WO2005088200A1

WO2005088200A1 - A heat exchanger

Info

Publication number: WO2005088200A1
Application number: PCT/DK2005/000179
Authority: WO
Inventors: Ole Hansen
Original assignee: Danfoss A/S
Priority date: 2004-03-18
Filing date: 2005-03-17
Publication date: 2005-09-22
Also published as: EP1740889A1

Abstract

The invention provides a system with a pipe and a ventilator forcing a stream of air across an outer surface of the pipe. The pipe is separated by a partition member to form a first and a second conduit for conducting a fluid flow in an upstream and a downstream direction from a heating or cooling system. Due to the separation, it has been facilitated that ventilating devices could be located at various locations along the pipe with substantially equal exchange of thermal energy. The invention could be used for heating or cooling purposes in a building. The invention further provides a method of making such a system and a method of retrofitting an existing system to conduct two oppositely directed streams of a thermally convective fluid for heating or cooling purposes.

Description

A HEAT EXCHANGER

INTRODUCTION

The present invention relates to a method and a system for distributing a fluid medium, and for exchanging thermal energy between the medium and its ambience. More specifically, the invention relates to a system with a pipe which extends in a longitudinal direction, and which has an internal conduit for conducting a fluid flow. For exchanging thermal energy between the fluid and its ambience, the system comprises a ventilating device for forcing a stream of air across an outer surface of the pipe .

BACKGROUND OF THE INVENTION

Systems of the above mentioned kind are used e.g. for heating and cooling of buildings. In the following, the invention will be disclosed only in combination with a heating system but it could also be used in combination with a cooling system. The pipe could be a regular water pipe, e.g. an iron pipe conducting hot water from a heating system. The ventilating device could include a cross-flow blower of a kind known in the art. In WO 02/04871, a system of this kind is disclosed wherein a cross-flow blower is attached directly to one or two hot- water-pipes for heating a building.

In systems of the disclosed kind, several ventilating devices could be fastened at different locations along the pipe for increasing conductivity between the pipe and the ambience. The air-stream is normally directed across one pipe which distributes hot or cold water in a loop in the building from an outlet to an inlet of the heating system.

In the vicinity of the outlet, the temperature is normally relatively high compared to the temperature in the vicinity of the inlet . Due to the temperature gradient along the pipe, identical and equally operated ventilating devices create different increases in conductivity between the pipe and the surroundings, and therefore, temperature control in buildings with several ventilating devices along a long pipe can be difficult. In one attempt to compensate for the temperature gradient, each ventilating device is controlled, to operate at different speeds. This, however, introduces other problems, e.g. in relation to the control of the ventilators, and in some installations it is not possible to fully compensate a large temperature gradient between an inlet section and an outlet section of the pipe only by regulation of speed of the ventilating devices .

DESCRIPTION OF THE INVENTION

It is an object of the invention to enable a more equal exchange of thermal energy from a pipe. Accordingly, the invention, in a first aspect, provides a system of the above-mentioned kind wherein the pipe comprises a partition member for separating the conduit into a first conduit and a second conduit . In the first conduit of the pipe, the fluid medium, e.g. water could be distributed in a forward direction from the heating system and out into the building, and in the second conduit, the fluid medium could be distributed in an opposite backward direction back towards the heating system. Since one and the same pipe on any spot along the pipe is influenced by the relatively high-temperature forwardly flowing fluid and the less hot low-temperature backwardly flowing fluid, the temperature gradient could be reduced along the pipe. Accordingly, thermal exchange along the pipe could be more uniform even with several identical and equally operated ventilating devices located along the pipe.

In particular, the ventilating device may comprise a cross-flow blower which is fastened with an axis of rotation substantially parallel to the longitudinal direction and which forces the stream of air to flow substantially parallel to the partition member. In that way a substantially equal amount of air is forced across a hot and a cold site of the pipe, i.e. across each side of the partition member, and exchange of heat along the pipe could be even more equal. As an alternative, the partition member may be arranged perpendicular to the stream of air to create a counter current heat exchange where cold air is heated in two steps, firstly by the low-temperature backwardly flowing fluid, and secondly by the high- temperature forwardly flowing fluid.

The pipe could be an extruded pipe where the partition member is created during the extrusion process, i.e. as an integrated part of the pipe. Sometimes, it may however be an advantage to enable insertion of a partition member into an existing pipe, e.g. in connection with refitting of an existing heating system. For that purpose, the partition member could advantageously be brought into a first state wherein it has a width which is smaller than the internal diameter of the pipe to form a clearance therein between to support an easy insertion of the partition member into the pipe. When inserted into the pipe, the partition member should be brought into a second state with a larger width of the partition member to establish contact with an inner surface of the pipe, e.g. along two oblong contact portions along each oblong side of the partition member.

The partition member could be brought from the second state into the first state by an elongation of the partition member in a longitudinal direction, e.g. by an elastic elongation to create a lateral constriction. For that purpose, the partition member could be made from an elastically resilient material, e.g. a polymeric material, e.g. EPDM-rubber. When being inserted into the pipe, the partition member could be elongated whereby a transverse measure is reduced. When the member is in place inside the pipe, the elongation could be released whereby the member flexes back to its original length and original transverse measure to come into contact with an inner surface of the pipe.

A member of the above-mentioned kind which can be brought into two states with different width could also be provided by a partition member which elastically reverts to a non-planar shape when released after being stretched. Such a member could be made from a planar strip of a sheet material which is bent to form a longitudinally extendable spring structure to facilitate the elongation of the partition member. In a second aspect, the invention provides a method of making a system comprising:

- a pipe extending in a longitudinal direction and with an internal conduit for conducting a fluid flow, and

- a ventilating device for forcing a stream of air across an outer surface of the pipe, for distributing a thermally convective medium, and for exchanging thermal energy between the medium and its ambience,

the method being characterized in that a partition member for separating the conduit into a first conduit and a second conduit is inserted into the pipe. A first one of the conduits could be connected to an upstream flow of the medium, and the second conduit could be connected to an opposite downstream flow of the medium from a heating or cooling system.

In a third aspect, the invention provides a method of retrofitting an existing system with at least one pipe for distributing a thermally convective medium between two heat exchangers. The method comprises inserting a partition member for separating the pipe into two conduits for an upstream and a downstream flow of the medium in the pipe . Any of the methods according to the second and third aspect of the invention may be combined with the features of the first aspect, e.g. combined with attaching a ventilating device such as a cross flow blower to the pipe for forcing a stream of air across the pipe, preferably for forcing the stream in a direction parallel to the partition member. DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be described in further details with reference to the drawing in which:

Fig. 1 shows a cross sectional view of a pipe and a ventilating device,

Fig. 2 shows a perspective view of the pipe and ventilating device shown in Fig. 1,

Fig. 3 shows details of an end fitting for the pipe,

Fig. 4 shows details of a branch fitting for the pipe,

Figs. 5 and 6 show two prior art heating systems for a building,

Fig. 7 shows two different alternative embodiments of partition members, and

Figs. 8-11 show different view of an embodiment with the partition member being perpendicular to the stream of air.

Referring to Fig. 1, the system comprises a pipe 1 with an internal conduit 2, 3 for conducting a fluid flow, and a ventilating device 4 forcing a stream of air 5 across an outer surface of the pipe 1. A partition member 6 is inserted into the pipe 1 for separating the conduit into a first conduit 2 and a second conduit 3. During operation, thermal energy of the fluid medium will be exchanged to the outer surface of the pipe, and facilitated by the ventilating device, the energy will be further exchanged to the ambience. The ventilating device is a cross-flow blower with a cylindrical wheel comprising a plurality of impellers 7. As indicated, the cross-flow blower is located relative to the pipe to force the air in a stream which is parallel to the partition member.

Fig. 2 shows a perspective view of the pipe.

In Fig 3, it is shown that the pipe 1, in one end is sealed by a closure member 8 which is attached to the pipe. The partition member 6 extends to a point in the vicinity of the closure member but in order to allow the upstream fluid to pass between the two conduits, a clearance exists between the partition member and the closure member.

Fig. 4 shows a view of a branch 9. The arrows 10, 11 indicate the flow directions.

Fig. 5 shows a prior art system with one forward pipe 12 for an upstream flow of fluid from a heating system, and one backward pipe 13 for a downstream flow of fluid to a heating system. When a plurality of cross-flow blowers 14 are arranged along a long pipe to improve convection from the forward pipe or the backward pipe, the output from each blower will depend on its position along the pipe. Fig. 6 shows a simpler prior art system comprising only one single pipe 15 which is looped around in a building between an outlet and an inlet of a heating system. Cross- flow blowers 16 arranged along this pipe will provide a thermal output which is even more depending on the position of the cross-flow blower along the pipe. Fig. 7 shows two embodiments 17, 18 of the partition member. Both members have a shape which facilitates that they can be brought into a first state with a clearance between the member and an inner surface of the pipe for insertion of the member into the pipe, and into a second state wherein the member has contact with an inner surface of the pipe at least along two contact portions. In the first embodiment 17, the partition member is non-planar and comprises a plurality of sections 19 separated by folds. The partition member could be made from a flexibly resilient material, e.g. spring-steel or rubber. During insertion into the pipe 20, the springy member is elongated in the lengthwise direction, i.e. the direction indicated by the arrow 21, whereby its size in the direction indicated by arrow 22 is reduced which facilitates an easy insertion into the pipe. The elongating force is released when the partition member is located in the pipe and the member thereby bounce back to its original shape, i.e. the dimensions in the directions indicated by the arrows 21 and 22 reverts to the original dimensions whereby the member engages an inner surface of the pipe .

The partition member 18 comprises corrugated edges. During elongation of the member in the direction indicated by the arrow 21, the size of the member in the direction indicated by arrow 24 is reduced. The principles of operation correspond to those described above with reference to the partition member 17.

In addition to the advantage relating to the insertion, the two members 17, 18 further increases turbulent currents in the flow of a fluid inside the pips. The turbulent currents improve the heat exchange rate between the fluid and the pipe, in particular at low flow speeds of the fluid.

The partition members could be made from epdm- rubber or from any similar resilient polymeric or metallic material. Polymeric materials may, however, isolate the two conduits in the pipe better than metallic materials and may therefore sometimes be preferred.

In Fig. 8, the partition member 25 is perpendicular to the stream of air 26. In that way counter-current heat exchange is established, wherein the stream can be directed in the direction indicated by the arrow 27 firstly towards a low-temperature side 28 of the pipe, and from this side towards an opposite high-temperature side 29 of the pipe. Since the cold air is pre-heated with the low-temperature side of the pipe before arriving at the high-temperature side of the pipe, the temperature gradient between the air and the low-temperature side of the pipe is more equal to the temperature gradient between the air and the high-temperature side of the pipe.

Fig. 9 shows a cross sectional view of the pipe, the ventilator and the stream of air. Fig. 10 shows an enlarged view of the end-section 30 of pipe and ventilator of Fig. 8.

Fig. 11 shows an enlarged view of the pipe with a connection-piece 31. As shown, the arrangement of the partition member perpendicular to the stream of air enables that the connection-piece can be located in extension to the ventilating device, i.e. extending outwardly from that side of the pipe where the cross flow blower 32, c.f. Fig. 8 is located.

Claims

1. A system for distributing a fluid medium, and for exchanging thermal energy between the medium and its ambience, said system comprising:

- a ventilating device for forcing a stream of air across an outer surface of the pipe,

characterized in that the pipe comprises a partition member for separating the conduit into a first conduit and a second conduit .

2. A system according to claim 1, wherein the ventilating device comprises a cross-flow blower which is fastened with an axis of rotation substantially parallel to the longitudinal direction.

3. A system according to claim 1 and 2, wherein the partition member can be brought into a first state with a clearance between the member and an inner surface of the pipe for insertion of the member into the pipe, and into a second state wherein the member has contact with an inner surface of the pipe at least along two contact portions.

4. A system according to claim 3 , wherein the member is brought from the second state into the first state by an elongation of the member in a longitudinal direction.

5. A system according to any of the preceding claims, wherein the partition member has a non-planer shape.

6. A system according to claim 4 or 5, wherein the partition member is formed from a substantially planar strip of a sheet material with folds to form a longitudinally extendable spring structure to facilitate the elongation of the partition member.

7. A system according to any of the preceding claims, wherein the partition member is made from an elastically flexible material .

8. A method of making a system for distributing a thermally convective medium, and for exchanging thermal energy between the medium and its ambience, said system comprising:

- a pipe extending in a longitudinal direction and with an internal conduit for conducting a fluid flow, and - a ventilating device for forcing a stream of air across an outer surface of the pipe,

the method being characterized in that a partition member for separating the conduit into a first conduit and a second conduit is inserted into the pipe.

9. A method according to claim 8, wherein the first conduit is connected to an upstream flow of the medium, and the second conduit is connected to an opposite downstream flow of the medium.

10. A method of retrofitting an existing system comprising at least one pipe for distributing a thermally convective medium between two heat exchangers, said method comprising inserting a partition member for separating the pipe into two conduits for an upstream and a downstream flow of the medium in the pipe .

11. A method according to claim 10, further comprising the step of attaching a ventilating device to the pipe for forcing a stream of air across the pipe.