Absorber for solar collector

The invention relates to the field of heliotechnics and can be used in solar collectors for water heating and thermal energy production.

It is known the absorbent panel for the flat solar collector, which is made of aluminum profile, at the rear of which is mounted in the hole of the profile of the copper pipe о for the circulation of the thermal agent [1].

The disadvantages of this absorbent panel are that the high-angle incidence of direct sunlight or ambient light flow on the flat surface of the absorbent panel leads to reduced absorption rates of incident radiation fluxes, and the process of making the absorbent panel does not ensure an adequate thermal contact between the copper pipe and the aluminum profile.

It is known the absorbent panel for the flat solar collector, which includes о absorption surface of the incident solar radiation, the channel through which the heated agent circulates in the form of a metal pipe, which is placed behind the sheet or the corrugated sheet of thin metal, in which the transfer heat to the heated thermal agent from the channel is made through thermal bridges, which have rigid mechanical and thermal contacts with the tips of the corrugated sheet and the pipe with heated thermal agent [2]. '

The disadvantage of this absorbent panel lies in the reduced surface of heat transfer from the corrugated film through the thermal bridges made of small diameter wire and the outer surface of the pipe (channel) with heated agent. The corrugated sheet of aluminum or copper has a thickness of 0.03 mm and a length of 1250 mm, which creates great difficulties in forming rigid mechanical and thermal contacts with the tips of this sheet, as well as in ensuring the mechanical rigidity of the constructive element formed by the corrugated sheet. . At the same time, the formation of the thermal contacts of the thermal bridges of the wire with the corrugated tips of the foil presents a very difficult technological problem, which undoubtedly raises the cost of such solar collectors, because it is necessary to make hundreds of thermal contacts with the corrugated foil.

The most appropriate solution is the absorbent panel of the flat solar thermal collector, made up of two corrugated interlocking plates, which together form the circulation channels of the heated thermal agent, which are in the form of pipes consisting of two semi-cylindrical sheet surfaces with horizontal longitudinal outer ribs, which together with the semisurface of the channel, it forms the absorption surface of the energy of the solar incident flow. The flat portions and the horizontal ribs have mechanical contact points in the middle of the flat parts of the absorbent elements. The size of the absorbent panel in the solar thermal collector between the contact points of the planar portions determines the surface area (capture) of the solar energy and has an impact on the mechanical rigidity of the collector [3].

The disadvantages of this solution consist in the reduced heat absorption capacity of the solar incident flow due to the small area of ​​the absorbent surface and the low efficiency of the lateral irradiation, as well as the small value of the ratio between the absorbent surface and the volume of the heated agent in the pipe of the absorbent panel, which influences the dynamics of the heating process of the thermal agent.

The problem solved by the present invention is to increase the capacity and uniformity of absorption of solar radiation throughout the day without following the sun.

The absorber for the solar collector includes three troughs, each with a о arc-shaped portion in the section, fixed between them with the convex part pointing inwards along longitudinal lines with the formation of a channel for the circulation of the thermal agent, and with lateral portions, executed at the level. lines. The lateral portions of the adjacent troughs are fixed to each other with the formation of longitudinal ribs, located at an angle of 120 ° to each other. The lateral portions of the troughs can be executed at an angle of 30 ° to the chord of the wedge-shaped portion of the troughs.

This combination of elements ensures the conditions of uniform absorption of solar radiation by the absorber, due to the fact that it includes three longitudinal ribs located at an angle of 120 °. The nerve of the absorber is oriented at the zenith. As a result, at small angles of incidence of the solar radiation flux the energy is absorbed by the oriented rib in the plane of the zenith point section. When the sun rises, the rate of absorption of the flow by the nerves located at angles of 120 ° to the longitudinal rib oriented towards the zenith increases. When reaching the zenith position, the energy is absorbed only by the nerves located at an angle of 120 °. At the crossing of the zenith point, the share of energy absorbed by the zenith-oriented nerve begins to increase again. Thus, during the day there is a redistribution of the rates of radiation flux captured between the nerves

MD 908 Z 2016.02.29 longitudinal of the absorber. As a result, the amplitude of the variation of the captured power of the radiation flux does not exceed the value of 0.067, whereas in the case of the nearest solution, this variation of the average power constitutes about 0.36 of the maximum value of the power at the location of the reduced sun.

The invention is explained by the drawings in FIG. 1-7, which represents:

FIG. 1, the absorber diagram for the solar collector, cross section;

FIG. 2, the schematic of the absorber for the solar collector with the portion angle In the form of a wax arc of the gutter greater than 60 ° and less than or equal to 180 ° with the indication of the longitudinal ribs;

FIG. 3, the schematic of the absorber for the solar collector with the wedge-shaped portion of the gutter arc greater than 60 °, indicating the longitudinal ribs executed at an angle of 30 ° to the wedge-shaped portion of the gutter wedge;

FIG. 4, the geometrical diagram of the gutter with the lateral portion executed at an angle of 30 ° to the rope of the portion in the form of an arc of wax of the gutter;

FIG. 5, schematic diagram of the absorber for the solar collector by cutting from the pipe with diameter D of six troughs;

FIG. 6, the schematic diagram of the absorber for the solar collector by cutting from the pipe with diameter D of three troughs;

FIG. 7, schematic diagram of the absorber for the solar collector by cutting from the pipe with diameter D of two troughs.

The absorber for the solar collector includes three troughs, each with a о arc-shaped portion In section 4, fixed between them with the inwardly convex part along the longitudinal lines 5 with the formation of a channel 9 for the circulation of the thermal agent, and with lateral portions, executed at the level of lines 5. The lateral portions of the adjacent troughs 4 are fixed to each other with the formation of longitudinal ribs 10, located at an angle of 120 ° to each other. The dimensions of the longitudinal ribs 10 are determined by the central angle of the side portion 7 and the distance between the longitudinal lines 5 and the edge of the gutter 2. The lateral portions of the gutter can be executed at an angle of 30 ° to the string of the m-shaped arc of the gutter.

The solar collector absorber works as follows.

In the morning the sun is to the left of the absorber, which is positioned so that the vertical longitudinal rib 10 is oriented towards the zenith (see fig. 1). The sun at this time of day is also on the left side of the absorber shown in fig. 2 and 3. In this position, the radiation flux of the sun is absorbed by the illuminated surface on the left side of the vertical plane of symmetry of the absorber, namely by the arc-shaped porphyry in section 4 of the gutter, which forms channel 9 for the circulation of the heated thermal agent. of the absorber. The heat absorbed by this portion is transmitted to the thermal agent, which flows through channel 9. From channel 9 the heated thermal agent is transmitted to the consumer. This process is carried out until the moment that corresponds to the passage of the sun from the zenith point. After the sun passes the zenith point, the solar radiation is absorbed by the arc-shaped porphyry in the section 4 of the gutter, which forms the channel 9 of the absorber, located to the right of the seephony plane, which passes through the zenith point (see fig. . 1). The sun in this time of day is on the right side of the vertical plane passing through the zenith point and the absorber shown in fig. 2 and 3. The heat absorbed by the surface of the portion 4 located on the right side of the vertical plane, which passes through the zenith point and the longitudinal rib, coinciding with this plane, is transmitted to the thermal agent, which flows through channel 9. From channel 9 the thermal agent heated is transmitted to the consumer. Fixing the portions 4 along lines 8 ensures the mechanical rigidity of the absorber construction. The movement of the fixing lines 8 from the circulation channel 9 of the thermal agent ensures the protection of the construction of the absorber when changing the volume of the thermal agent conditioned by the variation of its temperature, for example as a result of its freezing. Lines 5 represent the granules of channel 9 with thermal agent. In various positions of the sun on the celestial vault on portions 4 there are areas where the sun's rays fall perpendicular. As a result, a high degree of uniform absorption of the radiation of the incident light flux throughout the day is ensured, thus ensuring the solution of the invention problem.

In the proposed absorber and intended for use in the flat solar thermal collector, the mentioned disadvantages are excluded by modifying the constructive realization of the absorber regarding the formation of the circulation channel 9 of the thermal agent and the surface of the absorption of the solar radiation and the spatial location of the ribs 10, which ensures the increase of the absorption surface of the solar energy, including, for high values ​​of the lateral solar irradiation angle. The absorber is made of three troughs, each with о arc-shaped portion in section 4, which have

MD 908 Z 2016.02.29 the length of the spring I = 2nR-, where GC is the portiumil angle in the shape of a wax arch, R 360 ° 'the radius of the circumference of the cross section of the pipe with diameter D. The gutters are made by cutting the pipe with the diameter Dpe line, which represents the edge of the trough 2. Six, three or two troughs can be made from a pipe with diameter D. The manufacture of the absorber is performed by rigidly fixing three troughs, which are mounted with the convex surface facing inwards and with the concave surface on the outside. Installation and fixing of the gutters in the absorber is performed by soldering, welding or gluing along the longitudinal lines 5. At the installation of three troughs and their mechanical rigid fixation on lines 5, the circulation channel 9 is formed for the thermal agent, which in the cross-section has the form of an equilateral curb triangle. The length of the side of this curvilinear triangle is equal to the length of the wedge-shaped portion with an angle equal to 60 °. The concave surfaces of two troughs, which are oriented outwards, represent the surfaces of absorption of the solar radiation, and their chords form an angle of 60 °. The third gutter represents the back of the absorber and its surface oriented outside is not affected by the sun's rays, because it is shaded by the first two troughs with absorbing outer surfaces of the solar radiation. In case of the pipe with diameter D three troughs are made, when they are installed in the absorber composition, three longitudinal ribs 10 are formed by the lateral portions of the troughs. In the case of three troughs being cut from the pipe, the angle of the wedge-shaped portion is 120 °, and when making only two troughs from the pipe, this angle is equal to 180 °. When installing three troughs, lines 5 will permanently coincide with the edges of the wax-shaped portions of the trough with an angle equal to 60 °. Portions of the surface of the troughs for which the angle is greater than 60 ° contribute to the increase of the surface of absorption of the solar radiation, as a result of the formation of the longitudinal ribs 10 of the absorber. At the same time, the longitudinal ribs of the absorber formed by troughs contribute to the increased mechanical rigidity of the absorber. The mechanical rigidity is ensured by the longitudinal ribs 10 and the shape of the channel 9. One of the absorber troughs is shaded by solar radiation by the other two, which are intended to absorb this radiation, because they are oriented towards the sun. In order to reduce the heat loss, the concave surface of the shaded trough is covered with thermal insulation material. The spatial orientation of the longitudinal ribs 10 forms the recessed Y symbol. Increasing the height of the ribs 10 by increasing the value of the angle of the wedge-shaped portion of the gutter above 60 ° ensures the increase of the absorption surface without increasing the cross-sectional area of ​​the channel 9. This method of constructing the longitudinal rib absorber 10 contributes to increasing the ratio of the absorption surface area to the volume of the thermal agent in channel 9.

The absorber can be made from metal sheet troughs and from transparent optical material troughs, but with obvious thermal insulation properties. Thermal insulation troughs have the same geometric profile or one identical to the profile of metal sheet troughs. The concave surfaces of the metal sheet troughs can be covered with a selective absorbent layer, which contributes to the increase of the absorption performance of the incident solar radiation. The heat insulation troughs lining the absorber made of sheet metal and thus ensure the reduction of heat losses following the processes of thermal convection by increasing the value of the thermal resistance coefficient of the absorber. The thermal insulation trough shaded by the troughs capturing the solar radiation can also be made of non-transparent optical material. There are no special requirements regarding the stiffness of ultraviolet radiation with respect to the thermal insulation material, because it is shaded by the thermoconductive absorption surfaces of the metal. This leads to the increase of the efficiency of the absorption of the solar energy and its transfer to the thermal agent, which has direct contact with the walls of the channel, as a result of diminishing the losses of convection of the thermal energy on the surface of the absorber.

The absorber with the spatial configuration of the restrained Y symbol can be equipped with a о tire of transparent optical material. This tire is made, for example, by wrapping the absorber with о film of transparent plastic or other material, for example glass, which is rigid for the ultraviolet component of the spectrum of sunlight, so it is stabilized. Providing the absorber with a transparent tire for solar radiation leads to the increase of the efficiency of the absorber as a result of diminishing the convection losses of the thermal energy provided by the tire.

The lifting capacity and uniformity of absorption of the solar energy of the absorber during the day without following the sun are conditioned by the fact that the absorber is made of three cylindrical troughs mounted with the concave surfaces of absorption of the solar energy In the outside, and with the convex surfaces in the interior forming a similar geometric figure

MD 908 Ζ 2016.02.29 Y symbol with vertical longitudinal rib oriented towards zenith. In the center of the figure Y recumbent is channel 9 for the thermal agent with the cross-sectional area of ​​the curblinear triangle formed by the wedge-shaped portions of the trough equal to 60 °, and the lateral portions of the troughs corresponding to the angles (Ct -60 °) / 2 forms three longitudinal ribs 10 located at equal angles, where CL is the angle of the wedge-shaped portion of the gutter, made by cutting the pipe with diameter D. The value of this angle is within the limits of 60 ° <CL <180 °, and the most reasonable values ​​in terms of the use of consumable mortar when making the absorber are considered the values ​​of angles equal to: CL = 120 ° and a = 180 °. '

The increase of the heat efficiency transmitted to the thermal agent circulating through the channel 9 of the longitudinal rib absorber 10 is ensured by the direct thermal contact of the thermal agent with the heat transfer surface, and the reduction of the heating agent's heating time is ensured by the higher value of the surface ratio. of absorption to the volume of the thermal agent in channel 9.

Increasing the efficiency of the absorber is also ensured by placing it in a tire of optically transparent thermal insulation material, for example, by wrapping the absorber with о plastic film, which reduces the loss of heat convection on the outer surface of the absorber or by lining it. metal absorber with troughs of the same shape, made of plastics with reduced thermal conductivity, of which two lining elements covering the concave absorption surfaces are optically transparent.

The simplification of the construction and manufacturing technology, as well as the increased mechanical rigidity of the absorber as a result of the demands caused by natural phenomena, for example, low temperatures, is done by using the troughs with the profile in the cross-section of the brake line, in which the lateral portions of the troughs can be executed at an angle of 30 ° to the rope of the porch in the form of a bow of the troughs.

The result of the invention consists in increasing the efficiency of the absorber without the pursuit of the sun. The use of concave surfaces for the absorption of solar radiation, as well as the inclusion in the construction of the absorber of three longitudinal ribs 10 located at an angle of 120 ° to each other, contributes to a much smaller variation of the solar flux captured by the absorber depending on the position of the sun. on the celestial vault. The installation of three troughs with the convex surfaces inside when making the absorber ensures a better ratio of the absorption surface of the solar radiation to the volume of the heated thermal agent in the circulation channel 9. This contributes to the improvement of the heat transfer conditions in the proposed absorber compared to the proposed absorber. the nearest solution, as well as to reduce the heating time of the thermal agent. This ensures the intensification of the heat transfer processes in the proposed absorber. The proposed solution for constructive construction of the absorber also ensures the simplification of the technology of production of these components used in solar collectors, because the absorber can be made from standard elements made from sub-metal strips by bending their lateral portions at an angle of 30 °. The fixing of the troughs and the hermeticization of the channel 9, through which the thermal agent circulates in the absorber, is done by the local welding on the longitudinal line 5, which determines the inner boundary of the longitudinal rib, so on the line of bending of the lateral portions of the troughs or with the displacement of this fixing line. of the gutter to the periphery of the longitudinal ribs. This manufacturing solution excludes the deterioration of the absorber, when installed in solar collectors. Due to this property, it is ensured that the operating expenses and losses of the thermal agent are diminished at the time of the season's leakage and leakage. The formation of a tire by winding on the longitudinal ribs of the absorber of an optically transparent film makes it possible to reduce the heat loss through convection, as well as to increase the thermal efficiency of the absorber with minimal technological costs and efforts.

Also the result of the invention consists in that the absorber allows to obtain a uniform characteristic of the absorption of the energy of the solar radiated flux throughout the day for all the positions of the sun in the celestial vault. This is impossible for flat thermal solar collectors, because to ensure uniform capture of solar radiation throughout the day it is necessary for the absorption surface to follow the sun.

For example, for the geometry of the absorber with the equivalent value of the absorption surface for the case of the equilateral triangle profile oriented with a peak of the zenith triangle, which also has the similar section of the absorber, the maximum deviation of the solar radiation flux absorbed during the whole day does not exceed 14. % of the maximum possible absorption value of о flat surface, which follows the sun. As a result of the harmonic character of the evolution of the solar radiation flux

MD 908 Ζ 2016.02.29 absorbed, the absorber will absorb about 93% of the maximum characteristic value for the position of the sun at the zenith and the respective orientation of the absorber.

For the collectors, the daily average plane of the absorbed energy power constitutes 0.637 of the value of the solar radiation flux in the zenith position of the sun. For the proposed absorber, the amplitude of the oscillations of the absorbed flux during the day is at the level of 0.067 from the amplitude of the solar radiation flux at the zenith position, whereas for the case of the absorber with the flat surface and the installation of the circulation beam of the thermal agent behind this capture surface, in the absence of the sun tracking actions, the value of the captured power of the solar radiation varies from zero to the maximum characteristic value for positioning the sun at the zenith point.

Because during the day three periods of oscillation of the magnitude of the radiation flux absorbed by the proposed absorber are distinguished, the average value of the absorbed solar radiation flux constitutes 0.933 of the maximum value. For these reasons the proposed absorber will have a higher efficiency of capture during a day of solar radiation compared to the absorber according to the nearest solution. Quantitatively this efficiency is characterized by the following report:

(0.933 / 0.63) = 1.465. Therefore, the absorbers made on the basis of the proposed solution provide an increase in fish

46% of the absorption capacity of the solar radiation during the day compared to the absorbers used in the flat solar thermal collectors.

The possibility of making absorbers from thin metal strips by bending the lateral portions at an angle of 30 ° simplifies the manufacturing technology, ensuring a good ratio between the absorption surface of the solar radiation and the volume of the heated thermal agent.

All the indicated signs of the technical solution proposed for constructive construction of the absorber ensure the solution of the problem regarding the lifting of the uniformity of absorption of the solar radiation during the day without following the sun.

(56) Bibliographic references cited in the description: