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Vacuum interrupter is widely used in the medium-voltage power system. Controlling the arc by the magnetic field is an effective method to improve the breaking capacity. The transverse magnetic field (TMF) forces the constricted arc to rotate to reduce local overheating. In this paper, three kinds of TMF contacts, which are Swastika-type contact, cup-shaped contact, and double-TMF contact that combines Swastika-type and cup-shaped contacts coaxially, are investigated in a demountable vacuum chamber with a high-speed camera. The arc voltage and current are also recorded. The experiments were conducted with circuit currents from 5 to 20 kA (root mean square) with a frequency of 50 Hz. There are four current levels in the experiment, which are 5, 10, 15, and 20 kA, and at least three tests are taken for each current level. The results showed that under low current (I = 10 kA), the arc of the three TMF contacts did not rotate. Under high current (I = 20 kA), it was observed that the arc of Swastika-type and double-TMF contacts rotated in the gap. The arc speed of double-TMF contacts is higher than that of Swastika-type contacts. The cup-shaped contacts have the highest arc voltage and noise among the three TMF contacts. The Swastika-type contacts were eroded most seriously. The simulation results show the force distribution of the arc on different locations. The resultant force makes the arc rotate counterclockwise.

Using magnetic fields to control the vacuum arc is a major way to improve the breaking capacity of vacuum interrupters. Besides the single transverse magnetic field (TMF) and single axial magnetic field (AMF), new type of TMF-AMF contact and TMF-TMF contact structures have been put forward to control the vacuum arc in recent years. In this paper, three different structural contacts are used in the experiments. The arc evolution was captured by an high-speed digital video camera, and at the same time, the arc current and arc voltage wave were recorded. The experiment was conducted under current ranging from 5 to 20 kA (root mean square) and 10 mm of gap distance. There are 12 current shots performed on one contact design. There are four current levels in the experiment which are 5, 10, 15, and 20 kA, and three tests are taken for each current level. The results showed that for TMF-AMF contacts, under low current (I = 5 or 10 kA), the arcs of the two kinds of contacts both kept diffused and rotating. Under high current (I = 20 kA), the arc of the TMF-AMF contact with six slots was constricted and rotated on the plate, and the melting was uniform and slight. As for the eight-slot contacts, the arc was constricted but did not rotate which resulted in significant melting in the local region. As for TMF-TMF contacts, the result is similar under low current, while the arc was constricted and rotated quickly on the inner plate under high current. The simulation results show that when the arc core is located on the outer plate; the total Lorentz force is near zero. When the arc core is located on the inner plate, the direction of total force is counterclockwise.

The effects of the initial preheating perturbation on the dynamical behaviors of FGC wave propagation instability for low-velocity FGC in packed bed are studied numerically. The behaviors of the flame front inclination, break, and shrinking instabilities are always observed in experiments. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed as to predict the deformation behaviors of the flame front instabilities. The typical flame shapes are obtained depending on filtration velocity, equivalence ratio, and initial preheating temperature difference. It is demonstrated that the development of flame front inclination instability is proportional to the magnitude of initial preheating perturbation. At a lower equivalence ratio, the initial thermal perturbation of 300 K leads to the evolution of flame front break. Increasing filtration velocity leads to the appearance of flame front break, due to the intensification of the hydrodynamic instability. In addition, a perculiar instability of flame front shifting is also confirmed with the initial thermal perturbation of 400 K, which results in a fuel leakage of incomplete combustion.

An improved two-dimensional axisymmetric swirl model based on former work has been developed to describe the detailed physical process in the formation and development of vacuum arc cathode spot. In the current model, the influence of plasma cloud, evaporation, backing ion, thermo-field (T-F) emission, back-diffused electron, self-generated magnetic field and Lorentz force are all considered. External parameters include electron temperature, near cathode voltage drop, average charge number, ion number density, space function and time function. The compositions of current density, energy flux density and external pressure are discussed and the influence of external parameters are studied. Simulation results show that electron current density from T-F emission is the most important component for current density; as for energy flux density and pressure, ion flux from plasma cloud is dominant. Ablation on a refractory metal is much less than that on a fusible metal under the same external conditions. The simulation results are in good agreement with other researchers' results.

In this paper, the arc characteristics of cup-shaped AMF contacts in vacuum arc experiments under different materials was studied. The experiment was conducted in a detachable vacuum chamber with a gas pressure of 10-4Pa. The arc voltage and current were measured at the same time by high-voltage probe and Rogowski coil, and the arc pictures were photographed with a high-speed camera. The cup and the rod of the contact are made of pure copper material, and the contact pieces are selected ten common contact materials for comparison (CuCr10, CuCr 20, CuCr 30, CuCr 40, CuCr 50, WCu10, WCu20, WCu30, CuW-WC). Fixed-distance trigger experiments were conducted with currents of 5kA (rms), 10kA (rms), and 15kA (rms) for each contact. The arc appearance, cathode surface morphology, and anode status morphology were observed. The shape of the arc was analyzed in conjunction with the voltage and current after the experiment. The morphology of cathode and anode surface was analyzed by combining the erosion after the experiment. The effect of various material properties was discussed under the AMF. It’s found that the center of the anode erosion area is approximately hexagonal, and the slot is burned more outward than the plane. WCu contact has better erosion resistance than CuCr contact. For CuCr, the erosion of CuCr30 is the slightest with low depth and small area.In this paper, the arc characteristics of cup-shaped AMF contacts in vacuum arc experiments under different materials was studied. The experiment was conducted in a detachable vacuum chamber with a gas pressure of 10-4Pa. The arc voltage and current were measured at the same time by high-voltage probe and Rogowski coil, and the arc pictures were photographed with a high-speed camera. The cup and the rod of the contact are made of pure copper material, and the contact pieces are selected ten common contact materials for comparison (CuCr10, CuCr 20, CuCr 30, CuCr 40, CuCr 50, WCu10, WCu20, WCu30, CuW-WC). Fixed-distance trigger experiments were conducted with currents of 5kA (rms), 10kA (rms), and 15kA (rms) for each contact. The arc appearance, cathode surface morphology, and anode status morphology were observed. The shape of the arc was analyzed in conjunction with the voltage and current after the experiment. The morphology of cathode and anode surface was analyzed by combining the erosion after the exp...

The performance of a dual-function solar collector (DFSC) that can work as either water heater or air heater depending on seasonal requirement is investigated via both experimental and numerical approaches in this paper. The numerical results are well consistent with the experimental results. Daily efficiency of the thermosiphon system with DFSC is more than 55% in water heating mode and the instantaneous air heating efficiency of the collector reaches 60%. The effects of inner parameters on the thermal efficiency of the collector are analyzed by numerical simulations of the operation of DFSC in two working modes. It is found that the depths of the two air channels in DFSC have an optimal range suitable for both working modes. The thickness of back insulation should be no less than 0.06 m to prevent heat loss via backboard, and the diameter and number of copper tubes show notable effect on the efficiency of DFSC in water heating mode but slight effect in air heating mode.