WO2016124207A1

WO2016124207A1 - Energy absorber provided with a tube having s-shaped curves for use in solar collectors

Info

Publication number: WO2016124207A1
Application number: PCT/DZ2016/050003
Authority: WO
Inventors: Yassine DEMAGH
Original assignee: Demagh Yassine
Priority date: 2015-02-04
Filing date: 2016-02-04
Publication date: 2016-08-11

Abstract

The invention relates to an energy absorber (1) for absorbing solar radiation and transferring said solar radiation energy to a heat-transfer fluid (4) which flows inside at least one central tube (2) located in the energy absorber. The central tube has at least one S-shaped curve (figure 2A and figure 2B), otherwise it has at least one combined "S/straight" shape (figure 2C). The central tube (2) includes a surface coated with at least one absorbent selective coating layer in order to absorb the most solar radiation possible. The central tube (2) is surrounded (3) by at least one shell tube (31). The shell tube includes at least one surface which is transparent to solar radiation. The shell tube includes at least one inner surface. The central tube and the shell tube may optionally be positioned coaxially, creating an inner space bounded by the surface of the central tube and the inner surface of the shell tube (3). At least one unit for collecting solar radiation comprises at least one reflective inner surface for directing the solar radiation towards the central tube arranged inside the energy absorber. The solar collector includes a parabolic mirror (6) having a reflective surface (6E) for directing the radiation toward the focal line (7) of the reflective surface (6E), the reflective surfaces optionally being Fresnel mirrors. The energy absorber may optionally be positioned on the focal line of the reflective surface.

Description

1. Title of the invention

Energy absorber provided with a tube having curved "S" shapes for use in solar collectors.

2. Technical field to which the invention relates The invention is characterized by an energy absorber provided with a tube having at least one curved "S" shape, otherwise it has at least one combined form "S / Right" . Similarly, the invention relates to a solar collector equipped with the absorber just cited. This invention is used in the field of solar capture and especially in installations with solar radiation energy concentration. 3. State of the prior art

Solar concentrator technology involves concentrating and converting solar radiation into useful thermal energy for the purpose of generating electricity; taking the example of a cylindro-parabolic whose reflective surfaces concentrate the solar radiation, which reaches them, along a focal line, where is installed the absorber which has the function of absorbing the incident solar radiation and of convert it into useful heat via a coolant that flows into the central tube.

To date, the absorbers used in this field have straight cylindrical tubes. They generally consist of a metal tube with or without selective coating, installed and kept under vacuum in a second glass tube. The glass tube could be provided with a special coating that would allow transmission of almost all of the radiation while emitting virtually no energy. At both ends are bellows of dilations and metal / glass joints. In order to maintain the absolute vacuum created between the glass tube and the metal tube, a "Getters" or a gas trap is often installed which absorbs any gases that may remain. In the current level of technology, this type of absorber has the disadvantage of a low thermal efficiency which limits its operation.

Another disadvantage is the large temperature gradient in the solid wall of the cylindrical tube containing the coolant. The main reason is the concentration of solar radiation on specific areas. This unfavorable temperature gradient will favor the appearance of cracks on the central tube and will have the main effect of reducing its service life. 4. Purpose of the invention

The object of the present invention is to intensify the heat exchange and to increase the efficiency of solar radiation energy absorbers.

Another objective is the reduction, in the azimuthal (circumferential) direction, of the temperature gradient in a considerable way so as to prolong the lifetime of the central tube and the absorber.

These objects will be made according to the invention presented in the claims.

5. Statement of Figures

Our invention is illustrated and explained by way of indication and not limitation, by appended drawings. Are represented:

FIG. l. Schematic of a cross section of the absorber with a circular cross section;

FIG. 2. Schematization of three examples of the possible configurations of the absorber,

FIG. 2A- Presents a curved variant in the shape of "S";

FIG. 2B and FIG. 2C - Present two combined variants "S / Right".

- FIG.3. Schematization of an example of a solar collector-cylindro-parabolic mirror with the absorber provided with a tube having curved shapes in "S".

6. Presentation of the essence of the invention

An energy absorber is provided for the absorption of solar radiation and the transfer of this energy from solar radiation to a heat transfer fluid flowing inside at least one central tube of said energy absorber. The energy absorber 1 will have the role of absorbing solar thermal energy and transfer it via the central tube 2 to a heat transfer fluid 4 which flows inside. The energy absorber 1 mainly comprises:

• a central tube 2 which has at least one curved shape in "S", otherwise it has at least one combined form "S / Right". The facet 2E of the central tube 2 is coated with at least one layer of selective coating to absorb the maximum energy of solar radiation; and • an envelope tube 3 made of transparent materials. Its outer face 3E could be coated with at least one layer of antireflection coating.

As a consequence of what has preceded the distribution of the energy density on the external facet 2E of the new central tube 2 will be better distributed, the circumferential gradient of this flow density will decrease causing in turn an appreciable temperature gradient of the solid wall of the central tube 1 and a longer life.

The spacing 5 bordered by the faces 2E and 31 is kept under vacuum.

The central tube 2 and casing tube 3 could be positioned coaxially or not. the energy absorber 1 could be positioned on the focal line 7.

Curved pipes are present in various industrial applications, such as heat exchangers. The importance of this equipment lies in the presence of a secondary flow configuration, which significantly promotes the exchange rate and transfer, mass, heat and the amount of movement of the mixture. To exploit these phenomena in the solar, a configuration of a pipe having at least one section of longitudinally curved tube "S" is proposed. Until then, the linear concentration solar collectors only used energy absorbers fitted with straight cylindrical tubes. The straightness of the focal line, a consequence of the shape of the reflecting surfaces that concentrate all the solar radiation on this line, has favored the use of straight cylinders. The determination of the heat flux density distribution on the outer face of these straight cylinders is widely known and controlled.

This curved shape "S" could possibly be combined with sections of cylindrical tubes that would again constitute another configuration, not at least conventional, called combined sections "S / Right".

The "S" specification used in the context of this invention is a general term characterizing curved and longitudinally curved shapes. A special case of these "S" curved forms is the sinusoidal form which obeys well-established mathematical laws and well-known trigonometric functions, in the image of the sine and cosine functions. The exploitation of these mathematical laws might be more appropriate to describe the "S". These curved "S" shapes, generally or sinusoidal in a particular way, are characterized by a peak-to-peak amplitude Δ and a periodicity length λ, or FIG. 2. These two characteristics may vary along the central tube 2 of the energy absorber 1. · The possible configurations of this type of absorber consisting of a central tube formed of curved section "S" or combined sections " S / Right "are so simply designed that they could replace the old absorbers without making any changes to the metal structure of the solar collectors already in use.

• The cost of maintenance and know-how remain unchanged compared to conventional absorbers, if not longer life and better performance.

• Any closed curve could be a possible shape of the cross section of the central tube 2, but it would favor the adoption of a shape is circular or oval, or a slice of these two sections (example: semi-circular , 1/3 circular, ½ oval). "The heat transfer fluid 4 could be a liquid, a gas or a liquid-gas mixture. The coolant could have a certain level of nanoparticles to further improve the exchanges.

• Operating temperatures could be low, medium or high, with or without phase change.

· FIG. 2A. illustrates one of the possibilities of a energy absorber provided with a tube consisting of curved "S" shapes.

FIG. 2B and FIG. 2C illustrate two possibilities of an energy absorber provided with a tube consisting of curved shapes combined "S / Right".

• In addition to what has been described above, a solar collector is provided. The solar collector has at least one reflecting surface 6 which reflects and concentrates solar radiation on the focal line 7. The focal line is a consequence of the shape of the reflecting surface. A part of the reflected and concentrated solar radiation on the focal line 7 will be absorbed by the absorber 1 via its central tube 2 for the transfer to the heat transfer fluid 4 which flows inside.

· The reflective plane 6 could be a mirror in parabolic form. Otherwise the reflecting surface is a Fresnel mirror.

Claims

/. Claims (5)

An energy absorber (1) for absorbing the solar radiation energy and transferring it to a coolant (4) which may be located within at least one central tube (2) constituting one of the elements of the energy absorber (1). the energy absorber (1) is characterized by:

- A central tube (2) of solid materials whose thickness consists of at least one layer of solid materials;

- The central tube (2) which takes the form of one or more curved configurations in

"S", otherwise the central tube (2) will take the combined form between one or more "S" curved configurations and one or more configurations of straight cylindrical shapes;

- The surface (2E) of the central tube (2) can be coated with at least one layer of selective coating for better absorption of solar radiation energy;

- The central tube (2) is enveloped by at least one envelope tube (3) which is at least partially transparent to solar thermal energy;

- The casing tube (3) comprises at least one wall of the casing tube (3E) which is transparent to solar radiation;

- The casing tube (3) comprises at least one inner casing surface (31); and

- The central tube and the casing tube may or may not be arranged coaxially with each other; a space (5) delimited by the face of the main tube and the inner face of the casing tube is disengaged from this arrangement.

The energy absorber characterized in accordance with claim 1, wherein the envelope tube may comprise glass.

The energy absorber according to claims 1 or 2, wherein the internal space (5) is evacuated.

A solar collector (8) which is characterized by:

At least one mirror (6) having a reflective surface (6E) for directing sunlight (11) onto the focal line (7) of the reflecting surface (6E); and - At least one energy absorber (1) characterized according to one of claims 1 to 3, would be installed on the focal line (7), and further characterized according to claim 4, wherein the mirror is a parabolic mirror or a Fresnel mirror.

- A solar collector according to one of the above claims is characterized by use in a solar thermal power plant to convert solar thermal energy into electrical energy, in which the solar collector is used to absorb solar radiation energy .