Xu Han

Previous studies have shown that the heat transfer of air cooling towers is mainly affected by crosswind. To improve the cooling performance of air-cooled towers under crosswind and the efficiency of power plants, this paper studies the influence mechanism of buildings on the heat dissipation performance of natural draft dry cooling towers (NDDCTs). The numerical simulation of a 2 × 1000 MW NDDCT is carried out to analyze the distribution of the aerodynamic shadow area and its influence on the heat transfer performance of the NDDCT. The study found that at a wind speed of 12 m/s, the heat dissipation efficiency of the NDDCT under the influence of the original building decreased by 4.74%, and the total ventilation volume decreased by 2595.76 kg/s. When the NDDCT was located in the aerodynamic shadow wake area of the building, the heat dissipation efficiency increased by 8.36%. This shows that the aerodynamic shadow area of the building will lead to deflection deceleration and a steady flow effect of the flow field near the tower base, which has a double-sided effect on the heat transfer of the NDDCT. By adjusting the interference of the aerodynamic shadow wake area of the building on the NDDCT, the high wind speed sensitivity and the heat dissipation deviation of the two towers can be reduced.

Internal steam leakage in steam turbines from the high-pressure side to the low-pressure side through clearances causes loss, resulting in reduced efficiency and potentially compromising the safe operation of the turbine. Therefore, a comprehensive understanding of the flow characteristics of leakage through blade tip clearances is crucial to improve the efficiency of steam turbines. In this paper, the last stage blades of the low-pressure cylinder of a certain 600 MW ultra-supercritical steam turbine unit were studied. A wet steam flow model and a turbulence model were established, and the flow characteristics of the last stage under different inlet parameters, outlet parameters, and tip clearance sizes were analyzed. The results showed that an increase in the clearance size affects the inlet and outlet steam angles of the rotor blades, with significant changes occurring near the blade tip. The main flow velocity inside the rotor blade channel fluctuates violently starting from the 70% axial position. The high entropy region is located near the exit flow region of the rotor blade, with its range expanding as the clearance size increases. The entropy change is significant at 60% blade height and above, with more intense changes occurring in the blade tip area. The relative leakage amount and efficiency change uniformly with clearance variation. Generally, for every 0.1% increase in clearance height, the relative leakage amount increases by ∼0.31%–0.42%, and the stage efficiency decreases by 0.34%–0.44%. The results of this study can provide a theoretical basis and guidance for improving the flow efficiency of steam turbines.

The rapid development of new energy sources has brought a certain impact on the original power grid structure, accelerated the wear of unit equipment, and affected the stability, safety, and economy of thermal power unit operation, so it is proposed to add an energy storage system to solve the above problems. To analyze the secondary frequency regulation effect of thermal power units assisted by a flywheel energy storage system, a mathematical model of the control strategy on both sides of the boiler, steam turbine, and flywheel permanent magnet synchronous motor is proposed, and a two-regional power grid model is built through MATLAB/Simulink to simulate the frequency regulation effect of units with or without energy storage participation through step disturbance and continuous disturbance, which are 0.045 and 0.023 p.u. MW. Under step disturbance, the frequency fluctuation of the coupled energy storage system changed by 0.025 228 p.u. Hz, the time for the system to return to a steady state was shortened by 5.85 s, the maximum change of the frequency of the system in Region 2 was reduced by 0.025 579 p.u. Hz, and under continuous disturbance, the fluctuation of the output power of the steam turbine in Region 1 was reduced by 0.022 982 p.u. MW. In summary, under the same disturbance conditions in the outside world, the use of flywheel energy storage to assist the frequency regulation of thermal power units can effectively reduce the frequency fluctuation of the system, reduce the fluctuation of the output power of the steam turbine, reduce the loss of mechanical equipment, and extend the service life of the unit to a certain extent.

In heterogeneous polymers and emulsions, the volume fraction of the discrete phase and the frequency of electromagnetic waves affect the accuracy of the dielectric model. The integral method was used to modify the Maxwell–Wagner (M–W) heterogeneous dielectric theory, and a new model for the complex dielectric constant of polymers and emulsions was established. The experimental data were compared with the results of the M–W heterogeneous dielectric integral modification model and other theoretical models for different frequencies and volume fractions of the discrete phase. We discovered that with a decreasing volume fraction of the discrete phase, the dominant frequency range of the integral modification model expanded. When the volume fraction of the discrete phase is 10%, the dominant frequency range reaches 3 GHz. When the volume fraction of the discrete phase is 1%, the dominant frequency range reaches 4 GHz. When the volume fraction of the discrete phase is 0.06%, the dominant frequency range of the real part reaches 9.6 GHz, and the dominant frequency range of the imaginary part reaches 7.2 GHz. These results verify the advantages of the M–W modification model, which provides a theoretical basis to study the dielectric properties of polymers and emulsions, as well as for microwave measurement.