ABSORPTION OF INFRARED RADIATION AND THE RADIATION TRANSFER MECHANISMIN PAPER - PART I - THEORETICAL-MODEL

Infrared dryers, both gas fired and electrically healed, have become a widespread technology in the paper industry. This work proposes a mod el for the absorption of thermal radiation in the thickness direction of a paper sheet. The model is based on the multilayer idealization of a paper sheet proposed by Scallan and Porch. In this model, the optic al properties of paper are considered as the result of multiple reflec tions and transmission processes between the layers in the paper sheet . Measurements on a number of commercial paper grades indicate that th e basis weight per layer is close to 4 g/m(2). The model parameters, t he reflectivity and transmissivity of a single layer; have been fitted to experimental literature data for the reflectivity and transmissivi ty of paper at different wavelengths, basis weights and moisture conte nts. In Part II of this work, the model will be used to study the abso rption of thermal radiation in the thickness direction of a paper shee t during infrared drying.