The drying time required for complete dehydration of the carrot samples (water content: 12–13%, d.b.) with the USV technique at 65 °C and 75 °C was determined to be about 5.0 h and 2.5 h, respectively (Fig. 2). Among the drying techniques used in this study, the shortest drying period was observed for the USV drying technique performed at 75 °C, which was approximately 2.4 times quicker than the vacuum drying techniques (about 5.6 h, 75 °C) for the carrot samples. As mentioned above, compared to the vacuum drying, USV drying significantly reduced the drying time. Employment of ultrasound modified the diffusion boundary layer due to pressure variations, oscillating viscosities, and internal effects [22]. This modification can be explained by the characteristics of acoustic waves that are mechanical waves requiring a material medium to propagate. In solid materials, alternative compressions and expansions generated by the ultrasonic waves produce a similar effect to that observed when a sponge is squeezed and released repeatedly [23] and [24]. This “sponge effect’’ produces the release of a liquid from the inner part of the particle to the solid surface and the entry of fluid from outside [23]. The forces involved in this mechanism are generally greater than the surface tension, which maintains the water molecules inside the capillaries of the material, creating microscopic channels and facilitating the transformation of matter [25]. All of the factors mentioned above influence the internal resistance to mass transfer [26]. Ultrasound treatment can also increase the heat transfer coefficient [27], which can also accelerate the removal of moisture from the sample due to a higher heat transfer.
As seen in Table 2, the differences in drying time between the USV and the vacuum techniques decreased as the drying temperature increased. Decreasing the drying period is very important for the food industry, especially for products that contain thermolabile substances. Experimentally obtained data for drying time versus MR by drying carrot samples using different techniques at various temperatures were modeled with 10 different models. The equations and related parameters correlated with these models are presented in Table 1. The Wang and Singh model (MR = 1 + a·t + b·t2) exhibited the best fit for the obtained drying data (time versus MR). As seen from the Table 2, the R2 values were larger than 0.99, indicating a good fit since an R2 value close to unity implies that the predicted data were near the experimental drying data. This signifies that all established models successfully described the relation between time and MR. Obtaining drying kinetics data and their modeling are necessary to design, simulate, and optimize the drying process or equipment.
The drying time required for complete dehydration of the carrot samples (water content: 12–13%, d.b.) with the USV technique at 65 °C and 75 °C was determined to be about 5.0 h and 2.5 h, respectively (Fig. 2). Among the drying techniques used in this study, the shortest drying period was observed for the USV drying technique performed at 75 °C, which was approximately 2.4 times quicker than the vacuum drying techniques (about 5.6 h, 75 °C) for the carrot samples. As mentioned above, compared to the vacuum drying, USV drying significantly reduced the drying time. Employment of ultrasound modified the diffusion boundary layer due to pressure variations, oscillating viscosities, and internal effects [22]. This modification can be explained by the characteristics of acoustic waves that are mechanical waves requiring a material medium to propagate. In solid materials, alternative compressions and expansions generated by the ultrasonic waves produce a similar effect to that observed when a sponge is squeezed and released repeatedly [23] and [24]. This “sponge effect’’ produces the release of a liquid from the inner part of the particle to the solid surface and the entry of fluid from outside [23]. The forces involved in this mechanism are generally greater than the surface tension, which maintains the water molecules inside the capillaries of the material, creating microscopic channels and facilitating the transformation of matter [25]. All of the factors mentioned above influence the internal resistance to mass transfer [26]. Ultrasound treatment can also increase the heat transfer coefficient [27], which can also accelerate the removal of moisture from the sample due to a higher heat transfer.As seen in Table 2, the differences in drying time between the USV and the vacuum techniques decreased as the drying temperature increased. Decreasing the drying period is very important for the food industry, especially for products that contain thermolabile substances. Experimentally obtained data for drying time versus MR by drying carrot samples using different techniques at various temperatures were modeled with 10 different models. The equations and related parameters correlated with these models are presented in Table 1. The Wang and Singh model (MR = 1 + a·t + b·t2) exhibited the best fit for the obtained drying data (time versus MR). As seen from the Table 2, the R2 values were larger than 0.99, indicating a good fit since an R2 value close to unity implies that the predicted data were near the experimental drying data. This signifies that all established models successfully described the relation between time and MR. Obtaining drying kinetics data and their modeling are necessary to design, simulate, and optimize the drying process or equipment.
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