JP2008309402A - Heat collecting method and heat collecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar heat collecting means capable of saving energy by dispensing with power, reducing costs by simplifying a device constitution, and achieving high recovering temperature even in winter. <P>SOLUTION: This heat collecting device comprising a solar-heat heating device provided with a closed circuit 1 for circulating working fluid mainly composed of CO<SB>2</SB>, and collecting heat in the working fluid, and a heat exchanger 3 recovering heat from the working fluid in which heat is collected, comprises the heat exchanger 3 for recovering heat retained by the working fluid w, liquefying the same, and forming a liquid head pressure H by the working fluid 2 at an outlet side by having the difference in heights between an inlet side where the working fluid w flows in and the outlet side where the working fluid w flows out, and the solar-heat heating device 2 disposed in the closed circuit 1, and collecting heat in the liquefied working fluid 2 to keep the working fluid w at the outlet side in a supercritical state, and natural circulation of the working fluid 2 is formed in the closed circuit 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a solar heat collecting method and apparatus in which a closed circuit in which a working fluid containing CO ₂ as a main fluid circulates is formed. The working fluid can be circulated without power, and solar heat can be collected efficiently and used at low cost. It is a thing.

  In recent years, research on the development and practical application of new energy sources to replace fossil fuels has been conducted against the background of environmental pollution problems such as global warming due to greenhouse gases and the problem of exhaustion of fossil fuels. Among them, solar energy is poured almost all over the earth, and the amount of energy is overwhelmingly large and inexhaustible compared with other natural energies. Has been made.

  The effects of using natural energy, including solar energy, include energy saving and carbon dioxide emission reduction, but the challenges in using solar energy include reducing the installation area of solar thermal utilization systems, improving the heat collection rate, and lowering the price. Is desired.

The present applicants have previously proposed a solar system that enables simultaneous power generation, cold / hot heat, and hot water supply using solar energy in Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-263944). This system uses CO ₂ , NH ₃ , H ₂ O, hydrocarbon-based natural refrigerant as the working fluid, and a pump-up unit that uses the liquefied working fluid as a supercritical pressure fluid. An evaporator as a high-temperature supercritical pressure fluid, an expansion turbine that adiabatically expands the high-temperature supercritical pressure fluid to form a low-pressure gas and generates power, heat recovery from the low-pressure gas and liquefaction and supercritical, near supercritical, And a heat recovery device that forms a subcritical working fluid.

JP 2004-263944 A

  The solar system disclosed in Patent Document 1 requires a pump power for forcibly circulating a working fluid in the system, and has a problem that the apparatus becomes large, and the equipment cost and the maintenance cost become high.

  In general, the solar heat utilization system has a problem that the heat collection efficiency is poor and the capital investment is increased. In particular, the recovery temperature in winter is low, and it is necessary to catch up when using it. Moreover, like the system disclosed in Patent Document 1, power is required for the heat collection itself, and further, there is a problem that batch-type heat recovery is inferior in terms of usability.

  In view of the problems of the prior art, the present invention is a solar heat collecting means that can save energy without requiring motive power, can simplify the apparatus configuration and reduce the cost, and can obtain a high recovery temperature even in winter. It aims at realizing.

In order to achieve this object, the heat collection method of the present invention comprises:
In a heat collecting method for forming a closed circuit in which a working fluid having CO ₂ as a main fluid circulates and recovering heat from the working fluid collected by a solar heating device using a heat exchanger,
Forming a liquid head pressure by the working fluid on the working fluid outflow side of the heat exchanger by creating a difference in height between the inflow side and the outflow side of the working fluid in the heat exchanger;
A natural circulation of the working fluid is formed in the closed circuit by bringing the working fluid on the outlet side of the solar heating device into a supercritical state by collecting heat from the solar heating device.

Moreover, the heat collecting apparatus of the present invention is
In a heat collecting apparatus including a solar heating device that forms a closed circuit in which a working fluid having CO ₂ as a main fluid circulates and collects heat in the working fluid, and a heat exchanger that recovers heat from the collected working fluid ,
Heat exchange that collects and liquefies the retained heat of the working fluid and creates a head pressure with the working fluid on the working fluid outflow side by creating a level difference between the working fluid inflow side and the working fluid outflow side And
A solar heating device that collects heat into the liquefied working fluid interposed in the closed circuit and brings the working fluid on the outlet side into a supercritical state,
The closed circuit is configured to form a natural circulation of the working fluid.

In the method of the present invention, a working fluid whose main fluid is CO ₂ is used. The specific heat of CO ₂ decreases as the pressure increases, and it becomes easier to collect heat particularly at high temperatures. In addition, the viscosity does not change significantly even at high pressure and high density, it becomes supercritical at the critical point (pressure 7.3 MPa, temperature 31 ° C.) or higher, and the viscosity decreases in the supercritical state. When the closed circuit arranged in the circuit is circulated, the moving power can be reduced. Then, the retained heat of the working fluid is recovered by the heat exchanger, the working fluid is liquefied, and the liquid head pressure of the working fluid liquefied in the closed circuit at the outlet of the heat exchanger is formed, thereby closing the working fluid. The circuit is naturally circulated. Therefore, it is not necessary to provide a physical forced circulation device with the compression or lifting action of the working fluid in the closed circuit.

  In the apparatus of the present invention, a head pressure is generated by the working fluid in the closed circuit on the outflow side of the working fluid by providing a difference in height between the inflowing side of the working fluid and the outflow side of the working fluid in the heat exchanger. Thus, the working fluid is naturally circulated in the closed circuit.

In addition, since CO ₂ is liquefied or gasified in the normal temperature range, a natural circulation flow can be formed without power by utilizing the phase change in the vicinity of the normal temperature range, and heat transfer is continuously performed by this circulation flow. be able to.

As described above, in the present invention, the working fluid having CO ₂ as the main fluid is used, and the liquid head pressure is formed by the working fluid on the outlet side of the heat exchanger that recovers heat from the working fluid. By making the working fluid in a supercritical state on the side, the natural circulation of the working fluid is formed in the closed circuit, and thereby the working fluid is circulated without power, thereby simplifying the device configuration, saving energy and reducing the The cost is realized.

  In the method of the present invention, when at least a portion of the heat collecting tube provided in the solar heating device until heating of the working fluid starts and changes to the supercritical state is arranged to have an upward gradient toward the downstream side in the flow direction of the working fluid. Good. If comprised in this way, the rising force which the working fluid which became the supercritical state by the phase change (liquid-> supercritical state) of the working fluid in the heat collecting tube which makes this upward gradient will go to the exit side of a solar heating apparatus will be carried out. appear. This ascending force serves to help the formation of a natural circulation in the closed circuit.

  Because the amount of solar heat collected by the solar heating device varies from day to day, or due to seasonal fluctuations, the amount of heat collected from the solar fluid varies depending on the season. It is necessary to prevent becoming. In the method of the present invention, the presence or absence of a supercritical state of the working fluid is detected by a detector provided in the closed circuit on the outlet side of the solar heating device, and the outlet side of the solar heating device and the heat exchanger are detected according to the detection result. The supercritical state of the working fluid may be always formed in the closed circuit on the outlet side of the solar heating device by adjusting the opening degree of the flow rate adjusting valve provided in the closed circuit connecting the inlet side.

  As a result, a supercritical state of the working fluid can always be formed in the closed circuit on the outlet side of the solar heating device, so the amount of heat collected from the working fluid is increased, the working fluid is heated to a high temperature, and the heat recovery efficiency in the heat exchanger is increased. Alternatively, it is possible to prevent the closed circuit from becoming a high pressure by controlling the circulation amount of the working fluid. For this reason, the temperature of the heat recovery fluid can be controlled to a required temperature according to the application, or a high temperature heat recovery fluid can be obtained even when the amount of solar radiation from the sun is small in winter.

  The detector for detecting the presence or absence of the supercritical state of the working fluid is a device that measures the amount of solar radiation and calculates the amount of heat collected by the solar heating device from the amount of solar radiation, or the entrance and exit of the solar heating device. The temperature difference or pressure difference of the working fluid is measured, and the temperature or pressure of the working fluid at the outlet of the solar heating device or the device that calculates the heat collection amount of the solar heating device from the measured value is detected and the detected value A device for detecting the supercritical state of the working fluid can be applied.

Further, in the method of the present invention, preferably, as the working fluid, the dimethyl ether with respect to CO ₂ and CO ₂ may be used a material obtained by blending 1 to 35 mol%. When heat recovery is performed by circulating the heat recovery fluid in the heat exchanger, the temperature of the heat recovery fluid supplied to the heat exchanger becomes higher when the amount of heat collected by the solar heating device is large in summer, etc. In some cases, the condensation of the working fluid in the heat exchanger becomes insufficient.

When dimethyl ether is added to CO ₂ as a working fluid, dimethyl ether dissolves in CO ₂ . As a result, the boiling point of the working fluid rises more than when only CO ₂ is present.
Although the critical temperature of carbon dioxide is 31.05 ° C., the condensation temperature of the working fluid can be increased by adding dimethyl ether. This makes it easy to condense even if the temperature range of the working fluid increases. Accordingly, the working fluid is easily liquefied in the heat exchanger and the liquid head pressure is easily formed, so that natural circulation in a closed circuit can be stably formed.

In addition, by blending dimethyl ether CO _2, it is possible to reduce the pressure of the working fluid. CO ₂ has a physical property of a vapor pressure as high as 3.485 MPa (293 K), but by adding dimethyl ether, the pressure of the working fluid can be lowered, and the cost of the closed circuit piping system through which the working fluid flows is reduced. be able to. In addition, when the compounding ratio of dimethyl ether is increased, it becomes combustible and dimethyl ether has a relatively high liquid viscosity (149.0 × 10 −6 Pa / s (298 K)), so that the transportation power increases. Therefore, it is desirable to use the compounding ratio with respect to CO _{2 in the} range of 1 to 35 mol% (non-combustible region or slightly combustible region).

Further, in the process of the present invention, it may be assumed that the working fluid is 1 to 35 mol% blended hydrocarbon natural refrigerant with respect to CO ₂ and CO _2. As described above, when a natural hydrocarbon refrigerant such as isobutane, propane, ethane or the like is blended, there is an advantage that the condensation temperature is raised and the pressure of the working fluid is lowered.

  In the device of the present invention, it is preferable that at least a portion of the heat collecting tube provided in the solar heating device until the working fluid starts to change to the supercritical state has an upward gradient toward the downstream side in the working fluid flow direction. The working fluid flows in from the bottom of the solar heating device and flows out from the top, and the heat transfer pipe connected to the closed circuit in the heat exchanger is directed downward toward the downstream side in the flow direction of the working fluid. It is good to arrange | position so that it may become a gradient and to comprise so that a working fluid may flow in from the upper part of this heat exchanger, and may flow out from a bottom part.

With this configuration, at least a portion of the heat collection tube provided in the solar heating device until the working fluid starts to be heated and changes to the supercritical state is arranged upward, so that the phase change of the working fluid (liquid → super Ascending force is generated in the working fluid that has become supercritical due to the critical state) toward the outlet of the solar heating device. This ascending force serves to help form a natural circulation in the closed circuit.
Further, since the heat transfer tube through which the working fluid flows is formed downward in the heat exchanger, it is easy to form the head pressure of the working fluid on the outlet side of the heat exchanger. In this way, the configuration facilitates the formation of a natural circulation flow of the working fluid.

To form a natural circulation of the working fluid is typically disposed solar heating apparatus to the position of the lower, but so as to place the heat exchanger in the upper position, in the apparatus of the present invention, the viscosity is less CO ₂ Is used as the main fluid of the working fluid, and the above configuration allows natural circulation even when the heat exchanger is arranged at the same height with respect to the solar heating device. Therefore, the heat collecting device does not become bulky, and the heat collecting device can be made compact.

  In the apparatus of the present invention, a detector for detecting the temperature of the working fluid flowing into or out of the heat exchanger, or the temperature of the heat recovery fluid flowing out of the heat exchanger, and the heat exchange An inlet / outlet pipe for allowing the heat recovery fluid to flow through the vessel, a flow rate adjusting valve provided in the inlet / outlet pipe, and a controller for adjusting the opening degree of the flow rate adjusting valve based on the temperature detection value of the detector. Good. Thereby, the temperature of the heat recovery fluid can be adjusted to a necessary temperature according to the application. Therefore, a high temperature heat recovery fluid can be obtained even in winter when the amount of solar radiation is small.

In the apparatus of the present invention, a branch pipe is provided in parallel with the closed circuit of the outlet portion of the heat exchanger, and a storage container for carbon dioxide gas liquefied through an on-off valve is provided on the branch pipe, and the storage is stored in the storage container. It is preferable that the liquid head pressure of the working fluid can be adjusted by adjusting the amount of working fluid to be adjusted.
The specific gravity of the working fluid differs between summer and winter. Therefore, there is a difference in the liquid head pressure formed on the downstream side of the heat exchanger between summer and winter. When the liquid head pressure fluctuates, the natural circulation of the working fluid cannot be stably maintained. On the other hand, since the liquid head pressure can always be adjusted to a predetermined height with the above-described configuration, the natural circulation can always be stably formed.

  Moreover, in the solar heating apparatus of this invention apparatus, it is good to arrange | position the heat collection tube through which a working fluid flows inside a vacuum vessel. Thereby, heat dissipation due to conduction and convection from the collecting pipe can be reduced, and heat loss can be reduced.

  The method of the present invention creates a head pressure due to the working fluid on the working fluid outflow side of the heat exchanger by providing a difference in height between the working fluid inflow side and the outflow side in the heat exchanger, and also collecting the solar heating device. Since the working fluid on the outlet side of the solar heating device is brought into a supercritical state by heat, a natural circulation of the working fluid is formed in the closed circuit through which the working fluid flows, so that the power to circulate the working fluid is unnecessary and energy is saved. In addition, the apparatus configuration can be simplified and low cost can be realized.

  In addition, the device of the present invention recovers and liquefies the retained heat of the working fluid, and creates a difference in level between the inflow side of the working fluid and the outflow side from which the working fluid flows out. A heat exchanger for generating a head pressure and a solar heating device for collecting heat into the liquefied working fluid interposed in the closed circuit of the working fluid to bring the working fluid on the outlet side into a supercritical state, and operate in the closed circuit Since it is configured to form a natural circulation of fluid, it enables the natural circulation of carbon dioxide gas flowing in a closed circuit, which can save energy by eliminating the power to circulate the working fluid, and simplify the device configuration And low cost can be realized.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.
[Embodiment 1]

Next, 1st Embodiment of the solar-heat collecting apparatus which concerns on this invention is described based on FIGS. 1-4. FIG. 1 is a system diagram according to the present embodiment. In FIG. 1, a heat collector 2 that collects solar heat and a heat exchanger 3 that recovers solar heat collected by the heat collector 2 are provided at substantially the same height. Between these, the flow path 1a connecting the outlet portion of the heat collector 2 and the inlet portion of the heat exchanger 3, and the flow connecting the outlet portion of the heat exchanger 3 and the inlet portion of the heat collector 2 are connected. A closed circuit 1 including a path 1 b is provided, and the working fluid is circulated between the heat collector 2 and the heat exchanger 3 through the closed circuit 1. As the working fluid, a working fluid made of dimethyl ether blended at a ratio of ₁ to 35 mol% with respect to CO ₂ or CO ₂ and CO ₂ is used.

  The structure of the heat collector 2 is demonstrated based on FIG.2 and FIG.3. FIG. 2 is a perspective view of the heat collector 2, and FIG. 3 is an enlarged view of a portion A in FIG. 2 and 3, the lower collecting pipe 22 connected to the flow path 1 b is disposed with an inclination in the vertical direction, and the upper end thereof is attached to the casing 21 of the heat collector 2. The lower collecting pipe 22 is connected to a lower header 23 disposed inside the casing 21. A plurality of heat collecting tubes 24 are connected in parallel to the lower header 23 inside the casing 21. The working fluid w flowing into the lower collecting pipe 22 from the flow path 1 b is distributed to the heat collecting pipe 24 through the lower header 23. The heat collecting tubes 24 are arranged with a certain inclination so that the inlet side is low in the vertical direction and the outlet side is high, and are arranged so as to have a height difference between the inlet side and the outlet side.

The periphery of the heat collecting tube 24 is surrounded by a transparent glass tube 25 having a sealed structure, and the inside of the glass tube 25 is maintained in a vacuum state. Thus, heat conduction from the heat collecting tube 24 and heat dissipation due to heat convection can be reduced, and heat loss can be reduced.
A parabolic reflector 26 is disposed around the lower side of the glass tube 25. The reflection plate 26 is composed of a parabola and an involute curve, and is manufactured by pressing an aluminum plate to which a high reflection coating having a high reflectance is applied. The sunlight s reflected by the reflecting plate 26 is collected on the heat collecting tube 24.

  The working fluid w is heated by sunlight s collected toward the heat collecting tube 24 while passing through the heat collecting tube 24. Thereafter, the working fluid w joins at the upper header 27 provided in the casing 21, flows out into the upper collecting pipe 28, and flows out from the upper collecting pipe 28 into the flow path 1a. The upper collecting pipe 28 is also arranged with an inclination in the vertical direction, and the lower end thereof is attached to the casing 21. A heat insulating material (not shown) made of glass wool or the like is disposed on the lower side of the reflection plate 26 to prevent heat from being diffused to the outside of the casing 21.

  In FIG. 1, the working fluid w heated by the heat collector 2 (70 to 90 ° C. at the outlet portion of the heat collector 2) reaches the heat exchanger 3 through the electromagnetic valve 9. In the heat exchanger 3, the inlet part of the working fluid w is connected to the upper part of the heat exchanger 3, and the outlet part of the working fluid w is connected to the lower part of the heat exchanger 3. The inlet portion and the outlet portion are connected by a heat transfer tube 3a disposed in the vertical direction inside the heat exchanger 3. The heat exchanger 3 is supplied with a heat recovery fluid f from a supply pipe 4 connected to the lower part of the heat exchanger 3, and the heat recovery fluid f performs indirect heat exchange with the working fluid w to recover heat from the working fluid w. Then, the heat is discharged from the return pipe 5 connected to the upper part of the heat exchanger 3.

  Since the working fluid w flowing through the heat transfer tube 3a and the heat recovery fluid f flowing around the heat transfer tube 3a flow in opposite directions as shown in FIG. 1, heat exchange efficiency can be improved. As described above, the heat collection tube 24 is placed in the glass tube 25 in a vacuum state, and the working fluid w and the heat recovery fluid f are counterflowed by the heat exchanger 3, so that the high temperature heat recovery fluid f is changed. It can be recovered.

  As described above, in the heat collector 2, the lower collecting pipe 22, the heat collecting pipe 24, and the upper collecting pipe 28 are arranged so as to have an upward gradient toward the downstream side in the flow direction of the working fluid w. Since 22 and the upper collecting pipe 28 have a height difference, the working fluid w heated in the heat collecting pipe 24 to be in a supercritical state generates a rising force toward the outlet side of the heat collecting pipe 24. The working fluid w that has exited the heat collector 2 enters the heat exchanger 3 from the inlet portion disposed at the upper portion of the heat exchanger 3 through the flow path 1 a, and the outlet portion disposed at the lower portion of the heat exchanger 3. And connected to the flow path 1b. Therefore, the flow path 1a is disposed above the flow path 1b, and the flow path 1a and the flow path 1b have a height difference.

  The heat recovery fluid f recovered from the working fluid w exits from the return pipe 5 and is used for various purposes such as hot water supply, heating, and snow melting. On the other hand, the working fluid w that has been subjected to heat exchange with the heat recovery fluid f and cooled to a temperature equal to or lower than the condensation temperature of the working fluid w (for example, 15 to 25 ° C.) is liquefied and flows downward. The outlet pipe 1c of the heat exchanger 3 is arranged in the vertical direction, and a liquid head pressure H is formed by the working fluid w liquefied in the heat transfer pipe 3a and accumulated in the lower part of the heat transfer pipe 3a and the outlet pipe 1c. It is configured to be able to. By forming the liquid head pressure H, the working fluid w in the closed circuit 1 can form a natural circulation flow in the direction of arrow a. Therefore, the working fluid w exiting the heat exchanger 3 moves to the heat collector 2.

  The upper collecting pipe 28 at the outlet of the heat collector 2 is provided with a temperature detector 7 for detecting the temperature of the working fluid w, and the flow rate adjusting valve 9 is interposed in the flow path 1a. The detected value detected by the temperature detector 7 is input to the controller 6, and the controller 6 adjusts the flow rate of the working fluid w flowing through the flow path 1a by adjusting the opening of the flow rate adjusting valve 9. By adjusting the opening of the flow rate adjusting valve 9, the temperature of the working fluid w at the outlet of the collector 2 is controlled so that the working fluid w always forms a supercritical state at the outlet of the collector 2. can do.

  Instead of the temperature detector 7, a solar radiation amount measuring device 8 is provided in the heat collector 2, and the solar radiation amount irradiating the heat collector 2 is measured by the solar radiation amount measuring device 8, and this solar radiation amount is measured. You may make it adjust the opening degree of the flow regulating valve 9 based on a measured value. Alternatively, the temperature difference or pressure difference between the inlet and outlet of the heat collector 2 is detected, the amount of heat collected by the heat collector 2 is calculated from the difference, and the flow rate adjustment valve 9 is adjusted based on the calculated value. You may make it do. Alternatively, the pressure of the working fluid w at the outlet of the heat collector 2 may be detected, and the flow rate adjustment valve 9 may be adjusted based on the pressure value.

  The return pipe 5 for the heat recovery fluid is provided with a flow rate adjusting valve 10 and a temperature detector 11 for detecting the temperature of the heat recovery fluid f, and the detected value of the temperature detector 11 is input to the controller 6. The temperature of the heat recovery fluid f flowing through the return pipe 5 can be adjusted by adjusting the flow rate adjustment valve 10 based on the detected value. Thereby, the heat recovery fluid f having a desired temperature can be obtained.

  Further, a branch pipe 12 is provided in parallel with the outlet pipe 1c in the outlet pipe 1c, and a storage container 13 for storing a part of the working fluid w flowing through the outlet pipe 1c is interposed in the branch pipe 12. It is installed. Opening and closing valves 14 and 15 are provided on the inlet side and the outlet side of the storage container 13.

  In order to stabilize the flow of the working fluid w in the closed circuit 1, an evaporation region of the working fluid w is formed by the heat collector 2, and a condensing region of the working fluid w is formed by the heat exchanger 3, It is necessary to make the head pressure H of the working fluid w formed in the heat transfer pipe 3a and the outlet pipe 1c of the heat exchanger 3 constant. However, since the specific gravity of the working fluid w differs depending on the temperature in summer and winter, a difference appears in the liquid head pressure H. For this reason, as mentioned above, the storage container 13 is interposed in the branch pipe 12 provided in parallel with the outlet pipe 1c, a part of the working fluid w is stored in the storage container 13, and the storage amount is adjusted. By this, while ensuring the evaporation area | region of the heat collector 2 and the condensation area | region of the heat exchanger 3, it can adjust so that the liquid head pressure H may become always constant.

  In the present embodiment having such a configuration, the rising force generated in the working fluid evaporated in the supercritical state by evaporating inside the heat collecting tube 24 and the upper collecting tube 28 arranged to have an upward gradient, and the heat exchanger 3 The working fluid w is naturally circulated in the closed circuit 1 by the heat transfer pipe 3a and the liquid head pressure H formed in the outlet pipe 1c. Then, the heat of the sunlight s is collected by the heat collector 2 to heat the working fluid w, and the heated working fluid w is indirectly heat-exchanged with the heat recovery fluid f by the heat exchanger 3. As a result, the retained heat of the working fluid w is recovered in the heat recovery fluid f, and the heat recovered in the heat recovery fluid f is used for each application, for example, hot water supply, heating, or snow melting.

A Mollier diagram (pressure-enthalpy diagram) of the working fluid w of this embodiment is shown in FIG. In FIG. 4, K is a critical point (pressure 7.3 MPa, temperature 31 ° C.), and becomes a supercritical state above the critical point. In this embodiment, since the working fluid w naturally circulates in the closed circuit 1, there is no fluctuation in pressure, and vaporization (supercritical state) in the heat collector 2 and condensation in the heat exchanger 3 at the same pressure. Cycle b that reciprocates between them is repeated. The viscosity of CO ₂ contained in the working fluid w does not change even at high pressure and high density, becomes a supercritical state at a critical point (pressure 7.3 MPa, temperature 31 ° C.) or higher, and decreases in the supercritical state. When w is circulated through the closed circuit 1 disposed between the heat collector 2 and the heat exchanger 3, natural circulation can be easily formed and the force required to move the working fluid w can be reduced. In addition, CO ₂ has an advantage that the specific heat decreases as the pressure increases, and heat collection is particularly easy at a high temperature.

  According to the present embodiment, the heat collecting pipes 24 provided in the heat collector 2 are arranged so as to have an upward gradient toward the downstream side in the flow direction of the working fluid w, and the upper and lower collecting pipes 22 and 28 are similar. The heat exchanger tube 3a of the heat exchanger 3 is arranged in the vertical direction, the outlet side of the heat collector 2 and the inlet side of the heat exchanger 3 are connected by a flow path 1a, and the outlet side of the heat exchanger 3 By connecting the inlet side of the heat collector 2 with the flow path 1b, it is possible to make a height difference between the flow path 1a and the flow path 1b.

  With this configuration, the working fluid w that has become a supercritical state due to a phase change (liquid → supercritical state) in the heat collecting tube 24 generates a rising force toward the outlet side of the heat collector 2. This ascending force serves to assist the formation of natural circulation in the closed circuit 1.

  Moreover, the head pressure H of the working fluid w can be formed by the heat transfer tube 3a and the outlet pipe line 1c connected to the outlet side of the heat transfer tube 3a. Then, a natural circulation flow of the working fluid w is formed in the closed circuit 1 by the ascending force generated by forming the supercritical state in the outlet-side flow path 1a of the heat collector 2 and the liquid head pressure H. Can do. This eliminates the need for pump power to circulate the working fluid w, so that the heat collecting device can be operated with energy saving and low cost.

  Further, a storage container 13 is provided in the branch pipe 12 arranged in parallel with the outlet pipe 1c of the heat exchanger 3, a part of the working fluid w is stored in the storage container 13, and the storage amount is adjusted so that the storage container 13 is closed. The circulation of the working fluid w in the circuit 1 can be stabilized.

In addition, when a working fluid containing ₁ to 35 mol% dimethyl ether based on CO ₂ and CO ₂ is used as the working fluid w, the boiling point of the working fluid is higher than when only CO ₂ is used as the working fluid. Can be made. Thereby, the condensation temperature range can be increased. Therefore, even if the temperature range of the working fluid increases, the working fluid is likely to condense and the liquid head pressure H is easily formed, so that natural circulation of the working fluid can be performed reliably.

  Furthermore, by blending dimethyl ether, the pressure of the working fluid can be lowered, the piping system of the working fluid can be made into a low pressure specification, and the cost can be reduced.

  Further, a temperature detector 7 for detecting the temperature of the working fluid w is provided in the upper collecting pipe 28 at the outlet of the heat collector 2 or a solar radiation amount measuring device 8 for measuring the solar radiation amount of the heat collector 2 is provided. Since the controller 6 adjusts the opening degree of the flow rate adjusting valve 9 based on these measured values, the temperature of the working fluid w on the outlet side of the heat collector 2 can be adjusted to a desired temperature. As a result, the supercritical state of the working fluid w can be stably formed in the outlet-side flow path 1a of the heat collector 2, so that natural circulation can be stably formed, and the working fluid w in the heat collector 2 can be collected by the working fluid w. Thermal efficiency can be improved.

Further, the return pipe 5 is provided with a flow rate adjusting valve 10 and a temperature detector 11 for detecting the temperature of the heat recovery fluid, and the controller 6 adjusts the opening degree of the flow rate adjusting valve 10 based on the detected temperature value. Therefore, the temperature of the heat recovery fluid can be adjusted to a desired temperature according to the application. Therefore, a high temperature heat recovery fluid can be obtained even when the amount of solar radiation is small, such as in winter.
[Embodiment 2]

  Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 5, devices or parts having the same reference numerals as those in the first embodiment indicate the same devices or parts as those in the first embodiment, and thus description thereof is omitted. In the present embodiment, the heat recovery unit 30 that recovers the heat of the working fluid w heated by the heat collector 2 does not exchange heat with the heat recovery fluid, and does not exchange heat with the target that requires direct heat supply. This is a case where heat exchange is performed. Other configurations are the same as those of the first embodiment.

For example, by arranging the heat transfer pipe 31 connected to the closed circuit 1 in the heat recovery unit 30 in the air conditioning target space r and circulating the atmosphere of the air conditioning target space r so as to hit the heat transfer pipe 31 by the fan 32, the air conditioning The target space r is heated. Alternatively, as another application, the heat transfer tube 31 is buried in a place where snow melting is required, for example, a road in a cold region, so as to melt snow. Thus, in this embodiment, in addition to the effect of the said 1st Embodiment, since the working fluid w which flows through the heat exchanger tube 31 is directly heat-exchanged with a heating target object, heat recovery efficiency can be improved.
[Embodiment 3]

  Next, a third embodiment of the present invention will be described with reference to FIG. The configuration of the heat collecting apparatus of the third embodiment shown in FIG. 6 is the same as that of the first embodiment shown in FIG. Accordingly, in the third embodiment, the same devices or parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description of those same devices or parts is omitted.

  Hereinafter, in the present embodiment, points different from the first embodiment will be described. In FIG. 6, a heat recovery fluid is recovered by connecting a storage tank 41 to the return pipe 5 of the heat recovery fluid that has indirectly recovered heat from the working fluid w in the heat exchanger 3 and recovered the heat held by the working fluid w. Is stored in the storage tank 41. The partition wall of the storage tank 41 is made of a heat insulating material and has heat insulating properties. By storing the high-temperature heat recovery fluid obtained by the daytime heat collecting device in the storage tank 41, the retained heat of the heat recovery fluid f can be used even at night.

  Further, the heat recovery fluid in the storage tank 41 is configured to be supplied to the absorption refrigerator 42. Since the heat recovery fluid f stored in the storage tank 41 has a high recovery temperature, supplying the heat recovery fluid f to the absorption refrigerator 42 can be applied to air conditioning in summer. Moreover, it is applicable to hot water supply by using drinking water such as tap water as the heat recovery fluid f stored in the storage tank 41. In addition, it is applicable to heating in winter, heating in a greenhouse, auxiliary heat source for a hot water pool, and snowmelt countermeasures in cold regions. For example, when high temperature recovery such as hot water supply is desirable as the heat exchange method, as described above, the vacuum insulation by the double tube method in the heat collector 2 and the counter flow type heat exchange in the heat exchanger 3 are adopted. Good.

Thus, according to this embodiment, in addition to the effect by the said 1st Embodiment, the above effect can be obtained.
[Example]

  Next, an example in which the first embodiment of the present invention is actually implemented will be described with reference to FIGS. FIG. 7 shows the operating conditions of this example, and FIG. 8 shows the experimental data obtained. In addition, the present Example shows the average value of the experiment conducted at the time of fine weather in winter (January to March), and water is used as the heat recovery fluid f in the heat exchanger 3. It can be seen from FIG. 8 that a high heat collection rate and recovery rate of 80% or more can be obtained.

Incidentally, as the working fluid, in the case of using a working fluid containing a combination of dimethyl ether to CO _2, compared with the case of using only CO _2, it is possible to increase the condensation temperature, it becomes easy to form a Ekiatama圧. In addition, the heat recovery rate when water is used as the working fluid is 60%, whereas when the working fluid containing CO ₂ and dimethyl ether is used as the working fluid, a high heat of 80% or more. A recovery rate can be obtained.

FIG. 9 shows experimental data performed in winter (February) on a clear day. This is a measurement of the amount of heat collected and the amount of solar radiation by the heat collector 2 (per 1.5 m ² ) when a working fluid containing 10 mol% of dimethyl ether in CO ₂ is used as the working fluid. The experiment started after 10:00 am and was performed at an outside temperature of 8 to 16 ° C. It can be seen from FIG. 9 that a high amount of heat collection is obtained with respect to the amount of solar radiation.

According to the present invention, a closed circuit in which a working fluid whose main fluid is CO ₂ circulates is formed, and the working fluid is naturally circulated in the closed circuit, so that no power is required, and the heat collecting capability is low and high in cost. A solar heat collecting means can be realized.

It is a systematic diagram of a 1st embodiment of the present invention. It is a perspective view of the heat collector of the first embodiment. It is the A section enlarged view in FIG. It is a Mollier diagram of the first embodiment. It is a systematic diagram of 2nd Embodiment of this invention. It is a systematic diagram of 3rd Embodiment of this invention. It is a graph which shows the driving | running conditions of the Example which implemented the said 1st Embodiment of this invention. It is a graph which shows the experimental data of the said Example. It is a diagram which shows the experimental data of the said Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Closed circuit 1c Outlet pipe line 2 Heat collector (solar heating device)
DESCRIPTION OF SYMBOLS 3 Heat exchanger 3a Heat transfer pipe 4 Heat recovery fluid supply pipe 5 Heat recovery fluid return pipe 6 Controller 7,11 Temperature detector 8 Solar radiation amount measuring instrument 9,10 Flow control valve 12 Branch pipe 13 Storage container 14,15 On-off valve 24 Heat collection tube 25 Glass tube (vacuum container)
f Heat recovery fluid H Liquid head pressure r Air-conditioned space w Working fluid

Claims (13)

In a heat collecting method for forming a closed circuit in which a working fluid having CO ₂ as a main fluid circulates and recovering heat from the working fluid collected by a solar heating device using a heat exchanger,
Forming a liquid head pressure by the working fluid on the working fluid outflow side of the heat exchanger by creating a difference in height between the inflow side and the outflow side of the working fluid in the heat exchanger;
A heat collecting method, wherein the working fluid on the outlet side of the solar heating device is brought into a supercritical state by collecting heat from the solar heating device, thereby forming a natural circulation of the working fluid in the closed circuit.   2. The heat collecting method according to claim 1, wherein a physical forced circulation device with a working fluid compression or lifting action is not interposed in the closed circuit.   Of the heat collecting tubes provided in the solar heating device, at least a portion until heating of the working fluid starts and changes to a supercritical state is arranged so as to have an upward gradient toward the downstream side in the flow direction of the working fluid, The heat collecting method according to claim 1. The presence or absence of a supercritical state of the working fluid is detected by a detector provided in the closed circuit on the outlet side of the solar heating device,
According to the detection result, the outlet side of the solar heating device is adjusted by adjusting the opening of a flow rate adjusting valve provided in a closed circuit connecting the outlet side of the solar heating device and the inlet side of the heat exchanger. 2. The heat collecting method according to claim 1, wherein a supercritical state of the working fluid is always formed in the closed circuit.   The detector is a detector that detects a heat collection amount of the solar heating device, or a detector that detects a temperature or pressure of a working fluid flowing in a closed circuit on the outlet side of the solar heating device. 4. The heat collecting method according to 4. The heat collecting method according to claim 1, wherein the working fluid is a mixture of 1 to 35 mol% of dimethyl ether with respect to CO ₂ and CO ₂ . The heat collecting method according to claim 1, wherein the working fluid is a blend of 1 to 35 mol% of a hydrocarbon-based natural refrigerant with respect to CO ₂ and CO ₂ . In a heat collecting apparatus including a solar heating device that forms a closed circuit in which a working fluid having CO ₂ as a main fluid circulates and collects heat in the working fluid, and a heat exchanger that recovers heat from the collected working fluid ,
Heat exchange that collects and liquefies the retained heat of the working fluid and creates a head pressure with the working fluid on the working fluid outflow side by creating a level difference between the working fluid inflow side and the working fluid outflow side And
A solar heating device that collects heat into the liquefied working fluid interposed in the closed circuit and brings the working fluid on the outlet side into a supercritical state,
A heat collecting apparatus configured to form a natural circulation of a working fluid in the closed circuit.   Of the heat collecting tubes provided in the solar heating device, at least a portion until the working fluid starts heating and changes to a supercritical state is arranged so as to have an upward gradient toward the downstream side in the flow direction of the working fluid, and the working fluid is The solar heat heating device flows in from the bottom and flows out from the top, and the heat exchanger tube connected to the closed circuit in the heat exchanger is disposed so as to have a downward gradient toward the downstream side in the flow direction of the working fluid. The heat collecting apparatus according to claim 8, wherein the fluid is configured to flow in from the top of the heat exchanger and flow out from the bottom.   The heat collecting apparatus according to claim 9, wherein the heat exchanger is disposed at a height that is about the same as or higher than the height of the solar heating apparatus. A detector for detecting the temperature of the working fluid flowing into or out of the heat exchanger, or the temperature of the heat recovery fluid flowing out of the heat exchanger;
An inlet / outlet pipe through which the heat recovery fluid flows through the heat exchanger, and a flow rate adjusting valve provided in the inlet / outlet pipe;
The heat collecting apparatus according to claim 8, further comprising a controller that adjusts an opening degree of the flow rate adjustment valve based on a temperature detection value of the detector. A branch pipe is provided in parallel with the closed circuit at the outlet of the heat exchanger, and a storage container for the working fluid liquefied via an on-off valve is provided in the branch pipe.
The heat collecting apparatus according to claim 8, wherein the head pressure of the working fluid can be adjusted by adjusting the amount of the working fluid stored in the storage container.   The heat collecting apparatus according to any one of claims 8 to 10, wherein a heat collecting tube through which a working fluid flows in the solar heating apparatus is disposed inside a vacuum vessel.

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