Drying Kinetics of Carrot Cubes by Infrared-Fluidized Bed Dryer

Among the various hot air drying methods, fluidized bed drying has significant advantages such as high heat and mass transfer, uniform moisture reduction of products with short time and high drying rate and uniform process at entire surface of the product due to efficient mixing with the drying air and high efficiency of process. In recent years, usage of infrared drying to dry food products has increased over conventional drying methods due to higher product quality, uniform heat distribution, high energy efficiency, high heat transfer rate and less processing time, facilitating the control of raw material temperature, reduced necessity for air flow across and the high ability to control process parameters in infrared heating. In this study, kinetics of carrot cubes drying by infrared-fluidized bed dryer were investigated.

Fresh carrot were washed with tap water and peeled manually then diced by dicer. To drying carrot cubes by combined infrared- fluidized bed method a laboratory scale dryer was designed and performed. In this study, drying of carrot cubes (0.5 and 1 cm3) was performed in factorial design experiments using air temperatures of 50, 60 and 70 °C and three levels of infrared power (200, 400 and 600 W) in three replications. To describing the infrared-fluidized bed drying behavior of carrot cubes, five mathematical models (Page, Modified Page, Henderson & Pabis, Midilli and Logarithmic) were evaluated.

The results demonstrated that the change in inlet air temperature, size of carrot cubes and infrared power had a significant effect (P <0.05) on water withdrawal from the sample and drying time decreased with increasing air temperature and infrared power and decreasing carrot cubes size. Therefore, the energy consumption was also reduced considerably, decreasing from 12.63 Kwh/kg in bed fluidized method (without infrared power) to 2.28 Kwh/kg using infrared -fluidized bed drying. The Page model was identified as the suitable model to describe the drying kinetics of carrot cubes by infrared-fluidized bed dryer that showed a good agreement with experimental data.

The statistical analysis of variance showed that air temperature, sample size and infrared power had a significant effect on water withdrawal rate of samples and therefore drying time. According to the results, using infrared-fluidized bed drying as a combined method in comparison with conventional hot air drying methods can reduce drying time and energy consumption and costs considerably.