Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2013
Publication Date: 5/21/2013
Citation: Trabelsi, S., Nelson, S.0., Paz, A.M. 2013. Microwave dielectric method for the rapid, non-destructive determination of bulk density and moisture content of peanut hull pellets. Biosystems Engineering. 115(3):332-338. Interpretive Summary: Dielectric properties are electrical characteristics that determine how materials interact with electric fields such as those of high-frequency and microwave electromagnetic energy. Therefore, the dielectric properties of materials determine how rapidly they will heat in microwave ovens and lower radio-frequency dielectric heating equipment. Dielectric properties are also important in low power applications, such as the rapid measurement of moisture content in grain and other commodities. Biofuels are an attractive alternative source of energy to fossil fuels. Moisture content of solid biofuels is an important factor in pricing, conditioning for combustion, and storage management. This paper discusses the measurement of dielectric properties at microwave frequencies between 5 and 15 GHz for pelleted peanut hulls prepared as a biofuel. The moisture contents of the peanut-hull pellets were adjusted to various levels and their dielectric properties were measured from 4% to 13% moisture, as determined by standard methods, over ranges of bulk density and temperature. Analysis of the variations of the dielectric properties of the peanut-hull pellets with moisture content, bulk density, and temperature revealed that the dielectric properties can be used for microwave sensing of moisture content in peanut-hull pellets with accuracies of less than 0.5% moisture content. Simultaneously, bulk densities of peanut-hull pellets were determined from the microwave measurements with accuracies of about 3 percent. The new data on peanut-hull pellets are of interest to engineers and scientists working on biofuels applications. The microwave measurement method, based on dielectric properties sensing, offers promise for the monitoring of moisture and bulk density in biofuels processing and utilization and can improve the energy efficiency in such applications.
Technical Abstract: A dielectric-based method was used to determine rapidly and nondestructively moisture content and bulk density of peanut-hull pellets from free-space measurement of their dielectric properties at microwave frequencies. For moisture content determination, a permittivity-based function which allows moisture prediction from measurement of the dielectric properties at microwave frequencies independent of bulk density was used. For bulk density, an analytical expression was obtained from a representation of the dielectric properties in the complex plane. Results of moisture and density prediction from measurement of the dielectric properties are shown at 5 GHz, 10 GHz, and 15 GHz and 22 oC.