Systematic Study on Heating Characteristics of a Rotating Coaxial Probe-Type Microwave Reactor

In this study, a coaxial rotating probe-type microwave (MW) reactor for nanoparticle synthesis was designed, and its performance was analyzed using numerical modeling. The heating characteristics of the reactor were systematically analyzed in terms of average temperature, maximum temperature, temperature variance coefficient, and maximum temperature difference. The results showed that the introduction of rotating probes effectively eliminated the hot spots in the reactor, which could preclude the nanoparticle synthesis process from being affected by the temperature difference inside the reactor and greatly improve the MW heating efficiency. The maximum temperature difference inside the reactor was reduced by more than five times at a heating time of 60 s with the rotating probes. Subsequently, the effects of the main factors, such as MW input power, frequency, solution dielectric properties, probe configuration, and probe rotational speed, were analyzed. The results showed that the hot spot indicator Hs and the temperature variance COVT can be reduced by at least three times at the conditions of MW frequency f = 2.45 GHz with probe configurations of Ψ2* = 0.08333 and Ψ3* = 0.29166 when selecting the probe rotational speed of Ω1 = 16,513. Reasonable regulation of the dielectric constant and dielectric loss factor of the solution can make the solution's response to MW heating ideal. Increasing the probe rotational speed is very effective at weakening the hot spot. In addition, comparison among the designed reactor, a multimode cubic cavity reactor, and a stationary coaxial probe reactor was conducted, showing that the designed reactor exhibited much better performance in terms of Hs and COVT.