Porosity of flowing rice layer: Experiments and numerical simulation

Porosity is an essential characteristic parameter for the design optimisation of drying and its intelligent control since it can affect the drying behaviour, drying uniformity, drying efficiency, and energy consumption by altering the tortuosity of the medium, the effective evaporation area coefficient of the drying phase interface, and airflow resistance. To reveal the dynamic characteristics of the porosity of a flowing rice layer, experimental equipments for determining and validating the porosity were constructed based on mass conservation and the theory of poroelasticity, and a function of the porosity was established using response surface methodology and multivariate regression analysis. Three factors, namely, moisture content (12.64-33.37% w.b.), rice velocity (2.4 x 10 (3)-3.04 x 10 (2) m s(-1)), and depth of the rice layer (0.3-1 m) were studied to investigate the porosity of the flowing rice layer. Results indicated that porosity was significantly affected by moisture content, rice velocity, and depth of the rice layer. The measured values of porosity were in close agreement with that calculated using the fitted function, with a correlation coefficient of 0.997. The function was validated by comparing the values measured with the theoretical values calculated using the function of porosity and the Ergun equation, and an average relative difference of 5.33% was obtained. (C) 2018 IAgrE. Published by Elsevier Ltd. All rights reserved.