A concentrated downcomer stub of a boiler drum with 13MnNiMoR steel in a power plant, which was replaced due to cracks and non-metallic inclusions after 14 years in service, was dissected, and the behavior characteristics and influence of the non-metallic inclusion were analyzed through chemical composition analysis, mechanical property testing, microstructure and defect morphology observation. The results show that under service load, non-metallic inclusions become crack sources and microcracks by means of self cracking, interface separation from matrix or hole formation at the end, and microcracks converge to form macro cracks. When tensile and impact tests on the serviced materials, the area without inclusions was cracked and expanded in plastic mode. While innon-metallic inclusions area, the cracks nucleated with non-metallic inclusions and expanded in a brittle mode, resulting in a significant reduction in the strength and plastic toughness of the materials compared with that before service.

The growing complexity observed in the structures of cast aluminum fittings has posed significant challenges to conventional non-destructive testing techniques, rendering them inadequate in fulfilling the requirements for swift on-site inspection of irregularly shaped cast aluminum fittings. Consequently, an ultrasonic testing method based on flexible phased array probes was proposed. Firstly, a dynamic focusing algorithm for flexible phased array ultrasonic probes was introduced, and the basic simulation theory of CIVA multi-technique software platform was analyzed. Then, the dynamic focusing algorithm used to achieve deflection and focusing of ultrasonic beam was verified by simulation with CIVA, and the parameters of the flexible phased array ultrasonic probes were optimized through simulation. Finally, the effectiveness and feasibility of the testing method were verified through the inspection of typical cast aluminum fittings. The results show that phased array ultrasonic testing technology based on flexible array probes can meet the requirements of outgoing quality control and on-site rapid inspection of cast aluminum fittings with irregular shape.

The hybrid gas foil thrust bearings have excellent performance, but few studies have been reported on them. In this regard, a model of this bearings is proposed and a numerical research is carried out for the static and elasto-hydrodynamic characteristics. Based on MATLAB software, a steady fluid-structure interaction method was proposed for the numerical prediction of hybrid gas foil thrust bearings. The foil deformation, static load and frictional torque were calculated and analyzed at various rotating speeds, supply gas pressures and locations of air supply holes. The influences of operating parameters and locations of air supply holes on the static performance of hybrid gas foil thrust bearings were presented. The results show that: increasing the gas pressure has a small effect on the frictional torque, but increases the axial load of the bearing, and increasing the speed will lead to a significant increase in the frictional torque of the bearing. The location of the gas supply hole arrangement has a large effect on the static characteristics of the hybrid gas foil thrust bearings, so the location arrangement should be reasonably selected. The priority is given to the arrangement of the gas supply hole in the tilted area on the basis of meeting the bearing load requirements. The conclusions are of guidance for the design and application of hybrid gas foil thrust bearings.

During the low load operation of coal-fired units, the SCR denitration catalyst may be deactivated by ammonium bisulfate (ABS). The experimental tests are carried out on this phenomenon and the results show that: 1) with the flue gas temperature below the ABS condensation temperature, the catalyst will be deactivated due to the gradual deposition of ABS in the micropores. The ABS condensation temperature is inversely proportional to the micropore diameter, and the ABS concentration is positively related to the product of NH₃ and SO₃ concentrations in the flue gas; 2) the micropores with pore diameters of 2~20 nm are still the main structure of wide temperature denitration catalyst as well as the conventional catalysts, which cannot change its fate of ABS deactivation under low load; 3) the physical reversibility of catalyst ABS deactivation makes “combination of prevention and treatment” still the fundamental method to solve the ABS problem.

The Shockley-Queisser (SQ) limit sets an upper limit on the efficiency of conventional semiconductor photovoltaic devices. A thermophotovoltaic system (consisting of a heat source, a spectrally selective emitter and low bandgap photovoltaic cell) can work as an alternative to break this theoretical efficiency limit. To further improve the power generation efficiency of thermophotovoltaic (TPV) systems, an emitter with a multilayer cross structure based on metamaterials was designed in this work. Through optimization of its geometric size, the emitter demonstrates an excellent narrow-band emission spectrum. This effectively reduces the loss of low-energy photons below the bandgap of PV cells and avoids the absorption of high-energy photons that exacerbate lattice vibrations to cause thermal losses. Its application to TPV systems enables a perfect match with In_0.69Ga_0.31As cells with a bandgap of 0.6 eV. Detailed theoretical calculations of this TPV system show that the power generation efficiency can exceed the Shockley-Queisser (SQ) limit (41%) at 1 117 ℃, and will be further improved as the emitter temperature increases. When the temperature reaches 2 000 K, the efficiency is as high as 46.75%. Additionally, the narrowband emitter shows good angular insensitivity in the range of 0~60 degrees.

The floating platform undergoes six degrees-of-freedom of motion in the marine environment, making the flow field around the blade fluctuate drastically, and the changing flow field will have a huge impact on the dynamic response of the blade. A two-way fluid-structure interaction simulation of the NREL 5 MW wind turbine was carried out using the CFD-CSD coupling method. Based on this, the UDF technique introduced the floating platform motion to study the blade deformation and the overall torque and thrust changes under the surge, pitch, and yaw motion. The results show that the three typical platform motions of the surge, pitch, and yaw make the blade deformation amplitude increase, and the increase of flapwise and torsional deformation is more significant than that of edgewise deformation; the surge motion has the greatest influence on the blade deformation and aerodynamic performance, the maximum change range of torsional deformation can reach 70%, the peak values of the torque and thrust are increased by 30.51% and 11.75% respectively; the pitch and yaw motions reduce the average torque and thrust.

In the actual operation status of dry-type air-core reactor, the focus and difficulty of the fault diagnosis method is to reduce the false alarm rate and the missing alarm rate. About it, this paper proposes a weighted Naïve Bayes state evaluation method for a dry-type air-core reactor. First, a simulation model of a reactor inter-turn short circuit fault is established using multi-physical field coupling, and the effectiveness of the simulation method is validated by constructing a reactor operation test platform. Second, simulation and analysis of reactor current amplitude, current harmonics, impedance angle, and hot spot temperature under multiple operating conditions are performed to obtain the reactor’s normal and known fault sample sets. Finally, a weighted Naïve Bayes state evaluation model is developed using multi-state feature quantities. The example demonstrates that this method is effective for reactor operation state recognition and classification because it has high classification accuracy and requires fewer training samples.

Under the background of the goal of “carbon peak and carbon neutrality”, environmental protection requirements are becoming increasingly stringent, and methanol as a recognized high-efficiency, clean and low-carbon fuel has received more and more attention. In order to analyze the feasibility of methanol for boiler fuel, a comprehensive evaluation model of methanol, coal, diesel and natural gas as boiler fuel was established, and the four indicators of energy saving, environmental protection, economy and sociality were considered through analytic hierarchy process (AHP) and entropy weight method (EWM), and comprehensive evaluation was carried out under five scenarios with different importance of each index. The following conclusions are drawn: the energy saving of methanol is better than that of other fuels, the environmental protection and economy are comparable to natural gas, and the social aspect is second only to coal, which is 3.2 times that of diesel and 2.2 times that of natural gas; in terms of importance, environmental factors first, economic factors and energy-saving factors second, social factors are the weakest importance (scenario 3); the comprehensive evaluation score of methanol as boiler fuel is 0.318 6, which has great advantages compared with natural gas (0.292 9), coal (0.232 4) and diesel (0.156 1).

The synergy of fireside corrosion and stress is one of the challenges for austenitic steels used in modern fossil-fuel power plants during their service process. The creep rupture tests of Super 304H steel are carried out under static air and fireside corrosion environment at 650 ℃. The stress range is set at 200 to 300 MPa. The creep rupture life and microstructure evolution of different samples were studied. The results show that creep rupture life of Super 304H steel in corrosion condition decreases significantly, compared with that in static air. The rupture life decreases more seriously as the stress decreases, up to 83% at 200 MPa. The complete and continuous corrosion products scale is damaged by fireside corrosion, including the occurrence of cracks and spallation of these surface products. The formation of internal sulfide in the matrix caused by fireside corrosion leads to the deterioration of grain boundaries. Then it tends to crack along grain boundaries during creep rupture tests to accelerate the accumulation of creep damage. The surface of matrix undergoes recrystallization upon to the combination of high temperature and stress due to the loss of alloy elements caused by corrosion/oxidation. The formation of these fine recrystallized grains is unfavorable to creep properties of metals. The ferrite transformation also occurs in the same area during the cooling process after creep tests. Fireside corrosion increases the width of recrystallized grains area, thus expands its influence on the creep rupture life of the alloy. The fireside corrosion accelerates the creep rupture of Super 304H steel by promoting its corrosion process and the microstructure evolution.

Aiming at the problem that it is difficult to accurately and timely measure the inlet NOx concentration in the denitrification system of selective catalytic reduction (SCR) in thermal power plants, due to the excessive factors affecting the inlet NO_x concentration and the large delay and inertia of the system, the Max-Relevance and Min-Redundancy (mRMR) combined with Bayesian optimization (BO) algorithm is proposed, optimize the dynamic soft measurement model of NO_x concentration at the inlet of the SCR denitration system of the stacking ensemble model. Aiming at the problem of reduced prediction accuracy of static single model and asynchronous timing of auxiliary variables and inlet NOx concentration in the process of dynamic NO_x generation, the mRMR-BO combined with model was used to screen the auxiliary variables, Copula Entropy (CE) determined the delay of auxiliary variables, the BO combined with model determined the order of auxiliary variables, and TCN and LASSO were integrated by Stacking method. The auxiliary variables containing delay time and order information were used to construct a dynamic stacking ensemble soft measurement model, and the simulation results showed that the root mean square error, average absolute error, and average absolute percentage error of the integrated model compared with TCN and LASSO single networks were the smallest. Compared with the static ensemble model, the dynamic ensemble model has higher prediction accuracy and can achieve accurate soft measurement of the inlet NO_x concentration.