Dewetting of liquid films on solid surfaces in the presence of evaporation is a common phenomenon and has been studied by many researchers. The previous numerical approach has revealed that evaporation accelerates the dewetting speed of the triple contact line and established correlations between the dewetting speed and the surface wettability and superheating. However, such a numerical calculation is time- and resource-consuming. ,We examine dewetting physics and propose a time-averaged approach based on the multiscale theory. The new approach averages the dewetting process over time and consists of only several algebraic equations, making the problem easier to solve. It can produce time-averaged values of essential quantities, such as the dewetting speed and contact angle as a function of superheating, which agrees with the previous numerical results. This simple approach is valuable for many applications, such as modeling pulsating heat pipes and describing the microlayer dynamics under growing vapor bubbles in nucleate boiling.
The rapid development of mobile networks has revolutionized the way of accessing the Internet. The exponential growth of mobile subscribers, devices and various applications frequently brings about excessive traffic in mobile networks. The demand for higher data rates, lower latency and seamless handover further drive the demand for the improved mobile network design. However, traditional methods can no longer offer cost-efficient solutions for better user quality of experience with fast time-to-market. Recent work adopts SDN in LTE core networks to meet the requirement. In these software defined LTE core networks, scalability and security become important design issues that must be considered seriously. In this paper, we propose a scalable channel security scheme for the software defined LTE core network. It applies the VxLAN for scalable tunnel establishment and MACsec for security enhancement. According to our evaluation, the proposed scheme not only enhances the security of the channel communication between different network components, but also improves the flexibility and scalability of the core network with little performance penalty. Moreover, it can also shed light on the design of the next generation cellular network.
Fuel consumption is a crucial challenge for ACC (Adaptive Cruise Control) scenarios. This paper focuses on a synthesized controller of ACC based on a PnG (Pulse-and-Gliding) strategy to reduce fuel consumption in a car-following situation. A switching logic module is proposed for real-time control. A gear shifting algorithm and braking logic are added to the controller concerning the real following situation and structure of powertrain. Simulations are implemented in Matlab/Simulink and the results demonstrate that, compared with a MPC (Model Predictive Control) based benchmark controller, the synthesized controller could save fuel up to 14.5%. The significant fuel saving attributes to keeping the working point at or around at the best fuel economy point of engine. The algorithm could be implemented to some heavy commercial vehicles.
Estimates indicate that the electron cloud effect could be a limiting factor for Main Injector intensity upgrades, with or without the presence of a new 8 GeV superconducting 8 GeV Linac injector. The effect may turn out to be an issue of operational relevance for other parts of the Fermilab accelerator complex as well. To improve our understanding of the situation, two sections of specially made vacuum test pipe outfitted for electron cloud detection with ANL provided retarding field analyzers (RFAs) were installed in the Tevatron and the Main Injector. In this report we present some measurements and discuss future plans for studies.
The application of campus Grid is introduced.Both the architecture and technique characteristics of grid technology are analyzed.Finally its application in future is conceived.
Dewetting of a substrate, i.e. the liquid film retraction under partial wetting conditions, has been studied extensively over the past decades. This theoretical work deals with the dewetting phenomenon in the presence of liquid evaporation into the pure vapour atmosphere driven by substrate superheating with respect to the saturation temperature corresponding to the vapour pressure. The dynamic profile of the vapour–liquid interface is analysed numerically by using the generalised lubrication approximation that can be applied to an interface slope larger than its conventional counterpart. This approximation uses a phenomenological argument to increase the precision of calculations. For small slopes, it reduces to the conventional lubrication approach. Several nanoscale effects are included in the theory to obtain more precise results: the Kelvin effect, the hydrodynamic slip, the Marangoni effect, the vapour recoil and the interfacial thermal resistance. Their relative importance is discussed. The results include the film shape evolution, the apparent contact angle and the contact line speed, all defined by the substrate superheating and its wetting properties. These dependencies agree with existing experimental results. It is found that the dewetting is accelerated by evaporation. The numerical results are compared to those of the multiscale theory that uses two main parameters, the Voinov angle (the apparent angle obtained within the microregion problem) and the Voinov length. The latter is studied for several fluids as a function of superheating, and an approximate expression for it is proposed. A good agreement between the numerics and the multiscale theory shows the validity of the latter. This means that the dewetting speed in the presence of evaporation can be calculated with an analytical expression that requires only the Voinov angle as a numerical input. Such results are important for many applications, for instance, bubble growth in boiling or film dynamics in heat pipes.
Hydrogen may be released by Fuel and Cladding interaction with the steam at very high temperatures into the containment during a severe accident at the nuclear power plant (NPP). Locally, high hydrogen concentration may be achieved that might probably result in detonation or fast deflagration and challenges the reliability of the containment. The mixing and distribution of hydrogen is a serious safety issue for scientists to preserve the structural reliability of the containment. Although the Three Miles Island (TMI) accident in 1979 was the initiator to study the production and buildup of hydrogen in the containment. Subsequently, the hydrogen explosion in the Fukushima Dai-ichi NPP accident (2011), modeling of the gas behavior turn out to be a significant topic in the nuclear safety analysis. Computational fluid dynamics (CFD) codes can be used to investigate the hydrogen distribution in the containment during accidental scenarios and predicts the local hydrogen concentration in different regions of the containment vessel. In such a way, the associated risk of hydrogen safety can be determined, and safety assessment and procedures can be measured. The current paper presents the results of systematic work done by using the HYDRAGON code, developed by Department of Engineering Physics, Tsinghua University, to study (I) Mesh sensitivity (II) Buoyancy-driven flows analysis, for various turbulence models i.e., a standard k-ε (SKE) model, a renormalization k-ε (RNG) model and a realizable k-ε (RLZ) model and, to demonstrate the HYDRAGON code thermal-hydraulic simulation capability during a severe accident at the NPP. The HYDRAGON code simulation results were compared to the published data performed by Jordan et al., and it has been observed that the simulation results obtained by refined mesh have given generally satisfactory results. However, the global effect of the buoyancy term in the turbulence equations on the HYDRAGON code simulated results is very small.
The pressurizer of a pressurized water reactor (PWR), as a spray-heating degasser, has been widely used to remove dissolved gas in the primary coolant of PWRs. In the real degassing process, the boundary conditions of the pressurizer may change, causing fluctuations in the degassing state and affecting the efficiency of degassing. However, open-published studies have focused mainly on the steady-state degassing characteristics of the pressurizer. This paper studies the dynamic characteristics of a spray-heating degasser as applied to the pressurizer of a PWR. First, a lumped parameter dynamic degassing model for the spray-heating degasser is proposed based on basic gas dissolution and transport theory. Second, this model is extended, and a dynamic degassing model for the pressurizer is obtained. Third, two sets of numerical hydrogen degassing tests are carried out using the pressurizer dynamic degassing model. These two sets of numerical tests take the Shippingport pressurizer as the research object and integrate the structure and operating parameters of the Shippingport pressurizer with the system parameters of a Bettis Atomic Power Laboratory hydrogen degassing test as the numerical test condition.The spray-heating degasser degassing model is universal and applicable to this pressurizer as well as other devices with similar structures. The first set of numerical tests carried out reveals the physical mechanism of degassing with the spray-heating degasser. The pressurizer degassing model can be used for transient degassing analysis, and it also provides a basis for the subsequent design of the control system of pressurizer degassing.
The large-scale growth of monolayer transition metal dichalcogenide (TMDC) films is a determinant for the implementation of two-dimensional materials in industrial applications. However, the simultaneous realization of uniform monolayer thickness and large-area coverage is still a challenge, because it requires precise control of reaction kinetics in both space and time dimensions. Herein, we achieve a variety of large-area monolayer TMDCs films by a dual-limit growth (DLG) that is realized through nanoporous carbon nanotube (CNT) films. In the DLG, a precursor-loaded CNT film placed face-to-face with a substrate provides a space-limited environment facilitating the monolayer growth, while the byproducts formed in the CNT film timely limits the supply of precursors released from nanopores of the CNT film, inhibiting the growth of multilayer TMDCs on the substrate. Consequently, large-area monolayer TMDC films are grown in a wide range of reaction times and show good homogeneity in thickness, optical properties, and device performance over the entire substrate. The DLG strategy is widely applicable for the growth of a variety of TMDC films including WSe
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