Abstract:ResumoDurante o aquecimento dielétrico, a distribuição do campo elétrico dentro de uma cavidade ocorre a partir de uma propagação multimodal, ocasionada por inúmeras refl exões das micro-ondas provenientes das paredes metálicas da cavidade. Essas refl exões múltiplas geram regiões de maior e menor intensidade de campo elétrico no espaço e, por consequência, um aquecimento não uniforme no produto. O objetivo deste estudo foi o levantamento dos valores de temperaturas obtidos durante o tratamento térmico por mic… Show more
“…A literature review has shown that several studies have been conducted on microwave drying. The studies are related to the production of husked cherry coffee (Cunha, Canto, & Marsaioli, 2003), coconut husk (Valadez-Carmona, Cortez-García, Plazola-Jacinto, Necoechea-Mondrágon, & Ortiz-Moreno, 2016), dried carrots (Béttega et al, 2014), strawberries (Böhm, Kühnert, Rohm, & Scholze, 2006), macadamia nuts (Silva, Maximo, Marsaioli, & Silva, 2007), and granulated solids (Berteli, Nogueira, & Marsaioli, 2015). However, there is a lack of studies on the microwave drying of Araucaria seeds.…”
Microwave drying has shorter processing times compared with convection drying, which results in high-quality products and reduced energy consumption. The objective of this study is to evaluate the drying process of Araucaria angustifolia seeds using hot air at atmospheric pressure by applying microwaves (300 W and 500 W), and comparing them with the conventional drying process using hot air (80 °C). The drying time using hot air with microwaves at 500 W and 300 W was reduced by 83.33% and 73.89%, respectively, compared with conventional drying. The drying process occurred in the transient regime, with the predominance of a period of decreasing drying rate. The internal temperature of Araucaria seeds increased with the exposure time to the drying process, whereas the moisture content decreased. This tendency was greater for seeds subjected to electromagnetic fields, especially those exposed to higher power. The total phenolic compounds (TPCs) were lower by microwave drying when compared with conventional drying. The TPC loss was influenced by the internal temperature of the seed. Alternative methods to promote the increased retention of phenolic compounds during the drying process include decreasing the microwave power before the end of drying, combining traditional microwave-associated drying methods, and controlling the applied microwave power.
“…A literature review has shown that several studies have been conducted on microwave drying. The studies are related to the production of husked cherry coffee (Cunha, Canto, & Marsaioli, 2003), coconut husk (Valadez-Carmona, Cortez-García, Plazola-Jacinto, Necoechea-Mondrágon, & Ortiz-Moreno, 2016), dried carrots (Béttega et al, 2014), strawberries (Böhm, Kühnert, Rohm, & Scholze, 2006), macadamia nuts (Silva, Maximo, Marsaioli, & Silva, 2007), and granulated solids (Berteli, Nogueira, & Marsaioli, 2015). However, there is a lack of studies on the microwave drying of Araucaria seeds.…”
Microwave drying has shorter processing times compared with convection drying, which results in high-quality products and reduced energy consumption. The objective of this study is to evaluate the drying process of Araucaria angustifolia seeds using hot air at atmospheric pressure by applying microwaves (300 W and 500 W), and comparing them with the conventional drying process using hot air (80 °C). The drying time using hot air with microwaves at 500 W and 300 W was reduced by 83.33% and 73.89%, respectively, compared with conventional drying. The drying process occurred in the transient regime, with the predominance of a period of decreasing drying rate. The internal temperature of Araucaria seeds increased with the exposure time to the drying process, whereas the moisture content decreased. This tendency was greater for seeds subjected to electromagnetic fields, especially those exposed to higher power. The total phenolic compounds (TPCs) were lower by microwave drying when compared with conventional drying. The TPC loss was influenced by the internal temperature of the seed. Alternative methods to promote the increased retention of phenolic compounds during the drying process include decreasing the microwave power before the end of drying, combining traditional microwave-associated drying methods, and controlling the applied microwave power.
This work aims to experimentally study the drying of agricultural products using microwaves, with particular reference to grains. Microwave drying experiments were carried out with paddy rice grains in natura (BRSMG Conai variety) for three levels of incident microwave power per mass of fresh grain (6.27, 14.63 and 22.99 W/g). Results of grain drying and heating kinetics are presented and analyzed. It was verified that the ideal average moisture content for grain storage and marketing, 15% (d.b.), occurred at 20 min (6.27 W/g), 13 min (14.63 W/g) and 7 min (22.99 W/g), and that the equilibrium moisture content of the samples reached 4.4%, 2.7% and 1.9%, at 310, 180 and 110 min, for each of the three power levels studied, respectively. The drying with the highest absorbed power caused discoloration of the grains at the end of the drying process.
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