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Summary: In the field of measurement, high‐precision thermocouples need higher precision calibration equipment. However, the metal temperature equalizing block used in traditional thermocouple calibration equipment has poor temperature uniformity, and the structure of gas‐controlled heat pipe is complex and expensive, and the concentric annular heat pipes have high isothermal performance and simple structure, which can be used to improve the calibration equipment. In this study, a temperature comparison source based on potassium concentric annular heat pipe was fabricated to replace the metal temperature equalizing block, the temperature stability and temperature uniformity within 0 to 16 cm of the different metering wells at 400°C, 500°C, and 600°C were experimentally studied. The temperature stability was ±0.0026 K and the maximum axial temperature difference within 6 to 10 cm of the metering well was 0.027 K. On the vertical section of concentric annular heat pipe, due to the high specific heat of liquid working fluid, the temperature of the metering well near the bottom is higher. [ABSTRACT FROM AUTHOR]

Summary: Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement: Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed.Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance.Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on. [ABSTRACT FROM AUTHOR]

Summary: The transfer processes of reactants and products affect each other in proton exchange membrane fuel cells (PEMFCs), because they have contrast transfer directions between flow channels and gas diffusion layers (GDLs). In this study, a two‐dimensional, two‐phase, non‐isothermal and steady state model is developed to analyze the species transportation behaviors through diffusion and convection in PEMFCs with orientated‐type flow channels. Five conventional shape baffles effects on mass transfers are compared, and the relationships between convection and diffusion of reactants and produced water vapor are discussed. Simulation results reveal that baffle shapes affect the mass transportation through the baffles leading angles and volumes, and larger leading angles enhance the reactants and the water vapor convective transferring into GDLs; meanwhile, larger baffle volumes enhance the reactant transferring into GDLs and water vapor transferring out from GDLs through diffusion processes. In addition, transportation processes of reactants and vapor affect each other, where more reactants convectively transferring into GDLs causes more water vapor entering GDLs; enhancing the reactants diffusively transferring into GDLs reduces water vapor diffusive transportation out from GDLs. [ABSTRACT FROM AUTHOR]

Summary: With the occurrence of reversible electrochemical reactions, mode switching considerably affects the electric performance of unitized regenerative fuel cells (URFCs) owing to the complicated mass and heat transfer. Although limited researches have been done, no such studies on mass and heat transfer through a three‐dimensional view are envisioned during mode switching. A three‐dimensional full‐cell model was developed and validated to study the dynamic characteristics of a proton exchange membrane‐based URFC during mode switching. Mode switching was performed by changing operation voltage from 0.60 to 1.65 V. Results showed that species and heat transfer affect the electric performance of the cell during mode switching, especially through the third dimensional. Local water starvation occurs on oxygen side catalyst layer and thus results in slight reduction on current density and hydrogen generation. Restricted to heat transfer capacity through ribs, heat transfer process adds total response time in URFCs. Heat flux and surface heat transfer coefficient are forecasted on the hydrogen and oxygen sides. A total time of 4 seconds is essential for URFC reaching a new relative balanced state. [ABSTRACT FROM AUTHOR]

Summary: Mode switching is an important process in unitized regenerative fuel cells. The complex interactions of heat and mass transfer during the operation of mode switching have a significant effect on cell performance. Twelve different ways of mode switching were proposed by controlling inlet boundary conditions of supplies and operating voltage. Numerical simulations were applied to analyze the dynamic response of heat and mass transfer as well as electrochemical signals under the different ways of mode switching. Current density increased with mass fraction of reactants. Cell heat source had an instant response to current density, but the temperature was slow to respond to the heat source. Hydrogen‐side inlet velocity had minimal impact on mode switching. The time for cell reaching stability increased with the increase of voltage change time, and the time for current density, mass transfer, and temperature reaching stable values increased in order. Unitized regenerative fuel cell had similar dynamic response in the 2 period: cell temperature increased in the fuel cell mode and decreased in the water electrolysis mode after mode switching. [ABSTRACT FROM AUTHOR]