The cathode erosion rate, arc root velocity and output power of a well-type cathode (WTC), non-transferred plasma torch operating in air are studied experimentally in this paper. An external solenoid to generate a magnetically driven arc and a circular swirler to produce a vortex flow structure are equipped in the studied torch system, which is designed to reduce the erosion rate at the cathode. A least square technique is applied to correlate the system parameters, i.e. current, axial magnetic field and mass flow rate, with the cathode erosion rate, arc root velocity and system power output. In the studied WTC torch system, the cathode erosion has a major thermal erosion component and a minor component due to the ion-bombardment effect. The cathode erosion increases with the increase of current due to the enhancement in both Joule heating and ion bombardment. The axial magnetic field can significantly reduce the cathode erosion by reducing the thermal loading of cathode materials at the arc root and improving the heat transfer to gas near the cathode. But, the rise in the mass flow rate leads to the deterioration of erosion, since the ion-bombardment effect prevails over the convective cooling at the cathode. The most dominant system parameter to influence the arc root velocity is the axial magnetic field, which is mainly contributed to the magnetic force driving the arc. The growth in current has a negative impact on increasing the arc root velocity, because the friction force acting at the spot due to a severe molten condition becomes the dominant component counteracting the magnetic force. The mass flow rate also suppresses the arc root velocity, as a result of which the arc root moves in the direction against that of the swirled working gas. All system parameters such as current, magnetic field and gas flow rate increase with the increase in the torch output power. The experimental evidences suggest that the axial magnetic field is the most important parameter to operate the straight-polarity WTC plasma torch at high output power with a limited cathode erosion rate. This emphasizes the importance of an external magnetic field on a WTC torch system for reducing the erosion at the cathode.

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Harvesting energy using roof turbine ventilator and electroactive material has been investigated to verify its performance. Since electric power gained from a single piece of regular size is usually small, auxiliary device to vibrate multiple pieces of electroactive materials in order to harvest more power is required. In this paper, an attempt of using the developed nozzle wind collector associated with the popular roof turbine ventilator employed with gear mechanism to impact and vibrate a group of electroactive material to generate electricity is proposed. Number of blade and blade angle of the roof turbine ventilator are influential to the effectiveness of wind collection. Also, number of electroactive material employed on the turbine ventilator under the wind speed in environment eventually determines the efficiency of wind harvest. A simple model is derived to estimate the minimum driving force from the wind power that needs to overcome the inertia of the turbine ventilator mechanism and the electromechanical energy conversion of electroactive materials. Wind drag force is calculated by using CFD is assumed to provide such driving force. Various combinations of the blade angle, number of blade and electroactive material actuators are investigated in simulations. Optimum design concerning the environment wind resource and configuration of turbine ventilator is discussed. According to several case studies, a few of design trends is addressed for better efficiency of energy harvest. Since multiple electroactive materials are employed, circuitry design with parallel input sources is implemented to sum up the current and integrate the power.