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Design of a mixer for uniform heating of particulate solids in microwave ovens

Çevik, Mete
The aim of this study is to design a mixer with appropriate parts for uniform treatment of the material in household microwave ovens which can not be achieved with the turntable. The designed mixer’s performance was tested by the help of color and surface temperature values. In the design of the mixer primarily mixing in the vertical and radial directions were sought and for this purpose blades and wings for directing the material especially in these directions were present. The rotational motion of the mixer was provided by a shaft actuated by the motor of the turntable where the motor was replaced by a speed adjustable one. Couscous macaroni beads wetted with CoCl2 solution were dried for processing in the microwave oven. The initial color values of the samples were L*= 52.0±0.35, a*= 8.8±0.21 and b*= 14.1±0.11 . The studied parameters were microwave power level (10%, 40%, 67% and 100% ), processing time (60,90, 120 sec), speed of rotation of the mixer (5,10,15 rpm) , location (4up, 4bt, 6up, 6bt) for the cases of with and without the mixer. v The macaroni beads were well arranged in a mixing container and then put into the microwave oven for operation. Same parameters with coloring experiments were used for the surface temperature determination. After operation the container was photographed by an IR camera. Whether the designed mixer was present or not, average a* and b* values decreased while temperature increased . All these values were significantly affected by the time and power increase. The L* value became an insignificant parameter to decide for the performance Location of the particles in the container appeared as a significant parameter affecting the a*, b* and temperature values without the mixer whereas, with the use of the mixer it became an insignificant parameter indicating uniform energy distribution. Speed of rotation of the mixer was a significant parameter for both cases. However, the color values obtained did not show the same trend with mixer which it showed without mixer. It is concluded that the designed mixer is effective in providing homogeneity of the product by providing sufficient mixing in the container hence the particles can receive about equal energy. Keywords: Microwave oven, particulate solids, mixing, mixer design, testing performance, uniform treatment.