Modelling and simulation of cross flow grain dryers

• Mathematical model and software for simulating multiple-stage cross flow dryers.
• Non uniformity of output temperature and humidity depends strongly on dryer design.
• Reversing of airflow direction equalises distribution of parameters across the dryer.
• Air humidity increase due to reuse of air on the dryer performance can be neglected.
• Upward motion of the reuse air gives higher energy saving than downwards.

A mathematical model, algorithm, and computer program were developed to simulate the performance of cross flow grain dryers and cross flow dryers with energy saving. The mass and heat transfer processes were described by a system of four non-linear partial differential equations. This system of equations was solved by the MacCormack method with time splitting. The Neumann method was used to determine convergence. The source-terms in these equations were computed by auxiliary semi-empirical equations obtained by experimental data from thin layer drying. Equipment developed to obtain these data permitted variation of the initial air humidity, temperature, and velocity. Fixed bed drying experiments were conducted to validate the model. Simulations using various control regimens were made to determine the impact on energy consumption and cross flow dryer performance due to recycling air exhausted from various stages of the dryer. An iterative process was used to determine the initial conditions at the entrance to each section of the dryer. The computer simulations were used to evaluate the non-uniformity of temperature and grain moisture content distributions in dryers, the duration of the drying process and the energy efficiency for each geometry and control regimen.