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Jouybari, N., Maerefat, M., Lundström, T. S., Eshagh Nimvari, M. & Gholami, Z. (2018). A General Macroscopic Model for Turbulent Flow in Porous Media. Journal of Fluids Engineering - Trancactions of The ASME, 140(1), Article ID 011201.
Open this publication in new window or tab >>A General Macroscopic Model for Turbulent Flow in Porous Media
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2018 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 140, no 1, article id 011201Article in journal (Refereed) Published
Abstract [en]

The present study deals with the generalization of a macroscopic turbulence model in porous media using a capillary model. The additional source terms associated with the production and dissipation of turbulent kinetic energy due to the presence of solid matrix are calculated using the capillary model. The present model does not require any prior pore scale simulation of turbulent flow in a specific porous geometry in order to close the macroscopic turbulence equations. Validation of the results in packed beds, periodic arrangement of square cylinders, synthetic foams and longitudinal flows such as pipes, channels and rod bundles against available data in the literature reveals the ability of the present model in predicting turbulent flow characteristics in different types of porous media. Transition to the fully turbulent regime in porous media and different approaches to treat this phenomenon are also discussed in the present study. Finally, the general model is modified so that it can be applied to lower Reynolds numbers below the range of fully turbulent regime in porous media.

Place, publisher, year, edition, pages
ASME Press, 2018
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65199 (URN)10.1115/1.4037677 (DOI)000415379500009 ()2-s2.0-85029753712 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-10-03 (andbra)

Available from: 2017-08-19 Created: 2017-08-19 Last updated: 2017-12-01Bibliographically approved
Wibron, E., Ljung, A.-L. & Lundström, S. (2018). Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center. Energies, 11(3), Article ID 644.
Open this publication in new window or tab >>Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center
2018 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 3, article id 644Article in journal (Refereed) Published
Abstract [en]

The worldwide demand on data storage continues to increase and both the number and the size of data centers are expanding rapidly. Energy efficiency is an important factor to consider in data centers since the total energy consumption is huge. The servers must be cooled and the performance of the cooling system depends on the flow field of the air. Computational Fluid Dynamics (CFD) can provide detailed information about the airflow in both existing data centers and proposed data center configurations before they are built. However, the simulations must be carried out with quality and trust. The k–ɛ model is the most common choice to model the turbulent airflow in data centers. The aim of this study is to examine the performance of more advanced turbulence models, not previously investigated for CFD modeling of data centers. The considered turbulence models are the k–ɛ model, the Reynolds Stress Model (RSM) and Detached Eddy Simulations (DES). The commercial code ANSYS CFX 16.0 is used to perform the simulations and experimental values are used for validation. It is clarified that the flow field for the different turbulence models deviate at locations that are not in the close proximity of the main components in the data center. The k–ɛ model fails to predict low velocity regions. RSM and DES produce very similar results and, based on the solution times, it is recommended to use RSM to model the turbulent airflow data centers.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
data center; airflow; computational fluid dynamics (CFD); turbulence models
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-67958 (URN)10.3390/en11030644 (DOI)000428304300172 ()
Note

Validerad;2018;Nivå 2;2018-03-19 (andbra)

Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-07-26Bibliographically approved
Altorkmany, L., Kharseh, M., Ljung, A.-L. & Lundström, S. (2018). Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems. Applied Thermal Engineering, 141, 435-443
Open this publication in new window or tab >>Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems
2018 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, p. 435-443Article in journal (Refereed) Published
Abstract [en]

The objective of the current study is to analyze the effect of different working parameters on the thermal performance of the Anti-Bact Heat Exchanger system (ABHE). The ABHE system is inspired by nature and implemented to achieve continuous disinfection of Legionella in different human-made water systems at any desired disinfection temperature. In the ABHE system, most of the energy is recovered using an efficient plate heat exchanger (PHE). A model by Engineering Equation Solver (EES) is set-up to figure out the effect of different working parameters on the thermal performance of the ABHE system. The study shows that higher supplied water temperature can enhance the regeneration ratio (RR), but it requires a large PHE area and pumping power (PP) which consequently increase the cost of the ABHE system. However, elevate temperature in use results in a reduced PHE area and PP, which accordingly reduce the cost of the ABHE system. On the other hand, the EES-based model is used to study the effect of the length and the width of the plates used in the PHE on the RR and the required area of the PHE. Finally, taking into account the geometrical parameters, flow arrangement and the initial operating conditions of the PHE, the EES-based model is used to optimize the PHE in which its area is minimized, and the RR of the ABHE system is maximized.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Legionella; thermal disinfection; simulation; thermal performance; plate heat exchanger
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-67443 (URN)10.1016/j.applthermaleng.2018.06.002 (DOI)2-s2.0-85048500460 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-06-13 (andbra)

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2018-06-28Bibliographically approved
Karlsson, L., Ljung, A.-L. & Lundström, T. S. (2018). Modelling the dynamics of the flow within freezing water droplets. Heat and Mass Transfer
Open this publication in new window or tab >>Modelling the dynamics of the flow within freezing water droplets
2018 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181Article in journal (Refereed) Epub ahead of print
Abstract [en]

The flow within freezing water droplets is here numerically modelled assuming fixed shape throughout freezing. Three droplets are studied with equal volume but different contact angles and two cases are considered, one including internal natural convection and one where it is excluded, i.e. a case where the effects of density differences is not considered. The shape of the freezing front is similar to experimental observations in the literature and the freezing time is well predicted for colder substrate temperatures. The latter is found to be clearly dependent on the plate temperature and contact angle. Including density differences has only a minor influence on the freezing time, but it has a considerable effect on the dynamics of the internal flow. To exemplify, in the vicinity of the density maximum for water (4 C) the velocities are about 100 times higher when internal natural convection is considered for as compared to when it is not.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-69879 (URN)10.1007/s00231-018-2396-1 (DOI)
Available from: 2018-06-26 Created: 2018-06-26 Last updated: 2018-08-08
Sarkar, C., Westerberg, L.-G., Höglund, E. & Lundström, S. T. (2018). Numerical simulations of lubricating grease flow in a rectangular channel with and without restrictions. Tribology Transactions, 61(1), 144-156
Open this publication in new window or tab >>Numerical simulations of lubricating grease flow in a rectangular channel with and without restrictions
2018 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 1, p. 144-156Article in journal (Refereed) Published
Abstract [en]

This article presents numerical simulations of the laminar flow of lubricating greases in a channel with rectangular cross section. Three greases with different consistencies (NLGI grades 00, 1, and 2) have been considered in three different configurations composed of a rectangular channel without restrictions, one rectangular step restriction, and one double-lip restriction. The driving pressure drop over the channel spans from 30 to 250 kPa. The grease rheology is described by the Herschel-Bulkley rheology model, and both the numerical code and rheology model have been validated with analytical solutions and flow measurements using micro-particle image velocimetry.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Fluid Mechanics and Acoustics Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Fluid Mechanics; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-61479 (URN)10.1080/10402004.2017.1285090 (DOI)000432222500015 ()
Note

Validerad;2018;Nivå 2;2018-02-01 (rokbeg)

Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2018-06-04Bibliographically approved
Larsson, S., Lundström, S. & Lycksam, H. (2018). Tomographic PIV of flow through ordered thin porous media. Experiments in Fluids, 59(6), Article ID 96.
Open this publication in new window or tab >>Tomographic PIV of flow through ordered thin porous media
2018 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 6, article id 96Article in journal (Refereed) Published
Abstract [en]

Pressure-driven flow in a model of a thin porous medium is investigated using tomographic particle image velocimetry. The solid parts of the porous medium have the shape of vertical cylinders placed on equal interspatial distance from each other. The array of cylinders is confined between two parallel plates, meaning that the permeability is a function of the diameter and height of the cylinders, as well as their interspatial distance. Refractive index matching is applied to enable measurements without optical distortion and a dummy cell is used for the calibration of the measurements. The results reveal that the averaged flow field changes substantially as Reynolds number increases, and that the wakes formed downstream the cylinders contain complex, three-dimensional vortex structures hard to visualize with only planar measurements. An interesting observation is that the time-averaged velocity maximum changes position as Reynolds number increases. For low Reynolds number flow, the maximum is in the middle of the channel, while, for the higher Reynolds numbers investigated, two maxima appear closer to each bounding lower and upper wall.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-68773 (URN)10.1007/s00348-018-2548-6 (DOI)2-s2.0-85047216388 (Scopus ID)
Note

Validerad;2018;Nivå 1;20180525 (marisr)

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-06-19Bibliographically approved
Burström, P., Frishfelds, V., Ljung, A.-L., Lundström, T. S. & Marjavaara, D. (2017). Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres (ed.). Heat and Mass Transfer, 53(1), 151-160
Open this publication in new window or tab >>Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres
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2017 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 1, p. 151-160Article in journal (Refereed) Published
Abstract [en]

Convective heat transport in a relatively thin porous layer of monosized particles is here modeled. The size of the particles is only one order of magnitude smaller than the thickness of the layer. Both a discrete three-dimensional system of particles and a continuous one-dimensional model are considered. The methodology applied for the discrete system is Voronoi discretization with minimization of dissipation rate of energy. The discrete and continuous model compares well for low velocities for the studied uniform inlet boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The new result is thus that a special correlation must be used when using a continuous model for flow perpendicular to a thin porous media in order to predict the dispersion in proper manner, especially in combination with higher velocities.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-9656 (URN)10.1007/s00231-016-1792-7 (DOI)000391384700014 ()2-s2.0-84962175661 (Scopus ID)85295f62-d81d-468a-a26b-53cc1547fcd2 (Local ID)85295f62-d81d-468a-a26b-53cc1547fcd2 (Archive number)85295f62-d81d-468a-a26b-53cc1547fcd2 (OAI)
Note

Validerad; 2017; Nivå 2; 2017-03-15 (inah)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Misiulia, D., Andersson, A. G. & Lundström, S. (2017). Effects of the inlet angle on the collection efficiency of a cyclone with helical-roof inlet. Powder Technology, 305, 48-55
Open this publication in new window or tab >>Effects of the inlet angle on the collection efficiency of a cyclone with helical-roof inlet
2017 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 305, p. 48-55Article in journal (Refereed) Published
Abstract [en]

The effects of inlet angle on the collection efficiency of a cyclone with helical-roof inlet have been computationally investigated using Large Eddy Simulations with the dynamic Smagorinsky-Lilly subgrid-scale model for five different inlet angles (7°, 11°, 15°, 20° and 25°). Forty thousand individual particles were tracked through the unsteady flow field using the Lagrangian approach. In order to reveal the collection efficiency of a cyclone with helical-roof inlet properly, simulation time should not be < 3.5 times the average flow residence time. Particles which diameter is close to the cyclone cut size have the longest residence times while particles of 10–25 μm in diameter have the shortest. Based on the simulations, expressions for the cut size and Euler number normalized with the mean axial velocity in a cyclone with helical-roof inlet of different inlet angles are derived. The results show that, increasing the inlet angle increases the cyclone cut size and as a result reduces cyclone collection efficiency. At the same time, it decreases the cyclone pressure drop coefficient (Euler number) leading to lower pressure losses. For most cases where high separation efficiency at moderate pressure drop is required the optimum inlet angle is in the range 10–15°.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-59743 (URN)10.1016/j.powtec.2016.09.050 (DOI)000390732000006 ()2-s2.0-84989182792 (Scopus ID)
Note

Validerad; 2016; Nivå 2; 2016-10-14 (andbra)

Available from: 2016-10-14 Created: 2016-10-14 Last updated: 2018-07-10Bibliographically approved
Altorkmany, L., Kharseh, M., Ljung, A.-L. & Lundström, S. (2017). Experimental and Simulation Validation of ABHE for Disinfection of Legionella in Hot Water Systems. Applied Thermal Engineering, 116, 253-265
Open this publication in new window or tab >>Experimental and Simulation Validation of ABHE for Disinfection of Legionella in Hot Water Systems
2017 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 116, p. 253-265Article in journal (Refereed) Published
Abstract [en]

The work refers to an innovative system inspired by nature that mimics the thermoregulation system that exists in animals. This method, which is called Anti Bacteria Heat Exchanger (ABHE), is proposed to achieve continuous thermal disinfection of bacteria in hot water systems with high energy efficiency. In particular, this study aims to demonstrate the opportunity to gain energy by means of recovering heat over a plate heat exchanger. Firstly, the thermodynamics of the ABHE is clarified to define the ABHE specification. Secondly, a first prototype of an ABHE is built with a specific configuration based on simplicity regarding design and construction. Thirdly, an experimental test is carried out. Finally, a computer model is built to simulate the ABHE system and the experimental data is used to validate the model. The experimental results indicate that the performance of the ABHE system is strongly dependent on the flow rate, while the supplied temperature has less effect. Experimental and simulation data show a large potential for saving energy of this thermal disinfection method by recovering heat. To exemplify, when supplying water at a flow rate of 5 kg/min and at a temperature of 50 °C, the heat recovery is about 1.5 kW while the required pumping power is 1 W. This means that the pressure drop is very small compared to the energy recovered and consequently high saving in total cost is promising.

Keywords
Heat transfer, Legionella, Plate heat exchanger, Modeling Water thermal treatment
National Category
Water Engineering Fluid Mechanics and Acoustics
Research subject
Water Resources Engineering; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-61706 (URN)10.1016/j.applthermaleng.2017.01.092 (DOI)000397550300024 ()2-s2.0-85011632887 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-02-17 (andbra)

Available from: 2017-01-30 Created: 2017-01-30 Last updated: 2018-07-10Bibliographically approved
Bin Asad, S. M., Lundström, S. & Andersson, A. G. (2017). Experimental study of the flow past submerged half-cylinders. Paper presented at 7th BSME International Conference on Thermal Engineering, Dhaka, Bangladesh, 22–24 December, 2016. AIP Conference Proceedings, 1851, Article ID 020001.
Open this publication in new window or tab >>Experimental study of the flow past submerged half-cylinders
2017 (English)In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1851, article id 020001Article in journal (Refereed) Published
Abstract [en]

This investigation studies the details of the flow behind and over two identical semicircular cylinderspositioned in tandem. Laser Doppler Velocimetry (LDV) measurements are carried out in a laboratory waterflume using two different gap ratios (Sp/d = 1 and Sp/d = 0.5; where Sp indicates distance between the cylindersand d indicates cylinder diameter) under two different flow situations. These LDV measurement are used toderive velocities, formation length and Power spectral density for the various flow conditions. Flowvisualizations are also added in this investigation. The results indicate that the flow is significantly affected dueto gap ratios.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-64318 (URN)10.1063/1.4984630 (DOI)000412828600001 ()2-s2.0-85022041470 (Scopus ID)
Conference
7th BSME International Conference on Thermal Engineering, Dhaka, Bangladesh, 22–24 December, 2016
Note

2017-06-21 (andbra);Konferensartikel i tidskrift

Available from: 2017-06-21 Created: 2017-06-21 Last updated: 2018-05-22Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-1033-0244

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