An experimental study of moisture uptake and transport in a bed of urea particles

Abstract

Urea, a widely used nitrogen fertilizer, is susceptible to moisture adsorption from ambient air which leads to caking and handling problems. Scanning Electron Microscopy (SEM) images of a nearly spherical urea particle and a fractured cross-sectional area of a urea particle show internal porosity and external surface roughness. BET test analysis indicates that the internal surface area available for water vapour adsorption is comparable to, or larger than, the external surface area of urea particles. In this research, experiments were undertaken to obtain the transient response of a packed and initially dry porous urea bed after humid air starts to flow slowly through the bed. The experimental data for local and total bed moisture content shows that the internal moisture diffusion inside the porous urea particles is a very slow process which limits the rate of moisture accumulation in the bed.