WO2014023831A1

WO2014023831A1 - Solar thermosiphon system

Info

Publication number: WO2014023831A1
Application number: PCT/EP2013/066736
Authority: WO
Inventors: Karin LUNZ; Alexander KEMP; Nelly GACHIGNARD; Uwe Clement
Original assignee: Robert Bosch Gmbh
Priority date: 2012-08-10
Filing date: 2013-08-09
Publication date: 2014-02-13
Also published as: EP2883008A1; IN2014DN09487A; CN104520652A; AU2013301468B2; AU2013301468A1; BR112015002619A2; WO2014023456A1; MX2015001786A; DE102012015984B4; DE102012015984A1

Abstract

The invention relates to a solar thermosiphon system (1) for heating water, comprising a housing (2), in which a tank volume (3) is formed. The object of the invention is to provide a low-cost and robust thermosiphon system with high efficiency. The thermosiphon system (1) according to the invention is characterized in that in the housing (2) there is arranged a separating element (4), which separates the tank volume (3) into an absorber volume (6) and a reservoir volume (7), wherein the absorber volume (6) is arranged geodetically above the reservoir volume (7) in the operationally ready state of the thermosiphon system (1).

Description

DESCRIPTION

Solar thermosiphon system The invention relates to a solar thermosiphon system for heating a heat transfer fluid according to the preamble of claim 1.

A solar thermosyphon system is used to generate heat from solar energy through passive natural convection in a fluid circuit. From a surface absorbing the solar radiation, heat is transferred to a heat transfer fluid or solar fluid, which removes the heat from the absorber. Due to the temperature and density difference while a movement of the heat transfer fluid is caused without a circulation by means of a pump. As a rule, serves as a heat transfer fluid service or drinking water, which can be fed directly to another use.

Thermosiphon systems in which absorber and storage volumes are integrated in one component are also called integrated collector storages. Integrated collector storage systems are relatively widespread and serve, in particular in sunshine-rich countries, as a cost-effective system for heating drinking water by means of solar energy.

The simplest embodiment of such an integrated collector memory is formed by a black container whose black outer side absorbs the solar radiation and releases it in the form of heat to the heat transfer fluid inside the container. Such an integrated collector memory is very inexpensive to produce. However, the heating is uncontrolled and relatively slow, so that warm water or warm heat transfer fluid can be tapped only after several hours of intensive irradiation.

The invention is based on the object to eliminate the disadvantages of the prior art and to provide a cost-manufacturable Thermosiphonsystem ready, which is very simple and therefore robust and has a good efficiency.

According to the invention, this object is achieved with the features of patent claim 1. Advantageous developments can be found in the dependent claims. According to the invention, it is provided to arrange a separating element in the housing that separates the container volume into an absorber volume and a storage volume, wherein the absorber volume is adjacent at least to a part of a housing wall.

The housing, which is formed in the simplest case by a black, closed tube, is thus supplemented by a separating element which divides the container volume into an absorber volume and a storage volume. In an operational position, the part of the housing wall adjacent to the volume of the absorber is oriented in such a way that it is exposed to solar radiation. For this, the housing can be arranged inclined with respect to a horizontal. This results in temperature and density differences between the heat transfer fluid facing the absorbing surface in the absorber volume and the heat transfer fluid arranged in the storage volume. This leads to a buoyancy flow and a mass flow of the heat transfer fluid, whereby heat is removed from the absorber volume. This is the absorber volume and the storage volume in a fluid-conducting connection, wherein at least one flow and a return are provided for a closed circuit. It is advantageous if the absorber volume or the separating element is aligned at an angle to the horizontal, so that heated heat transfer fluid ascend in the absorber volume and can fall in the storage volume. In this case, a vertical alignment is possible. The housing generally has an elongated, in particular cylindrical shape, wherein the separating element extends in the longitudinal direction or parallel to a central axis (longitudinal axis) of the housing. The housing may also have an inlet for filling of heat transfer fluid and an outlet for tapping the heat transfer fluid, which is particularly required when heating drinking water.

In a preferred embodiment, the absorber volume is much smaller than the storage volume. This can be done in the absorber volume optimal heat transfer and thus high temperature increases, with sufficient storage capacity is provided by the relatively large storage volume. Also, in the absence of solar radiation then only a slight cooling of the heat transfer fluid is to be expected, since the storage volume can be isolated to the outside usually better than the absorber volume, and in the absorber volume is significantly less heat transfer fluid than in the storage volume. Preferably, the part of the housing wall adjoining the absorber volume is designed as a solar absorber. For example, the housing is made of a black plastic, other, especially metallic materials are also suitable. The housing wall thus represents a very simple absorber for sun rays. Overall, this results in a very simple, cost-effective and at the same time robust construction.

The storage volume and the absorber volume can be connected to one another via at least one inlet opening and at least one outlet opening. The outlet opening through which the heat transfer fluid flows from the absorber volume into the storage volume should, as far as possible, be above the inlet opening in the ready-to-operate arrangement of the thermosiphon system, through which the heat transfer fluid from the storage volume returns to the absorber volume. Thus, a mass flow is performed by heating in the longitudinal direction between the separator and the solar radiation facing part of the housing and from there back into the storage volume, the flow direction is clearly specified. A high mass flow is advantageous for high efficiency and good stratification in the storage volume. It is particularly preferred that a backflow valve is arranged in the inlet opening and / or the outlet opening. The return flow valve ensures that, in the absence of solar radiation, no opposite fluid flow is formed, which would lead to a cooling of the heat transfer fluid in the housing. Rather, the heat transfer fluid can only flow through the absorber volume when it absorbs heat there.

The inlet and outlet opening can be formed at the respective ends of the separating element. It is also possible to make the separating element shorter in the longitudinal direction than the housing, so that the inlet opening and the outlet opening are formed by the free spaces formed between the separating element and the housing at the end faces. In any case, no connecting lines between storage volume and absorber volume are required, so that a very simple, robust construction is obtained. Also, a hydraulic resistance is kept small within the thermosiphon, which is advantageous for a high mass flow and thus high efficiency. In a preferred embodiment, the separating element runs substantially parallel to the part of the housing adjoining the absorber volume, wherein a clear distance between the separating element and the part of the housing wall can be predetermined. With this solution, the gap height between the separating element and the housing wall and thus the absorber volume can be designed and the circulated volume flow in the absorber can be adapted to frequent or current operating and installation conditions.

Preferably, at least one projecting and / or connected to the separating element and / or the housing and / or to the separating element and / or on the housing, in particular at the absorber volume facing surfaces of the separating element and / or the part of the housing or molded onto the housing element for setting the clear distance between the separating element and the part of the housing wall arranged. For this, the at least one element in particular has a predefinable height. Each thermosiphon system may be a single, several or even many such elements arranged on the separating element and / or on the housing, which - optionally additionally - have the function of a reinforcing bead, a flow guiding and swirling element and / or a spacer. A reinforcing bead increases the inherent rigidity of the separator and reduces unwanted shape changes, for example, during assembly or due to heat. A Strömungsleit- or swirling element leads and distributes the heat transfer fluid flow along the absorber volume, breaks up laminar flows, swirls and mixes them and causes better heat transfer from the housing to the heat transfer fluid. A spacer ensures the maintenance of a desired (minimum) absorber volume, a flow, a temperature and / or a volume flow.

In an advantageous embodiment, the element is an element which is essentially rigid during operation of the thermosiphon system for prescribing a clear minimum distance between the separating element and the part of the housing wall. Such a rigid element can be molded, for example, in a deep-drawing process in the flat separating element.

The separating element preferably extends at least partially parallel to the part of the housing adjoining the absorber volume, a distance between the separating element and the part of the housing wall being between 2 mm and 20 mm, in particular between 3 mm and 10 mm, in particular 4 mm. The distance between Separating element and the housing wall has a great influence on the heat transfer from the absorber forming housing wall to the heat transfer fluid, which is located below in the absorber volume. A height of the absorber volume of 2 mm to 20 mm, in particular of 4 mm, represents a good compromise between increased heat losses and high temperature in the heat transfer fluid. The distance can be determined for example by means of spacers, which may optionally be integrally formed with the separating element can and position the separator with respect to the housing wall. In an alternative embodiment, the element is a height-variable (variable in length) element during operation of the thermosiphon system for changing the clear distance between the separating element and the part of the housing wall. In particular, it can be an element that changes its height as a function of a temperature, so that the distance adjusts itself as a function of the temperature. The height variability of the element can either be sudden in nature at a predeterminable temperature value, in particular at a setpoint temperature or switching temperature of the heat transfer fluid. Then, the change of the clear distance occurs abruptly or abruptly in the presence of a predeterminable temperature. Or the height variability of the element can be continuous and set over a temperature interval. Then, the variation of the clear distance gradually occurs over a changing temperature. The drive mode of movement of the variable-height element may be motor, hydraulic, pneumatic, magnetic, bimetallic and / or thermal. The movement can be predetermined in the case of a temperature dependence via a temperature sensor - in particular in or on the thermosiphon system - and an associated control device and executed by an electric motor. Alternatively, the movement may also be transmitted to the separating element by one or more bimetal elements, which deform under the influence of temperature and change their shape, length, angle or height. In a further embodiment, the movement may also start from a special expansion element, for example a cylinder-piston arrangement filled with an expansion substance or a metal bellows, in which a gas, a liquid or a wax expands under the influence of temperature and alters a length dimension of the expansion element , The bimetallic elements, the expansion element as well as the temperature sensor can be arranged in the thermosiphon system in the direct or indirect sphere of influence of the heat transfer fluid. Other dependencies of height variability as a temperature dependence are also conceivable, for example, a user-specified time-dependent requirement profile. If a user of the thermosyphon system needs hot water within a short time, the distance between housing and separating element must be small, for example 2 mm to 4 mm, so that a large temperature increase per throughflow occurs along the absorber extension. However, the large increase in temperature is accompanied by higher heat radiation losses from an external environment. On the other hand, if a user requires a high transmission efficiency of solar radiation to the water throughout the day, the distance must be large, for example 4 mm to 10 mm. This reduces the temperature increase per cycle, but at the same time also reduces the heat losses by radiation to the environment.

Preferably, the separating element is designed as a thermal insulator. For this purpose, the separating element may for example comprise a foamed polyethylene or polypropylene. However, the separating element can also be designed as a closed hollow chamber profile. By forming the separating element as a thermal insulator better heat absorption during solar radiation is achieved because the heat from the absorber volume is not delivered directly to the storage water, but first the heat transfer fluid is heated in the absorber volume. This leads to an increased available temperature in the absorber volume and thus to a higher mass flow due to the greater temperature-induced expansion of the heat transfer fluid and finally to a better temperature stratification in the storage volume. In the absence of solar radiation prevents the separator as a thermal insulator a heat transfer from the storage volume to the absorber volume and to the environment. Only the heat from the very small absorber volume is released to the environment during this time, so that compared to thermosiphon systems without separating element, the heat transfer fluid after a period without solar radiation, for example on the morning of a subsequent day, has a higher temperature.

In an advantageous embodiment, the housing is formed circular-cylindrical, wherein the separating element has a C-shaped or Ω-shaped cross-section and is supported with its longitudinal edges on an inner wall of the housing. The separating element should have a substantially curved shape about the longitudinal axis, wherein the longitudinal edges are also parallel to the longitudinal axis. The shape of the separating element can thus be modeled on the shape of the large letter Ω of the Greek alphabet. The separator can then relatively easily within the Housing can be placed, which is for example designed as a tube, with no additional fasteners are required. Optionally, a press fit may be used. Frequently, however, the friction between the longitudinal edges and the inner wall for a secure hold of the separating element is already sufficient. In particular, when the separating element extends laterally beyond a central axis of the housing, a secure support of the separating element on the housing inner wall with simultaneous sealing between the absorber volume and storage volume can take place.

The drawing illustrates an embodiment of the invention. It shows:

FIG. 1 shows a longitudinal section through a solar thermosiphon system,

Figure 2: a cross section through the thermosiphon system and Figure 3: a perspective view of a separating element.

FIG. 1 shows a longitudinal section of a solar thermosiphon system 1. The thermosiphon system 1 is designed as an integrated collector storage and has a closed at its end faces, tubular housing 2, in which a container volume 3 is formed. By a separating element 4, which is associated with an upwardly directed portion 10 of the housing wall 5, which serves as an absorber, the container volume 3 is divided into an absorber volume 6 and a storage volume 7. The absorber volume 6 and the storage volume 7 are connected via an inlet opening 8 and an outlet opening 9 with each other.

By solar radiation, a heating of the geodetically overhead housing wall 5, which serves as an absorber. The heat is transferred from the part 10 of the housing wall 5 to a heat carrier fluid located in the absorber volume 6, which is usually drinking water. Due to the temperature and density difference of the heat carrier fluid located in the absorber volume, compared to the heat transfer fluid located in the storage volume 7, a fluid circuit is formed, which is symbolized by arrows.

So that the direction of flow is clearly defined, the thermosyphon system 1 is arranged in an operational position at an angle (for example 10 ° <angle <90 °) to a horizontal. The outlet opening 9 is thus arranged geodetically higher than the input opening 8. Also, a vertical arrangement (angle = 90 °) of the Thermosiphonsystems is possible.

In the outlet opening 9, a return flow valve 1 1 is arranged, which is formed for example as a duckbill valve. The return flow valve 1 1 prevents a reversal of the flow direction, for example, overnight, when no solar radiation hits the housing wall 5 and the absorber surface.

The absorber volume 6 is much smaller than the storage volume 7. This results in optimal heat transfer at low heat transfer losses with a high temperature increase of the heat transfer fluid in the absorber volume. 6

A longitudinal extent of the separating element 4 is shorter than the longitudinal extent of the housing 2, so that the inlet opening 8 and the outlet opening 9 are formed by corresponding gaps on the narrow sides of the separating element 4 relative to the housing 2. The thermosiphon system 1 thus comes with very few components and is therefore simple and robust.

The separating element 4 runs essentially parallel to the part 10 of the housing wall 5 adjoining the absorber volume 6 and forms the absorber volume 6 by its areal extent in the longitudinal and circumferential direction and by the clearance (gap height) between the separating element 4 and the part 10 of the housing wall 5 out. The measure of the clear distance corresponds to the length of the element 14 and can be specified. This element 14 may be a relative to the separator 4 and / or the part 10 of the housing wall 5 protruding and / or a connected thereto and / or an integrally molded element 14 and serves to specify the clear distance. Shown in the figure 1 are two rod-shaped elements 14 at the lower and upper end of the separating element 4. Not shown are any further arranged over the extension in the longitudinal and circumferential direction of the separating element 4 elements 14. The at least one element 14 may be a rigid, during operation of the Thermosiphonsystems be invariable element and set the clear distance as a minimum distance between the separator 4 and the part 10 of the housing wall 5 fixed. On the other hand, the at least one element 14 may be a variable-length (variable-length) element 14 during operation. With a change in the height or the length of the element 14, the clear distance is changed and adjusted. Thus, the height of the flow gap and the size of the absorber volume is changed and adjusted. Not shown are eventual, the element 14 associated and its change in height or length Required actuators and / or sensors that can be located within, but also outside of the housing.

FIG. 2 shows the thermosiphon system in cross section. The housing 2 is formed circular cylindrical, so for example by a black plastic pipe. The upper half of the housing 2 in this case represents the part 10 of the housing wall 5, which serves as an absorber surface and on which the solar radiation, which is symbolized by arrows, acts. This leads to a heating of the housing wall 5, wherein the heat is transferred to the heat transfer fluid located in the absorber volume 6. By the separating element 4, which is designed as a thermal insulator, the absorber volume 6 is separated from the storage volume 7, wherein a fluid-conducting connection between the absorber volume 6 and the storage volume 7 is provided only on narrow sides of the thermosyphon system 1, as shown in Fig. 1 , The separating element 4 has an Ω-shaped cross-section and is supported by its longitudinal edges 12, 13 on the inner wall of the housing wall 5. This results in a positioning of the separating element within the circular cylindrical housing 2 and at the same time a seal between the absorber volume 6 and storage volume 7, wherein a particularly high density is not required.

Between the absorber volume limiting part 10 of the housing wall 5 and the separating element 4 is further provided at least one element 14 in the form of a spacer, for example, a rigid in operation, invariable vertical extent (longitudinal extension) of 4 mm and thus a corresponding height of the absorber volume. 6 Are defined. In the longitudinal and circumferential direction, several spacers can be behind each other and next to each other. In addition to the function as a spacer, the elements 14 can also take over the function of flow guide elements and / or Strömungsverwirungsungselementen and swirl the flow of the heat transfer fluid through the absorber volume for a more effective heat absorption. Optionally, the separating element 4 can be radially compressed slightly when inserting over the longitudinal edges 12, 13 and the spacer or spacers 14, so that a frictional and non-positive arrangement of the separating element 4 takes place within the housing 2 and the separating element 4 play and rattle within of the housing 2 is held. Additional fasteners are not required. Figure 3 shows a perspective view of a C-shaped separating element 4 with a plurality of rigid elements 14 which are arranged over the planar extension of the separating element 4 in the longitudinal and circumferential directions. The thermosiphon system according to the invention represents an integrated collector memory, wherein a housing is divided by a passive component, namely a separating element, into an absorber volume and a storage volume, wherein the absorber volume is much smaller than the storage volume. In the simplest embodiment, the housing is formed as a black tube, wherein a part of the housing wall, which is adjacent to the absorber volume, constitutes a solar absorber. However, the principle can also be used for example in so-called Sydney vacuum glass tubes, wherein the housing represents the inner tube of the vacuum glass tube.

The thermosiphon system according to the invention has a very simple structure and yet a relatively high efficiency. By separating the separation element takes place between absorber volume and storage volume. Thus, a targeted, layered heat distribution in the storage volume and at the same time heating of the heat transfer fluid in the absorber volume is achieved at relatively high temperatures. This results in an effective heating of the heat transfer fluid, so that the thermosiphon system according to the invention can be used in particular as a solar drinking water heating system in developing countries. Due to the simple structure and the small number of elements required cost-effective production is possible, the thermo-siphon system is very robust. In this case, the thermosiphon has a very low hydraulic resistance, since no additional lines between the storage volume and absorber volume must be provided, but a fluid flow can easily pass through openings in the separator or by gaps on the narrow sides between the separator and the housing. By one or more spacers can thereby position the separating element independently within the housing and optionally held non-positively. Overall, this results in an optimized and controlled heat input through a defined fluid management and a time earlier availability of heated heat transfer fluid such as warm water. At the same time, storage downtime heat losses are minimized.

Claims

1 . Solar thermosiphon system (1) for heating a heat transfer fluid with a housing (2) in which a container volume (3) is formed,

characterized in that a separating element (4) is arranged in the housing (2), which separates the container volume (3) into an absorber volume (6) and a storage volume (7), wherein the absorber volume (6) is connected to a part (10) of a Housing wall (5) adjacent.

2. Thermosiphon system according to claim 1,

characterized in that the absorber volume (6) is much smaller than the storage volume (7).

3. thermosiphon system according to claim 1 or 2,

characterized in that the part adjacent to the absorber volume (10) of the housing wall (5) is designed as a solar absorber.

4. thermosiphon system according to one of the preceding claims,

characterized in that the storage volume (7) and the absorber volume (6) are interconnected via at least one inlet opening (8) and at least one outlet opening (9),

5. Thermosiphon system according to claim 4,

characterized in that in the inlet opening (8) and / or the outlet opening (9) a check valve (1 1) is arranged.

6. Thermosiphon system according to one of the preceding claims,

characterized in that the separating element (4) runs substantially parallel to the part of the housing wall (5) adjoining the absorber volume (6), wherein a clear distance between the separating element (4) and the part of the housing wall (5) can be predetermined.

7. Thermosiphon system according to one of the preceding claims,

characterized in that on the separating element (4) and / or on the housing (5) at least one projecting and / or connected to the separating element (4) and / or the housing (5) and / or to the separating element (4) and / or to the housing (5) integrally formed element (14) for setting the clear distance between the separating element (4) and the part of the housing wall (5) is arranged.

8. Thermosiphon system according to claim 7,

characterized in that the element (14) is an essentially rigid element (14) during operation of the thermosyphon system for prescribing a clear minimum distance between the separating element (4) and the part of the housing wall (5).

9. thermosiphon system according to one of the preceding claims,

characterized in that the separating element (4) extends at least partially parallel to the part of the housing wall (5) adjoining the absorber volume (6), the clear distance between the separating element (4) and the part of the housing wall (5) being between 2 mm and 20 mm, in particular between 3 mm and 10 mm, in particular 4 mm.

10. Thermosiphon system according to claim 7,

characterized in that the element (14) is a variable in height during operation of the Thermosiphonsystems element (14) for changing the clearance between the separating element (4) and the part of the housing wall (5).

1 1. Thermosiphon system according to one of the preceding claims,

characterized in that the separating element (4) is designed as a thermal insulator.

12. Thermosiphon system according to one of the preceding claims,

characterized in that the housing is formed circular cylindrical and the separating element (4) has a C-shaped or Ω-shaped cross section and with its longitudinal edges (12, 13) on the inner wall (10) is supported.

13. Thermosiphon system according to claim 7,

characterized in that the separating element (4) extends beyond a central axis of the housing (2).