Pressure drop in macroporous medium with forced air: calibration of the Ergun equation

Cooling is an important practice that extends the shelf life of fruit and vegetable products. The arrangement of these products for cooling is similar to a macroporous bed, where a cold fluid circulates between packed particles. The study of these systems is essential to estimate characteristic operation variables so that they can be suitably designed. The aim of this study was to evaluate the use of the Ergun equation in estimating the pressure drop in a forced-air cooling unit. As study geometry, a pipe 30.0 cm long and 15.5 cm in diameter, which was filled with Styrofoam spheres and subjected to experimental evaluation of pressure drop (ΔPexp) with various sphere diameters and mass air flux, was used. Void fraction, temperature and air density and viscosity were evaluated in each condition. The pressure drop was calculated with the Ergun equation (ΔPest) and the parameters of this model were calibrated through the MatLab® lsqnonlin.m subroutine, with which the adequate estimation of the packed bed was obtained. Based on geometry of packed objects, the results are applicable to fruit such as apples, oranges, peaches, lemons and plums, among others.