Heat exchanger with helical flow paths

A heat exchanger includes a body 4 on the surface of which are provided helical or spiral paths 5 which will provide multiple and turbulent flow paths A for a first fluid such as water which is caused to flow through chamber 3 relative to a spirally wound heat exchange tube 6 and in a heat transfer relationship with a second fluid flowing through the tube 6. The tube 6 has one or more further helical or spiral flow paths 9 on its external surface. The multiple flow paths A will extend the residence time for the first fluid within the heat exchanger 1 and this together with the turbulence will maximise heat transfer. Preferably a portion of the first fluid flow will be through a central aperture in body 4 where turbulence is also created by the helical or spiral paths of the tube 6 as it extends through the aperture.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/NZ2004/000008, filed Jan. 29, 2004.

TECHNICAL FIELD

The present invention relates to improvements in and relating to heat exchangers.

BACKGROUND

In our New Zealand Patent Specification No. 508895 (also WO 99/67584) there is described a heat exchanger tracking including a spiral heat exchanger with coils and the track between the coils providing a second flow path which improves the efficiency of the heat exchange.

In the design of heat exchangers it is important to ensure that the fluid being heated or cooled stays in the heat exchanger for an optimum time. Another design criteria is to obtain a low pressure drop through the heat exchanger and optimise the heat exchange taking place within the heat exchanger.

OBJECTS OF THE INVENTION

It is thus an object of the present invention to provide a heat exchanger and/or a method of providing heat exchange which will provide for an effective heat exchange and/or will at least provide the public with a useful choice. Further objects of the invention may become apparent from the following description.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a heat exchanger including a body and at least one first substantially spiral or helical flow path provided for an external surface thereof, the body positioned within a housing to define a chamber between said external surface and an internal wall of said housing, a tube assembly helically or spirally positioned about said external surface, said tube assembly having at least one second substantially helical or spiral flow path provided for its external surface, the relationship between the said at least first and said at least second helical or spiral flow paths being such that a first fluid flowing through said chamber is caused to flow along multiple turbulent flow paths, in heat transfer relationship with a second fluid flowing through said tube assembly.

Preferably the body as defined in the paragraph immediately above is substantially cylindrical and said at least first substantially spiral or helical flow path extends along a longitudinal axis of said body.

Preferably said at least first spiral or helical flow path directs, in use, at least a portion of said first fluid flowing therein so that it impacts with a portion of said first fluid flowing in said at least one second flow path to create said turbulence.

According to a further aspect of the present invention a heat exchanger is substantially as herein described with reference to any one of the embodiments of the invention as described and/or as shown in the accompanying drawings.

According to a still further aspect of the present invention a method of providing fluid flow control for a heat exchanger is substantially as herein described with reference to any one of the embodiments of the invention as described and/or as shown in the accompanying drawings.

Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description given by way of example of possible embodiments thereof.

BRIEF DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

The present invention will now be described in respect of one particular form of heat exchanger and for simplicity will relate to a particular form of heat exchanger in which a particular fluid, water, is required to be cooled by its controlled flow past the heat exchange tubes in which a refrigerant is provided. It will be appreciated by those skilled in heat exchange technology however that this is only by way of example and that the present invention could find application where ever a first fluid is to be either heated or cooled and accordingly in which the heat exchange coils would be containing a second fluid which would be transferring heat to or from the first fluid so as to provide the required heating or cooling action. The first and second fluids may in some instances be the same.

Subject to the above provisos, it is seen that inFIG. 1a heat exchanger referenced generally by arrow1includes by way of example only a mounting base2on which, in this example, two heat exchange housings8are provided extending upwardly therefrom. Water in this example is caused to flow in a direction indicated by arrows A in series through the heat exchange housings8as it is cooled by the refrigerant flowing through the heat exchange coils6which may be in a direction indicated by arrows B and C, although alternative directions may be chosen for either housing. Also the tubes6in the respective columns could be connected together to provide a common fluid circuit. That would normally be a top connection.

The heat exchange coils6are tightly wrapped in a spiral or helical path having a tread direction around an elongate support body or mandrel4. The coils6have one or more (only one being shown) spiral or helical, ribs, corrugations, protrusions, intrusions, tracks, or the like9having a tread direction. The body4has an external surface with spiral or helical, ribs, corrugations, protrusions, intrusions, tracks, or the like5having a tread direction defining a plurality of fluid paths along the length of the body4, any of these alternatives being included whenever the term “fluid paths” is used hereinafter.

External smooth portions11and12, of the coils6can provide the connection for an inlet and/or outlet for the refrigerant or heating fluid flowing in the direction of arrows B and C in the example shown.

It is seen that multiple complex flow paths A exist in each housing8with the water flowing between the tube6and the body4, both in the longitudinal spacing therebetween and in gaps left as they abut. Also water flow is between the tube6and the housing8. This is further described with reference toFIGS. 4 and 5particularly.

In contrast, inFIG. 2the flow of water in the direction of arrows A is seen to be in parallel through the pair of heat exchange housings8in heat exchanger1A.

As with the embodiment ofFIG. 1, inFIG. 2the disposition of the helical or spiral paths9on the surface of the spirally or helically wound tube6, relative to the helical or spiral paths on the body4, result in a plurality of turbulent flow paths A for the water or other fluid flowing through the two housings8.

It will be appreciated that any number of heat exchange housing assemblies8, not necessarily two as shown, could be provided. In the exchangers1,1A ofFIGS. 1 and 2each body4is shown located in an upstanding portion10of the base2. Each body4is, however, suitably supported by means of the respective tube ends11,12which are securely fastened with a top assembly (seeFIG. 3) by means of tensioning nuts or the like. The flow of the refrigerant or heating fluid through the tubes6may be in the same or opposite direction to that of the water or other fluid being cooled or heated as it passes through the housings8although by way of example the fluid is shown flowing in the directions B, C in the figures. Typically, for a heat exchanger capacity of 400 liters/minute the water or other fluid may be under a pressure of perhaps 10 psi, and a suitable pump will be provided for that purpose. The body4may be of any suitable material. However, a moulding of polyethylene or other plastic material may be appropriate. The tubes6may suitably be of metal, titanium being a preferred option.

Referring toFIG. 3a single heat exchange housing8is shown in some greater detail. The flow of the water or other fluid in the direction of arrows A is shown being both longitudinally and transverse of the body4and the tube6and within the chamber3. Also a proportion of the water flow is centrally through the aperture through the body4.

It is mentioned that in all the above examples any suitable refrigerant could be used e.g. a liquid, such as water or glycol, or a suitable gas or the like.

The housing or casing8in all the aboveFIGS. 1 to 3may be of any suitable material such as a hard plastics such as polyethylene or nylon, or a metal such as stainless steel.

The heat exchange assembly1ofFIG. 3is also shown provided with a possible top assembly7which could be suitably secured to the top end of the housing8such as by gluing, welding, bolting, screwing or the like. A lateral water outlet is shown provided for the top7for the flow of water A. A nut assembly or the like including O-rings may be provided to secure the top ends11,12of the refrigerant tube6in position extending through the top7and through the appropriate apertures provided for that purpose. As the tube6is tightly wound about the body4and its bottom end extends beneath the bottom of the body4, the body4and the tube6will be thereby supported. A thermostat holder or recess25is also shown provided for top7.

In all the above examples of possible heat exchange assemblies, heat exchange efficiency is improved by extending the residence time of the water and particularly by the water flow being provided with a turbulence which will improve heat transfer to the refrigerant through the refrigerant tubes.

The improved heat transfer efficiency is such that in a typical 33 KW shell and tube heat exchanger the present invention may only require approximately 10 meters of titanium tube6compared with the over 20 meters which other designs would typically require. This means that a heat exchanger according to the present invention may be substantially smaller and less expensive than previously available units.

Referring now toFIGS. 4 and 5cross sectional and end views of the exchanger1ofFIG. 3are shown enlarged and in greater detail.

It is seen that the helical or spiral flow paths5on the surface of body4define with the outer helical or spiral surface of the refrigerant tube6multiple and complex flow paths A for the water which will both extend the residence time for the water within the assembly1so as to maximise heat transfer but will also provide a turbulence in the water flow which will again enhance the heat transfer, the turbulence being created as the water impacts on the tube6and body4and as it changes direction. As is seen especially fromFIG. 5, as the tube6passes around the body4it may abut it in places or leave gaps so that water is forced between and around the body4and tube6and will become turbulent and will also separate into numerous flow paths as shown. The pitch of the flow paths9on the outer surface layer of the refrigerant tube6and/or the gaps between the refrigerant tube6and the outer casing8and/or the flow paths5may be such as to enhance turbulence and/or the control of pressure drop through the heat exchanger1. It is mentioned in the latter regard that a low pressure drop through a heat exchanger is desirable in order to achieve required pump size and energy requirements.

It is also seen inFIG. 4that a gap16is present between the vertical return15of the refrigerant tube6and the central aperture or tube14of the body4. The passage of water through the gap16and around the helical or spiral track of the return15will also create turbulence. It is envisaged that a reasonable proportion of the water may be caused to flow through the central aperture14rather than through the chamber3. It is also seen that inFIG. 4the body4has been rotationally moulded so as to provide a hollow central portion13. Alternatively the body4could be moulded or cast for example as a solid body, apart from the central aperture14.

Referring particularly toFIG. 5, it is seen how the body4may be provided with multiple spiral or helical flow paths or tracks5which can be in or out of phase with the positioning of the flow paths or tracks9on the tube6, wrapped around the body4.

Within the distance P it is seen that the tube6may include three tracks9A whereas the body4has only one track5A. Suitably the pitch of the helix or spiral on the tube6may be at least twice the length of that of the body4. The water flowing around the flow paths9A of tube6will therefore be impacting three times on the water flowing in the flow path5A of the body4. These impacts will be, in the example shown, at an angle, resulting in substantial turbulence being created.FIG. 5also illustrates that the tube6is tightly wound on the body4. Suitably the coiled tube6may have the body4inserted into it so that the tube6springs back into position about the body4. This tight wrapping of the tube6will assist in preventing the vibration of the tube6and also it trying to unwind itself as the pressurised refrigerant or other fluid flows through it. The tube6is also provided so as to be a close fit against the housing8, again preventing vibrations and possible unwinding.

Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope or spirit of the invention as defined in the appended claims.