The Design and Numerical Study of a 2MWh Molten Salt Thermocline Tank

AbstractThe two tank molten salt thermal storage system is widely used in the commercialized solar thermal power plant. However, the thermocline storage system with a low-cost filler material is a more economically feasible option. In this study, a transient two-dimensional and two-temperature model is developed to investigate the heat transfer and fluid dynamics in a molten salt thermocline thermal storage system. After model validation, the effects of inlet flow boundary condition and storage medium properties including fluid and solid materials on the thermal performance of thermocline storage system are investigated. The results show that thermoclne thickness increases slowest with solar salt as heat transfer fluid (HTF) and Cofalit® as solid material in the thermocline tank. Any non-uniformity in the inlet velocity flow would only enhance mixing and widen the thermocline appreciably, which contributes to the loss of thermodynamic availability of stored energy. The thermocline thickness increases with the non-uniformity of the inlet velocity boundary condition. So smaller non-uniformity of inlet flow is better in non-uniform flow though it may causes larger fluctuations in average outlet temperature. Smaller inlet mass flow rate is better for the thermocline storage tank, while it also causes smaller discharging power. With the chosen basic design parameters such as fluid and solid materials, the size of a 2MWh thermocline tank is determined by a simple one-dimensional design method. Tank with larger H/D ratio has higher discharge efficiency. It helps to figure out the thermal stratification mechanism of a storage tank and thereby to determine optimum design and operating conditions

A novel layer-structured PtN₂: first-principles calculations

Platinum nitride as the first successfully synthesized noble metal nitride shows superior mechanical properties and exotic electronic structure that rival those of conventional transition metal nitrides. In the past diverse crystal structures have been proposed to understand its unusual properties. However, very few works pay attention to the dynamic stability of these phases. Here, we examine the potential structures of platinum nitride with a chemical composition of PtN₂ by utilizing a widely adopted evolutionary methodology for crystal structure prediction. Except reproducing the previously proposed phases, we also identify a Pmmm symmetric novel layer structure with a low formation enthalpy that is slightly lower than those of marcasite and CoSb₂ structures but slightly higher than that of pyrite structure. The elastic constants and the lattice dynamical calculations show that this layer-structured PtN₂ is mechanically and dynamically stable. The calculated band structures suggest this new phase together with the simple tetragonal phase are metallic, while other phases are insulators. In addition, it is found that the fluorite structure is dynamically unstable by the phonon spectrum calculations, although it is mechanically stable as suggested by calculated elastic constants.Розглянуто потенційні структури нітриду платини з хімічним складом PtN₂, використовуючи широко прийняту еволюційну методологію прогнозування кристалічних структур. Крім відтворення раніше запропонованих фаз, ідентифіковано нову симетричну шарувату структуру, просторова група Pmmm, з низькою ентальпією формування, яка трохи менша, ніж ентальпії структур марказиту і CoSb₂, але дещо більша, ніж ентальпія структури піриту. Постійні пружності і динамічні розрахунки решітки показують, що цей нітрид платини (PtN₂) з шаруватою структурою механічно і динамічно стабільний. Розраховані зонні структури дозволяють припустити, що ця нова фаза разом з простою тетрагональною фазою є металічною, тоді як інші фази є діелектричні. Розрахунками фононного спектру встановлено, що структура флюориту динамічно нестабільна, хоча механічно стабільна, як передбачається розрахованими константами пружності.Рассмотрены потенциальные структуры нитрида платины с химическим составом PtN₂, используя широко принятую эволюционную методологию прогнозирования кристаллических структур. Кроме воспроизведения ранее предложенных фаз, идентифировано новую симметричную слоистую структуру, пространственная группа Pmmm, с низкой энтальпией формирования, которая немного меньше, чем энтальпии структур марказита и CoSb₂, но немного больше, чем энтальпия структуры пирита. Постоянные упругости и динамические расчеты решетки показывают, что этот нитрид платины (PtN₂) со слоистой структурой механически и динамически стабилен. Рассчитанные зонные структуры позволяют предположить, что эта новая фаза вместе с простой тетрагональной фазой является металлической, тогда как другие фазы являются диэлектрическими. Расчетами фононного спектра установлено, что структура флюорита динамически нестабильна, хотя механически стабильна, как предполагается рассчитанными константами упругости

Role of the Coulomb interaction in the flow and the azimuthal distribution of kaons from heavy ion reactions

Coulomb final-state interaction of positive charged kaons in heavy ion reactions and its impact on the kaon transverse flow and the kaon azimuthal distribution are investigated within the framework of QMD (Quantum Molecular Dynamics) model. The Coulomb interaction is found to tend to draw the flow of kaons away from that of nucleons and lead to a more isotropic azimuthal distribution of kaons in the target rapidity region. The recent FOPI data have been analyzed by taking into accout both the Coulomb interaction and a kaon in-medium potential of the strong interaction. It is found that both the calculated kaon flows with only the Coulomb interaction and with both the Coulomb interaction and the strong potential agree within the error bars with the data. The kaon azimuthal distribution exhibits asymmetries of similar magnitude in both theoretical approaches. This means, the inclusion of the Coulomb potential makes it more difficult to extract information of the kaon mean field potential in nuclear matter from the kaon flow and azimuthal distribution data.Comment: 14 pages Latex, 4 PS-file

Acoustic emission characteristics of instability process of a rock plate under concentrated loading

It can facilitate the understanding of the mechanical properties and failure laws of rocks to research on the rock failure mechanism and evolution characteristics of Acoustic Emission (AE). Under the concentrated loading condition, the fracture and instability test of a rock plate was conducted by using the rock Mechanics Testing System (MTS), meanwhile, these AE events were recorded through the AE recording system. Based on the laboratory test, the numerical simulation was completed by using FLAC3D technique under the criterion that the rupture of a cell or several adjacent cells was regarded as an AE event. The results show that the process of the fracture and instability of the rock plate can be divided into four stages, such as the stress adjusting stage, the brittle fracture stage, the rock-arch bearing load stage and the rock-arch instability stage. And the acoustic emissions display the different characteristics in each one of the four stages. The temporal and spatial distribution characteristics of the AE events with large magnitudes are very similar to those of the natural earthquakes

Antiflow of kaons in relativistic heavy ion collisions

We compare relativistic transport model calculations to recent data on the sideward flow of neutral strange K^0_s mesons for Au+Au collisions at 6 AGeV. A soft nuclear equation of state is found to describe very well the positive proton flow data measured in the same experiment. In the absence of kaon potential, the K^0 flow pattern is similar to that of protons. The kaon flow becomes negative if a repulsive kaon potential determined from the impulse approximation is introduced. However, this potential underestimates the data which exhibits larger antiflow. An excellent agreement with the data is obtained when a relativistic scalar-vector kaon potential, that has stronger density dependence, is used. We further find that the transverse momentum dependence of directed and elliptic flow is quite sensitive to the kaon potential in dense matter.Comment: 5 pages, Revtex, 4 figure

Electrically tunable solid-state silicon nanopore ion filter

We show that a nanopore in a silicon membrane connected to a voltage source can be used as an electrically tunable ion filter. By applying a voltage between the heavily doped semiconductor and the electrolyte, it is possible to invert the ion population inside the nanopore and vary the conductance for both cations and anions in order to achieve selective conduction of ions even in the presence of significant surface charges in the membrane. Our model based on the solution of the Poisson equation and linear transport theory indicates that in narrow nanopores substantial gain can be achieved by controlling electrically the width of the charge double layer

Lambda collective flow in heavy ion reactions

Collective flow of Lambda hyperons in heavy ion reactions at SIS energies is investigated. It is found that a $\Lambda$ mean field constructed on the basis of the quark model leads to a good description of the experimental data of the in-plane transverse flow of $\Lambda$'s. The attractive mean field can also give rise to an additional "virtual" $\Lambda$ radial flow directed inwards, which is reflected by a "concave" structure of the transverse mass spectrum of the $\Lambda$ hyperons emitted at midrapidity. The $\Lambda$ radial flow is found to exhibit a strong mass dependence: The flow is visible in the Ni+Ni system, but is strongly reduced in the system of Au on Au.Comment: 18 pages LeTex, using Elsevier style, 6 PS-figures, accepted for publication in Nuclear Physics

Ultrastrong conductive in situ composite composed of nanodiamond incoherently embedded in disordered multilayer graphene

Traditional ceramics or metals cannot simultaneously achieve ultrahigh strength and high electrical conductivity. The elemental carbon can form a variety of allotropes with entirely different physical properties, providing versatility for tuning mechanical and electrical properties in a wide range. Here, by precisely controlling the extent of transformation of amorphous carbon into diamond within a narrow temperature–pressure range, we synthesize an in situ composite consisting of ultrafine nanodiamond homogeneously dispersed in disordered multilayer graphene with incoherent interfaces, which demonstrates a Knoop hardness of up to ~53 GPa, a compressive strength of up to ~54 GPa and an electrical conductivity of 670–1,240 S m(–1) at room temperature. With atomically resolving interface structures and molecular dynamics simulations, we reveal that amorphous carbon transforms into diamond through a nucleation process via a local rearrangement of carbon atoms and diffusion-driven growth, different from the transformation of graphite into diamond. The complex bonding between the diamond-like and graphite-like components greatly improves the mechanical properties of the composite. This superhard, ultrastrong, conductive elemental carbon composite has comprehensive properties that are superior to those of the known conductive ceramics and C/C composites. The intermediate hybridization state at the interfaces also provides insights into the amorphous-to-crystalline phase transition of carbon