| 1. |
|
|
| 2. |
- Ottosson, Anders, 1978-, et al.
(författare)
-
A mathematical model of heat and mass transfer in Yankee drying of tissue
- 2017
-
Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 35:3, s. 323-334
-
Tidskriftsartikel (refereegranskat)abstract
- Final dewatering in the production of dry creped tissue is performed by Yankee drying, which includes hot pressing followed by simultaneous contact and impingement drying. The present study models Yankee drying and compares simulation results to the data obtained from trials on a pilot tissue machine. It advances models published previously by the representations developed for the transport of heat in the pressing stage and for the heat transfer involved in the dehydration of the cylinder coating spray. The model predicts an average specific drying rate within 4% in the range of the experimental data used.
|
|
| 3. |
|
|
| 4. |
- Rezk, Kamal, 1983-, et al.
(författare)
-
Characterizing flow resistance in 3-dimensional disordered fibrous structures based on Forchheimer coefficients for a wide range of Reynolds numbers
- 2016
-
Ingår i: Applied Mathematical Modelling. - : Elsevier. - 0307-904X .- 1872-8480. ; 40:21-22, s. 8898-8911
-
Tidskriftsartikel (refereegranskat)abstract
- The flow resistance in 3-dimensional fibrous structures are investigated in particle Reynolds number representing flow characteristics with strong inertia. The resistance coefficients are established based on steady state simulations of single-phase processes of water numerically. An automatized simulation process in COMSOL is developed with a MATLAB algorithm in which production runs could be carried for various 3-dimensional fibrous structures. Simulation of flow processes ranging from Reynolds numbers at creeping flow levels to high Reynolds number at approximately 1000 are calculated and a numerical data set is established in order to estimate Forchheimer coefficients which are used to correlate a dimensionless friction factor to a modified Reynolds expression for porous media.The friction factor and dimensionless permeability are calculated for fibrous structures with (i) disordered unidirectional fibers (ii) an isotropic fiber orientation in-plane perpendicular to the flow, and (iii) an isotropic fiber structure in a the 3-dimensional space. Empirical correlations of the friction factor and Reynolds number are used to compare our simulation data in order to assess the validity of our models and flow resistance estimations. The dimensionless permeability is moreover compared to other numerical simulations of flow through fibrous structures in order to assess flow resistance at low Reynolds number.It is concluded that flow resistance in the isotropic fiber arrangement in space is lower than the in-plane isotropic orientation and disordered unidirectional fiber arrangements at creeping flow conditions, however, all friction actors converges towards the same value at higher Reynolds numbers indicating that fiber orientation is independent at high inertia flow regimes. Overall, our numerical simulations agree well to classical empirical formulations for a wide range of Reynolds number. However, the comparison differs considerably depending on the porosity level.
|
|
| 5. |
- Rezk, Kamal, 1983-, et al.
(författare)
-
Modelling of water removal during a paper vacuum dewatering process using a Level-Set method
- 2013
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 101, s. 543-553
-
Tidskriftsartikel (refereegranskat)abstract
- Water removal in paper manufacturing is an energy-intensive process. The dewatering process generally consists of four stages of which the first three stages include mechanical water removal through gravity filtration, vacuum dewatering and wet pressing. In the fourth stage, water is removed thermally, which is the most expensive stage in terms of energy use.In order to analyse water removal during a vacuum dewatering process, a numerical model was created by using a Level-Set method. Various different 2D structures of the paper model were created in MATLAB code with randomly positioned circular fibres with identical orientation. The model considers the influence of the forming fabric which supports the paper sheet during the dewatering process, by using volume forces to represent flow resistance in the momentum equation.The models were used to estimate the dry content of the porous structure for various dwell times. The relation between dry content and dwell time was compared to laboratory data for paper sheets with basis weights of 20 and 50 g/m2 exposed to vacuum levels between 20 kPa and 60 kPa. The comparison showed reasonable results for dewatering and air flow rates. The random positioning of the fibres influences the dewatering rate slightly. In order to achieve more accurate comparisons, the random orientation of the fibres needs to be considered, as well as the deformation and displacement of the fibres during the dewatering process.
|
|
| 6. |
- Rezk, Kamal, 1983-, et al.
(författare)
-
Simulation of water removal in paper based on a 2D Level-Set model coupled with volume forces representing fluid resistance in 3D fiber distribution
- 2015
-
Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 33:5, s. 605-615
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical model of a vacuum dewatering process was established with a Level-Set method to simulate two-phase flow in a 2-dimensional paper sheet model with constructed volume forces representing flow resistance in a 3-dimensional environment. Nine cases of various volume force representations were compared to numerical and experimental data. Based on the dry content and dwell time relation, the case with the influence of the paper/wire interface showed the most pleasing result compared to experimental data. Compared to the other numerical cases, considering the blockage of the pore space at the top layer of the forming fabric plays an essential role in determining the flow resistance during the vacuum process. Also, the dynamics of the dewatering rate is captured well with the influence of the blockage of fibers on the top layer of the forming fabric. The peak of the dewatering rate could be investigated further with a higher frequency of sample points on new experimental data.The computational time for the two-phase flow models in this study is extensively reduced due to the removal of the internal structure. This distinction enables time efficient simulations of vacuum dewatering process in which several dewatering parameters such as level of vacuum, influence of moving vacuum pulse and higher basis weights could be investigated.
|
|
| 7. |
|
|
| 8. |
- Anukam, Anthony, et al.
(författare)
-
A comparative analysis of the gasification performances of torrefied and untorrefied bagasse : Influence of feed size, gasifier design and operating variables on gasification efficiency
- 2018
-
Ingår i: International Journal of Engineering & Technology. - : Science Publishing Corporation. - 2227-524X. ; 7:2, s. 859-867
-
Tidskriftsartikel (refereegranskat)abstract
- This study conducted a comparative assessment of the gasification performances of torrefied and untorrefied bagasse with emphasis on feed size, gasifier design and operating conditions that would influence gasification efficiency. Torrefaction greatly improved the characteristics of bagasse and had significant impact on its gasification performance. The gasifier design parameters studied were throat angle and throat diameter. Temperature of input air and feed input were the gasifier operating conditions examined in the course of the gasification processes of both torrefied and untorrefied bagasse. These parameters were considered the most critical operating parameters that affect gasifier performance and, correlation between the parameters was established in the course of gasification. The results obtained showed higher gasification efficiency for torrefied bagasse in comparison to untorrefied bagasse under varied conditions of gasification, which was attributed mainly to changes in the characteristics of the torrefied material.
|
|
| 9. |
- Anukam, Anthony, et al.
(författare)
-
A review of the mechanism of bonding in densified biomass pellets
- 2021
-
Ingår i: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 148
-
Tidskriftsartikel (refereegranskat)abstract
- The production of durable biomass pellets have always been challenged by several factors including the lack of understanding of the mechanism involved in how particles combine to form pellets under standard conditions of the pellet press. This is because contributing factors span several molecular, microscopic, and even nanoscopic levels as biomass undergoes pelleting. The characteristics of the bonds formed between the combining particles and their relevance to the quality of pellets remains vague, no matter how quality is defined. However, even though few researchers have attempted to explain the mechanism of bonding in densified biomass pellets using different theories, none of their hypotheses supports particle bonding from a structural chemistry perspective. There are still no clear explanations which consider the role of molecular structure and the interactions of substances as milled biomass undergo pelleting. In view of these arguments therefore, this review presents an in-depth analysis of a structural chemistry perspective of the mechanism of bonding and the use of additives in densified biomass pellets and helps identify research areas needed to facilitate better understanding of bonding in densified biomass pellets. The status of current research in biomass pelleting, types of materials suitable as additives and their structural characteristics, as well as the current technical specifications of using additives are also discussed.
|
|
| 10. |
- Anukam, Anthony Ike, et al.
(författare)
-
Characterization of pure and blended pellets made from Norway spruce and pea starch : A comparative study of bonding mechanism relevant to quality
- 2019
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:23, s. 1-22
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanism of bonding in biomass pellets is such a complex event to comprehend, as the nature of the bonds formed between combining particles and their relevance to pellet quality are not completely understood. In this study, pure and blended biomass pellets made from Norway spruce and pea starch were characterized using advanced analytical instruments able to provide information beyond what is visible to the human eye, with intent to investigate differences in bonding mechanism relevant to quality. The results, which were comprehensively interpreted from a structural chemistry perspective, indicated that, at a molecular level, the major disparity in bonding mechanism between particles of the pellets and the quality of the pellets, defined in terms of strength and burning efficiency, were determined by variation in the concentration of polar functional groups emanating from the major organic and elemental components of the pellets, as well as the strength of the bonds between atoms of these groups. Microscopic-level analysis, which did not provide any clear morphological features that could be linked to incongruity in quality, showed fracture surfaces of the pellets and patterns of surface roughness, as well as the mode of interconnectivity of particles, which were evidence of the production of pellets with dissimilarities in particle bonding mechanism and visual appearance.
|
|
