Solar direct-driven refrigeration equipment for low-temperature grain storage

Abstract

The invention discloses solar direct-driven refrigeration equipment for low-temperature grain storage, and belongs to the technical field of grain storage refrigeration, the solar direct-driven refrigeration equipment comprises a granary and a mounting frame mounted at the top end of the granary, a solar panel and an electric power storage assembly are mounted on the upper surface of the mounting frame, and the solar panel is connected with the electric power storage assembly through a wire; a carbon dioxide refrigerating system is further arranged on the upper surface of the mounting frame, the carbon dioxide refrigerating system supplies power through a power storage assembly, a convex cavity and an annular cavity are formed in the inner top end of the granary, and a mounting cover is fixedly connected into the convex cavity. The device can realize environment-friendly refrigeration through combination of a carbon dioxide refrigeration system and solar power generation, is environment-friendly, quiet in operation and low in maintenance cost, in addition, can spray out cold air at high frequency, and is helpful for the cold air to permeate into a grain pile under the action of air pressure, thereby being helpful for improving the grain cooling efficiency and reducing the energy consumption. In addition, when the air is exhausted, cold air can be sprayed out in an auxiliary mode through the extrusion effect of the air.

Description

Technical Field

[0001] The present invention relates to the technical field of grain storage absorption refrigeration, and specifically provides a refrigeration device for low-temperature grain storage directly driven by solar energy. Background Technique

[0002] When storing grains, in order to avoid grain deterioration, it is very necessary to keep the grains at a low temperature. This is because after the grains are piled up, high temperature is easily generated inside. Under high temperature conditions, grains are very likely to develop mildew, pests and aging. However, when the grains are at a low temperature (below 15°C), the deterioration of grain quality can be significantly delayed, and the nutritional components and freshness can be maintained. In order to reduce the internal temperature of the piled grains to below 15°C, a refrigeration device is generally used for cooling. The existing refrigeration methods mainly include air cooling and water cooling. The temperature of the grains is gradually reduced through air cooling or water cooling to delay the time of grain deterioration. When the existing refrigeration device for grain storage is in use, the following technical problems still exist, such as: The existing refrigeration device for grain storage has a low efficiency in cooling grains. This is because the existing refrigeration device for grain storage generally cools the grain pile by air cooling and water cooling. When using water cooling, condensation is likely to occur, which is not conducive to grain preservation. When using air cooling, since there is a large amount of grains piled up in the granary, it is very difficult to transfer the low temperature to the inside of the grains through external air cooling. The published split solar low-temperature grain storage absorption refrigeration system with the publication number of CN100458311C cools the grain pile by gradually absorbing heat. Although it can avoid the occurrence of condensation, due to its step-by-step cooling by heat conduction, its efficiency is much lower than that of water cooling. Therefore, a refrigeration device for low-temperature grain storage directly driven by solar energy is needed to solve the above problems. Summary of the Invention

[0003] The purpose of the present invention is to provide a refrigeration device for low-temperature grain storage directly driven by solar energy to solve the problem of poor cooling efficiency of the existing refrigeration device for grain storage mentioned in the above background technique.

[0004] To achieve the above purpose, the present invention provides the following technical solutions: A refrigeration device for low-temperature grain storage driven directly by solar energy, comprising a grain bin and a mounting frame installed on the top thereof. The upper surface of the mounting frame is provided with a solar panel and a power storage component, and the solar panel is connected to the power storage component through a wire. The upper surface of the mounting frame is further provided with a carbon dioxide refrigeration system, and the carbon dioxide refrigeration system is powered by the power storage component. The inner top of the grain bin is provided with a convex cavity and an annular cavity, and an installation cover is fixedly connected in the convex cavity. A servo motor is installed in the installation cover. The grain bin is equiangularly provided with air guide pipes with sealed tops penetrating into the annular cavity, and the convex cavity is equiangularly provided with air delivery pipes. The two ends of the air delivery pipe are respectively connected to the annular cavity and the installation cover in a penetrating manner. The servo motor is connected to the air delivery pipe and the air guide pipe through an extrusion type air delivery and cooling mechanism.

[0005] Preferably, each of the air guide pipes is evenly distributed with one-way air injection holes at equal intervals. The top of the convex cavity is provided with an exhaust hole penetrating to the outside of the grain bin. The convex cavity is further provided with air dispersion holes evenly distributed at equal angles with respect to the axis of the installation cover, and a pressure air dispersion mechanism for assisting the movement of the extrusion type air delivery and cooling mechanism is arranged on the air dispersion holes.

[0006] Preferably, the carbon dioxide refrigeration system includes a compressor, a condenser, a throttle valve and an evaporator installed on the upper surface of the mounting frame, and the four are connected in sequence to form a circulating structure. The upper surface of the mounting frame is further provided with a gas guide cover, and the gas guide cover is sleeved outside the evaporator.

[0007] Preferably, the top of the gas guide cover is provided with a strip-shaped hole penetrating through its inner and outer sides. The outside of the evaporator is provided with a copper sleeve for conducting temperature, and a part of the copper sleeve extends into the interior of the evaporator to cool the gas flowing between the gas guide cover and the copper sleeve. A gas guide channel penetrating into the installation cover is arranged at the part between the gas guide cover and the copper sleeve on the mounting frame.

[0008] Preferably, the extrusion type air delivery and cooling mechanism includes a piston column whose two ends are respectively and seamlessly slidably connected to the corresponding air guide pipe and air delivery pipe. The piston column is of a tubular structure, and one-way air guide valves are arranged inside both its interior and the air guide pipe. The one-way air guide valve inside the air guide pipe is arranged above the uppermost one-way air injection hole.

[0009] Preferably, the extrusion type air delivery and cooling mechanism further includes a control shaft movably penetrating through the partition between the convex cavity and the annular cavity, and the end of the control shaft arranged in the annular cavity is in a square shape. A flat plate is fixedly connected to the middle of the piston column, and an inclined groove penetrating through both sides thereof is arranged on the flat plate. The inclined groove is in snap-fit sliding connection with the square-shaped end of the corresponding control shaft.

[0010] Preferably, the extrusion type gas transmission and cooling mechanism further includes a pushing disk key-connected to the end of the servo motor shaft, and a pressure-bearing block is slidably connected to the teeth of the pushing disk. The pressure-bearing block is provided at the end of each control shaft in the convex cavity. A partition disk is fixedly connected to the middle of the control shaft in the convex cavity, and springs are provided on both sides of the partition disk. The springs on both sides of the partition disk are respectively connected to the outer wall of the installation cover and the partition between the convex cavity and the annular cavity.

[0011] Preferably, the surface of the pressure-bearing block facing the axis of the pushing disk is a curved surface, and the distance from the curved surface to the axis of the pushing disk changes step by step.

[0012] Preferably, the pressure-dissipating air mechanism includes limiting tubes evenly distributed at equal angles on the circumferential side of the lower surface of each air-dissipating hole. A blocking plug is movably connected to the upper end of the air-dissipating hole, and a connecting disk coaxial with it is fixedly connected to the lower end of the blocking plug. Limiting rods are evenly distributed on the connecting disk, and the limiting rods on the connecting disk movably extend into the lower part of the corresponding limiting tube.

[0013] Preferably, the upper end of the blocking plug is a conical structure, and the conical structure is in contact connection with the corresponding partition disk, which is convenient to assist the movement of the control shaft by squeezing the partition disk.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The solar direct-drive refrigeration equipment for low-temperature grain storage can combine the carbon dioxide refrigeration system with the solar power generation system to achieve environmental-friendly refrigeration, which is friendly to the environment, operates quietly, and has low maintenance costs. In addition, it can spray cold air at a high frequency, which helps the cold air to penetrate into the interior of the grain pile under the action of air pressure, thereby helping to improve the efficiency of cooling the grain. In addition, when discharging gas, it can assist the spraying of cold air through the extrusion action of the gas: 1. The solar power generation system composed of solar panels and energy storage components, and the carbon dioxide refrigeration system mainly composed of a compressor, a condenser, a throttle valve and an evaporator can greatly reduce the impact of refrigeration on the environment and avoid damaging the ozone layer. This is because its greenhouse effect is much lower than that of traditional synthetic refrigerant of Freon type, and the global warming potential value is only 1, so that the solar power generation system composed of solar panels and energy storage components is more friendly to the environment, and it also has the advantages of quiet operation and low maintenance costs; 2. Through the operation of the servo motor, the pushing disc continuously squeezes the pressure-bearing block. Cooperating with the spring, the control shaft can move reciprocally. During the reciprocating movement of the control shaft, through the inclined slots provided on the flat plate, the piston column can move reciprocally up and down at a high frequency. During the reciprocating movement of the piston column up and down, through the one-way air guide valve, it can continuously suck the air cooled by the carbon dioxide refrigeration system and transport the cold air into the air guide pipe. Since the bottom end inside the air guide pipe is a sealed structure, the cold air entering the air guide pipe will be ejected through multiple one-way air injection holes. Since there are enough one-way air injection holes and the piston column reciprocates at a high frequency, multiple one-way air injection holes will continuously eject cold air, which helps the cold air penetrate into the interior of the grain pile to effectively cool the interior of the grain pile. 3. After the cold air entering the granary absorbs heat, it forms hot air with a certain amount of heat. The more cold air enters the granary, the greater the pressure inside the granary will be, which will cause the hot air to enter the convex cavity through the air dispersion holes. Due to the setting of the pressure air dispersion mechanism, for the hot air to enter the convex cavity, it needs to squeeze the blocking plug to make the blocking plug move upward. During the upward movement of the blocking plug, it will squeeze the partition disc, which is conducive to the movement of the control shaft provided with the partition disc and reduces the difficulty of the reciprocating movement of the piston column. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the front view structural schematic diagram of the present invention; Figure 2 is the rear view structural schematic diagram of the present invention; Figure 3 is the front cross-sectional structural schematic diagram of the present invention; Figure 4 of the present invention Figure 3 is the enlarged structural schematic diagram of point A in; Figure 5 is the enlarged side cross-sectional structural schematic diagram of the present invention; Figure 6 of the present invention Figure 5 is the enlarged structural schematic diagram of point B in; Figure 7 is the connection structural schematic diagram of the servo motor and the air guide pipe of the present invention; Figure 8 is the connection top view structural schematic diagram of the air guide pipe and the pushing disc of the present invention; Figure 9 of the present invention Figure 8 is the enlarged structural schematic diagram of point C in.

[0016] In the figure: 1, grain bin; 2, mounting frame; 3, solar panel; 4, power storage component; 5, compressor; 6, condenser; 7, throttle valve; 8, air guide hood; 9, air guide pipe; 10, convex cavity; 11, annular cavity; 12, mounting cover; 13, exhaust hole; 14, evaporator; 15, servo motor; 16, gas transmission pipe; 17, piston column; 18, flat plate; 19, inclined groove; 20, control shaft; 21, one-way air guide valve; 22, one-way air injection hole; 23, partition disc; 24, spring; 25, pushing disc; 26, limiting pipe; 27, connecting disc; 28, blocking plug; 29, pressure bearing block. Specific implementation mode

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Please refer to Figures 1 - 9 , the present invention provides the following technical solutions: Embodiment 1: To solve the problem that the cooling efficiency of the refrigeration equipment for low-temperature grain storage in the past was not good for cooling the grain pile, the following technical solutions are provided. Specifically, a solar direct-drive refrigeration equipment for low-temperature grain storage includes a grain bin 1 and a mounting frame 2 installed on its top. The upper surface of the mounting frame 2 is provided with a solar panel 3 and a power storage component 4, and the solar panel 3 is connected to the power storage component 4 through a wire. The upper surface of the mounting frame 2 is also provided with a carbon dioxide refrigeration system, and the carbon dioxide refrigeration system is powered by the power storage component 4. A convex cavity 10 and an annular cavity 11 are provided at the inner top of the grain bin 1, and a mounting cover 12 is fixedly connected in the convex cavity 10. A servo motor 15 is installed in the mounting cover 12. The grain bin 1 is provided with air guide pipes 9 at equal angles with their tops sealed and penetrating into the annular cavity 11, and air transmission pipes 16 are provided at equal angles in the convex cavity 10. The two ends of the air transmission pipe 16 are respectively connected to the annular cavity 11 and the mounting cover 12 in a penetrating manner. The servo motor 15 is connected to the air transmission pipe 16 and the air guide pipe 9 through an extrusion type air transmission cooling mechanism.

[0019] The carbon dioxide refrigeration system includes a compressor 5, a condenser 6, a throttle valve 7, and an evaporator 14 installed on the upper surface of the mounting bracket 2. The four are connected in sequence to form a circulating structure. A gas guide cover 8 is also installed on the upper surface of the mounting bracket 2, and the gas guide cover 8 is sleeved outside the evaporator 14. A strip-shaped hole penetrating the inner and outer sides is provided at the top of the gas guide cover 8. A copper sleeve for conducting temperature is provided outside the evaporator 14, and a part of the copper sleeve extends into the interior of the evaporator 14 for cooling the gas flowing between the gas guide cover 8 and the copper sleeve. A gas guide channel penetrating into the mounting cover 12 is provided at the part between the gas guide cover 8 and the copper sleeve on the mounting bracket 2. During use, the compressor 5 in the carbon dioxide refrigeration system sucks in carbon dioxide. After being compressed by the compressor 5, the carbon dioxide becomes a high-temperature and high-pressure gas, and then enters the condenser 6 for heat exchange and condenses into a high-pressure liquid. Subsequently, it passes through the throttle valve 7 to form a low-temperature and low-pressure gas-liquid two-phase mixture. After that, it enters the evaporator 14 again to absorb the heat of the gas flowing between the gas guide cover 8 and the copper sleeve, thereby cooling the gas. The cooled cold air enters the interior of the mounting cover 12 through the gas guide channel. The evaporated low-temperature and low-pressure carbon dioxide gas is sucked in by the compressor 5 again to form a cycle.

[0020] The extrusion type air supply cooling mechanism includes a piston column 17 whose two ends are seamlessly and slidably connected to the corresponding air guide pipe 9 and air delivery pipe 16 respectively. The piston column 17 is of a tubular structure, and one-way air guide valves 21 are provided inside both it and the air guide pipe 9. The one-way air guide valve 21 inside the air guide pipe 9 is arranged above the uppermost one-way air injection hole 22. The extrusion type air supply cooling mechanism also includes a control shaft 20 that movably penetrates the partition between the convex cavity 10 and the annular cavity 11, and one end of the control shaft 20 arranged inside the annular cavity 11 is in a square shape. A flat plate 18 is fixedly connected to the middle of the piston column 17, and an inclined groove 19 penetrating both sides thereof is provided on the flat plate 18. The inclined groove 19 is in snap-fit sliding connection with the square-shaped end of the corresponding control shaft 20. The extrusion type air supply cooling mechanism also includes a push plate 25 key-connected to the shaft end of the servo motor 15, and a pressure-bearing block 29 is slidably connected to the teeth of the push plate 25. The pressure-bearing block 29 is provided at the end of each control shaft 20 inside the convex cavity 10. A partition plate 23 is fixedly connected to the middle of the control shaft 20 inside the convex cavity 10, and springs 24 are provided on both sides of the partition plate 23. The springs 24 on both sides of the partition plate 23 are respectively connected to the outer wall of the mounting cover 12 and the partition between the convex cavity 10 and the annular cavity 11. The surface of the pressure-bearing block 29 facing the axis of the push plate 25 is a curved surface, and the distance from the curved surface to the axis of the push plate 25 changes step by step. During use, through the operation of the servo motor 15, the push plate 25 is driven to rotate. When the push plate 25 rotates, it squeezes the pressure-bearing block 29. Through the cooperation of the spring 24, the control shaft 20 provided with the pressure-bearing block 29 can reciprocate. During the reciprocating movement of the control shaft 20, the flat plate 18 provided with the inclined groove 19 will be driven to reciprocate up and down. Since the flat plate 18 is fixedly connected to the piston column 17, the piston column 17 will synchronously reciprocate up and down. During the reciprocating movement of the piston column 17, by using the one-way air guide valve 21 provided on the piston column 17, the cold air inside the mounting cover 12 can be continuously delivered to the inside of the air guide pipe 9 through the air delivery pipe 16. The cold air entering the air guide pipe 9 will cause the air pressure inside the air guide pipe 9 to increase, and then the cold air will gradually be ejected through the one-way air injection holes 22. Since the push plate 25 rotates, the piston column 17 will reciprocate up and down at a high speed, and thus the one-way air injection holes 22 can eject cold air at a high frequency, which is beneficial to the penetration of the cold air into the grain pile and is convenient for cooling the grains in the granary 1.

[0021] Embodiment 2: To solve the problem that the previous refrigeration equipment for low-temperature grain storage is not convenient to utilize the exhausted hot air, the following technical solution is provided. Specifically, one-way air injection holes 22 are evenly distributed at equal intervals on each air guide pipe 9. An exhaust hole 13 penetrating to the outside of the granary 1 is provided at the top of the convex cavity 10. The convex cavity 10 is also provided with air dispersion holes distributed at equal angles with respect to the axis of the mounting cover 12, and a pressure air dispersion mechanism for assisting the movement of the extrusion type air supply cooling mechanism is provided on the air dispersion holes.

[0022] The pressure air release mechanism includes limiting tubes 26 which are equally angularly distributed on the circumferential side of the lower surface of each air release hole. The upper end of the air release hole is movably connected with a blocking plug 28, and the lower end of the blocking plug 28 is fixedly connected with a connection disk 27 coaxial with it. Limiting rods are equally angularly distributed on the connection disk 27, and the limiting rods on the connection disk 27 movably extend into the lower part of the corresponding limiting tube 26. The upper end of the blocking plug 28 is of a conical structure, and the conical structure is in contact connection with the corresponding partition disk 23, which is convenient for assisting the movement of the control shaft 20 by squeezing the partition disk 23. During use, due to the gravity of the blocking plug 28, the blocking plug 28 will block the air release hole (the maximum diameter of the blocking plug 28 is greater than the inner diameter of the air release hole). When there is more gas in the granary 1, the internal pressure will be relatively high, which will push open the blocking plug 28, facilitating the air for heat absorption to pass through the air release hole and then be discharged from the exhaust hole 13 out of the granary 1. During the process of the blocking plug 28 being pushed open, it will squeeze the partition disk 23, thereby helping the control shaft 20 provided with the partition disk 23 to move, and helping to reduce the difficulty of the pushing disk 25 squeezing the pressure-bearing block 29 to make the control shaft 20 move. Thus, the discharged hot air can be utilized to reduce the waste of energy.

[0023] The content not detailedly described in this specification belongs to the prior art well-known to those skilled in the art.

[0024] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A refrigeration device for low-temperature grain storage directly driven by solar energy, comprising a grain bin (1) and a mounting frame (2) installed at the top thereof, characterized in that: The upper surface of the mounting frame (2) is equipped with a solar panel (3) and a power storage component (4), and the solar panel (3) is connected to the power storage component (4) through a wire. The upper surface of the mounting frame (2) is also provided with a carbon dioxide refrigeration system, and the carbon dioxide refrigeration system is powered by the power storage component (4). The inner top end of the granary (1) is provided with a convex cavity (10) and an annular cavity (11), and a mounting cover (12) is fixedly connected inside the convex cavity (10). A servo motor (15) is installed inside the mounting cover (12). The guide air pipes (9) with their tops sealed and penetrating into the annular cavity (11) are arranged equiangularly inside the granary (1), and the air delivery pipes (16) are arranged equiangularly inside the convex cavity (10). The two ends of the air delivery pipe (16) are respectively connected through to the annular cavity (11) and the mounting cover (12). The servo motor (15) is connected to the air delivery pipe (16) and the guide air pipe (9) through an extrusion type air delivery and cooling mechanism.

2. The low-temperature grain storage refrigeration equipment directly driven by solar energy according to claim 1, characterized in that: Each of the guide air pipes (9) is evenly distributed with one-way air injection holes (22) at equal intervals. The top end of the convex cavity (10) is provided with an exhaust hole (13) penetrating to the outside of the granary (1). The convex cavity (10) is also provided with air dispersion holes evenly distributed around the axis of the mounting cover (12), and a pressure air dispersion mechanism for assisting the movement of the extrusion type air delivery and cooling mechanism is arranged on the air dispersion holes.

3. The low-temperature grain storage refrigeration equipment directly driven by solar energy according to claim 2, characterized in that: The carbon dioxide refrigeration system includes a compressor (5), a condenser (6), a throttle valve (7) and an evaporator (14) installed on the upper surface of the mounting frame (2), and the four are connected in sequence to form a circulating structure. The upper surface of the mounting frame (2) is also installed with a guide air hood (8), and the guide air hood (8) is sleeved outside the evaporator (14).

4. A refrigeration device for low-temperature grain storage directly driven by solar energy according to claim 3, characterized in that: The top end of the guide air hood (8) is provided with a strip-shaped hole penetrating its inner and outer sides. The outside of the evaporator (14) is provided with a copper sleeve for conducting temperature, and a part of the copper sleeve extends into the interior of the evaporator (14) to cool the gas flowing between the guide air hood (8) and the copper sleeve. The part between the guide air hood (8) and the copper sleeve on the mounting frame (2) is provided with a guide air channel penetrating into the mounting cover (12).

5. The low-temperature grain storage refrigeration equipment directly driven by solar energy according to claim 4, characterized in that: The extrusion type air delivery and cooling mechanism includes a piston column (17) whose two ends are respectively and seamlessly slidably connected to the corresponding guide air pipe (9) and air delivery pipe (16). The piston column (17) is of a tubular structure, and one-way air guide valves (21) are arranged inside both its interior and the interior of the guide air pipe (9). The one-way air guide valve (21) inside the guide air pipe (9) is arranged above the uppermost one-way air injection hole (22).

6. The low-temperature grain storage refrigeration equipment directly driven by solar energy according to claim 5, characterized in that: The extrusion type air delivery and cooling mechanism also includes a control shaft (20) movably penetrating through the partition between the convex cavity (10) and the annular cavity (11), and the end of the control shaft (20) arranged inside the annular cavity (11) is in a square shape. A flat plate (18) is fixedly connected to the middle of the piston column (17), and an inclined slot (19) penetrating both its two sides is arranged on the flat plate (18). The inclined slot (19) is in clamping and sliding connection with the square-shaped end of the corresponding control shaft (20).

7. A refrigeration device for low-temperature grain storage directly driven by solar energy according to claim 6, characterized in that: The extrusion type gas transmission and cooling mechanism further includes a pushing disk (25) key-connected to the shaft end of the servo motor (15), and a pressure-bearing block (29) is slidably connected to the teeth of the pushing disk (25). The pressure-bearing block (29) is provided at the end of each control shaft (20) in the convex cavity (10). A partition disk (23) is fixedly connected to the middle of the control shaft (20) in the convex cavity (10), and springs (24) are arranged on both sides of the partition disk (23). The springs (24) on both sides of the partition disk (23) are respectively connected to the outer wall of the mounting cover (12) and the partition between the convex cavity (10) and the annular cavity (11).

8. A refrigeration device for low-temperature grain storage directly driven by solar energy according to claim 7, characterized in that: The surface of the pressure-bearing block (29) facing the axis of the pushing disk (25) is a curved surface, and the distance from the curved surface to the axis of the pushing disk (25) changes step by step.

9. A refrigeration device for low-temperature grain storage directly driven by solar energy according to claim 8, characterized in that: The pressure dispersion mechanism includes limiting tubes (26) evenly distributed at equal angles on the circumferential side of the lower surface of each air dispersion hole. A blocking plug (28) is movably connected to the upper end of the air dispersion hole, and a connecting disk (27) coaxial with it is fixedly connected to the lower end of the blocking plug (28). Limiting rods are evenly distributed on the connecting disk (27), and the limiting rods on the connecting disk (27) movably extend into the lower end interior of the corresponding limiting tube (26).

10. The low-temperature grain storage refrigeration equipment directly driven by solar energy according to claim 9, characterized in that: The upper end of the blocking plug (28) is a conical structure, and the conical structure is in contact connection with the corresponding partition disk (23), which is convenient for assisting the movement of the control shaft (20) by squeezing the partition disk (23).

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