Permittivity Measurements for Cypress and Rockrose Biomass Versus Temperature, Density, and Moisture Content

Permittivity of materials is of utmost importance for microwave applicators’ design and to predict high-frequency dielectric heating of materials. In the case of aromatic plant biomass, however, there are few data that help researchers design microwave applicators for microwave-assisted extraction. In this work, the permittivity of cypress and rockrose biomass samples were measured versus temperature, density, and moisture content. A resonant technique based on a coaxial bi-reentrant microwave cavity was employed to obtain the complex permittivity of biomass samples as a function of those magnitudes around the 2.45 GHz ISM frequency. The obtained measurements show that large variations for permittivity values can be found with moisture content and density changes for both cypress and rockrose biomass. Temperature also has effects in a lesser degree, although it has an important influence on the cypress biomass loss factor. Polynomial expressions fitting the experimental data were provided in order to facilitate the estimation of intermediate values, which were not explicitly arranged in this work. As a general trend, the permittivity of cypress and rockrose biomass increases with increasing values of moisture content and density, whereas the biomass loss factor increases when temperature rises.

Effect of Drilling Conditions on Microwave-Metal Discharge during Microwave Drilling of Stainless Steel

Processing of metallic materials using microwave energy offer benefits of time compression and energy saving during applications such as sintering, casting, melting, joining and cladding. However, use of microwave energy is uncommon for machining of metallic materials because of high reflectivity. The present work aims to study microwave-metal (MW-m) discharge-induced plasma channel (PC) characteristics during microwave drilling of thin stainless steel (SS) sheet (0.6 mm) at 2.45 GHz. Experimental trials inside two different microwave applicators A1 and A2 were monitored and recorded. The images of the plasma channel generated in both the microwave applicators were obtained at different time intervals to analyze the plasma channel diameter (PCD). Experimental results revealed that variation in the microwave power significantly affects the dimension of plasma channel generated in the tool-work gap and heat affected zone (HAZ) formed around the drilling zone. Reduction in microwave drilling time of approximately 80% was observed at 3 kW power compared to drilling time at 0.7 kW power. The HAZ observed in the samples drilled at 0.7 kW was significantly higher than the HAZ observed at 3 kW owing to higher drilling time of samples at 0.7 kW.

Methodology for the synthesis of methacrylate monomers using designed single mode microwave applicators

A novel single-well prototype high throughput microwave reactor geometry has been produced and shown to be capable of synthesizing an array of non-commercially available methacrylate monomers.

Periodical metal cylinders for improving heating uniformity of small batch materials in microwave applicators with rotating turntables

Microwave applicators with rotating turntables have been widely applied in many fields, but the heating non-uniformity still limits the further applications. Specifically, when microwave applicators are used to process small batch materials, materials have to be away from the center of rotating turntables, where the problem of heating non-uniformity is more prominent. In order to overcome this difficulty, this paper presents a novel periodical metal cylinder structure to improve the heating uniformity for microwave applicators. With the proposed periodical metal cylinders being placed beneath rotating turntables, electromagnetic fields can be well adjusted, thus improving the heating uniformity. To demonstrate the heating uniformity with the proposed structure, the heating process of the arrays of two and three potato slices in a practical microwave applicator is simulated by the finite element method, respectively. The results show that both the heating uniformity of the two and three potato slices can be improved, which is validated by experiments. Furthermore, the results show that the temperature similarity among the processed potato slices with the proposed structure is better than that without the proposed structure.