An OVD deposition reaction device and reaction system

Abstract

The present invention discloses an OVD deposition reaction device and a reaction system, which relate to the technical field of optical fiber preform manufacturing. On the one hand, the device includes two spaced cavity plates and a partition plate. The two cavity plates form a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform; a partition plate is spaced inside at least one of the cavity plates, and a channel for the cooling gas to flow is formed between the partition plate and the cavity plate. A baffle is provided at one end of the channel close to the air inlet side for making the cooling gas entering the channel from the air outlet side flow back to the air outlet side after being discharged from the channel. On the other hand, the reaction system includes the above reaction device, a burner, a deposition amount detection device and a control device. By spacing the partition plates on the cavity plates to form a channel for the cooling gas to flow, the partition plates and the cavity plates are cooled and temperature is reduced. By providing the baffle, the cooling gas flows back to the air outlet side after being discharged from the channel, so as to prevent glass particles from adhering to the partition plates.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber preform manufacturing, and particularly relates to an OVD deposition reaction device and a reaction system. Background Art

[0002] Representative manufacturing methods of optical fiber preforms include the OVD method (Outside Vapor Deposition) or the VAD method (Vapor Phase Axial Deposition). Both the OVD method and the VAD method deposit glass particles generated by a hydrogen-oxygen flame and then form transparent glass by heating. The OVD method is formed circumferentially outside a rotating target rod, and the VAD method is formed axially on a rotating target rod.

[0003] These manufacturing methods all perform deposition inside a reaction vessel. A part of the glass particles generated by the hydrogen-oxygen flame adheres to the target rod, and the remaining unadhered glass particles are discharged. By increasing the adhered glass particles, a deposited loose body is formed, and after subsequent dehydration and sintering, an optical fiber preform is manufactured.

[0004] In the existing OVD manufacturing method, the high temperature of the hydrogen-oxygen flame causes the temperature inside the reaction vessel to rise, resulting in deformation or rupture of the deposition reaction vessel. At the same time, if the unadhered glass particles are not completely discharged by the exhaust gas, the unadhered glass particles will adhere to the surface of the reaction vessel. When the gas flow is disordered, the adhered powder will adhere to the surface of the loose body again, etc., resulting in bright spots or foreign objects and affecting the properties. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide an OVD deposition reaction device and a reaction system to solve the problems in the prior art that glass particles are easily attached to the surface of the container and the high temperature causes the container to rupture.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] On the one hand, the present application provides an OVD deposition reaction device, including:

[0008] Two spaced-apart cavity plates, and the two cavity plates form a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform;

[0009] At least one of the inner sides of the cavity plates is provided with a partition plate at intervals, and a channel for the cooling gas to flow is formed between the partition plate and the cavity plate. One end of the channel close to the air inlet side is provided with a baffle cover for making the cooling gas entering the channel from the air outlet side flow back to the air outlet side after being discharged from the channel.

[0010] In some alternative embodiments, the baffle includes an arc-shaped plate, one end of the arc-shaped plate is connected to the cavity plate forming the channel, and the opening direction of the arc-shaped plate is opposite to the opening of the channel.

[0011] In some alternative embodiments, the baffle further includes a flat plate, the flat plate is connected to the other end of the arc-shaped plate and is parallel to the isolation plate.

[0012] In some alternative embodiments, a plurality of exhaust holes are spaced along the length direction on the isolation plate.

[0013] In some alternative embodiments, a baffle connected to the isolation plate is provided on one side of each exhaust hole close to the baffle, for causing the cooling gas in the channel to flow back to the gas outlet side when discharging from the exhaust hole.

[0014] In some alternative embodiments, the baffle is an arc-shaped plate, and the opening of the baffle faces the gas outlet side.

[0015] In some alternative embodiments, the included angle between the plane where the two ends of the baffle are located and the isolation plate is 75°.

[0016] In some alternative embodiments, the distance between the isolation plate and the cavity plate forming the channel is less than or equal to the distance between the flat plate and the isolation plate.

[0017] In some alternative embodiments, the two cavity plates are spaced apart in the vertical direction, and an isolation plate is spaced and connected to the inner wall of the upper cavity plate.

[0018] On the other hand, the present application also provides an OVD deposition reaction system, including:

[0019] Two spaced cavity plates, the two cavity plates form a cavity with an air inlet side and an air outlet side and are used for depositing an optical fiber preform;

[0020] At least one isolation plate is spaced inside at least one of the cavity plates, and a channel for cooling gas to flow is formed between the isolation plate and the cavity plate. A baffle is provided at one end of the channel close to the air inlet side, for causing the cooling gas entering the channel from the air outlet side to flow back to the air outlet side after discharging from the channel;

[0021] A blowtorch, which is located inside the cavity, and the airflow ejected by the blowtorch flows from the air inlet side to the air outlet side;

[0022] A deposition amount detection device, which is used for detecting the deposition amount of the target rod;

[0023] A control device, which is used for adjusting the flow rate of the cooling gas according to the obtained deposition amount to improve the cooling efficiency.

[0024] Compared with the prior art, the advantages of the present invention are as follows: By arranging partition plates at intervals on the inner side of at least one cavity plate, a channel for the flow of cooling gas is formed to cool the partition plates and the cavity plates, solving the problem that the heat generated by the blowtorch in the deposition reaction causes deformation or rupture of the cavity plates; By arranging a flow baffle at one end of the channel close to the air inlet side, the cooling gas flows back to the air outlet side after being discharged from the channel, so as to avoid the adhesion of glass particles on the partition plates. When the air flow is disordered, the adhered powder will adhere to the surface of the loose body again, resulting in bright spots or foreign matters and affecting the characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 is a schematic structural diagram of an OVD deposition reaction system of the present invention;

[0027] Figure 2 is a linear diagram showing the relationship between the diameter of the loose body and the gas flow rate in the embodiment of the present invention.

[0028] In the figure: 1, blowtorch; 2, partition plate; 21, exhaust hole; 22, baffle; 3, cavity plate; 31, flow baffle; 311, arc plate; 312, flat plate; 4, target rod. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0030] The following will further describe in detail the embodiments of an OVD deposition reaction device and a reaction system of the present invention with reference to the accompanying drawings.

[0031] On the one hand, as Figure 1As shown in the figure, the present application provides an OVD deposition reaction device, which includes two spaced cavity plates 3 and a partition plate 2. The two cavity plates 3 form a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform; at least one of the inner sides of the cavity plates 3 is provided with a partition plate 2 at intervals, and a channel for the cooling gas to flow is formed between the partition plate 2 and the cavity plate 3. A baffle 31 is provided at one end of the channel close to the air inlet side for causing the cooling gas entering the channel from the air outlet side to flow back to the air outlet side after being discharged from the channel.

[0032] It can be understood that a burner 1 and a target rod 4 for depositing an optical fiber preform are provided in the cavity. The burner 1 is used to introduce a raw material gas, such as SiCl4, into the hydrogen-oxygen flame to generate glass particles. The glass particles are deposited on the surface of the target rod 4 to form a loose body. The raw material gas enters the cavity from the air inlet side, and the waste gas and excess glass particles are discharged from the air outlet side. Therefore, in order to avoid the heat generated by the burner 1 from affecting the cavity plate 3, a partition plate 2 is provided and a cooling gas is introduced into the channel formed between the partition plate and the cavity plate 3 to cool the cavity plate 3.

[0033] In some alternative embodiments, the two cavity plates 3 are spaced apart in the vertical direction. Since hot air rises, a partition plate 2 is provided on the upper cavity plate 3.

[0034] In some alternative embodiments, the two cavity plates 3 are spaced apart in the horizontal direction. At this time, a partition plate 2 can be provided on any one of the cavity plates 3 close to the burner 1, or on both cavity plates 3 at the same time.

[0035] It can be understood that regardless of how the cavity plate 3 is placed, it should be ensured that a partition plate 2 is provided on the cavity plate 3 on the side close to the burner 1 or affected by the flame of the burner 1 to reduce the heat influence.

[0036] In this example, the cooling gas is air or an inert gas. It enters from the opening of the channel close to the air outlet side and flows out from the opening of the channel close to the air inlet side. Then, under the action of the baffle 31, the cooling gas flows back from the outside of the channel to the air outlet side. At this time, the flow direction of the cooling gas is the same as the direction of the raw material gas ejected by the burner 1. Thus, without disturbing the operation of the burner 1 and causing disorder to affect the deposition flame, a "wind curtain" is formed on the upper surface of the reaction vessel. While taking away the surface temperature of the cavity plate 3, the glass particles that are not attached to the target rod 4 can be blown from the surfaces of the cavity plate 3 and the partition plate 2 to the air outlet side and taken out of the cavity, avoiding the attachment of glass particles.

[0037] In some alternative embodiments, the baffle 31 includes an arc-shaped plate 311. One end of the arc-shaped plate 311 is connected to the cavity plate 3 forming the channel, and the opening direction of the arc-shaped plate 311 is opposite to the opening of the channel.

[0038] It can be understood that the baffle 31 is used to reflux the cooling gas flowing out of the channel and discharge it from the air outlet side, so that the cooling gas can flow from one end near the air outlet side to one end near the air inlet side in the channel, and then flow from the air inlet side to the air outlet side in the cavity after flowing out of the channel, so as to cool the cavity plate 3 and prevent glass particles from adhering to the cavity plate 3 and the isolation plate 2. Therefore, the arc plate 311 is arranged on the side of the channel close to the torch 1, and the opening direction of the arc plate 311 is opposite to the opening of the channel.

[0039] In some alternative embodiments, the baffle 31 further includes a flat plate 312, and the flat plate 312 is connected to the other end of the arc plate 311 and is parallel to the isolation plate 2.

[0040] In order to make the cooling gas discharged from the channel reflux to the air outlet side under the action of the baffle 31 and can be ejected close to the outer wall of the isolation plate 2, a flat plate 312 parallel to the isolation plate 2 is arranged at the other end of the arc plate 311 far from the connection with the cavity plate 3.

[0041] Preferably, the flat plate 312 partially overlaps with the isolation plate 2, so that a flow channel for the cooling gas to reflux to the air outlet side and close to the outer wall of the isolation plate 2 on the side close to the cavity can also be formed between the flat plate 312 and the isolation plate 2.

[0042] In some alternative embodiments, a plurality of exhaust holes 21 are arranged at intervals along the length direction on the isolation plate 2.

[0043] It can be understood that exhaust holes are opened on the isolation plate 2, so that part of the cooling gas in the channel can be discharged from the exhaust holes 21, and cooperate with the part of the cooling gas discharged from the opening near the air inlet side of the channel and refluxed, so as to further improve the cooling effect of the isolation plate 2 and the cavity plate 3 and reduce the adsorption of glass particles on the isolation plate 2.

[0044] In some alternative embodiments, a baffle 22 connected to the isolation plate 2 is provided on one side of each exhaust hole 21 close to the baffle 31, for making the cooling gas in the channel reflux to the air outlet side when discharging from the exhaust holes 21.

[0045] It can be understood that in order to cooperate with and strengthen the reflux of the cooling gas to the air outlet side after flowing out of the channel, a baffle is arranged at each exhaust hole 21, so that part of the cooling gas flowing out of the exhaust holes 21 is also discharged towards the air outlet side.

[0046] Preferably, the baffle 22 is an arc plate, one end of which is connected to the isolation plate 2 near the air inlet side of the exhaust hole 21, and the opening of the baffle 22 faces the air outlet side.

[0047] The arc-shaped baffle 22 allows the cooling gas flowing out of the exhaust hole 21 to flow back along the inner wall of the baffle 22. Compared with a flat baffle, it enables the cooling gas to adhere to the outer wall of the isolation plate 2, thereby blowing away the glass particles adhering to the isolation plate 2.

[0048] Furthermore, the angle between the plane where the two ends of the baffle 22 are located and the isolation plate 2 is 75°.

[0049] It can be understood that the angle of the baffle 22 has a great influence on the gas cooling effect. If the angle is too small, the cooling gas cannot flow out, affecting the cooling efficiency. On the contrary, if the angle is too large, the cooling gas will also blow towards the deposited loose body, forming a turbulent flow and affecting the deposition process. Therefore, in this example, it is preferred that the angle between the plane where the two ends of the baffle are located and the isolation plate 2 is 75°. Experiments have proved that this angle facilitates the outflow of the cooling gas and does not form a turbulent flow to affect the deposition process.

[0050] In some alternative embodiments, the diameter of the exhaust hole 21 is smaller than the straight-line distance between the end of the isolation plate 2 and the inner wall of the flow baffle 31.

[0051] It can be understood that if the diameter of the exhaust hole 21 is too large, the cooling gas will directly flow out of the exhaust hole instead of flowing out from the outlet on the intake side of the channel, resulting in poor cooling effect on the isolation plate 2. To ensure that most of the cooling gas can enter from one end of the channel and flow out from the other end, not only the flow rate and flow volume of the cooling gas need to be controlled, but also the diameter of the exhaust hole 21 should be sized to match the flow rate and flow volume of the cooling gas and be smaller than the size of the opening formed by the isolation plate 2 and the flow baffle 31, that is, the straight-line distance between the end of the isolation plate 2 and the inner wall of the flow baffle 31.

[0052] In some alternative embodiments, the distance between the isolation plate 2 and the cavity plate 3 forming the channel is less than or equal to the distance between the flat plate 312 and the isolation plate 2.

[0053] It can be understood that to facilitate the cooling gas discharged and flowing back from the channel to form an "air curtain" on the side wall of the isolation plate 2 close to the cavity and cooperate with the cooling gas discharged from the exhaust hole 21 without forming a turbulent flow to affect the deposition process, it is preferred that the distance between the cavity plate 3 and the isolation plate 2 is less than or equal to the distance between the flat plate 312 and the isolation plate 2, so that the cooling gas flowing out and flowing back from the channel covers the cooling gas discharged from the exhaust hole 21.

[0054] Preferably, the baffle 22 is located between the plane where the flat plate 312 is located and the isolation plate 2.

[0055] On the other hand, as Figure 1 shown, the present application also provides an OVD deposition reaction system, including a cavity plate 3, an isolation plate 2, and a blowtorch 1.

[0056] Specifically, two cavity plates 3 are spaced apart, forming a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform. On the inner side of at least one cavity plate 3, partition plates 2 are spaced apart, and a channel for the cooling gas to flow is formed between the partition plates 2 and the cavity plate 3. At one end of the channel close to the air inlet side, a flow baffle 31 is provided to make the cooling gas entering the channel from the air outlet side flow back to the air outlet side after discharging from the channel. The above burner 1 is located in the above cavity, and the air flow ejected by the burner 1 flows from the air inlet side to the air outlet side.

[0057] During the processing, a target rod 4 is placed at one end of the burner 1 close to the air outlet side. The burner 1 is used to introduce a raw material gas, such as SiCl4, into the hydrogen-oxygen flame to generate glass particles, and the glass particles are deposited on the surface of the target rod 4 to form a loose body. The raw material gas enters the cavity from the air inlet side, and a part of the unadhered glass particles and waste gas are discharged from the exhaust side.

[0058] Optionally, the two cavity plates 3 are spaced apart in the vertical direction. Since hot air rises, a partition plate 2 is provided on the upper cavity plate 3.

[0059] Optionally, the two cavity plates 3 are spaced apart in the horizontal direction. At this time, the partition plate 2 can be provided on any one of the cavity plates 3 close to the burner 1, or on both cavity plates 3 at the same time.

[0060] In some alternative embodiments, the above deposition reaction system further includes a deposition amount detection device and a control device. The deposition detection device is used to detect the deposition amount of the target rod 4, and the control device is used to adjust the flow rate of the cooling gas according to the obtained deposition amount to improve the cooling efficiency.

[0061] It can be understood that as the deposition amount increases, the volume of the loose body formed by the target rod 4 gradually increases, so it will gradually approach the cavity plate 3. It is necessary to adjust the gas flow rate to improve the cooling efficiency.

[0062] As Figure 2 shown, according to the change in the diameter of the loose body, the flow rate of the cooling gas is gradually adjusted, so as to achieve a better effect of cooling and preventing glass particles from adhering.

[0063] The working principle of the embodiment of the present application is as follows: By arranging two spaced cavity plates 3 and arranging a blowtorch 1 in the cavity formed by the cavity plates 3, when the blowtorch 1 passes a raw material gas, such as SiCl4, into the hydrogen-oxygen flame to generate glass particles, a cooling gas is passed into the channel formed by the cavity plate 3 and the isolation plate 2 to cool the isolation plate 2 and the cavity plate 3; through the baffle 31 arranged near the intake side of the channel and the arc-shaped baffle of a plurality of exhaust holes 21 on the isolation plate 2, the cooling gas in the channel flows out from the exhaust holes 21 and the outlet near the intake side of the channel and flows back to the outlet side to form an air curtain on the outer wall of the isolation plate 2 close to the cavity, so as to prevent excessive glass particles from adhering to the isolation plate 2; as the glass particles are deposited on the surface of the target rod 4 to form a loose body and the diameter of the loose body gradually increases, the flow rate of the cooling gas in the channel is adjusted to improve the cooling efficiency.

[0064] An OVD deposition reaction device and reaction system of the present invention form a channel for the flow of a cooling gas by arranging an isolation plate at intervals on the inner side of at least one cavity plate to cool the isolation plate and the cavity plate, solving the problem that the heat generated by the blowtorch during the deposition reaction causes deformation or rupture of the cavity plate; by arranging a baffle at one end of the channel near the intake side, the cooling gas flows back to the outlet side after flowing out of the channel to prevent glass particles from adhering to the isolation plate; by making the opening of the arc-shaped plate of the baffle face the opening of the channel and making the flat plate parallel to the isolation plate, the refluxing cooling gas can be ejected close to the outer wall of the isolation plate close to the cavity, better preventing glass particles from adhering to the isolation plate; by arranging a plurality of exhaust holes on the isolation plate and arranging a baffle connected to the isolation plate on the side of the exhaust hole close to the baffle, the cooling efficiency is further improved, and in cooperation with the cooling gas refluxing from the channel outlet, an air curtain is formed on the outer wall of the isolation plate to prevent glass particles from adhering; by setting the included angle between the plane where the two ends of the baffle are located and the isolation plate to 75°, the interference between the cooling gas flowing out of the exhaust hole and the cooling gas flowing out of the channel outlet is prevented, affecting the deposition flame and avoiding the formation of turbulent flow.

[0065] In the description of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application. Unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0066] It should be noted that in the present application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0067] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. An OVD deposition reaction device, characterized in that, Comprising: Two cavity plates (3) arranged at intervals, and the two cavity plates (3) form a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform; At least one inner side of the cavity plate (3) is provided with a partition plate (2) at intervals, and a channel for the cooling gas to flow is formed between the partition plate (2) and the cavity plate (3). A baffle cover (31) is provided at one end of the channel close to the air inlet side, so that the cooling gas entering the channel from the air outlet side flows back to the air outlet side after being discharged from the channel. When flowing back, the flowing direction of the cooling gas is the same as the direction of the raw material gas ejected by the burner (1) for depositing the optical fiber preform; The baffle cover (31) includes an arc-shaped plate (311), one end of the arc-shaped plate (311) is connected to the cavity plate (3) forming the channel, and the opening direction of the arc-shaped plate (311) is opposite to the opening of the channel; The baffle cover (31) further includes a flat plate (312), the flat plate (312) is connected to the other end of the arc-shaped plate (311) and is parallel to the partition plate (2). The distance between the partition plate (2) and the cavity plate (3) forming the channel is less than or equal to the distance between the flat plate (312) and the partition plate (2); A plurality of exhaust holes (21) are arranged at intervals along the length direction on the partition plate (2).

2. The OVD deposition reaction device according to claim 1, characterized in that, A baffle (22) connected to the partition plate (2) is provided on one side of each exhaust hole (21) close to the baffle cover (31), so that the cooling gas in the channel flows back to the air outlet side when being discharged from the exhaust hole (21).

3. The OVD deposition reaction device according to claim 2, wherein The baffle (22) is an arc-shaped plate, and the opening of the baffle (22) faces the air outlet side.

4. The OVD deposition reaction device according to claim 3, wherein, The included angle between the plane where the two ends of the baffle (22) are located and the partition plate (2) is 75°.

5. The OVD deposition reaction device according to claim 1, characterized in that, The two cavity plates (3) are arranged at intervals in the vertical direction, and a partition plate (2) is connected to the inner wall of the upper cavity plate (3) at intervals.

6. An OVD deposition reaction system, characterized in that, Comprising: Two cavity plates (3) arranged at intervals, and the two cavity plates (3) form a cavity with an air inlet side and an air outlet side for depositing an optical fiber preform; At least one inner side of the cavity plate (3) is provided with a partition plate (2) at intervals, and a channel for cooling gas to flow is formed between the partition plate and the cavity plate (3). One end of the channel close to the intake side is provided with a baffle cover (31) for causing the cooling gas entering the channel from the outlet side to flow back to the outlet side after discharging from the channel. When flowing back, the flow direction of the cooling gas is the same as the direction of the raw material gas ejected by the burner (1) for depositing the optical fiber preform; the baffle cover (31) includes an arc-shaped plate (311), one end of the arc-shaped plate (311) is connected to the cavity plate (3) forming the channel, and the opening direction of the arc-shaped plate (311) is opposite to the opening of the channel; the baffle cover (31) further includes a flat plate (312), the flat plate (312) is connected to the other end of the arc-shaped plate (311) and is parallel to the partition plate (2), the distance between the partition plate (2) and the cavity plate (3) forming the channel is less than or equal to the distance between the flat plate (312) and the partition plate (2), and a plurality of exhaust holes (21) are arranged at intervals along the length direction on the partition plate (2); A burner (1) located inside the cavity, and the air flow ejected by the burner (1) flows from the intake side to the outlet side; A deposition amount detection device for detecting the deposition amount of the target rod (4); A control device for adjusting the flow rate of the cooling gas according to the obtained deposition amount to improve the cooling efficiency.

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