Tip seal leakage in shrouded steam turbines can significantly affect the aerodynamic performance of downstream blade rows. An unsteady three-dimensional numerical model of a 1.5-stage high-pressure steam turbine is established using ANSYS CFX (ANSYS2021) with the SST k–ω turbulence model. Tip seal clearances of 1.0, 1.5, and 1.9 mm are investigated using the Q-criterion and vorticity transport equation to characterize leakage-vortex evolution and its interaction with the mainstream. The results show that increasing tip seal clearance strengthens leakage flow and expands its interaction region. The expansion term exhibits a relatively stronger influence on vorticity variation near the seal teeth, whereas the vortex stretching term plays a significant role in leakage-vortex evolution near the seal inlet, outlet, and cavity. Leakage vortices interact with the rotor wake, intensifying velocity gradients and aerodynamic loss, with pronounced flow distortion near 85% rotor span. The disturbance is further transported to the downstream stator, causing marked variations in flow angle, circumferential velocity, and static pressure in the upper-span region. At 95% and 99% blade heights, pronounced differences in suction-surface static pressure occur within the forward 80% of the chord length. These findings clarify the aerodynamic consequences of tip seal leakage and its downstream effects.

Daily periodic variations in solar radiation intensity lead to an unsteady inlet temperature for latent heat thermal energy storage units (LHTESU). This paper uses comparative analysis to systematically study the effects of inlet temperature on the thermal storage performance of a horizontally up-under cascaded LHTESU. The results show that the horizontally up-under cascaded LHTESU (Case-b, Case-B) significantly enhances the amount of heat storage quality, heat storage rate density, exergy storage and exergy storage rate under steady-state and unsteady-state inlet temperature conditions, compared to single-stage LHTESU (Case-a, Case-A). Additionally, heat storage quality, heat storage rate density and exergy storage of four cases increased uniformly in the early stage of the steady-state and the unsteady-state conditions. However, the growth rate of heat storage quality of two cases slowed down in the later stage of the unsteady-state conditions due to the decrease of the temperature. The final heat storage quality of Case-B was 39.57 %, 10.12 % and 16.89 % higher than that of Case-a, Case-A and Case-b, respectively. Meanwhile, the final exergy storage of Case-B was 24.89 % and 20.39 % higher than that of Case-a and Case-b, respectively. The results show that the combination of horizontal upper and lower cascade design and unsteady inlet temperature conditions can effectively utilize the synergistic effect of multiphase change materials, enhance heat transfer through structural design, and provide a feasible optimization direction for improving the heat storage performance of LHTESU in actual solar energy utilization scenarios.

This study explores a novel cascaded phase change material (PCM) heat storage structure, utilizing symmetric division boards and an annular fin to create a non-uniform upper-and-lower (UAL) cascade PCM configuration combined with an equal-ratio front-and-rear (FAR) cascade PCM layout (Case 4). This design is based on a horizontal shell-and-tube latent thermal energy storage (LTES) unit (Case 1) and aims to achieve an all-around thermodynamic performance enhancement. The results are compared with those from single 'annular fin + FAR cascade PCM' LTES units (Case 2), 'division boards + UAL cascade PCM' LTES units (Case 3), and Case 1. The findings demonstrate that Case 4 successfully integrates the technical advantages of Case 2 and Case 3, addressing their respective limitations and achieving a more comprehensive thermodynamic performance improvement. Compared with Cases 1, 2, and 3, Case 4 achieves the optimum melting and temperature field uniformity in the annulus, shortening the complete melting time and increasing the heat storage rate. Besides, Case 4 has advantages in exergy performance. This research fills gaps in the combined application of FAR and UAL cascade PCM technologies, offering a novel design approach for LTES units with significant practical application potential.

Latent heat thermal energy storage (LHTES) is critical for solar thermal utilization due to its high energy density, yet the impact of unsteady heat transfer fluid (HTF) inlet temperatures on cascaded LHTES units remains underexplored. This study numerically compares four unsteady inlet temperature profiles (TA, TB, TC, TD) with their steady counterparts (Ta, Tb, Tc, Td) by assessing phase change material (PCM) liquid fraction, temperature distribution, melting uniformity, and heat/exergy storage capacity. Results demonstrate enhanced melting uniformity under all unsteady conditions. Specifically, the peak value of liquid fraction increased by 12.06 % (TA), 22.01 % (TB), 15.16 % (TC) and 41.95 % (TD), respectively, heat storage capacity increased by 2.12 % (TA), 16.89 % (TB), and 12.14 % (TD) but decreased by 5.93 % (TC); concurrently, exergy storage rose by 0.883 % (TA), 20.388 % (TB), and 13.993 % (TD) yet declined by 7.862 % (TC). A novel cut-off time determination method is proposed to optimize thermodynamic performance of cascaded LHTES under both steady and unsteady operations, providing critical theoretical guidance for real-world system efficiency.

To investigate the impacts of different phase change materials（PCM） ratios in the cascade packed bed on the thermal performance, seven kinds of physical models of phase change capsule thermal accumulation beds with different packing ratios were established. Via monitoring the heat exchange fluid and PCM temperature using numerical simulation, other indicators acquired from calculation were the heat storage, the exergy efficiency, the heat storage rate, and the heat storage rate density which were compared with relative indicators to characterize the thermal performance of the packed bed. Results show that with the increase of the proportion of high melting point PCM, the exergy efficiency of the packed bed increases. However, all other indicators increase with the increase of the proportion of low melting point PCM. In addition, the cascade packed bed with a stepped increase（or decrease） in the percentage of PCM from low to high melting point has a significant improvement in thermal storage quality（thermal storage efficiency） compared to the evenly divided cascade packed bed, which proves that the reasonable optimized ratio of PCM in the cascade packed bed can effectively improve its thermal performance.

Direct heating of wind turbine is a form of heating production using wind energy. Because of its low requirements for wind quality, relatively simple device structure and high heating efficiency, the wind turbine-driven heating devices can take the place of traditional fossil energy for winter heating and achieve the purpose of reducing carbon emissions to a certain extent. Through the heater experimental platform constructed at Northeast Electric Power University, it is concluded that the liquid stirring heater can operate at 7 m/s, however; the efficiency is extremely low in the low-temperature environment. The permanent magnet eddy current heater must operate at the wind speed above 13 m/s, but it also can operate normally under the low-temperature condition. Combining the advantages and disadvantages of the two experimental devices and setting the vertical axis wind generator as the original motor, the heating efficiency of the two types of heating devices are analyzed under different working conditions, and then the adaptability of the wind turbine and the heating efficiency of the heating device are also studied.

建立相变蓄热胶囊的三维有序及无序堆积模型,在此基础上分析相变蓄热胶囊有序及无序对蓄热系统特性的影响.通过对蓄热系统的蓄热量、蓄热用时、蓄热效率及系统内温度分布等关键性能指标情况分析,提出一种判定蓄热终点的新方法.结果表明:当采用有序堆积时系统的各项性能指标最优,叉排堆积时蓄热效率最低,而无序堆积时蓄热总量最少.另外,换热流体流速增加可加快蓄热过程,但此时蓄热系统蓄热效率较低.

相变胶囊梯级布置是改善堆积床蓄热性能的有效手段.建立三维相变胶囊无序堆积梯级布置堆积床模型,并对其蓄热特性进行数值研究.分析了换热流体进口速度、温度和相变材料初始温度对其蓄热特性的影响.比较在蓄热过程中相变胶囊无序堆积级联布置堆积床的蓄热时间、液相率、蓄热速率、蓄热量和?效率等参数变化.结果表明,换热流体入口温度对相变胶囊无序堆积梯级布置堆积床的蓄热性能有明显的影响,而换热流体进口速度和相变材料初始 温度的影响相对较小,该研究为其的优化运行提供重要的指导作用.

为了研究混合纳米颗粒复合有机相变材料蓄热性能,以肉豆蔻酸为基体,利用2步法将纳米氮化硼碳纳米管按照不同配比与不同混合质量分数,制备了碳纳米管-氮化硼/肉豆蔻酸复合相变材料.采用热常数分析仪、差示扫描量热仪以及X射线衍射仪对其进行了蓄热性能测试,并重点分析了这2种纳米颗粒的配比、碳纳米管的管径、混合纳米颗粒的质量分数以及不同环境温度对复合相变材料的等效导热系数的影响.结果表明:复合相变材料的相变潜热、相变温度等热性能变化不大,而导热系数有明显增高.同时,在Maxwell模型基础上建立了适用于碳纳米管–氮化硼的复合相变蓄热材料等效导热系数计算模型,并将计算结果与实验结果对比,验证了其正确性.

蓄热胶囊级联设计是提高相变蓄热系统性能的一种有效的方法.为解决相变胶囊级联的优化组合问题,建立了相变胶囊级联布置堆积床蓄热装置,采用4种不同热物性的石蜡作为相变材料(phase change materials,PCMs),根据熔点不同分层布置.研究了蓄、放热过程中相变胶囊级数和相变材料熔点对蓄热系统性能的影响,通过计算蓄、放热时间,蓄、放热量,能效率,?,?效率和火积耗散等指标来分析和评估系统的性能.结果 表明:相变材料的熔点组合和级数对系统性能影响大,在从蓄、热过程中平均熔点更高的级联布置方式储存能和?更多,能效率更高,火积耗散小.但温升慢,蓄热时间长.

相变蓄热作为一种较为高效的储能方式,为太阳能、风能等可再生能源的高效利用提供了一种技术保障.应用EDEM软件建立了相变胶囊无序堆积床的三维模型,应用FLUENT软件中的凝固融化模型计算了该模型的蓄热特性.在蓄热材料质量相同的情况下,模拟分析了蓄热胶囊粒径和换热流体的流动状态对蓄热能效、蓄热时间、压降及温度分布的影响.研究结果表明,增大换热流体流速可以加快无序堆积床的蓄热进程,但系统的能量效率和内部温度场的均匀性会降低,压降增大;减小蓄热胶囊粒径造成压降增加、蓄热总量减小,但瞬时能量效率得到提高,蓄热用时减少,且无序堆积床的内温度场的均匀性得到改善.

The central shaft is an important and indispensable part of a small scale urban vertical axis wind turbines (VAWTs). Normally, it is often operated at the same angular velocity as the wind turbine. The shedding vortices released by the rotating shaft have a negative effect on the blades passing the wake of the wind shaft. The objective of this study is to explore the influence of the wake of rotating shaft on the performance of the VAWT under different operational and physical parameters. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 9%, the power loss of the wind turbine in one revolution increases from 0% to 25% relative to that of no-shaft wind turbine (this is a numerical experiment for which the shaft of the VAWT is removed in order to study the interactions between the shaft and blade). When the downstream blades pass through the wake of the shaft, the pressure gradient of the suction side and pressure side is changed, and an adverse effect is also exerted on the lift generation in the blades. In addition, α = 5% is a critical value for the rotating shaft wind turbine (the lift-drag ratio trend of the shaft changes differently). In order to figure out the impacts of four factors; namely, tip speed ratios (TSRs), α, turbulence intensity (TI), and the relative surface roughness value (ks/ds) on the performance of a VAWT system, the Taguchi method is employed in this study. The influence strength order of these factors is featured by TSRs > ks/ds > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (Cp) occurred under the condition of TSR = 4, α = 5%, ks/ds = 1 × 10−2, and TI = 8%.

Permanent magnet eddy current heating is a heating form using wind energy. Because of its low requirement on wind quality, relatively simple device structure and high heating efficiency, it is an effective application of distributed energy. Taking the permanent magnetic eddy current heating device as the research object, the input torque of the heating device, which was deduced according to the principle of electromagnetic field, was compared with the input torque of the vertical axis wind turbine. A mathematical model of the relationship between the geometric parameters of different components inside the device was established, and the components of the permanent magnet eddy current heating device were determined, which provides a theoretical basis for the design of a more reasonable permanent magnet eddy current heating device structure.

In this paper, the theory of aerodynamics and NACA series airfoil is used to analysis Darrieus type vertical axis wind turbine of wind heating system after setting up the relevant structure parameters. Through reasonable correction, the curve of wind energy utilization coefficient of wind turbine is obtained. According to the operating characteristics of wind turbine, the reliability of the wind energy heating system installed in certain area is analyzed. At the same time, the system configuration suggestions are put forward. Based on the curve of wind energy utilization coefficient, Description of variable speed operation of wind turbine will effectively improve the efficiency of wind energy utilization.

The research for the impacting factors of the real operation process for wind turbines mostly concentrates in the explanation of the influence mechanism at present.And the quantitative evaluation of impacting on the actual operating wind turbine units is far from enough.In this paper,the calculation method of grey correlation analysis is used.The average of power generation is the main sequence,while the average wind speed and the average temperature are the subsequences when calculating.Thus obtains the average wind speed and average temperature on the wind turbine power affecting of quantitative calculation results.The results show that the connection between wind speed in the process of wind turbine operation and power generation is greater than temperature.At the same time,the influence of temperature effect should not be ignored.

Improving plate heat exchanger's performance by increasing the overall heat transfer,as well as minimising pressure drop is one of the promising fields of research to focus on.In order to analyze the effects of distribution region construction on heat transfer,pressure drop performance and field synergy of plate heat exchanger,the two calculation models for plate heat exchanger is established.The flow and heat transfer characteristics of plate heat exchanger are simulated with computational fluid dynamic software.The velocity,temperature and pressure field of two models and their synergy relationship are compared and analyzed in the various conditions.At the same time,the enhanced heat transfer performances of plate heat exchanger are evaluated detailedly by performance evaluation criteria (PEC).The results show that the uniformity temperature field and better pressure drop effect is got for plate heat exchanger with new distribution region,and its general performances are better than traditional plate heat exchanger.Based on field synergy principle,the synergy between both pressure field and velocity field is improved by distribution region construction.The developed new distribution region of plate heat exchanger can be used for designing of plates with geometry.

Phase change energy storage technology is an efficient way of energy storage which guarantees the the efficient conversion and utilization of renewable energy, such as solar and wind energy. A two dimensional model of the encapsulated phase change materials(EPCM)with an air void is developed in this paper. The numerical simulation of the thermal energy storage process was conducted for the EPCM model using the enthalpy-porosity method and volume of fluid method(VOF) of the Fluent software. The effect of gravity,buoyancy-driven convection and the air void in the capsule, on the thermal energy storage process was considered. At the same time, the effect of various velocities and flow directions relative to gravity of the heat transfer fluid(HTF)and the blockage ratios on encapsulated phase change were studied. The results showed that the flow direction of HTF had little effect on the thermal energy storage process. However, the air void in capsule had negative effect on the thermal energy storage process. With the proper ratios of velocity to the blockage, the thermal energy storage process of the EPCM would be accelerated. The results provide a reference for the future research and application of the EPCM.

Micro-scale random pore spatial structure of heat exchange surface fouling was simulated by using the finite element method,and then material parameters and cell properties were assigned by APDL parametric language of ANSYS.Based on the energy conservation law and the Fourier heat transfer law of porous media,a method for calculating the equivalent thermal conductivity,of heat transfer surface was proposed.The coupled heat conduction of fouling was studied by the application of steady-state plate method,and it is proved that the effective thermal conductivity of fouling micro model is feasible by the method of steady-state plate.Furthermore,the influence of micro-scale pore on the effective thermal conductivity of fouling was analyzed under various conditions of porosity and pore size.The results showed that the effective thermal conductivity of fouling linear decreases with the increase of the porosity,and linear increases with the increase of the pore size.The analysis method brings convenience for design and cleaning of heat exchangers,at the same time,it opens up a new way for the further study of heat surface fouling in complex heat transfer process,make the calculation results are more accordant with practical circumstances.

利用分形理论及其相关的图像处理方法对板式换热器内不同粒径的颗粒污垢所沉积的表面形态进行研究.结果表明:颗粒污垢具有分形特性,而且颗粒粒径变化影响污垢表面分形维数,纳米级颗粒污垢的分形维数比微米级颗粒污垢的大.分形维数还可用来定量描述颗粒污垢的孔隙和粗糙表面形貌,分形维数越大污垢表面越粗糙.

对人字形板式换热器冷热双流道计算模型进行分配区结构改造,建立了新计算模型.利用计算流体力学软件对不同工况下两换热器模型内流体的流动和传热进行了数值模拟,对比了两模型内的速度场和温度场,并运行场协同原理分析了流道内的速度场和温度场及速度场和压力场的协同性.结果表明:新模型的速度场和压力场的协同性更好,在换热能力相同情况下,压降较低,经济性得到提高.