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.

A comparative analysis between simulation and test with roughness is carried out for a supercritical carbon dioxide (S-CO₂) axial turbine with different operating conditions, focusing on the roughness impact of the turbine performance. The results show that the numerical calculation method of wall roughness is able to assess the performance of the turbine at different load conditions accurately. Compared with test result, the maximum efficiency error is 1.82 percentage point. Wall roughness degrades the overall performance of the turbine, with a maximum efficiency drop of 2.8 percentage point at Ra1.6 roughness level during the five working condition, and the turbine stage roughness has a more obvious effect on the turbine performance. In addition, the more severe of wall roughness, the greater reduction of turbine efficiency. In non-design operating conditions, the efficiency drops by 11.6 percentage point at Ra6.3 roughness level. The wall roughness exacerbates flow separation of pressure surface, causing greater friction losses and serious affecting of turbine performance. The research can provide technical support for the design and performance simulation of S-CO₂ axial turbines.

This paper proposes a multi-parameter collaborative monitoring system and method for degassed hydrogen conductivity based on the combination of double water membrane degassed method and electric regeneration ion exchange technology, which can quickly measure a number of key water quality indicators such as conductivity, hydrogen conductivity, degassed hydrogen conductivity and pH. It can make comprehensive evaluation of water quality, guide thermal equipment shutdown and startup. And it can adjust normal operating water conditions. It has a great significance for ensuring water vapor quality and thermal equipment corrosion, salt accumulation and scale formation. Double water membrane degassing technology is used to measure degassed hydrogen conductivity, which can effectively remove CO₂ from water. On this basis, a method of calibration degassed hydrogen conductivity measured by standard solution is proposed, so that the accuracy of the measured value can be effectively evaluated. This method has been applied to typical gas combined cycle units and heating units for on-site supervision. It proves that the method has high measurement accuracy, can quickly and comprehensively evaluate water vapor quality, and it can assist in solving various technical problems on site. Therefore, it has strong popularization and application value.

Numerical and experimental studies are conducted on convective heat transfer performance of carbon dioxide (S-CO₂) flowing in a heated vertical helically coiled tube under supercritical pressure. The influence of flow characteristics and structural characteristics such as heat flux q, mass flow rate G, pitch P, tube inner diameter d, and spiral radius R on heat transfer are discussed, and the sensitivity of each structural parameter is studied quantitatively. A closed-loop S-CO₂ test platform was built to conduct experimental research on the convective heat transfer performance of S-CO₂ in the helically coiled tube, and the accuracy of the numerical simulation is verified based on the experimental data. Finally, the heat transfer correlation of S-CO₂ is fitted. The research has laid foundation for the thermal design method of S-CO₂ spiral-wound heat exchanger, and has certain engineering application value for the application and promotion of the spiral-wound S-CO₂ heat exchangers in nuclear power and solar thermal power generations.

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.

The non-minimum phase plants with unstable zeros exists widely in the process of power production. Because of the non-minimum phase characteristics, the control system should ensure internal stability while completing output tracking, and improve response speed while overcoming the undershoot. The general PID control cannot meet the requirements of engineering applications. An engineering control and tuning method for non-minimum phase plants is proposed in this paper. Firstly, a robust PID controller is designed to ensure the stability of the closed-loop control system and overcome the under shoot of the system. Secondly, design a second-order filter that includes system position error, velocity error, and acceleration error to improve the response speed and dynamic performance of the control system. This method is simple, easy to tune, easy to configure in DCS, and has strong robustness to model uncertainty, which is worth promoting in engineering.

To study the thermal hydraulic characteristics of the printed circuit heat exchanger with rhombic fin channels, variations in thermal hydraulic characteristics on the hot and cold sides were analyzed by numerical simulation, with cold side inlet temperature of 313.15~353.15 K and hot side inlet temperature of 553.15~593.15 K. The working medium on the cold side and the hot side were S-CO₂ and gaseous CO₂ respectively. The comprehensive performance was compared between NACA0030 airfoil fin channels and rhombic fin channels. The results show that when the inlet temperature of S-CO₂ increases by 40 K, the total heat transfer decreases by 23.91%, and the pressure drop of hot and cold increases by 29.95% and 11.14% respectively. When the temperature of gaseous CO₂ increases by 40 K, the total heat transfer increases by 16.40%, and the pressure drop of hot and cold increases by 9.42% and 7.43% respectively.The inlet temperature of S-CO₂ has more obvious influences on the thermal hydraulic characteristics. The printed circuit heat exchanger with rhombic fin channels has less flow resistance and better comprehensive performance. The results have a certain reference significance for the design of printed circuit heat exchangers with discontinuous channels.

The high-performance supercritical CO₂ heat exchanger is the key core equipment to realize the efficient and compact S-CO₂ Brayton cycle system. S-CO₂ has a low heat transfer coefficient in the smooth channel, and seeking high heat transfer performance and low-resistance heat transfer structure is the key to the development of efficient and compact heat exchangers. Five-axis EDM was used to fabricate the straightly ribbed tube, and the heat transfer behaviors of S-CO₂ in the four-headed straight rib tube was experimentally studied, the effect of flow parameters on the heat transfer characteristics of the straight rib tube was systematically analyzed, and the difference in the heat transfer performance between the straight rib tube and the smooth tube was quantitatively evaluated. The influence of structural parameters on the enhanced heat transfer and resistance characteristics was studied by numerical simulation method, and the optimal straight rib tube structure was obtained. The results show that increasing the pressure and mass flow rate can reduce the wall temperature, improve the convective heat transfer coefficient, and the average heat transfer capacity of straight rib tube is about 1.96 times that of smooth tube. Compared with smooth tubes, straight ribbed tubes can effectively delay the occurrence of heat transfer deterioration, the ability to delay the occurrence of heat transfer deterioration by using straightly-ribbed tubes is increased by 0.3~1.8 times. When the fixed rib width W=0.5 mm and the rib height H=2.5 mm, the PEC is the best, and the value of PEC is1.58. However, the fixed rib height is H=0.5 mm, ε=0.33, and PEC of the straightly-ribbed tube is the best, with the value of PEC is 1.22.

During frequent long-term standby state of gas turbine generator unit, the surface of 08Al carbon steel of waste heat boiler economizer fin tube will have serious corrosion problems. In this paper, the macroscopic corrosion phenomenon and corrosion rate of 08Al carbon steel above the critical humidity were studied by the method of hanging piece and electrical resistance probe. The results show that the corrosion rate of 08Al carbon steel is the fastest in the first 5 days under the constant environment of 20 ℃ and relative humidity of 70%, and the corrosion depth reaches up to 0.85 μm, accounting for 47.7% of the total change in the whole process. However, the most obvious corrosion phenomenon, including the change of weight and the surface corrosion area, occurred from about the 19th to the 25th day. With the relative humidity gradually increasing from the critical humidity of 70% (ambient temperature 20 ℃), the corrosion evaluation indexes of 08Al carbon steel show a linear upward trend. Nitrogen filling maintenance strategy under long-term standby state was formulated, effectively alleviating the corrosion condition of economizer fin tube of waste heat boiler.

The carbon dioxide (CO₂) Brayton cycle system is compact, efficient and flexible, and has a good application prospect in the third generation photothermal system and the fourth generation nuclear power system. The deterioration of CO₂ heat transfer affects the safe operation of the unit. In order to study the deterioration of CO₂ heat transfer in the vertical riser, a CO₂ heat transfer characteristic system is established for experimental research, and the CO₂ heat transfer characteristics under subcritical and supercritical conditions are compared. The influence of thermal parameters on the deterioration of CO₂ heat transfer is obtained, and the prediction correlation of CO₂ critical heat flux is established. The predicted value is in good agreement with the experimental value (error ±30%). It is found that the peak value of wall temperature is higher when CO₂ heat transfer deteriorates at subcritical pressure. Far away from the critical pressure and increasing the mass flow rate are conducive to restraining the occurrence of heat transfer deterioration.