Abonnement à la biblothèque: Guest

ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

A NUMERICAL STUDY OF DRYING AND PREHEATING OF FOOD IN A ROTARY DRYER WITH SUPERHEATED STEAM AND AIR AS THE DRYING MEDIA

Get access (open in a dialog) DOI: 10.1615/IHTC16.cms.023036
pages 1719-1725

Résumé

This paper presents a numerical study of drying and preheating of apple and carrot pieces in a rotary dryer with superheated steam (Case I), dry air (Case II), and humid air with 20% moisture and 80% dry air by volume (Case III) at 1 bar as the drying media. The initial water content is 19% with respect to dry solids (by weight). The solids inlet and exit temperatures are 288.6 K and 413 K, respectively. The gas exit temperature is 416 K. The thermal model includes turbulent convection heat transfer from the gas to the refractory wall and solids, and radiation exchange among the gas, refractory wall and the solid surface, conduction in the refractory wall, and mass and energy balances of the gas and the solids. Finite-difference techniques are used and steady state conditions are assumed. False Transient Method is used to solve the wall conduction equation. The solution is initiated at the inlet of the kiln and proceeds to the exit. The direction of gas flow is opposite to that of the solids. The inlet temperature of the superheated steam (Case I) predicted by the present model is 512.8 K for apple, as compared to 460 K, calculated by Sinhal et al. (2012). The deviation may be attributed to the curvature effect of the kiln considered in the present model in contrast with Sinhal et al. (2012) which used Cartesian coordinate system. The predicted kiln length for both the models is 93.6 m for apple drying. Interestingly, it is found that for apple drying with superheated steam there is an optimum kiln inner diameter at which the kiln length is highest. It is also observed from the model predictions that, out of the three media, that is, superheated steam, dry air and humid air, dry air is the most effective drying medium from the point of view of economy as it gives rise to requirement of least kiln length and lowest gas inlet temperature.