A state evaluation method for water turbine unit air cooler based on relative heat transfer coefficient

Abstract

A method for assessing the condition of air coolers in hydropower units based on relative heat transfer coefficients involves collecting operational data such as the inlet and outlet temperatures of hot and cold fluids and the mass flow rate of the cooling medium. After steady-state screening, outlier filtering, and cold fluid temperature correction, the logarithmic mean temperature difference and cooling capacity Q are calculated to obtain the relative heat transfer coefficient. k ri Sorted by unit model k ri The values ​​are calculated, the top 5 minimum values ​​are extracted, and combined with a preset threshold to determine the air cooler degradation risk. The output includes the unit model number, etc. k ri The method provides an evaluation table of values ​​and corresponding equipment, along with graded maintenance recommendations. It can detect the performance of air coolers even when the heat exchange area is unknown, and compare the performance of different air coolers. This method eliminates area errors by using conventional data, saves costs, and achieves accurate performance evaluation, early warning, and cross-equipment performance comparison.

Description

Technical Field

[0001] This invention belongs to the field of hydropower equipment condition monitoring and fault diagnosis technology, and relates to a method for assessing the condition of air coolers in hydropower units based on relative heat transfer coefficient. Background Technology

[0002] Hydropower generator sets generate a significant amount of heat during operation due to electromagnetic losses and mechanical friction. As a critical cooling device, the performance of the air cooler directly impacts the unit's efficiency and operational safety. Currently, hydropower plants commonly use temperature monitoring to indirectly assess the condition of air coolers, primarily by monitoring simulated temperatures at the air cooler's inlet (hot air) and outlet (cold air) and relying on manual experience to determine if blockages or other faults have occurred. However, this traditional assessment method faces significant limitations: the complexity of the air cooler's internal fin structure and the accumulation of fouling make it difficult to accurately measure the actual effective heat transfer area, leading to significant errors in thermal calculations based on the heat transfer area; secondly, differences in structure, materials, and process design among different air coolers make it difficult to quantify their performance under a unified benchmark. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for evaluating the condition of air coolers in hydropower units based on the relative heat transfer coefficient, to solve the problem of evaluating the performance of air coolers when the heat exchange area is unknown, and to realize the performance comparison between different air coolers.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients, comprising the following steps: S1: Defines the relative heat transfer coefficient k ri The formula, combined with the logarithmic mean temperature difference ΔT m mass flow rate m and heat exchange Q Eliminate the influence of heat exchange area and achieve dimensionless standardized evaluation; S2: Collect operational data, perform steady-state screening, remove dead values ​​and outliers, and verify the inlet and outlet of cold fluid to ensure data validity; S3: Classify by unit model, calculate the relative heat transfer coefficient for air coolers of the same model and component. k ri Sort by value in ascending order, extract the first... N A smaller value; S4: According to k ri The comparison results between the numerical value and the preset threshold determine the performance degradation risk level of the corresponding air cooler; S5: Output includes unit model, the first N smaller ones k riThe table shows the values ​​and corresponding air cooler evaluation results. Based on the results, fault warnings are issued and graded maintenance recommendations are proposed.

[0005] The relative heat transfer coefficient in S1 k ri The construction and definition of the formula include, Analysis of heat transfer coefficient k The formula for calculating W / (m²·K) is as follows: (1) in Q Cooling capacity (kW); A To obtain the effective heat exchange area (m²), the fin contact thermal resistance must be deducted (the resistance of bimetallic finned tubes is taken as 0.0002 m²·K / W). Relative heat transfer coefficient k ri The calculation formula is: (2) in Q i / ΔT mi This is the ratio of the cooling capacity of the air cooler to the logarithmic mean temperature difference. For all air coolers of the same model and with the same components Q / Δ T m The maximum value; Logarithmic mean temperature difference (3) in T h,in The inlet temperature of the hot fluid is (°C). T h,out The outlet temperature of the hot fluid is (°C). T c,in The inlet temperature of the cold fluid is (°C). T c,out The outlet temperature of the cold fluid is (°C).

[0006] The operational data collected in S2 includes the inlet temperature of the hot fluid. T h,in 、 hot fluid outlet temperature T h,out 、 Cold fluid inlet temperature T c,in 、 Cold fluid outlet temperature T c,out 、 Cooling medium mass flow rate m。

[0007] The data preprocessing in S2 includes steady-state screening, dead value removal, outlier filtering, and cold fluid temperature correction. The outlier filtering method involves calculating the maximum value with a statistical probability of 99.9% for the mass flow rate of the cooling medium and the data at each temperature measurement point, and then removing the top 0.1% of the maximum values ​​to filter out abrupt changes in data. The cold fluid temperature correction is used to correct the temperature in scenarios where the cold fluid inlet and outlet of the air cooler are switched, ensuring the accuracy of the temperature data.

[0008] The correction formula for the inlet and outlet temperatures of the cold fluid is as follows: (4) SF is the import / export switch indicator, and 1 indicates a switch status. This indicates the historical reference value for the inlet temperature of the cold fluid.

[0009] (5) (6) in These represent the corrected inlet and outlet cold fluid temperatures, respectively. This is the temperature relationship verification value. 1 indicates a normal relationship. If the verification value is not 1, the data will be re-acquired and corrected.

[0010] Then calculate the logarithmic mean temperature difference, the core parameter. ΔT m and cooling capacity Q。

[0011] (7)

[0012] In the formula m The mass flow rate of the cooling medium (km / s) is measured using an ultrasonic flow meter according to DL / T 244-2012, with an accuracy of ±0.5%. Specific heat capacity at constant pressure (kJ / (km·K)); ΔT The temperature difference (K) between the inlet and outlet of the medium.

[0013] In S3, calculation Q i / ΔT mi When taking all steady-state operating conditions within a statistical period The average value, k ri A dimensionless number between 0 and 1 k ri =1 indicates that the corresponding air cooler is the best performing air cooler among those of the same model and components. k riThe smaller the value, the more severe the performance degradation of the air cooler.

[0014] In S3, N is 5, and the five smallest values ​​after ascending sorting are extracted. k ri The values ​​and corresponding air coolers are the key performance monitoring targets.

[0015] In S4, the preset threshold is k ri When the value is ≥0.9, routine inspection of the air cooler is sufficient; 0.75≤ k ri When the value is <0.85, the air cooler should be flushed or its performance fully inspected during the planned shutdown of the hydropower unit. k ri When the value is less than 0.75, the hydropower unit should be temporarily shut down immediately, and the air cooler should be inspected and thoroughly cleaned.

[0016] In S2, the operating data is collected by sensors in the existing monitoring system of the hydropower plant. The temperature sensor is a calibrated platinum resistance temperature sensor, and the flow sensor is an ultrasonic flow meter.

[0017] In S2, the inlet temperature of the hot fluid T h,in (°C) The sensor is located at the hot air inlet duct of the air cooler, at least twice the duct diameter from the air cooler body, to avoid eddy current interference; hot fluid outlet temperature T h,out (°C) The sensor is located at the cold air outlet duct of the air cooler; the inlet temperature of the cold fluid. T c,in (°C) The sensor is located at the cooling water inlet header, and the cold fluid outlet temperature; T c,out (°C) The sensor is located at the cooling water outlet header; ultrasonic flow meters are installed on the inlet and outlet main pipes of the cooling medium, and the distance between the measuring points is not less than 10 times the pipe diameter.

[0018] The main beneficial effects of this invention are as follows: 1. By combining parameters such as logarithmic mean temperature difference, mass flow rate, and heat transfer, a dimensionless standardized evaluation model independent of heat transfer area was constructed. This method fundamentally overcomes the calculation errors caused by the difficulty in accurately measuring the effective heat transfer area in traditional evaluations, and solves the key technical bottleneck in the quantitative evaluation of air cooler performance.

[0019] 2. This method relies only on conventional sensor data such as temperature and flow rate, without the need to install high-cost special equipment, thus lowering the threshold for engineering implementation. It can be easily integrated into the existing monitoring system of hydropower plants and has good practicality.

[0020] 3. A unified performance evaluation framework was established through cross-sectional performance comparisons of air coolers of the same model. This method utilizes... Q i / ΔT mi The ratio to the maximum value defines the relative heat transfer coefficient, eliminating the impact of differences in air cooler structure, material, and process design. This enables cross-equipment performance comparison of different air coolers, providing a reliable basis for equipment condition evaluation and selection optimization.

[0021] 4. Based on actual engineering needs, a verification method for switching the inlet and outlet of the cold fluid was established to improve the accuracy of air cooler operation monitoring and maintenance efficiency. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Figure 1 This is an exemplary flowchart of the present invention; Figure 2 This is a schematic diagram showing the changes in state quantities before and after blockage of the air cooler pipeline of the present invention. Detailed Implementation

[0024] like Figure 1 A method for assessing the condition of air coolers in hydropower units based on relative heat transfer coefficients includes the following steps: S1: Defines the relative heat transfer coefficient k ri The formula, combined with the logarithmic mean temperature difference ΔT m mass flow rate m and heat exchange Q Eliminate the influence of heat exchange area and achieve dimensionless standardized evaluation; S2: Collect operational data, perform steady-state screening, remove dead values ​​and outliers, and verify the inlet and outlet of cold fluid to ensure data validity; S3: Classify by unit model, calculate the relative heat transfer coefficient for air coolers of the same model and component. k ri Sort by value in ascending order, extract the first... N A smaller value; S4: According to k ri The comparison results between the numerical value and the preset threshold determine the performance degradation risk level of the corresponding air cooler; S5: Output includes unit model, the first N smaller ones k ri The table shows the values ​​and corresponding air cooler evaluation results. Based on the results, fault warnings are issued and graded maintenance recommendations are proposed.

[0025] The relative heat transfer coefficient in S1 k ri The construction and definition of the formula include, Analysis of heat transfer coefficient k The formula for calculating W / (m²·K) is as follows: (1) in Q Cooling capacity (kW); A To obtain the effective heat exchange area (m²), the fin contact thermal resistance must be deducted (the resistance of bimetallic finned tubes is taken as 0.0002 m²·K / W). Relative heat transfer coefficient k ri The calculation formula is: (2) in Q i / ΔT mi This is the ratio of the cooling capacity of the air cooler to the logarithmic mean temperature difference. For all air coolers of the same model and with the same components Q / Δ T m The maximum value; Logarithmic mean temperature difference (3) in T h,in The inlet temperature of the hot fluid is (°C). T h,out The outlet temperature of the hot fluid is (°C). T c,in The inlet temperature of the cold fluid is (°C). T c,out The outlet temperature of the cold fluid is (°C).

[0026] The operational data collected in S2 includes the inlet temperature of the hot fluid. T h,in 、 hot fluid outlet temperature T h,out 、 Cold fluid inlet temperature T c,in 、 Cold fluid outlet temperature T c,out 、 Cooling medium mass flow rate m。

[0027] The data preprocessing in S2 includes steady-state screening, dead value removal, outlier filtering, and cold fluid temperature correction. The outlier filtering method involves calculating the maximum value with a statistical probability of 99.9% for the mass flow rate of the cooling medium and the data at each temperature measurement point, and then removing the top 0.1% of the maximum values ​​to filter out abrupt changes in data. The cold fluid temperature correction is used to correct the temperature in scenarios where the cold fluid inlet and outlet of the air cooler are switched, ensuring the accuracy of the temperature data.

[0028] To address invalid and outlier values ​​in the collected raw data, filtering is essential to remove "dead values" that have remained unchanged for extended periods. Next, steady-state screening is necessary to ensure the thermal calculations of the air cooler are performed under steady-state conditions. Finally, to filter out abrupt changes caused by sensor interference, electromagnetic pulses, or brief system disturbances, statistical methods are employed. For the data after steady-state screening, the statistical distribution of each parameter is calculated, and the top 0.1% of data points with the largest values ​​are removed to ensure greater accuracy. If the air cooler experiences a switching process between the inlet and outlet of the cold fluid during operation, the cold fluid temperature needs to be corrected using the following formula: The correction formula for the inlet and outlet temperatures of the cold fluid is as follows: (4) SF is the import / export switch indicator, and 1 indicates a switch status. This indicates the historical reference value for the inlet temperature of the cold fluid.

[0029] (5) (6) in These represent the corrected inlet and outlet cold fluid temperatures, respectively. This is the temperature relationship verification value. 1 indicates a normal relationship. If the verification value is not 1, the data will be re-acquired and corrected.

[0030] Then calculate the logarithmic mean temperature difference, the core parameter. ΔT m and cooling capacity Q。

[0031] (7)

[0032] In the formula m The mass flow rate of the cooling medium (km / s) is measured using an ultrasonic flow meter according to DL / T 244-2012, with an accuracy of ±0.5%. The specific heat capacity at constant pressure (kJ / (km·K)) is taken as 4.18 for water-cooled systems and calculated based on refrigerant properties for phase change systems. ΔT The temperature difference (K) between the inlet and outlet of the medium.

[0033] In S3, the relative heat transfer coefficient is calculated. k ri ;calculate Q i / ΔT mi When taking all steady-state operating conditions within a statistical period The average value, with a statistical period of one month. k ri A dimensionless number between 0 and 1 k ri =1 indicates that the corresponding air cooler is the best performing air cooler among those of the same model and components. k ri The smaller the value, the more severe the performance degradation of the air cooler.

[0034] like Figure 2 As shown, in S3, N takes the value of 5, and the five smallest values ​​after ascending sorting are extracted. k ri The values ​​and corresponding air coolers are the key performance monitoring targets. To verify the change in the relative heat exchange efficiency of the air cooler with respect to its state trend, a blockage in the air cooler pipes is used as an example. When the cooling water pipes of the air cooler are blocked, the flow rate of the air cooler branch pipes continuously decreases, reaching approximately 62.5% of the normal operating flow rate. The air cooler's cold air temperature is approximately 135.71% of the normal operating temperature, and the heat exchange efficiency of the air cooler decreases significantly. The values ​​are then taken from the top... N Smaller k ri The values ​​are recorded, and the specific air coolers corresponding to these values ​​are recorded. It is known that among the air coolers involved in the calculation, air cooler No. 02 experienced pipe blockage and had poor cooling effect, while the cooling effect of the other air coolers was within an acceptable range. The final results are shown in Table 1.

[0035] Table 1. Top five minimum relative heat transfer coefficients of air coolers

[0036] As shown in Table 1, the No. 02 air cooler has the lowest relative heat transfer coefficient, which is consistent with the expected result.

[0037] In S4, the preset threshold is k ri When the value is ≥0.9, routine inspection of the air cooler is sufficient; 0.75≤ k ri When the value is <0.85, the air cooler should be flushed or its performance fully inspected during the planned shutdown of the hydropower unit. k ri When the value is less than 0.75, the hydropower unit should be temporarily shut down immediately, and the air cooler should be inspected and thoroughly cleaned.

[0038] In S2, the operating data is collected by sensors from the existing monitoring system of the hydropower plant. Calibrated platinum resistance temperature sensors or temperature sensors of the same accuracy level are installed at the four key interface positions of the air cooler. The temperature sensors are calibrated platinum resistance temperature sensors and can ensure sufficient insertion depth to measure the core temperature of the fluid. The flow sensor is an ultrasonic flow meter.

[0039] In S2, the inlet temperature of the hot fluid T h,in (°C) The sensor is located at the hot air inlet duct of the air cooler, at least twice the duct diameter from the air cooler body, to avoid eddy current interference; hot fluid outlet temperature T h,out (°C) The sensor is located at the cold air outlet duct of the air cooler; the inlet temperature of the cold fluid. T c,in (°C) The sensor is located at the cooling water inlet header, and the cold fluid outlet temperature; T c,out (°C) The sensor is located at the cooling water outlet header; ultrasonic flow meters are installed on the inlet and outlet main pipes of the cooling medium, with the distance between measuring points not less than 10 times the pipe diameter. Installation must strictly comply with relevant standards such as "DL / T 244-2012 Performance Test Procedure for Direct Air-Cooled Systems," ensuring the length of the straight pipe sections before and after the measurement to guarantee accuracy (±0.5%). The measured value is the mass flow rate of the cooling medium. m The unit is usually kg / s. For large units, the flow meter should have online, uninterrupted monitoring capabilities.

[0040] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients, characterized in that: The steps include the following: S1: Defines the relative heat transfer coefficient k ri The formula, combined with the logarithmic mean temperature difference ΔT m mass flow rate m and heat exchange Q Eliminate the influence of heat exchange area and achieve dimensionless standardized evaluation; S2: Collect operational data, perform steady-state screening, remove dead values ​​and outliers, and verify the inlet and outlet of cold fluid to ensure data validity; S3: Classify by unit model, calculate the relative heat transfer coefficient for air coolers of the same model and component. k ri Sort by value in ascending order, extract the first... N A smaller value; S4: According to k ri The comparison results between the numerical value and the preset threshold determine the performance degradation risk level of the corresponding air cooler; S5: Output includes unit model, the first N smaller ones k ri The table shows the values ​​and corresponding air cooler evaluation results. Based on the results, fault warnings are issued and graded maintenance recommendations are proposed.

2. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficient according to claim 1, characterized in that: The relative heat transfer coefficient in S1 k ri The construction and definition of the formula include, Analysis of heat transfer coefficient k The formula for calculating W / (m²·K) is as follows: （1） in Q Cooling capacity (kW); A To obtain the effective heat exchange area (m²), the fin contact thermal resistance must be deducted (the resistance of bimetallic finned tubes is taken as 0.0002 m²·K / W). Relative heat transfer coefficient k ri The calculation formula is: （2） in Q i / ΔT mi This is the ratio of the cooling capacity of the air cooler to the logarithmic mean temperature difference. For all air coolers of the same model and with the same components Q / Δ T m The maximum value; Logarithmic mean temperature difference (3) in T h,in The inlet temperature of the hot fluid is (°C). T h,out The outlet temperature of the hot fluid is (°C). T c,in The inlet temperature of the cold fluid is (°C). T c,out The outlet temperature of the cold fluid is (°C).

3. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: The operational data collected in S2 includes the inlet temperature of the hot fluid. T h,in 、 hot fluid outlet temperature T h,out 、 Cold fluid inlet temperature T c,in 、 Cold fluid outlet temperature T c,out 、 Cooling medium mass flow rate m .

4. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: The data preprocessing in S2 includes steady-state screening, dead value removal, outlier filtering, and cold fluid temperature correction. The outlier filtering method involves calculating the maximum value with a statistical probability of 99.9% for the mass flow rate of the cooling medium and the data at each temperature measurement point, and then removing the top 0.1% of the maximum values ​​to filter out abrupt changes in data. The cold fluid temperature correction is used to correct the temperature in scenarios where the cold fluid inlet and outlet of the air cooler are switched, ensuring the accuracy of the temperature data.

5. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: The correction formula for the inlet and outlet temperatures of the cold fluid is as follows: （4） SF is the import / export switch indicator, and 1 indicates a switch status. This represents the historical reference value of the cold fluid inlet temperature; （5） （6） in These represent the corrected inlet and outlet cold fluid temperatures, respectively. This is the temperature relationship verification value. 1 indicates a normal relationship. If the verification value is not 1, the data should be re-acquired and corrected. Then calculate the logarithmic mean temperature difference, the core parameter. ΔT m and cooling capacity Q ; （7） In the formula m The mass flow rate of the cooling medium (km / s) is measured using an ultrasonic flow meter according to DL / T 244-2012, with an accuracy of ±0.5%. Specific heat capacity at constant pressure (kJ / (km·K)); ΔT The temperature difference (K) between the inlet and outlet of the medium.

6. The method for assessing the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: In S3, calculation Q i / ΔT mi When taking all steady-state operating conditions within a statistical period The average value, k ri A dimensionless number between 0 and 1 k ri =1 indicates that the corresponding air cooler is the best performing air cooler among those of the same model and components. k ri The smaller the value, the more severe the performance degradation of the air cooler.

7. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: In S3, N is 5, and the five smallest values ​​after ascending sorting are extracted. k ri The values ​​and corresponding air coolers are the key performance monitoring targets.

8. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: In S4, the preset threshold is k ri When the value is ≥0.9, routine inspection of the air cooler is sufficient; 0.75≤ k ri When the value is <0.85, the air cooler should be flushed or its performance fully inspected during the planned shutdown of the hydropower unit. k ri When the value is less than 0.75, the hydropower unit should be temporarily shut down immediately, and the air cooler should be inspected and thoroughly cleaned.

9. The method for assessing the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: In S2, the operating data is collected by sensors in the existing monitoring system of the hydropower plant. The temperature sensor is a calibrated platinum resistance temperature sensor, and the flow sensor is an ultrasonic flow meter.

10. The method for evaluating the condition of air coolers in hydropower units based on relative heat transfer coefficients according to claim 1, characterized in that: In S2, the inlet temperature of the hot fluid T h,in (°C) The sensor is located at the hot air inlet duct of the air cooler, at least twice the duct diameter from the air cooler body, to avoid eddy current interference; hot fluid outlet temperature T h,out (°C) The sensor is located at the cold air outlet duct of the air cooler; the inlet temperature of the cold fluid. T c,in (°C) The sensor is located at the cooling water inlet header, and the cold fluid outlet temperature; T c,out (°C) The sensor is located at the cooling water outlet header; ultrasonic flow meters are installed on the inlet and outlet main pipes of the cooling medium, and the distance between the measuring points is not less than 10 times the pipe diameter.

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