GB2065288A - Turbulators - Google Patents

Abstract

A turbulator, for example in a heat exchange tube, comprises a plurality of coils (12) distributed symmetrically about an axis, and means for holding the coils in predetermined relationship one with another. <IMAGE>

Description

SPECIFICATION Improvements relating to turbulators This invention relates to turbulators, which are inserts for tubes intended to render the flow within the tube turbulent, so as to improve mixing or heat exchange for example.

In heat exchanger usage, the "best" known turbulators may have the effect of increasing the rate of heat transfer between the tube wall and the fluid by as much as twenty fold, with a penalty in terms of pressure drop along the tube. In general the object of any turbulator design is to achieve the desired increase in heat transfer rate at minimum pressure drop. This is particularly important in energy conservation devices recovering waste heat, or upgrading heat for example by a heat pump, since pressure drop leads to power consumption for pumping the fluid, and if the pressure drop is excessive the turbulator might even be counter productive in nett terms.

Nevertheless, a high pressure drop is sometimes economically acceptable.

U.K. Patent No. 1,328, 371 proposes a turbulator made by forming a twisted core from a pair of core wires located respectively within and without a coil of wire, so that successive convolutions of the coil extend in spiral fashion about the core. This is very satisfactory in certain applications but not all.

In an unpublished Patent Specification it has been proposed to use a pair of nested coils of different diameters in like fashion, so that the convolutions of one coil lie respectively inside the convolutions of the other after the twisting step. A further modification of both of these possibilities is to use multi-filaments for the coils. Using all of these possibilities, it is possible to produce a whole series of turbulators ranging from a simplest to a most complex, and possibly having increasing degrees of effectiveness but increasing pressure drops along the series.

The object of the present invention is to provide improvements which may enable increasing heat exchange rates to be achieved with less pressure drop, at least in particular circumstances.

In accordance with the invention considered broadly, a turbulator comprises a plurality of coils distributed symmetrically about an axis (intended to be coincident with the axis of the tube in which the turbulator is to be used) and means for holding said coils in predetermined relationship one with the other.

In general there are two possibilities in that the turbulator may need to be removable from the tube or may be a permanent fixture in the tube. In the latter case, the turbulator may be bonded to the tube wall. If the turbulator is made from metal wire it may be soldered to the tube, for example by dipping the assembly of turbulator and tube in a flux bath and then in a solder bath, or spraying with solder paste, and in particularly simple constructions of this nature according to the invention the solder may alone suffice to hold the parts in the predetermined relationship. In general however and in all cases where the turbulator is to be detachable as a unit, it is preferred to fix the respective coils in position reiative to one another by some additional means.These means may comprise sheet metal pressings, for example if four coils are to be utilised with their axes located at corners of an imaginary square, the sheet metal pressings may be assembled to provide a cruciform shape and the coils may be fixed to the metal pressings by soldering, by wire ties, or by lugs struck out of the pressings and fastened to individual convolutions of the respective coils. An alternative possibility for fixing respective coils together is by wire ties between respective convolutions of different coils or by core like members threaded through the coils.

There are also two possibilites for the general arrangement of the plurality of coils, in that each coil may be effectively separate and distinct from the other coils, apart from the possibility of ties or other means which fix the coils in the respective positions, or the coils may be overlapped, so that two (for example) small portions of each convolution lie within the adjacent coils, and hence a secant extending radially from the axis of the whole assembly will be common to two adjacent coils. In this latter possibility, a core type wire may be threaded through the overlapped and effectively linked portions to hold adjacent coils together.

Where the turbulator is for use in an annular tube, that is one comprising (typically) concentric inner and outer tubes, possibly with different fluids flowing through the inner tube and through the annular space respectively, and where the turbulator is to be used in the annular space, it may be assembled from the required plurality of separate coils, arranged with their axes co-planar and with the convolutions (all except the first and last) slightly overlapping, and with core wires then threaded through the overlapped portions following which the respective coils may be displaced so as to take them into the annular formation for threading into the larger of the tubes or wrapping about the smaller of the tubes.

The number of coils used will be related to the size of the individual coils in relation to the size of the tube which is to receive the turbulator, and in general will have a diameter of no more than the radius of the turbulator tube.

The coils may be wound from wire or strip of any desired cross-section and may be combined with baffles extending lengthwise of the coils or arranged at intervals. The coils may extend along the whole length of a tube or over short lengths with intervals which may be vacant or occupied by separate structural parts. For example, a coil set may be connected to an axially spaced coil set by continuation of the tie wires or core members, but without coils over the length of the interval and so on.

The coils may be springs, that is to say made of a resilient material such as a spring steel wire, and this is particularly useful in the arrangements which are intended to be inserted in and removed from heat exchanger tubes from time to time since it may ensure a good fit which is important for the purpose of ensuring heat transer between the tube wall and the turbulator per se and thus of enabling heat transfer to the fluid other than directly through the tube wall. Further, such turbulators may have a cleaning effect on the tube bore in their removal and insertion.

A number of possibilities are illustrated in the accompanying drawings by way of example only: the same reference numerals are used in different drawings to indicate the same parts.

Fig. 1 shows a circular heat exchanger tube 10 containing a fluid for heat exchange via the tube wall. The turbulator comprises eight coils 12 which are symmetrically distributed and held in the assembled condition by a larger diameter tie coil 14.

Fig. 2 shows an arrangement with six equal sized coils, in this case overlapped so that core wires 16 thread through the overlapped portions, and secure the assembly together.

In Fig. 3 the coils are of a diameter substantially equal to the radius of the tube 10, enabling the core wires 16 to be clustered closely together and possibly given a twist along the length of the turbulator for the purpose of holding the assembly together.

Fig. 4 shows one possible elevation of any of the arrangements in which the coils 12 are provided in short lengths 18, and each bundle of coils 18 is connected to the next by an axially located core member 20 which may be a sheet metal baffle or may be a continuation of the core wires 1 6 or an extension of the tie coil 14.

Fig. 5 shows a version of Fig. 2 in which the tube 10 forms the outer wall of an annular space further defined by concentrically located inner tube 22, and the annular space is effectively filled by coils connected in the same sort of manner as in Fig. 2.

FiB. 6 shows a further version in which adjacent coils are connected by tie wires 24, and Fig. 7 shows how such an arrangement may appear before assembly, when the axes of all of the coils lie parallel in a common plane.

Fig. 8 shows each coil wound about an individual strip metal core member 26 which may be planar or twisted, so as to further increase the turbulence effects.

Fig. 9 shows (for purposes of illustration only) four different kinds of baffle used in the four coils.

Fig. 10 shows four coils held in predetermined relationship by a baffle or cradle 28 which may be of sheet metal and one form of this is separately illustrated in Fig. 11.

In the situation where a baffle or other strip extends within the coil, it may have for example a castellated edge so as to locate successive convolutions of the coils.

It will be appreciated that various combinations of these separately illustrated features can be used, for example the cradle of Fig. 11 could be used in the Fig. 8 configuration, and the baffles of Fig. 8 could be used in the Fig. 3 configuration.

Whilst all of the illustrations are based upon circular cross-section tubes and coils, alternative possibilities exist in that respect also. In addition multifilament materials can be used for the coils.

A preferred arrangment in general is one in which the typical cross-section of the assembled turbulator within the tube shows a number of possible flow paths which are all of generally similar total cross-sectional area. Figure 8 is the best example of this in the drawings. However, no such flow path should extend throughout the length of any one complete turbulator without being interrupted, for example because of a continuous spiral twist to the complete assembly, or by the arrangement of Fig. 4 for example in which each bundle 1 8 is angularly offset to the next, so that fluid streams are continually divided and reformed along the length of the tube. The similarities in the total cross-sectional area may be aided by the use of baffles which act as restriction, and the division and re-forming may also be aided by the baffles. Certain baffles may combine these functions with the functions of holding the wire or like parts in their required positions.

Claims (6)

1. A turbulator comprising a plurality of coils distributed symmetrically about an axis, and means for holding said coils in predetermined relationship one with the other.

2. A turbulator as claimed in Claim 1 wherein each coil is separate and distinct from the others apart from a tie connecting that coil to at least one adjacent coil.

3. A turbulator as claimed in Claim 1 wherein convolutions of one coil overlap those of an adjacent coil and a core wire is threaded through the overlapped portions.

4. A turbulator as claimed in Claim 1 wherein the coils are fixed in position relative to one another by being secured about a sheet metal pressing.

5. A turbulator as claimed in any preceding claim, wherein each coil is combined with a baffle extending lengthwise of the coil.

6. A turbulator substantially as described with reference to the accompanying drawings.