GB2136945A

GB2136945A - A tube assembly heat exchanger with plastic tube plate

Info

Publication number: GB2136945A
Application number: GB08406183A
Authority: GB
Inventors: Manfred Sassenberg; Hans-Joachim Kreichelt
Original assignee: QVF GLASTECH GmbH
Current assignee: QVF GLASTECH GmbH
Priority date: 1983-03-25
Filing date: 1984-03-09
Publication date: 1984-09-26
Also published as: GB8406183D0; DE3310986A1; FR2543283A1

Abstract

A tube assembly heat exchanger comprises plastic tube plate (1), in which the tubes (5) are disposed in stepped bores (2, 4) and each sealed by a seal (6) surrounding the tube and held under tension by a threaded bush (7) screwed into the other part of the bore (4). The seal (6) is a cylindrical clamping ring, the two end faces of the ring being conical and tapering. Tube plate (1), ring (6) and bush (7) may all be made of PTFE. Tube (5) may be made of glass. <IMAGE>

Description

SPECIFICATION A tube assembly heat exchanger with plastics tube ends The invention relates to a tube assembly heat exchanger with plastics tube ends, into which a metal plate is inserted if required, and in which the tubes are disposed in stepped bores and each sealed by a seal surrounding the tube, the seal being held under tension by a threaded bush screwed into the other part of the bore.

About 1 5 years ago it was proposed to make known tube assembly heat exchangers from glass instead of metal. Before then, glass had been used only for coil heat exchangers. Difficulties, however, arose. For example glass tube ends are expensive to manufacture, and it is also very expensive to connect glass tubes to glass tube ends, because glass tubes cannot be expanded in the ends but have to be melted thereto. This method, of course, makes repairs very difficult.

Accordingly, tube ends were made of chemically resistant plastics such as polytetrafluoroethylene (PTFE), a metal plate being incorporated in the plastics if required, to counteract undesired flow thereof. Particular difficulties occurred in sealing the glass tube from the plastics ends. At present, the conventional method of sealing is via gland-like devices as described in detail hereinbefore.

The seals are O-rings, usually comprising a resilient core with an overlapping or closed jacket of resistant material, and cylindrical resilient rings for packing of graphite, asbestos or unsintered PTFE.

All these seals have disadvantages in that they may cause undesired leakages through loss of elasticity during operation and/or because of flow processes in the tube-end material. This particularly applies when heat exchangers are used at elevated temperatures, at which changes in tension occur because of differences in the coefficient of expansion of different materials. This difficulty cannot be completely avoided even by inserting a metal plate in the tube ends.

The object of the invention, in the case of a tube assembly heat exchanger of the initiallydescribed kind, was to provide an efficient seal between the tubes and the plastics tube ends.

To this end, according to the invention, in the case of the tube assembly heat exchanger in question, the seal comprises a plastics clamping ring having a cylindrical passage, the two end faces of the ring tapering conically.

it has unexpectedly been found that if a clamping ring according to the invention is used, the tube end material is less inclined to flow, particularly in the radial direction, which is mainly responsible for the aforementioned leakages in the known embodiments. In the known embodiments, the pressure exerted on the seal has the general effect of compressing it, resulting in radial forces.

The invention is particularly important if the heat exchanger tubes are made of glass or ceramics, since in metal heat exchangers the tube ends are usually also made of metal, and metal connections are much easier to make. However, the heat exchanger tubes can be made of metal without departing from the invention.

The tube ends may be made more particularly of high-strength plastics such as PTFE. Similar materials are used for the clamping ring.

In a preferred embodiment, the two end faces.

of the clamping ring extend at the same angle towards its axis. Preferably also, the outer surface of the clamping ring is cylindrical Advantageous tension conditions are obtained if the step in the bore and/or the end face of the threaded bush facing the clamping ring extends parallel to the adjacent end face of the clamping ring.

In a preferred embodiment, the outer surface of the clamping ring is at a distance from the bore.

This avoids radial forces on the tube ends if the sealing ring is compressed during clamping.

The tube ends are usually cylindrical although this is not absolutely necessary. In the case of cylindrical tube ends, a metal ring is preferably placed on the cylinder surface so as to counteract the flow of the cylinder-end material.

The invention will now be explained in detail with reference to the accompanying drawings in which: Fig. 1 is a partial section through a tube assembly heat exchanger according to the invention (in the assembled state on the left and in exploded view on the right) and Fig. 2 is a smaller-scale view of the tube ends, only part of which is shown in Fig. 1.

More particularly Fig. 1 shows a tube end 1 having a bore for receiving a glass tube 5. The bore has a narrow part 2 and a wide part 4, with a conical transition at an angle a1. A clamping ring 6 is disposed on tube 5 and is bevelled at an angle at at the bottom and an angle p2 at the top. The other part 4 of the bore has an inner thread 3 into which a threaded bush 7 is screwed, the end face of the bush facing ring 6 being conical so as to include an angle 2 with the axis of bush 7. As can be seen, a, is different from /3, whereas a2 and p2 are equal.

Tube end 1, ring 6 and bush 7 are all made of PTFE.

When a glass tube 5 is incorporated in a tube end 1, a ring 6 is first pushed over the glass tube, which is then inserted into bore 2, 4. A threaded bush 7 is then slid over it and tightened.

As shown in Fig. 2, the tube end 1 is surrounded by a metal ring 8 which prevents the material of end 1 from flowing.

1. A tube assembly heat exchanger with plastics tube ends, into which a metal plate is inserted if required, and in which the tubes are disposed in stepped bores and each sealed by a seal surrounding the tube, the seal being held under tension by a threaded bush screwed into the other part of the bore, characterised in that the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A tube assembly heat exchanger with plastics tube ends The invention relates to a tube assembly heat exchanger with plastics tube ends, into which a metal plate is inserted if required, and in which the tubes are disposed in stepped bores and each sealed by a seal surrounding the tube, the seal being held under tension by a threaded bush screwed into the other part of the bore. About 1 5 years ago it was proposed to make known tube assembly heat exchangers from glass instead of metal. Before then, glass had been used only for coil heat exchangers. Difficulties, however, arose. For example glass tube ends are expensive to manufacture, and it is also very expensive to connect glass tubes to glass tube ends, because glass tubes cannot be expanded in the ends but have to be melted thereto. This method, of course, makes repairs very difficult. Accordingly, tube ends were made of chemically resistant plastics such as polytetrafluoroethylene (PTFE), a metal plate being incorporated in the plastics if required, to counteract undesired flow thereof. Particular difficulties occurred in sealing the glass tube from the plastics ends. At present, the conventional method of sealing is via gland-like devices as described in detail hereinbefore. The seals are O-rings, usually comprising a resilient core with an overlapping or closed jacket of resistant material, and cylindrical resilient rings for packing of graphite, asbestos or unsintered PTFE. All these seals have disadvantages in that they may cause undesired leakages through loss of elasticity during operation and/or because of flow processes in the tube-end material. This particularly applies when heat exchangers are used at elevated temperatures, at which changes in tension occur because of differences in the coefficient of expansion of different materials. This difficulty cannot be completely avoided even by inserting a metal plate in the tube ends. The object of the invention, in the case of a tube assembly heat exchanger of the initiallydescribed kind, was to provide an efficient seal between the tubes and the plastics tube ends. To this end, according to the invention, in the case of the tube assembly heat exchanger in question, the seal comprises a plastics clamping ring having a cylindrical passage, the two end faces of the ring tapering conically. it has unexpectedly been found that if a clamping ring according to the invention is used, the tube end material is less inclined to flow, particularly in the radial direction, which is mainly responsible for the aforementioned leakages in the known embodiments. In the known embodiments, the pressure exerted on the seal has the general effect of compressing it, resulting in radial forces. The invention is particularly important if the heat exchanger tubes are made of glass or ceramics, since in metal heat exchangers the tube ends are usually also made of metal, and metal connections are much easier to make. However, the heat exchanger tubes can be made of metal without departing from the invention. The tube ends may be made more particularly of high-strength plastics such as PTFE. Similar materials are used for the clamping ring. In a preferred embodiment, the two end faces. of the clamping ring extend at the same angle towards its axis. Preferably also, the outer surface of the clamping ring is cylindrical Advantageous tension conditions are obtained if the step in the bore and/or the end face of the threaded bush facing the clamping ring extends parallel to the adjacent end face of the clamping ring. In a preferred embodiment, the outer surface of the clamping ring is at a distance from the bore. This avoids radial forces on the tube ends if the sealing ring is compressed during clamping. The tube ends are usually cylindrical although this is not absolutely necessary. In the case of cylindrical tube ends, a metal ring is preferably placed on the cylinder surface so as to counteract the flow of the cylinder-end material. The invention will now be explained in detail with reference to the accompanying drawings in which: Fig. 1 is a partial section through a tube assembly heat exchanger according to the invention (in the assembled state on the left and in exploded view on the right) and Fig. 2 is a smaller-scale view of the tube ends, only part of which is shown in Fig. 1. More particularly Fig. 1 shows a tube end 1 having a bore for receiving a glass tube 5. The bore has a narrow part 2 and a wide part 4, with a conical transition at an angle a1. A clamping ring 6 is disposed on tube 5 and is bevelled at an angle at at the bottom and an angle p2 at the top. The other part 4 of the bore has an inner thread 3 into which a threaded bush 7 is screwed, the end face of the bush facing ring 6 being conical so as to include an angle 2 with the axis of bush 7. As can be seen, a, is different from /3, whereas a2 and p2 are equal. Tube end 1, ring 6 and bush 7 are all made of PTFE. When a glass tube 5 is incorporated in a tube end 1, a ring 6 is first pushed over the glass tube, which is then inserted into bore 2, 4. A threaded bush 7 is then slid over it and tightened. As shown in Fig. 2, the tube end 1 is surrounded by a metal ring 8 which prevents the material of end 1 from flowing. CLAIMS

1. A tube assembly heat exchanger with plastics tube ends, into which a metal plate is inserted if required, and in which the tubes are disposed in stepped bores and each sealed by a seal surrounding the tube, the seal being held under tension by a threaded bush screwed into the other part of the bore, characterised in that the seal comprises a plastics clamping ring having a cylindrical passage, the two end faces of the ring tapering conically.

2. A heat exchanger according to claim 1, characterised in that the two end faces of the clamping ring extend at the same angle towards its axis.

3. A heat exchanger according to claim 1 or 2, characterised in that the outer surface of the clamping ring is cylindrical.

4. A heat exchanger according to any of the preceding claims, characterised in that the step in the bore and/or the end face of the threaded bush facing the clamping ring extends parallel to the adjacent end face of the clamping ring.

5. A heat exchanger according to any of the preceding claims, characterised in that the outer surface of the clamping ring is at a distance from the bore

6. A heat exchanger according to any of the preceding claims, characterised in that the tube ends are cylindrical and bear a metal ring on their cylindrical surface.

7. A heat exchanger substantially as hereinbefore described and as shown in the accompanying drawing.