With the rapid development of new energy power equipment and high-power electronic devices, the heat flux density generated during the operation of equipment has been continuously increasing, and the heat dissipation bottleneck has become a critical constraint on performance enhancement and operational safety. Evaporative cooling technology, which utilizes the latent heat of phase change of evaporative coolant to achieve cooling, has become an effective solution to the heat dissipation problem in scenarios with high heat flux density. During the operation of evaporative cooling systems, the evaporative coolant may be in liquid phase, gas-liquid two-phase, or even pure gas phase. Both the phase states and working frequency have an impact on the insulation performance of the coolant. This paper investigated the breakdown characteristics of a polar evaporative coolant in multiphase states, within a frequency range of 50–150 Hz. Through experimental testing and comparative analysis, the variation laws of the insulation breakdown strength of evaporative coolant with phase state and frequency were obtained. The relevant research can provide theoretical and experimental support for the application of evaporative cooling technology, and is of great significance for the design of evaporative cooling systems.

The electric field can control the bubble behavior during boiling heat transfer, which is important to enhance the heat dissipation of the heated surface. However, most existing studies have focused on uniform electric field conditions. The mechanism of boiling heat transfer under the action of pulsed electric field is still unclear. In this study, we investigate the effect of pulsed electric fields on the boiling characteristics of vertical surfaces via the lattice Boltzmann method. We have analyzed the effects of electric field strength, pulse period, duty cycle, dielectric constant ratio, and wall superheat on nucleation, growth, merging, and departure during boiling heat transfer. Further, we reveal the mechanisms of the changes in liquid supply capacity and wall heat transfer performance induced by bubble behavior under pulsed electric field. The results are informative for the design of heat dissipation techniques with electric field-enhanced vertical heated surfaces.

Accurate temperature prediction for hollow conductors in evaporative cooling hydrogenerators is critical for design optimization but hampered by the high cost of experiments and simulations. To address this, this paper proposes a physics-guided surrogate modeling framework using experimental data from 12 conductor designs. An optimized Gaussian Process Regression (GPR) model is shown to outperform Random Forest and XGBoost, reducing RMSE by 16.2% and 9.7%, respectively. The framework identifies two physically distinct feature subsets for complementary use cases. A six-feature (6D) monitoring model that achieves 𝑅2=0.893 and RMSE =1.770 ∘𝐶 under random 5-fold cross-validation, and a four-feature (4D) design model that obtains pooled 𝑅2=0.616 and RMSE =3.200 ∘𝐶 under rigorous Leave-One-Group-Out (LOGO) validation, sufficient for ranking candidate designs. The analysis further identifies outlet measurements as information-leaking features that inflate within-design accuracy but degrade extrapolation to unseen geometries, highlighting the importance of causal feature selection for robust design-stage surrogate models.

An electric field can effectively control the shape and motion of bubbles, which is of great significance for enhancing boiling heat transfer performance. This study employs an integrated computational approach, combining the 3D lattice Boltzmann framework with a perfect dielectric model, to investigate bubble dynamics during vertical migration under pulsed electric field excitation. The focus is on analyzing the effects of different electrocapillary numbers, pulse periods, duty cycles, bubble sizes, and surface tension coefficients on bubble rise motion. The results show that, under the pulsed electric field, the bubble rising process is intermittently compressed by the electric force, causing the gas-liquid interface morphology to periodically switch between hemispherical and ellipsoidal shapes. For bubbles with high surface tension coefficients and small sizes, the effect of the electric field on the deformation of the gas-liquid interface is weaker, and the bubble rise process almost maintains a spherical shape. Increasing the electrocapillary number and duty cycle is conducive to the formation of ellipsoidal bubbles, which reduces the bubble rise speed. For different pulse periods, the bubble rise speed remains constant.

With the rapid advancement of modern power systems, the capacity and power density of power electronic converters continue to escalate. Thermal performance has emerged as the primary limitation to further capacity increases in converters. To enhance the thermal performance of converters, this study introduces a beveled-cut enhanced heat transfer heat sink utilizing phase-change cooling and investigates its heat transfer characteristics. First, an experimental platform for phase-change cooling of power devices was established to compare the cooling performance of various beveled-cut enhanced heat transfer heat sinks. Second, the internal heat transfer and flow characteristics of the working fluid within the beveled-cut heat sink were analyzed, with a focus on the impact of bevel angle on thermal performance under varying fin heights, fin widths, and fin counts. The findings reveal that for heat sinks with large fin heights and widths exhibiting superior flow characteristics, bevel cutting has a limited effect on optimizing the working fluid’s flow dynamics. Conversely, for heat sinks with weaker flow characteristics and high, wide fins, bevel cutting significantly improves the working fluid’s flow dynamics, thereby enhancing the thermal performance of the heat sink.

With the continuous grid connection of new energy sources, the capacity of converters increases accordingly, and the demand for cooling capacity becomes increasingly stronger. To enhance the heat dissipation capacity of the converter, this paper proposes a straight-ribbed enhanced heat exchange radiator based on phase change cooling and studies its enhanced heat exchange characteristics. Firstly, an IGBT phase change cooling experimental platform was established to compare the differences in cooling capacity among straight-ribbed enhanced heat exchange radiators. Secondly, the internal heat exchange characteristics and the internal working medium flow characteristics of the straight-ribbed enhanced heat exchange radiator were studied, and the influences of the rib height, rib width and rib number inside the straight-ribbed enhanced heat exchange radiator on the heat dissipation characteristics of the radiator were explored. The research results show that, under the condition of a certain heat exchange area, increasing the rib height, widening the rib width and reducing the number of ribs are beneficial to improving the flow characteristics of the working medium inside the radiator and enhancing the heat exchange capacity of the radiator.

Extensive research has investigated the enhancement of boiling heat transfer through electric fields, primarily focusing on the effects of direct current (DC) electric fields. This study seeks to deepen the understanding of the mechanisms involved in boiling heat transfer enhancement when using alternating current (AC) electric fields. By examining the deformation of bubbles in uniform electric fields and the electric potential distribution at the bubble edges, we assess the impact of electric field strength and frequency on boiling heat transfer. The variation in density and dielectric constants between the gaseous and liquid phases results in a polarization charge density at the bubble boundary, causing the bubbles to elongate in the direction of the electric field. Our findings reveal that the electric field not only induces significant bubble deformation but also facilitates bubble detachment, thereby enhancing heat transfer. Specifically, the electric field influences the diameter of detached bubbles, leading to a reduction in size and an increase in detachment frequency, which collectively contribute to improved boiling heat transfer.

Dropwise condensation of steam occurs on a horizontal copper tube treated with a fluorination modification technique. Experiments were conducted to measure the condensation heat transfer of steam on a horizontal copper tube. The condensation heat transfer performance was systematically investigated across a wide range of subcooling temperatures and vapor velocities, with corresponding droplet dynamics behaviors visually observed. The maximum condensation heat transfer coefficient of the modified surface reaches 6.6 W/(cm2 degrees C) at a subcooling temperature of 4.8 degrees C and a vapor velocity of 0.76 m/s, whereas the coefficient on the Nusselt curve under the same subcooling is only 1.8 W/(cm2 degrees C), which is attributed to the high efficiency of droplet condensation. Field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometer (EDS), surface roughness measurement (SRM) instrument, and X-ray diffraction (XRD) were employed to analyze the morphological structure and composition of the modified copper surface. Microscopic results demonstrate the novel fluorination modification technique, which creates Cu2O nanostructures on the copper surface in an atmosphere containing fluoride. The modified copper surface and tube exhibit excellent hydrophobic characteristics, with average contact angles of 120 degrees and 112 degrees, respectively. Hydrophobic surfaces facilitate dropwise condensation, leading to improved condensation heat transfer performance. The influence of vapor velocity, subcooling temperature, and Jakob number on the condensation heat transfer properties of the modified surface was analyzed. The degradation in condensation heat transfer characteristics is closely associated with increases in both subcooling temperature and the Ja number. The fluorination modification technique provides an effective approach to wettability control, enhancing condenser efficiency, and broadening industrial applications.

Due to the advantages of high efficiency, energy saving, and safety, the application of phase change liquid cooling technology in data centers has great prospects. But there are few leak detection methods for the specific coolant used in liquid cooling system. So in this paper, first build a surrogate model based on machine learning, and then the real-time leak position method was studied based real-time data from gas detection sensors and proxy models. After testing, the effectiveness of the method has been verified and it can be applied in phase change liquid cooling data center in future.

With the evolution of hydroelectric generators toward larger capacity and higher rotational speeds, the significa++nt increase in power density has rendered rotor cooling technology a critical bottleneck restricting performance enhancement. Addressing the need for feasibility verification and thermodynamic characteristic analysis of evaporative cooling applied to rotors, this study innovatively proposes an internal-cooling-based evaporative cooling architecture for rotor windings. By establishing a single-channel experimental platform for a rotor evaporative cooling system, the key parameters of the system circulation flow under varying centrifugal accelerations and thermal loads are obtained, revealing the flow mechanism of the cooling system. The experimental results demonstrate that the novel architecture has outstanding heat dissipation performance. Furthermore, the experimental findings reveal that the flow characteristics of the medium are governed by the coupled effect of centrifugal acceleration and thermal load; the flow rate decreases with increasing centrifugal acceleration and increases with rising thermal load. Centrifugal acceleration reduces frictional losses in the heating pipe, leading to a decrease in the inlet–outlet pressure difference. Through the integration of experimental data with classic formulas, this study refines the friction factor model, with the modified formula showing a discrepancy of −10% to +5% compared with the experimental results. Finally, the experiment was rerun to verify the universality of the modified friction factor.

Self-circulating evaporative cooling technology makes use of the latent heat of working medium phase change to meet high heat flux requirement during the operation of flexible HVDC converter valve. In this paper, a one-dimensional simulation model is established to solve the problem of multi-branch parallel heat source with strong non-uniform heat flux, and a multi-branch self-circulating evaporative cooling experimental system is designed. The accuracy of this model is verified to be better than 9.3

In this study, to ensure the applicability and reliability of phase-change coolants in high-frequency power electronic equipment, two kinds of environmentally friendly room-temperature phase-change coolants were taken as research objects, and a concept 80 broadband dielectric impedance spectrometer was used with a specially designed sealed test chamber to test the spectrum characteristics of the dielectric properties of the phase-change coolants. Then, the spectrum variation law was analyzed under different operating temperatures. The comparative analysis results showed that the two environmentally friendly coolants have different polarity and different temperature response law of relative permittivity. The dielectric properties of the nonpolar coolant EPRTEC#1 showed to be significantly better than those of the polar coolant EPRTEC#2 and transformer oil. Thus, coolant EPRTEC#1 can play the dual functions of insulation and cooling and can be suitable for all kinds of cooling structures and mainstream power electronic equipment. Regarding coolant EPRTEC#2, it can only be recommended for indirect cooling structures; however, its insulation performance showed to be better than that of deionized water.

This paper explores the dynamics of large-scale offshore wind farms comprised of full-power variable frequency wind turbines, interconnected with VSC-HVDC (voltage source converter-based high-voltage direct current) converter stations. These systems are susceptible to broad frequency oscillations due to the rapid response characteristics of power electronic devices, potentially compromising their operational safety and stability under various conditions. To mitigate the impact of these oscillations on offshore wind turbines and the connected systems, the study first outlines the structure and operational mode of the offshore wind power electronic system with VSC-HVDC transmission. It then analyzes the mechanisms underlying these broad frequency oscillations. Subsequently, the paper presents a model construction and stability analysis for wind farms and transmission systems. It specifically focuses on offshore wind power systems based on symmetric monopolar topology, involving multiple branches and multiple wind farm access points. The research includes an in-depth oscillation analysis, supported by real-world case studies, demonstrating that strategically optimized control and protection strategies can effectively reduce the oscillation risks associated with wind farms connected through VSC-HVDC systems, thereby ensuring their safe and stable operation.

As the core of the high-voltage DC transmission system, the DC bias characteristics of the VSC-HVDC converter valve lead to thermal imbalance inside the sub-module, and its impact on the reliability of the insulate-gate bipolar transistor(IGBT) inside the sub-module cannot be ignored, while the phase change cooling technology has gradually become a key technology for solving the thermal imbalance problem of high-power power electronic converters by virtue of its excellent heat dissipation performance. To this end, this paper takes a VSC-HVDC converter valve sub-module as the research object, establishes a three-dimensional simulation model of the converter valve sub-module with the traditional water cooling method and phase-change cooling method, and compares and analyzes the distribution characteristics of the temperature field and structural field of the two types of cooling systems under different working conditions. The results show that the phase-change cooling technology can effectively reduce the temperature difference inside the sub-module and also reduce the junction temperature and stress fluctuations, which demonstrates the feasibility and technical advantages of the phase-change cooling technology applied to the VSC-HVDC converter valve.

The pumped two-phase cooling system has been proven to be effective in dissipating battery heat. However, the system configuration and performance of the integrated thermal management system(ITMS) based on the pumped two-phase cooling system still lacks in-depth investigation. In this paper, a novel integration system configuration coupling the pumped two-phase cooling system and air-conditioning system for EVs is developed. A simulation platform is established for the proposed integrated system. Two cooling modes named as radiator cooling mode and chiller cooling mode are numerically investigated under different operating parameters. The results showed that the pack average temperature raised with moist air mass flow rate, compressor speed, ambient temperature and discharge rate. The temperature non-uniformity was aggravated when the R1233zd mass flow rate, the moist air mass flow rate and the compressor speed increased. This aggravation would be more significant with the increasing discharge rate. The energy consumption of radiator cooling mode was only around 3 % of that of chiller cooling mode when achieving the same pack average temperature at an ambient tem-perature of 15 & DEG;C. While, the chiller cooling mode was more adaptable to harsh conditions. The pack average temperature can be used as an index to determine the system cooling mode. The up limit of the discharge rate in RCM were 1.8C, 1.6C, 1.4C and 1.2C for the ambient temperature at 16 & DEG;C, 20 & DEG;C, 24 & DEG;C and 26 & DEG;C, respectively. The novel findings of this work are intended to provide a theoretical tool for the optimal design and control strategy of the ITMS based on the pumped two-phase cooling system.

In this paper, a linear active disturbance rejection controller (LADRC) is introduced to control the speed loop and current loop of a permanent magnet synchronous generator (PMSG). The speed loop uses a first-order LADRC (FLADRC) to avoid overshoot and to speed up the dynamic response of speed tracking. In the current loop, considering the influence of the converter, a second-order LADRC (SLADRC) is designed. In addition, the convergence of the proposed strategy is verified, and the tuning method of the control parameters is given. The proposed control strategy has strong anti-interference capability in a wide frequency band, and its effectiveness and practicability are verified by simulation and experimental results.

The self-circulating evaporative cooling system, utilizing latent heat, can meet the cooling requirements of high-power electronics. However, the conventional structure of ribbed columns is not effective for gas-phase fluid discharge and timely liquid-phase fluid feedback, thereby hindering the improvement of heat dissipation. Therefore, a hybrid rib array structure heat exchanger is proposed with advantages of efficient separation of bubbles. This structure consists of a significant number of parallelogram section columns, constructed by a further oblique milling step with 30 & DEG;, 45 & DEG; or 60 & DEG; bevel angles relative to the main flow direction, based on traditional ribbed columns. This study aims to investigate the effect of rib height, rib width, spacing, and angle on the heat transfer performance of hybrid rib array heat exchangers. The experimental data shows that the 30 & DEG; hybrid rib structure reduces temperatures by 9.3celcius compared to the traditional structure under 100 kW/m2. Moreover, the 30 & DEG; angle significantly enhances the heat transfer performance compared to the other angles tested. The heat transfer performance of traditional structures improves when using 1:3 width-to-height ratio in the rib section. In contrast, the heat transfer performance of hybrid rib arrays is influenced by the rib height in conjunction with rib width and spacing.

电动汽车用永磁电机普遍使用的高性能钕铁硼永磁材料在高温、强磁场等条件作用下易发生的不可逆失磁故障已成为该类电机高可靠性设计的主要瓶颈.针对电动汽车用永磁电机的失磁问题,该文利用永磁体虚拟分块方法,建立基于永磁体磁特性参数、工作温度、空间位置等变量的永磁体失磁分析模型;利用电磁场和温度场双向耦合的三维多物理场计算方法,研究了永磁电机失磁的空间分布特性及其影响因素.结果表明,永磁电机失磁空间分布存在明显的不均匀性.永磁体失磁分布规律受其工作温度、退磁电流幅值与角度等因素影响.最后,通过一台 115 kW的永磁驱动电机样机在永磁体工作温度、转子表磁磁场分布、电机性能方面的测试,验证了该文所提分析方法和结论的准确性.