Bengt Sundén

Bio: Bengt Sundén is an academic researcher from Lund University. The author has contributed to research in topics: Heat transfer & Heat transfer coefficient. The author has an hindex of 51, co-authored 822 publications receiving 13119 citations. Previous affiliations of Bengt Sundén include Harbin Institute of Technology & Northwestern Polytechnical University.

Effect of aspect ratio on entropy generation in a rectangular cavity with differentially heated vertical walls

Abstract: In the present study, entropy generation in rectangular cavities with the same area but different aspect ratios is numerically investigated. The vertical walls of the cavities are at different constant temperatures while the horizontal walls are adiabatic. Heat transfer between vertical walls occurs by laminar natural convection. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation due to heat transfer and fluid friction, the local Bejan number and local entropy generation number are determined and related maps are plotted. The variation of the total entropy generation and average Bejan number for the whole cavity volume at different aspect ratios for different values of the Rayleigh number and irreversibility distribution ratio are also evaluated. It is found that for a cavity with high value of Rayleigh number (i.e., Ra = 10(5)), the total entropy generation due to fluid friction and total entropy generation number increase with increasing aspect ratio, attain a maximum and then decrease. The present results are compared with reported solutions and excellent agreement is observed. The study is performed for 10(2) < Ra < 10(5), 10(-4) < 0 < 10(-2), and Pr = 0.7. (Less)

Review on modeling development for multiscale chemical reactions coupled transport phenomena in solid oxide fuel cells

Abstract: A literature study is performed to compile the state-of-the-art, as well as future potential, in SOFC modeling. Principles behind various transport processes such as mass, heat, momentum and charge as well as for electrochemical and internal reforming reactions are described. A deeper investigation is made to find out potentials and challenges using a multiscale approach to model solid oxide fuel cells (SOFCs) and combine the accuracy at microscale with the calculation speed at macroscale to design SOFCs, based on a clear understanding of transport phenomena, chemical reactions and functional requirements. Suitable methods are studied to model SOFCs covering various length scales. Coupling methods between different approaches and length scales by multiscale models are outlined. Multiscale modeling increases the understanding for detailed transport phenomena, and can be used to make a correct decision on the specific design and control of operating conditions. It is expected that the development and production costs will be decreased and the energy efficiency be increased (reducing running cost) as the understanding of complex physical phenomena increases. It is concluded that the connection between numerical modeling and experiments is too rare and also that material parameters in most cases are valid only for standard materials and not for the actual SOFC component microstructures.

Optimization of Compact Heat Exchangers by a Genetic Algorithm

Abstract: In this study a plate-fin type Compact Heat Exchanger (CHE) is considered for optimization. The optimization method uses a Genetic Algorithm (GA) to search, combine and optimize structure sizes of the CHE. The minimum total volume or/and total annual cost of the CHE are taken as objective functions in the GA, respectively. The geometries of the fins are fixed while three shape parameters are varied for the optimization objectives with or without pressure drop constraints, respectively. Performance of the CHE is evaluated according to the conditions of the structure sizes that the GA generated, and the corresponding volume and cost are calculated. It is shown that with pressure drop constraints the optimized CHE provides about 30% lower volume or about 15% lower annual cost, while without pressure drop constraints the optimized CHE provides about 49% lower volume or about 16% lower annual cost than those presented in the literature.

Effects of hybrid nanofluid mixture in plate heat exchangers

Abstract: Heat transfer and pressure drop characteristics of a hybrid nanofluid mixture containing alumina nanoparticles and multi-walled carbon nanotubes (MWCNTs) were experimentally investigated in a chevron corrugated-plate heat exchanger. A MWCNT/water nanofluid with a volume concentration of 0.0111% and an Al2O3/water nanofluid with a volume concentration of 1.89% were mixed at a volume ratio of 1:2.5. A small amount of MWCNTs was added in order to increase the mixture thermal conductivity. Experiments with water used as both hot and cold fluids were carried out first to obtain a heat transfer correlation for fluids flowing in the chevron plate heat exchanger. The results of the nanofluid mixture were compared with those of the Al2O3/water nanofluid and water. Results show that the heat transfer coefficient of the hybrid nanofluid mixture is slightly larger than that of the Al2O3/water nanofluid and water, when comparison is based on the same flow velocity. The hybrid nanofluid mixture also exhibits the highest heat transfer coefficient at a given pumping power. The pressure drop of the hybrid nanofluid mixture is smaller than that of the Al2O3/water nanofluid and only slightly higher than that of water. Therefore, hybrid nanofluid mixtures might be promising in many heat transfer applications.

A brief review on convection heat transfer of fluids at supercritical pressures in tubes and the recent progress

Abstract: This study presents a state-of-the-art overview on heat transfer characteristics of fluids (mainly water, carbon dioxide and hydrocarbon fuels) flowing in smooth tubes and enhanced tubes at supercritical pressures and tries to obtain a fundamental understanding of the unique characteristics. Heat transfer in enhanced tubes is much better than that in smooth tubes with a larger pressure drop penalty at supercritical conditions. Thermo-physical properties of fluids at supercritical pressures and relevant parametric effects (e.g., effects of mass flux, heat flux, pressure and flow direction) on heat transfer performance are outlined. Inconsistencies in the literature on heat transfer are emphasized and evaluated. Possible reasons are suggested to explain those inconsistencies. Moreover, the mechanisms for heat transfer deterioration at supercritical pressures are discussed and different correlations for predicting heat transfer deterioration are compared and assessed with experimental data. These predictive correlations based on one working fluid cannot be applied directly to other working fluids. Besides, several common buoyancy criteria proposed in the literature to distinguish forced convection and mixed convection are evaluated and show large discrepancies with experimental data. There is no buoyancy criterion developed for hydrocarbon fuels. Future research needs are warranted for heat transfer of near-critical and supercritical fluids.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Recent advances in friction-stir welding : Process, weldment structure and properties

Abstract: Friction-stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, the reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.