Modeling the influence of forming fabric structure on vacuum box dewatering

Sjöstrand, Björn; Barbier, Christophe; Nilsson, Lennart

doi:10.32964/tj16.8.477

Cited by 6 publications

(14 citation statements)

References 5 publications

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“…The logged pressure drops of the vacuum dewatering test were used to calculate the air volume that passed through the sheet using Eq. 1 (Granevald et al 2004;Sjöstrand et al 2016). The air volume for TAD sheets consists of the forming fabric dewatering air volume for 20 ms, added with the respective TAD dewatering air volume, because these sheets effectively are dewatered twice.…”

Section: Methodsmentioning

confidence: 99%

Method for studying water removal and air penetration during through air drying of tissue in laboratory scale

Sjöstrand

Danielsson

Lestelius

2023

BioRes

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Energy use, together with consumption of raw materials, machine clothing, and wet end chemicals, are some of the most critical aspects in successful tissue making today. This work was aimed at developing a laboratory-scale method of estimating dewatering mechanisms, vacuum efficiency, and energy use of Through Air Drying (TAD) of tissue. When compared to pilot data, the results of the new laboratory method for investigating dewatering during TAD were in the same magnitude, around 24 to 26% dryness after vacuum dewatering, and 27 to 29% dryness after TAD molding. Sheet properties, such as caliper and surface profile, were evaluated and compared to commercial tissue sheets. The results indicate that it will be possible to precisely measure accurate dryness development and penetrated air volume for tissue sheet forming and TAD molding at a laboratory scale. This can contribute to the efforts of implementing a circular forest-based bioeconomy by increasing the fundamental understanding of dewatering of tissue paper materials, which is facilitated by improvements in energy use. The new method developed in this work will make it easier to assess ideas that are difficult to bring to pilot scale or full scale before learning more of the dewatering capabilities. The authors are convinced that improved knowledge of tissue dewatering mechanisms, forming, and material transport during and after TAD dewatering can increase the efficiency of the industrial manufacturing processes.

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Section: Methodsmentioning

confidence: 99%

Method for studying water removal and air penetration during through air drying of tissue in laboratory scale

Sjöstrand

Danielsson

Lestelius

2023

BioRes

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“…Some of the calculated Reynolds numbers are much higher than 2, and a few are below 1, for the experimental data behind the air volume models. [23] Flow models used in [11] are based on an extension of Darcy's law [12] where the range of Reynolds numbers is much broader due to the introduction of a non-linear term. Equation ( 2) is therefore modified into Equation ( 10) based,…”

Section: Air Volume Modelmentioning

confidence: 99%

“…where a is a fitting parameter. With the same derivation as for Equation ( 9), using Equations ( 5) through 8, but starting with Equation (10) instead of Equation ( 2), an updated model for air penetration is deduced and shown in Equation (11). Equation (11) has the advantage of describing flow for high Reynolds numbers as well as for low.…”

Section: Air Volume Modelmentioning

confidence: 99%

“…The model predicts most accurate with higher sheet grammage where the flow rate is lower. A combination of this air volume model and the work on modeling in Sj€ ostrand et al [11] where a quadratic term is included in the relationship between vacuum level and flow rate. This is the foundation of the updated air volume model (Equation ( 11)).…”

Section: Air Volume Modelmentioning

confidence: 99%

“…Sj€ ostrand et al [11] used COMSOL Multiphysics to investigate forming fabric influence on vacuum dewatering, much like Rezk et al. [7] Single-phase models of airflow through fabrics were successfully made with Ergun's [12] flow through porous media.…”

Section: Introductionmentioning

confidence: 99%

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Numerical model of water removal and air penetration during vacuum dewatering

Sjöstrand

Nilsson

Ullsten³

et al. 2020

Drying Technology

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Dewatering and air flow in high vacuum suction boxes was examined. The work was mainly numerical and was based on, and compared with, previously published experimental results of vacuum dewatering from laboratory equipment and from a pilot paper machine. A previously published numerical model for wet pressing is used as the basis for this work. The aims of this study were to find new fitting parameters that allows the previous model to be used for vacuum dewatering instead of pressing, and to examine two extensions to the original model. The results indicate that the new vacuum dewatering model for moisture can predict the dewatering behavior for several different experimental data series both from laboratory equipment and a pilot paper machine using the same set of fitting parameters. Two different numerical models for air flow through the paper sheet, during vacuum dewatering, were developed based on postulating that the decrease in moisture permeability is accompanied by a simultaneous increase in air permeability. The models for air flow can also be fitted to experimental data and predict the magnitudes of air flow during vacuum dewatering. The data sets for air flow exhibit a certain degree of operator dependence though, so that one set of fitting parameters is not enough for obtaining good agreement with all data sets.

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