Besides a typical high-density plasma source, electrical explosion of conductors is also indispensable in switches, nanomaterial synthesis, shock-wave sources, etc. In this paper, an experimental study regarding plasma dynamics of electrical wire explosions (μstimescale) is presented, with spatiotemporal resolved diagnostics. Pure Cu/Ni wire and Cu-Ni alloy wire were used and compared. The alloy wire usually has a higher resistivity, resulting in a higher initial energy deposition (heating) rate. Abel inverse transformation indicated that the plasma radiation focussed on the outer region of the discharge channel for the alloy wire. In addition, the metallic vapour determined by the material properties had a considerable influence on the plasma process and resulting nanomaterials. In particular, both transverse and axial-layered structures were observed in alloy wire vapour. In addition, for the first time, the expanding arc-like plasma of explosion products was understood and examined from aspects of material properties and energy relaxation. The later stage of wire explosion resembled the state of regular metal vapour arcs under 1 MPa pressure. Finally, the core factor for the fast energy deposition stage of wire explosion was ascertained. Correlations between pre-exposition circuit parameters and post-explosion dynamic effects were found, which is significant for practical applications.

The physical image of breakdown dynamics inside striations is depicted. High-speed photography along with electrophysical and spectral diagnostics reveals three modes for plasma development in Cu wire explosion: current cutoff, initial breakdown (with quenching), and main breakdown (with re-strike). The growth of spatial heterogeneity by electrothermal instability (ETI) provides a stratified structure before the initial breakdown. The characteristic wavelength of the strata is <100 μm for thinner wires (d = 90/130 μm) but in mm level for thicker ones (d = 240/290 μm). By increasing the stored energy from 200 to 220 J, the 290-μm-diameter Cu wire experiences a transition from current cutoff to initial breakdown, with a deposited energy of 2.64 and 3.10 eV/atom. Although the energy is not sufficient to vaporize the wire, axial micro-plasma-channels develop among bright layers (higher temperature but lower density), forming a crossed low-conductive “plasma-network” connecting two electrodes. If the residual energy is enough, the scenario (main breakdown) would be similar to “streamer-spark transition” and enhance the expansion of discharge channel. Two paralleled wires are exploded simultaneously but only one establishes main breakdown; therein, three stronger shock waves are detected, namely, two for vaporization and one for breakdown.

2D nanosheet is indispensable for the design and production of functional materials and devices. [1,2] Particularly, 2D layered materials, including graphene, phosphorene, and 2D bismuth selenide (Bi 2 Se 3 ), exhibit massive potential due to their unique electrical, optical, thermal, and mechanical properties. [3,4] Compared with classical graphene, phosphorene, 2D Bi 2 Se 3 , and other materials have shown more intriguing features and application prospects. [5][6][7][8] For example, single-and few-layer BP (2D BP) endow with a direct and tunable bandgap ranging from 0.3 eV (bulk) to 2.0 eV (monolayer), [9] which is favorable for making electric devices and photoelectric detectors. Bi and Se elements contained compounds are always selected as the electrode materials for supercapacitors and achieve satisfactory performance. [10][11][12] Khalafallah et al. designed the selenium-enriched reduced graphene oxide hybridized hetero-structured nickel bismuth selenide (RGO/Ni-Bi-Se) and bismuth selenide (RGO/Bi 2 Se 3 )based materials as positive and negative electrodes, respectively. The synthesized two electrode materials showed desirable performances (electrochemical behavior, pseudocapacitive properties, etc.). Furthermore, the established supercapacitor achieved admirable energy density with great capacity retention. [13] In addition, the layer 2D material has a considerable value of specific surface area and can be feasible for surface modification as catalysts. [14] The mainstream methodology to synthesize 2D thin nanosheets would be the exfoliation from the layered bulk form. [2] Due to the relatively weak van der Waals interlayer interaction of the materials, sometimes the exfoliation can be achieved via mechanical methods directly. [15] However, not all 2D materials can be easily exfoliated by the mechanical approach. The most prevalent and feasible way is the liquid exfoliation, where the layered bulk is immersed in suitable solutions. [16] In this case, chemical reactions intentionally introduce to facilitate the exfoliation process, such as oxidation reaction, intercalation, etc. Additional tools, including ultrasonic wave and electrochemical reaction, are also proposed to enhance liquid exfoliation. [2] Electrical explosion, characterized by ultrafast atomization and quenching rate (dT/dt ≈ 10 10 -10 12 K s -1 ) of the sample, is a unique approach for "onestep" synthesis of nanomaterials. Experiments are carried out with layered graphite and Bi 2 Se 3 under the action of electrical explosion in a confined reaction tube. High-speed photography and electrophysical diagnostics are applied to characterize dynamic processes. SEM and EDS are used to characterize surface micro-morphology of reaction products. The layered materials are first exfoliated to thin nanosheets/nanocrystals by shock waves and turbulent flow of the explosion. As the ionized explosion products (>10 000 K) contacts the sample, intense heat transfer happens, simultaneously atomizing the sample and quenching the plasmas. As a result, nanoparti...

The physical image of the confined electrical explosion in the source region is depicted. Metallic plasma/vapor dynamics and its fragmentation effect (on the confining structure) under μs-timescale are diagnosed via high-speed photography, electrophysical, and spectral measurements. When adding a 1-mm-thick Teflon tube outside the exploding wire, the growth of spatial heterogeneity by electro-thermal instability (ETI) is largely compressed and the deposited energy almost doubled from about 85 to 150 J. During the short period after breakdown, considerable energy depositing into the confined space, e.g., 100 J for 0.1 cm3, drives the fast inflation and burst of the 0.5 g confining tube to ~500 m/s (kinetic energy of ~62.5 J). Intense plasma jets eruption with supersonic speed >1.5 km/s and induced shock waves of 2-3 km/s are observed from cracks of the inflated tube. Besides, the erupted plasma jets gradually evolve Rayleigh-Taylor instability (RTI) and finally cause turbulent mixing with the ambient medium. This mechanism is very likely to explain the plasma cavity evolution in underwater explosion. Interestingly, although the confining effect of water is stronger than a Teflon tube, the latter has a better response to the high-rate impulse loading and absorbs more deposited energy by deformation, phase transition, and acceleration.

The central heating technology with thermal storage technology is an important means to realize thermoelectric decoupling, meet heating demand, reduce primary energy consumption, and protect the ecological environment. For this paper, the numerical simulation method was used to study the temperature variation of large-capacity hot water storage tank (HWST) in an actual combined heat and power system. The influence of various factors, including the length diameter ratio, water supply temperature, and water supply flow, as well as the orifice diameter and number of the water distributor, on the flow uniformity and performance of the HWST was investigated. The results show that the heat storage efficiency and flow uniformity of the HWST can be improved by properly increasing the water supply flow, the orifice diameter, and number of the water distributor. Increasing the length diameter ratio can improve the flow uniformity, but it will reduce the heat storage efficiency of the HWST. Increasing the water supply temperature can increase heat storage efficiency of the HWST and accelerate the stratification of cold and hot water in the tank. Besides, the comprehensive analysis of the non-dimensional exergy loss calculation results, velocity field, and temperature field show that there is a certain coupling relationship between the non-dimensional exergy loss and flow uniformity at the initial stage of heat storage. In practical application, the influence of these factors on flow uniformity, heat storage efficiency, and non-dimensional exergy loss should be comprehensively considered in order to achieve the best heat storage and release performance of the HWST. This paper provides some engineering guidance for the application of large-capacity heat storage tanks in the combined heat and power (CHP) system.