Temperature self-driven battery phase change heat management device

Abstract

The invention discloses a temperature self-driven battery phase change heat management device, which comprises a box body, a cavity for accommodating a battery is arranged in the box body, and a liquid cooling system for cooling the battery is arranged in the cavity; a vacuum layer is arranged on the inner wall of the cavity, the vacuum layer is provided with an inner cavity, a porous heat conduction framework is arranged in the inner cavity, and a powdery or granular phase change material is adsorbed on the porous heat conduction framework. The heat transfer performance of the battery to the external environment is spontaneously regulated and controlled at different temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a temperature self-driven battery phase change thermal management device. Background Art

[0002] As a core component of electric vehicles, battery safety is particularly important. The most important factor affecting battery safety is the operating temperature of the battery, that is, the temperature has a great impact on the performance of the battery. When the battery is lower than the normal operating temperature, the internal resistance of the battery increases, the capacity decreases, and it may even fail to work; when the battery is higher than the normal operating temperature, the battery may expand and leak, overheat, or even have the risk of spontaneous combustion, so the battery temperature needs to be controlled within a certain range. Different batteries have different normal operating temperature ranges. Taking lithium-ion batteries as an example, their normal operating temperature is -20°C to 60°C. Exceeding the upper limit of the operating temperature or falling below the lower limit of the operating temperature will cause adverse effects.

[0003] At present, the battery thermal management technology on the market mainly adopts liquid cooling. At low temperatures, the battery is usually heated directly by a heating plate or heated by antifreeze. At high temperatures, the antifreeze takes away the heat of the battery. Considering that phase change materials have high energy storage capacity, that is, high-temperature heat storage and low-temperature heat release, it can achieve the "peak shifting and valley filling" of heat, change the temporal and spatial distribution of heat, and alleviate the mismatch of heat in time, space and intensity. Phase change materials are usually combined with liquid cooling systems to achieve thermal management of batteries, thereby enhancing the uniformity of battery temperature, avoiding thermal runaway of batteries and reducing energy consumption.

[0004] However, the current thermal management system cannot take into account the needs of heat dissipation at high temperatures and heat preservation at low temperatures at the same time. Therefore, if the battery is working in a severe cold environment, part of the energy needs to be used to heat the battery. In order to reduce energy loss, it is necessary to strengthen the insulation of the battery and reduce the heat dissipation of the battery to the external environment. If the insulation of the battery is strengthened, the battery will heat up severely in a high temperature environment or when the battery is working under high load, and the heat will be difficult to transfer to the external environment, causing a series of safety risks. Summary of the invention

[0005] The purpose of the present invention is to provide a temperature self-driven battery phase change thermal management device designed to solve the deficiencies of the above-mentioned technology.

[0006] The present invention designs a temperature self-driven battery phase change thermal management device, comprising a box body, wherein the box body is provided with a cavity for accommodating a battery, and the cavity is provided with a liquid cooling system for cooling the battery; The inner wall of the cavity is provided with a vacuum layer. The vacuum layer has an inner cavity, and the inner cavity is provided with a porous heat-conducting framework. The porous heat-conducting framework adsorbs a powder or granular phase-change material. When the battery generates heat to a relatively high temperature, the temperature of the vacuum layer rises, and at the same time, the temperature of the porous heat-conducting framework also rises accordingly. The phase-change material sublimes from a solid state to a gaseous state and diffuses into the vacuum layer, increasing the heat-conducting coefficient in the vacuum layer, thereby promoting the continuous heat dissipation of the battery through the vacuum layer to the outside; When the battery dissipates heat to a relatively low temperature, the temperature of the vacuum layer decreases, and at the same time, the temperature of the porous heat-conducting framework also decreases accordingly. The gaseous phase-change material is cooled and re-condensed into a powder or granular form to be adsorbed on the porous heat-conducting framework. At this time, the heat-conducting coefficient in the vacuum layer decreases, making the battery adiabatic and heat-insulating.

[0007] Preferably, it further includes a control system. The control system includes a temperature control component and a heating wire arranged in the porous heat-conducting framework. The temperature control component is electrically connected to the battery and the heating wire. When the temperature control component senses that the temperature of the battery is too low due to heat dissipation, the temperature control component controls the heating wire to work, increasing the temperature of the vacuum layer, thereby making the battery adiabatic and heat-insulating.

[0008] Further optimized, the temperature control component includes a magnetic contact and a bimetallic strip. The magnetic contact is connected to the battery, and the bimetallic strip is connected to the heating wire. The bimetallic strip includes two metal sheets, metal sheet one and metal sheet two, with different coefficients of thermal expansion. Metal sheet one is arranged close to the magnetic contact and can be magnetically connected or disconnected from the magnetic contact; When the temperature of the battery is too low due to heat dissipation, the magnetic attraction force of the magnetic contact is greater than the thermal deformation force of metal sheet one and metal sheet two, causing the magnetic contact to be attracted to and connected to metal sheet one. At this time, the heating wire works; When the temperature of the battery rises to a preset value due to the work of the heating wire, the thermal deformation force generated by the thermal deformation of metal sheet one and metal sheet two is greater than the magnetic attraction force of the magnetic contact, causing the magnetic contact to disconnect from metal sheet one. At this time, the heating wire stops working, so that the battery remains in an adiabatic state.

[0009] Preferably, the liquid cooling system includes a liquid cooling channel arranged along the battery arrangement direction. The box body is provided with a coolant inlet and a coolant outlet that communicate with the liquid cooling channel.

[0010] Preferably, the vacuum layer includes an inner wall surface and an outer wall surface, and the inner wall surface and the outer wall surface enclose to form an inner cavity.

[0011] Further optimized, the inner wall surface is made of a material with a high heat-conducting coefficient; the outer wall surface is provided with a reflective layer to reflect the thermal radiation on the inner wall surface.

[0012] Preferably, a filler port for filling the phase change material is provided on the box body.

[0013] Further optimized, the phase change material is iodine.

[0014] Further optimized, after the phase change material is filled into the inner cavity of the vacuum layer, the vacuum layer is evacuated at low temperature so that the pressure in the inner cavity of the vacuum layer is reduced to.MPa or below, and then the phase change material is heated by a heating wire to sublime and fill the inner cavity of the vacuum layer. Then, after cooling, the phase change material recondenses into powder or granular form, so that most of the phase change material enters and adsorbs into the porous heat-conducting framework.

[0015] Further optimized, the porous heat-conducting framework is arranged close to the inner wall surface.

[0016] The technical effect of the present invention is that a vacuum layer is added to the box body for accommodating the battery, and a porous heat-conducting framework and a phase change material are arranged in the vacuum layer. When the battery temperature rises, the phase change material sublimes from solid state to gaseous state, so that the air pressure in the vacuum layer rises, and thus the heat conduction coefficient in the vacuum layer increases, and the heat transfer ability of the battery to the external environment increases, accelerating the heat dissipation and cooling of the battery, and the energy consumption required for heat dissipation can be reduced.

[0017] When the battery temperature drops, the phase change material condenses from gaseous state to solid state, so that the air pressure in the vacuum layer drops, and thus the heat conduction coefficient in the vacuum layer decreases, and the heat transfer ability of the battery to the external environment decreases, realizing the heat preservation effect on the battery and reducing the energy consumption required for heating.

[0018] That is, the phase change material undergoes solid-gas phase change at different temperatures, so that the heat conduction coefficient in the vacuum layer increases or decreases, realizing the heat dissipation or heat preservation of the battery through the inner cavity to the outside, reducing the pressure of the cooling system, cooperating with the liquid cooling system and the heat preservation system, avoiding the battery from being in too low or too high temperature states for a long time, and timely and quickly insulating and dissipating heat from the battery. Therefore, the present invention realizes the self-driven regulation and management of the battery's external heat transfer performance at different temperatures, realizes the heat preservation of the battery at low temperatures and heat dissipation at high temperatures, and improves the energy utilization efficiency, playing a certain role in energy conservation and emission reduction; at the same time, based on the characteristics of the phase change material, not only the overall structure is simple and easy to implement, but also it can work in multiple cycles in high-temperature and low-temperature environments, realizing the passive temperature control of the battery. Description of the Drawings

[0019] Figure 1 is a structural sectional view when the phase change material in the present invention is in solid state; Figure 2 is a schematic diagram of the flow direction of the liquid cooling system in the present invention; Figure 3 is a structural sectional view when the phase change material in the present invention is in gaseous state.

[0020] In the figure: 1, box body; 2, cavity; 3, battery; 4, vacuum layer; 41, inner wall surface; 42, outer wall surface; 43, inner cavity; 5, porous heat-conducting framework; 6, phase change material; 7, heating wire; 8, magnetic contact; 9, metal sheet one; 10, metal sheet two; 11, liquid cooling channel; 12, coolant inlet; 13, coolant outlet; 14, filler port. Specific embodiments

[0021] 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 belong to the scope of protection of the present invention.

[0022] The present invention includes a box body 1. A cavity 2 is provided inside the box body 1. A battery 3 is accommodated in the cavity 2. A vacuum layer 4 is provided on the inner wall of the cavity 2. The vacuum layer 4 has an inner cavity 43. The inner cavity 43 is evacuated to form a vacuum inner cavity. A porous heat-conducting framework 5 is provided in the inner cavity 43. The porous heat-conducting framework 5 forms a coverage along the inner wall of the cavity 2. The porous heat-conducting framework 5 is made of materials such as carbon foam, metal foam, porous graphite, graphite fiber or metal wire mesh, etc., which have high gas adsorption capacity. It has the characteristics of high thermal conductivity and high porosity. The porous heat-conducting framework 5 adsorbs a powdery or granular phase change material 6.

[0023] As Figure 3 shown, when the battery 3 generates heat to a relatively high temperature, the temperature inside the cavity 2 of the box body 1 also rises accordingly. Through heat conduction, the temperature of the vacuum layer 4 also rises accordingly. The temperature of the porous heat-conducting framework 5 in the vacuum layer 4 also rises accordingly. The phase change material 6 sublimes from solid to gas. The phase change material 6 diffuses from the porous heat-conducting framework 5 into the vacuum layer 4, so that the gaseous phase change material 6 fills the vacuum layer 4, and further increases the thermal conductivity inside the vacuum layer 4, thereby promoting the continuous heat dissipation of the battery 3 through the vacuum layer 4; the porous heat-conducting framework 5 not only enables the phase change material 6 to be evenly and quickly heated and sublimated, but also enables the phase change material 6 to be evenly distributed after condensation, facilitating the phase change of the phase change material 6.

[0024] As Figure 1 shown, when the battery 3 dissipates heat to a relatively low temperature, the temperature of the vacuum layer 4 is reduced. At the same time, the temperature of the porous heat-conducting framework 5 also decreases accordingly. The gaseous phase change material 6 is cooled and re-condensed into a powdery or granular state to be adsorbed on the porous heat-conducting framework 5. At this time, the thermal conductivity inside the vacuum layer 4 decreases, making the battery 3 adiabatic and achieving heat preservation for the battery 3.

[0025] In this embodiment, the phase change material 6 is made of a material that is easy to sublime and has a significantly different saturated vapor pressure at different temperatures, such as iodine. The saturated vapor pressures of iodine at different temperatures are shown in the following table: 。

[0026] When the temperature changes from -20°C to 60°C, the saturated vapor pressure of iodine changes from 0.04 Pa to 622.61 Pa, corresponding to an increase of about three orders of magnitude in the thermal conductivity in the inner cavity 43 of the vacuum layer 4, from 10 -5 W / (m•K) to 10 -2 W / (m•K), realizing automatic regulation of the gas thermal conductivity in the inner cavity 43 of the vacuum layer 4 at different temperatures.

[0027] Taking the lithium-ion battery 3 as an example, the normal operating temperature is -20°C to 60°C, and it generally needs to be controlled within the range of 0°C to 40°C. When the battery 3 is in a low-temperature environment for a long time, the heating wire 7 heats the battery 3 (or the battery 3 can also be heated by the coolant), so that the battery 3 is maintained at about 0°C. At this time, the internal air pressure in the inner cavity 43 of the vacuum layer 4 is about 1.4 Pa, and the thermal conductivity of the iodine vapor (i.e., the phase change material 6) in the inner cavity 43 is about 10 -5 W / (m•K), isolating the heat dissipation of the battery 3 to the external environment and also improving the energy utilization efficiency of the heating wire 7.

[0028] A liquid cooling system for cooling the battery 3 is provided in the cavity 2. As Figure 2 shown, the liquid cooling system includes a liquid cooling channel 11 arranged along the arrangement direction of the battery 3. A coolant inlet 12 and a coolant outlet 13 communicating with the liquid cooling channel 11 are provided on the box body 1 for circulating and exchanging the coolant. The liquid cooling channel 11 can be a straight channel, a z-shaped channel, a corrugated channel, etc., and is used to dissipate heat from the battery 3 during operation and can also heat the battery 3 under extremely cold conditions.

[0029] The present invention further includes a control system. The control system includes a temperature control component and a heating wire 7 arranged in the porous heat-conducting framework 5. The temperature control component is electrically connected to the battery 3 and the heating wire 7. When the temperature control component senses that the battery 3 dissipates heat and its temperature is too low, the temperature control component controls the heating wire 7 to work, so that the temperature of the vacuum layer 4 rises to form an adiabatic state for the battery 3.

[0030] The temperature control component includes a magnetic contact 8 and a bimetallic strip. The magnetic contact 8 is connected to the battery 3, and the bimetallic strip is connected to the heating wire 7. That is, the heating wire 7, the bimetallic strip, the magnetic contact 8, and the battery 3 form an electrical circuit loop. The bimetallic strip includes two metal sheets 9 and 10 with different thermal expansion coefficients. The metal sheet 9 is arranged close to the magnetic contact 8 and can be magnetically connected or disconnected from the magnetic contact 8.

[0031] When the battery 3 dissipates heat and its temperature becomes too low, usually when the temperature is lower than -10°C, the magnetic attraction force of the magnetic contact 8 is greater than the thermal deformation force of the first metal sheet 9 and the second metal sheet 10, causing the magnetic contact 8 to attract and connect with the first metal sheet 9, and the circuit is connected. At this time, the heating wire 7 works, and the temperature of the porous heat-conducting skeleton 5 rises accordingly, and the heat is transferred to the cavity 2 through the vacuum layer 4 to supply heat to the battery 3.

[0032] When the temperature of the battery 3 rises to the preset value through the work of the heating wire 7, the preset value is usually 0°C, the thermal deformation force generated by the thermal deformation of the first metal sheet 9 and the second metal sheet 10 is greater than the magnetic attraction force of the magnetic contact 8, causing the magnetic contact 8 to disconnect from the first metal sheet 9, and the circuit is disconnected. At this time, the heating wire 7 stops working, so that the battery 3 is kept in an adiabatic state through the vacuum layer 4 to keep the battery 3 warm.

[0033] It should be noted that the magnetic contact 8 is made of a magnetic material, and the first metal sheet 9 is a magnetizable metal material, such as a thin iron sheet; the first metal sheet 9 and the second metal sheet 10 are arranged in contact. As the temperature rises, the second metal sheet 10 will undergo thermal deformation, driving the first metal sheet 9 to deform together. The magnetic contact 8 is generally close to the first metal sheet 9, so that when the first metal sheet 9 deforms, it can be magnetically attracted and connected or disconnected from the magnetic contact in a timely and accurate manner.

[0034] The relationship among the above-mentioned phase change material 6, the control system and the liquid cooling system is that when the temperature of the battery 3 rises or falls, the phase change material 6 automatically adjusts the heat conduction coefficient in the inner cavity 43 of the vacuum layer 4 through its sublimation at high temperature and condensation at low temperature characteristics, that is, through the vacuum layer 4, the heat management requirements of the battery 3 for heat dissipation at high temperature and heat preservation at low temperature are realized; taking the lithium battery 3 as an example, its normal operating temperature is -20°C to 60°C, but generally the temperature of the battery 3 needs to be controlled within the range of 0 to 40°C. Exceeding the upper limit of the operating temperature or being lower than the lower limit of the operating temperature will cause adverse effects. Therefore, when the temperature of the battery 3 is lower than -10°C, the control system controls the heating wire 7 to heat, so that the temperature of the battery 3 rises until it reaches 0°C. At this time, the battery 3 is at a normal temperature, and then the control system controls the heating wire 7 to stop heating, that is, when the temperature of the battery 3 exceeds the controllable range of the phase change material 6, the control system can timely adjust the temperature of the battery 3 to the normal range; when the temperature is too high, that is, when it exceeds 40°C, at this time the liquid cooling system works, and the coolant enters from the coolant inlet 12, flows through the liquid cooling channel 11 and then flows out from the coolant outlet 13 to cool the battery 3, the vacuum layer 4 and the cavity 2 at the same time, and the cooling effect is very significant, so that the temperature quickly drops below 40°C.

[0035] It should be noted that when the liquid cooling system reduces the temperature to 40°C, the air pressure in the inner cavity 43 of the vacuum layer 4 is about 133.47 Pa at this time, and the thermal conductivity of the iodine vapor in the inner cavity 43 of the vacuum layer 4 is about 10-2 W / (m•K), which is similar to the thermal conductivity of air. Heat dissipation can be formed to the external environment through the natural convection of iodine vapor to reduce the heat load of the liquid cooling system, thereby reducing the power of the liquid cooling system.

[0036] Furthermore, the vacuum layer 4 includes an inner wall surface 41 and an outer wall surface 42, and the inner wall surface 41 and the outer wall surface 42 enclose to form an inner cavity 43. The inner wall surface 41 and the outer wall surface 42 are made of materials with high thermal conductivity, such as aluminum alloy, which has a high thermal diffusion rate and can enhance heat transfer while ensuring strength; among them, the outer wall surface 42 is processed into a mirror surface or a silver-plated surface for reflecting the thermal radiation of the inner wall surface 41 and reducing the radiation heat dissipation of the inner wall surface 41 to the outside.

[0037] The battery 3 in the present invention is usually various batteries 3 suitable for operating temperatures within this range, such as lithium-ion batteries 3, lead-acid batteries 3, etc.

[0038] The box body 1 is provided with a filler port 14 for filling the phase change material 6. After the phase change material 6 is filled into the inner cavity 43 of the vacuum layer 4, the vacuum layer 4 is evacuated at low temperature so that the pressure in the inner cavity 43 of the vacuum layer 4 is reduced to 0.01 MPa or below. Then, the phase change material 6 is heated by the heating wire 7 to sublime and fill the inner cavity 43 of the vacuum layer 4. Then, after cooling, the phase change material 6 recondenses into powder or granular form, so that most of the phase change material 6 enters and adsorbs in the porous heat-conducting framework 5, so that most of the phase change material 6 can be adsorbed in the porous heat-conducting framework 5. By heating, the gaseous phase change material 6 can uniformly and quickly fill the entire inner cavity 43 of the vacuum layer 4. The box body 1 is also provided with a plugging port communicating with the inner cavity 43 of the vacuum layer 4, and the inner cavity 43 of the vacuum layer 4 can be evacuated through the plugging port to maintain the vacuum degree of the inner cavity 43.

[0039] Furthermore, the porous heat-conducting framework 5 is arranged close to or attached to the inner wall surface 41, so that heat transfer is faster and more timely.

[0040] The control system in the present invention further includes a control center, and the control center includes various temperature sensors and a circuit control board. Since it is a conventional technology, the specific structure and working principle will not be elaborated here.

[0041] The present invention is not limited to the above-mentioned best implementation mode. Anyone can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has a technical solution identical or similar to the present application, it falls within the protection scope of the present invention.

Claims

1. A temperature self-driven battery phase change thermal management device, characterized in that: It comprises a box (1), wherein a cavity (2) for accommodating a battery (3) is provided in the box (1), and a liquid cooling system for cooling the battery (3) is provided in the cavity (2); The inner wall of the cavity (2) is provided with a vacuum layer (4), the vacuum layer (4) has an inner cavity (43), the inner cavity (43) is provided with a porous heat-conducting skeleton (5), the porous heat-conducting skeleton (5) is adsorbed with a powdered or granular phase-change material (6), when the battery (3) generates heat to a relatively high temperature, the temperature of the vacuum layer (4) rises, and at the same time, the temperature of the porous heat-conducting skeleton (5) also rises accordingly, the phase-change material (6) sublimates from a solid state to a gaseous state, and diffuses into the vacuum layer (4), so that the thermal conductivity of the vacuum layer (4) increases, thereby promoting the battery (3) to continuously dissipate heat to the outside through the vacuum layer (4); When the battery (3) dissipates heat to a lower temperature, the temperature of the vacuum layer (4) decreases, and at the same time, the temperature of the porous heat-conducting skeleton (5) also decreases accordingly. The gaseous phase change material (6) is cooled and recondenses into powder or granules to be adsorbed on the porous heat-conducting skeleton (5). At this time, the thermal conductivity in the vacuum layer (4) decreases, so that the battery (3) forms thermal insulation and keeps warm.

2. A temperature self-driven battery phase change thermal management device according to claim 1, characterized in that: The invention also comprises a control system, the control system comprising a temperature control component and a heating wire (7) arranged in the porous heat-conducting skeleton (5), the temperature control component being electrically connected to the battery (3) and the heating wire (7), and when the temperature control component senses that the battery (3) is dissipating heat and its temperature is too low, the temperature control component controls the heating wire (7) to operate, so that the temperature of the vacuum layer (4) is increased, thereby making the battery (3) form thermal insulation and keep warm.

3. A temperature self-driven battery phase change thermal management device according to claim 2, characterized in that: The temperature control component comprises a magnetic contact (8) and a bimetallic strip, wherein the magnetic contact (8) is connected to a battery (3), and the bimetallic strip is connected to a heating wire (7). The bimetallic strip comprises two metal strips (9) and (10) having different thermal expansion coefficients, wherein the metal strip (9) is arranged close to the magnetic contact (8) and can be connected or disconnected with the magnetic contact (8) by magnetic attraction. When the battery (3) dissipates heat and its temperature is too low, the magnetic attraction of the magnetic contact (8) is greater than the thermal deformation force of the metal sheet 1 (9) and the metal sheet 2 (10), so that the magnetic contact (8) and the metal sheet 1 (9) are attracted to each other and connected, and the heating wire (7) works at this time; When the temperature of the battery (3) rises to a preset value through the operation of the heating wire (7), the thermal deformation force generated by the thermal deformation of the metal sheet 1 (9) and the metal sheet 2 (10) is greater than the magnetic attraction force of the magnetic contact (8), so that the magnetic contact (8) is disconnected from the metal sheet 1 (9). At this time, the heating wire (7) stops working, so that the battery (3) remains in an insulated state.

4. The temperature self-driven battery phase change thermal management device according to claim 1, characterized in that: The liquid cooling system comprises a liquid cooling channel (11) arranged along the arrangement direction of the batteries (3), and the box body (1) is provided with a cooling liquid inlet (12) and a cooling liquid outlet (13) which are in communication with the liquid cooling channel (11).

5. The temperature self-driven battery phase change thermal management device according to claim 1, characterized in that: The vacuum layer (4) comprises an inner wall surface (41) and an outer wall surface (42), and the inner wall surface (41) and the outer wall surface (42) enclose an inner cavity (43).

6. A temperature self-driven battery phase change thermal management device according to claim 5, characterized in that: The inner wall surface (41) is made of a material with a high thermal conductivity; and the outer wall surface (42) is provided with a reflection layer to reflect heat radiation on the inner wall surface (41).

7. The temperature self-driven battery phase change thermal management device according to claim 1, characterized in that: The box body (1) is provided with a filling port (14) for filling the phase change material (6).

8. The temperature self-driven battery phase change thermal management device according to claim 7, characterized in that: The phase change material (6) is iodine.

9. A temperature self-driven battery phase change thermal management device according to claim 8, characterized in that: After the phase change material (6) is filled into the inner cavity (43) of the vacuum layer (4), the vacuum layer (4) is evacuated at low temperature so that the pressure of the inner cavity (43) of the vacuum layer (4) is reduced to 0.01 MPa or below, and then the phase change material (6) is heated by the heating wire (7) so that the phase change material (6) sublimates and fills the inner cavity (43) of the vacuum layer (4). Then, after cooling, the phase change material (6) is re-condensed into powder or granules, so that most of the phase change material (6) enters and is adsorbed in the porous heat-conducting skeleton (5).

10. The temperature self-driven battery phase change thermal management device according to claim 5, characterized in that: The porous heat-conducting skeleton (5) is arranged close to the inner wall surface (41).

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