WO2007147562A1

WO2007147562A1 - Heat exchanger

Info

Publication number: WO2007147562A1
Application number: PCT/EP2007/005390
Authority: WO
Inventors: Wim Meijer; Willem Alexander Gevers Deynoot
Original assignee: Colbond B.V.
Priority date: 2006-06-24
Filing date: 2007-06-19
Publication date: 2007-12-27
Also published as: EP1870657A1

Abstract

A heat exchanger is suggested for fluids comprising each an inlet and an outlet for a fluid to be heated up and for a fluid to be cooled down, at least one heat-up chamber and at least one cooling chamber, wherein the chambers are separated by a means to carry out heat transfer there between and wherein at least one of the chambers comprises a spacer, characterized in that the spacer comprises a three-dimensional mat from thermoplastic filaments, which mat has an open and random structure, and which filaments are bonded at least partly at their crossing points and which mat creates micro turbulence in the flow of fluid to increase efficiency of heat exchange between the two flows of fluid.

Description

Heat Exchanger

Description:

The present invention relates to a heat exchanger, which is used in a heat recovery system wherein supplying fresh fluid to be heated up and exhausting fluid to be cooled down are simultaneously carried out to perform heat exchange between the supply fluid and the exhaust fluid. Such heat exchangers are commonly used e.g. for ventilation of buildings, wherein the fluid is a gaseous fluid, such as air.

In order to meet both the requirements of maximizing heat transfer while at the same time handling a high volume stream of - in particular gaseous - fluids with a minimum pressure loss, it is necessary to install heat exchangers exhibiting high efficiency, which is commonly accompanied by relatively large units to be installed. The heat recovery units presently used in single-family houses for instance have dimensions of about height x width x depth of 0.85 x 0.60 x 0.55 m³. They contain an internal heat exchanger of about 0.50 x 0.50 x 0.30 m³, four 150 mm air pipes and two small ventilators. As these heat recovery units should produce little noise only, they usually operate with low air flow velocities of 1 m/sec to 2 m/sec. As a consequence of these low air flow velocities the flow will usually be laminar, resulting in a very low heat transfer coefficient in the order of 5 W/m².K (reference: calculation according to VDI-Warmeatlas, 5^th edition, 1988, formula 2).

In particular in big cities costs for buildings have been increasing drastically over the years, followed by free space in these buildings being continuously diminished. Demands thus have increased for heat recovery units having not only high an efficiency, but also requiring reduced room for installation and thus requiring a compact heat exchanger.

Such a compact heat exchanger is known for example from DE-A-100 08 681. DE-A-100 08 681 discloses a heat exchanger that has a gas inlet and outlet to include heat-up and cooling chambers completed with corrugated spacers, which are - preferably - made of corrugated paper. The chambers are preferably stacked in rows with fleece material, which is placed round the chamber and fixed to the respective spacers. The chambers are fixed by stacked arrangement of spacers and joined by fleece materials as secured to any one spacer in each case. Inlets and outlets should be arranged at right angles to one another. According to DE-A- 100 08 681 the heat exchanger disclosed should have high efficiency and at the same time a more compact size than the prior art units.

Although meeting some of the requirements as set up by the building industry, the heat exchanger of DE-A-100 08 681 still leaves room for improvement. First of all, the prior art heat exchanger is limited to gaseous fluids. Secondly, also when dealing only with gaseous fluids, such as air, there are some drawbacks when applying the heat exchanger of DE-A-100 08 681 , in particular when the air is very humid. For example, the demand for a ventilation system with a heat exchanger in cold areas or indoor warm swimming pools has increased with the spread of such kind of heat exchanges. Such environments have a problem in that a great temperature difference between supplied air and exhaust air is apt to form large amounts of vapour condensation and that the above mentioned corrugated paper - although preferably being resistant to humidity - cannot withstand long use because of its deformation and degradation due to the wet environment.

Further, it is still desired to increase heat transfer efficiency within the heat exchangers by avoiding as much as possible "dead corners", i.e. regions that exhibit no or only reduced flow of fluids, and by creating more turbulence in the flows of fluid, which will result in a higher heat transfer coefficient.

The present invention has for its object to reduce the mentioned drawbacks of the prior art. Further objects will become evident by studying the embodiments in the description.

In order to achieve the object of the invention a heat exchanger for fluids is proposed which heat exchanger comprise each an inlet and an outlet for a fluid to be heated up and for a fluid to be cooled down, at least one heat-up chamber and at least one cooling chamber, wherein the chambers are separated by a means to carry out heat transfer there between and wherein at least one of the chambers comprises a spacer, the invention being that the spacer comprises a three- dimensional mat made from thermoplastic filaments, which mat has an open and random structure, and which filaments are bonded at least partly at their crossing points.

Although bonding of the filaments that form the mat can be accomplished by various methods, including but not limited to applications of glues, it is preferred that the filaments are bonded by thermal fusion, applying partially or fully molten filaments onto each other where they cross. The skilled person knows those measures.

Preferably, at least one of the fluids to be heated up or to be cooled down by the heat exchanger of the invention is a gaseous fluid, even more preferably both fluids to be heated up and to be cooled down consist mainly or entirely of air. This is due to the fact that the main use of the heat exchanger is in ventilation systems of buildings, where both fluids to be treated consist of air. As a matter of fact the invention, however, is not limited to that and the heat exchangers according to the invention may also be used to treat cooling air or exhaust air in industrial processes or any other gaseous fluids. The application of an open and random three-dimensional structure, which filaments are bonded, preferably by thermal fusion, at least partly at their crossing points, as spacer in the heat exchanger according to the invention leads to various advantages in view of the prior art.

First of all, the spacer allows - due to its open structure - high amounts of fluids to pass through the respective chambers with only very low pressure losses. On the other hand, however, due to its random structure, the mat causes the flows of fluid, such as a gaseous stream, to become not only turbulent, but also micro- turbulent without causing a substantial increase of the pressure losses. In fact, the open and random structures lead to multidirectional flow paths throughout the mat with no preferred direction for the fluids. The random presence of filaments causes micro turbulence and prevents the natural formation of laminar flows. Micro turbulence is the flow pattern that exists during the natural formation of fully developed flows known in heat transfer text books as laminar or turbulent flows. The natural formation of these flows is interrupted by the random presence of filament loops. Micro turbulence exists during the transition phase between a random flow and the naturally formed laminar or turbulent flow and which consists of micro cross flows and eddies. According to VDI-Warmeatlas, GB1 , formula 3 the heat transfer is highest during this micro turbulent transition phase. This maximised heat transfer does not increase the mean velocity of the flows of fluid and therefore does not increase any noise levels.

Due to the micro turbulence on either side of the means to carry out heat transfer, the overall heat transfer increases substantially compared to the known heat exchangers, which in turn allows making them compacter. This additional reduction in size - as mentioned above - is a major advantage; this applies as well to small units for private housing as for large units for large buildings and industrial use. It is noted that WO-A-0127552 discloses a heat exchanger for fluids comprising an inlet and an outlet for a fluid to be heated up and for a fluid to be cooled down, wherein the chambers are separated by a means to carry out heat transfer there between and where at least one of the chambers comprises a spacer, wherein the spacer comprises a three dimensional mat from a thermoplastic material. According to US-A-5527590 which is incorporated into WO-A-0127552 by reference the thermoplastic material may consist of filaments, which filaments are bonded at least partly at their crossing points. The disclosure of WO-A-0127552 (with incorporated US-A-5527590) deviates, however, from the heat exchanger according to the invention in the fact that the three dimensional mats of the prior art structure have a regular and not a random structure.

As a result of the increased heat transfer the heat exchangers equipped with the random shaped mats according to the invention are more compact in size than those equipped with the regular shaped mats at the same efficiency. Preferably, the random structure of the mats is such that there is one obstacle, e.g. a filament forming a loop, within a distance of about maximum 15 mm. This ensures an efficient micro turbulence.

Further, the fact that the spacer is made from thermoplastic filaments, bonded by thermal fusion where they cross, renders it entirely insensitive to humidity, increasing the lifetime of the heat exchanger, in particular in environments with a high humidity.

An additional advantage lies in the fact that such mats as spacer render a better resilience to the entire structure, which also leads to an increase of the durability of the structure and is of help during the production of the heat exchanger, when the matting is to be handled, and during cleaning operations.

The more so, if - in a preferred embodiment - the heat exchanger comprises a series of heat-up chambers and a series of cooling chambers that are piled up. In order to allow good performance, it is worthwhile, if the chambers are piled up in an alternating manner, i.e. a cooling chamber followed by a heat-up chamber followed by a cooling chamber and so on.

It is also preferred that any of the chambers comprises an open and random three- dimensional mat from thermoplastic filaments as spacer.

For the means to carry out heat transfer between the chambers, it is preferred that this consists of a thin plate or a foil which is made of a material that is gas impermeable, i.e. tight and insensitive to humidity. Furthermore, good heat conductivity will contribute to the efficiency of the heat exchanger. Any plate that is sufficiently thin or any foil could for example achieve this.

As already mentioned above, although the application of the heat exchanger according to the invention is not restricted to particular gaseous fluids - as long as they are not hazardous to the structure - it is of course preferred that both the gaseous fluids to be cooled down or heated up consist of air.

Therefore, in a further preferred embodiment the means to carry out heat transfer between the chambers is a foil made of a material that is air impermeable and water vapour permeable.

This leads to good exchange and transport of water vapour throughout the entire structure, rendering the heat exchanger less susceptible to condensates.

The skilled man knows foils that are air impermeable and water vapour permeable.

An example is foils made of a copolyetherester and sold under the trade name

Sympatex® by Sympatex Technologies GmbH, Wuppertal (Germany).

The thermoplastic filaments applied for the three-dimensional mats are not restricted to any particular material. It is however preferred if the three-dimensional mats comprise a polymer selected from a group consisting of polyolefin, polyester, polyamide or blends thereof. These polymers can be easily and economically produced and extruded to form filaments exhibiting the desired structural integrity and resistance when formed into mats.

In order to achieve the desired structure, the filaments, preferably monofilaments, are spun and randomly laid, and are being thermally fused at least partly at their crossing points. The spinning and fusing steps can be done continuously by spinning the molten polymer into suitable forming devices. The skilled person knows these measurements.

It is particularly preferred if the thermoplastic filaments of the three-dimensional mat comprise polyamide 6 as main component. This material can be spun laid into various three-dimensional structures in a convenient and reproducible way. Furthermore, polyamide 6 is a very durable polymer, which is insensitive to low temperatures.

The three-dimensional mat comprises an open random structure, i.e. forming flow paths for the fluids without a preferred flow direction, thus enhancing the formation of micro-turbulences and avoiding high pressure losses during operation.

Suitable mats comprising random structures are e.g. described in DE-A- 1810921 and consist of a plurality of amorphous threads produced from a molten mass of a synthetic polymer, the threads having a diameter of 0.1-1.5 mm, and being in a three-dimensional structure, and bonded together at the points of intersection. Specifically the mat has a uniform structure and density, and all the surfaces are formed by projecting loops, where the loops are distributed at random.

When applying the three-dimensional mat of the invention, micro turbulence is created.

A particularly preferred three-dimensional mat exhibiting such a structure is commercially available under the trade name Enka®-Spacer from Colbond Geosynthetics B.V., Arnhem (Netherlands).

Three-dimensional mats from the Enka®-Spacer type have the advantage that they can be used in a convenient and reproducible manner due to the fact that their weight-area-ratio is very constant. This facilitates dosage of the material and as a consequence the reproducibility of the efficiency of the heat exchanger.

In another preferred embodiment of the heat exchanger according to the present invention the means to carry out heat transfer - also known as separation layer between the heat-up and the cooling chamber - is fixed to the topside and/or to the bottom side of the three-dimensional mat.

This can preferably be accomplished by thermal fixing of this means to the three- dimensional mat, which renders the assembly of the heat exchanger very easy and durable. In particular, if the heat exchanger is formed by simply piling up the means to carry out heat transfer that are (pre-) fixed to the top side or to the bottom side of the three-dimensional mat.

In operation it must be ensured that the inlet(s) and outlet(s) are arranged such that the fluids to be heated up and the fluids to be cooled down have a maximum contact without being intermixed. This can be achieved for example in that the inlet(s) and the outlet(s) for the fluid to be heated up and for the fluid to be cooled are arranged transverse, in particular, perpendicular to each other. It must then be ensured that the fluid to be heated up can only stream into and through the heat-up chamber(s) of the heat exchanger and the fluid to be cooled down only into and through the cooling chambers). This can be performed e.g. by sealing those sides of the chambers that should not be reached by a respective fluid.

The skilled person knows those measures. Examples for such constructions for gaseous fluids can be found in DE 100 08 681 (Fig. 1 and Fig. 3), which are hereby incorporated by reference.

Claims

Heat ExchangerClaims:

1. Heat exchanger for fluids comprising each an inlet and an outlet for a fluid to be heated up and for a fluid to be cooled down, at least one heat-up chamber and at least one cooling chamber, wherein the chambers are separated by a means to carry out heat transfer there between and wherein at least one of the chambers comprises a spacer, characterized in that the spacer comprises a three-dimensional mat from thermoplastic filaments, which mat has an open and random structure, and which filaments are bonded at least partly at their crossing points.

2. The heat exchanger according to claim 1 , characterized in that the filaments are bonded by thermal fusion.

3. The heat exchanger, characterized in that at least one of the fluids to be heated up or to be cooled down is a gaseous fluid.

4. The heat exchanger of claim 3, characterized in that both fluids to be heated up and to be cooled down consist mainly or entirely of air.

5. The heat exchanger of any of the preceding claims, characterized in that a series of heat-up chambers and a series of cooling chambers are piled up.

6. The heat exchanger of any of the preceding claims, characterized in that the means to carry out heat transfer between the chambers is a thin plate or foil made of a material that is gas tight.

7. The heat exchanger of any of the preceding claims, characterized in that the means to carry out heat transfer between the chambers is a foil made of a material that is air impermeable and water vapor permeable.

8. The heat exchanger of any of the preceding claims, characterized in that the thermoplastic filaments of the three-dimensional mat comprise a polymer selected from a group consisting of polyolefin, polyester, polyamide or blends thereof.

9. The heat exchanger of any of the preceding claims, characterized in that the thermoplastic filaments of the three-dimensional mat comprise polyamide 6 as main component.

10. The heat exchanger of any of the preceding claims, exhibiting micro turbulence in the flows of fluids during operation.

11.The heat exchanger of any of the preceding claims, characterized in that the means to carry out heat transfer is fixed to the topside and/or to the bottom side of the three-dimensional mat.

12. The heat exchanger of claim 11 , characterized in that the means to carry out heat transfer is thermally fixed to the three-dimensional mat.

13. The heat exchanger of claim 4, characterized in that the heat exchanger is formed by piled-up means to carry out heat transfer that are fixed to the top side or to the bottom side of the three-dimensional mat.

14. The heat exchanger according to any of the preceding claim, characterized in that the inlet(s) and the outlet(s) for the fluid to be heated up and for the fluid to be cooled are arranged transverse, in particular, perpendicular to each other.