Investigation of Heat Transfer in Combined Infrared-Hot Air Drying: A Strategy for Evaluation in Potato Food Model

Abstract

The simultaneous heat and mass transfer in the drying processes is a complicated unit operation. In the present study, the modelling of heat and mass transfer was conducted via investigating temperature distribution and moisture content along with calculating the heat and mass transfer coefficients during the combined infrared-hot air drying (IR-HAD) in the potato food model. The potato drying process was done with cylindrical cutting geometry (disc form) and through the recording of temperature changes in the samples during the process. The selected radiation intensity for this process was 400 and 800 W. Then three-channel thermocouples were placed in the centre, surface, and between these two points in the radius direction of the sample to record the temperature changes during the process. The sample temperature was recorded by a data logger at 200-s intervals. The results of the temperature recording indicated that temperature changes were significant in different parts of the sample along the radius. Mass and heat transfer coefficients, including the convective heat transfer coefficient (\({h}\)), were calculated to be 5.32 and 9.98 W/m².K; similarly, the effective moisture diffusivity \({(D}_{eff})\) was measured to be 5.18 × 10⁻⁸ and 9.93 × 10⁻⁸ m²/s, and the mass transfer coefficient \(({h}_{m })\) persisted at 0.005 and 0.010 m/s. An approximate doubling of the calculated coefficients was also observed by doubling the intensity of the radiation. The convective heat transfer coefficient has been introduced as the most important index in transport phenomena modelling and it is also applied in software simulation. Mathematical equations for the moisture transfer by Fick’s law and the heat transfer equation by Fourier’s law were solved using numerical methods and the results were applied in the computational simulation by COMSOL Multiphysics (5,3a). Then resulted profiles were also compared to simulated fried potato profiles. This simulation can help to control the temperature of the sample and it is further useful for quality control by reducing the moisture content.