| 1. |
- Holst, Anders, et al.
(author)
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Heat transfer augmentation in an oscillating flow
- 2002
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. ; 372:2, s. 89-93
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Conference paper (peer-reviewed)abstract
- For combustors a heat transfer augmentation of two to five times higher than expected has been reported. Experiments, where the temperature profile in the tail pipe of the pulse combustor has been measured, give no indication why the heat transfer should be augmented. The objective is to study the heat transfer of an oscillating flow between two parallel plates. A set of governing equations is formulated from first principles. Analytical solutions can then be obtained for both the velocity and temperature fields for the special flow considered. The heat conduction vector can so be determined and the heat transfer at the plates over one cycle is found to be dependent of the frequency of the oscillations as well as the phase difference between the pressure and temperature oscillations. From the analysis it is found that for certain intervals of the phase difference and the frequency of the oscillations an augmented heat transfer can be found. This means that an augmented heating (or cooling) process can be arranged in a steady flow by superimposing oscillations.
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| 2. |
- Krajnovic, Sinisa, 1970, et al.
(author)
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Development of Large-Eddy Simulation for Vehicle Aerodynamics
- 2002
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In: Proceedings of the Heat Transfer Division - 2002 Volume 2: Theory and Fundamentals of Heat Transfer Thermophysical Properties Heat Transfer Education Heat Transfer Visualization. - 0272-5673. ; 372:2, s. 165-172
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Journal article (peer-reviewed)abstract
- The feasibility of use of large-eddy simulation (LES) in external vehicle aerodynamics is investigated. The computational cost needed for LES of the full size car at road conditions is beyond the capability of the computers in the near future (Krajnovic (2002)). Since LES cannot be used for quantitative prediction of this flow, i.e. obtaining the aerodynamic forces and moments, an alternative use of this technique is suggested that can enhance the understanding of the flow around a car. It is found that making LES of the flow around simplified car-like shapes at lower Reynolds number can increase our knowledge of the flow around a car. Two simulations are made, one of the flow around a cube and the other of the flow around a simplified bus. The former simulation proved that LES with relatively coarse resolution and simple inlet boundary condition can provide accurate results. The latter simulation resulted in flow in agreement with experimental observations and displayed some flow features that were not observed in experiments or steady simulations of such flows. This simulation gave us possibility to study the transient mechanisms that are responsible for the aerodynamic properties of a car. The knowledge gained from this simulation can be used by the stylist to tune the aerodynamics of the car's design but also by the CFD specialists to improve the turbulence models.
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| 3. |
- Mumic, Fadil, et al.
(author)
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Effect of free-stream turbulence on heat transfer and fluid flow in a transonic turbine stage
- 2006
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. - 0791837904
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Conference paper (peer-reviewed)abstract
- In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer. Copyright
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| 4. |
- Mumic, Fadil, et al.
(author)
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Numerical simulations of unsteady fluid flow and heat transfer in a transonic turbine stage
- 2006
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. - 0791837904
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Conference paper (peer-reviewed)abstract
- In this work, a numerical study has been performed to simulate the unsteady fluid flow and heat transfer in a transonic high-pressure turbine stage. The main objective of this study is to understand the unsteady flow field and heat transfer in a single transonic turbine stage using an unsteady structured Navier-Stokes solver. For the time accurate computation, a fully implicit time discretization, dual-time stepping, is performed. The results of the CFD simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with experimental data. In particular, the results show significant fluctuations in heat transfer and pressure at mid-span on the rotor blade, and that the rotor has a limited influence on the heat transfer to the NGV at mid span. Copyright
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| 5. |
- Nilsson, Thomas, et al.
(author)
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Thermal radiation heat transfer and biomass combustion in a large-scale fixed bed boiler
- 2003
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. ; 374:2, s. 405-413
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Conference paper (peer-reviewed)abstract
- The main focus of this work is to investigate the performance of some simple radiation models used in the thermal radiative heat transfer calculations in a 55 MWe fixed bed boiler with wet wood-chips as the fuel. An optically thin approach, Rosseland approximation, and the P1-approximation were utilised in the investigation. A new optimised version, as it comes to computational speed, of the exponential wide band model (EWBM) is used. The initial calculations showed that the optically thick approach failed, The optically thin approach actually gave the best prediction of the temperature, if the mean beam length (Lm) was chosen carefully. The P 1-approximation gave less good predictions than the best optical thin case, but it could be the best engineering model to use if little was known about the mean beam length. The conclusion is that the optically thin model is sensitive to the chosen mean beam length (Lm) used in the EWBM. The P1-approximation is almost insensitive to the choice of L m, due to the consideration of radiation self-absorption, where the different predicted values of the incident radiation compensate for different values of Lm. For the same reason, the use of other solution techniques, such as DOM or DTM, may lead to the same conclusion, i.e., the insensitivity of the choice of Lm.
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| 6. |
- Selimovic, Faruk, et al.
(author)
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Computational analysis of an O2separating membrane for a CO2-emission-free power process
- 2004
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. ; 375:2, s. 9-18
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Conference paper (peer-reviewed)abstract
- The increased demand for clean power in recent years has led to the development of various processes that include different types of CO2 capture. Several options are possible: pre-combustion concepts (fuel de-carbonization and subsequent combustion of H2), post-combustion concepts (tail-end CO2 capture solutions, such as amine scrubbing), and integrated concepts in which combustion is carried out in pure a O2 or oxygen-enriched environment instead of air. The integrated concepts involve the use of oxygen-, hydrogen-, or CO2- separating membranes resulting in exhaust gas containing CO2 and water, from which CO2 can easily be separated. In contrast to traditional oxygen pumps, where a solid oxide electrolyte is sandwiched between two gas-permeable electrodes, a dense, mixed ionic-electronic conducting membrane (MIECM) shows high potential for oxygen separation without external electrodes attached to the oxide surface. Models for oxygen transport through dense membranes have been reported in numerous recent studies. In this study, an equation for oxygen separation has been integrated into a steady-state heat and mass transfer membrane model. Oxygen transfer through a porous supporting layer of membrane is also taken into account. The developed FORTRAN code has been used for numerical investigation and performance analysis of the MIECM and the oxygen transport potential over a range of operating conditions. Preliminary results indicate that a non-uniform temperature distribution, for a given set of oxygen inlet boundary conditions has considerable impact on the oxygen flux and membrane efficiency. Since the implementation of detailed membrane models in heat and mass balance calculations for system studies would result in excessive calculation time, results from this study will be utilized for the generation of correlations describing the oxygen transfer as a function of operating parameters such as temperature and partial pressure. This modeling approach is expected to improve the accuracy of system studies.
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| 7. |
- Selimovic, Faruk, et al.
(author)
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Dynamic Analysis of an O2 Separating Membrane Reactor for CO2-Emission-Free Power Processes
- 2006
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In: Proceedings of IMECE2006.
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Conference paper (peer-reviewed)abstract
- The need to reduce CO2 emissions from fossil-fuel based power production creates the need for new power plant solutions where the CO2 is captured and stored or reused. Oxygen Transfer Membrane (OTM) is the key component of oxy-fuel combustion processes as pure oxygen is usually required to process reactions (e.g. Natural Gas Combined cycle NGCC, Pulverised Coal-fired power plants PC-plants, Integrated Gasification Combined Cycle IGCC). The transfer of oxygen across such OTM is limited by a number of processes, such as surface exchange and ambipolar diffusion through mixed-conducting gas separation layer. This paper shows a mathematical model of an oxygen transfer membrane incorporated into OTM reactor (OTM reactor consists of High Temperature Heat Exchanger and OTM), where transient behavior takes place. The modeling of the OTM reactor has been carried out to show the importance of optimizing OTM parameters (temperatures, oxygen partial pressures, oxygen flux) and reactor design that enables a high oxygen transfer for optimum performance of future power cycles with CO2 capture. All modeling work was carried out in the modeling language Modelica, which is an open standard for equation-based, object-oriented modeling of physical systems. The OTM reactor model has been built using the CombiPlant Library, a modeling library for combined cycle power plants which is under development.
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| 8. |
- Wang, Lei, et al.
(author)
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Experimental investigation of local heat transfer in a square duct with continuous and truncated large ribs
- 2004
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In: American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD. - 0272-5673. ; 375:1, s. 589-597
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Conference paper (peer-reviewed)abstract
- Repeated ribs are frequently employed to promote turbulence and to enhance heat transfer in various ducts. In the present study, liquid crystal thermography was applied to the study of heat transfer from a square channel having one surface heated at uniform heat flux and roughened by repeated ribs. The continuous and truncated ribs, having square sections, with height-to-hydraulic diameter ratio of 0.15, were deployed normal to the mainstream direction of flow. Detailed distributions of the local heat transfer coefficient were obtained at various Reynolds number within the turbulent flow regime. Averaged data were calculated in order to evaluate the augmentation of heat transfer by the presence of different ribs. Copyright
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