A freezing device and a freezing method

Abstract

This application discloses a freezing device and freezing method, comprising: an insulated outer shell having a freezing chamber; a cooling mechanism configured to inject liquid nitrogen into the freezing chamber, wherein the liquid nitrogen level is lower than the height of the submarine cable; and a temperature control mechanism electrically connected to the cooling mechanism, configured to detect the temperature of the submarine cable and the liquid nitrogen level in the freezing chamber, and to control the amount of liquid nitrogen injected into the freezing chamber by the cooling mechanism according to the temperature of the submarine cable to regulate the liquid nitrogen level. This device utilizes low-temperature nitrogen vapor formed by the vaporization of liquid nitrogen as a heat exchange medium, making the cooling process of the submarine cable more uniform. Simultaneously, by controlling the liquid nitrogen level in the freezing chamber, the temperature and concentration of the low-temperature nitrogen vapor at the submarine cable can be precisely controlled, thereby achieving free control of the freezing temperature of the submarine cable.

Description

Technical Field

[0001] This application relates to the field of cable freezing technology, and in particular to a freezing apparatus and freezing method. Background Technology

[0002] Currently, in the maintenance of oil-filled cables, especially high-voltage oil-filled cables, it is essential to seal the internal insulating oil. Using liquid nitrogen to freeze the outside of the cable conduit, causing the internal insulating oil to solidify and form an oil plug, is a common technique for temporary on-site sealing.

[0003] Traditional liquid nitrogen freezing methods mainly use direct spraying to freeze cables. However, the above freezing method has the following problems in practical applications: the temperature fluctuation error of spray freezing is more than ±40℃. If the temperature is controlled by controlling the liquid nitrogen supply during the freezing process, the temperature of the freezing chamber will fluctuate, making it difficult to maintain a constant low temperature environment and resulting in poor temperature control accuracy. Summary of the Invention

[0004] This application aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the purpose of this application is to provide a freezing device and freezing method that utilizes low-temperature nitrogen vapor formed by the vaporization of liquid nitrogen as a heat exchange medium, making the cooling process of the submarine cable more uniform. Simultaneously, by adjusting the liquid nitrogen level in the freezing chamber, the temperature and concentration of the low-temperature nitrogen vapor at the submarine cable can be precisely controlled, thereby achieving free control of the freezing temperature of the submarine cable.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a refrigeration apparatus, comprising: An insulated outer shell, wherein the insulated outer shell is provided with a freezing chamber; A cooling mechanism configured to inject liquid nitrogen into the freezing chamber, wherein the liquid nitrogen level is lower than the height of the submarine cable; A temperature control mechanism is electrically connected to the cooling mechanism. The temperature control mechanism is configured to detect the temperature of the submarine cable and the liquid nitrogen level in the freezing chamber, and to control the amount of liquid nitrogen injected into the freezing chamber by the cooling mechanism according to the temperature of the submarine cable to regulate the liquid nitrogen level.

[0006] The freezing device provided in this application has at least the following beneficial effects: when the submarine cable is placed in the freezing chamber, liquid nitrogen is injected into the freezing chamber through the cooling mechanism. Since liquid nitrogen will vaporize under normal pressure, the low-temperature nitrogen vapor formed by the vaporization of liquid nitrogen is used as a heat exchange medium, making the cooling process of the submarine cable more uniform. At the same time, in conjunction with the temperature control mechanism to detect the temperature of the submarine cable and control the cooling mechanism to regulate the liquid nitrogen level in the freezing chamber, the temperature and concentration of the low-temperature nitrogen vapor at the submarine cable can be precisely controlled, thereby realizing free control of the freezing temperature of the submarine cable and achieving a wide temperature range, high precision, and uniform freezing effect.

[0007] In some embodiments, the bottom of the heat-insulating shell is provided with a liquid inlet communicating with the cooling mechanism. The liquid inlet is used to introduce liquid nitrogen. An exhaust port is provided on one side of the heat-insulating shell. The exhaust port is used to discharge liquid nitrogen vapor. Both the liquid inlet and the exhaust port are provided with valves, which are used to control the opening degree of the liquid inlet and the exhaust port.

[0008] In some embodiments, the temperature control mechanism includes a temperature sensor, a liquid level sensor, and a controller. The temperature sensor is disposed on the surface of the submarine cable to detect the surface temperature of the submarine cable. The liquid level sensor is used to detect the liquid nitrogen level in the freezing chamber. Both the temperature sensor and the liquid level sensor are electrically connected to the controller. The controller is used to receive temperature and liquid level signals and control the operation of the cooling mechanism.

[0009] This application also provides a freezing method based on a freezing apparatus, comprising the following steps: The submarine cable is placed in the freezing chamber; Low-temperature nitrogen gas is continuously supplied into the freezing chamber for pre-cooling and purging; Liquid nitrogen is injected into the freezing chamber to a predetermined height, and the vapor formed by the evaporation of liquid nitrogen is used to cool the submarine cable to the target temperature; The liquid nitrogen level in the freezing chamber is adjusted in real time according to the surface temperature of the submarine cable to maintain a constant surface temperature of the submarine cable.

[0010] The freezing method provided in this application has at least the following beneficial effects: After the submarine cable is placed in the freezing chamber, liquid nitrogen is injected into the freezing chamber. Since liquid nitrogen will vaporize under normal pressure, the low-temperature nitrogen vapor formed by the vaporization of liquid nitrogen is used as a heat exchange medium, making the cooling process of the submarine cable more uniform. At the same time, by controlling the liquid nitrogen level in the freezing chamber, the temperature and concentration of the low-temperature nitrogen vapor at the submarine cable can be precisely controlled, thereby realizing free control of the freezing temperature of the submarine cable and achieving a wide temperature range, high precision, and uniform freezing effect.

[0011] In some embodiments, before injecting liquid nitrogen into the freezing chamber to a predetermined height and using the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable, the following steps are included: Low-temperature nitrogen is continuously supplied into the freezing chamber for pre-cooling and purging, and to remove humid air and impurities from the freezing chamber.

[0012] In some embodiments, the continuous supply of cryogenic nitrogen gas into the freezing chamber for pre-cooling and purging, and for removing humid air and impurities from the freezing chamber, includes: During the purging process, the temperature of the freezing chamber is monitored in real time, and purging is stopped when the temperature of the freezing chamber drops below 0°C.

[0013] In some embodiments, injecting liquid nitrogen into the freezing chamber and using the vapor formed by the evaporation of the liquid nitrogen to cool the submarine cable includes: Liquid nitrogen is slowly injected into the bottom of the freezing chamber to control the cooling rate of the freezing chamber to be 2℃ / min~3℃ / min.

[0014] In some embodiments, before injecting liquid nitrogen into the freezing chamber to a predetermined height and using the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable to the target temperature, the following steps are included: The surface temperature of the submarine cable was tested, and a curve showing the relationship between the surface temperature of the submarine cable and the liquid nitrogen level in the freezing chamber was established. The predetermined height value corresponding to the target temperature of the submarine cable is determined based on the relationship curve.

[0015] In some embodiments, testing the surface temperature of the submarine cable and establishing a curve showing the relationship between the surface temperature of the submarine cable and the liquid nitrogen level in the cryogenic chamber includes: The liquid nitrogen level in the freezing chamber is controlled to increase according to a preset liquid level height gradient. After each increase in water level, the surface temperature of the submarine cable is detected after maintaining the current liquid level for a predetermined time. Based on the surface temperature data of the submarine cable within a preset liquid level height gradient, a curve showing the relationship between freezing temperature and liquid level height is plotted.

[0016] In some embodiments, the liquid nitrogen level in the freezing chamber is adjusted in real time according to the surface temperature of the submarine cable to maintain the surface temperature of the submarine cable at a preset temperature, including: The surface temperature fluctuation range of the submarine cable shall not exceed ±5℃ / 20min of the target temperature; When the surface temperature of the submarine cable is higher than the maximum value of the fluctuation range, the inflow rate of liquid nitrogen and the outflow rate of liquid nitrogen vapor in the freezing chamber are increased. When the surface temperature of the submarine cable is lower than the minimum value of the fluctuation range, the inflow rate of liquid nitrogen and the outflow rate of liquid nitrogen vapor in the freezing chamber are reduced. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the refrigeration device provided in this embodiment; Figure 2 A schematic diagram of the exploded structure of the thermal insulation shell; Figure 3 This is a control principle diagram of the temperature control mechanism; Figure 4 This is a flowchart of the freezing method provided in this embodiment; Figure 5 This is a curve showing the fit between the liquid level-temperature calculation formula and the measured data.

[0018] 100. Insulated outer shell; 110. Upper shell; 120. Lower shell; 130. Freezing chamber; 140. Through hole; 150. Liquid inlet; 160. Exhaust port; 200. Cooling mechanism; 300. Temperature control mechanism; 310. Temperature sensor; 320. Liquid level sensor; 330. Controller; 400. Submarine cable. Detailed Implementation

[0019] The embodiments of this application are described in detail below with reference to the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] In the description of this application, it should be understood that the terms "center", "middle", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0021] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0022] In the description of this application, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] In the description of this application, the use of terms such as "one embodiment," "some embodiments," "an example," "some instances," "some embodiments," "illustrative embodiment," "example," "specific example," and "some examples" indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0024] Reference Figures 1 to 4 This embodiment provides a refrigeration apparatus, including: The thermal insulation outer shell 100 includes a freezing chamber 130. Both sides of the thermal insulation outer shell 100 have through holes 140 for the submarine cable 400 to pass through the freezing chamber 130. The thermal insulation outer shell 100 is composed of an upper shell 110 and a lower shell 120, both of which are hollow U-shaped shells. The closed cavity formed by the two hollow U-shaped shells is the freezing chamber 130. The lower shell 120 has a perforated storage platform inside, used to place and support the submarine cable 400. It is understood that the joint between the upper shell 110 and the lower shell 120 is sealed with a sealing strip to ensure that the freezing chamber 130 is completely sealed, preventing the leakage of low-temperature vapor and the intrusion of external hot air, thus ensuring a stable temperature environment inside the freezing chamber 130. It is understandable that an outer heat-insulating layer is also provided on the outer walls of the upper shell 110 and the lower shell 120. The outer heat-insulating layer is a double-layer heat-insulating layer composed of liquid nitrogen interlayer and polyurethane interlayer to prevent the loss of cold energy in the freezing chamber 130 and to ensure that there will be no drastic temperature fluctuations inside the freezing chamber 130.

[0025] A cooling mechanism 200 is configured to inject liquid nitrogen into a freezing chamber 130. In this embodiment, the cooling mechanism 200 includes a first nitrogen storage tank, a first pump body, a second nitrogen storage tank, and a second pump body. The first nitrogen storage tank stores liquid nitrogen. The input end of the first pump body is connected to the output end of the first nitrogen storage tank, and the output end of the first pump body is connected to the freezing chamber 130. The first pump body can pump the liquid nitrogen in the first nitrogen storage tank into the freezing chamber 130 to cool the submarine cable 400. The second nitrogen storage tank stores cryogenic nitrogen gas at -50°C. The input end of the second pump body is connected to the output end of the second nitrogen storage tank, and the output end of the second pump body is connected to the freezing chamber 130. The second pump body can pump the cryogenic nitrogen gas in the second nitrogen storage tank into the freezing chamber 130 to purge and pre-cool the freezing chamber 130.

[0026] The liquid nitrogen level is lower than the height of the submarine cable 400. On the one hand, this avoids direct contact between the liquid nitrogen and the submarine cable 400, thus preventing cracks or mechanical damage to the insulation layer of the submarine cable 400 due to excessively rapid cooling or low temperature. On the other hand, the liquid nitrogen vapor formed when the liquid nitrogen evaporates is used to cool the submarine cable 400, which can achieve precise and fixed-point control of the cooling temperature within the range of -196℃ to -40℃. This enables various cooling effects such as uniform cooling, gradient cooling, and constant temperature cold preservation, which is fully adaptable to the freezing process requirements of different materials. Moreover, because the heat exchange of the gaseous medium is gentle, the cooling process of the submarine cable 400 is more uniform, fundamentally avoiding local overcooling.

[0027] Temperature control mechanism 300 is electrically connected to cooling mechanism 200. Temperature control mechanism 300 is configured to detect the temperature of submarine cable 400 and the liquid nitrogen level in freezing chamber 130, and control cooling mechanism 200 to adjust liquid nitrogen level according to the temperature of submarine cable 400.

[0028] In some embodiments, the bottom of the insulation shell 100 is provided with a liquid inlet 150 communicating with the cooling mechanism 200. The liquid inlet 150 is used to introduce liquid nitrogen, and an exhaust port 160 is provided on one side of the insulation shell 100 for discharging liquid nitrogen vapor. In this embodiment, the liquid inlet 150 has a threaded structure, and a manifold is threadedly connected and fixed at the liquid inlet 150 for easy disassembly and installation. The output ends of the first pump body and the second pump body are respectively connected to one of the ports of the manifold. The exhaust port 160 has an L-shaped tubular structure. The exhaust port 160 is located on the top side of the lower shell 120, and the lowest point of the exhaust port 160 should be higher than the liquid nitrogen level in the freezing chamber 130 to ensure that the liquid nitrogen vapor can be smoothly discharged through the exhaust port 160.

[0029] In some embodiments, both the liquid inlet 150 and the vent 160 are equipped with valves, which are flow control valves. The valve at the liquid inlet 150 is used to control the opening degree of the liquid inlet 150, thereby controlling the liquid nitrogen inflow rate. For example, when the opening degree of the liquid inlet 150 increases, the liquid nitrogen inflow rate increases, thereby raising the liquid nitrogen level in the freezing chamber 130. Conversely, when the opening degree of the liquid inlet 150 decreases, the liquid nitrogen level decreases. The valve at the vent 160 is used to control the opening degree of the vent 160, thereby controlling the liquid nitrogen vapor discharge rate. For example, when the opening degree of the vent 160 increases, the higher temperature liquid nitrogen vapor can be discharged from the vent 160 more quickly, thus allowing space for liquid nitrogen evaporation.

[0030] Understandably, after the liquid nitrogen vapor in the upper layer of the freezing chamber 130 is discharged, the temperature in the upper layer of the freezing chamber 130 will gradually rise, which will accelerate the evaporation rate of liquid nitrogen and lower the liquid nitrogen level. The newly evaporated liquid nitrogen vapor is even colder, resulting in a better cooling effect on the submarine cable 400. In other words, by adjusting the opening of the inlet 150 and the outlet 160, the inflow rate and evaporation rate of liquid nitrogen in the freezing chamber 130 can be balanced, thereby controlling the liquid nitrogen level in the freezing chamber 130 to regulate the cooling effect.

[0031] In some embodiments, the temperature control mechanism 300 includes a temperature sensor 310, a liquid level sensor 320, and a controller 330. The temperature sensor 310 can be a Pt100 temperature sensor, and at least two temperature sensors 310 are provided. In this embodiment, six temperature sensors 310 are spaced apart on the surface of the submarine cable 400 to detect the surface temperature of different parts of the submarine cable 400. The liquid level sensor 320 can be a capacitive liquid level sensor with a resolution of ±1 mm. The liquid level sensor 320 is used to detect the liquid nitrogen level in the freezing chamber 130.

[0032] Temperature sensor 310 and liquid level sensor 320 are both electrically connected to controller 330. Controller 330 can be a PLC controller. Controller 330 is used to receive the surface temperature signal of submarine cable 400 detected by temperature sensor 310 and the liquid nitrogen level signal in freezing chamber 130 detected by liquid level sensor 320. Then, it can control the operation of cooling mechanism 200 according to the temperature and liquid level signals. For example, when the surface temperature of submarine cable 400 is too high, the cooling mechanism 200 is controlled to replenish liquid nitrogen into freezing chamber 130, so that the liquid nitrogen level rises. Since the liquid nitrogen level is closer to the submarine cable 400, the temperature of submarine cable 400 will gradually drop. Conversely, when the surface temperature of submarine cable 400 is too low, the cooling mechanism 200 is controlled to reduce the liquid injection rate. At this time, the evaporation rate of liquid nitrogen is greater than the injection rate, and the liquid nitrogen level will drop. Since the liquid nitrogen level is farther from the submarine cable 400, the temperature of submarine cable 400 will slowly rise. Understandably, the valve is also electrically connected to the controller 330, which is capable of controlling the valve's operation.

[0033] This embodiment also provides a freezing method based on a freezing device, including the following steps: To facilitate understanding of the scheme in this embodiment, the target of the operation is a 500kV oil-filled single-core cable with a total length of 20 meters. The cable is filled with insulating oil. It is necessary to freeze the target section of the cable to form an oil circuit ice plug with a length of 2 meters to facilitate terminal and joint maintenance operation tests.

[0034] The freezing requirement is to reduce the temperature of the target section of the oil passage to -135℃±5℃ and maintain the constant temperature for 24 hours to ensure that the oil completely solidifies and forms a reliable seal.

[0035] Step 1: Place the submarine cable 400 into the cryogenic chamber 130. 11) Place the lower shell 120 of the insulation shell 100 in the refrigeration station; 12) Place the submarine cable 400 into the hollowed-out storage platform in the lower shell 120, and make both ends of the submarine cable 400 fit into the through holes 140 to ensure that the submarine cable 400 is not stacked or obstructed, so that liquid nitrogen vapor can come into full contact with the surface of the submarine cable 400 during subsequent freezing; wherein, the distance between the submarine cable 400 and the bottom wall of the freezing chamber 130 is set to 50cm; 13) Six temperature sensors 310 are attached to the surface of the submarine cable 400 at 30cm intervals along the axial direction to read the freezing temperature data at different positions on the surface of the submarine cable 400 in real time during freezing. At the same time, a liquid level sensor 320 is installed inside the lower housing 120 to read the liquid nitrogen level inside the freezing chamber 130 in real time. 14) The upper shell 110 of the insulation shell 100 is fastened to the top of the lower shell 120 by a crane, and the upper shell 110 and the lower shell 120 are connected and fixed by fastening bolts so that a sealed freezing chamber 130 is formed inside the insulation shell 100. 15) Inspect the insulation shell 100 to confirm there is no leakage.

[0036] Step 2: Continuously supply cryogenic nitrogen gas into the freezing chamber 130 for pre-cooling and purging: 21) Turn on the second pump body and continuously purge the freezing chamber 130 with -50°C cryogenic nitrogen gas. The flow rate of the cryogenic nitrogen gas is controlled at 20L / min and the duration is controlled at 20min. During the purging process, the ambient temperature inside the freezing chamber 130 will continue to decrease. At the same time, the humid air and impurities in the freezing chamber 130 and each connecting pipe will be discharged through the exhaust port 160 to prevent them from freezing and interfering with the heat exchange process in the subsequent liquid nitrogen freezing stage. 22) Monitor the ambient temperature inside the freezing chamber 130 in real time. Stop purging when the temperature of the freezing chamber 130 drops below 0°C and prepare for liquid nitrogen input.

[0037] Step 3: Test the surface temperature of the submarine cable 400 and establish a curve showing the relationship between the surface temperature of the submarine cable 400 and the liquid nitrogen level in the freezing chamber 130. 31) Open the first pump body and continuously add liquid nitrogen into the freezing chamber 130; in this embodiment, the liquid nitrogen injection rate is set to 20L / min, so that the initial cooling rate is controlled at 2℃ / min~3℃ / min, so as to avoid the thermal stress generated inside the insulation layer of the submarine cable 400 due to excessive temperature drop. At the same time, the circulation rate of liquid nitrogen vapor in the freezing chamber 130 can be controlled by adjusting the opening of the exhaust port 160, thereby enhancing the uniformity of convective heat transfer. 32) Based on the preset liquid level height gradient, control the liquid nitrogen level height gradient increase in the freezing chamber 130; 33) After each increase in the gradient, the surface temperature of the submarine cable 400 is detected and recorded after maintaining the current liquid level for a predetermined time. Each gradient is set to 5 cm and the predetermined time is set to 6 hours. 34) Based on the surface temperature data of the submarine cable 400 within the preset liquid level gradient, as shown in Table 1 below, which illustrates the change in surface temperature of the submarine cable 400 with the liquid nitrogen level in the freezing chamber 130 when liquid nitrogen is injected into the freezing chamber 130 at a rate of 20 L / min, the relationship curve between the measured freezing temperature and the liquid level is plotted, as shown in the figure below. Figure 5 As shown, the black curve represents the actual relationship between freezing temperature and liquid level. In this embodiment, the temperature of liquid nitrogen vapor is more affected by the ambient temperature closer to the inner wall of the freezing chamber 130, resulting in a poorer cooling effect of the liquid nitrogen vapor on the submarine cable 400. Therefore, to ensure the accuracy of the detection results, the temperature data detected by the temperature sensor 310 at the center of the submarine cable 400 is taken as the surface temperature of the submarine cable 400. The temperature sensors 310 located at both ends of the submarine cable 400 are used to monitor the temperature changes in the freezing chamber 130 in real time to ensure that abnormal temperatures can be detected in time. For example, when the temperature sensors 310 at both ends of the submarine cable 400 detect that the temperature is significantly higher, the operator can control the cooling mechanism 200 to increase the liquid injection speed, thereby increasing the liquid level in the freezing chamber 130 and further reducing the surface temperature of the submarine cable 400.

[0038] Table 1. Data on the variation of submarine cable surface temperature with liquid nitrogen level.

[0039] 35) Determine the value of the predetermined height corresponding to the target temperature of the submarine cable 400 based on the relationship curve. In this embodiment, as can be seen from Table 1, when the fixed height of the submarine cable 400 is set to 50cm and the target temperature is set to -140℃, the liquid nitrogen level at this temperature is 35cm, which is the predetermined height of 35cm. Therefore, the distance between the liquid nitrogen level and the submarine cable 400 can be obtained as 15cm. 36) Substitute the surface temperature data of the submarine cable 400 within the preset liquid level height gradient into the empirical formula to obtain the corrected empirical formula: 361) Based on Fourier's law of thermal conduction and the thermal resistance model of nitrogen vapor layer, a theoretical calculation formula (i.e., an empirical formula) for liquid level-temperature is established:

[0040] Among them, T 液氮 The temperature of liquid nitrogen; T 环境 The ambient temperature at the freezing site; T 工件The measured temperature of the frozen workpiece surface; k is an empirical coefficient; d is the distance from the liquid nitrogen surface to the frozen workpiece. 362) Confirmation of experimental conditions: In this embodiment, the fixed height of the submarine cable 400 is set to 50cm, and as can be seen from Table 1, when the surface temperature of the submarine cable 400 is set to T... 工件 At -140℃, the liquid nitrogen level is 35cm, therefore the distance d from the liquid nitrogen level to the 400m cable is 50-35=15cm; the ambient temperature is set to T. 环境 =25℃, and the ambient temperature remained basically constant during the experiment; the liquid nitrogen temperature was set to T 液氮 =-196℃; simultaneously adjust the valve to set the opening of the exhaust port 160 to 15%, thereby controlling the circulation speed of liquid nitrogen vapor to 3m. 3 / h; 363) With d=15cm, T 工件 Substituting -140℃ into the liquid level-temperature calculation formula for verification, the empirical coefficient k≈0.0195 is obtained. Therefore, the liquid level-temperature calculation formula is: T 工件 =25-221·e -0.0195d By comparing the theoretical calculation formula with the plotted curve showing the relationship between measured freezing temperature and liquid level, it can be seen that the theoretical calculation formula is quite close to the actual measured curve. Specifically, as shown below... Figure 5 As shown, the red curve represents the fitted curve of the corrected empirical formula, indicating that the theoretical calculation formula can correctly describe the relationship between freezing temperature and liquid level.

[0041] Understandably, since the corrected empirical formula has been obtained through calculation, it is no longer necessary to retest the actual relationship curve between freezing temperature and liquid level when freezing other parts of submarine cable 400 or other submarine cables 400. The corrected empirical formula can be used directly for calculation, which helps to improve the applicability of this freezing method.

[0042] Step 4: Inject liquid nitrogen into the freezing chamber 130 to a predetermined height, and use the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable 400. 41) Turn on the first pump and slowly inject liquid nitrogen into the bottom of the freezing chamber 130 at a rate of 20L / min to control the cooling rate of the freezing chamber 130 to 2℃ / min~3℃ / min, so as to avoid thermal stress inside the insulation layer of the submarine cable 400 due to excessive cooling. 42) Adjust the opening of the exhaust port 160 to control the discharge rate of liquid nitrogen vapor in the freezing chamber 130, thereby achieving the purpose of controlling the circulation rate of liquid nitrogen vapor; 43) Liquid nitrogen rapidly vaporizes under normal pressure to form cryogenic liquid nitrogen vapor. After about 15 minutes, liquid nitrogen begins to accumulate in the freezing chamber 130. After about 60 minutes, the surface temperature of the cable drops from 0℃ to -140℃ and enters the constant temperature stage. During this process, the liquid level sensor 320 provides real-time feedback on the liquid nitrogen level in the freezing chamber 130. When the liquid nitrogen level in the freezing chamber 130 rises to 35cm, which is 15cm from the submarine cable 400, the opening of the inlet 150 and the outlet 160 is automatically adjusted by the valve to keep the liquid level stable near this height.

[0043] Step 5: Adjust the liquid nitrogen level in the freezing chamber 130 in real time according to the surface temperature of the submarine cable 400 to maintain a constant surface temperature of the submarine cable 400. 51) Set the surface temperature fluctuation range of submarine cable 400 to not exceed ±5℃ / 20min of the target temperature; 52) If the surface temperature of the submarine cable 400 is higher than the maximum value of the fluctuation range (i.e., higher than -135℃), increase the liquid nitrogen inlet flow rate and liquid nitrogen vapor outlet flow rate in the freezing chamber 130; specifically, increase the liquid nitrogen inlet flow rate from 20L / min to 20.1L / min, and at the same time, temporarily increase the opening of the exhaust port 160 by 5% by adjusting the valve to promote liquid nitrogen vaporization and generate more low-temperature vapor, so that the temperature drops; 53) If the surface temperature of the submarine cable 400 is lower than the minimum value of the fluctuation range (i.e., lower than -145℃), reduce the liquid nitrogen inlet flow rate and liquid nitrogen vapor outlet flow rate in the freezing chamber 130; specifically, reduce the liquid nitrogen inlet flow rate from 20L / min to 19.8L / min, and at the same time reduce the opening of the exhaust port 160 by 5% by adjusting the valve to reduce the supply of cold energy and allow the temperature to rise slowly.

[0044] By performing the above operations, we can ensure that the surface temperature fluctuation of the submarine cable 400 is small, thereby better protecting the submarine cable 400 and preventing damage caused by excessively low local temperatures.

[0045] Step 6: End freezing and thawing: 61) After the freezing operation is completed, first close the valve at the liquid inlet 150, then open the drain port at the bottom of the insulation shell 100, and gradually release the liquid nitrogen in the freezing chamber 130 according to the liquid level-temperature calculation formula and the gradient temperature thawing method. At the same time, open the exhaust port 160 to allow ambient room air to enter the freezing chamber 130, so that the temperature inside the chamber can rise naturally. When the surface temperature of the submarine cable 400 rises above 0°C, open the upper shell 110 of the insulation shell 100, and then remove the submarine cable 400 from the freezing chamber 130 to complete the freezing operation of the submarine cable 400.

[0046] The freezing apparatus provided in this embodiment also has at least the following beneficial effects: The submarine cable 400 was frozen using a low-temperature nitrogen vapor freezing method, effectively achieving precise control of its freezing temperature. During the freezing process, the surface temperature of the submarine cable 400 was effectively maintained at -140℃±5℃ by controlling the liquid level in the freezing chamber 130. Under low flow rate insulation conditions, the temperature fluctuation range was ≤±5℃ / h, thus effectively protecting the submarine cable 400 and preventing damage caused by excessively low local temperatures.

[0047] The above embodiments are preferred embodiments of this application, but the implementation of this application is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A refrigeration apparatus, characterized in that, include: An insulated outer shell, wherein the insulated outer shell is provided with a freezing chamber; A cooling mechanism configured to inject liquid nitrogen into the freezing chamber, wherein the liquid nitrogen level is lower than the height of the submarine cable; A temperature control mechanism is electrically connected to the cooling mechanism. The temperature control mechanism is configured to detect the temperature of the submarine cable and the liquid nitrogen level in the freezing chamber, and to control the amount of liquid nitrogen injected into the freezing chamber by the cooling mechanism according to the temperature of the submarine cable to regulate the liquid nitrogen level.

2. The refrigeration apparatus according to claim 1, characterized in that: The bottom of the heat-insulating shell is provided with a liquid inlet that communicates with the cooling mechanism. The liquid inlet is used to introduce liquid nitrogen. An exhaust port is provided on one side of the heat-insulating shell. The exhaust port is used to discharge liquid nitrogen vapor. Both the liquid inlet and the exhaust port are provided with valves, which are used to control the opening degree of the liquid inlet and the exhaust port.

3. The refrigeration apparatus according to claim 1, characterized in that: The temperature control mechanism includes a temperature sensor, a liquid level sensor, and a controller. The temperature sensor is disposed on the surface of the submarine cable to detect the surface temperature of the submarine cable. The liquid level sensor is used to detect the liquid nitrogen level in the freezing chamber. Both the temperature sensor and the liquid level sensor are electrically connected to the controller. The controller is used to receive temperature and liquid level signals and control the operation of the cooling mechanism.

4. A freezing method, based on the freezing apparatus according to any one of claims 1 to 3, characterized in that, Includes the following steps: The submarine cable is placed in the freezing chamber; Liquid nitrogen is injected into the freezing chamber to a predetermined height, and the vapor formed by the evaporation of liquid nitrogen is used to cool the submarine cable; The liquid nitrogen level in the freezing chamber is adjusted in real time according to the surface temperature of the submarine cable to maintain the surface temperature of the submarine cable at a preset temperature.

5. The freezing method according to claim 4, characterized in that, Before injecting liquid nitrogen into the freezing chamber to a predetermined height and using the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable, the process includes: Low-temperature nitrogen is continuously supplied into the freezing chamber for pre-cooling and purging, and to remove humid air and impurities from the freezing chamber.

6. The freezing method according to claim 5, characterized in that, The continuous supply of low-temperature nitrogen gas into the freezing chamber for pre-cooling and purging, and the removal of humid air and impurities from the freezing chamber, includes: During the purging process, the temperature of the freezing chamber is monitored in real time, and purging is stopped when the temperature of the freezing chamber drops below 0°C.

7. The freezing method according to claim 4, characterized in that, The step of injecting liquid nitrogen into the freezing chamber and using the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable includes: Liquid nitrogen is slowly injected into the bottom of the freezing chamber to control the cooling rate of the freezing chamber to be 2℃ / min~3℃ / min.

8. The freezing method according to claim 4, characterized in that, Before injecting liquid nitrogen into the freezing chamber to a predetermined height and using the vapor formed by the evaporation of liquid nitrogen to cool the submarine cable, the process includes: The surface temperature of the submarine cable was tested, and a curve showing the relationship between the surface temperature of the submarine cable and the liquid nitrogen level in the freezing chamber was established. The predetermined height value corresponding to the target temperature of the submarine cable is determined based on the relationship curve.

9. The freezing method according to claim 8, characterized in that, The process of testing the surface temperature of the submarine cable and establishing a curve showing the relationship between the surface temperature of the submarine cable and the liquid nitrogen level in the freezing chamber includes: The liquid nitrogen level in the freezing chamber is controlled to increase according to a preset liquid level height gradient. After each increase in water level, the surface temperature of the submarine cable is detected after maintaining the current liquid level for a predetermined time. Based on the surface temperature data of the submarine cable within a preset liquid level height gradient, a curve showing the relationship between freezing temperature and liquid level height is plotted.

10. The freezing method according to claim 4, characterized in that, The liquid nitrogen level in the freezing chamber is adjusted in real time according to the surface temperature of the submarine cable to maintain the surface temperature of the submarine cable at a preset temperature, including: The surface temperature fluctuation range of the submarine cable shall not exceed ±5℃ / 20min of the target temperature; When the surface temperature of the submarine cable is higher than the maximum value of the fluctuation range, the inflow rate of liquid nitrogen and the outflow rate of liquid nitrogen vapor in the freezing chamber are increased. When the surface temperature of the submarine cable is lower than the minimum value of the fluctuation range, the inflow rate of liquid nitrogen and the outflow rate of liquid nitrogen vapor in the freezing chamber are reduced.

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