Date of Award
The paper industry provides important consumer products comprised of paper, tissue, paper board, and pulping. The papermaking process requires a lot of energy, in the form of steam, to dry the paper web in rotating dryers. As steam condenses inside the dryers by releasing heat to the dryer walls, the condensate is removed using either stationary or rotary siphons. Since the condensate is usually at a saturated state, part of the condensate flashes into vapor during the extraction process and becomes difficult to extract. Thus, additional blow-through steam is used to push the condensate out. Since this blow-through steam is not used for drying, it is deemed a waste of energy. The objectives of this project are to conduct computational and experimental investigation to understand the fundamental physics of the two-phase flow behavior during condensate extraction process to find means of minimizing or completely removing the blow-off steam and thus significantly saving energy.
The project is focused on four areas: (a) investigating three two-phase modeling methods—Volume of Fluid (VOF), Mixture, and Eulerian-Eulerian (E-E)—to simulate condensate rimming behavior in a rotating cylinder, (b) developing a two-phase flow computational model to simulate the condensate flashing and re-condensation phenomena inside a siphon, (c) constructing an experimental test bench to study the maximum void fraction that can be sustained in a cold natural siphon flow and to find various means for repriming the siphon, (d) constructing a boil water experiment to investigate if the natural siphon principle holds valid with hot water flashing under actual operating conditions, (e) investigating the heating uniformity inside a rotating dryer under the influence of steam injection distribution, steam condensation, and conjugate heat transfer with the paper web cover part of the dryer.
The results show that (a) up to 70% void fraction can be sustained in a natural siphon, (b) the natural siphoning of hot saturated water can be sustained even with flashing, (c) condensate rimming has been successfully simulated with all three models and the results are consistent with experimental data, (d) a two-phase flow model successfully predicts the alternating flashing-recondensation phenomenon in the two-phase siphon flow, and (e) the heat transfer uniformity of the dryer is predicted.
Majeed, Hamed Abdul, "Investigation of Two-Phase Flow Phenomena in Rotating Paper Dryer to Achieve Effective Heat Transfer with Low Energy Consumption" (2021). University of New Orleans Theses and Dissertations. 2868.
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