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Wibron, E., Ljung, A.-L. & Lundström, S. (2019). Comparing Performance Metrics of Partial Aisle Containments in Hard Floor and Raised Floor Data Centers Using CFD. Energies, 12(8), Article ID 1473.
Open this publication in new window or tab >>Comparing Performance Metrics of Partial Aisle Containments in Hard Floor and Raised Floor Data Centers Using CFD
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 8, article id 1473Article in journal (Refereed) Published
Abstract [en]

In data centers, efficient cooling systems are required to both keep the energy consumption as low as possible and to fulfill the temperature requirements. The aim of this work is to numerically investigate the effects of using partial aisle containment between the server racks for hard and raised floor configurations. The computational fluid dynamics (CFD) software ANSYS CFX was used together with the Reynolds stress turbulence model to perform the simulations. Velocity measurements in a server room were used for validation. Boundary conditions and the load of each rack were also retrieved from the experimental facility, implying an uneven load between the racks. A combination of the performance metrics Rack Cooling Index (RCI), Return Temperature Index (RTI) and Capture Index (CI) were used to evaluate the performance of the cooling systems for two supply flow rates at a 100% and 50% of operating condition. Based on the combination of performance metrics, the airflow management was improved in the raised floor configurations. With the supply flow rate set to operating conditions, the RCI was 100% for both raised floor and hard floor setups. The top- or side-cover fully prevented recirculation for the raised floor configuration, while it reduced the recirculation for the hard floor configuration. However, the RTI was low, close to 40% in the hard floor case, indicating poor energy efficiency. With the supply flow rate decreasing with 50%, the RTI increased to above 80%. Recirculation of hot air was indicated for all the containments when the supply rate was 50%, but the values of RCI still indicated an acceptable performance of the cooling system

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
data center, aisle containment, computational fluid dynamics (CFD), measurements, energy efficient
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-74676 (URN)10.3390/en12081473 (DOI)000467762600066 ()2-s2.0-85065507938 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-18 (johcin)

Available from: 2019-06-18 Created: 2019-06-18 Last updated: 2019-06-18Bibliographically approved
Wibron, E., Ljung, A.-L. & Lundström, S. (2018). Comparison of hard floor and raised floor cooling of servers with regards to local effects. In: IECON 2018: 44th Annual Conference of the IEEE Industrial Electronics Society. Paper presented at 44th Annual Conference of the IEEE Industrial Electronics Society, IECON 2018, October 21-23 2018, Washington D.C., USA..
Open this publication in new window or tab >>Comparison of hard floor and raised floor cooling of servers with regards to local effects
2018 (English)In: IECON 2018: 44th Annual Conference of the IEEE Industrial Electronics Society, 2018Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:ltu:diva-73013 (URN)10.1109/IECON.2018.8592885 (DOI)2-s2.0-85061534694 (Scopus ID)
Conference
44th Annual Conference of the IEEE Industrial Electronics Society, IECON 2018, October 21-23 2018, Washington D.C., USA.
Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-02-26
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, 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: 2018-11-26Bibliographically 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)000440958800041 ()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: 2018-08-30Bibliographically approved
Karlsson, L., Ljung, A.-L. & Lundström, T. S. (2018). Modelling the dynamics of the flow within freezing water droplets. Heat and Mass Transfer, 54(12), 3761-3769
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 1432-1181, Vol. 54, no 12, p. 3761-3769Article in journal (Refereed) Published
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)000450640100020 ()2-s2.0-85049030106 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-12-04 (inah)

Available from: 2018-06-26 Created: 2018-06-26 Last updated: 2019-01-10Bibliographically approved
Sandberg, M., Risberg, M., Ljung, A.-L., Varagnolo, D., Xiong, D. & Nilsson, M. (2017). A modelling methodology for assessing use of datacenter waste heat in greenhouses. In: : . Paper presented at Third International Conference on Environmental Science and Technology, ICOEST, Budapest, 19-23 October 2017.
Open this publication in new window or tab >>A modelling methodology for assessing use of datacenter waste heat in greenhouses
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2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In Sweden, the number of datacenters establishments are steadily increasing thanks to green, stable and affordable electricity, free air cooling, advantageous energy taxes and well-developed Internet fiber infrastructures. Even though datacenters use a lot of energy, the waste heat that they create is seldom reused. A possible cause is that this waste heat is often low grade and airborne: it is therefore hard to directly inject it into a district heating system without upgrades, which require additional energy and equipment that generate extra costs. One option for reusing this heat without needs for upgrades is to employ it for heating up greenhouses. But assessing the feasibility of this approach by building physical prototypes can be costly, therefore using computer models to simulate real world conditions is an opportunity. However, there is a lack of computer modelling methodologies that can assess the possibility of using waste heat from datacenters in greenhouses in cold climates.

The objective of this paper is therefore to propose such a methodology and discuss its benefits and drawbacks in comparison with other research studies. This methodology combines computational fluid dynamics, process modelling and control engineering principles into a computer model that constitutes a decision support system to study different waste heat and greenhouse or mushroom house scenarios.

The paper validates the strategy through a case study in northern Sweden, where we assess the amount of produced waste heat by collecting temperature, relative humidity, and fan speed data for the air discharged from the datacenter.

The resulting methodology, composed by conducting measurements and computer models, calculations can then be used for other datacenter operators or greenhouse developers to judge whether it is possible or not to build greenhouses using datacenter waste heat.

National Category
Energy Engineering Other Civil Engineering Fluid Mechanics and Acoustics Control Engineering Other Biological Topics
Research subject
Construction Engineering and Management; Control Engineering; Energy Engineering; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-66466 (URN)
Conference
Third International Conference on Environmental Science and Technology, ICOEST, Budapest, 19-23 October 2017
Funder
Swedish Energy Agency, 41845-1
Available from: 2017-11-08 Created: 2017-11-08 Last updated: 2017-12-01Bibliographically 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.

Place, publisher, year, edition, pages
Springer, 2017
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: 2018-09-27Bibliographically approved
Lucchese, R., Olsson, J., Ljung, A.-L., Garcia-Gabin, W. & Varagnolo, D. (2017). Energy savings in data centers: A framework for modelling and control of servers’ cooling. Paper presented at 20th IFAC World Congress, Toulouse, France, 9-14 July 2017. IFAC-PapersOnLine, 50(1), 9050-9057
Open this publication in new window or tab >>Energy savings in data centers: A framework for modelling and control of servers’ cooling
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2017 (English)In: IFAC-PapersOnLine, ISSN 1045-0823, E-ISSN 1797-318X, Vol. 50, no 1, p. 9050-9057Article in journal (Refereed) Published
Abstract [en]

Aiming at improving the energy efficiency of air cooled servers in data centers, we devise a novel control oriented, nonlinear, thermal model of the servers that accounts explicitly for both direct and recirculating convective air flows. Instrumental to the optimal co-design of both geometries and cooling policies, we propose an identification methodology based on Computational Fluid Dynamics (CFD) for a generic thermal network of m fans and n electronic components. The performance of the proposed modelling framework is validated against CFD measurements with promising results. We formalize the minimum cooling cost control problem as a polynomially constrained Receding Horizon Control (RHC) and show, in-silico, that the resulting policy is able to efficiently modulate the cooling resources in spite of the unknown future computational and electrical power loads.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Control Engineering Fluid Mechanics and Acoustics
Research subject
Control Engineering; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-66199 (URN)10.1016/j.ifacol.2017.08.1624 (DOI)000423965100009 ()2-s2.0-85031817824 (Scopus ID)
Conference
20th IFAC World Congress, Toulouse, France, 9-14 July 2017
Note

Konferensartikel i tidskrift

Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2018-03-08Bibliographically 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.

Place, publisher, year, edition, pages
Elsevier, 2017
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: 2018-09-13Bibliographically approved
Ljung, A.-L. & Lundström, S. (2017). Heat and mass transfer boundary conditions at the surface of a heated sessile droplet. Heat and Mass Transfer, 53(12), 3581-3591
Open this publication in new window or tab >>Heat and mass transfer boundary conditions at the surface of a heated sessile droplet
2017 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 12, p. 3581-3591Article in journal (Refereed) Published
Abstract [en]

This work numerically investigates how the boundary conditions of a heated sessile water droplet should be defined in order to include effects of both ambient and internal flow. Significance of water vapor, Marangoni convection, separate simulations of the external and internal flow, and influence of contact angle throughout drying is studied. The quasi-steady simulations are carried out with Computational Fluid Dynamics and conduction, natural convection and Marangoni convection are accounted for inside the droplet. For the studied conditions, a noticeable effect of buoyancy due to evaporation is observed. Hence, the inclusion of moisture increases the maximum velocities in the external flow. Marangoni convection will, in its turn, increase the velocity within the droplet with up to three orders of magnitude. Results furthermore show that the internal and ambient flow can be simulated separately for the conditions studied, and the accuracy is improved if the internal temperature gradient is low, e.g. if Marangoni convection is present. Simultaneous simulations of the domains are however preferred at high plate temperatures if both internal and external flows are dominated by buoyancy and natural convection. The importance of a spatially resolved heat and mass transfer boundary condition is, in its turn, increased if the internal velocity is small or if there is a large variation of the transfer coefficients at the surface. Finally, the results indicate that when the internal convective heat transport is small, a rather constant evaporation rate may be obtained throughout the drying at certain conditions.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-64815 (URN)10.1007/s00231-017-2087-3 (DOI)000415999800015 ()
Note

Validerad;2017;Nivå 2;2017-11-22 (andbra)

Available from: 2017-07-06 Created: 2017-07-06 Last updated: 2017-12-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-8235-9639

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