Method and apparatus for cooling electric machine using carbon dioxide

Abstract

The present disclosure provides a method of cooling an electric machine with carbon dioxide. The method for cooling the motor by using the carbon dioxide comprises the following steps: repeatedly carrying out iterative calculation to determine a first target mass flow rate; cooling the motor by using the carbon dioxide with the first target mass flow; wherein any kth iterative calculation comprises the following steps: calculating the (k-1) th estimated mass flow rate of the carbon dioxide required for cooling the motor by utilizing the (k-1) th surface friction coefficient of the carbon dioxide flowing through the surface of the motor; calculating the kth surface friction coefficient of the carbon dioxide flowing through the surface of the motor according to the (k-1) th estimated mass flow and the flowing property parameter of the carbon dioxide flowing through the motor; calculating the kth estimated mass flow rate of the carbon dioxide by using the kth surface friction coefficient of the carbon dioxide flowing through the surface of the motor; and k is progressively increased until the difference between the kth estimated mass flow and the (k-1) th estimated mass flow satisfies an iteration termination condition, and the kth estimated mass flow is used as a first target mass flow. The invention also provides a device for cooling the motor by using the carbon dioxide.

Description

Technical Field

[0001] The present disclosure relates to the technical field of motor cooling, and particularly to a method and device for cooling a motor using carbon dioxide. Background Art

[0002] In fields such as carbon dioxide power generation, energy storage, or heat pumps, turbomachinery such as compressors and expanders constitutes a key link in energy conversion and transmission. As a driving or power generation device for turbomachinery, a motor is usually directly connected to a compressor or an expander and is an indispensable part of the power input and power output of the entire system.

[0003] However, the inventors found that there are at least the following problems in the prior art: Since the carbon dioxide turbomachinery is directly connected to the motor, it is inevitable that the working medium leaks at the turbine shaft end. If air is used to cool the motor, it is necessary to reinject the leaked carbon dioxide, increasing the sealing performance of the entire system. Summary of the Invention

[0004] In view of the above problems, the present disclosure provides a method and device for cooling a motor that can improve the efficiency of cooling the motor and avoid the leakage of the working medium.

[0005] According to a first aspect of the present disclosure, there is provided a method for cooling a motor using carbon dioxide, including: performing iterative calculations multiple times to determine a first target mass flow rate; cooling the motor using carbon dioxide with the first target mass flow rate; wherein, any k-th iterative calculation includes: calculating a (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface, where k is a positive integer greater than or equal to 2; calculating the k-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the motor; calculating the k-th estimated mass flow rate of carbon dioxide using the k-th surface friction coefficient of carbon dioxide flowing through the motor surface; incrementing k until the difference between the k-th estimated mass flow rate and the (k - 1)-th estimated mass flow rate satisfies the iteration termination condition, and taking the k-th estimated mass flow rate as the first target mass flow rate.

[0006] According to an embodiment of the present disclosure, the method of cooling an electric machine using carbon dioxide further includes: when the windage loss corresponding to the first target mass flow rate exceeds the windage loss threshold, performing multiple iterative calculations to determine a second target mass flow rate; wherein, any l-th iterative calculation includes: adjusting the intake pressure corresponding to the first target mass flow rate; updating the specific enthalpy of carbon dioxide at the inlet of the electric machine according to the adjusted intake pressure; using the updated specific enthalpy at the inlet to calculate the l-th estimated mass flow rate, where l is a positive integer greater than or equal to 1; incrementing l until the (l + 1)-th windage loss is less than or equal to the windage loss threshold, and taking the estimated mass flow rate corresponding to the (l + 1)-th windage loss as the second target mass flow rate.

[0007] According to an embodiment of the present disclosure, calculating the k-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine according to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the electric machine includes: calculating the flow performance parameters of carbon dioxide flowing through the electric machine according to the (k - 1)-th estimated mass flow rate and the friction area of carbon dioxide flowing through the electric machine; calculating the Reynolds number for characterizing the flow state of carbon dioxide according to the flow performance parameters; and calculating the k-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine according to the Reynolds number.

[0008] According to an embodiment of the present disclosure, calculating the k-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine according to the Reynolds number includes using the following method:

[0009]

[0010] wherein: M, p, q, s, and t are all empirical coefficients, is the axial Reynolds number, is the rotational Reynolds number, is the radius ratio, is the aspect ratio.

[0011] According to an embodiment of the present disclosure, the method further includes: adjusting the k-th surface friction coefficient using the kinematic viscosity parameter, using the following method:

[0012]

[0013] wherein, is the kinematic viscosity of carbon dioxide under the conditions of inlet temperature T = 105 °C and inlet pressure P = 14 MPa, is the kinematic viscosity of carbon dioxide under the current temperature and pressure conditions.

[0014] According to an embodiment of the present disclosure, calculating the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor by using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface includes: determining the (k - 1)-th windage loss generated when carbon dioxide flows through the motor surface by using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface; calculating the (k - 1)-th total heat loss according to the (k - 1)-th windage loss and the electromagnetic loss generated by the motor movement; and calculating the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor according to the (k - 1)-th total heat loss and the specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor.

[0015] According to an embodiment of the present disclosure, the method for cooling the motor by using carbon dioxide further includes: obtaining the inlet temperature of carbon dioxide; determining the specific enthalpy of carbon dioxide at the motor inlet according to the inlet temperature and the inlet pressure; calculating the outlet temperature of carbon dioxide; determining the specific enthalpy of carbon dioxide at the motor outlet according to the outlet temperature and the outlet pressure; and calculating the specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor according to the specific enthalpy at the inlet and the specific enthalpy at the outlet.

[0016] According to an embodiment of the present disclosure, calculating the outlet temperature of carbon dioxide includes: calculating the Nusselt number for characterizing the heat transfer performance of carbon dioxide; calculating the convective heat transfer coefficient of carbon dioxide between the rotor and stator of the motor by using the Nusselt number; calculating the heat transfer area of carbon dioxide between the rotor and stator of the motor; and calculating the outlet temperature of carbon dioxide according to the convective heat transfer coefficient and the heat transfer area.

[0017] According to an embodiment of the present disclosure, calculating the Nusselt number for characterizing the heat transfer performance of carbon dioxide includes: calculating the equivalent Reynolds number according to the initial axial Reynolds number and the rotational Reynolds number; and calculating the Nusselt number according to the equivalent Reynolds number, the Prandtl number, the radius ratio of carbon dioxide in contact with the motor, and the aspect ratio.

[0018] The second aspect of the present disclosure provides an apparatus for cooling an electric machine using carbon dioxide, comprising: a calculation module configured to perform iterative calculations multiple times to determine a first target mass flow rate; a cooling module configured to cool the electric machine using carbon dioxide at the first target mass flow rate; wherein, any k-th iterative calculation includes: a first calculation sub-module configured to calculate a (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the electric machine using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine, where k is a positive integer greater than or equal to 2; a second calculation sub-module configured to calculate the k-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine according to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the electric machine; a third calculation sub-module configured to calculate the k-th estimated mass flow rate of carbon dioxide using the k-th surface friction coefficient of carbon dioxide flowing through the surface of the electric machine; a determination sub-module configured to increment k until the difference between the k-th estimated mass flow rate and the (k - 1)-th estimated mass flow rate satisfies an iteration termination condition, and take the k-th estimated mass flow rate as the first target mass flow rate.

[0019] According to an embodiment of the present disclosure, estimating the initial surface friction coefficient generated by carbon dioxide flowing through the surface of the electric machine provides a base value for calculating the estimated mass flow rate in the iterative calculation process. Further, iteratively calculating the surface friction coefficient generated by carbon dioxide flowing through the surface of the electric machine in combination with the actual flow performance parameters of carbon dioxide enables the process data of the iterative calculation to gradually approach the true value of cooling the electric machine with carbon dioxide. After multiple iterations, when the estimated mass flow rates of two adjacent times satisfy the iteration termination condition, the mass flow rate of carbon dioxide required to cool the electric machine can be determined. Thus, the iterative process can converge faster to a range close to the true value, which helps to improve the accuracy of the final result, reduces the complexity and workload of the calculation, and improves the calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, the above content and other objects, features and advantages of the present disclosure will become clearer. In the drawings:

[0021] Figure 1 Schematically shows a flowchart of a method for cooling an electric machine using carbon dioxide according to an embodiment of the present disclosure;

[0022] Figure 2 Schematically shows a flowchart of a method for cooling an electric machine using carbon dioxide according to another embodiment of the present disclosure;

[0023] Figure 3 Schematically shows a structural block diagram of an apparatus for cooling an electric machine using carbon dioxide according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions, and advantages of the present disclosure more clearly understood, the following further elaborates on the present disclosure in detail with reference to specific embodiments and the accompanying drawings.

[0025] Since it is inevitable that working medium leakage occurs at the turbine shaft end, in order to achieve long-term stable operation of the system, the leaked gas must be recovered continuously. However, using air to cool the motor will greatly increase the difficulty of leakage reinjection. The entire system must be equipped with complex purification equipment to possibly achieve high-purity reinjection of CO 2 leakage gas. Therefore, in the embodiments of the present disclosure, the cooling medium of the motor is also selected as CO 2 . After the leakage gas of the turbomachinery is mixed with the cooling medium of the motor, the mass flow rate of the leakage gas is extracted and reinjected into the internal pipeline of the system, greatly improving the intensiveness of the system.

[0026] Regarding the method of using air to cool the motor, due to the small density and viscosity of air, high wind friction losses will not be generated in the gaps between the motor rotor and stator. Therefore, the wind friction losses generated by the air cooling gas are usually ignored. However, compared with air, carbon dioxide has a large density and high viscosity. If carbon dioxide is used as the cooling medium of the motor, relatively large wind friction losses will be generated in the motor cavity, increasing the heat loss of the motor. Ignoring the wind friction losses may cause the motor to be unable to dissipate heat normally, affecting the safety and reliability of the motor. Even though there are existing methods that can calculate the wind friction losses generated by air, the physical properties such as density and viscosity of carbon dioxide are different from those of air, which makes its flow characteristics and the generated wind friction losses in the gaps between the motor rotor and stator very different from those of air. The existing methods for calculating the wind friction losses of air are not applicable to the carbon dioxide cooling gas.

[0027] In view of this, the present disclosure provides a method for cooling a motor using carbon dioxide, including: performing multiple iterative calculations to determine a first target mass flow rate; using carbon dioxide with the first target mass flow rate to cool the motor; wherein, any k-th iterative calculation includes: using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface to calculate the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor, where k is a positive integer greater than or equal to 2; calculating the k-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the motor; using the k-th surface friction coefficient of carbon dioxide flowing through the motor surface to calculate the k-th estimated mass flow rate of carbon dioxide; incrementing k until the difference between the k-th estimated mass flow rate and the (k - 1)-th estimated mass flow rate meets the iteration termination condition, and taking the k-th estimated mass flow rate as the first target mass flow rate.

[0028] Figure 1 Schematically shows a flowchart of the method for cooling a motor using carbon dioxide according to an embodiment of the present disclosure.

[0029] As Figure 1 shown, this embodiment includes operations S110 to S120.

[0030] In operation S110, iterative calculations are performed multiple times to determine the first target mass flow rate.

[0031] In operation S120, the motor is cooled with carbon dioxide at the first target mass flow rate. Among them, any k-th iterative calculation includes steps 11 to 14.

[0032] Step 11: Using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface, calculate the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor, where k is a positive integer greater than or equal to 2. Step 12: According to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the motor, calculate the k-th surface friction coefficient of carbon dioxide flowing through the motor surface.

[0033] Step 13: Using the k-th surface friction coefficient of carbon dioxide flowing through the motor surface, calculate the k-th estimated mass flow rate of carbon dioxide.

[0034] Step 14: Increment k until the difference between the k-th estimated mass flow rate and the (k - 1)-th estimated mass flow rate satisfies the iteration termination condition, and take the k-th estimated mass flow rate as the first target mass flow rate.

[0035] According to the embodiment of the present disclosure, since the wind friction loss generated between carbon dioxide and the motor cannot be directly calculated, the calculation method of the wind friction loss generated between air and the motor is used to estimate the wind friction loss generated between carbon dioxide and the motor.

[0036] Specifically, when k = 2, before calculating the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface, it further includes:

[0037] Estimate the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the empirical algorithm applicable to air transcritical flow (air TC flow). Air TC flow is the abbreviation of Taylor-Couette flow, which is the rotational flow of the working fluid in the annular gap where the rotor rotates and the stator is stationary. TC flow does not consider the axial Poiseuille flow of the working fluid and only considers the circumferential rotation generated by the inner cylinder acting on the working fluid. The specific calculation method refers to Equation (1):

[0038] Equation (1)

[0039] Among them, is the rotational Reynolds number, referring to Equation (2):

[0040] Equation (2)

[0041] where is the carbon dioxide density is the rotational speed is the outer diameter of the motor rotor is the inner diameter of the motor stator is the dynamic viscosity of the working fluid

[0042] According to an embodiment of the present disclosure, in addition to Equation (1), other calculation methods applicable to the wind friction loss of TC flow can also be used, which will not be listed one by one here

[0043] According to an embodiment of the present disclosure, due to the small density and viscosity of air, the predicted mass flow rate at the (k - 1)th time corresponding to the surface friction coefficient estimated by using the empirical algorithm applicable to air transcritical flow (air TC flow) is less than the mass flow rate of carbon dioxide required to actually cool the motor. Therefore, it is necessary to comprehensively and iteratively calculate the surface friction coefficient generated by carbon dioxide and the motor according to the flow performance when carbon dioxide flows through the motor

[0044] According to an embodiment of the present disclosure, when k > 2, the kth surface friction coefficient of carbon dioxide flowing through the motor surface is calculated according to the predicted mass flow rate at the (k - 1)th time and the flow performance parameters of carbon dioxide flowing through the motor

[0045] According to an embodiment of the present disclosure, further iterative calculation is performed. When the difference between the predicted mass flow rates obtained from two adjacent iterative calculations satisfies the iteration termination condition, it indicates that the obtained predicted mass flow rate gradually approaches the true value or meets a certain accuracy requirement. Using the carbon dioxide with the predicted mass flow rate obtained from the current iterative calculation to cool the motor can meet the cooling requirement, that is, the carbon dioxide cooling gas can take away the wind friction loss generated when carbon dioxide flows through the motor surface, and the calculation result converges

[0046] According to an embodiment of the present disclosure, the iteration termination condition can be a predetermined threshold or a threshold range; it can also be a predetermined number of iterations, etc. For example, when the difference between the predicted mass flow rate at the kth time and the predicted mass flow rate at the (k - 1)th time satisfies the range of 0.001 kg / s to 0.01 kg / s, the iteration is stopped

[0047] According to an embodiment of the present disclosure, estimating the initial surface friction coefficient generated by carbon dioxide flowing through the surface of the motor provides a base value for calculating the estimated mass flow rate during the iterative calculation process. Further, by combining the actual flow performance parameters of carbon dioxide, the surface friction coefficient generated by carbon dioxide flowing through the surface of the motor is iteratively calculated, so that the process data of the iterative calculation gradually approaches the true value of the carbon dioxide-cooled motor. After multiple iterations, when the estimated mass flow rates in two adjacent iterations meet the iterative termination condition, the mass flow rate of carbon dioxide required to cool the motor can be determined. Thus, the iterative process can converge faster to a range close to the true value, which helps to improve the accuracy of the final result, reduces the complexity and workload of the calculation, and improves the calculation efficiency.

[0048] Figure 2 Schematically shows a flowchart of a method for cooling a motor using carbon dioxide according to another embodiment of the present disclosure.

[0049] As Figure 2 shown, based on operations S110 to S120, this embodiment further includes operation S210.

[0050] In operation S210, when the windage loss corresponding to the first target mass flow rate exceeds the windage loss threshold, multiple iterative calculations are performed to determine the second target mass flow rate.

[0051] Wherein, any l-th iterative calculation includes steps 21 to 24.

[0052] In step 21, adjust the intake pressure corresponding to the first target mass flow rate.

[0053] In step 22, update the specific enthalpy of carbon dioxide at the motor inlet according to the adjusted intake pressure.

[0054] In step 23, use the updated specific enthalpy at the inlet to calculate the l-th estimated mass flow rate, where l is a positive integer greater than or equal to 1.

[0055] In step 24, increment l until the (l + 1)-th windage loss is less than or equal to the windage loss threshold, and take the estimated mass flow rate corresponding to the (l + 1)-th windage loss as the second target mass flow rate.

[0056] According to an embodiment of the present disclosure, due to excessive wind friction loss, components are prone to problems such as difficult speed increase and overheating, which affect the performance and lifespan of the motor. Based on the first target mass flow rate already calculated according to operations S110 to S120, it is determined whether the wind friction loss corresponding to the first target mass flow rate is greater than the wind friction loss threshold. Herein, the wind friction loss threshold can be determined according to the working conditions and historical experience. By determining whether the wind friction loss is greater than the threshold and timely adjusting the carbon dioxide inlet pressure, intervention can be carried out when the wind friction loss is excessive, effectively reducing problems such as difficult speed increase and overheating of components caused by wind friction loss, enabling the motor components to be in a more stable working state, thereby extending the overall service life of the motor and ensuring the stability and reliability of the motor performance. To ensure that the efficiency of carbon dioxide cooling the motor remains unchanged, the estimated mass flow rate of carbon dioxide is iteratively calculated again to calculate the required mass flow rate according to the adjusted pressure. Adjusting the carbon dioxide inlet pressure to reduce wind friction loss without affecting the cooling performance achieves a balance between the cooling effect and wind friction loss. It not only ensures that the motor can be fully cooled to prevent performance problems caused by overheating but also avoids excessive wind friction loss caused by unreasonable intake methods, making the cooling system more optimized and efficient.

[0057] According to an embodiment of the present disclosure, step 11 further includes steps 111 to 113.

[0058] In step 111, the (k - 1)th wind friction loss generated when carbon dioxide flows through the motor is determined using the (k - 1)th surface friction coefficient of carbon dioxide flowing through the motor surface.

[0059] According to an embodiment of the present disclosure, the reference formula (3) for calculating the (k - 1)th wind friction loss is:

[0060] Formula (3)

[0061] Wherein, is the (k - 1)th wind friction loss, is the (k - 1)th surface friction coefficient, is the density of carbon dioxide, is the outer diameter of the motor rotor, is the motor speed, and L is the length of the motor rotor.

[0062] According to an embodiment of the present disclosure, when k = 2, the first wind friction loss generated when carbon dioxide flows through the motor is determined using the estimated first surface friction coefficient.

[0063] In step 112, the (k - 1)th total heat loss is calculated based on the (k - 1)th wind friction loss and the electromagnetic loss generated by the motor movement.

[0064] According to an embodiment of the present disclosure, the k-1th windage and friction loss is calculated by the above step 111.

[0065] According to an embodiment of the present disclosure, the electromagnetic loss of the motor is calculated based on the electromagnetic parameters and structural parameters of the motor. The electromagnetic parameters include the power, voltage, current, speed, types of windings and rotors, etc. of the motor. The structural parameters include the stator-rotor gap, length, inner diameter of the stator, outer diameter of the rotor, bearing clearance, structural dimensions of the thrust disk, etc. Specifically, the electromagnetic loss of the motor can be obtained through electromagnetic simulation based on the above parameters. It is also possible to estimate the electromagnetic loss of the motor according to experience, taking 3% - 5% of the motor power, so as to provide an initial heat load value for subsequent design calculations. According to an embodiment of the present disclosure, the k-1th total heat loss is calculated by summing the k-1th windage and friction loss and the electromagnetic loss generated by the motor movement, referring to Equation (4):

[0066] Equation (4)

[0067] Where, is the k-1th total heat loss, is the electromagnetic loss, is the k-1th windage and friction loss.

[0068] In step 113, the k-1th estimated mass flow rate of carbon dioxide required to cool the motor is calculated based on the k-1th total heat loss and the specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor.

[0069] According to an embodiment of the present disclosure, the k-1th estimated mass flow rate of carbon dioxide required to cool the motor is calculated, referring to Equation (5):

[0070] Equation (5)

[0071] Where, is the specific enthalpy of carbon dioxide at the inlet, is the specific enthalpy of carbon dioxide at the outlet.

[0072] According to an embodiment of the present disclosure, the specific enthalpy of carbon dioxide at the inlet and the specific enthalpy at the outlet are obtained by referring to the physical property table according to the pressure and temperature parameters at the inlet and outlet respectively.

[0073] Specifically, the inlet temperature of carbon dioxide is obtained. The inlet temperature can be taken as the ambient temperature; according to the inlet temperature and the inlet pressure , the specific enthalpy of carbon dioxide at the inlet of the motor , that is .

[0074] And calculate the outlet temperature of carbon dioxide according to the inlet temperature and the average temperature of the solid wall inside the motor. According to the outlet temperature and the outlet pressure , query the specific enthalpy of carbon dioxide at the outlet of the motor , that is . Among them, the inlet pressure can be set by the staff according to experience. The pressure loss will not cause great changes in physical properties. For simplicity of calculation, the outlet pressure can be designed to be equal to the inlet pressure.

[0075] According to the embodiments of the present disclosure, calculate the specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor according to the specific enthalpy at the inlet and the specific enthalpy at the outlet. .

[0076] According to the embodiments of the present disclosure, calculating the outlet temperature of carbon dioxide according to the inlet temperature and the average temperature of the solid wall inside the motor includes steps (1) to (5).

[0077] In step (1), calculate the equivalent Reynolds number according to the initial axial Reynolds number and the rotational Reynolds number. Refer to Equation (6):

[0078] Equation (6)

[0079] Among them, C is an empirical coefficient, is the initial axial Reynolds number, is the rotational Reynolds number. When k is equal to 2, the initial axial Reynolds number is 0.

[0080] In step (2), calculate the Nusselt number according to the equivalent Reynolds number, the Prandtl number, the radius ratio of carbon dioxide in contact with the motor, and the aspect ratio. Refer to Equation (7):

[0081] Equation (7)

[0082] Among them, A, w, x, y, and z are all empirical coefficients, is the Prandtl number, is the radius ratio, and the calculation formula refers to Equation (8); is the aspect ratio, and the calculation formula refers to Equation (9).

[0083] Equation (8)

[0084] Equation (9)

[0085] In step (3), use the Nusselt number to calculate the convective heat transfer coefficient of carbon dioxide between the rotor and stator of the motor . Refer to Equation (10):

[0086] Equation (10)

[0087] wherein is the equivalent diameter of the rotor-stator gap. For an annular gap, ; is the thermal conductivity of carbon dioxide, with the unit of W / mK.

[0088] According to the embodiments of the present disclosure, for carbon dioxide under low-pressure conditions, the Nusselt number applicable to air can be used for the calculation method. For example, A = 0.03, w = 0.8, x = y = z = 0, C = 4. Other convective heat transfer coefficient methods can also be used. For carbon dioxide in the high-pressure state up to the supercritical state, A = 0.00718, w = 0.847, x = 0.328, y = z = 0, C = 4 can be used; or A = 0.00545, w = 0.847, x = 0.328, y = -2.84, z = -0.00248, C = 4. A = 0.0082, w = 0.84, x = y = z = 0, C = 4 can also be used. For the near-critical state, due to the drastic change in the physical properties of carbon dioxide, specific coefficients are required: A = 0.0087, w = 1.22, x = y = z = 0, C = 4.

[0089] In step (iv), calculate the heat transfer area of carbon dioxide between the rotor and stator of the motor. Refer to Equation (11):

[0090] Equation (11)

[0091] In step (v), calculate the outlet temperature of carbon dioxide based on the convective heat transfer coefficient and the heat transfer area. Refer to Equations (12) and (13):

[0092] Equation (12)

[0093] Equation (13)

[0094] wherein is the average temperature of the carbon dioxide cooling gas; is the average temperature of the solid wall surface inside the motor, which is taken within the range of 80°C to 120°C according to safety requirements.

[0095] According to the embodiments of the present disclosure, step 12 further includes steps 121 to 123.

[0096] In step 121, calculate the flow performance parameters of carbon dioxide flowing through the motor based on the predicted mass flow rate at the (k - 1)th time and the friction area of carbon dioxide flowing through the motor. Refer to Equation (14):

[0097] Equation (14)

[0098] wherein, is the axial flow velocity of the carbon dioxide cooling gas between the stator and rotor of the motor.

[0099] In step 122, the Reynolds number for characterizing the flow state of carbon dioxide is calculated according to the flow performance parameters. Refer to Equation (15):

[0100] Equation (15)

[0101] In step 123, the k-th surface friction coefficient of the carbon dioxide flowing through the motor surface is calculated according to the Reynolds number.

[0102] According to an embodiment of the present disclosure, a calculation formula for calculating the k-th surface friction coefficient is derived based on the axial Reynolds number and the rotational Reynolds number. Refer to Equation (16):

[0103] Equation (16)

[0104] where: M, p, q, s, and t are all empirical coefficients, is the axial Reynolds number, is the rotational Reynolds number, is the radius ratio, is the aspect ratio.

[0105] According to an embodiment of the present disclosure, a calculation method for the surface friction coefficient applicable to the conditions of an inlet temperature of 105 °C and an inlet pressure of 14 MPa. Among them, M = 0.0735, p = 0.16, q = -0.3328, s = 0.1055, and t = -0.2543 can be used for calculation According to the calculation method for the surface friction coefficient applicable to the conditions of an inlet temperature of 105 °C and an inlet pressure of 14 MPa, Equation (16) is adjusted to obtain a calculation method for the surface friction coefficient at any inlet temperature and pressure.

[0106] Furthermore, the k-th surface friction coefficient is adjusted by using the kinematic viscosity parameter. Refer to Equation (17):

[0107] Equation (17)

[0108] wherein, is the kinematic viscosity of carbon dioxide under the conditions of an inlet temperature T = 105 °C and an inlet pressure P = 14 MPa, is the kinematic viscosity of carbon dioxide under the current temperature and pressure conditions.

[0109] According to an embodiment of the present disclosure, when k > 2, the k-th surface friction coefficient of carbon dioxide flowing through the motor surface is calculated using Equation (17) for iterative calculation. According to an embodiment of the present disclosure, when the first target mass flow rate is determined according to the above iterative calculation method, the wind friction loss, total heat loss, and carbon dioxide inlet temperature corresponding to the first target mass flow rate are determined, so as to facilitate the staff to cool the motor based on the above parameters.

[0110] According to an embodiment of the present disclosure, when the second target mass flow rate is determined according to the above iterative calculation method, the wind friction loss, total heat loss, and carbon dioxide inlet temperature corresponding to the second target mass flow rate are determined, so as to facilitate the staff to cool the motor based on the above parameters.

[0111] According to an embodiment of the present disclosure, although the present disclosure only proposes the above method for motor cooling for carbon dioxide working medium, for other working media that need to pay attention to wind friction loss, the method proposed by the present disclosure can be adopted, and the calculation methods of wind friction loss and convective heat transfer coefficient can be replaced with algorithms applicable to the working medium.

[0112] Figure 3 The structural block diagram of a device for cooling a motor using carbon dioxide according to an embodiment of the present disclosure is schematically shown.

[0113] As Figure 3 shown, the device 300 for cooling a motor using carbon dioxide includes: a calculation module 310 and a cooling module 320.

[0114] The calculation module 310 is configured to perform iterative calculations multiple times to determine the first target mass flow rate.

[0115] The cooling module 320 is configured to cool the motor using carbon dioxide with the first target mass flow rate; wherein, any k-th iterative calculation includes: a first calculation sub-module, configured to calculate the (k - 1)-th estimated mass flow rate of carbon dioxide required to cool the motor using the (k - 1)-th surface friction coefficient of carbon dioxide flowing through the motor surface, where k is a positive integer greater than or equal to 2; a second calculation sub-module, configured to calculate the k-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the (k - 1)-th estimated mass flow rate and the flow performance parameters of carbon dioxide flowing through the motor; a third calculation sub-module, configured to calculate the k-th estimated mass flow rate of carbon dioxide using the k-th surface friction coefficient of carbon dioxide flowing through the motor surface; a determination sub-module, configured to increment k until the difference between the k-th estimated mass flow rate and the (k - 1)-th estimated mass flow rate satisfies the iterative termination condition, and take the k-th estimated mass flow rate as the first target mass flow rate.

[0116] In the above specific embodiments, the objectives, technical solutions, and beneficial effects of the present disclosure have been further described in detail. It should be understood that the above are only specific embodiments of the present disclosure and are not used to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A method for cooling a motor using carbon dioxide, characterized in that: The method comprises: Performing multiple iterations of calculation to determine a first target mass flow rate; Cooling the motor using the first target mass flow of carbon dioxide; Among them, any k-th iteration calculation includes: Calculating the k-1th estimated mass flow rate of carbon dioxide required to cool the motor by using the k-1th surface friction coefficient of carbon dioxide flowing through the motor surface, where k is a positive integer ≥ 2; Calculating a k-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the k-1-th estimated mass flow rate and the flow performance parameter of carbon dioxide flowing through the motor; Calculating a kth estimated mass flow rate of carbon dioxide using the kth surface friction coefficient of the carbon dioxide flowing through the motor surface; Increment k until the difference between the k-th estimated mass flow and the k-1-th estimated mass flow meets the iteration termination condition, and take the k-th estimated mass flow as the first target mass flow.

2. The method according to claim 1, characterized in that The method further comprises: When the wind friction loss corresponding to the first target mass flow exceeds a wind friction loss threshold, performing multiple iterative calculations to determine a second target mass flow; Among them, any iterative calculation of the lth time includes: adjusting the intake pressure corresponding to the first target mass flow rate; updating the specific enthalpy of the carbon dioxide at the motor inlet according to the adjusted intake pressure; Calculating the l-th estimated mass flow rate using the updated specific enthalpy at the inlet, where l is a positive integer ≥ 1; Increment by l until the (l+1)th wind friction loss is less than or equal to the wind friction loss threshold, and take the estimated mass flow corresponding to the (l+1)th wind friction loss as the second target mass flow.

3. The method according to claim 1, characterized in that Calculating the kth surface friction coefficient of carbon dioxide flowing through the motor surface according to the k-1th estimated mass flow rate and the flow performance parameter of carbon dioxide flowing through the motor, including: Calculating flow performance parameters of carbon dioxide flowing through the motor according to the k-1th estimated mass flow rate and the friction area of ​​carbon dioxide flowing through the motor; Calculating a Reynolds number for characterizing the flow state of the carbon dioxide according to the flow performance parameter; The kth surface friction coefficient of the carbon dioxide flowing through the motor surface is calculated according to the Reynolds number.

4. The method according to claim 3, characterized in that Calculating the kth surface friction coefficient of carbon dioxide flowing through the motor surface according to the Reynolds number includes using the following method: Among them: M, p, q, s, t are all empirical coefficients, is the axial Reynolds number, is the rotational Reynolds number, is the radius ratio, is the aspect ratio.

5. The method according to claim 3, characterized in that: The method further comprises: The k-th surface friction coefficient is adjusted using the kinematic viscosity parameter, using the following method: in, is the kinematic viscosity of carbon dioxide at inlet temperature T = 105°C and inlet pressure P = 14MPa, is the kinematic viscosity of carbon dioxide under current temperature and pressure conditions.

6. The method according to claim 1, characterized in that Calculating the k-1th estimated mass flow rate of carbon dioxide required for cooling the motor by using the k-1th surface friction coefficient of carbon dioxide flowing through the motor surface, including: Determine the k-1th wind friction loss generated when the carbon dioxide flows through the motor by using the k-1th surface friction coefficient when the carbon dioxide flows through the motor; Calculating the k-1th total heat loss according to the k-1th wind friction loss and the electromagnetic loss generated by the motor movement; The k-1th estimated mass flow rate of carbon dioxide required for cooling the motor is calculated according to the k-1th total heat loss and the specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor.

7. The method according to claim 6, characterized in that The method further comprises: obtaining an inlet temperature of the carbon dioxide; Determining the specific enthalpy of the carbon dioxide at the motor inlet according to the inlet temperature and the inlet pressure; calculating the outlet temperature of the carbon dioxide; Determining the specific enthalpy of the carbon dioxide at the motor outlet according to the outlet temperature and the outlet pressure; The specific enthalpy difference of carbon dioxide at the inlet and outlet of the motor is calculated based on the specific enthalpy at the inlet and outlet.

8. The method according to claim 7, characterized in that Calculating the outlet temperature of the carbon dioxide, comprising: calculating a Nusselt number for characterizing the heat transfer performance of the carbon dioxide; Calculating the convection heat transfer coefficient of the carbon dioxide between the rotor and the stator of the motor using the Nusselt number; Calculate the heat exchange area of ​​the carbon dioxide between the rotor and stator of the motor; The outlet temperature of the carbon dioxide is calculated according to the convection heat transfer coefficient and the heat exchange area.

9. The method according to claim 8, characterized in that Calculate the Nusselt number used to characterize the heat transfer performance of the carbon dioxide, including: Calculate the equivalent Reynolds number based on the initial axial Reynolds number and the rotational Reynolds number; The Nusselt number is calculated according to the equivalent Reynolds number, the Prandtl number, the radius ratio and the aspect ratio of the contact between the carbon dioxide and the motor.

10. A device for cooling a motor using carbon dioxide, characterized in that: The device comprises: A calculation module, used for performing multiple iterations of calculation to determine a first target mass flow rate; A cooling module, used for cooling the motor using the carbon dioxide at the first target mass flow rate; Among them, any k-th iteration calculation includes: A first calculation submodule, configured to calculate a k-1th estimated mass flow rate of carbon dioxide required for cooling the motor by using a k-1th surface friction coefficient of carbon dioxide flowing through the motor surface, wherein k is a positive integer ≥ 2; A second calculation submodule, configured to calculate a k-th surface friction coefficient of carbon dioxide flowing through the motor surface according to the k-1-th estimated mass flow rate and a flow performance parameter of carbon dioxide flowing through the motor; A third calculation submodule, configured to calculate a kth estimated mass flow rate of carbon dioxide by using the kth surface friction coefficient of the carbon dioxide flowing through the surface of the motor; The determination submodule is used to increment k until the difference between the kth estimated mass flow and the k-1th estimated mass flow meets the iteration termination condition, and the kth estimated mass flow is used as the first target mass flow.

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