WO2016102772A1

WO2016102772A1 - Heat exchanger

Info

Publication number: WO2016102772A1
Application number: PCT/FI2015/050924
Authority: WO
Inventors: Jari Backman; Juha Honkatukia; Jaakko Larjola; Antti UUSITALO; Ollimatti KOSAMO; Mika Lohtander; Jari HÄMÄLÄINEN; Jukka Huttunen
Original assignee: Lappeenrannan Teknillinen Yliopisto
Priority date: 2014-12-22
Filing date: 2015-12-21
Publication date: 2016-06-30
Also published as: EP3247959A4; FI20146129A; EP3247959A1

Abstract

A heat exchanger unit (3) and a heat exchanger (1) comprising primary flow channels (4) for primary fluid flow (FP) and secondary flow channels (5) for secondary fluid flow (FS). At least one secondary flow channel (5) comprises a number of adjacent secondary flow channel portions (5'). Each secondary flow channel portion (5') has an inlet end and an outlet end for the secondary fluid flow (FS). The secondary flow channel portions (5') of the secondary flow channel (5) are interconnected by the inlet ends (11) and the outlet ends (12) so as to provide a number of consecutive secondary flow channel portions (5') in a flow direction of the secondary fluid flow (FS).

Description

HEAT EXCHANGER

FIELD OF THE INVENTION

The invention relates to a heat exchanger unit comprising primary flow channels for primary fluid flow and secondary flow channels for secondary fluid flow.

The invention relates also to a heat exchanger.

BACKGROUND OF THE INVENTION

Heat exchangers are devices used to transfer thermal energy from a primary fluid flow, such as a gaseous fluid flow, having a higher volumetric flow, to a secondary fluid flow, such as a liquid fluid flow, having a lower volumetric flow.

In a design of a heat exchanger it is attempted to combine the requirements set for a heat rate, a heat exchanger effectiveness, pressure drops as well as a size and a weight of the heat exchanger so as to provide an appropriate heat exchanger. However, a problem relating especially to a heat exchanger having high effectiveness with strict pressure drop requirements for a gaseous fluid flow side, is a considerable size (m³) and weight (kg) per heat rate (kW) of the heat exchanger. The heat exchangers like that are not practical in small-scale energy systems.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a novel heat exchanger.

The heat exchanger unit according to the invention is characterized by the features of independent claim 1 .

The heat exchanger unit according to the invention is characterized in that the heat exchanger comprises at least one heat exchanger unit as claimed in any one of claims 1 to 6.

By the heat exchanger unit disclosed it is possible to provide a heat exchanger unit with a small physical size but with a large heat transfer surface density in a volume of the heat exchanger unit.

According to an embodiment of the heat exchanger unit, the secondary flow channel comprises a number of flow guide elements for dividing the secondary flow channel into a number of adjacent secondary flow channel portions and guiding the secondary fluid flow in the adjacent secondary flow channel portions to opposite directions.

According to an embodiment of the heat exchanger unit, the secondary flow channel comprises a first end and a second end opposite to the first end, and that the flow guide element is arranged to extend from one end of the secondary flow channel towards an opposite end of the secondary flow channel but not to extend up to the opposite end of the secondary flow channel, and that immediately adjacent flow guide elements are arranged to extend towards different ends of the secondary flow channel.

According to an embodiment of the heat exchanger unit, the secondary flow channels are arranged between the primary flow channels.

According to an embodiment of the heat exchanger unit, the heat exchanger unit comprises adjacent groups of the primary flow channels, the groups of the primary flow channels being substantially parallel to each other, each group of the primary flow channels comprising a number of the primary flow channels arranged in a row-like manner immediately adjacently to each other, and that the secondary flow channels are arranged between the rows of the primary flow channels, whereby the primary flow channels of the heat exchanger unit are arranged into a number of adjacent and substantially parallel rows in the heat exchanger unit.

According to an embodiment of the heat exchanger unit, the heat exchanger unit comprises adjacent groups of the primary flow channels, the groups of the primary flow channels being substantially parallel to each other, each group of the primary flow channels comprising a number of primary flow channels arranged in a row-like manner at a distance from each other, and that each group of the primary flow channels is fitted into the secondary flow channel, whereby the primary flow channels of the heat exchanger unit are arranged into a matrix form in the heat exchanger unit.

According to an embodiment of the heat exchanger unit, a shape of a cross-section of the primary flow channel is a square.

According to an embodiment of the heat exchanger unit, a direction of the primary flow channel is arranged to alternate in its longitudinal direction.

According to an embodiment of the heat exchanger unit, a cross- sectional area of the primary flow channel is between 0.25mm² and 100mm².

According to an embodiment of the heat exchanger unit, the heat exchanger unit comprises primary flow channels for primary fluid flow and secondary flow channels for secondary fluid flow, wherein the secondary flow channel comprises a number of flow guide elements for dividing the secondary flow channel into a number of adjacent secondary flow channel portions, each secondary flow channel portion having an inlet end and an outlet end for the secondary fluid flow, the secondary flow channel portions being interconnected with each other through the respective inlet ends the and the outlet ends such that an outlet end of a preceding secondary flow channel portion is open to an inlet end of a following secondary flow channel portion in a flow direction of the secondary fluid flow, whereby the secondary fluid flow flows into opposite directions in immediately adjacent secondary flow channel portions as guided by the flow guide elements, and that the heat exchanger unit comprises adjacent groups of the primary flow channels, the groups of the primary flow channels being substantially parallel to each other, each group of the primary flow channels comprising a number of primary flow channels arranged in a row-like manner at a distance from each other, and that each single group of the primary flow channels is fitted into the secondary flow channel, whereby the primary flow channels of the heat exchanger unit are arranged into a matrix form in the heat exchanger unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 shows schematically a heat exchanger;

Figure 2 shows schematically a cross-section of a secondary flow channel;

Figure 3 shows schematically a top view of a portion of a heat exchanger unit;

Figure 4 shows schematically a top view of a portion of another heat exchanger unit; and

Figure 5 shows schematically a cross-section of primary flow channels in the heat exchanger.

For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference numerals identify like elements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows schematically a heat exchanger 1 comprising frame 2 and a heat exchanger unit 3 mounted in the frame 2. The heat exchanger unit 3 is an active part of the heat exchanger 1 , i.e. the part providing the heat transfer from a primary fluid flow FP having the higher volumetric flow, to a secondary fluid flow FS having the lower volumetric flow. The number of the heat exchanger units 3 in a single heat exchanger 1 may vary.

The heat exchanger unit 3 comprises primary flow channels 4 for the primary fluid flow FP, such as a gaseous fluid flow, having the higher volumetric flow, and secondary flow channels 5 for the secondary fluid flow FS, such as a liquid fluid flow, having the lower volumetric flow. The secondary flow channels 5 are provided between the primary flow channels 4 and schematically disclosed by broken lines in Figure 1 . In the embodiment of Figure 1 , the primary flow channels 4 and the secondary flow channels 5 are straight but their implementation may vary, as shown later in Figure 5 relating to the implementation of the primary flow channels 4. The walls between the primary flow channels 4 and the secondary flow channels 5 form heat transfer surfaces of the heat exchanger unit 3.

In the position of the heat exchanger 1 as shown in Figure 1 , the primary flow channels 4 extend in a vertical direction, whereby the primary fluid flow FP having the higher volumetric flow may have a principal flow direction for example downwards, as schematically shown with arrows FP. The secondary flow channels 5, in turn, extend in a horizontal direction, whereby the secondary fluid flow FS having the lower volumetric flow may have a principal flow direction for example from left to right, as schematically shown with arrows FS. The direction of the extension of the secondary flow channels 5 is thus transversal to the direction of the extension of the primary flow channels 4. Furthermore, a position of an inlet opening for the secondary fluid flow at a left side of the heat exchanger 1 is pointed schematically with an arrow indicated with reference sign 6 and an outlet opening for the secondary fluid flow at an opposite side of the heat exchanger 1 is indicated with reference sign 7.

Figure 2 shows schematically a cross-section of a secondary flow channel 5 along line A-A in Figure 1 . The secondary flow channel 5 has a first end 8 directed towards the inlet opening 6 of the heat exchanger 1 . Between the first end 8 of the secondary flow channel 5 and the inlet opening 6 of the heat exchanger 1 there is a free volume 15, which provides an end channel 15 from the inlet opening 6 to the secondary flow channel 5. The secondary flow channel 5 has also a second end 9 opposite to the first end 8, the second end 9 being directed towards the outlet opening 7 of the heat exchanger 1 . Between the second end 9 of the secondary flow channel 5 and the outlet opening 7 of the heat exchanger 1 there is a free volume 16, which provides an end channel 16 from the secondary flow channel 5 to the outlet opening 7 of the heat exchanger 1 .

The secondary flow channel 5 further comprises, in a vertical direction in the position of the heat exchanger 1 shown in Figure 2, a number of adjacent flow guide elements 10 that are arranged to extend from one end of the secondary flow channel 5 towards the opposite end of the secondary flow channel 5 but not to extend up to the opposite end of the secondary flow channel 5 in such a way that the immediately or directly adjacent flow guide elements 10, i.e. two neighbouring flow guide elements 10, are arranged to extend towards different ends of the secondary flow channel 5.

In other words, in the embodiment shown in Figure 2, the secondary flow channel 5 comprises a number of adjacent or neighbouring flow guide elements 10 in such a way that every other flow guide element 10 is arranged to extend from the first end 8 of the secondary flow channel 5 towards the second end 9 of the secondary flow channel 5 but not to extend up to the second end 9 of the secondary flow channel 5, and every other flow guide element 10 is arranged to extend from the second end 9 of the secondary flow channel 5 towards the first end 8 of the secondary flow channel 5 but not to extend up to the first end 8 of the secondary flow channel 5. Because of that first openings 1 1 are provided between the first end 8 of the secondary flow channel 5 and every other flow guide element 10 and second openings 12 are provided between the second end 9 of the secondary flow channel 5 and every other flow guide element 10.

In the embodiment shown in Figure 2 a number of flow guide elements 10 in the secondary flow channel 5 is thus arranged to divide a volume of the secondary flow channel 5 into a number of adjacent secondary flow channel portions 5', which in the position of the heat exchanger unit 3 shown in Figure 2 thus lie or remain one on the other. Each secondary flow channel portion 5' has an inlet end and an outlet end, provided alternately by the first openings 1 1 and the second openings 12. The secondary flow channel portions 5' are thus interconnected with each other through the respective inlet ends and the outlet ends such that an outlet end of a preceding secondary flow channel portion 5' is open to an inlet end of a following secondary flow channel portion 5' in a flow direction of the secondary fluid flow FS, whereby the secondary fluid flow FS flows into opposite directions in immediately adjacent, i.e. in two neighbouring secondary flow channel portions 5', as guided by the flow guide elements 10. The secondary flow channel portions 5' are thus arranged consecutively to each other in the flow direction FS of the secondary fluid flow, and the secondary fluid flow FS flows into opposite directions in two adjacent secondary flow channel portions 5' as guided by the flow guide elements 10.

The flow guide elements 10 as disclosed above provide in the secondary flow channels 5 passageways, i.e. the secondary flow channel portions 5', and when the number of these passageways is increased, the flow of the secondary fluid flow FS will more and more resemble a flow that has an opposite flow direction in respect of the primary fluid flow FP. This will increase the effectiveness of the heat exchanger unit 3 and the respective heat exchanger 1 . Also a cross-sectional area of the secondary fluid flow FS, i.e. a cross-sectional area of the secondary flow channel portions 5', may be selected independently of the number and the shape of the primary flow channels 4.

In the embodiment shown in Figure 2 the number of the flow guide elements 10 in the secondary flow channel 5 is ten, that providing eleven adjacent secondary flow channel portions 5'. In its minimum the number of the flow guide elements 10 is only one, that providing two adjacent secondary flow channel portions 5'. Preferably the number of the flow guide elements 10 is more than one and the number of the flow guide elements 10 in the secondary flow channel 5 may depend for example on dimensions of the secondary flow channel 5 or on the intended effectiveness of the heat exchanger unit 3 or the heat exchanger 1 .

Figure 3 shows schematically a top view of a portion of a heat exchanger unit 3. The heat exchanger unit 3 of Figure 3 comprises adjacent groups 13 of the primary flow channels 4, the groups 13 of the primary flow channels 4 being substantially parallel to each other. The secondary flow channels 5 are arranged between the groups 13 of the primary flow channels 4. Each group 13 of the primary flow channels 4 comprises a number of the primary flow channels 4 arranged in a row-like manner immediately adjacently to each other. The primary flow channels 4 in the heat exchanger unit 3 of Figure 3 are thus arranged into a number of adjacent and substantially parallel rows, the secondary flow channels 5 being arranged between these rows of the primary flow channels 4.

Figure 4 shows schematically a top view of another heat exchanger unit 3. The heat exchanger unit 3 of Figure 4 comprises adjacent groups 14 of the primary flow channels 4, the groups 14 of the primary flow channels 4 being substantially parallel to each other. Each group 14 of the primary flow channels 4 comprise a number of the primary flow channels 4 arranged in a row-like manner but at a distance from each other. Each single group 14 of the primary flow channels 4 are further fitted into the secondary flow channel 5, whereby the secondary flow channel 5 is arranged to surround the primary flow channels 4 in the single group 14 of the primary flow channels 4. As seen from the ends of the secondary flow channels 5, the primary flow channels 4 are thus pipes that extend through the secondary flow channels 5. The primary flow channels 4 in the heat exchanger unit 3 of Figure 4 are thus arranged into a matrix form.

In the embodiment of Figure 4 the common area of the heat transfer surfaces between the primary flow channel 4 and the secondary flow channel 5 is higher than in the embodiment of Figure 3, because in the embodiment of Figure 4 the secondary fluid flow FS in the secondary fluid channel 5 surrounds the primary flow channels 4, the secondary fluid flow FS in the secondary fluid channel 5 thus being in contact with all the side walls of the primary flow channels 4, which side walls of the primary flow channels 4 provide the heat transfer surfaces of the heat exchanger unit 3.

Figure 5 shows schematically a cross-section of a group 13 of the primary flow channels 4, along line B-B in Figure 3. The group 13 of the primary flow channels 4 of Figure 5 comprises a number of the primary flow channels 4 arranged in a row-like manner immediately adjacently to each other. In the longitudinal direction of the primary flow channels 4, i.e. in the direction of the extension of the primary flow channels 4, that being in the vertical direction in Figure 5, the primary flow channels 4 comprise a number of consecutive changes of direction, whereby the direction of the primary flow channel 4 is arranged to alternate in its longitudinal direction. This structure of the primary flow channels 4 increases the heat transfer surface area between the primary flow channels 4 and the secondary flow channels 5 when compared to an embodiment having straight primary flow channels 4.

The dimensioning of the primary flow channels 4 and the secondary flow channels 5 and the secondary flow channel portions 5' is made on the basis of the requirement set for the heat exchanger 1 to be manufactured. The requirements set for the heat exchanger 1 may relate to for example pressure losses, a heat flow rate, effectiveness and a shape and a size of the heat exchanger 1 . Therefore the size of the heat exchanger unit 3 and the heat exchanger 1 may vary in many ways.

According to an embodiment, the size of the cross-section of the primary flow channel 4 is very small, for example between 0.5mm x 0.5mm and 2mm x 2mm, whereby the cross-sectional area of the primary flow channel 4 is between 0.25mm² and 4mm² in order to obtain high heat transfer surface density. A thickness of the side walls of the primary flow channels 4 is very small, for example 0.1 mm - 1 mm. A width of the secondary flow channels 5 may also be very small, for example 0.5 mm and a height of the secondary flow channels 5 may also be very small, for example between 0.3mm and 5mm. For example, in a heat exchanger unit of about 40 kilowatts a number of the primary flow channels 4 in the heat exchanger unit 3 can be several thousands or even several tens of thousands if the primary flow channel dimensions are very small. When channel size decreases, the heat transfer surface density increases. The weight per heat rate (kg/kW) of that kind of the heat exchanger unit 3 may be below 25% of that of conventional heat exchangers. The heat exchanger unit 3 may be manufactured of for example aluminium or stainless steel, or other material.

Generally, the size of the primary flow channels 4 and the secondary flow channels 5 may vary. The cross-sectional area of the primary flow channels 4 may vary for example between 0.25mm² and 100mm². This dimensioning may provide a heat transfer surface density as high as 2000m²/m³, i.e. 2000m² in one cubic meter volume of the heat exchanger unit 3. A specific weight of that kind of the heat exchanger unit may be as low as 0.15kg per kW heat exchanger heat rate.

In prior art heat exchangers the heat transfer surface density is typically only about 100m²/m³, which means that the size and the weight of conventional heat exchangers may be many times of the size and the weight of the heat exchanger disclosed herein with the same effectiveness. In other words, the heat transfer surface density of the presented heat exchanger may be many times of that of the prior art heat exchangers in the same volume of the heat exchanger unit 3. In addition to that, the pressure losses in the primary flow channels of the disclosed heat exchanger unit are only a small portion of the pressure losses of conventional heat exchangers, or in other words, the size of the conventional heat exchanger is many times of the size of the heat exchanger disclosed herein with the same requirements for the pressure losses in the primary flow channels. The pressure losses in the secondary flow channels, in turn, are about the same with the heat exchanger disclosed herein and the conventional heat exchanger with the same operational requirements. This all means that with the solution disclosed herein it is possible to provide a heat exchanger with high effectiveness in a small size, this kind of heat exchangers being especially suitable to be used in small- scale powerhouses and in movable vehicles, for example.

Although the solution disclosed herein is especially useful for providing heat exchangers with a small physical size, the same solution may also be applied in heat exchangers of any size classes and power or heat rate classes.

In the embodiments of Figure 1 , the primary flow channel 4 has a rectangular cross-section, and in the embodiments of Figures 3 and 4, the primary flow channel 4 has a quadratic cross-section. However, the cross- sectional shape of the primary flow channels 4 may vary in many ways. Therefore the shape of the cross-section of the primary flow channel 4 may for example be round or triangular.

The heat exchanger unit 3 may be manufactured in one piece, for example by laser sintering, wherein manufacturing material of the heat exchanger unit 3 is supplied to the laser sintering process until a desired heat exchanger unit 3 is completed.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A heat exchanger unit (3) comprising primary flow channels (4) for primary fluid flow (FP) and secondary flow channels (5) for secondary fluid flow (FS), wherein the secondary flow channel (5) comprises a number of flow guide elements (10) for dividing the secondary flow channel (5) into a number of adjacent secondary flow channel portions (5'), each secondary flow channel portion (5') having an inlet end and an outlet end for the secondary fluid flow (FS), the secondary flow channel portions (5') being interconnected with each other through the respective inlet ends and the outlet ends such that an outlet end of a preceding secondary flow channel portion (5') is open to an inlet end of a following secondary flow channel portion (5') in a flow direction of the secondary fluid flow (FS), whereby the secondary fluid flow (FS) flows into opposite directions in immediately adjacent secondary flow channel portions (5') as guided by the flow guide elements (10), c h a r a c t e r i z e d in that the heat exchanger unit (3) comprises adjacent groups (14) of the primary flow channels (4), the groups (14) of the primary flow channels (4) being substantially parallel to each other, each group (14) of the primary flow channels (4) comprising a number of primary flow channels (4) arranged in a row-like manner at a distance from each other, and that each single group (14) of the primary flow channels (4) is fitted into the secondary flow channel (5), whereby the primary flow channels (4) of the heat exchanger unit (3) are arranged into a matrix form in the heat exchanger unit (3).

2. A heat exchanger unit as claimed in claim 1 , c h a r a c t e r i z e d in that the secondary flow channel (5) comprises a first end (8) and a second end (9) opposite to the first end (8), and that the flow guide element (10) is arranged to extend from one end (8, 9) of the secondary flow channel (5) towards an opposite end (8, 9) of the secondary flow channel (5) but not to extend up to the opposite end (8, 9) of the secondary flow channel (5), and that immediately adjacent flow guide elements (10) are arranged to extend towards different ends (8, 9) of the secondary flow channel (5).

3. A heat exchanger unit as claimed in claim 1 or 2, c h a r a c t e r i z e d in that a shape of a cross-section of the primary flow channel (4) is a square.

4. A heat exchanger unit as claimed in any one of the preceding claims, characterized in that a direction of the primary flow channel (4) is arranged to alternate in its longitudinal direction.

5. A heat exchanger unit as claimed in any one of the preceding claims, characterized in that a cross-sectional area of the primary flow channel (4) is between 0.25mm² and 100mm².

6. A heat exchanger unit as claimed in any one of the preceding claims, characterized in that the heat exchanger unit is made in one piece.

7. A heat exchanger (1), characterized in that the heat exchanger (1) comprises at least one heat exchanger unit (3) as claimed in any one of claims 1 to 6.