reactor and heat transfer into a single step. Moving toward renewable electricity as the source of heat for chemical reactions will enable the decarbonization of the chemical process industries as around 60% of process heating at present comes from fossil fuels. [3] Direct RF heating elevates the catalyst temperature above the bulk reactor temperature. This reduces the impact of noncatalytic hot-spots and has been shown to enhance yields for a variety of organic synthesis and pyrolysis reactions. [4][5][6] Lower coke formation is also reported in pyrolysis, [5,7] caused by a rapid quenching of side reactions as products quickly diffuse from the heated catalyst surface to the cooler bulk fluid. [8] RF heating uses lower frequencies than microwave heating, resulting in different advantages and challenges between the two methods. Lab-scale microwave reactions typically operate at 2.45 GHz and are heated through microwave absorption within a high dielectric solvent. [9] Larger microwave systems suffer from non-uniform heating due high absorption and low penetration of microwaves in the reactor solvent and hot-spots caused by constructive interference on the scale of the microwave wavelength, 12 cm for 2.45 GHz. [9] Higher frequencies are used to achieve greater heating power when scaling up microwave heating systems, which lead to lower heating efficiencies of 30% or less. [10] RF heated systems can achieve theoretical efficiencies greater than 80%, and efficiency increases with scale. [11] Finally, the absorption of microwaves in the human body leads to increased Radiofrequency heating of magnetic particles promises highly efficient and direct heating of catalytic reactors for coupling of low carbon electricity with energy intensive chemical transformations. In this work, a novel real-time and in situ magnetometry method is developed to measure minor and major hysteresis loops of soft magnetic nanopowders. It is applied to measure the magnetic properties and hysteresis power absorption of magnetite and maghemite powders up to 500 °C. An arctangent model for saturation magnetization is adapted for minor hysteresis loops. It produces an excellent fit for hysteresis loop power across field strengths up to 18.5 kA m −1 and allows prediction of heating power, remanence, and susceptibility. Samples of magnetite and maghemite are shown to heat rapidly from room temperature at more than 25 °C s −1 , with maghemite giving the strongest heating response. The peak heating power occurs at the transition beyond the ellipsoidal Rayleigh law region. These findings suggest that the properties of magnetic powders, coupled with variable magnetic field strengths and frequencies, can be tuned to optimize the heating power for a variety of applications.
Reflected Impedanceometry is a new technique that can remotely measure the power absorbed during radiofrequency induction heating. It measures the total system impedance from the phase difference between current and voltage in the electromagnetic field work coil and uses the characteristic impedance of the work coil circuit to infer the heating power transferred into a susceptor bed. Induction heating of susceptor materials within alternating magnetic fields occurs by magnetic hysteresis, eddy currents, Néel relaxation or Brownian relaxation. It shows potential for replacing fossil fuels with renewable electricity in carbon-intensive industrial applications but requires advances in measurement techniques. Previously developed methods for measuring heating power, such as pick-up coils, are limited to applications involving magnetic materials. Results presented here show that reflected impedanceometry accurately measures heating power for both magnetic hysteresis and eddy currents, fulfilling the requirement for measuring induction heating power.
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