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  • 1.
    Burström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Liepaja University .
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, B. Daniel
    LKAB, Kiruna.
    Modelling heat transfer during flow through a random packed bed of spheres2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 4, p. 1225-1245Article in journal (Refereed)
    Abstract [en]

    Heat transfer in a random packed bed of monosized iron ore pellets is modelled with both a discrete three-dimensional system of spheres and a continuous Computational Fluid Dynamics (CFD) model. Results show a good agreement between the two models for average values over a cross section of the bed for an even temperature profiles at the inlet. The advantage with the discrete model is that it captures local effects such as decreased heat transfer in sections with low speed. The disadvantage is that it is computationally heavy for larger systems of pellets. If averaged values are sufficient, the CFD model is an attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also on non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.

  • 2.
    Burström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB.
    Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres2017In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 1, p. 151-160Article in journal (Refereed)
    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.

  • 3. Fukagata, K.
    et al.
    Zahrai, S.
    Bark, Fritz H.
    KTH, Superseded Departments (pre-2005), Mechanics.
    Dynamics of Brownian particles in a turbulent channel flow2004In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 40, no 9, p. 715-726Article in journal (Refereed)
    Abstract [en]

    Turbulent channel flows with suspended particles are investigated by means of numerical simulations. The fluid velocity is computed by large eddy simulation. Motion of small graphite particles with diameter of 0.01-10 mum, corresponding to the Schmidt number, Sc, of 2.87 x 10(2)-6.22 x 10(6) and the particle relaxation time in wall unit, tau(p)(+), of 9.79 x 10(-5)-4.51, is computed by Lagrangian particle tracking. Relation between the particle relaxation time and the computed deposition velocity is found to be in good agreement with an empirical relation. The statistics of the particle motion in the vicinity of the wall are studied. Clear differences are found in dynamical behavior of particles with different sizes. Medium size particles show a strong dependence on the structure of the fluid flow, while small and large particles are considerably less sensitive.

  • 4.
    Ghanbarpour, Morteza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Vafai, K.
    An investigation of thermal performance improvement of a cylindrical heat pipe using Al2O3 nanofluid2016In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, p. 1-11Article in journal (Refereed)
    Abstract [en]

    In this study, effect of Al2O3 nanofluid on thermal performance of cylindrical heat pipe is investigated. An analytical model is employed to study the thermal performance of the heat pipe utilizing nanofluid and the predicted results are compared with the experimental results. A substantial change in the heat pipe thermal resistance, effective thermal conductivity and entropy generation of the heat pipe is observed when using Al2O3 nanofluid as a working fluid. It is found that entropy generation in the heat pipe system decreases when using a nanofluid due to the lower thermal resistance of the heat pipe which results in an improved thermal performance. It is shown that the proposed model is in reasonably good agreement with the experimental results and can be used as a fast technique to explore various features of thermal characteristics of the nanofluid based heat pipe.

  • 5. Haraldsson, H. O.
    et al.
    Li, H. X.
    Yang, Z. L.
    Dinh, Truc-Nam
    KTH, Superseded Departments (pre-2005), Physics.
    Sehgal, B. R.
    Effect of solidification on drop fragmentation in liquid-liquid media2001In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 37, no 4-5, p. 417-426Article in journal (Refereed)
    Abstract [en]

    This paper presents results of experimental and analytical investigation on molten alloy drop fragmentation in water pool. Emphasis is directed towards delineating the roles which melt to coolant heat transfer and melt solidification play in the fragmentation process. The strong impact of coolant temperature upon fragmentation process is addressed. A set of 23 drop fragmentation experiments were performed, in which 8 experiments employed a low melting point alloy, cerrobend-70 and 15 experiments using Pb-Bi eutectic alloy as drop fluid. The results show strong impact of coolant temperature on particle size distribution of the fragmented drops. A linear stability analysis of the interface between the two liquid fluids with thin crust growing between them, is performed. A modified dimensionless Aeroelastic number, for Kelvin-Helmholtz instability, is obtained and used as a criteria for fragmentation of molten drops penetrating into another liquid coolant media with lower temperature. The nondimensionalized mean diameter of the fragmented particles is correlated with the Aeroelastic number.

  • 6.
    Kalisz, Sylwester
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Pronobis, M
    Influence of non-uniform flow distribution on overall heat transfer in convective bundle of circulating fluidized bed boiler2005In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 41, no 11, p. 981-990Article in journal (Refereed)
    Abstract [en]

    In the paper the results of comparative investigations on heat transfer performance of boiler convective bundle and its additional surface, i.e. membrane water wall are presented. For this purpose the non-uniform flow field was modelled in an isothermal test stand operated in self-modeling mode. Then the heat transfer characteristics of such arrangement were estimated by means of naphthalene heat/mass transfer analogy technique. The bundle samples in the shape of round bars (rods) were cast with naphthalene and placed in 27 locations in the bundle while water-wall-modeling samples were coated with naphthalene by painting. Both types of samples were exposed to cold air flow. The results were then compared to the mean heat transfer performance of the same bundle exposed to uniform flow field. The differences of approximately 10% were noticed. Moreover, the heat transfer coefficients for additional surface were even three times lower than those of the bundle. In view of results obtained in the work, the commonly made assumption of equality of heat transfer coefficients for both the bundle and its additional surface may lead to certain errors in heat transfer calculations and discrepancies between the calculated values of heating surfaces area and later operational needs of steam generator.

  • 7.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling the dynamics of the flow within freezing water droplets2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 12, p. 3761-3769Article in journal (Refereed)
    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.

  • 8.
    Kohlstaedt, S.
    et al.
    Volkswagen AG, Dept Casting Res, Wolfsburg, Germany..
    Vynnycky, M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gebauer-Teichmann, A.
    Volkswagen AG, Dept Casting Res, Wolfsburg, Germany..
    Experimental and numerical CHT-investigations of cooling structures formed by lost cores in cast housings for optimal heat transfer2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 11, p. 3445-3459Article in journal (Refereed)
    Abstract [en]

    This paper investigates the cooling performance of six different lost core designs for automotive cast houses with regard to their cooling efficiency. For this purpose, the conjugate heat transfer (CHT) solver, chtMultiregion, of the freely available CFD-toolbox OpenFOAM in its implementation of version 2.3.1 is used. The turbulence contribution to the Navier-Stokes equations is accounted for by using the RANS Menter SST k - model. The results are validated for one of the geometries by comparing with experimental data. Of the six investigated cooling structures, the one that forces the fluid flow to change its direction the most produces the lowest temperatures on the surface of the cast housing. This good cooling performance comes at the price of the highest pressure loss in the cooling fluid and hence increased pump power. It is also found that the relationship between performance and pressure drop is by no means generally linear. Slight changes in the design can lead to a structure which cools almost as well, but at much decreased pressure loss. Regarding the absolute values, the simulations showed that the designed cooling structures are suitable for handling the cooling requirements in the particular applications and that the maximum temperature stays below the critical limits of the electronic components.

  • 9.
    Lichtenegger, Klaus
    et al.
    Bioenergy 2020+ GmbH.
    Hebenstreit, Babette
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Pointner, Christian
    Bioenergy 2020+ GmbH.
    Schmidl, Christoph
    Bioenergy 2020+ GmbH.
    Höftberger, Ernst
    Bioenergy 2020+ GmbH.
    The role of leak air in a double-wall chimney2015In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 51, no 6, p. 787-794Article in journal (Refereed)
    Abstract [en]

    In modern buildings with tight shells, often room-independent air supply is required for proper operation of biomass stoves. One possibility to arrange this supply is to use a double-wall chimney with flue gas leaving through the pipe and fresh air entering through the annular gap. A one-dimensional quasi-static model based on balance equations has been developed and compared with experimental data. Inclusion of leak air is crucial for reproduction of the experimental results.

  • 10.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Heat and mass transfer boundary conditions at the surface of a heated sessile droplet2017In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 12, p. 3581-3591Article in journal (Refereed)
    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.

  • 11. Motahar, Sadegh
    et al.
    Alemrajabi, Ali A.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Enhanced thermal conductivity of n-octadecane containing carbon-based nanomaterials2016In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 52, no 8, p. 1621-1631Article in journal (Refereed)
  • 12.
    Niebles Atencio, Bercelay
    et al.
    Chalmers University of Technology, Sweden.
    Jamshidi, Hamed
    Chalmers University of Technology, Sweden.
    Liljemark, Marcus
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Sweden.
    Chernoray, Valery
    Chalmers University of Technology, Sweden.
    Assessment of the naphthalene sublimation technique for determination of convective heat transfer in fundamental and industrial applications2019In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 56, no 5, p. 1487-1501Article in journal (Refereed)
    Abstract [en]

    The naphthalene sublimation technique is an experimental method for indirectly determining convective heat transfer. The technique is here assessed for two different configurations: the local heat transfer distribution for a circular air jet impinging normal to a flat surface, and the heat transfer occurring in the stator core of an electric generator model. The turbulent impinging jet is fully developed. Two Reynolds numbers based on the nozzle exit condition, 15000 and 23000, and two nozzle diameter distances from the jet exit to the surface, 6 and 8, are considered. For the generator turbulent internal flow with Reynolds number of 4100 is considered, based on the hydraulic diameter of stator ventilation ducts. Modern surface scanning methods and imprints of the naphthalene specimens were used for measuring the naphthalene sublimation rate. The impinging jet results are compared with experimental data found in the literature. Results from the generator model and numerical simulations are compared. For the impinging jet, the results show agreement with the already published experimental data sets. For the generator model, heat transfer results from experiments differ by around 13% compared to numerical results if a scanning of the surface is used for measuring the naphthalene sublimation and around 5% if weights are used for measuring the sublimation rate. Therefore, the results depend on the way the sublimation rate is quantified. From this study, it is possible to affirm that with advanced scanning procedures, the heat transfer can be resolved with very small naphthalene sublimation in cases of both fundamental and complex industrial applications such as electric generators.

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  • 13.
    Siddique, Waseem
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    El-Gabry, Lamyaa
    American University in Cairo; Egypt.
    Shevchuk, Igor
    MBtech Group GmbH & Co. Germany.
    Hushmandi, Narmin B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular smooth channels2012In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 48, no 5, p. 735-748Article in journal (Refereed)
    Abstract [en]

    Two-pass channels are used for internal cooling in a number of engineering systems e.g., gas turbines. Fluid travelling through the curved path, experiences pressure and centrifugal forces, that result in pressure driven secondary motion. This motion helps in moving the cold high momentum fluid from the channel core to the side walls and plays a significant role in the heat transfer in the channel bend and outlet pass. The present study investigates using Computational Fluid Dynamics (CFD), the flow structure, heat transfer enhancement and pressure drop in a smooth channel with varying aspect ratio channel at different divider-to-tip wall distances. Numerical simulations are performed in two-pass smooth channel with aspect ratio W-in/H = 1:3 at inlet pass and W-out/H = 1:1 at outlet pass for a variety of divider-to-tip wall distances. The results show that with a decrease in aspect ratio of inlet pass of the channel, pressure loss decreases. The divider-to-tip wall distance (W-el) not only influences the pressure drop, but also the heat transfer enhancement at the bend and outlet pass. With an increase in the divider-to-tip wall distance, the areas of enhanced heat transfer shifts from side walls of outlet pass towards the inlet pass. To compromise between heat transfer and pressure drop in the channel, W-el/H = 0.88 is found to be optimum for the channel under study.

  • 14.
    Siddique, Waseem
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Shevchuk, Igor
    MBtech Group GmbH & Co. KGaA, Germany..
    El-Gabry, Lamyaa
    American University in Cairo, Egypt.
    Hushmandi, Narmin B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    On flow structure, heat transfer and pressure drop in varying aspect ratio two-pass rectangular channel with ribs at 45 degrees2013In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 49, no 5, p. 679-694Article in journal (Refereed)
    Abstract [en]

    To increase the thermal efficiency of gas turbines, inlet temperature of gas is increased. This results in the requirement of cooling of gas turbine blades and vanes. Internal cooling of gas turbine blades and vanes is one of several options. Two-pass channels are provided with ribs to enhance heat transfer at the expense of an increased pressure drop. The space in the blade is limited and requires channels with small aspect ratios. Numerical simulations have been performed to investigate heat transfer, flow field and pressure loss in a two-pass channel equipped with 45A degrees ribs with aspect ratio (W-in/H) equal to 1:3 in the inlet pass and 1:1 in the outlet pass with both connected together with a 180A degrees bend. The results are compared with a higher aspect ratio channel (W-in/H = 1:2, inlet pass). In the ribbed channel, a decrease in pressure drop was observed with a decrease in the aspect ratio of the channel. The smaller aspect ratio channel not only allows using more cooling channels in the blade, but also results in more heat transfer enhancement. The divider-to-tip wall distance (W-el) has influence on the pressure drop, as well as on the heat transfer enhancement at the bend and outlet pass. Heat transfer decreases with decrease in aspect ratio of the inlet pass of the two-pass channel. With increase in divider-to-tip wall distance, heat transfer tries to attain a constant value.

  • 15. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments (pre-2005), Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Evaluation of the Darcy's law performance for two-fluid flow hydrodynamics in a particle debris bed using a lattice-Boltzmann model2000In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 36, no 4, p. 295-304Article in journal (Refereed)
    Abstract [en]

    In the present paper, multiphase flow dynamics in a porous medium are analyzed by employing the lattice-Boltzmann modeling approach. A two-dimensional formulation of a lattice-Boltzmann model, using a D2Q9 scheme, is used. Results of the FlowLab code simulation for single phase flow in porous media and for two-phase flow in a channel are compared with analytical solutions. Excellent agreement is obtained. Additionally, fluid-fluid interaction and fluid-solid interaction (wettability) are modeled and examined. Calculations are performed to simulate two-fluid dynamics in porous media, in a wide range of physical parameters of porous media and flowing fluids. It is shown that the model is capable of determining the minimum body force needed for the nonwetting fluid to percolate through the porous medium. Dependence of the force on the pore size, and geometry, as well as on the saturation of the nonwetting fluid is predicted by the model. In these simulations, the results obtained for the relative permeability coefficients indicate the validity of the reciprocity for the two coupling terms in the modified Darcy's law equations. Implication of the simulation results on two-fluid flow hydrodynamics in a decay-heated particle debris bed is discussed.

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