Role of bubble and impurity dynamics in electrical breakdown of dielectric liquids

Abstract

Electrical discharges in liquids with and without gas injection was experimentally studied with two circuits (RC and single spark gap). Electrical breakdown could be initiated from the following mechanisms: electrode initiation; impurity initiation; and Taylor cone driven initiation. Discharges initiated by electrodes were observed only with the single spark gap circuit. Impurities and Taylor cones can initiate discharges when using the RC circuit. With the single spark gap circuit, bubbles were nearly stationary in the gap before and during discharges because of the limited time to respond to the electric field growth (dV/dt = 1 kV ns −1 ). Bubbles and impurities gain significant energy and undergo significant dynamic changes with the RC circuit under a long rising time. Charge relaxation time on bubbles or impurities in the fluids were close to 100 ms, which is comparable with the circuit rising time. Bubble dynamics observed include reduced bubble size, increased bubble speed and shape change. Taylor cones were observed on bubble surface using a high-speed camera during multiple discharge events, and usually led to breakdown. Taylor cones develop on a bubble surface through multiple states over a period of 10-500 μs. State one was typically seen on a bubble surface with a sharp tip caused by the residual charge. A single streamer was initiated on the tip of the cone at state two. State three developed multiple bush-like streamers on the cone and usually triggered a breakdown in the gap. Discharge behaviors in liquids were also investigated with the RC circuit at different pulsing frequencies. At a low pulsing frequency (1 Hz), discharge events are independent from each other. When pulsed above 10 Hz, bubbles created in the gap accumulate and participate in the next discharge event. Bubble accumulation results in a cloud where local secondary discharges are observed with a much higher frequency up to a few kHz for several milliseconds.

Greenhouse gas emission reduction and energy impact of electrifying upgraders in refineries using plasma processing technology

“…50 Wang et al also investigated the role of bubble and impurity dynamics in the electrical breakdown and the relative breakdown voltage and energy deposition in the liquid and gas phase of multiphase hydrocarbon plasmas, for in-depth research on hydrocarbon conversion using plasmas. 51,52 While researchers have invented different novel plasma processing technologies for heavy oil upgrading, research on the impact of plasma processing technologies in terms of energy consumption and greenhouse gas emissions, compared to traditional catalytic thermal cracking technologies is non-existent. An LCA has also never been performed for comparing these two technologies and how they t into the entire oil and gas industry, making this paper a rst in the literature.…”

“…Modeling the scaleup of this reactor to the renery scale is based upon a multiplicity of small reactors. 53 Plasma processing reactors are amenable to a method of process intensication 54 wherein the individual micro-scale reactor is highly efficient and large-scale efficiency is obtained by linear scaling of the reactions by having thousands of reactors. This maintains the conversion and efficiency of the smallscale reactor.…”

“…Low price PPAs are only negotiable when there is the ability to shut down a process relatively rapidly, as with the modular and scalable PPT demonstrated here. 53 The response of the cost difference between traditional and plasma renery congurations is reported. A negative cost difference indicates that the PPT is more expensive than the traditional method whereas a positive cost difference means PPT is more economical than BAU and can be implemented without compromising prot or functionality.…”

Controlling Parameters in the Efficiency of Hydrogen Production via Electrification with Multi-Phase Plasma Processing Technology

“…This oil conversion process has higher efficiency and significantly lower GHG emissions than traditional technologies. Wang et al also investigated the role of bubble and impurity dynamics in the electrical breakdown and the relative breakdown voltage and energy deposition in the liquid and gas phase of multiphase hydrocarbon plasmas for in-depth research on hydrocarbon conversion using plasmas [48,49].…”