Double-ridged waveguide for efficiently heating ultrafine filament fibers

Microwave heating has attracted wide attention in fiber dyeing, refining, drying and modification due to its energy saving and environmental protection. However, effectively heating ultrafine filament fibers is difficult to achieve using conventional microwave heating devices because of their low power density and rapid heat dissipation at their surfaces. Thus, we designed a double-ridged waveguide operating at 2.45 GHz, facilitating rapid heating of ultrafine structure by increasing the electric field strength, subse-quently causing higher power absorption by the ultrafine materials. First, the proposed waveguide was compared with other types of cavities by building a multiphysics model, incorporating electromagnetics and heat conduction of the heated filament fiber with a relative permittivity of 5.7-0.2j and a diame-ter of 0.008 times of the wavelength of vacuum. The electric field strength and power absorbed of the filament fiber located in the proposed ridged waveguide were approximately 13.3 and 180 times higher than that in WR430, a commonly used rectangular waveguide in system designs. Additionally, we built an experimental system to demonstrate that the design can efficiently heat a single filament fiber at low input power of 70 W. Furthermore, the effects of the filament fiber size, material permittivity, and cavity temperature on heating were investigated based on the constructed model.(c) 2022 Elsevier Ltd. All rights reserved.