RU192396U1 - DESIGN OF THE HEAT EXCHANGER OF THE SOLAR VACUUM COLLECTOR - Google Patents

Abstract

The utility model relates to the field of thermal energy and is intended for energy supply of agricultural and individual facilities. In the design of the heat exchanger of the solar vacuum collector, including the collector tube, made in the form of a glass bulb having an external and internal wall, as well as the central cavity of the bulb formed by the surface of the inner wall, the space between the outer and inner walls being filled with vacuum, and placed inside the central cavity of the bulb thermal absorber, inside which a heat channel is fixed in contact with it, use a U-shaped glass tube as a heat channel, as a heat carrier I use air, as a heat absorber, use talc chlorite cylindrical washers placed on the heat channel, and a glass bulb is placed inside a protective aluminum cylinder having a longitudinal slit along the surface through which the heat absorber is heated by a focused light beam placed above the cylinder of the Fresnel lens. The utility model is aimed at increasing the maximum heating temperature of the heat absorber and increasing the duration of the return to the heat channel of the heat accumulated by the heat absorber. 2 ill. 1 tab.

Description

The utility model relates to the field of thermal energy and is intended for energy supply of agricultural and individual facilities.

A known design of the solar collector containing a vacuum tube made of two tubes, one of them, the inner one, is inserted into the outer one with a large diameter, the vacuum tube having a reflective element that regulates its thermal power and is made in the form of a plate of opaque heat-resistant and UV resistant material installed on the outer surface of one of the sides of the outer tube parallel to the axis of the vacuum tube and with the possibility of rotation around it, or a reflective element of the vacuum tube, made in the form of a strip deposited on the outer surface of the inner tube. The vacuum tube of the solar collector can be installed with the possibility of rotation around its axis (RF Patent No. 2527220 of 10.25.2012) [3].

The disadvantages of this design include the need for additional equipment of the vacuum tube with a mechanism for the periodic movement of reflective elements around the vacuum tube. All this significantly increases the cost of the design, and also eliminates the use of standard commercially available vacuum tubes.

Also known is the design of a heat exchanger containing a vacuum tube with an outer wall and an inner wall and located inside the vacuum tube along its length (coaxial with it) is a heat removal unit, consisting of coaxially arranged tubes, and between the outer surface of the heat removal unit and the inner surface of the vacuum tube heat-conducting elements supported by the external wall of the heat removal unit (or attached to the specified external wall) and pressed with prestress to the internal wall e vacuum tube (RF Patent №2382294 of 15.03.2005 r.) [4].

The disadvantages of this design include the complexity of the assembly of the heat exchanger elements, due to the need for precision placement of heat-conducting elements inside the vacuum tube. All this leads to an increase in operating costs of the design of the heat exchanger.

A heat exchanger of a solar vacuum collector is also known, including a collector tube made in the form of a glass flask having an outer and inner wall, as well as a central bulb cavity formed by the surface of the inner wall, the space between the outer and inner walls being filled with vacuum, and placed inside the central cavity of the bulb heat absorber, inside which a direct-flow thermal U-shaped channel (copper thin-walled tube) is fixed in contact with it, as a heat carrier, heated absorber Emer, water is used, and an aluminum cylindrical insert is used as a heat absorber, on the inner wall of which a U-shaped channel is fixed (Vacuum tube collector “Meibes MVK 001”; - URL: http://www.meibes.ru/system/ documents / files / 000/001/502 / original / Meibes_Flamco_2015_188.pdf? 1435963598.) [5].

The solar collector is a set of vacuum glass tubes with an absorber (aluminum cylindrical insert), inside each vacuum tube there is a U-shaped direct-flow heat exchanger. A heat carrier flows through the heat exchanger (in this design - water), which receives heat from the absorber heated by solar energy. For a greater concentration of sunlight, vacuum tubes are mounted on a mirror substrate.

The cylindrical shape of the tubes allows you to maximize the collection of sunlight, which at any time of the day or year is directed perpendicular to the axis of the tube - this greatly increases the efficiency of the entire system and allows even in very weak sunlight to heat the water in the hot water system.

Each individual block of the solar collector is connected (via fitting connections) to the collector (manifold) which transmits the heated coolant to a heat storage device (storage tank) having a heat exchanger. In this capacity, further transfer of heat carrier energy to external heat consumers occurs.

The solar panel shows the greatest efficiency with a bright day, when ultraviolet rays prevail. In cloudy weather, the collector mainly runs on infrared radiation, which is less powerful, but the collector will be able to maintain water in the right temperature conditions.

The disadvantage of this technical solution is that collectors using direct-flow thin-walled copper U-tubes cannot work under high pressure, quickly lose accumulated heat and provide high-quality heat transfer to the coolant only during the warm season.

Closest to the claimed technical solution is the design of the heat exchanger of the vacuum solar collector, including the solar collector tube, made in the form of a glass bulb, which has an outer and inner wall, as well as a central cavity formed by the surface of the inner wall, and the space between the outer and inner walls is filled with vacuum and inside the central cavity of the flask with the help of a stopper a copper heat pipe (heat pipe) is structurally fixed. In this case, the central cavity of the flask around the heat copper tube is filled. To ensure a longer period of operation of the system, the internal cavity of the tube (namely, the space around the heat pipe, which is located in the inner cavity of the bulb) is filled with a thermal absorber (8) - a heat-accumulating substance (aluminum powder). The filling of the inner space of the flask with a heat-accumulating substance is such that the outer surface of the heat copper tube is completely in contact and surrounded by this substance, moreover, this substance is completely adjacent to the inner surface of the inner wall of the glass bulb. The objective of this substance is the accumulation in its mass of thermal energy at a time when the tube is in working condition, i.e. lit by the sun. The amount of accumulated energy will be determined by the product of the mass of the heat-accumulating substance by its specific heat capacity.

After the tube is stopped illuminated by sunlight and, accordingly, the external energy is stopped, the energy accumulated in the heat-accumulating substance will be transferred through the heat pipe to the coolant, thereby ensuring the operation of the entire system.

A tube with a heat accumulator maintains its operability even in the absence of sun, which means that it helps to maintain the operability of the entire solar system without the sun for a certain amount of time.

The disadvantages of the considered technical solution include the low thermal energy efficiency of the design of the heat exchanger, due to the fact that the heat exchanger quickly loses the accumulated heat, and provide an acceptable level of heat transfer to the coolant mainly only during the warm season.

On the other hand, ethylene glycol used as a heat carrier has a boiling point of 197.3 ° C, and for the purpose of safe operation of the solar collector (to prevent the heat pipe from exploding due to boiling of the heat carrier), the temperature of the heat exchanger absorber is forcibly limited to this value.

The problem to which the claimed technical solution is directed is to increase the maximum heating temperature of the heat absorber and increase the duration of the return to the heat channel of the heat accumulated by the heat absorber.

This is achieved due to the fact that in the design of the heat exchanger of the solar vacuum collector, including the collector tube, made in the form of a glass bulb having an outer and inner wall, as well as a central bulb cavity formed by the surface of the inner wall, the space between the outer and inner walls being filled with vacuum and a thermal absorber is placed inside the central cavity of the flask, inside of which a heat channel is fixed in contact with it, characterized in that it uses a heat channel They use a U-shaped glass tube, air is used as a heat carrier, cylindrical washers made of talchochlorite placed on a heat channel are used as a heat absorber, and a glass bulb is placed inside a protective aluminum cylinder having a longitudinal slit along the surface through which the heat absorber is heated by a focused light a beam of Fresnel lens placed above the cylinder.

The technical result consists in increasing the maximum heating temperature of the heat absorber and increasing the duration of the return to the heat channel of the heat accumulated by the heat absorber.

The structural elements of the heat exchanger of the claimed utility model and the sequence of basic assembly operations of the heat exchanger (schematically) are shown in the drawing (figure 2), where:

1 - vacuum tube (glass flask);

4 - the outer wall of the vacuum tube;

6 - heat channel (U-shaped glass tube);

7 - cork;

8 - thermal absorber (a package of washers of talclochlorite);

9 - through holes in the washers for the heat channel;

10 - spring cylindrical bracket;

11 - an aluminum cylinder;

12 - longitudinal slit.

As a vacuum tube (1), a commercially available vacuum tube of the Shentai company model VTUBE_58 / 1800_EM [7] was used:

- tube length 1800 mm;

- inner diameter 58 mm;

- absorbent coating of the outer surface of the inner wall of the vacuum tube: SS-CU-AIN / ALN.

As a heat channel (6), a standard U-shaped glass tube made of borosilicate glass was used, the tube wall thickness was 1 mm, and the outer diameter was 18 mm. The distance between the axes of the parallel shoulders of the U-shaped glass tube is 25 mm.

- the design of the heat channel is made of glass instead of the expensive material - copper;

- instead of toxic ethylene glycol, a cheap and safe substance - air, is used as the energy carrier of the heat channel.

However, the main advantage of the design is the use as a thermal absorber of cylindrical talc chloride chlorine washers instead of aluminum powder.

The table shows that almost at identical values of the density and specific heat of the absorber materials, the claimed utility model is characterized by lower thermal conductivity compared to the prototype.

The consequence of this is a slower process of heat transfer by the absorber, i.e. long duration of storage of heat accumulated by the heat exchanger.

This conclusion is confirmed by the results of comparative tests of the claimed design with a prototype - a heat exchanger made using a vacuum tube with a heat channel in the form of a coaxial copper tube “Heat Pipe” (RF Patent No. 171104 from 06/13/2016 - prototype) [6].

The tests were carried out in two stages. At the first stage, the maximum values of the heating temperatures of the heat absorbers of the heat exchangers of the prototype and the claimed utility model (PR and PM, respectively) were determined.

The heat exchangers were insolated (direct sunlight), while the level of insolation was ~ (0.6 ÷ 10.7) kW )h / m ² .

The PR heat exchanger was exposed to direct solar radiation and reflected sunlight from a semi-cylindrical mirror placed under it, and the PM heat exchanger was irradiated with a focused light beam (from a Fresnel lens placed above the cylinder) through a gap in a protective aluminum cylinder.

The ambient air temperature during insolation was 12 ° C ± 1 ° C. At the same time, the masses of the heat absorbers of both structures were approximately the same and amounted to 9.6 kg and 7.9 kg, respectively.

The tests were carried out under conditions close to stationary heat transfer modes: there was no forced selection of heat accumulated in the heat accumulators through the heat channels of the tested heat exchangers, and heat losses due to re-radiation through the walls of the vacuum tubes were negligible and did not significantly affect the test results.

The measured temperature T ₁ (pr) of the PR object after ~ 2 hours reached the maximum permissible value of ~ 200 ° C, after which the insolation of the PR object was stopped.

After about the same time, a stationary heating mode of the PM object was established. In this case, the maximum temperature of the object T (pm) reached ~ 380 ° C, and did not increase during further insolation.

At the second stage of the tests, the time was determined for which the thermal absorbers of the PR and PM objects completely cool from the maximum temperatures of 200 ° C and 380 ° C to the ambient temperature, i.e. full return of thermal energy accumulated by thermal absorbers to the thermal channels of objects.

The calculated values of the thermal energy accumulated by the absorbers were Q _PR = 1793.3 kJ and Q _PM = 1875 kJ, respectively.

The tests were carried out indoors at an ambient temperature of T _CP = 20 ° C.

The measured values of the duration of heat transfer by the PR and PM objects (i.e., cooling to ambient temperature T _SR amounted to 2.0 hours and 3.9 hours, respectively.

The test results allow us to state that the energy efficiency of the heat exchanger of the claimed technical solution significantly exceeds the energy efficiency of the prototype heat exchanger: the maximum heating temperature of the heat absorber increased by 1.9 times, while the duration of the heat transfer to the heat channel accumulated by the heat absorber also almost doubled.

In the solutions of a similar problem known to science and technology, the use of a solar vacuum collector in heat exchangers to increase heat storage as a thermal absorber of talc chloride chlorine washers was not found.

Claims (1)

The design of the heat exchanger of the solar vacuum collector, including the collector tube, made in the form of a glass flask having an outer and inner wall, as well as a central cavity of the bulb formed by the surface of the inner wall, the space between the outer and inner walls being filled with vacuum, and inside the central cavity of the bulb is placed a thermal an absorber inside which a heat channel is fixed in contact with it, characterized in that a U-shaped glass tube is used as a heat channel, air is used as a heat carrier, cylindrical washers of talcchlorite placed on a heat channel are used as a heat absorber, and a glass bulb is placed inside a protective aluminum cylinder having a longitudinal slit along the surface through which the heat absorber is heated by a focused light beam placed above the cylinder of the Fresnel lens.

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