Numerical thermofluid simulation on tandem type of induction thermal plasmas with and without current modulation in a lower coil

Abstract

This paper describes numerical calculations on tandem-type induction thermal plasmas with and without current modulation of the lower coil. The tandem type of induction thermal plasma (tandem-ITP) has been developed with two independent rf coils in one plasma torch for stable operation and spatial control of temperature field in ITP. Furthermore, the coil current modulation for tandem-ITP, i.e. tandem type of pulse-modulated induction thermal plasma (tandem-PMITP), is expected to offer a temporo-spatially varying temperature field in the plasma torch. First, as described in this paper, a numerical thermofluid model was developed for tandem-ITP/PMITP with an upper coil and a lower coil to investigate unique temperature and gas flow fields. Secondly, the influence of gap length between the upper coil and the lower coil was studied in the tandem-ITP under steady state conditions. Results show that a shorter gap length between two coils of the tandem-ITP is favourable for materials processing because it suppresses unfavourable radial gas flow to the wall in the plasma torch. Thirdly, transient calculation was conducted for the tandem-PMITP with current modulation in the lower coil to investigate effects of an off-time modulation parameter on the temperature field. Results showed that coil current modulation provides unique temporo-spatially varying temperature and gas flow fields. Finally, calculation results for a tandem-PMITP were compared with those for a single-coil PMITP. Comparison revealed that tandem-PMITP has higher robustness in modulated induction thermal plasma by maintaining a higher-temperature region than that of the single-coil MITP. The tandem-PMITP can provide more controlled temperature and gas flow fields.

Numerical study of nanoparticle formation in two-coil tandem-type modulated induction thermal plasmas with simultaneous modulation of upper- and lower-coil currents

“…Furthermore, we developed two-coil tandem type MITP for NPs [25,26,28,42]. Tandem MITP consists of twoindependent coils surrounding one plasma torch.…”

“…The frequencies of the upper-coil current and lower-coil current were set respectively to 430 and 300 kHz. These frequencies of the upper-coil and the lowercoil currents were determined experimentally and theoretically to reduce mutual inductive coupling between the two coils [25,26,28,42]. Both coil currents were modulated into rectangular waveforms with the time-averaged power of 10 kW under modulation condition.…”

“…To improve PMITP robustness and efficiency processes for NP synthesis, the author's group has developed a twocoil tandem-type modulated induction thermal plasma (tandem MITP) [25][26][27]. Tandem MITP is maintained in one torch by two independent induction coils and two radio-frequency (RF) power sources.…”

Recent development of new inductively coupled thermal plasmas for materials processing

“…The tandem-MITP can be realized using two RF power sources with different frequencies at reasonable prices. Figure 16 depicts a schematic diagram of the tandem type of modulated induction thermal plasma (Tandem-MITP) system [66,67]. The tandem-MITP is sustained by two RF power supplies: an RF power supply for the upper coil and an RF power supply for the lower coil.…”

“…Because of rapid cooling in thermal plasma, MITP is useful for diamond particle nucleation in the first stage of diamond film deposition. The fourth topic is a new tandem MITP with two coils, which has been established [66,67]. In this case, two coil currents are modulated for temporal and spatial control of the thermal plasma.…”