The Forgotten Dimension – Z Direction Drying Evaluation, 19PaperCon
Often a paper web is simply thought of as a two-dimensional object; with the machine (MD) and cross (CD) directions getting most of the attention. Papermaking behaviors in the third dimension, the thickness (ZD), have been studied in the forming and pressing sections, but the sheet in the drying section is often thought of as nothing more than a simple heat and mass transfer without consideration of the transient conditions in the sheet thickness. This paper investigates the heat transfer in the Z direction through the sheet in the dryer section utilizing observed behaviors and a simplified explicit transient heat conduction model.
Comparing common drying modeling approaches to the model developed to account for the Z direction highlights some of the mechanics behind why the standard drying calculations seem to be less accurate on thicker paper webs. Additionally, smoothing press and breaker stack applications are discussed and how their use may impact drying, which is much more than simply improving the contact of the sheet to the dryers.
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The Forgotten Dimension – Z Direction Drying Evaluation, 19PaperCon
