GB2083603A

GB2083603A - A pipe made from flexible or rigid plastics material, for conveying heat transfer fluids

Info

Publication number: GB2083603A
Application number: GB8103936A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-12
Filing date: 1981-02-09
Publication date: 1982-03-24
Also published as: NL8006636A; IT1136221B; BE886542A; LU82956A1; IT8015260V0; FR2490312A1; DE3034888A1; IT8012754A0

Abstract

The invention relates to a pipe (12) made from plastics material for conveying a heat transfer fluid typically hot water for heating. The periphery (16) of the pipe (12) incorporates troughs (18) and outwardly curved portions (20) which extend in a longitudinal direction along the pipe and alternate successively around the circumference of the pipe. These troughs (18) and outwardly curved portions (20) increase the surface area of the pipe (12) and thus improve the transfer of heat from or to the heat transfer fluid flowing through the pipe (12). <IMAGE>

Description

SPECIFICATION A pipe, made from flexible or rigid plastics material, for conveying heat transfer fluids The invention relates to a pipe, made from flexible or rigid plastics material, for conveying heat transfer fluid, typically a liquid such as water for heating or cooling.

Floor heating systems, also referred to as "surface heating systems", include a pipe which is laid and held in the floorforthe purpose of conveying the heat transfer fluid. Parallel straight portions of the pipes and curved portions etc. of the pipes are laid in the floor in accordance with a predetermined layout and are connected to the flow and return pipes of a central heating system.

The pipe has to satisfy mechanical and thermal requirements. The mechanical requirements are that it must have adequate strength which is found to increase with the wall thickness. On the other hand, the thermal requirements are that the pipe shall have high thermal conductivity, which is found to increase with decreasing wall thickness.

It is obviously desirable to obtain high thermal conductivity, so as to reduce the losses during heat transfer, and this allows a reduction in the flow temperature. Thus, when constructing heating pipes of this type a compromise has to be sought between these opposing requirements.

Hitherto it has been common to use pipes having circular cross section. They can be readily manufactured and can be laid in a relatively simple manner.

The diameter and the wall thickness can be varied.

However, the ideal fulfilment of the two requirements is opposed by the fact that a circle is that geometrical figure which has the smallest circumference with the largest area. Thus, the surface area per unit length of a circular section pipe (and thus its thermal conductivity i.e. the extent of heat transfer to the surrounding floor) is less than that of any other cross section shape.

If the diameter of the pipe is increased the overall height of the floor has to be increased. This is necessary in order to retain the static load-bearing capability of the floor. However, this also results in a larger floor mass which has to be heated, due to the increased thickness of the floor. This implies a loss of heat, since the aim is to heat the air space above the floor and not the floor itself.

If the diameter of a pipe is increased, its wall thickness also has to be increased, otherwise the static strength of the pipe is impaired. Increasing the wall thickness also counteracts the risk of out-ofroundness occurring in the curved portions of the pipe when laid. However, plastics materials generally have a relatively low thermal conductivity, so that there is a further decrease in thermal conductivity when the wall thickness is increased. Such endeavours to reduce the flow temperature are therefore virtually ineffective.

Pipes having an oval cross section are also known.

With the same cross sectional area, a pipe having an oval cross section has a larger surface area than a pipe of circular cross section. However, a pipe of oval cross section requires a floorofgreaterthick- ness and/or a larger wall thickness in order to obtain the required strength. The increased thermal conductivity resulting from the larger surface area is thus virtually eliminated. A further disadvantage is that is is difficult to lay a pipe of oval cross section.

There is also the risk of constrictions occurring in the cross section of the curved portions of the pipe when they are laid. It is also difficult to connect fittings to non-circular section pipes and make such connections fluid-tight.

To summarise, it can be stated that any advantages obtained by increasing the diameter and wall thickness, and using oval cross section pipes are outweighed by attendant disadvantages. Furthermore, material costs and wages are high and are not normally compensated for by savings in thermal efficiency.

It is an object of the present invention to provide a pipe for conveying a heat transfer fluid which has a larger surface area than a conventional circular section pipe but in which its static strength is not impaired and in which there are found none of the other above-mentioned disadvantages.

In accordance with the invention, this object is achieved in that the periphery of a generally circular cross section pipe incorporates radial depressions extending in a longitudinal direction.

By this means, the pipe surface area can be increased in the region of 20 to 30% by means of these depressions. The emission or adsorption of heat is increased due to the larger surface area. The efficiency is thus increased and in a heating system the flow temperature can be reduced.

A further advantage is that the wall thickness of the pipe in the regions of the hollows of the depressions can be less than the wall thickness of a corresponding pipe of circular cross section, since it is found that the strength of the pipe due to the increased thickness between the radial depressions, is sufficient to maintain the overall strength of the pipe. A so-called "support effect" is established.

Pressure tests performed on pipe constructed in accordance with the invention indicated such a pipe is commensurate in strength with that of a pipe of circular cross section.

Advantages also attend the manufacture of pipe in accordance with the invention. During extrusion of the pipe, improved thermal conditions are obtained in the extrusion die as a result of the larger surface area of the pipe. This leads to increased dimensional accuracy. Smaller tolerance can be held so that there can be a saving on material.

During the laying operation, the pipe in accordance with the invention can also be handled more conveniently than known pipes of circular cross section. Virtually no cross sectional collapse occurs in the curved portions of the pipes as they are laid. This implies a relative increase in thermal efficiency.

Advantageous characteristics ensue when laying pipe constructed in accordance with the invention in flooring plaster. The bonding and adhesion between the pipe and the flooring plaster is improved as a result of the larger surface area of the pipe. A key is established between the pipe and the flooring plas ter as a result of the longitudinal depressions or profiling provided in accordance with the invention.

According to a preferred feature of the invention of the invention the flooring plaster is pressed into the depressions. The flooring plaster grips the pipe and this is of particular value owing to the different coefficients of thermal expansion of plastics materials and flooring plasters. In the case of the pipes of circular cross section which are laid in accordance with the prior art, slight movement is found to occur between the pipe and the flooring plaster as a result of the differing coefficients of thermal expansion of the pipe material and the flooring plaster, particularly when the latter is not manufactured properly. Such relative movements between flooring plaster and pipe which can occur often with continued heating and cooling of the pipes can lead to wear on the pipe.Relative movements of this kind are excluded by the positive connection, between the pipe and the flooring plaster, achieved by the invention.

In order to fix the pipes in their desired positions in the floor, the pipes are inserted into clips. These clips are made from a slightly resilient material, and have notches or slots into which the pipes are inserted.

In order to fix pipes of circular cross section, the clips have sockets, into which the pipes are pressed.

As a result of the elasticity of the materials of the clips and the pipes a certain "snap action effect" is obtained upon inserting the pipe into the socket. The pipes are thus securely held.

The longitudinal depressions provided in accordance with the invention themselves constitute sockets into which projections of a clip can engage. The clips for fixing the pipes in accordance with the invention can thus be manufactured without sockets.

Laying and fixing of pipes in accordance with the invention is thus simplified and rendered less expensive.

Pipes of circular cross section tend to retain a coiled configuration after they have been wound onto a reel or a drum, even afterthey have been uncoiled therefrom. When laying pipes of circular cross section, this leads to a twist which renders it difficult to lay the pipes in desired positions. Pipes profiled in accordance with the invention do not have this twist and can be laid more uniformly and substantially more accurately.

It will thus be seen that the manufacture of a pipe in accordance with the invention only requires a once-for-all purchase of high cost extrusion tool with the resulting advantages during manufacture, when laying and during heat transfer.

The depressions in accordance with the invention can be of virtually any configuration. It has been proved to be advantageous for the depressions to be constituted by equally spaced troughs equally disposed circumferentially. The troughs may be arcuate in shape, or can be partly oval or any other serviceable geometrical cross section. Preferably however, the troughs should not have a cross section in which acute-angled cuts are made in the material, so as to avoid local stresses and strains associated with notches and grooves.

Where the depressions are uniformly spaced round the circumference of the pipe it is desirable to dispose between the depressions outwardly convex curved portions which are complementary to the depressions. In this embodiment, the periphery of the pipe can be described as an undulating line comprising successively uniform curved crests and troughs.

When shaping these crests and troughs, it is advisable to ensure that pipe fittings, such as clamping rings to be applied to the periphery of the pipe, can be adapted to the profile of the pipe in accordance with the invention. The function of the clamping ring is thus ensured, and the tightness of the fitting on the circular inner circumference of the pipe ie ensured.

The invention will now be further described with reference to the accompanying drawing.

Fig. 1 is a view of a portion of a pipe constructed in accordance with the invention, and Fig. 2 is a cross section on the section line Il-Il of Fig..1.

The Figures show a pipe 12 having a circular inner wall 14 and an outer profiled wall 16. The latter comprises successive depressions or troughs 18 between outwardly curved portions or crests 20. The troughs and crests extend along the surface of the pipe parallel to the longitudinal direction thereof and merge smoothly into one another along straight lines 22. In the illustrated embodiment, the troughs 18 and also the outwardly curved portions 20 are of arcuate configuration. However, although not shown they can have an oval cross section or some other geometrical cross section.

A pipe constructed in accordance with the invention is defined by its internal diameter a, its smaller external diameterb and its larger external diameter c. Thickness of the pipe wall i.e. (b - a)/2 can be less than the wall thickness of pipes of circular cross section, without reducing the strength of the pipe relative to that of an equivalent circular section pipe of the same diameter and nominal wall thickness.

Referring to Figs. 1 and 2 it will be seen that the sum of the surface area of the troughs 18 and of the outwardly curved portions 20 is greater than the surface area of a pipe having a circular cross section and external diameter equal to the diameterc. Within the scope of the invention, the radius of curvature of the troughs 18 or of the outwardly curved portions 20 can vary within wide limits. In general, this radius will be less than 50% of the difference (c - a).

The pipe shown in the drawing has been described with reference to a floor heating system. It is to be understood that the same pipe may be used in a wall heating system or in a system for absorbing heat from the environment or, alternatively, in systems in which a coolant heat transfer fluid flows through the pipe instead of hot water.

Claims

1. A pipe made from plastics material for conveying a heat transfer fluid, characterised in that the exterior (16) of the pipe incorporates spaced radial depressions which extend in a longitudinal direction along the pipe.

2. A pipe as claimed in claim 1, characterised in that the depressions comprise troughs (18) which are equally spaced circumferentially around the pipe section.

3. A pipe as claimed in claim 1 or 2, characterised in that the troughs (18) are arcuate.

4. A pipe as claimed in claim 1 or 2, characterised in that the troughs (18) are part-oval.

5. A pipe as claimed in any of claims 1 to 4, characterised in that there between the troughs (18) are located outwardly convex curved portions or crests (20) which are complementary to the troughs.

6. A pipe as claimed in any of claims 1 to 5, characterised in that the plastics material is flexible.

7. A pipe as claimed in any of claims 1 to 5, characterised in that the plastics material is rigid.

8. A plastics pipe for conveying a heat transfer fluid, constructed and arranged substantially as herein described with reference to and as illustrated in the accompanying drawing.