings. The increased area produced with the fins 11, is derived by a simple addition of an imaginary rectangle, the height of which is the sum a of the height of the fins, and the width of which is equal to the diameter D of the spiral tube 3. This gives the equation:

where D is the diameter of the spiral tube 3, and a is the sum of the height of the fins, i.e. the increased spacing between the individual turns of the spiral tube.

A similar effect is obtained with the embodiment according to fig. 4, where spacers 13 with the height a are inserted instead of fins. With this embodiment the spiral tube 3 does not have to be specially manufactured, and the space between the turns of the spiral tube can also be made wider than where these are provided with fins, whose height cannot be too big for reasons of stability.

An increase of the space between the turns of the spiral tube can also be obtained with the embodiment according to fig. 6, in which the spacing is produced by means of a secondary tube, which is inserted from outside between the turns of the spiral tube already sited. The diameter d of the secondary tube must here be smaller than the diameter D of the primary spiral tube 3. It should, however, be ensured that the secondary tube is sited in such a way that it does not touch the wall of the vessel 9, but primarily the shell 6. This will ensure a sec¬ tional area of flow of a more complicated form, with more convex sur¬ faces which extend into the flow. This will increase the friction rela¬ tively and thereby the generation of turbulence.

Fig. 5 shows a further embodiment of the spiral tube heat ex- changer according to the present invention, in which a further spiral tube 3* is fitted on the internal surface of the vessel 9, similarly filled with a filler 8* and enveloped by an internal shell 6' and fil¬ led with a filler 7'. This embodiment provides the possibility of esta¬ blishing a counterflow heat exchanger which, due to the friction and the consequent turbulence generated, provides a heat exchanger with a high efficiency.

With process tanks or spiral tube heat exchangers according to the present invention, fibre-reinforced materials may be applied for the external shell, which will ensure a high mechanical resistance to high- pressure fluids in the process tanks or the spiral tube heat exchangers at the same time as the structure of these spiral tube heat exchangers may weigh less than corresponding steel structures for such pressures. Therefore weight may be saved, and as it is at the same time possible to mount them in narrow spaces with maintenance of a high efficiency, spiral tube heat exchangers according to the present invention are. well suited for use as e.g. flow hot-water heaters. This will eliminate the risk of large bacteria colonies in hot-water tanks, where the tempera¬ ture in a hot-water tank falls when the distance from the outlet in¬ creases.

Claims

P A T E N T C L A I M S

1. A spiral tube heat exchanger with a spiral tube (3) wound and pos¬ sibly glued around the external wall of a vessel (9), with an external shell (6) which fits tightly around the spiral tube (3), and which may be provided with an insulating layer of a solid-hardening expanded ela- stomeric foam (7) on its internal surface, c h a r a c t e r i s e d in that the individual turn is welded or glued on to the adjacent turns either direct or by spacers, that the spiral tube itself (3) is filled with a solid-hardening expanded elastomeric foam (8), such as polyure¬ thane or similar, or expanded mineral silicates, for instance fibre gypsum or similar ceramic materials and composites.

2. A spiral tube heat exchanger according to claim 1, c h a r a c t¬ e r i s e d in that the spiral tube (3) which is wound around the ves¬ sel (2), is equipped with at least one fin (11) with for instance a rectangular cross section.

3. A spiral tube heat exchanger according to claim 2, where two fins (11) are used, c h a r a c t e r i s e d in that the fins are sited diametrically opposite each other.

4. A spiral tube heat exchanger according to claims 1-3, c h a ¬ r a c t e r i s e d in that the opposing edges of the fins (11) are provided with control features (12), for instance by way of a convex moulding with a corresponding concave moulding.

5. A spiral tube heat exchanger according to claim 1, c h a r a c t¬ e r i s e d in that, from outside, between the individual turns of the spiral tube of the primary spiral tube (3), a further secondary spiral tube (14) is inserted, the external diameter of which (d) is smaller than the diameter (D) of the primary spiral tube, but wider than the space between the individual turns of the primary spiral tube (3), and that this secondary spiral tube (14) is also filled with a material corresponding to the filler in the primary spiral tube (3).

6. A spiral tube heat exchanger according to each of the foregoing claims, c h a r a c t e r i s e d in that, on the internal surface of the wall of the vessel (9), a spiral tube (3') is sited, corresponding to that wound around the external surface, with a filler (8') and an internal shell (6").

7. A method for the manufacture of a spiral tube heat exchanger according to claims 1 - 6, c h a r a c t e r i s e d by the following method steps:

1) a spiral tube (3) is wound and fixed tightly around the vessel (2) designed as a process tank, on which spacers (11, 13, 14) may possibly be placed between the individual turns of the tube,

2) in the spiral tube (3) is filled a solid-hardening, expanding ela- stomeric foam (8), e.g. polyurethane,

3) a solid-hardening, expanding elastomeric foam is applied around the external part of the spiral tube, whereon a shell is fitted.