EP3559579A1

EP3559579A1 - Heat exchanger, air-conditioning machine, and method for condensation and evaporation

Info

Publication number: EP3559579A1
Application number: EP17826473.5A
Authority: EP
Inventors: Alexander WARLO; Lena Schnabel; Rahel VOLMER
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2016-12-23
Filing date: 2017-12-18
Publication date: 2019-10-30
Also published as: DE102016226163A1; WO2018114802A1

Abstract

The invention relates to a heat exchanger (1) having at least one heat transfer surface (100), wherein the heat transfer surface (100) has first partial surfaces (101), which are provided with a storage structure (2), and second partial surfaces (102), which do not have a storage structure (2). The invention further relates to an air-conditioning machine having such a heat exchanger and to a method for the condensation and evaporation of a working medium.

Description

Heat exchanger, air conditioning machine and condensation and evaporation process

The invention relates to a heat exchanger with at least one heat transfer surface. Furthermore, the concerns

Invention, a climate machine with such a heat exchanger and a method for condensation and evaporation of a working medium in which the working fluid is condensed on at least one heat transfer surface of a Wärmeüber ^¬ carrier and is subsequently evaporated again by supplying heat. Devices and methods of the type mentioned can be used as a component of an adsorption heat pump or an absorption refrigeration machine.

Sorption heat pumps or refrigeration machines are known in practice. The present description uses for both devices in summary the term air conditioning machine. The effect of these air conditioning machines is based on the fact that the heat of condensation and heat of sorption, which in the

Condensation and adsorption or absorption of a gaseous

Working medium is free, is provided as useful heat or used for the evaporation of a liquid working medium heat is used for cooling.

Condensation and evaporation can take place continuously on dedicated heat exchangers, which as

Condenser or evaporator are set up. In other embodiments, the evaporation and condensation may be cycled on a single heat exchanger.

There is a need to store the liquid working medium until re-evaporation. This can be done in known climate machines in memory structures, which are arranged on the surface of the heat exchanger and which can hold liquid working medium, for example by capillary forces.

However, these known heat exchangers have the disadvantage that the storage structures on the surface of the heat exchanger represent comparatively large heat capacities and thermal resistances, so that the condensation and evaporation performance of such heat exchangers is comparatively low.

Based on the prior art, the invention is therefore based on the object to provide a heat exchanger, which has a greater condensation and / or evaporation ^¬ performance and can nevertheless store working medium.

The object is achieved by a device according to claim 1, a climate machine according to claim 8 and a method according to claim 9. Advantageous developments of the invention can be found in the subclaims.

According to the invention, a heat exchanger is proposed, which has at least one heat transfer surface. The heat exchanger may in some embodiments of the

Invention have at least one tube which has a pipe wall. The pipe wall separates an interior of the pipe from an outer space surrounding the pipe. The pipe wall may consist of a metal or an alloy or a plastic material or such ent ^¬ hold. A plastic may be provided with a filler, which increases the thermal conductivity or reduces the heat ^¬ resistance. In some embodiments of the invention, the tube wall and / or the filler

Contain or consist of aluminum, stainless steel or copper. Inside the tube flows a heat transfer medium,

For example, a heating or cooling water, a thermal oil or a gas. As a result, the pipe wall thermal energy can be withdrawn or supplied.

The heat transfer surface of the heat exchanger may be at least a partial surface of the pipe wall. In other embodiments of the invention, the performance of the heat exchanger can be increased by the fact that the upper ^¬ surface of the pipe wall is increased by measures known per se. For example, the pipe wall may be thermally connected to fins or heat conducting plates, so that the surface of the fins for heat transfer is additionally available and the heat transfer surface ^{¬ of} the heat exchanger is increased in the same space.

The at least one tube of the heat exchanger may be polygonal or round. In particular, the heat exchanger

Flat tubes contain, whose width is substantially greater than the height. The heat exchanger can contain a multiplicity of tubes, which are flowed through in the same direction or in opposite directions by the heat transfer medium.

The heat transfer area of the heat ^¬ wearer so formed has first partial surfaces, which with a

Memory structure are provided. The storage structure may contain pores, which are set up and intended for the capillary storage of a condensate. In addition, the heat transfer surface has second partial surfaces which have no storage structure. According to the invention, it has been recognized that the performance of a heat exchanger

can be increased when second faces for

Are available, on which a gaseous working medium with low thermal resistance can be condensed efficiently. Since, however, only thin in this way

Store liquid films on the heat transfer surfaces In addition, first partial surfaces are available which are connected to the second partial surfaces in such a way that the condensate formed in the second partial surfaces is supplied to the first partial surfaces and thus to the storage structures arranged there. The freed in this way from the condensate second partial surfaces can then condense again with good efficiency gaseous working fluid, whereupon this condensate is again supplied to the storage structures in the first partial surfaces of the heat transfer surface. In some embodiments of the invention

Condensate continuously discharged from the second partial surfaces and the storage structures of the first partial surfaces are supplied.

During the subsequent evaporation of the liquid working medium heat is supplied to the heat exchanger by the heat transfer medium. On the one hand, this leads to the evaporation of the condensate film remaining on the second partial surface. In addition, the storage structure located on the first partial surface is also heated so that working medium can evaporate directly from the storage structure. Finally, in some embodiments, the memory structure may be the

Invention be adapted to liquid working medium by capillary forces on the second faces

transport, so that the working medium can be evaporated continuously from the second part surfaces.

The working medium is selected so that this at the desired temperature level and the desired

Working pressure a gaseous-liquid phase transition

takes place. In some embodiments of the invention, the working medium may include or consist of water and / or ammonia and / or an alcohol and / or a hydrocarbon.

In some embodiments of the invention, the

Memory structure fibers and / or knitted fabric and / or nonwoven and / or contain and / or consist of tissue and / or foam. The memory structure can be applied to the heat transfer surface of the heat exchanger by soldering, gluing or printing. In some embodiments, the

In the invention, the memory structure can also be fixed or formed by doctoring or painting on the heat transfer surface. The memory structure can through

Sintering from the tube material itself, e.g. by milling, etching (from the solid material) or by casting of

Sponges or foams are obtained on a pipe.

Cavities form between individual fibers or wires or in the pores of an open-pored foam, which allow capillary storage of condensate within the storage structure. The size of individual pores within the storage structure can be uniform. In other embodiments of the invention, pores of different sizes may be present

perform different tasks within the storage structure. For example, larger pores can do this

be provided to allow an effective 3-phase boundary between the solid body of the memory structure, the liquid condensate and the gaseous working medium, whereas smaller pores for capillary storage and / or capillary transport of the condensate may be present.

In some embodiments of the invention, the second partial surfaces may be provided with a hydrophobic coating. A hydrophobic coating may be selected in some embodiments of the invention

Polytetrafluoroethylene or a hydrocarbon-containing plasma polymer. In some embodiments of the invention, a hydrophobic surface may be replaced by mechanical

Material removal, such as roughening, laser structuring, sandblasting, etc. or chemical processes such as

For example, etching, galvanic, etc. are obtained. The hydrophobic coating of the second faces of the heat transfer surface avoids or reduces one Film condensation, so that the condensation of the

Heat exchanger can be increased. The goal is the generation of drops, which in turn are favorable for the flow and re-exposure of the surface.

In some embodiments of the invention, the second subarea may be provided with at least one condensate guide structure. A condensate guide structure may

be selected from at least one rib, a pin, a pin or a gutter. A gutter can have a constant width and / or depth along its longitudinal extent or else in the depth and / or width

be gradual or continuously variable. A condensate guide structure may be used for condensate formed on the second partial area during the condensation of the storage structure of the first partial area

supply. This can be avoided that the

Condensate runs uncontrolled from the heat transfer surface of the heat exchanger and thus lost the working cycle of the air conditioning machine.

In some embodiments of the invention, the first and second sub-areas may be arranged relative to each other such that condensate upon operation of the heat exchanger

Gravity driven expires from the second partial surface and the first partial surface can be fed. This ensures reliable storage of the condensed working medium in the storage structure, without causing it

Uncontrolled fluid losses occur and no further active conveyors are needed to move the condensate in the storage structures to the next

To save evaporation.

In some embodiments of the invention, at least one first partial area having a storage structure can be arranged below a second partial area.

As a result, drops dripping from the second partial surface Condensate inevitably on the memory structure, so that the condensate is stored reliably.

The invention is based on figures without

Restriction of the general inventive concept will be explained in more detail. Showing:

Figure 1 is a schematic representation of a sorption climatic machine.

FIG. 2 shows a heat exchanger according to the invention in a first embodiment.

FIG. 3 shows a heat exchanger according to the invention in a second embodiment.

FIG. 4 shows a first embodiment of a condensate guide structure.

Figure 5 shows a second embodiment of a condensate ^¬ management structure.

FIG. 6 shows an embodiment of a hydrophobic one

Coating.

FIG. 1 shows a schematic representation of a climate machine which can be used both as a sorption heat pump and as a sorption ^{refrigeration} machine.

The air conditioning machine includes a heat exchanger 1. This contains a pipe or a pipe system in which a heat transfer medium is circulated. As a result, heat can be removed or supplied to the heat exchanger.

The at least one tube of the heat exchanger 1 has a tube wall 120, which separates an inner space 105 of the tube from an outer space surrounding the tube. The pipe Wall 120 or a part of the pipe wall is used as heat transfer surface 100. In another execution form of the invention, the heat conducting ^¬ additionally or alternatively, not shown, or other structures may be before ^¬ hands which 100 further increase the heat transfer area.

The heat transfer surface 100 is divided into first partial surfaces 101, which are provided with storage structures 2. Furthermore, the heat transfer surface 100 is second

Partial surfaces 102, which have no memory structures 2. The storage structure 2 contains pores, which allow a capillary storage of a condensate. In addition, more pores with a larger diameter can be present, which allow an effective connection to the heat exchanger surrounding the gas space.

When operating as a chiller circulates in the interior 105 of the tube 10 of the heat exchanger 1, a comparatively warm heat transfer medium, which the second partial surfaces 101 and thus the existing in the memory structures 2 condensate heat flow Q _k supplies. As a result, the heat transfer medium cools down, so that heat can be dissipated, for example when used as a refrigerator or air conditioning.

The heat input into the heat exchanger 1 leads to the evaporation of the condensate, which is discharged as a gaseous working ^¬ medium 50 in the surrounding the heat exchanger 1 outer space 110.

Subsequently, the gaseous working medium 50 a

Compressor 30 supplied. In the illustrated embodiment, a thermal compressor 30 is shown.

This works with an adsorber on which the

gaseous working medium 50 is adsorbed. In this case, a heat flow Q _A is released. Subsequently, the gaseous Working medium 50 desorbed at a higher pressure level again, for which purpose a drive power is necessary, which is supplied in the form of a heat flow Q _P. The liberated from the thermal compressor 30 gaseous working medium 50 passes back to the heat exchanger 1 and is condensed at the second partial surfaces 102. The condensed, liquid working medium is then supplied to the storage structures 2 and stored there until the next evaporation. The released during the condensation heat Q _H can be used as heating heat, if the illustrated

Air conditioning machine is used as a heat pump. In the case of a chiller, the heat of condensation Q _{H can} also be released unused as waste heat.

Figure 2 shows a first embodiment of the heat exchanger according to Inventive ^¬ which is usable for example, in the embodiment shown in Figure 1 Air machine. Like reference numerals designate like components of the invention, so the following description is limited to the essential differences.

The heat exchanger shown in cross section in FIG. 2 shows by way of example three tubes 10a, 10b and 10c. The tubes 10 have a greater width and compared to a small height, so that the cross section is approximately rectangular. The tubes 10 according to FIG. 2 can therefore be referred to as flat tubes. The representation of the tubes 10 chosen in FIG. 2 can only be seen by way of example. The tubes 10 may also have a different polygonal or round or elliptical cross section. The number of tubes 10 is not set to exactly three. Rather, in some embodiments of the invention, the number of tubes 10 may also be larger or smaller and, for example

between 2 and about 30.

Each tube 10 has a first partial surface 101 and a second partial surface 102. In the illustrated Embodiment, the first part surfaces on the top of the horizontally disposed tube 10 are arranged and the second partial surfaces 102 on the opposite bottom of the tube 10th

As further apparent from FIG. 2, memory structures 2 are arranged on the first partial area 101. The

Memory structures 2 may, for example, contain or consist of a multiplicity of wires arranged in parallel, a knitted fabric, a woven fabric, a fleece or a foam. The memory structures 2 thereby form cavities or pores in which a liquid working medium or condensate 5 can be stored.

In contrast, the second partial surfaces 102 have no

Storage medium 2 on. Optionally, the second

Partial surfaces 102 may be provided with a hydrophobic coating, as will be explained in more detail below with reference to FIG.

The second partial surfaces 102 are arranged in this embodiment with respect to an associated first partial surface 101 of the underlying tube 10. This ensures that condensate dripping from a second partial surface 102 of the storage structure 2 of a

underlying tube is supplied. Thus, as the example ^¬ on the second area 102 of the tube 10a condensing working fluid as condensate 5

Storage structure 2 of the underlying tube 10b

fed. The working medium condensing on the second partial surface 102 of the tube 10b is supplied to the storage structure 2 of the tube 10c arranged therebelow. For a larger number of tubes, this is continued cyclically until reaching the last tube 10th

When supplying a warm heat transfer medium in the tubes 10 a, 10 b and 10 c, the in the memory structures. 2 stored working fluid gaseous expelled and is available for the next cycle, as described above with reference to FIG 1.

A second embodiment of the heat exchanger according to the invention will be explained with reference to FIG. The second ^embodiment shows a round tube 10 with a tube wall 120. The tube wall 120 is used as heat transfer surface 100. The round tube 10 is arranged substantially vertically. On the heat transfer surface 100 first partial surfaces 101 and second partial surfaces 102 are formed alternately. Thus, in the second partial surfaces 102, condensed working medium can flow, following gravity, into the first partial surfaces 101 arranged thereunder. The first partial surfaces 101 are provided with memory structures 2

provided, which contain a plurality of wires in the illustrated embodiment or consist thereof. The wires may be fixed to the tube wall 120 by soldering or gluing, so that pores or cavities 21 are formed between adjacent wires, in which the condensate is held in place by capillary forces, similar to one

Brush.

As the wires extend substantially radially away from the tube wall 120, their spacing increases at a greater distance from the heat transfer surface 100. This allows an efficient coupling of the memory structures 2 to the surrounding gas space, so that stored

Working medium also with good efficiency or higher

Evaporation rate can be evaporated directly from the memory structures 2 of the first partial surfaces 101 out.

The element shown in FIG. 3 can also have a greater length in other ^{embodiments of} the invention

have, so that a larger number of first and second partial surfaces along the longitudinal extent of the tube 10 are located. In addition, a variety of the in FIG 3 tubes 10 may be arranged side by side and one behind the other in a heat exchanger, so that the

Condensation and storage of the working medium for

Available area increases with the number of tubes 10.

FIG. 4 shows a heat transfer surface 100 in section. The heat transfer surface 100 shown in FIG. 4 again has a first partial surface 101 and a

opposite second partial surface 102. The first

Subarea 101 is provided with memory structures 2 as described above.

Serving for the condensation of the working medium second partial surface 102 may be provided with at least one condensate ^{¬ guide} structure 103. In the illustrated embodiment, the condensate guide structure 103 is an integral part of the pipe wall or the heat transfer surface 100. The condensate guide structure 103 may be a protruding beyond the second part surface 102 rib or a single pin or pin. The condensate ^{guide ¬} structure 103 causes condensed working fluid runs along the flanks of the structure 103 and at the

Tip drips off. As a result, the condensate can be specifically directed to a storage structure 2, so that losses of working fluid due to uncontrolled dripping of the second partial surface 102 are avoided.

Figure 5 shows condensate guide structures 103a and 103b in a second embodiment of the invention. According to the second embodiment, the heat exchange surface 100 is inclined, wherein the second partial surface 102 is arranged above the first partial surface 101. In the second part surface 102 grooves are incorporated, which have in the case of the condensate ^¬ guide structure 103 a substantially parallel side walls. In the case of the condensate guide structure 103b, the groove is at a greater distance from the first partial surface 101 widened funnel-shaped with the storage structure 2.

Alternatively or additionally, a groove 103a or 103b may also have a different depth and thus effectively collect and channel the condensate.

The grooves 103 according to Figure 5 cause the

Condensate on the second part surface 102 not

runs uncontrolled and thus the storage structures 2 is supplied only incomplete. Rather, that will

Condensate collected and guided in the groove acting as a drain channel and so effectively stored in the memory structures 2.

In turn, Figure 6 shows a heat exchange surface 100 with a first surface portion 101, on which is arranged a storage ^¬ structure. 2 On the second partial surface 102, which is provided for the condensation of the working medium, there is a hydrophobic coating 104.

For example, the hydrophobic coating 104 may include or consist of a polymer. The polymer may be selected from polytetrafluoroethylene and / or a plasma polymer which may be deposited from a hydrocarbon by a CVD process. In some embodiments of the invention, a hydrophobic

Surface by mechanical material removal, such as roughening, laser structuring, sandblasting, etc. or chemical processes such as etching, galvanic, etc. are obtained. The hydrophobic coating 104 causes no on the second partial surface 102

Film condensation takes place, but condenses the working medium in the form of individual drops. This has the effect that the working fluid drips more easily from the part surface 102 and expires and further when draining

Wash off condensate. As a result, the heat transfer resistance is reduced, so that the condensation ^¬ and / or evaporation performance can be increased. Of course, the invention is not limited to the illustrated embodiments. The foregoing Be ^¬ scription is therefore not to be considered as limiting, but as illustrative. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the foregoing description define "first" and "second" embodiments, this term is used to distinguish two similar embodiments without prioritizing them.

Claims

claims

1. Heat exchanger (1) with at least one heat transfer surface (100), characterized in that the heat transfer surface (100) first partial surfaces (101), which are provided with a storage structure (2) and second partial surfaces (102), which no memory structure (2).

2. Heat exchanger according to claim 1, characterized in that the storage structure (2) contains pores (21) for the capillary storage of a condensate (5).

3. Heat exchanger according to claim 1 or 2, characterized in that the storage structure (2) contains fibers and / or knitted fabric and / or non-woven and / or fabric and / or foam or consists thereof.

4. Heat exchanger according to one of claims 1 to 3, characterized in that the second partial surfaces (102) are provided with a hydrophobic coating (104) or a hydrophobic surface by mechanical material ^¬ erosion or chemical processes is generated.

5. Heat exchanger according to one of claims 1 to 4, characterized in that the second partial surface (102) is provided with at least one condensate guide structure (103).

6. Heat exchanger according to one of claims 1 to 5, characterized in that first and second partial surfaces (101, 102) are arranged so that during operation of the heat exchanger ^¬ over (1) condensate (5) gravity driven by the second partial surface (102) expires and the first

Partial surface (101) can be fed.

7. Heat exchanger according to one of claims 1 to 6,

further comprising at least one tube (10) with a Tube wall (120) having an interior space (105) surrounding one of the tube exterior (110), wherein the tube wall (120) at least partially forms the heat ^¬ tragungsfläche (100).

8. Air conditioning machine with a heat exchanger according to one of claims 1 to 7.

9. A method for condensing and evaporating a working medium, wherein the working fluid is condensed on at least one heat transfer surface (100) of a heat exchanger (1) and subsequently evaporated again by supplying heat, characterized in that

the heat transfer surface (100) has first partial surfaces (101) which are provided with a storage structure (2) and have second partial surfaces (102) which do not have a storage structure (2), the working medium condensing on the second partial surfaces (102) and the Condensate (5) is supplied to the first partial surfaces (101).

10. The method according to claim 9, characterized in that that first and second surface portions (101, 102) so attached are ^¬ arranged that the condensate (5) driven by gravity from the second partial surface (102) expires and the first partial surface (101) fed becomes.

11. The method according to any one of claims 9 or 10, characterized in that the second partial surfaces (102) are provided with a hydrophobic coating (104).

12. The method according to any one of claims 9 to 11, characterized in that the storage structure (2) contains pores (21) for capillary storage of the condensate (5).

13. The method according to any one of claims 9 to 12, characterized in that the second partial surface (102) is provided with at least one condensate guide structure (103) which supplies the condensate (5) of the storage structure (2).