Convective Air Drying Characteristics for Thin Layer Carrots
Abstract
Introduction: Carrot is one of the most commonly used vegetables for human nutrition due to high vitamin and fibre content. Drying is one of the oldest methods of food preservation, and it represents a very important aspect of food processing. Sun drying is the most common method used to preserve agricultural products in most tropical countries; this technique is extremely weather dependent, and has the problems of contamination with dust, soil, sand particles and insects. Also, the required drying time can be quite long. Therefore, using solar and hot-air dryers, which are far more rapid, providing uniformity and hygiene are inevitable for industrial food drying processes. Aim: This paper presents a kinetic study of convective drying without pre-treatment of carrot. The effects of the temperature of the drying agent, the speed of the drying agent and the thickness of the kinetics of drying the sample of carrots were investigated. Materials and methods: The experiments were carried out with the aid of an installation for drying food products, that is capable of ensuring the temperature of the drying agent (air) in the range of +25 ... +125 °C. The drying process was conducted at temperature of 45 °C in first hour of process, 2 hours at 55 °C, and 3 hours at 60 °C. The air velocity was setup at 1.0 - 2.5 m/s. Carrots were divided into segments of a thickness of 0.4 cm. Two mathematical models available in the literature were fitted to the experimental data. Results: The drying rate increases with temperature and decreases with the sample diameter. The Page model is given better prediction than the Henderson and Pabis model and satisfactorily described drying characteristics of carrot slices. Conclusions: The most important characteristics of carrot required for simulation and optimization of the drying were studied. The values of calculated effective diffusivity for drying at 45, 55 and 60oC of air temperature and 1.0, 1.5, 2.0 and 2.5 m/s of air flow velocity. The effective diffusivity increases as air-flow rate and temperature increases. Page’s empirical model showed a good fit curves than the Henderson and Pabis model.
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