WO2014059993A1

WO2014059993A1 - Heat exchanger

Info

Publication number: WO2014059993A1
Application number: PCT/DK2013/050331
Authority: WO
Inventors: Morten Espersen
Original assignee: Dantherm Air Handling A/S
Priority date: 2012-10-16
Filing date: 2013-10-15
Publication date: 2014-04-24

Abstract

The present invention relates to a heat exchanger for heat exchange between a liquid and air, which liquid circulates in a plurality of flat tubes, which heat exchanger is placed in a channel for circulating air, which heat exchanger is placed in the channels with an angular displacement in relation to the channel and the circulating air. It is the object of the invention to improve the heat conductivity from a circulating liquid to the air. The object can be fulfilled by forming the inlet and outlet as flat headers, which flat headers comprise a surface mostly parallel to the channel walls, which plurality of flat tubes are angularly displaced to be mostly parallel to the circulating air. Hereby can the headers be formed as relatively flat channels, which headers are reduced in their shadowing effect for circulating air in a duct comprising the heat exchanger. In that way the effective area of the heat exchanger is increased in relation to previously known heat exchangers. The resistance for the air flow in the channels is in that way also widely reduced. That means less energy is necessary for circulating air in a duct.

Description

Heat exchanger

Field of the Invention

The present invention relates to a heat exchanger for heat exchange between a liquid in the heat exchanger and air in an air duct, which liquid circulates in a plurality of flat tubes, which heat exchanger comprises at least one inlet and at least one outlet, which inlet and outlet are connected to flat tubes, which flat tubes are heat conductive connected to a plurality of heat conductive fins, which heat exchanger is placed in a channel for circulating air, which heat exchanger is placed in the channels with an angular displacement in relation to the channel and the circulating air.

The present invention also relates to an air duct comprising one or more heat exchangers.

Background of the Invention

Heat exchangers in air channels have been used in the past; tilting the heat exchanger to reach a bigger heat conductive surface has also being used in the past.

Object of the Invention

It is the object of the invention to improve the heat conductivity and air pressure drop ratio from a circulating liquid to the air. A further object is to improve the air flow in a channel. A further object is to decrease fouling on the heat exchanging surface.

Description of the Invention

The object can be fulfilled by the preamble to claim 1 and further modified by forming the inlet and outlet as flat headers, which flat headers comprise a surface being parallel or essentially parallel to the channel walls, which plurality of flat tubes are angularly displaced to be parallel or essentially parallel to the flow direction of the circulating air. Hereby can be achieved a highly effective heat exchanger where the size and thereby the volume of the headers are reduced so the heat exchanger itself has a larger surface, and the heat exchanger is thereby more effective. Forming the headers as relatively flat channels, it is possible that the headers which are supplying liquid to the heat ex- changing tube have the same effective volume for flow of liquid, but are reduced in their shadowing effect for circulating air in a duct comprising the heat exchanger. In that way, the effective area of the heat exchanger is increased in relation to previously known heat exchangers. The resistance for the air flow is in that way also widely reduced. That means less energy is necessary for circulating air in a duct. All in all is achieved a highly effective heat exchange between circulating air and a liquid streaming inside the tubes. Such a heat exchanger could be highly effective if it is operating as a condenser or an evaporator for a cooling system. In that way, the circulating liquid could be a refrigerant. Such condensers could be widely used in for example air condition systems and thermosyphons. Also for medium scale refrigeration systems such condensers could be widely used. Highly effective condensation together with relatively low flow resistance for air flowing through the condenser increases the efficiency of any cooling system.

In a preferred embodiment for the invention, the heat conductive fins can be angularly displaced to be parallel or essentially parallel to the flow direction of the circulating air. Heat conductive fins can increase the effective surface area that is in contact with the circulating air and in that way reach much more effective heat conduction. The conductive fins can be mechanically connected to the flat tubes, in order to achieve good heat conductivity. The surface of the fins can be folded in order to achieve in- creasing surface area. The heat conducting fins can comprise a high number of small protrusions in order to avoid a laminar air circulation around the fins. A turbulent air circulation can lead to a higher degree of heat transmission. Further, the surface area could be improved using the louver approach or Herringbone Wavy fin approach or Smooth Wavy fin approach etc.

In a further preferred embodiment, the flat headers can comprise fastening means for fastening the heat exchanger inside the channel for circulating air. Hereby can be achieved that fastening the heat exchanger inside a channel becomes very easy, and it is avoided that any tooling is necessary in the headers. Any tooling in a header could be critical if for example the liquid circulating is a refrigerant. Leaking refrigerant must be avoided, because some of the refrigerants are environmentally unfriendly. Therefore, fastening means are formed in a way where no tooling is necessary. If the header is produced partly as an extruded aluminium profile, it is possible in that aluminium profile to achieve an effective fastening maybe by forming some kinds of screw holds in the aluminium or forming a profile that can automatically connect to a counter part inside a duct. In a further preferred embodiment, the heat exchanger can have a larger size in one dimension than the channel or the same dimension, whereby the heat exchanger by angular displacement has the size to fill the opening of the channel. Hereby it can be achieved that the heat exchanger can have a size much bigger than the channel in the same direction. That can lead to a much more effective heat exchange, for example for a condenser for a refrigeration system.

In a further preferred embodiment, the flat headers can comprise half pipe headers to which flat surfaces of the half pipe headers the flat tubes are fastened. Hereby it can be achieved that the tooling and fixation of the flat tubes can be performed at the flat sur- face of the half pipe, because the half pipe has a good compromise between flat surface at the top and the active flow volume for the liquid, and further to use the free volume below the half pipe for fixation means. Other profiles for the headers are also possible. All profiles that maybe could be performed by extrusion of aluminium could be possible for the headers.

In a further preferred embodiment, more heat exchangers can be placed in parallel in the channel. Placing more heat exchangers parallel to each other can hereby be performed without the headers making any shadowing effect in the duct for circulating air. The total flow reduction is hereby reduced in situations where pluralities of heat exchangers are used. By using headers that have the same size for each of the heat exchangers, there is only the shadow effect that is performed from the first set of headers. In order to achieve highly effective condensation in refrigeration systems, it is in some situations necessary to operate with rather large condensers. A number of separate condensers could work in parallel or they could work in serial.

Further when two or more heat exchangers are arranged parallel in coil stacks, the same fins can go through all the coils in the stack. This means that the area between the coils that is otherwise wasted can be utilized and the effective convective area increased for the same volume. Further, as the gaps between the coils are eliminated, pressure drop decrease as there are no leading edges of the front surface as otherwise would have been the case in the coil gaps. Also, the elimination of the leading edges will decrease fouling, because the leading edges would have otherwise been exposed by foul impaction in the gaps. The gained area between the coils by introducing the angel fin profiles that will go all the way through the coil stack can be used to increase fin pith in order for the exchanger to allow particles with larger aerodynamic diameter to pass through the exchanger instead of being trapped. Also trapping elimination of the gap between coils is a key issue.

The objects and the effects mentioned above can also be fulfilled by an air duct comprising one or more heat exchangers according to any of the above mentioned embodiments, in which the one or more heat exchangers are arranged in the air duct so that the plurality of flat tubes are angularly displaced between inner surfaces of the air channel walls and positioned in the air duct to be parallel or essentially parallel to the flow direction of the circulating air.

Description of the Drawings

Figure 1 shows a sectional view of a heat exchanger placed in a duct.

Figure 2 shows a sectional view of a heat exchanger.

Figure 3 shows an enlarged sectional view of half pipe headers and tubes.

Figure 4 shows a heat exchanger placed in one direction.

Figure 5 shows another heat exchanger placed in an opposite direction. Detailed Description of the Invention

Figure 1 shows a sectional view of a heat exchanger 2 placed in a channel 18. The heat exchanger comprises, inside a closed circuit, a liquid 4. The heat exchanger is placed in circulated air 6 which air is circulated in the channel 18. The heat exchanger 2 com- prises a plurality of flat tubes 8 connecting headers 22 placed below and above the tubes 8. The headers 22 have a flat surface 24 which surface is parallel or essentially parallel to the inner surface 26 of the channel 18. Further is indicated the length 32 of the heat exchanger 2 and also is indicated the height of the channel 18 by the number 34, whereby is indicated that because of the angular displacement 20 of the heat ex- changer, the length of the heat exchanger is sufficiently longer than the height 34 of the channel 18.

In operation, a liquid 4 such as a refrigerant will be circulated inside the headers 22 and inside the flat tubes 8. If the heat exchanger is used as a condenser for refrigerant then refrigerant gas is probably sent through an inlet into the heat exchanger and liquid refrigerant is sent through a lube to an outlet from the heat exchanger. Because of the flat tubes 8 and the relatively low header 22, most of the channel 18 is open for flow. The flat tubes 8 can be combined with conductive fins 16 (fig. 4-5), the heat exchanger (2) has an extremely high surface that can perform heat conduction towards the circu- lating air 6. The heat exchanger as indicated at the figure 1 could be a very important improvement for condensers for refrigeration systems. In other applications the same invention could be used for evaporators also in refrigeration systems. Both in air condition and in directly cooling performances this heating exchanger is very effective. Figure 2 is a sectional view perpendicular in relation to figure 1 and only a plurality of flat tubes 8 are indicated. It can be seen that there is a relatively big opening for circulating air between the tubes 8.

Figure 3 shows a possible embodiment for the headers for a heat exchanger. The heat exchanger comprises the flat tubes 8 connected to a flat surface 22, now placed at a half pipe duct 40. The half pipe duct 40 has an upper surface 24, 42 to where the flat lubes 8 are connected. The liquid is circulating in the half pipes and in the flat tubes 8. The half pipes 40 comprise fastening means 30 used for fastening the heat exchanger inside for example a channel where air is circulated.

Figure 4 shows a heat exchanger 2 comprising a number of flat tubes 8 connecting the headers 40. The headers 40 have a flat surface 42 to which surface the flat tubes 8 are placed. The heat exchanger also comprises heat conductive fins 16 placed all over between the flat tubes 8.

In operation, a liquid will flow in the half pipe tubes 40 and through the flat tubes 8 where the heat conductive fins 16 are heat conductive towards the tubes 8. Therefore, the total surface of the heat exchanger is relatively high, but the flow resistance to the air flowing through the heat exchanger is relatively low. Especially by placing the headers side by side and reducing the height of the headers, the flow resistance for circulating is widely reduced.

Figure 5 shows another possible embodiment for a heat exchanger. This heat exchanger 2 also comprises flat tubes 8 connecting headers 40. Between all the flat tubes 8 are placed heat conductive fins 16, but these heat conductive fins are only indicated between the first two flat tubes 8. The header 40 also comprises fastening means 30 indi- cated below the half pipe tube.

In operation the flat tubes 8 will be placed parallel or essentially parallel to the circulating air and also the heat conductive fins 16 are placed parallel or essentially paral- lelto the circulating air. In that way, an effective heal transport from the tube 8 through the air circulating through the heal exchanger can be achieved. By using the flat headers such as half pipe headers 40 is achieved that the resistance towards airflow through the heat exchanger is reduced. Hereby is the total energy consumption of a heating system being reduced.

The term "essentially" e.g. used as "essentially parallel" is to be understood as encompassing normal tolerances in the measurements applied in the field of heat exchangers and air ventilation, as well as encompassing something, which at visual inspection seems to be resembling the feature used in the relevant connection. Thus "essentially parallel" may e.g. encompass the normal tolerance when measuring the distance between to items and will also encompass the situation where two items are seen as par- all when inspected visually.

Claims

CLAIMS 1. Heat exchanger (2) for heat exchange between a liquid (4) in the heat exchanger (2) and air (6) in an air duct, which liquid (4) circulates in a plurality of flat tubes (8), which heat exchanger (2) comprises at least one inlet and at least one outlet, which inlet and outlet are connected to flat tubes (8), which flat tubes (8) are heat conduc- tively connected to a plurality of heat conductive fins (16), which heat exchanger (2) is placed in channels (18) for circulating air (6), which heat exchanger (2) is placed in the channels (18) with an angular displacement (20) in relation to the channel (18) and the circulating air (6), characterized in, that the inlet (10) and outlet (12) are formed as flat headers (22), which flat headers (22) comprise a surface (24) which is parallel or essentially parallel to the channel walls (26), which plurality of flat tubes (8) are angularly displaced to be parallel or essentially parallel to the flow direction of the circulating air (6).

2. Heat exchanger (2) according to claim 1, characterized in, that the heat conductive fins (16) be parallel or essentially parallel to the flow direction of the circulating air (6).

3. Heat exchanger (2) according to claim 1 or 2, characterized in, that the flat headers (22) comprise fastening means (30) for fastening the heat exchanger (2) inside the channel (18) for circulating air (6).

4. Heat exchanger (2) according to one of the claims 1-3, characterized in, that the heat exchanger (2) has a larger size (32) in one dimension (34) than the channel (18) for the same dimension (34), whereby the heat exchanger (2) by angular displacement has the size (32) to fill the opening of the channel (18).

5. Heat exchanger (2) according to one of the claims 1-4, characterized in, that the flat headers (22) comprise half pipe headers (40), to which flat surfaces (42) of the half pipe headers (40) the flat tubes (8) are fastened.

6. Heat exchanger (2) according to one of the claims 1-5, characterized in, that more heat exchangers (2) are placed parallel or essentially parallel in the channel (18).

7. Heat exchanger (2) according to one of the claims 1-5, characterized in, that 2 or more heat exchangers (2) are arranged parallel or essentially parallel in coil stacks, the same heat conducting fins (16) are designed to go through all the coils in the coil stack.

8. An air duct comprising one or more heat exchangers according to any of the claims 1-7, in which the one or more heat exchangers (2) are arranged in the air duct (18) so that the plurality of flat tubes (8) are angularly displaced between inner surfaces (26) of the air channel walls (18) and positioned in the air duct to be parallel or essentially parallel to the flow direction of the circulating air (6).