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A biopolymer-carbon nanotube (CNT) composite exhibits a high power factor of >2500 μW m−1 K−2 with a high electrical conductivity of about 7450 S cm−1 at a relatively low CNT concentration.

MXene-based catalysts have shown excellent activities in various electrocatalytic reactions due to the two-dimensional structure, good electrical conductivity and abundant surface functional groups. However, because of the competitive reactions in aqueous electrolytes, the application of MXene materials in CO2 electroreduction still remains a challenge. Herein, a simple strategy was developed for the design of high efficient and stable CO2 electroreduction catalysts in aqueous electrolyte. A series of MXene composite catalysts were successfully synthesized by densely coating sulfur vacancy-rich CdS nanoparticles on Ti3C2. The two-dimensional MXene skeleton with good conductivity delivers fast electron transfer, improves the electrolyte infiltration and increases the electrochemical surface area. CdS nanoparticles with abundant sulfur vacancies are attached on Ti3C2 MXene surface, providing active sites for CO2 reduction. Faraday efficiency of the by-product hydrogen could be significantly reduced by minimizing the surface-exposed Ti of the catalyst. Benefited from these merits, the optimal CdS/Ti3C2 possesses fast CO2 electroreduction reaction kinetics, exhibiting a high CO Faraday efficiency of 94% at -1.0 V vs. reversible hydrogen electrode. This work provides a feasible pathway for the design of MXene-based catalysts of CO2 electroreduction.

The supercritical carbon dioxide (SCO2) Brayton cycle has become an ideal power conversion system for sodium-cooled fast reactors (SFR) due to its high efficiency, compactness, and avoidance of sodium-water reaction. In this paper, the 1200 MWe large pool SFR (CFR1200) is used as the heat source of the system, and the sodium circuit temperature and the heat load are the operating boundaries of the cycle system. The performance of different SCO2 Brayton cycle systems and changes in key equipment performance are compared. The study indicates that the inter-stage cooling and recompression cycle has the best match with the heat source characteristics of the SFR, and the cycle efficiency is the highest (40.7%). Then, based on the developed system transient analysis program (FR-Sdaso), a pool-type SFR power plant system analysis model based on the inter-stage cooling and recompression cycle is established. In addition, the matching between the inter-stage cooling recompression cycle and the SFR during the load cycle of the power plant is studied. The analysis shows that when the nuclear island adopts the flow-advanced operation strategy and the carbon dioxide flowrate in the SCO2 power conversion system is adjusted with the goal of maintaining the sodium-carbon dioxide heat exchanger sodium side outlet temperature unchanged, the inter-stage cooling recompression cycle can match the operation of the SFR very well.

Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering. A comprehensive review on the state-of-the-art of LDR system was carried out. The thermal design considerations of crucial components such as working fluid, droplet generator and collector, intermediate heat exchanger, circulating pump and return pipe were reviewed. The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized. Furthermore, thermal designs of three LDR systems were completed. The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated. Based on the review, some prospective studies of LDR system were put forward in this paper.

Supersonic shear layer development affects mixing between the primary and secondary fluids in a supersonic ejector substantially. The splitter plate plays a key role in shear layer development in the near-trailing-edge region. In this paper, supersonic shear layers with various splitter plate thicknesses are calculated and analyzed. Two types of instability modes are found when various splitter plate thicknesses are used. The shock wave strength and absolute unstable region determine the instability modes. Shock waves can limit instability development but an absolute unstable region promotes instability development. Velocity thickness growth rates are found to be the result of the merging process between two or more adjacent vortices in the transition region. The number of vortices that merge depends on the ratio of the vortex shedding and nature frequencies. The velocity thickness growth rates are larger under the local instability mode than under the global instability mode since three vortices merge under the former mode but two vortices merge under the latter. This study may provide a helpful reference for the design of supersonic ejectors.

When injectors are used in petroleum industries or sea water desalination system, it is a special case that the induced gas is accompanied by water, the ejector is in two-phase operation. In the present study, the ejector performance at two phase flow is investigated experimentally and numerically. The results indicate that: the entrainment ratio would decrease when the water is injected into the induced flow, as well as the pressure ratio. The maximum decrement of entrainment ratio is around 40.5% at sub-critical mode when the motive pressure is 1.0 MPa, the induced pressure is 0.2 MPa, liquid-air ratio is 22%. For the pressure ratio, the maximum decrement is 62.5% when the motive pressure is 1.0 MPa, the induced pressure is 0.5 MPa, liquid-air ratio is 2.87%. However, the lower the induced pressure is, the more obvious the effect of mass flow rate on entrainment rate is, while the effect on pressure ratio is just opposite. Moreover, the performance becomes worse in sub-critical mode than that in critical mode. The effect of NXP on ejector performance also has been analyzed. There exists an optimum NXP whether the two phase flow ejector is in critical mode or sub-critical mode. The optimum NXP for entrainment ratio enlarges from 3.6 mm to 4.4 mm with the increase of water mass flowrate, and is bigger than that of single phase ejector (the optimum NXP is 2.8 mm). This study may provide a beneficial reference for the operation of supersonic ejectors on two phase flow.

The shortage of freshwater resources is becoming increasingly serious. A thermal power plant coupled with a low-temperature multi-effect distillation seawater desalination (single-stage thermal vapor compressor (TVC)) has been widely used. To reduce the water production cost effectively, a two-stage TVC is proposed in this study. The simulation work for the system performance under single- and two-stage TVC is analyzed. Results show that the performance of the system coupled with the two-stage TVC is superior under most conditions, and an optimal intermediate pressure (16 kPa) of the two-stage TVC is found for minimum coal consumption. When the power plant load is higher than 70% THA, the cogeneration system performs well, and the motive steam of the two-stage TVC comes from extraction point No. 5. Otherwise, the motive steam that comes from extraction point No. 4 is a suitable choice. The maximum coal consumption reduction value is 1.48 t/h. To deal with the low operation load of power plants in China, 60% THA load of power plant is a suitable choice for two-stage TVC of power-water cogeneration system.

Solar-aided coal-fired power plant (SACFPP) is a cost-effective approach to overcome solar energy intermittency. SACFPPs frequently operate in dynamic processes due to power load and solar energy fluctuations. This study investigated the dynamic characteristics of SACFPPs; such characteristics are important for flexibility evaluation and control system design. The SACFPP used in this study was based on a 660 MW coal-fired power plant, and a trough collector system (TCS) operates in parallel with high pressure (HP) heaters. After model development and validation, the dynamic performance of the SACFPP was analyzed under four load ratios of power plant, with disturbances of two parameters: direct normal irradiance (DNI) and mass flowrate ratio to TCS. The performance was also compared with three parallel TCS connection modes. Results showed that the magnitude and response time for power variation under DNI disturbance increased with load ratio. With 500 W/m2 DNI step increments, power increased by approximately 18.4, 21.2, 24.7, and 29.8 MW in 2200, 2330, 2550 and 2620 s at 70%, 80%, 90%, and 100% load ratios, respectively, when all the HP heaters were replaced. The serial number and the number of HP heaters replaced also increased the power variation and response time. Under mass flowrate ratio to TCS increase disturbance, the power rapidly changed to its maximum and then slowly decreased, but the variation value depended on the load ratio.

Steam submerged jet condensation is a direct contact condensation widely used in many industries. However, this process may cause damage to related equipment due to pressure oscillation, especially at low steam mass flux. This study synchronously investigated the steam–water interface fluctuation of unstable condensation jet and its corresponding pressure oscillation through a horizontal pipe at low steam mass flux to research the condensation oscillation mechanism. Three typical flow patterns, namely, Chugging, hemispherical bubble oscillation (HBO), and encapsulating bubble oscillation (EBO), were distinguished based on the dynamic behavior of steam–water interface and oscillation pressure characteristics. Only the dynamic pressure in EBO region was periodic among the three flow patterns. In the EBO region, the pressure oscillation frequency increased with the increase of steam mass flux and decreased with the increase of water temperature. A flow pattern regime map for horizontal jet condensation related to steam mass flux and water temperature was presented based on experiments. Moreover, the influence of pipe diameters on low steam mass flux was analyzed. For the flow pattern regime map at low steam mass flux, the critical steam mass fluxes showed an inverse relationship with pipe diameter. An empirical criterion was introduced to determine the flow regime map at low steam mass flux.

The operational flexibility of coal-fired power plants has become a priority objective; however, the lifetime of main devices is reduced due to thermomechanical fatigue during transient processes. This study focuses on the safety of high-pressure heaters at operational flexibility measures. The dynamic characteristics of thermal parameters in the 1# HP heater were obtained and analyzed based on transient models of a coal-fired power plant. The change trends of pressure/temperature on the steam/feedwater side of the 1# HP heater at three throttling the extraction steam measures were different with that at the feedwater bypass measure. Subsequently, finite element analysis method was used, and the thermomechanical stresses under the four measures were calculated and analyzed. The time to reach the maximum mechanical stresses was shorter than that of thermal stresses. Finally, the fatigue lifetimes of the heater were estimated. The maximum fatigue damage ratio at the per load cycle was 0.0069%, and the minimal allowable number of cycle was 14413 in the upper region of the tube sheet when the extraction steams of #1, #2, and 3# HP heaters are regulated simultaneously. The study could offer data guidance to the safety and maintenance of coal-fired power plants during operational flexibility regulations.

Based on the GSE software, the simulation model of an ultra-supercritical double-reheat tower boiler was established, and its reliability was checked with design data. Then, the dynamic characteristics of the ultra-supercritical double-reheat boiler were studied. Simulation results reveal the response times of different input parameters greatly vary. When stepping disturbances to the feed-coal rate, feed-water rate, and feed-water temperature, the response time under feed-water’s temperature disturbance is the longest, which is about 1, 800 s. When the same input parameter disturbs, the output parameters have the same response tendency with different amplitudes. Moreover, the fiercer the disturbance is, the more greatly the parameter changes.

The relatively low entrainment ratio is the key problem that confines the ejector development in the industry. In this study, the adjustable-geometry ejectors (with three different spindle positions) and ejectors with bypass (with two different bypass inlet installations) were adopted to promote the entrainment ratio of an ejector. The performance of the adjustable-geometry combined with bypass was also investigated. Results showed that the adjustable-geometry ejector and ejector with bypass could improve the entrainment ratio, and both ejectors reached a peak value. Compared with the original ejector, the maximum increment was 51.47% for the adjustable-geometry ejector and 26.0% for the ejector with bypass, respectively. Meanwhile, the combined ejector increased the entrainment ratio, although the combination was only effective at higher induced pressures than that of the adjustable-geometry ejector without bypass. The maximum increment was up to 74.5% compared to that of the original ejector.

Although rapid load variation of coal-fired power plants has become a prior objective for improving the operational flexibility, it will cause a lifetime reduction of heaters due to alternating stresses during transient processes. In the paper, among four flexible regulating measures, the dynamic characteristics of thermal parameters were obtained by GSE software, and thermo-mechanical stresses of 1# high-pressure (HP) heater were calculated by Finite Element Analysis, then the fatigue lifetimes of 1# HP heater were estimated and compared. It turns out that the most stressed position is at water chamber baffle, the allowable numbers of cycles at four measures are 5913-9419, and fatigue damage ratios for per cycle are 0.0106-0.0169%. The study can provide a detailed reference for operators to ensure the operational security of coal-fired power plants within flexibility frameworks.

A solar-aided coal-fired power plant (SACFPP) facilitates the investment reduction and efficiency enhancement of concentrated solar power, having multiple input energy streams. The intermittent nature of solar energy requires new control strategies for SACFPP to generate controllable power. A revised control strategy considering solar/coal-to-power conversion characteristics is proposed, where the influences of solar irradiance changes are decomposed into the changes in live-steam working capacity and boiler heat absorption. Within the proposed control strategy, models to explicitly calculate the set points of coal consumption and feedwater mass flowrate are developed. The operational enhancement is evaluated with a 660 MW SACFPP where the trough collector system works in parallel with the second and third high-pressure heaters. The control effects on stability and energy conversion are analyzed under solar irradiance disturbances and actual conditions. Results show that the revised control strategy promotes the quick and smooth power stabilization. The settle time decreases from 1663 s to 701 s when solar irradiance step decreases from 700 W m−2 to 500 W m−2. Under actual conditions, the power ratio deviation reduces by 63.16% with the proposed strategy compared with the original strategy. The solar-to-electricity efficiency fluctuations are slightly reduced.

The operational flexibility of traditional coal-fired power generators has played crucial parts in many countries given the continuous integration of intermittent and fluctuant renewable power resources in their power system. This study is aimed at improving the short-term operational flexibility of thermal power units. The transient simulation models of a 660 MW supercritical coal-fired power system are developed by using the GSE software, and the six measures of regulating thermal system configuration, which can rapidly activate thermal storages in thermal systems, are introduced and compared. The greatest potential mode in each measure of regulating thermal system configuration is obtained on the basis of the utilization degree of the internal thermal storages. The dynamic characteristics of the thermal parameters of the selected measures are compared, and the results reveal that the measures of regulating extraction steam from low-pressure heaters has less negative effects on the live and reheat steam parameters but greater negative effects on the deaerator and condenser parameters than the measures of regulating extraction steam from high-pressure heaters. Moreover, the performance indexes of operational flexibility are also evaluated for all the measures of regulating thermal system configuration. Among five measures applied in the power-up process, the values of power ramp rate are from 1.26% to 6.31% of rated power per minute, the values of power capacity are from 12.87 to 48.35 MW, and the values of energy capacity during the regulating time of 120 s are 1009.73 to 5048.93 MJ. However, the measure of condensate water increasing of low-pressure heaters is an only way suitable for the power-down regulation process, and the value of power ramp rate is 0.61% of rated power per minute, the power capacity is −5.65 MW, and the energy capacity is −483.84 MJ. The best regulating measures are obtained on the basis of the different perspectives of operational flexibility. The findings of this study can help determine the best operational control strategies in different situations.

Free surface vortex, especially in a pattern of full air core vortex, causes serious security problems in the residual heat removal system. Vortex in a T-junction pipe system was numerically investigated under the premise that the simulation results are in agreement with the experimental results. First, four typical states were obtained in the formation and evolution process of vortex, namely, surface dimple, critical submergence state, air entrainment vortex state, and large air entrainment state. With increasing Froude (Fr) number, the time from an initiate flow field to the critical submergence state decreased, and the time interval between critical submergence state and large air entrainment state increased. Finally, the variation law of vortex intensity was analyzed during the evolution process. The vortex intensity initially increased with time and reached its maximum value and then decreased until it reached a minimum value before the large air entrainment state. With the increase of Fr, the maximum values of vortex intensity gradually increased.