The exhausted heat losses in the PRC and inefficiency in medium and low heat source applications are significant challenges affecting the application of supercritical carbon dioxide Brayton cycle for renewable energy sources. To achieve efficient utilization, a precooler-free power/cooling combined system with superior heat source adaptability is proposed and analyzed. Integrating with the precooling-heating coupled module and the absorption power/cooling module instead of the PRC, the waste heat from the LTR is completely recovered, moreover, multiple operating modes ensure that the system performance unaffected by ambient temperature and seasonal changes. Parametric studies indicate that the TUR2 inlet temperature, the WHE1 outflow overheat degree, and the hot end temperature difference have significant effects on the Split Ratio, energy outputs, and the coupling relations among modules. Moreover, due to the improvement of irreversibility and the decrease of exergy losses, the three-largest exergy destructions occur in the IHE, the TUR1, and the RET+GEN, which account for 56.1%, 6.9%, and 5.2% respectively. Furthermore, the optimized cases exhibit optimal η_thermal, η_exergy, c_P,total, and W_net of 84.2%, 74.1%, 9.48 dollars/GJ, and 397.4 MW respectively.

A Printed Circuit Heat Exchanger (PCHE), with straight channels and semi-circle cross section, was fabricated and experimental studies on heat transfer and fluid flow were conducted, during which the flow regime was transition flow, water was working fluid, and flow rate of water was various. The results obtained from correlations of macro circular tubes had obvious deviations from the experimental results. Specifically, the f factor obtained from experiments are larger, and the changes of the overall heat transfer coefficient were more complex with various Reynolds number. The heat transfer and flow correlations in transition zone of PCHE was calibrated within corresponding application ranges. In order to obtain the heat transfer correlations, a numerical method was introduced to obtain one-sided average convective heat transfer coefficients under transition flow. The results showed that the average deviations of the overall heat transfer coefficient obtained from average convective heat transfer coefficients was 8.5% comparing to experimental results, while the maximum deviation reached 17.2%. However, in spite of that, a correlation to predicted the overall heat transfer coefficients through average convective ones still can be obtained, and the deviations comparing with experimental results was within 10%. It is recommended that obtaining one-sided average convective heat transfer coefficient with numerical method is feasible especially when it was transition flow in PCHE.

The optimal scheduling and economy of new energy hydrogen production systems are closely related to hydrogen production efficiency. Aiming at the problem of low hydrogen production efficiency in existing new energy hydrogen production systems, this paper proposes a control strategy for new energy hydrogen production systems based on particle swarm optimization (PSO). Firstly, based on the polymer electrolyte membrane (PEM) electrolytic cell model, the relationship between the operating point of the electrolytic cell and the hydrogen production efficiency is analyzed. Secondly, a hydrogen production system operation control method based on particle swarm optimization algorithm is proposed to improve the hydrogen production efficiency of the hydrogen production system. Furthermore, an optimal scheduling model for new energy hydrogen production systems considering the efficiency of system hydrogen production was established, and particle swarm optimization algorithm was also used to solve the optimal hydrogen production power. Finally, through simulation analysis of actual power grid operation data, it is proved that the proposed control strategy can effectively improve the hydrogen production capacity and system revenue compared to traditional startup and shutdown strategies, providing a theoretical basis for the large-scale application of hydrogen production systems in power grids.

Combustion monitoring in large industrial furnace can be simplified to a radiation heat transfer problem within the enclosed cavity system, and precise quantification of its boundary radiation characteristic is the basis to carry out follow-up studyon the radiation inverse problem, but the coupled problem of wall radiation and media radiation need to be solved. A Monte Carlo priciple was involved to solve the radiation heat transfer equation in the enclosed cavity, and to decouple the shares of wall radiation and media radiation in the boundary detection information. The influence of temperature distribution and radiation properties on the share of wall radiation were discussed, at last the experiment verifies the feasibility of using the radiation information of boundary detection to retrieve the wall source term. This study will provide a reference to the exploration of physical field detection method of wall surface in industrial furnace.

Based on a DC microgrid system coupled with photovoltaic power generation, lithium battery-supercapacitor hybrid energy storage, electrolysistank and hydrogen-burning micro gas turbine, a power allocation strategy that integrates the lithium battery state of charge (SOC) and hydrogen storage tank hydrogen state (LOH) is proposed. A PV-electrolysistank-micro gas turbine DC microgrid system model is constructed. The allocation logic of the power judgment module of the coordination control layer is designed, and three operation modes are given when the residual power exists in the DC network. The power allocation strategy is simulated and verified using MATLAB/Simulink software. The simulation results show that the power allocation strategy of DC microgrid system based on hydrogen energy storage can make the lithium battery charge state gradually converge to a reasonable storage interval and can improve the service life of lithium battery.

Test for large-size wind turbine rotor under static and rotating conditions have been carried out for rotor dynamic characteristis. Based on experimental modal and operational deflection shape, firstly this test obtained modal data using LMS TEST.Lab system by calculating FRFs and curve fitting. Secondly the resonate speed was obtained according to the vibration sweep test. Then modal parameters were analyzed through operational deflection shape test under the resonate speed. The results show that the resonate frequency under rotating condition is different from the resonate frequency under the static condition. And the modal shape of rotor under rotating condition is travelling wave while it is standing wave under static condition. In conclusion, the integral stiffness is decreased when the rotor is rotating which results in the decrease of the resonate frequency, the modal shape turns to be the travelling wave resulting from the rotating magnetic force. This research results can offer a reference and guidance for rotor dynamics evaluation, simulation model modification and parameter input, and optimization design of rotor structure .

Aiming at the problem of low prediction accuracy of single power prediction model due to the impact of photovoltaic power fluctuation, a combined photovoltaic power prediction model based on similar day clustering is proposed. Firstly, k-means clustering is selected to divide the original power data into three similar day sample sets of sunny, rainy and cloudy according to different weather types, and the variational mode decomposition (VMD) is used to decompose the similar day samples; Secondly, the convolution neural network is used to optimize the support vector machine (CNN-SVM) and bidirectional short-term and short-term memory (BiLSTM) neural network, respectively, to predict and superimpose the decomposed power data and combine the prediction results with weights, and the grid search algorithm (GS) is used to find the optimal combination weight to improve the performance of the combination prediction model. Finally, the validity of the PV power prediction model proposed in this paper is verified by the one-year measured data of a photovoltaic power station in Australia. The experimental results show that the model proposed in this paper can predict the photovoltaic power well and has strong adaptability no matter what weather type.

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).

In recent years, thermal power units have frequently participated in peak shaving to build a new type of power system with new energy as the theme. Accidents of pipeline weld cracking and failure often occur. The welds on both sides of the intersection between the pipeline behind the intermediate pressure bypass valve and the condenser casing frequently crack. The opening area of the muffler pipeline also frequently crack. The heat transfer process from the pipeline behind the medium pressure bypass valve to the condenser muffler is studied by using the finite element method，The distribution of thermal stress under normal and peak shaving conditions was compared. To investigate the causes of the problem, a comprehensive calculation model for the medium pressure bypass pipeline is first established to obtain the distribution of primary and secondary stresses in the pipeline under normal working conditions, as well as the displacement and bearing values of each node. The finite element method is used to study the heat conduction process from the local medium pressure bypass valve to the condenser silencer pipeline. The thermal stress distribution under normal and peak shaving conditions is studied. The results indicate that under peak shaving conditions, the poor atomization effect of the nozzle results in severe water entrainment in the steam, The temperature difference between the pipeline behind the bypass valve and the pipeline of the condenser muffler is larger and repeated operation and shutdown of the desuper heating water cause thermal fatigue fracture of the weld seam and the opening area.

In order to reduce the cost of fuel procurement, a power plant plans to burn economical coal with low calorific value, such as carbon 3500 and Shenhun 4500.The quality characteristics of the coal to be blended deviate from the coal currently used, which affects the safety, economy and environmental protection of the boiler operation.Through coal quality analysis, laboratory test, theoretical analysis and calculation, on-site pulverizing system optimization test, economic coal blending test and operation parameter optimization test, the technology of economic coal blending combustion of boiler is studiedsystematically .The research results show that the low grindability and serious wear characteristics of the carbon 3500 lead to its poor adaptability to the pulverizing system and the boiler, and the comprehensive power supply cost of the unit increases after blending combustion.The fuel characteristics of Shenhun 4500 are close to the main coal types of the power plant, the operation performance of large proportion of mixed burning boilers is good, the comprehensive power supply cost of the unit is reduced, and the economic benefits are significant.It is suggested that the power plant can determine Shenhun 4500 as an economic coal for long-term combustion.This study can provide reference for power plants with similar demand for mixed combustion.