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Abstract In AP1000 plant, the Automatic Depressurization System (ADS) 1–3 stages operate to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the large heat sink tank In-containment Refueling Water Storage Tank (IRWST) in accidental conditions. The key equipment’s specific shape and arrangement lead to the complicate flow and heat transfer characteristics in IRWST. In the present work, an overall scaled IRWST&ADS sparger experiment has been built up. The thermocouples matrix, flowmeters, pressure transmitters, heat flux sensors, Particle Image Velocimetry (PIV) technique, and high speed camera are employed for the measurements of the key thermal and flow parameters. The local steam jets condensation phenomena as well as the overall flow and thermal behavior are investigated. The experimental results indicate that the thermal stratification phenomenon is obvious in IRWST. The criteria of Richardson Number and Stratification Number are utilized to predict and evaluate the thermal stratification extent, respectively. An improved ADS arrangement design is further proposed to reduce the thermal stratification. Moreover, the multi-holes lumped “steam condensation column” is modeled with characteristic parameters, then the steam condensation heat transfer coefficient range in chugging condensation process is estimated. The experimental results provide practical engineering application reference for the effective operation of the passive safety system in AP1000 plant.

Abstract In AP1000 plant, the Automatic Depressurization System (ADS) 1–3 stages operate to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the large heat sink tank In-containment Refueling Water Storage Tank (IRWST) in accidental conditions. The key equipment’s specific shape and arrangement lead to the complicate flow and heat transfer characteristics in IRWST. In the present work, an overall scaled IRWST&ADS sparger experiment has been built up. The thermocouples matrix, flowmeters, pressure transmitters, heat flux sensors, Particle Image Velocimetry (PIV) technique, and high speed camera are employed for the measurements of the key thermal and flow parameters. The local steam jets condensation phenomena as well as the overall flow and thermal behavior are investigated. The experimental results indicate that the thermal stratification phenomenon is obvious in IRWST. The criteria of Richardson Number and Stratification Number are utilized to predict and evaluate the thermal stratification extent, respectively. An improved ADS arrangement design is further proposed to reduce the thermal stratification. Moreover, the multi-holes lumped “steam condensation column” is modeled with characteristic parameters, then the steam condensation heat transfer coefficient range in chugging condensation process is estimated. The experimental results provide practical engineering application reference for the effective operation of the passive safety system in AP1000 plant.

Abstract The sealing flow will inevitably affect the cooling airflow quality in a second air system of an aero-engine. In this study, theoretical derivation and numerical simulation were conducted to establish a modified mixing model that considers both the torque and the source of the mixing flow. Then, the effect of the sealing flow can be evaluated using the modified mixing model. The results demonstrate that the effects of the sealing outflow on the flow and temperature characteristics of the pre-swirl system are weak when the air supply mass flow rate and pressure are fixed. However, the effects of the sealing inflow are significant. When the inner sealing inflow mass flow rate is increased from 0 to 20%, the temperature drop effectiveness is decreased by 31.3%. The temperature drop effectiveness is decreased by 29.2% as the inner sealing inflow temperature rises by 37 K. Then, the temperature drop effectiveness is increased by 15.6% as the inner sealing inflow swirl ratio is increased from 0 to 0.8. The results of the modified mixing model are in satisfactory agreement with the numerical results, which show a maximum temperature drop deviation of 7.22%. Compared with the previous method, the prediction accuracy of the pre-swirl cavity temperature drop can be increased by 22.28%.

Abstract The sealing flow will inevitably affect the cooling airflow quality in a second air system of an aero-engine. In this study, theoretical derivation and numerical simulation were conducted to establish a modified mixing model that considers both the torque and the source of the mixing flow. Then, the effect of the sealing flow can be evaluated using the modified mixing model. The results demonstrate that the effects of the sealing outflow on the flow and temperature characteristics of the pre-swirl system are weak when the air supply mass flow rate and pressure are fixed. However, the effects of the sealing inflow are significant. When the inner sealing inflow mass flow rate is increased from 0 to 20%, the temperature drop effectiveness is decreased by 31.3%. The temperature drop effectiveness is decreased by 29.2% as the inner sealing inflow temperature rises by 37 K. Then, the temperature drop effectiveness is increased by 15.6% as the inner sealing inflow swirl ratio is increased from 0 to 0.8. The results of the modified mixing model are in satisfactory agreement with the numerical results, which show a maximum temperature drop deviation of 7.22%. Compared with the previous method, the prediction accuracy of the pre-swirl cavity temperature drop can be increased by 22.28%.

Abstract The transient cooling of rock surface by liquid nitrogen (LN2) jet was experimentally studied in this article. Experimental conditions cover a range of 1.4–2.4 MPa for jet pressure and 3–5 cm for stand-off distance. The nozzle diameter was fixed at 1 mm and the rock specimen was a circular plate, with diameter of 16 cm and thickness of 2 cm. The temperature curves at different radial locations in rock were measured during LN2 jet impingement. Based on these data we mapped the complete heat flux across the rock surface and attained the three dimensional temperature field within the rock. Thermal stresses inside the rock were further computed according to the experimentally determined temperature field. It is shown that the partial wetting of rock surface by LN2 jet created sharp thermal gradients in both radial and vertical directions. The induced thermal stress was in tensile state and the spatial range of thermal stress is consistent with the wetted region by LN2. The propagation speed of wetting front increases with increasing jet pressure and decreasing stand-off distance. Under the present experimental conditions, the maximum heat flux of LN2 jet was around 2.4 × 105 W/m2. The maximum tensile stress on rock surface was calculated to be ~5 MPa, which could potentially damage the rock structure and deteriorate rock’s strength.

Abstract The transient cooling of rock surface by liquid nitrogen (LN2) jet was experimentally studied in this article. Experimental conditions cover a range of 1.4–2.4 MPa for jet pressure and 3–5 cm for stand-off distance. The nozzle diameter was fixed at 1 mm and the rock specimen was a circular plate, with diameter of 16 cm and thickness of 2 cm. The temperature curves at different radial locations in rock were measured during LN2 jet impingement. Based on these data we mapped the complete heat flux across the rock surface and attained the three dimensional temperature field within the rock. Thermal stresses inside the rock were further computed according to the experimentally determined temperature field. It is shown that the partial wetting of rock surface by LN2 jet created sharp thermal gradients in both radial and vertical directions. The induced thermal stress was in tensile state and the spatial range of thermal stress is consistent with the wetted region by LN2. The propagation speed of wetting front increases with increasing jet pressure and decreasing stand-off distance. Under the present experimental conditions, the maximum heat flux of LN2 jet was around 2.4 × 105 W/m2. The maximum tensile stress on rock surface was calculated to be ~5 MPa, which could potentially damage the rock structure and deteriorate rock’s strength.

Abstract Nowadays, lithium-ion battery (LIB) technology provides one of the most important approaches for large-scale electricity storage. In this work, an electrical-thermal-fluidic coupled model is proposed for practical LIB-based energy storage systems (ESSs). The coupled model is established based on the equivalent circuit model (ECM) which describes electrical behavior of LIBs, the airflow turbulent model, and the “single domain of multiple sub-regions” thermal model. Currents and voltages of LIB cells, airflow velocity field and pressure field, and temperature distribution in the whole ESS, can be simulated by the developed full-scale model. Simulation results of a practical commercial LIB ESS (1 MW/2 MWh) in typical frequency regulation operation, including electrical-thermal characteristics represented by currents and heat generation rates of LIBs in the ESS, flow characteristics represented by airflow field and mass flow rate distribution, ambient temperature sensitivity analysis represented by temperature distributions of the ESS initially under 27℃ and 38℃ ambient respectively, are displayed and discussed, exhibiting the capability of the proposed model. The proposed model has been validated by comparing the simulated results with the actual measured data; the reasonably good agreement demonstrates the effectiveness of the proposed model. Therefore, the established model has the potential to provide a feasible and powerful approach or tool to perform multi-physics simulations of practical large-scale LIB ESSs for different functions, including but not limited to detailed temperature evaluations, cooling structure optimization, materials selection, and thermal-safety status evaluating and monitoring.

Abstract Nowadays, lithium-ion battery (LIB) technology provides one of the most important approaches for large-scale electricity storage. In this work, an electrical-thermal-fluidic coupled model is proposed for practical LIB-based energy storage systems (ESSs). The coupled model is established based on the equivalent circuit model (ECM) which describes electrical behavior of LIBs, the airflow turbulent model, and the “single domain of multiple sub-regions” thermal model. Currents and voltages of LIB cells, airflow velocity field and pressure field, and temperature distribution in the whole ESS, can be simulated by the developed full-scale model. Simulation results of a practical commercial LIB ESS (1 MW/2 MWh) in typical frequency regulation operation, including electrical-thermal characteristics represented by currents and heat generation rates of LIBs in the ESS, flow characteristics represented by airflow field and mass flow rate distribution, ambient temperature sensitivity analysis represented by temperature distributions of the ESS initially under 27℃ and 38℃ ambient respectively, are displayed and discussed, exhibiting the capability of the proposed model. The proposed model has been validated by comparing the simulated results with the actual measured data; the reasonably good agreement demonstrates the effectiveness of the proposed model. Therefore, the established model has the potential to provide a feasible and powerful approach or tool to perform multi-physics simulations of practical large-scale LIB ESSs for different functions, including but not limited to detailed temperature evaluations, cooling structure optimization, materials selection, and thermal-safety status evaluating and monitoring.