A domestic vacuum tube solar energy heat storage and naan baking device
Patent Information
- Application Number
- CN202610948085.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-29
- Publication Date
- 2026-09-04
AI Technical Summary
这种结构通常需要配置复杂的追光机械机构，导致设备整体结构庞大、制造成本较高，且安装调试过程繁琐，不适合普通家庭日常使用
1、本发明通过设置由保温层与蓄热内胆层构成的同轴嵌套结构，并在两者之间配置带有螺旋金属导流挡板的环形换热流道，实现了气食隔离的间接辐射烘烤，高温气流在流道内加热蓄热内胆层而不接触面胚，实现了无明火、无废气、无污染的干净烘烤过程，蓄热内胆层提供的粗糙多孔贴敷面可防止面胚脱落，通过蓄热壁面的辐射烘烤，使食物口感接近传统馕坑，适合在家庭庭院或阳台环境中使用。
Smart Images
Figure CN122681371A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of food processing equipment technology, specifically to a household vacuum tube solar thermal storage naan baking device. Background Technology
[0002] Naan is a common traditional bread, traditionally made primarily using earthen ovens. Traditional naan ovens typically use firewood or coal as fuel, which produces smoke and fumes, posing safety hazards due to open flames and polluting the environment, making them unsuitable for widespread use in modern homes, such as balconies and courtyards. To address the environmental and safety issues associated with fuel combustion, electric or gas-fired naan ovens or baking machines have emerged on the market. While these devices improve hygiene, they consume significant amounts of conventional energy, increasing household operating costs. Furthermore, conventional ovens often use metal interiors, which cannot provide the porous, absorbent properties and specific heat radiation environment of traditional earthen ovens, resulting in differences in texture and crispness compared to traditional methods.
[0003] To reduce energy consumption, some technological solutions attempt to apply solar energy to the food baking field. Existing solar baking equipment mostly uses reflective mirrors to concentrate sunlight and directly heat the object. This structure typically requires complex tracking mechanisms, resulting in a large overall structure, high manufacturing costs, and cumbersome installation and commissioning processes, making it unsuitable for ordinary household use. Furthermore, some baking systems using solar air-collecting technology exhibit poor adaptability to environmental changes during actual operation. When the device is first started or when there is cloudy weather, the collector cannot immediately provide high-temperature airflow. At this time, the low-temperature air pumped in by the fan directly intrudes into the baking cavity, causing a sharp drop in internal temperature. At night or after sunlight ceases, heat from the baking cavity easily flows back into the external environment through uninsulated pipes, leading to large temperature fluctuations in the system and failing to provide a stable and continuous heat storage baking environment for dough maturation. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides a household vacuum tube solar thermal storage naan baking device, which solves the problems mentioned in the background section.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a household vacuum tube solar thermal storage naan baking device, comprising: The heat collection unit includes a support frame, an air manifold and multiple heat collection tubes mounted on the support frame, wherein the two ends of the air manifold are respectively provided with a cold air outlet and a hot air outlet; The power transmission unit includes a photovoltaic panel and a fan electrically connected to the photovoltaic panel, wherein the air outlet of the fan is connected to the cold air inlet; The anti-reverse temperature self-locking heat exchange unit includes a three-way valve box, which has an air inlet, an air outlet and a pressure relief valve. The air inlet is connected to the hot air outlet. The three-way valve box is equipped with a damper and a bimetallic thermal lock. The damper and the bimetallic thermal lock cooperate to control the airflow of the air inlet to be directed to the air outlet or the pressure relief valve. A heat-storing naan baking unit includes an outer shell, an annular heat exchange channel, and a heat-storing inner liner; the annular heat exchange channel is sleeved on the outer periphery of the heat-storing inner liner, and the air inlet of the annular heat exchange channel is connected to the air outlet.
[0006] Preferably, the air manifold is provided with a partition along the axial direction inside, and the partition divides the inside of the air manifold into a cold air inlet chamber and a hot air outlet chamber that are not interconnected.
[0007] Preferably, each of the heat collection tubes is coaxially fitted with a guide inner tube. The top end of the guide inner tube passes through the partition and connects to the cold air inlet chamber. The bottom end of the guide inner tube is suspended and has a folding gap between it and the bottom inner wall of the heat collection tube. A reverse heat exchange channel is formed between the outer wall of the guide inner tube and the inner wall of the heat collection tube. The top end of the reverse heat exchange channel connects to the hot air outlet chamber.
[0008] Preferably, the top of the damper is suspended and mounted on the inner wall of the air outlet via a hinge. A U-shaped limiting frame is fixed to the lower end of the damper on the windward side. The bottom end of the bimetallic thermal lock is fixed to the bottom wall of the three-way valve box. The top of the bimetallic thermal lock extends into and engages with the U-shaped limiting frame, restricting the damper from swinging towards the air outlet. The bimetallic thermal lock is used to bend towards the windward side when heated and deformed, so that the top of the bimetallic thermal lock disengages from the U-shaped limiting frame.
[0009] Preferably, an L-shaped limiting block is fixed to the inner side wall of the three-way valve box. The L-shaped limiting block is located on the leeward side swing and fall trajectory of the damper, and is used to block the damper when it is lowered and reset by gravity. The pressure relief valve port is opened on the bottom wall of the three-way valve box, and the pressure relief valve port is located between the air inlet and the bimetallic thermal lock.
[0010] Preferably, the power output terminal of the photovoltaic panel is directly electrically connected to the power input terminal of the wind turbine to drive the wind turbine.
[0011] Preferably, the heat-storing naan baking unit further includes a heat-insulating layer, and the outer shell, the heat-insulating layer and the heat-storing inner liner are coaxially nested in sequence. The hollow area of the heat-storing inner liner is a baking cavity, and the annular heat exchange channel is located between the outer wall surface of the heat-storing inner liner and the inner wall surface of the heat-insulating layer.
[0012] Preferably, a spiral metal flow guide baffle is fixed axially inside the annular heat exchange channel.
[0013] Preferably, the heat storage inner liner is a refractory clay cylinder or a porous cordierite ceramic cylinder, and the inner wall surface of the heat storage inner liner is a rough porous adhesive surface.
[0014] Preferably, the top of the outer shell is movably connected to a top cover via a hinge. The top cover covers the top opening of the heat storage inner liner. The top cover has an exhaust hole. A ventilation cap is rotatably mounted above the exhaust hole. The ventilation cap is used to adjust the opening degree of the exhaust hole.
[0015] This invention provides a household vacuum tube solar-powered naan baking device. It has the following beneficial effects: 1. This invention achieves indirect radiative baking with gas-food isolation by setting up a coaxial nested structure consisting of a heat insulation layer and a heat storage inner liner layer, and configuring an annular heat exchange channel with a spiral metal baffle between the two. The high-temperature airflow heats the heat storage inner liner layer in the channel without contacting the dough, realizing a clean baking process without open flame, exhaust gas, or pollution. The rough and porous surface provided by the heat storage inner liner layer can prevent the dough from falling off. Through radiative baking of the heat storage wall, the taste of the food is close to that of a traditional tandoor oven, making it suitable for use in home courtyards or balcony environments.
[0016] 2. This invention achieves zero-fuel, zero-electricity operation by setting up a heat collection tube with an internal guide pipe and a photovoltaic panel direct-drive fan. The output power of the photovoltaic panel is synchronized with the external sunlight, so that the airflow of the fan is automatically matched with the heat collection capacity of the system. There is no need to configure a complex light-tracking mechanism and an electronically controlled energy storage device. Combined with the high heat collection efficiency and heat preservation characteristics of the heat collection tube, the overall structure of the device is simple, the manufacturing cost is low, and the installation is convenient. It lowers the threshold for home use while saving energy and protecting the environment.
[0017] 3. This invention achieves anti-reverse temperature control through a three-way valve box with a damper and a bimetallic thermostatic latch in the gas path, ensuring stable internal temperature of the device and preventing it from being affected by cold air and low light conditions. In cold start conditions, the thermostatic latch restricts the damper from opening, allowing low-temperature airflow to escape from the pressure relief valve. When low light causes the air pressure to decrease, the damper naturally droops and closes due to gravity, completely cutting off the air convection between the heat storage inner liner and the outside. This structure effectively prevents cold air intrusion and internal heat backflow, improving the operational stability of the device under variable weather conditions. Attached Figure Description
[0018] Figure 1 This is a front perspective view of the present invention; Figure 2 This is a rear perspective view of the present invention; Figure 3 This is a schematic diagram of the internal structure of the air manifold of the present invention; Figure 4 The diagram illustrates the position of the inner guide tube in this invention. Figure 5 This is a schematic diagram of the internal structure of the three-way valve box of the present invention; Figure 6 This is a schematic diagram of the airflow direction inside the three-way valve box of the present invention; Figure 7 This is a schematic diagram illustrating the open state of the top cover of the outer casing of the present invention; Figure 8 This is a schematic diagram showing the assembly position of the annular heat exchange channel of the present invention.
[0019] The components include: 1. Air manifold; 2. Support frame; 3. Heat collector tube; 4. Inner guide tube; 5. Cold air outlet; 6. Hot air outlet; 7. Fan; 8. Photovoltaic panel; 9. Three-way valve box; 10. Air inlet; 11. Air outlet; 12. Bimetallic thermal lock; 13. L-shaped limit block; 14. Air damper; 15. U-shaped limit frame; 16. Pressure relief valve; 17. Heat storage inner liner; 18. Annular heat exchange channel; 19. Insulation layer; 20. Outer shell; 21. Top cover; 22. Ventilation cap; 23. Exhaust vent. Detailed Implementation
[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Please see the appendix Figure 1 - Appendix Figure 2 This invention provides a household vacuum tube solar thermal storage naan baking device, including a heat collection unit, a power transmission unit, an anti-reverse temperature self-locking heat exchange unit, and a thermal storage naan baking unit. The heat collection unit includes a support frame 2 and an air manifold 1 and multiple heat collection tubes 3 installed on the support frame 2. The two ends of the air manifold 1 are respectively provided with a cold air outlet 5 and a hot air outlet 6. The power transmission unit includes a photovoltaic panel 8 and a fan 7 electrically connected to the photovoltaic panel 8. The air outlet of the fan 7 is connected to the cold air outlet 5. The anti-reverse temperature self-locking heat exchange unit includes a three-way valve box 9. The three-way valve box 9 is provided with an air inlet 10, an air outlet 11, and a pressure relief valve 16. The air inlet 10 is connected to the hot air outlet 6. The thermal storage naan baking unit includes an outer shell 20, an annular heat exchange channel 18, and a thermal storage inner liner 17. The annular heat exchange channel 18 is sleeved on the outer periphery of the thermal storage inner liner 17. The air inlet of the annular heat exchange channel 18 is connected to the air outlet 11. Please see the appendix Figure 3- Appendix Figure 4 The air manifold 1 has a baffle plate installed axially inside, which divides the air manifold 1 into a cold air inlet chamber and a hot air outlet chamber that are not connected to each other. Each heat collector tube 3 has a guide inner tube 4 coaxially fitted inside. The top end of the guide inner tube 4 passes through the baffle plate and connects to the cold air inlet chamber. The bottom end of the guide inner tube 4 is suspended and has a folding gap between it and the bottom inner wall of the heat collector tube 3. The outer wall of the guide inner tube 4 and the inner wall of the heat collector tube 3 form a reverse heat exchange channel. The top end of the reverse heat exchange channel connects to the hot air outlet chamber. The cold air delivered by the fan 7 enters the cold air inlet chamber through the cold air outlet 5. The air is distributed to each inner guide pipe 4 and flows downward. After reaching the bottom of the heat collector tube 3, the air enters the reverse heat exchange channel through the reversal gap. The air flows from bottom to top in the reverse heat exchange channel and absorbs the heat energy collected by the heat collector tube 3. The heated air is gathered in the hot air outlet chamber and discharged through the hot air outlet 6. The power output terminal of the photovoltaic panel 8 is directly connected to the power input terminal of the fan 7. The output power of the photovoltaic panel 8 changes with the intensity of the external light, causing the speed and air pressure of the fan 7 to change accordingly, so as to realize the synchronous adjustment of the airflow input and the heat collection power of the heat collector tube 3. Please see the appendix Figure 5 - Appendix Figure 6 The three-way valve box 9 is equipped with a damper 14 and a bimetallic thermal lock 12. The damper 14 and the bimetallic thermal lock 12 work together to control the airflow direction of the air inlet 10. The top of the damper 14 is suspended and installed on the inner wall of the air outlet 11 by a hinge. A U-shaped limiting frame 15 is fixed to the lower end of the windward side of the damper 14. The bottom end of the bimetallic thermal lock 12 is fixed to the bottom wall of the three-way valve box 9. An L-shaped limiting block 13 is fixed to the inner side wall of the three-way valve box 9. The L-shaped limiting block 13 is located on the swing and fall trajectory of the damper 14 on the leeward side. The pressure relief valve port 16 is opened on the bottom wall of the three-way valve box 9 and is located between the air inlet 10 and the bimetallic thermal lock 12. The internal structure of the three-way valve box 9 produces different mechanical actions under different operating conditions: In cold start condition, when the system generates high wind pressure but the airflow temperature does not reach the set threshold at the initial start-up, the bimetallic thermal lock 12 remains in a straight state. The top of the bimetallic thermal lock 12 extends into and engages with the U-shaped limiting frame 15, forming a mechanical interference limit on the damper 14, restricting the damper 14 from opening towards the outlet 11. At this time, the low-temperature airflow input into the inlet 10 is blocked and discharged to the external environment along the pressure relief valve 16 under the action of wind pressure, preventing the low-temperature airflow from entering the heat storage baking unit. Under normal heating conditions, the airflow temperature output by the heat collection unit rises and reaches the deformation threshold of the bimetallic thermal lock 12. The bimetallic thermal lock 12 is heated and bends and deforms towards the windward side. Its top end exits from the U-shaped limiting frame 15, releasing the limiting effect on the damper 14. Under the action of airflow thrust, the damper 14 deflects and opens along the top hinge towards the air outlet 11. The high-temperature airflow enters the annular heat exchange channel 18 through the air outlet 11. Under cloudy conditions, the output power of the photovoltaic panel 8 decreases, and the speed of the fan 7 decreases, resulting in insufficient aerodynamic thrust to overcome the gravity of the damper 14. Under the action of gravity, the damper 14 naturally droops and closes, cutting off the fluid passage between the air inlet 10 and the air outlet 11. During the descent of the damper 14, the L-shaped limit block 13 stops the damper 14, causing the damper 14 to stop at the preset position facing the bimetallic thermal lock 12. After the damper 14 closes, the heat storage baking unit forms a relatively closed heat preservation space, blocking the reverse convection of internal heat to the heat collection unit. Please see the appendix Figure 7 - Appendix Figure 8 The heat storage baking unit also includes an insulation layer 19. The outer shell 20, the insulation layer 19 and the heat storage inner liner 17 are coaxially nested in sequence. The hollow area of the heat storage inner liner 17 is the baking cavity. An annular heat exchange channel 18 is located between the outer wall of the heat storage inner liner 17 and the inner wall of the insulation layer 19. A spiral metal guide baffle is fixed axially inside the annular heat exchange channel 18. The heat storage inner liner 17 is a refractory clay cylinder or a porous cordierite ceramic cylinder. The inner wall of the heat storage inner liner 17 is a rough porous surface. The top of the outer shell 20 is movably connected to a top cover 21 through a hinge. The top cover 21 covers the top opening of the heat storage inner liner 17. The top cover 21 has an exhaust hole 23. A ventilation cap 22 is rotatably mounted above the exhaust hole 23. The ventilation cap 22 is used to adjust the opening of the exhaust hole 23. The high-temperature airflow discharged from the outlet 11 enters the annular heat exchange channel 18. Guided by the spiral metal baffle, the airflow spirals and rises along the outer wall of the heat storage inner liner 17, transferring heat to the heat storage inner liner 17. After the heat storage inner liner 17 heats up, it radiates heat to the central baking cavity. The dough is applied to the rough and porous application surface of the heat storage inner liner 17 to obtain heat and complete the baking. During the baking process, the evaporated gas gathers at the top. By rotating the ventilation cap 22, the flow cross-sectional area of the exhaust port 23 is adjusted to realize the discharge of gas inside the baking cavity and the regulation of micro-positive pressure.
[0022] Working principle: Under external sunlight, the photovoltaic panel 8 converts solar energy into electrical energy and directly drives the fan 7 to operate. The fan 7 forces external cold air into the cold air inlet 5 of the air manifold 1 fixed on the support frame 2 and into the cold air intake chamber. The cold air is compressed and distributed to multiple guide pipes 4 and flows downward. When the cold air reaches the bottom of the guide pipe 4 and is suspended, it changes its flow direction through the reversal gap and enters the reverse heat exchange channel formed between the guide pipe 4 and the inner wall of the heat collector pipe 3 and flows upward. During this process, the heat collector pipe 3 absorbs solar radiation energy and transfers it to the air in the reverse heat exchange channel, which heats up the cold air and turns it into a high-temperature airflow. The high-temperature airflow gathers into the hot air outlet chamber of the air manifold 1 and then exits from the hot air inlet 6 and enters the air inlet 10 of the three-way valve box 9. After the airflow enters the three-way valve box 9, the internal structure performs corresponding mechanical actions according to the temperature and wind pressure of the airflow: When the system is cold-started or insufficient light causes the heat collection temperature to fail to reach the set threshold, the bimetallic thermal lock 12 maintains a straight initial state, with its top end locked in the U-shaped limit frame 15 at the bottom of the damper 14. The damper 14 is mechanically locked and cannot swing towards the air outlet 11. At this time, the low-temperature airflow continuously pumped into the three-way valve box 9 by the fan 7 cannot pass through the damper 14. Under pressure, the low-temperature airflow is discharged into the external environment through the pressure relief valve 16 at the bottom. This process blocks the low-temperature air from entering the heat storage baking unit at the rear. When the airflow temperature output by the heat collector tube 3 continues to rise and reaches the deformation threshold of the bimetallic thermal lock 12, the bimetallic thermal lock 12 bends towards the air inlet 10 due to heat. The top of the bimetallic thermal lock 12 exits the U-shaped limiting frame 15, releasing the locking state of the damper 14. Under the action of the wind pressure thrust of the high-temperature airflow, the damper 14 deflects and opens towards the air outlet 11 along the hinge at the top. The high-temperature airflow passes through the three-way valve box 9 and is input to the air inlet end of the annular heat exchange channel 18 through the air outlet 11. When the outside is cloudy or the sunlight disappears, the output power of the photovoltaic panel 8 decreases and the speed of the fan 7 decreases, resulting in a weakening of the aerodynamic thrust. When the wind pressure thrust is less than the weight of the damper 14, the damper 14 naturally droops and closes, cutting off the fluid passage. The damper 14 falls back to the L-shaped limiting block 13 on the leeward side to allow the heat storage baking unit to circulate with the outside air, preventing the internal heat from being lost in the opposite direction. After the high-temperature airflow enters the annular heat exchange channel 18, it spirals and rises along the outer wall of the heat storage inner liner 17 under the guidance of the spiral metal guide baffle. The heat energy carried by the airflow is conducted to the heat storage inner liner 17, and the loss to the outer shell 20 is reduced by the insulation layer 19. The cooled airflow is discharged into the external environment from the top. After absorbing heat, the inner heat storage layer 17 increases in temperature and conducts the heat to the inner wall surface, radiating heat energy into the hollow baking cavity. During operation, the top cover 21 is opened, and the dough is applied to the rough, porous surface inside the inner heat storage layer 17. The dough completes the baking process through surface contact conduction and heat radiation inside the cavity. The water vapor released during the baking process gathers upwards. By rotating the ventilation cap 22 on the top cover 21, the flow cross-sectional area of the exhaust hole 23 is changed, and the gas is discharged.
Claims
1. A household vacuum tube solar thermal storage naan baking device, characterized in that, include: The heat collection unit includes a support frame (2) and an air manifold (1) and multiple heat collection tubes (3) installed on the support frame (2). The air manifold (1) has a cold air inlet (5) and a hot air inlet (6) at both ends. The power transmission unit includes a photovoltaic panel (8) and a fan (7) electrically connected to the photovoltaic panel (8), wherein the air outlet of the fan (7) is connected to the cold air outlet (5); The anti-reverse temperature self-locking heat exchange unit includes a three-way valve box (9), which is provided with an air inlet (10), an air outlet (11) and a pressure relief valve (16). The air inlet (10) is connected to the hot air outlet (6). The three-way valve box (9) is provided with a damper (14) and a bimetallic thermosensitive latch (12) inside. The damper (14) and the bimetallic thermosensitive latch (12) cooperate to control the airflow of the air inlet (10) to be directed to the air outlet (11) or the pressure relief valve (16). The heat storage baking naan unit includes an outer shell (20), an annular heat exchange channel (18), and a heat storage inner liner (17); the annular heat exchange channel (18) is sleeved on the outer periphery of the heat storage inner liner (17), and the air inlet of the annular heat exchange channel (18) is connected to the air outlet (11).
2. A household vacuum tube solar thermal storage naan baking device according to claim 1, characterized in that, The air manifold (1) has a partition along the axial direction inside, which divides the interior of the air manifold (1) into a cold air inlet chamber and a hot air outlet chamber that are not connected to each other.
3. A household vacuum tube solar thermal storage naan baking device according to claim 2, characterized in that, Each of the heat collection tubes (3) is coaxially fitted with a guide inner tube (4). The top end of the guide inner tube (4) passes through the partition and connects to the cold air inlet chamber. The bottom end of the guide inner tube (4) is suspended and has a folding gap between it and the bottom inner wall of the heat collection tube (3). The outer wall of the guide inner tube (4) and the inner wall of the heat collection tube (3) form a reverse heat exchange channel. The top end of the reverse heat exchange channel connects to the hot air outlet chamber.
4. A household vacuum tube solar thermal storage naan baking device according to claim 1, characterized in that, The top of the damper (14) is suspended and installed on the inner wall of the air outlet (11) by a hinge. A U-shaped limiting frame (15) is fixed to the lower end of the damper (14) on the windward side. The bottom end of the bimetallic thermal lock (12) is fixed to the bottom wall of the three-way valve box (9). The top of the bimetallic thermal lock (12) extends into and engages with the U-shaped limiting frame (15) to restrict the damper (14) from swinging towards the air outlet (11). The bimetallic thermal lock (12) is used to bend towards the windward side when heated and deformed, so that the top of the bimetallic thermal lock (12) is disengaged from the U-shaped limiting frame (15).
5. A household vacuum tube solar thermal storage naan baking device according to claim 4, characterized in that, An L-shaped limiting block (13) is fixed to the inner side wall of the three-way valve box (9). The L-shaped limiting block (13) is located on the leeward side swing and fall trajectory of the damper (14) and is used to block the damper (14) when it is lowered and reset by gravity. The pressure relief valve port (16) is opened on the bottom wall of the three-way valve box (9) and the pressure relief valve port (16) is located between the air inlet (10) and the bimetallic thermal lock (12).
6. A household vacuum tube solar thermal storage naan baking device according to claim 1, characterized in that, The power output terminal of the photovoltaic panel (8) is directly electrically connected to the power input terminal of the wind turbine (7) to drive the wind turbine (7) to operate.
7. A household vacuum tube solar thermal storage naan baking device according to claim 1, characterized in that, The heat storage baking unit also includes a heat insulation layer (19). The outer shell (20), the heat insulation layer (19) and the heat storage inner liner (17) are coaxially nested in sequence. The hollow area of the heat storage inner liner (17) is the baking cavity. The annular heat exchange channel (18) is located between the outer wall of the heat storage inner liner (17) and the inner wall of the heat insulation layer (19).
8. A household vacuum tube solar thermal storage naan baking device according to claim 7, characterized in that, The annular heat exchange channel (18) has a spiral metal guide baffle fixed inside along the axial direction.
9. A household vacuum tube solar thermal storage naan baking device according to claim 7, characterized in that, The heat storage inner liner (17) is a refractory clay cylinder or a porous cordierite ceramic cylinder, and the inner wall surface of the heat storage inner liner (17) is a rough porous adhesive surface.
10. A household vacuum tube solar thermal storage naan baking device according to claim 7, characterized in that, The top of the outer shell (20) is movably connected to a top cover (21) via a hinge. The top cover (21) covers the top opening of the heat storage inner liner (17). The top cover (21) has an exhaust hole (23). A ventilation cap (22) is rotatably mounted above the exhaust hole (23). The ventilation cap (22) is used to adjust the opening of the exhaust hole (23).