Uniformity Issue in Microwave Drying

Microwave-Assisted Spouted Bed Drying of Lettuce Cubes

“…Uneven drying may result in nonuniform moisture distribution in the drying material and=or nonuniform distribution of the electromagnetic field in the microwave cavity. [31] In this study, the four microwave generators were evenly distributed in the cavity, and the effect of nonuniform distribution of the electromagnetic field in the microwave cavity was reduced. When the samples were drying, hot air was spouted to the samples from the bottom by the swirling rings, to ensure that uniform particle circulation in the spouted bed was maintained, and the effect of nonuniform moisture distribution on the drying material was reduced as well.…”

Finite Element Analysis of Mode Stirrer Impact on Electric Field Uniformity in a Microwave Applicator

“…[7] This is a negative phenomenon because it can result in further material processing problems, including health hazards in the case of food. [8] That is one of the reasons why research has concentrated on uniformity problems from the beginning of MW use; for instance, Watanabe et al [9] and Watanabe and Suzuki [10] analytically computed the distribution of power density and electric field (EF) within a microwave applicator; Kayshyap and Wyslouzil [11] successfully used a multi-slot waveguide system to increase EM field uniformity; Risman et al [12] analyzed factors influencing the EM uniformity in an applicator and, most recently, these problems have been analyzed in review of Li et al [13] Li et al [13] also present two main approaches that can partly reduce the EM field non-uniformity. The first is to continually displace the material in the applicator during the MW application process.…”

“…[7,[16][17][18] The second, which is more relevant to our work, is based on increasing or changing coordinates of nodes and antinodes of the EM field. [13] To accomplish this we can use several techniques: a) to increase the number of waveguide ports in an applicator; b) to use a combination of different sources of EM with different frequencies, for instance to combine MWs with infrared or convective heating [19][20][21][22] ; c) to vary frequency of MWs [11,23] ; d) to use a moveable source of MWs [24] ; and e) to install EM field mode stirrers inside the applicator. [25] Mode stirrers are devices that mechanically change reflection conditions (geometrical configuration) as they move during the application of MWs.…”

Effects of Magnetron Arrangement and Power Combination of Microwave on Drying Uniformity of Carrot

“…This improvement not only expands the application of microwave drying but gradually improves the technology to alleviate process and equipment constraints. [1] These innovative combining techniques have been widely used in drying pumpkin, [7] jujube, [8] purple sweet potato, [9] apple, [10] lettuce cubes, [11] carrot, [12] and mushrooms. [13] Though microwave heating is widely used, it has a significant disadvantage of hot spots depending on sample geometry [1,14,15] due to its nonuniformity of heating.…”

“…[1] Many agricultural products (e.g., carrot, [2] sweet potato, [3] etc.) have been microwave dried for decades.…”