Method for constructing a thermodynamic-hydraulic coupling model for a high-temperature superconducting cable cooling system

Abstract

This invention discloses a method for constructing a thermodynamic-hydraulic coupling model for a high-temperature superconducting cable cooling system, comprising the following steps: 1. calculating the cooling load; 2. calculating the hydraulic loss; 3. determining whether the height difference during cable construction is less than the theoretically calculated maximum height difference during cable construction; 4. determining the relationship between the liquid nitrogen flow rate and the maximum temperature difference; 5. determining the temperature rise limit based on this relationship, and determining the optimal type of low-temperature circulating pump based on the liquid nitrogen flow rate range; and 6. selecting a refrigeration unit that meets the cooling temperature and has a cooling capacity that matches the cooling load. This invention provides a highly efficient cooling system capable of dynamically adjusting and controlling the cooling process, thereby extending the service life of high-temperature superconducting cables and reducing operating costs.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature superconducting cable cooling system design, and in particular to a method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system. Background Art

[0002] High-temperature superconducting cable is one of the most important applications of superconducting technology in the electric power industry. It has the advantages of small size, light weight, low loss, large transmission capacity and environmental friendliness. It can be used in situations where large currents are transmitted over short distances, such as from generators to transformers, new energy power supply transmission, from substations to urban power grid ports, and between power plants and substations, as well as large or super-large urban power transmission, to achieve low-loss, high-efficiency and large-capacity power transmission.

[0003] To ensure that high-temperature superconducting cables maintain their superconducting state, they must be cooled below their critical temperature, requiring an efficient and stable cryogenic cooling system. The cooling system for high-temperature superconducting cables is crucial for ensuring their safe and efficient operation. By properly designing the cooling system and selecting appropriate refrigeration equipment, the service life of the superconducting cable can be effectively extended and its stable operation ensured.

[0004] Accurately assessing the cooling load and hydraulic losses of a high-temperature superconducting cable system is fundamental to developing a cooling strategy. Cooling load represents the cooling power required to maintain the low temperature environment of a high-temperature superconducting cable system and is a core metric in cooling system design. System cooling load directly influences the capacity and specifications of the cooling equipment, ensuring stable operation of the cooling system. Furthermore, accurate cooling load calculation can avoid wasted cooling power and reduce system costs, thereby improving overall system efficiency and economic performance. Hydraulic losses refer to the pressure drop caused by friction and local resistance when liquid nitrogen flows through the pipeline. The magnitude of hydraulic losses directly influences the selection and energy consumption of the circulating pump. Hydraulic losses exceeding the pump head increase the pump load, reducing system efficiency and even rendering the system inoperable. Hydraulic losses below the pump head reduce the system's economic performance. Accurate hydraulic loss calculation helps optimize piping and circulation circuit design, ensuring efficient and stable circulation of the cooling medium, and safeguarding the reliability and long-term stability of the cooling system. In summary, accurate calculation of cooling load and hydraulic losses is not only fundamental to superconducting cable cooling system design but also a crucial factor in determining system cost, performance, and reliability.

[0005] Existing technologies primarily use thermodynamic coupling models to calculate cooling loads, and hydraulic coupling models to calculate hydraulic losses. However, for the operation of liquid nitrogen cooling systems for high-temperature superconducting cables, it is necessary to comprehensively consider key parameters such as cooling load, liquid nitrogen temperature rise, liquid nitrogen flow rate, and hydraulic losses in the liquid nitrogen cooling system to support the development of cooling plans and the selection of cooling equipment. Existing technologies do not have a thermodynamic-hydraulic coupling model specifically tailored to the operation of liquid nitrogen cooling systems for high-temperature superconducting cables.

[0006] Therefore, how to achieve dynamic regulation and control of the cooling process while ensuring stable operation of the cooling system through precise thermal and hydraulic calculations, as well as the coupling relationship between pump flow and liquid nitrogen temperature rise, so as to extend the service life of high-temperature superconducting cables and reduce operating costs has become a technical problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for constructing a thermodynamic-hydraulic coupling model of a high-temperature superconducting cable cooling system. The purpose of the present invention is to provide an efficient cooling system capable of dynamically adjusting and controlling the cooling process while ensuring stable operation of the cooling system through precise thermal and hydraulic calculations, combined with the coupling relationship between pump flow and liquid nitrogen temperature rise, to extend the service life of the high-temperature superconducting cable and reduce operating costs.

[0008] To achieve the above object, the present invention discloses a method for constructing a thermodynamic-hydraulic coupling model of a high-temperature superconducting cable cooling system, comprising the following steps:

[0009] Step 1: Calculate cooling load;

[0010] Step 2: Calculate hydraulic loss;

[0011] Step 3: Determine whether the height difference during cable construction is lower than the theoretical calculation result of the maximum height difference during cable construction;

[0012] If it is satisfied, the hydraulic loss is used as the basis for selecting the pump head;

[0013] If not, the height difference of the cable during construction in the specific project shall be used as the basis for calculating and selecting the circulation pump head;

[0014] Step 4: Determine the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen;

[0015] Step 5: Determine the temperature rise limit based on the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen, and determine the optimal type of the cryogenic circulation pump based on the range of the liquid nitrogen flow rate;

[0016] Step 6: Select a refrigeration unit that meets the cooling temperature and has a cooling capacity that matches the cooling load.

[0017] Preferably, in step 1, the cooling load is calculated by calculating the local cooling load of the insulated pipe per unit length, and the specific formula is as follows:

[0018]

[0019] Where Q is the cooling load per unit length of the insulated pipe, in W / m; k is the effective thermal conductivity of the insulated pipe, in W / (m·K); T ∞ is the ambient temperature, unit: K; is the working liquid nitrogen temperature, unit: K; D out D is the outer diameter of the insulation pipe, unit: mm; in The inner diameter of the insulation pipe, unit: mm.

[0020] More preferably, in step 2, the hydraulic loss calculation includes the hydraulic loss H along the way f and local hydraulic loss H L .

[0021] More preferably, the hydraulic loss H along the way f The calculation formula is as follows:

[0022]

[0023] Where f is the Darcy drag coefficient; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; v is the liquid nitrogen flow rate, in m / s; g is the acceleration due to gravity, in m / s 2 .

[0024] More preferably, when calculating the hydraulic loss along the bellows, the Reynolds number is 10 4 to April 10 4 The Darcy drag coefficient f of the bellows is only related to the bellows structure, and the expression is as follows:

[0025]

[0026] Wherein, e is the wave height of the bellows, unit: m; p is the wave distance, unit: m; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, and is calculated as follows:

[0027]

[0028] Among them, 3D out D is the outer diameter of the cable, in m; in The inner diameter of the insulation pipe, unit: mm.

[0029] More preferably, the local hydraulic loss H L The calculation formula is as follows:

[0030]

[0031] Where K is the local resistance coefficient of the specific accessory; v is the liquid nitrogen flow rate in m / s; g is the acceleration due to gravity in m / s 2 .

[0032] More preferably, in step 3, the calculation formula of the theoretical calculation result of the maximum height difference of the cable construction is specifically as follows:

[0033]

[0034] Where Δh max is the theoretical calculation result of the maximum height difference of the cable construction;

[0035] P inlet is the inlet pressure of liquid nitrogen, unit: Pa;

[0036] P inlet =P outlet +ΔP friction (L)+ρgΔh;

[0037] P outlet is the outlet pressure of liquid nitrogen, unit: Pa;

[0038] Δh is the height difference of the cable during the construction process, unit: m;

[0039] ΔP friction (L) is the pressure loss when the output distance of the high-temperature superconducting cable is L, in Pa, and the calculation formula is as follows:

[0040]

[0041] Where f is the Darcy drag coefficient of the liquid nitrogen flow pipeline; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; ρ is the density of liquid nitrogen, in kg / m 3 ; v is the liquid nitrogen flow rate, unit: m / s; g is the acceleration due to gravity, unit: m / s 2 .

[0042] P boil (T) is the output pressure of liquid nitrogen corresponding to the maximum height difference allowed during construction, which is equal to the saturated vapor pressure at the corresponding temperature. The unit is Pa. The calculation formula is as follows:

[0043] P boil(T)=P outlet .

[0044] More preferably, in step 4, the maximum operating temperature range of liquid nitrogen is determined to be between the triple point of liquid nitrogen, 63.4K, and the boiling point of liquid nitrogen at normal pressure, 77K; then the maximum temperature difference is 13.6K;

[0045] Then, the liquid nitrogen with a maximum temperature difference of 12K from the boiling point of liquid nitrogen at normal pressure of 77K is cooled to 65K as the starting temperature of the liquid nitrogen, and 80% of the maximum temperature difference, that is, 9.6K, is taken as the standard for determining whether the liquid nitrogen flow rate meets the thermodynamic limit. The formula for the relationship between the liquid nitrogen flow rate and the maximum temperature difference of liquid nitrogen is as follows:

[0046]

[0047] Where L is the output distance of the high-temperature superconducting cable, in meters; Q1 is the terminal unit loss, in W per terminal; N1 is the number of terminals; Q2 is the connector unit loss, in W per terminal; N2 is the number of connectors; Q3 is the loss of other pipelines in the system, in W; ρ is the density of liquid nitrogen, in kg / m 3 ; is the volume flow rate of liquid nitrogen, unit: m 3 / s;c p is the specific heat capacity of liquid nitrogen at constant pressure, unit: J / (kg·K).

[0048] More preferably, step 6 is as follows:

[0049] Step 6.1. Select the optimal operating condition of the circulating pump, that is, the circulating pump flow rate with the highest pump efficiency;

[0050] Step 6.2, calculating the temperature difference according to the circulation pump flow rate using the temperature rise formula;

[0051] Step 6.3, determine whether the temperature difference is satisfied;

[0052] If satisfied, the output includes a refrigeration solution for a low-temperature refrigerator and a low-temperature circulation pump;

[0053] If not, increase the circulation pump flow rate until the temperature rise of the liquid nitrogen satisfies the condition that is less than the maximum temperature difference, and then output a matching refrigeration solution including a low-temperature refrigerator and a low-temperature circulation pump.

[0054] Beneficial effects of the present invention:

[0055] Through precise thermal and hydraulic calculations, combined with the coupling relationship between pump flow and liquid nitrogen temperature rise, the present invention further provides a high-efficiency cooling system capable of dynamically adjusting and controlling the cooling process while ensuring stable operation of the cooling system, thereby extending the service life of high-temperature superconducting cables and reducing operating costs.

[0056] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 A flow chart showing an embodiment of the present invention is shown.

[0058] Figure 2 A schematic diagram of the internal structure of a superconducting cable in one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0059] Example

[0060] like Figure 1 As shown in FIG, a method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system includes the following steps:

[0061] Step 1: Calculate cooling load;

[0062] Step 2: Calculate hydraulic loss;

[0063] Step 3: Determine whether the height difference during cable construction is lower than the theoretical calculation result of the maximum height difference during cable construction;

[0064] In practical applications, the above judgment can avoid the vaporization problem caused by the liquid nitrogen pressure being lower than the saturated vapor pressure during the filling process.

[0065] If it is satisfied, the hydraulic loss is used as the basis for selecting the pump head;

[0066] If not, the height difference of the cable during construction in the specific project shall be used as the basis for calculating and selecting the circulation pump head;

[0067] Step 4: Determine the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen;

[0068] Step 5: Determine the temperature rise limit based on the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen, and determine the optimal type of the cryogenic circulation pump based on the range of the liquid nitrogen flow rate;

[0069] Step 6: Select a refrigeration unit that meets the cooling temperature and has a cooling capacity that matches the cooling load.

[0070] The present invention can simulate the cooling load estimation of high-temperature superconducting cables in liquid nitrogen cooling systems, and utilize the limited coupling of liquid nitrogen flow rate and liquid nitrogen temperature rise to provide the optimal selection of low-temperature circulation pumps. This provides a solid theoretical basis and optimization direction for the formulation of liquid nitrogen cooling schemes and the selection of equipment, ensuring the long-term, efficient and stable operation of high-temperature superconducting cables.

[0071] In some embodiments, in step 1, the cooling load calculation is to calculate the local cooling load per unit length of the insulated pipe, and the specific formula is as follows:

[0072]

[0073] Where Q is the cooling load per unit length of the insulated pipe, in W / m; k is the effective thermal conductivity of the insulated pipe, in W / (m·K); T ∞ is the ambient temperature, unit: K; is the working liquid nitrogen temperature, unit: K; D out D is the outer diameter of the insulation pipe, unit: mm; in The inner diameter of the insulation pipe, unit: mm.

[0074] The cooling load of high-temperature superconducting cables depends on the insulation performance of the insulation pipes used in the system. The insulation pipes of high-temperature superconducting cables are usually corrugated flexible double-wall structures, that is, with multiple layers of vacuum interlayers such as Figure 2 As shown in Figure 2, the corrugated geometry of the tube wall generally has a higher thermal load than rigid insulation systems, so it can be widely used in high-temperature superconducting cable insulation systems.

[0075] In some embodiments, in step 2, the hydraulic loss calculation includes the hydraulic loss H along the way. f and local hydraulic loss H L .

[0076] Hydraulic loss in the liquid nitrogen cooling system of a high-temperature superconducting cable is a key indicator for selecting a circulating pump. Hydraulic loss directly determines the pump's head range. Hydraulic loss within a high-temperature superconducting cable cooling system primarily includes longitudinal hydraulic loss and local hydraulic loss.

[0077] In some embodiments, the hydraulic loss H along the way f The calculation formula is as follows:

[0078]

[0079] Where f is the Darcy drag coefficient; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; v is the liquid nitrogen flow rate, in m / s; g is the acceleration due to gravity, in m / s 2 .

[0080] The hydraulic loss along the pipeline is the resistance loss caused by pipeline friction when liquid nitrogen flows in the pipeline.

[0081] In some embodiments, such as when calculating the hydraulic loss along the bellows, the Reynolds number is 10 4 to April 104 The Darcy drag coefficient f of the bellows is only related to the bellows structure, and the expression is as follows:

[0082]

[0083] Wherein, e is the wave height of the bellows, unit: m; p is the wave distance, unit: m; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, and is calculated as follows:

[0084]

[0085] Among them, 3D out D is the outer diameter of the cable, in m; in The inner diameter of the insulation pipe, unit: mm.

[0086] In certain embodiments, the local hydraulic loss H L The calculation formula is as follows:

[0087]

[0088] Where K is the local resistance coefficient of the specific accessory; v is the liquid nitrogen flow rate in m / s; g is the acceleration due to gravity in m / s 2 .

[0089] In some embodiments, in step 3, the calculation formula of the theoretical calculation result of the maximum height difference of the cable construction is specifically as follows:

[0090]

[0091] Where Δh max is the theoretical calculation result of the maximum height difference of cable construction;

[0092] P inlet is the inlet pressure of liquid nitrogen, unit: Pa;

[0093] P inlet =P outlet +ΔP friction (L)+ρgΔh;

[0094] P outlet is the outlet pressure of liquid nitrogen, unit: Pa;

[0095] Δh is the height difference of the cable during the construction process, unit: m;

[0096] ΔP friction (L) is the pressure loss when the output distance of the high-temperature superconducting cable is L, in Pa, and the calculation formula is as follows:

[0097]

[0098] Where f is the Darcy drag coefficient of the liquid nitrogen flow pipeline; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; ρ is the density of liquid nitrogen, in kg / m 3 ; v is the liquid nitrogen flow rate, unit: m / s; g is the acceleration due to gravity, unit: m / s 2 .

[0099] P boil (T) is the output pressure of liquid nitrogen corresponding to the maximum height difference allowed during construction, which is equal to the saturated vapor pressure at the corresponding temperature. The unit is Pa. The calculation formula is as follows:

[0100] P boil (T)=P outlet .

[0101] In some embodiments, in step 4, the maximum operating temperature range of liquid nitrogen is determined to be between the triple point of liquid nitrogen, 63.4K, and the boiling point of liquid nitrogen at normal pressure, 77K; the maximum temperature difference is 13.6K;

[0102] Then, the liquid nitrogen with a maximum temperature difference of 12K from the boiling point of liquid nitrogen at normal pressure of 77K is cooled to 65K as the starting temperature of the liquid nitrogen, and 80% of the maximum temperature difference, that is, 9.6K, is taken as the standard for determining whether the liquid nitrogen flow rate meets the thermodynamic limit. The formula for the relationship between the liquid nitrogen flow rate and the maximum temperature difference of liquid nitrogen is as follows:

[0103]

[0104] Where L is the output distance of the high-temperature superconducting cable, in meters; Q1 is the terminal unit loss, in W per terminal; N1 is the number of terminals; Q2 is the connector unit loss, in W per terminal; N2 is the number of connectors; Q3 is the loss of other pipelines in the system, in W; ρ is the density of liquid nitrogen, in kg / m 3 ; is the volume flow rate of liquid nitrogen, unit: m 3 / s;c p is the specific heat capacity of liquid nitrogen at constant pressure, unit: J / (kg·K).

[0105] Liquid nitrogen flow rate is an important indicator for selecting a cryogenic circulating pump (i.e., pump flow rate), and the change in liquid nitrogen flow rate is negatively correlated with the head of the circulating pump. Therefore, the above formula can be used to determine the range of liquid nitrogen flow rate according to the temperature rise limit for the optimal selection of the cryogenic circulating pump.

[0106] In some embodiments, step 6 is as follows:

[0107] Step 6.1. Select the optimal operating condition of the circulating pump, that is, the circulating pump flow rate with the highest pump efficiency;

[0108] Step 6.2: Calculate the temperature difference using the temperature rise formula based on the circulation pump flow rate;

[0109] Step 6.3, determine whether the temperature difference is satisfied;

[0110] If satisfied, the output includes a refrigeration solution for a low-temperature refrigerator and a low-temperature circulation pump;

[0111] If not, increase the circulation pump flow rate until the temperature rise of liquid nitrogen meets the condition of being less than the maximum temperature difference, and then output a matching refrigeration solution including a cryogenic refrigerator and a cryogenic circulation pump.

[0112] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system; characterized in that: The steps include: Step 1: Calculate cooling load; Step 2: Calculate hydraulic loss; Step 3: Determine whether the height difference during cable construction is lower than the theoretical calculation result of the maximum height difference during cable construction; If it is satisfied, the hydraulic loss is used as the basis for selecting the pump head; If not, the height difference of the cable during construction in the specific project shall be used as the basis for calculating and selecting the circulation pump head; Step 4: Determine the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen; Step 5: Determine the temperature rise limit based on the relationship between the liquid nitrogen flow rate and the maximum temperature difference of the liquid nitrogen, and determine the optimal type of the cryogenic circulation pump based on the range of the liquid nitrogen flow rate; Step 6: Select a refrigeration unit that meets the cooling temperature and has a cooling capacity that matches the cooling load.

2. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 1, characterized in that: In step 1, the cooling load is calculated by calculating the local cooling load of the insulated pipe per unit length. The specific formula is as follows: Where Q is the cooling load per unit length of the insulated pipe, in W / m; k is the effective thermal conductivity of the insulated pipe, in W / m / K; T ∞ is the ambient temperature, unit: K; is the working liquid nitrogen temperature, unit: K; D out D is the outer diameter of the insulation pipe, unit: mm; in The inner diameter of the insulation pipe, unit: mm.

3. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 2, characterized in that: In step 2, the hydraulic loss calculation includes the hydraulic loss along the way H f and local hydraulic loss H L .

4. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 3, characterized in that: The hydraulic loss along the way H f The calculation formula is as follows: Where f is the Darcy drag coefficient; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; v is the liquid nitrogen flow rate, in m / s; g is the acceleration due to gravity, in m / s 2 .

5. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 4, characterized in that: For example, when calculating the hydraulic loss along the bellows, the Reynolds number is 10 4 to April 10 4 The Darcy drag coefficient f of the bellows is only related to the bellows structure, and the expression is as follows: Wherein, e is the wave height of the bellows, unit: m; p is the wave distance, unit: m; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, and is calculated as follows: Among them, 3D out D is the outer diameter of the cable, in m; in The inner diameter of the insulation pipe, unit: mm.

6. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 3, characterized in that: The local hydraulic loss H L The calculation formula is as follows: Where K is the local resistance coefficient of the specific accessory; v is the liquid nitrogen flow rate in m / s; g is the acceleration due to gravity in m / s 2 .

7. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 3, characterized in that: In step 3, the calculation formula of the theoretical calculation result of the maximum height difference of the cable construction is specifically as follows: Where Δh max is the theoretical calculation result of the maximum height difference of the cable construction; P inlet is the inlet pressure of liquid nitrogen, unit: Pa; P inlet =P outlet +ΔP friction (L)+ρgΔh; P outlet is the outlet pressure of liquid nitrogen, unit: Pa; Δh is the height difference of the cable during the construction process, unit: m; ΔP friction (L) is the pressure loss when the output distance of the high-temperature superconducting cable is L, in Pa, and the calculation formula is as follows: Where f is the Darcy drag coefficient of the liquid nitrogen flow pipeline; L is the output distance of the high-temperature superconducting cable, in meters; D h is the hydraulic diameter of the liquid nitrogen bellows channel in the cable, in m; ρ is the density of liquid nitrogen, in kg / m 3 ; v is the liquid nitrogen flow rate, unit: m / s; g is the acceleration due to gravity, unit: m / s 2 ; P boil (T) is the output pressure of liquid nitrogen corresponding to the maximum height difference allowed during construction, which is equal to the saturated vapor pressure at the corresponding temperature. The unit is Pa. The calculation formula is as follows: P boil (T)=P outlet 。 8. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 3, characterized in that: In step 4, the maximum operating temperature range of liquid nitrogen is determined to be between the triple point of liquid nitrogen, 63.4K, and the boiling point of liquid nitrogen at normal pressure, 77K; the maximum temperature difference is 13.6K; Then, the liquid nitrogen with a maximum temperature difference of 12K from the boiling point of liquid nitrogen at normal pressure of 77K is cooled to 65K as the starting temperature of the liquid nitrogen, and 80% of the maximum temperature difference, that is, 9.6K, is taken as the standard for determining whether the liquid nitrogen flow rate meets the thermodynamic limit. The formula for the relationship between the liquid nitrogen flow rate and the maximum temperature difference of liquid nitrogen is as follows: Where L is the output distance of the high-temperature superconducting cable, in meters; Q1 is the terminal unit loss, in W per terminal; N1 is the number of terminals; Q2 is the connector unit loss, in W per terminal; N2 is the number of connectors; Q3 is the loss of other pipelines in the system, in W; ρ is the density of liquid nitrogen, in kg / m 3 ; is the volume flow rate of liquid nitrogen, unit: m 3 / s;c p is the specific heat capacity of liquid nitrogen at constant pressure, unit: J / (kg·K).

9. The method for constructing a thermal-hydraulic coupling model of a high-temperature superconducting cable cooling system according to claim 3, characterized in that: Step 6 is as follows: Step 6.

1. Select the optimal operating condition of the circulating pump, that is, the circulating pump flow rate with the highest pump efficiency; Step 6.2, calculating the temperature difference according to the circulation pump flow rate using the temperature rise formula; Step 6.3, determine whether the temperature difference is satisfied; If satisfied, the output includes a refrigeration solution for a low-temperature refrigerator and a low-temperature circulation pump; If not, increase the circulation pump flow rate until the temperature rise of the liquid nitrogen satisfies the condition that is less than the maximum temperature difference, and then output a matching refrigeration solution including a low-temperature refrigerator and a low-temperature circulation pump.

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