Investigation of radiation-convective drying of potato wafers with a variable heat supply

Abstract

As a result of research and analysis of kinetic dependencies of the pulsed radiation-convective drying process of potato slices under stationary conditions, a step-by-step regime for drying root crops was developed. Potatoes slices are subjected by combined radiation-convective drying. Moreover, the heating of the potato is carried out by infra-red rays with a wavelength in the range 1.16–1.65 mkm and a heat flux density of 2.69-5.44 kW/m2 with simultaneous convective air blowing for water vapor evaporated from the product removal with initial temperature of the environment 293 K. Stepwise regime essence is as follows. Total drying process duration is divided into a certain number of stages. Durations of each time step was determined experimentally as a result of drying and drying rate curves analysis potato tubers stationary drying regimes. At each stage a fixed value of product temperature and air speed is selected. At the graphical dependencies analysis it is possible to distinguish three drying periods: heating, constant and decreasing drying rate. At the first stage potato slices 1.5 mm thick are heated by infrared rays up to 318 K temperature with simultaneous airflow with speed of 1.6 m/s for 6 minutes; at the second stage-up to 323 K temperature with air speed 1.2 m/s for 18 minutes; at the third stage-up to 328 K temperature and with air speed 0.7 m/s for 12 minutes. Later dried to a final 12% humidity potato slices are processed with flavoring (spices).