Numerical investigation of the phase change in transpiration cooling with the VOF method

Transpiration cooling with phase change is numerically investigated in the present work. As shown in Figure 1, a liquid coolant flow is injected into a porous medium from the bottom side. The porous medium receives heat from the hot gas on the top surface and heats the coolant. Thus, phase change can occur in this porous medium. The surface temperature, the heat flux received by the porous medium, the phase distribution and the flow and cooling characteristics are the most important unknowns on this topic. Please download the full abstract below

Effective solid-to-fluid heat transfer coefficient in EGS reservoirs

The present work developed a three-equation local thermal non-equilibrium model to predict the effective solid-to-fluid heat transfer coefficient in the enhanced geothermal system reservoirs based on the volume averaging method. Due to the high rock-to-fracture size ratio, the solid thermal resistance effect in the internal rocks cannot be neglected in the effective solid-to-fluid heat transfer coefficient. The present three-equation local thermal non-equilibrium model can consider the dynamic variation of the solid thermal resistance in transient heat transfer by introducing the penetration temperature difference. The model was validated by comparison with pore-scale numerical simulations and macro-scale LTNE model numerical simulations. The results show that the three-equation local thermal non-equilibrium model has a high accurac

Fuel Consumption Evaluation of Connected Automated Vehicles Under Rear-End Collisions

Connected automated vehicles (CAV) can increase traffic efficiency, which is considered a critical factor in saving energy and reducing emissions in traffic congestion. In this paper, systematic traffic simulations are conducted for three car-following modes, including intelligent driver model (IDM), adaptive cruise control (ACC), and cooperative ACC (CACC), in congestions caused by rear-end collisions. From the perspectives of lane density, vehicle trajectory and vehicle speed, the fuel consumption of vehicles under the three car-following modes are compared and analysed, respectively. Based on the vehicle driving and accident environment parameters, an XGBoost algorithm-based fuel consumption prediction framework is proposed for traffic congestions caused by rear-end collisions. The results show that compared with IDM and ACC modes, the vehicles in CACC car-following mode have the ideal performance in terms of total fuel consumption; besides, the traffic flow in CACC mode is more stable, and the speed fluctuation is relatively tiny in different accident impact regions, which meets the driving desires of drivers

Quality test of clamping connection of transmission lines across tensile line

This paper develops a new technology for the quality inspection of the transmission line that is important across the tensile clamp. The new technology mainly based on the ultrasonic pulse echo thickness measurement mechanism tests the thickness of the aluminum sleeve after crimping the tensile clamp to reflect the relative position of the aluminum sleeve and the steel anchor after the crimping, thereby judging whether there is a crimping positioning defect. At the same time, it is supplemented by steel anchor model comparison, crimping position length comparison, and crimping to margin detection to determine whether the transmission line crimping quality is qualified

Task-technology Fit Aware Expectation-confirmation Model towards Understanding of MOOCs Continued Usage Intention

Massive Open Online Courses (MOOCs) have been playing a pivotal role among the latest e-learning initiative and obtain widespread popularity in many universities. But the low course completion rate and the high midway dropout rate of students have puzzled some researchers and designers of MOOCs. Therefore, it is important to explore the factors affecting students’ continuance intention to use MOOCs. This study integrates task-technology fit which can explain how the characteristics of task and technology affect the outcome of technology utilization into expectation-confirmation model to analyze the factors influencing students’ keeping using MOOCs and the relationships of constructs in the model, then it will also extend our understandings of continuance intention about MOOCs. We analyze and study 234 respondents, and results reveal that perceived usefulness, satisfaction and task-technology fit are important precedents of the intention to continue using MOOCs. Researchers and designers of MOOCs may obtain further insight in continuance intention about MOOCs

UHF RFID Tag Antenna Design for Challenging Environment Surfaces

We propose a low cost, long range UHF RFID tag antenna for challenging environment surfaces like metal, glass and a human body. It consists of a nested-slot based patch on upper substrate and parasitic parallel strips on the second grounded substrate. The parasitic strips provide isolation by exciting some multi-resonant modes in the presence of metal and high dielectric materials. Furthermore, the proposed design is suitable for platform-tolerant applications because it can work properly on general tagged objects such as metal, glass, and wood. Mounted on 200×200 mm 2 metal plate, the proposed tag covers whole US RFID band and a maximum read range of 9.5 m at 910 MHz

Distribution and conservation status of Camellia longzhouensis (Theaceae), a critically endangered plant species endemic to southern China

Camellia longzhouensis (Theaceae) is an endemic evergreen shrub or small tree with a distribution restricted to South China. It is listed as Grade-II in the National Key Protected Wild Plants List. In this study, we surveyed its distribution, examined its population structure, identified factors affecting its survival, and reassessed its extinction risk. We found that C. longzhouensis was only distributed in the Nonggang National Nature Reserve and the surrounding area. Its individuals only grew under the secondary forest canopy in the karst mountain. A total of 58 individuals of C. longzhouensis in three sub-populations were found. Soil fertility and understory light availability were the main habitat factors influencing the survival of C. longzhouensis. Anthropogenic disturbances and reproductive obstacles have caused a low seed-setting rate, poor seedling survival, and a lack of adult plants of C. longzhouensis in the natural habitat. The population structure of C. longzhouensis is spindle-shaped, indicating poor natural regeneration and inhibited seedling recruitment. Cleistanthus petelotii had a significant positive interspecific interaction with C. longzhouensis in the community. Based on the information obtained here and IUCN criterion C2ai, we recommend that C. longzhouensis be categorized in the International Union for Conservation of Nature (IUCN) Red List as Critically Endangered. We also developed a comprehensive protection strategy, consisting of in situ conservation, ex situ conservation, reintroduction, and commercial utilization. This strategy can be readily applied to protect other endangered plants with economic value in karst poor regions