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| 2. |
- Danielsson Norén, Kristina, et al.
(författare)
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15-Lipoxygenase-2 expression in human macrophages induces chemokine secretion and T cell migration.
- 2008
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Ingår i: Atherosclerosis. - : Elsevier BV. - 1879-1484 .- 0021-9150. ; 199:1, s. 34-40
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: We determined previously that hypoxia results in increased 15-lipoxygenase type 2 (15-LOX-2) expression and CXCL8 secretion in macrophages. This study sought to determine whether 15-LOX-2 expression links directly with the secretion of inflammatory molecules in macrophages and also investigated its subsequent effects on T cell migration. METHODS: Adenovirus-mediated gene delivery caused overexpression of 15-LOX-2 in human macrophages. We used cytometric bead array to measure chemokine secretion, and assessed T cell migration by counting cells in chemotaxis chambers. Expression of chemokine receptors was determined by FACS analysis. Using siRNA, we reduced 15-LOX-2 expression in human macrophages. We used scrambled siRNA as control. RESULTS: Macrophages that overexpress 15-LOX-2 showed increased secretion of chemokine CXCL10 after 24h incubation. In addition, preconditioned medium from 15-LOX-2-overexpressing cells increased T cell migration and surface expression of CXCR3, the CXCL10 receptor. Knockdown of 15-LOX-2 expression decreased CXCL10 secretion from hypoxic macrophages and also reduced T cell migration. CONCLUSION: In macrophages, overexpression of 15-LOX-2 results in increased secretion of CXCL10 and CCL2. Products released in response to increased 15-LOX-2 activation lead to increased expression of CD69, the T cell activation marker as well as increased T cell migration. Therefore, increased expression of 15-LOX-2 induced by hypoxia may participate in T cell recruitment in diseases such as atherosclerosis.
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| 4. |
- Rezk, Kamal, 1983-, et al.
(författare)
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A fast running numerical model based on the implementation of volume forces for prediction of pressure drop in a fin-tube heat exchanger
- 2014
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Ingår i: Applied Mathematical Modelling. - : Elsevier. - 0307-904X .- 1872-8480. ; :24, s. 5822-5835
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Tidskriftsartikel (refereegranskat)abstract
- Numerical based design of geometrical structures is common whenstudying systems involving heat exchangers, a central component inseveral fields, such as industrial, vehicle and household systems. Thegeometrical structure of heat exchangers is generally comprised byclosely placed fins and tube bundles. The creation of a mesh grid for ageometrically compact heat exchanger will result in a dense structure,which is not feasible for personal computer usage. Hence, volume forceswere created based on Direct Numerical Simulations (DNS) on a FlowRepresentative Volume (FRV) of a tube fin heat exchanger in an internalduct system of a heat pump tumble dryer. A relation of the volumeaveraged velocity and the volume averaged force was established in twodifferent FRV-models with a finite element simulation in COMSOL. Thisrelation was subsequently used to create flow resistance coefficientsbased on volume averaged expressions of fluid velocity and volume forces.These flow resistance coefficients were implemented in two respectiveporous models, which represent the entire heat exchanger except theinterior arrangements of fins and tube bundles. Hence, the computationtime was reduced thanks to the absence of a dense mesh grid. Experimentalresults of the entire heat exchanger showed good agreement with thesecond porous model in terms of pressure drop and volume flow rate.
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| 5. |
- Rezk, Kamal, 1983-, et al.
(författare)
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A volume averaged method applied to fluid flow in a tube-fin heat exchanger
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Numerical-based design of geometrical structures is common when studying systems involving heat exchangers, which are a central component in several fields such as industrial-, vehicle- and household systems. The geometrical structure of heat exchangers is generally comprised by narrow placed fins and tube bundles. Creating a mesh grid for a geometrically compact heat exchanger results in a dense structure which regularly is not feasible for personal computer usage. Hence, a Volume Averaged Model (VAM) was created based on a Representative Elementary Volume (REV) of tube-fin heat exchanger in an internal duct system of a heat pump tumble dryer. A correlation of the volume flow rate and the force balance was established in the REV model with a finite element method simulation in COMSOL. The volume flow rate and force balance correlation was subsequently used to create a volume averaged expression of the momentum transport equations. These equations were implemented in the VAM model which represents the entire heat exchanger except the interior arrangements of fins and tube bundles. Hence, the computation time was reduced due to the absence of a dense mesh grid. Experimental results of the heat exchanger showed good agreement with the VAM model in terms of pressure drop and volume flow rate.
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| 6. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Characterizing flow resistance in 3-dimensional disordered fibrous structures based on Forchheimer coefficients for a wide range of Reynolds numbers
- 2016
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Ingår i: Applied Mathematical Modelling. - : Elsevier. - 0307-904X .- 1872-8480. ; 40:21-22, s. 8898-8911
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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.
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| 7. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Geometry development of the internal duct system of a heat pump tumble dryer based on fluid mechanic parameters from a CFD software
- 2011
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 88:5, s. 1596-1605
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Tidskriftsartikel (refereegranskat)abstract
- One aspect of reducing the energy consumption of a household tumble dryer is to reduce the pressure drop of the circulating air in the internal duct system. It is, however, costly and time consuming to design several prototypes for airflow measurements. In this paper, several fluid mechanic parameters in a partial model of the internal duct system of a tumble dryer have been studied in the CFD software Comsol MultiPhysics. The purpose was to establish a numerically based design process, where the design is conducted based on visual analysis of air velocity and vorticity, and two design criteria. The geometry design was conducted by a CAD-engineer, which was the counterpart of this project. In order to enable a successful design process, it was essential to establish a strong relation between fluid parameters and design criteria in order to share knowledge effectively with the CAD engineer. Two geometry modifications, based on a standard model, were conducted on the duct. Based on the design criteria, the pressure drop and the non-uniformity coefficient of the outlet airflow, the second modification (Modification 2) represents an improvement as the pressure drop is reduced by 23% and the uniformity at the outflow section is increased by 3%.
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| 8. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Modelling of water removal during a paper vacuum dewatering process using a Level-Set method
- 2013
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 101, s. 543-553
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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.
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| 9. |
- Rezk, Kamal, 1983-, et al.
(författare)
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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
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Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 33:5, s. 605-615
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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.
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