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Summary: Supercritical heat transfer loops are widely used in large‐scale thermal equipment, which development is restricted by the thermal‐hydraulic characteristics, especially the safety and thermal efficiency under high‐heat fluxes. This study is focused on numerical simulation for a 4‐m test section of the loop and further analyzes the flow transitions and heat transfer mechanisms from subcritical to supercritical. The heat transfer characteristics of supercritical water in the vertical loop were simulated for conditions: P = 24 MPa, Tin = 320°C, 340°C, mass flux (G) = 1000 kg/m2s, 1500 kg/m2s, and heat fluxes varied from 100 to 1200 kW/m2. The heat transfer transitions are analyzed from the perspective of local parameters that affect the status of both core flow and boundary layers. The empirical correlation and the error backpropagation (BP) neural network prediction model are proposed and compared with experimental and numerical results. The results show that transitions of both boundary layer and core flow from subcritical to supercritical contribute to the heat transfer behaviors: normal heat transfer, heat transfer deterioration, and heat transfer enhancement. The zero‐velocity gradient (∂u/∂r = 0) on the M‐shaped velocity curve causes the turbulent shear stress near the wall to be close to zero, which leads to the suppression of the turbulence. At the same time, the thickness of the thermal boundary layer reaches the maximum, resulting in a large thermal resistance, which affects the heat transfer from the wall to the core area. [ABSTRACT FROM AUTHOR]

Summary The kinetic mechanism of the co‐combustion of sewage sludge (SS) and bituminous coal (BC) is studied. The separate combustion process of the SS can be divided into four stages, as follows: moisture precipitation, volatile precipitation, non‐volatile substance precipitation, and fixed carbon burnout. During the co‐combustion of the mixture, SS and BC maintained their respective combustion properties. The SS can significantly improve the ignition and combustion performance of BC. Through Fourier transform infrared spectroscopy analysis, we found that the main combustible component in the SS is the volatile organic matter, and the main emission product is CO2. These results provide a theoretical basis for the new technology of combined power generation of SS energy recycling. Co‐combustion synergies can be achieved.Provide theoretical support for new CFB combined power generation technology.Gas emission products are alkane and CO2. [ABSTRACT FROM AUTHOR]

Summary: The arrangement of downward flowing evaporation heating surface in the furnace can effectively reduce the height of the furnace in the ultrasupercritical circulating fluidized bed boiler. According to the structural parameters of 660 MW ultrasupercritical circulating fluidized bed boiler, the scaled experimental system was established on the basis of the similarity criterion. The distribution of the gas–liquid two‐phase flow in the parallel branch pipes of the downward and the upward water‐cooled wing‐wall was studied under the rated loads of 25%, 50%, and 70% THA. The void fraction distribution, flow distribution of each phase, and dryness distribution in each branch pipe of the downcomers and the risers of the water‐cooled wing‐wall were measured via the quick‐closing valve method and the split‐phase measurement method. In the downward water‐cooled wing‐wall, both the nonuniform coefficient of void fraction and dryness in each branch pipe decreased with the increase in dryness in the inlet header. Under the same average dryness, the nonuniform coefficient of the void fraction increased with the increase in load. In the upward water‐cooled wing‐wall, under the same load, the uniformity of flow distribution was improved as the dryness increases. Under the same dryness condition, as the boiler load increases, the deviation coefficient of each phase distribution between the parallel pipes increased and the unevenness increased. In the study of flow and heat transfer characteristics of two‐phase flow, the void fraction α is a very important intermediate calculation parameter. The correlation formula of the cross‐sectional void fraction in the downward water‐cooled wing‐wall was fitted, and the calculation result was better compared with drift‐flux model, with an error of −6% to 6%. [ABSTRACT FROM AUTHOR]