WO2017016656A1

WO2017016656A1 - Heat transfer tube, heat reservoir and method for producing a heat transfer tube

Info

Publication number: WO2017016656A1
Application number: PCT/EP2016/001273
Authority: WO
Inventors: Heinz Posselt; Manfred Schönberger; Stefan Hübner
Original assignee: Linde Aktiengesellschaft
Priority date: 2015-07-30
Filing date: 2016-07-21
Publication date: 2017-02-02

Abstract

A heat transfer tube (3), in particular a finned tube, for a heat reservoir (1), in particular a molten-salt PCM, said tube comprising: a pressure tube (5) for conveying a fluid (4); a heat transfer element (6) provided on the exterior of the pressure tube (5); and a fastening element (10) for fastening the heat transfer element (6) to the pressure tube (5), wherein the fastening element (10) is pressed onto the heat transfer element (6) in order to prevent heat-induced expansion of the heat transfer element (6).

Description

description

Heat transfer tube, heat accumulator and method for producing a

Heat transfer tube

The invention relates to a heat transfer tube, a heat accumulator with such a heat transfer tube and a method for producing such a heat transfer tube.

Heat storage, especially so-called latent heat storage, have a

Storage medium and a in the storage medium or passed through this heat transfer tube. Through the heat transfer tube, a fluid, such as heated water vapor, is passed. Such latent heat storage use the enthalpy of reversible thermodynamic state changes of

Storage medium, in particular the phase transition from solid to liquid and vice versa. When charging the latent heat storage, the storage medium is melted. During the melting process, the storage medium of the fluid absorbs a large heat energy in the form of the heat of fusion. Due to the

Reversibility of this process, the storage medium gives this heat energy during solidification back to the fluid. To a good heat transfer from the heat pipe to the

To ensure storage medium, the heat transfer tube may have in its longitudinal direction extending ribs. Since aluminum alloys have particularly good heat conduction properties and a filigree rib design, for example by means of extrusion, is possible with regard to a good

Heat transfer from the heat transfer tube to the storage medium and vice versa, an aluminum material is a suitable material for such

Heat transfer tubes. However, since aluminum alloys at higher

Temperatures have only a limited strength, it is necessary to provide the heat transfer tube with a pressure tube made of a steel alloy to absorb the pressure of the fluid.

WO 2011/0696693 A1 describes a heat transfer tube with a pressure tube made of a steel alloy and a heat transfer element, the an aluminum alloy is made. Since aluminum alloys have a significantly higher coefficient of thermal expansion than steel alloys, a heat transfer obstructing gap may form when a heat input into the heat transfer tube between the pressure tube and the heat transfer element. To prevent the formation of a gap, the heat transfer element is by means of resilient clamps, the two half shells of the

Clamp the heat transfer element to the pressure tube, attached to the pressure tube. Upon heat input into the heat transfer tube, the clips hold the heat transfer element in contact with the pressure tube.

Against this background, the object of the present invention is to provide an improved heat transfer tube for a heat storage available. Accordingly, a heat transfer tube, in particular a fin tube, for a heat storage, in particular for a molten salt latent heat storage, proposed. The heat transfer tube comprises a pressure tube for conveying a fluid, an outside of the pressure tube provided

A heat transfer member and a fixing member for fixing the heat transfer member to the pressure tube, wherein the fastener is pressed onto the heat transfer member to prevent heat-induced expansion of the heat transfer member.

The fact that the fastener is pressed onto the heat transfer element, it is ensured that the heat transfer element is always applied to a heat input into the heat transfer tube to the pressure tube, whereby a good heat transfer from the pressure tube to the

Heat transfer element is ensured. Under that, that

Fastening a thermal expansion of the

Prevents heat transfer element, is to be understood in the present case that a heat-related expansion of the heat transfer element is prevented or reduced so that no gap between the pressure tube and the first connecting tube. Here, the heat transfer element and in particular a part of the heat transfer element between the fastener and the pressure tube is constrained. A thermal expansion of the Heat transfer element is mechanically prevented by the fastener. In this case, the fastening element absorbs circumferential stresses resulting from thermal expansion of the heat transfer element. A

Operating temperature of the heat accumulator can be over 300 ° C. In this case, the material of the heat transfer element can flow. At the operating temperature of the heat accumulator is a yield point of the material of the

Heat transfer element so small that it can not absorb force. The power transmission takes place exclusively with the help of the pressure tube. Preferably, a plurality of heat transfer elements are provided on the pressure tube, which are arranged one behind the other in a longitudinal direction of the heat transfer tube. Each heat transfer element is preferably at least one

Assigned fastener.

According to one embodiment, the fastening element is annular and surrounds the heat transfer element.

The fastening element preferably surrounds the heat transfer element over an entire circumference thereof. The fastener can

For example, a semicircular, rectangular, circular or

have square cross-section.

According to a further embodiment, the fastening element has a predetermined contact width, with which it rests on the heat transfer element, wherein the fastening element is adapted to prevent a thermal expansion of the heat transfer element over the support width.

That is, the fastener prevents the thermal expansion of the heat transfer member in the region where the fastener rests on the heat transfer member. In areas where the

Fastening element does not rest on the heat transfer element, this can expand due to heat, which can form a gap in these areas between the heat transfer element and the pressure tube. A reliable heat transfer from the pressure tube to the

However, heat transfer element is ensured by the fact that the Heat transfer element is pressed in the region of the fastener of this on the pressure tube.

According to another embodiment, a plurality of fastening elements are provided, which are arranged spaced apart in a longitudinal direction of the heat transfer tube.

The number of fasteners is arbitrary. The fasteners may be spaced apart in the longitudinal direction of the heat transfer tube at a predetermined distance. The predetermined distance can be chosen arbitrarily.

According to a further embodiment, the heat transfer element has a tubular base portion and radially out of the base portion

extending ribs on.

Preferably, the heat transfer element has any number of ribs which are evenly distributed over a circumference of the tubular base portion. The ribs may have ramifications, causing the

Surface of the heat transfer element is increased. This improves the

Heat transfer from the heat transfer element to a storage medium of the heat storage or vice versa. The ribs are preferably formed materialeinstückig with the base portion. For example, the heat transfer element is a low-cost extruded profile.

According to a further embodiment, the fastening element surrounds the base section.

Preferably, the ribs are interrupted several times in the longitudinal direction of the heat transfer tube. At or in the interruptions of the ribs are the

Fastening elements or the fastening element is arranged such that it surrounds only the base portion.

According to a further embodiment, the fastening element is a press fitting. Under a press fitting is a prefabricated and especially standardized accessory to understand. As a result, the heat transfer tube can be made particularly inexpensive. According to a further embodiment, a material from which the

Heat transfer element is made, a higher

Thermal expansion coefficient as a material from which the pressure tube and / or the fastener are made. This ensures that the tubular base portion of the

Heat transfer element can only expand as far as it allows the material of the fastener.

According to a further embodiment, the heat transfer element is made of an aluminum alloy. Preferably, the aluminum alloy has a

Thermal expansion coefficient in a range of 23 * 10 ^"6 K ^{" 1} to 25 * 10 ^"6 K ^{" 1} on.

Aluminum alloys have particularly good heat conduction properties. This is a good heat transfer from the heat pipe to the

Storage medium of the heat storage and vice versa guaranteed.

According to a further embodiment, the pressure tube and the

Each fastener made of a steel alloy. For example, the heat transfer element and / or the

Fastener be made of the same or different steel alloys. In particular, the pressure tube and / or the fastening element can be made of a stainless steel or a stainless steel alloy. According to a further embodiment, the pressure tube and the

Fastening element made of different steel alloys.

For example, the different steel alloys can be different

Have thermal expansion coefficient. More precisely, the material of the Fastener have a lower coefficient of thermal expansion than the material of the pressure tube.

In order to obtain a permanent connection, it is advantageous, for example, if the pressure tube is preferably made of a stainless steel (eg: 1.4571) and / or preferably a thermal expansion coefficient in a range of 5 * 10 ^-6 K ^-1 to 17 * 10 ^-6 K ^"1 , more preferably 16 * 10 ^{" 6} K ¹ , and that

Fastening element is preferably made of a carbon steel (eg: 16Mo3) and / or preferably has a coefficient of thermal expansion in the range of 11Ί0 ^'6 K ^" to 13 * 10 ^{" 6} K ^"1 , particularly preferably 12 * 10 ^{" 6} K ^"1 . This combination ensures that when heating always enough bias is present to the best possible contact and thus a low

Heat transfer resistance between the pressure tube and the

To ensure heat transfer element.

Furthermore, a heat storage, in particular a molten salt latent heat storage with such a heat transfer tube and a

Storage medium, in particular a molten salt, in which the

Heat transfer tube is at least partially arranged, proposed.

The storage medium may be salts or salt mixtures, in particular

Alkali metal hydrates, nitrites, nitrates, sulfates, carbonates, chlorides, hydroxides, bromides, thiocyanates, fluorides and / or combinations of these. In particular, the storage medium comprises anhydrous salts or salt hydrates.

Furthermore, a method for producing a heat transfer tube, in particular a fin tube, proposed for a heat storage, in particular for a molten salt latent heat storage. The method comprises the following steps: providing a pressure tube, a heat transfer element and a fastener; Attaching the heat transfer element to the pressure tube; Attaching the fastener to the heat transfer element, and pressing the fastener onto the heat transfer element such that the fastener a heat-induced expansion of the

Heat transfer element prevented. The heat transfer element can be pushed onto the pressure tube without a bias. As a result, the heat transfer element can be easily mounted on the pressure tube. The heat transfer member has a tubular base portion and ribs extending radially outwardly from the base portion. In the areas where the fastener on the

Heat transfer element is pressed, the ribs are interrupted so that the fastener only the tubular base portion of

Heat transfer element surrounds. Preferably, a plurality of

Heat transfer elements attached to the pressure tube.

According to one embodiment, the fastener is so on the

Pressed heat transfer element that this is subjected to a bias voltage. In particular, the fastener is so on the

Heat transfer element and in particular the tubular base portion of the heat transfer member pressed that this completely abuts the pressure tube on the circumference. According to another embodiment, a plurality of

Attachment members are attached to the heat transfer member so as to be spaced from each other in a longitudinal direction of the heat transfer pipe. The number of fasteners is arbitrary. Good heat transfer from the pressure tube to the heat transfer element can by a small

Spacing the fasteners are achieved from each other.

Other possible implementations of the heat transfer tube, the

Heat storage and / or the method also include not explicitly mentioned combinations of previously or in the following with respect to the embodiments described features or embodiments. The skilled artisan will also add individual aspects as improvements or additions to the respective basic shape of the ^f heat transfer tube of the heat accumulator and / or the method. Further advantageous embodiments and aspects of the heat transfer tube, the heat accumulator and / or the method are the subject of the dependent claims and the embodiments of the heat transfer tube, the heat accumulator and / or the method described below. In addition, the

Heat transfer tube, the heat storage and / or the method with reference to preferred embodiments with reference to the accompanying figures explained in more detail.

Fig. 1 shows a schematic sectional view of an embodiment of a

Heat storage;

FIG. 2 shows a schematic perspective view of an embodiment of a heat transfer tube for the heat accumulator according to FIG. 1; FIG. and FIG. 3 shows a schematic block diagram of an embodiment of a

Method for producing a heat transfer tube according to FIG. 2.

In the figures, the same or functionally identical elements are the same

Unless otherwise indicated.

Fig. 1 shows a highly simplified schematic sectional view of a

Embodiment of a heat accumulator 1. The heat accumulator 1 may be a

Diameter of about 50 meters and have a height of about 30 meters. The heat storage 1 is a so-called latent heat storage. The heat storage 1 may be a molten salt latent heat storage. Such latent heat storage use the enthalpy reversible thermodynamic state changes of a process medium or storage medium 2 as a phase transition from solid to liquid and vice versa. Under enthalpy are the energy expenditure of

Phase transformations and the energy content of substances. At the

Charging the heat accumulator 1 is melted in this provided storage medium 2, which may be a phase change material. During the

Melting takes the storage medium 2 a large heat energy in the form of heat of fusion. Due to the reversibility of this process that gives

Storage medium 2 this heat energy when solidifying again. The

Storage medium may be a salt or a salt mixture. The storage medium 2 includes alkali metal hydrates, nitrites, nitrates, sulfates, carbonates, chlorides, hydroxides, bromides, thiocyanates, fluorides or combinations of these, in particular comprising anhydrous salts or salt hydrates. For example, the storage medium 2 may have a melting temperature of over 300 ° C. As a result, the

Heat accumulator with an operating temperature of over 300 ° C are operated.

The heat accumulator 1 further comprises at least one heat transfer tube 3, which is designed as a so-called fin tube or can be referred to as a fin tube. The heat accumulator 1 may have any number of heat transfer tubes 3. The heat transfer tube 3 is at least partially in the

Storage medium 2 arranged and / or passed therethrough. Through the heat transfer tube 3, a fluid 4, such as water vapor, are passed. When the storage medium 2 melts, the fluid 4 releases heat to the storage medium 2. Upon solidification or freezing of the storage medium 2, this heat is transferred to the fluid 4.

Fig. 2 shows a schematic perspective view of an embodiment of such a heat transfer tube 3. The heat transfer tube 3 comprises a pressure tube 5 for conveying the fluid 4. The pressure tube 5 is made of a steel alloy. The pressure tube 5 may be made of a stainless steel. On the outside of the pressure tube 5 is a heat transfer body or

Heat transfer element 6 is provided. The heat transfer element 6 is cylindrical and has a tubular base portion 7. The pressure tube 5 is disposed inside the tubular base portion 7. The pressure tube 5 is received in the tubular base portion 7 without the base portion 7 is biased. As a result, an easy assembly of the heat transfer element 6 to the pressure tube 5 is possible. The heat transfer element 6 comprises a plurality of radially extending out of the tubular base portion 7 out ribs 8, of which in Fig. 2, only two are provided with a reference numeral. The ribs 8 extend in a fin shape out of the tubular base section 7.

Therefore, the heat transfer tube 3 is also referred to as a fin tube.

The number of ribs 8 is arbitrary. As shown in FIG. 2, that can

Heat transfer element 6 eight ribs 8 have. The ribs 8 extend in a longitudinal direction L of the heat transfer tube 3. The ribs 8 may have a Variety in FIG. 2, not shown branching or ramifications. Thereby, a surface of the heat transfer member 6 can be increased, which improves the heat transfer from the heat transfer tube 3 to the storage medium 2 and vice versa. The ribs 8 are materialeinstückig formed with the tubular base portion 7. The ribs 8 have openings or recesses 9, which interrupt the ribs 8 in the longitudinal direction L several times.

The heat transfer element 6 is made of an aluminum alloy. By using an aluminum alloy for the heat transfer element 6, this can be made particularly delicate and has due to the high specific thermal conductivity of aluminum compared to that for the pressure tube. 5

used steel alloy good thermal conductivity on. At high

Temperatures such as at temperatures above 300 ° C falls the

Yield strength of aluminum alloys compared to steel alloys drastically, so that a force-transmitting construction with aluminum alloys at high temperatures is not possible. Therefore, only the pressure tube 5 is pressurized with the fluid 4 and the heat transfer element 6 is not mechanically stressed.

The heat transfer tube 3 has at least one attachment element 10 for attaching the heat transfer element 6 to the pressure tube 5. The

Fastening element 10 is pressed onto the heat transfer element 6 in order to prevent a heat-related expansion of the heat transfer element 6. More specifically, the fastener 10 is pressed in the region of the recesses 9 on the tubular base portion 7 of the heat transfer element 6. The fastening element 10 is preferably a so-called press fitting. The fastener 10 is annular and may have a circular, semicircular, square or rectangular cross-section. The fastener 10 surrounds the tubular base portion 7 around its entire circumference.

In the longitudinal direction L of the heat transfer tube 3 is a variety of

Fasteners 10 are provided, which are arranged spaced from each other. The number of fasteners 10 is arbitrary. The fasteners 10 are spaced from each other by a distance b. The distance b can For example, be a few inches to several decimeters. The distance b is at the same time the distance between two recesses 9 of a rib 8.

Each fastener 10 has a predetermined bearing width b ₀ . With the support width b ₁₀ , the fastener 10 is located on the tubular

Base portion 7 of the heat transfer element. The fastening element 10 is adapted to a thermal expansion of the

Heat transfer element 6 over the support width b ₁₀ to prevent. That is, between two fasteners 10, the heat transfer element 6 can expand due to heat, so that there where no fastener 10 rests on the tubular base portion 7 between this and the pressure tube 5 can form a gap. The heat transfer from the pressure tube 5 to the tubular base portion 7, however, is ensured by a heat-related

Expansion of the base portion 7 in the region of the fasteners 10 by the pressing of the same on the tubular base portion 7 is prevented.

The fastening element 10 is made of a steel alloy. The material from which the fastener 10 is made has a smaller one

Thermal expansion coefficient on as the material from which the

Heat transfer element 6 is made. This is a heat-related

Expansion of the tubular base portion 7 of the heat transfer member 6 prevents, so that the tubular base portion 7 in the region of

Fastener 10 circumferentially completely abuts the pressure tube 5. In an operational heat input into the heat transfer tube 3 of the tubular base portion 7 is applied in the region of the fasteners 10 by means of the pressure tube and the fastener 10 with radially acting pressure forces.

The pressure tube 5 and the fastener 10 may be made of the same

Be made steel alloy. Alternatively, the pressure tube 5 and the

Fastener 10 may be made of different steel alloys.

More specifically, the pressure tube 5 and the fastener 10 may be made of steel alloys having different thermal expansion coefficients. For example, the material of the fastening element 10 may have a lower thermal expansion coefficient than that of the pressure tube 5. As a result, it is always ensured that, when heat is introduced into the heat transfer tube 3, a circumferentially annular contact of the tubular base section 7 with the pressure tube 5 is ensured. When a heat input into the heat transfer tube 3, the tubular base portion 7 can not expand so far due to its arrangement between the pressure tube 5 and the fastener 10 in the region of the fastener 10 that forms a gap between the pressure tube 5 and the fastener 10. The fastener 0 receives at a heat input into the heat transfer tube 3 circumferential stresses resulting from a thermal expansion of the tubular base portion 7.

3 shows, in a schematic block diagram, an embodiment of a method for producing such a heat transfer tube 3. In a step S1, the pressure tube 5, the heat transfer element 6 and at least one attachment element 10 are provided. Depending on the length of the

Heat transfer tube 3, any number of fasteners 10 may be provided. The heat transfer element 6 can be made for example as extruded profile.

In a step S2, the heat transfer element 6 is attached to the pressure tube 5. The heat transfer element 6 can be applied to the pressure tube 5

be deferred. Here, the postponement of the

Heat transfer element 6 carried on the pressure tube 5 without a bias of the heat transfer element 6. As a result, a very simple assembly of the heat transfer element 6 to the pressure tube 5 is possible. Alternatively, in step S2, the heat transfer element 6 can also be pushed onto the pressure tube 5 with a bias voltage. As a result, a gap between the pressure tube 5 and the heat transfer element 6 in comparison to pushing without bias slightly smaller. Preferably, a plurality of heat transfer elements 6 are attached to the pressure tube 5, which are arranged one behind the other in the longitudinal direction L.

In a step S3, the fastening element 10 or the fastening elements 10 on the heat transfer element 6 or on the heat transfer elements 6 attached. In this case, alternately a heat transfer element 6 and a fastening element 10 can be threaded pearl-like onto the pressure tube 5. Alternatively, the fasteners 10 prior to attaching the

Heat transfer elements 6 on the pressure tube 5 on ends of

Heat transfer elements 6 are threaded, the

Heat transfer elements 6 are then pushed onto the pressure tube 5 together with the fastening elements 10.

In a step S4, the fastener 10 or the

Fastening elements 10 are pressed onto the heat transfer element 6 such that the fastener 10 or the fasteners 10 a

prevent thermal expansion of the heat transfer element 6. The fastening elements 10 are arranged so that they are arranged in the recesses 9 of the ribs 8. The fastening elements 10 can each have a closed annular cross-section. The fasteners 10 are pressed onto the heat transfer element 6 in such a way that the

Heat transfer element 6 and the base portion 7 of the

Heat transfer element 6 is subjected to a bias voltage. This ensures that the tubular base portion 7 is fully applied to the pressure tube 5 even with heat input into the heat transfer tube 3. When pressing the fasteners 10, either only one end of a heat transfer element 6 can be pressed, resulting in a fixed-loose storage, or it can both ends of a heat transfer element 6 are pressed.

Although the present invention has been described with reference to embodiments, it is variously modifiable. Used reference signs

1 heat storage

2 storage medium

3 heat transfer tube

4 fluid

5 pressure tube

6 heat transfer element

7 basic section

8 rib

9 recess

10 fastener b distance

bio overlay width

L longitudinal direction

51 step

52 step

53 step

S4 step

Claims

claims

1. heat transfer tube (3), in particular fin tube, for a heat accumulator (1), in particular for a molten salt latent heat accumulator, with a pressure tube (5) for conveying a fluid (4), an outside of the pressure tube (5) provided heat transfer element (6 ) and one

Fastening element (10) for fixing the heat transfer element (6) to the pressure tube (5), wherein the fastening element (10) on the

Heat transfer element (6) is pressed to a heat-related

Expansion of the heat transfer element (6) to prevent, characterized in that the pressure tube (5) and the fastening element (10) are made of different steel alloys.

A heat pipe according to claim 1, wherein the fixing member (0) is annular and engages around the heat transfer member (6).

A heat pipe according to claim 1 or 2, wherein the fastener (10) has a predetermined bearing width (b ₁₀ ) with which it rests on the

Heat transfer element (6) rests, and wherein the fastening element (10) is adapted to a thermal expansion of the

Heat transfer element (6) over the support width (b ₁₀ ) to prevent.

A heat pipe according to any one of claims 1-3, wherein there are provided a plurality of fixing members (10) spaced apart in a longitudinal direction (L) of the heat transfer pipe (3).

Heat transfer tube according to one of claims 1-4, wherein the

Heat transfer element (6) has a tubular base portion (7) and extending radially out of the base portion (7) outwardly extending ribs (8).

Heat transfer tube according to claim 5, wherein the fastening element (10) surrounds the base portion (7).

7. Heat transfer tube according to one of claims 1-6, wherein the

Fastener (10) is a press fitting.

8. Heat transfer tube according to one of claims 1-7, wherein a material from which the heat transfer element (6) is made, a higher

Has thermal expansion coefficient as a material from which the

Pressure tube (5) and / or the fastening element (10) are made.

9. Heat transfer tube according to one of claims 1-8, wherein the

Heat transfer element (6) is made of an aluminum alloy.

10. Heat transfer tube according to one of claims 1-9, wherein the pressure tube (5) and the fastening element (10) are each made of a steel alloy.

11. Heat storage (1), in particular molten salt latent heat storage, with a heat transfer tube (3) according to any one of claims 1-11 and a

Storage medium (2), in particular a molten salt, in which the

Heat transfer tube (3) is arranged at least partially.

12. A method for producing a heat transfer tube (3), in particular a fin tube, for a heat store (1), in particular for a molten salt latent heat store, with the following steps:

Providing (S1) a pressure tube (5), a heat transfer element (6) and a fastener (10);

Attaching (S2) the heat transfer element (6) to the pressure pipe (5);

Attaching (S3) of the fastener (10) on the

Heat transfer element (6), and

Pressing (S4) of the fastener (10) on the

Heat transfer element (6) such that the fastening element (10) prevents a heat-related expansion of the heat transfer element (6), characterized in that the provided pressure tube (5) and the provided fastener (10) were made of different steel alloys.

13. The method according to claim 12, wherein the fastener (10) is pressed onto the heat transfer element (6) in such a way that this with a

Bias is applied. The method of claim 12 or 13, wherein a plurality of

Fixing elements (10) are mounted on the heat transfer element (6) in such a way that they are in a longitudinal direction (L) of the

Heat transfer tube (3) are arranged spaced from each other.