| 1. |
- Löfgren, Hans B., et al.
(author)
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Initial solidification in liquid metal film flow over a moving bondary
- 2001
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In: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 44:4, s. 837-842
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Journal article (peer-reviewed)abstract
- The initial solidification problem of a two-dimensional liquid metal film flow over a heat extracting moving boundary is studied. Analytical solutions in the limit of large Peclet numbers are found. It is shown that the point of initial solidification depends on the Peclet number, the Biot number and the superheat. The initial growth of the solidified phase is found to have a quadratic dependence of the distance from the point of initial solidification. The results are applicable to continuous strip casters.
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| 2. |
- Yang, Z. L., et al.
(author)
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Numerical investigation of bubble growth and detachment by the lattice-Boltzmann method
- 2001
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In: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 44:1, s. 195-206
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Journal article (peer-reviewed)abstract
- A numerical study has been performed to investigate the characteristics of bubble growth on, and detachment from, an orifice. The FlowLab code, which is based on a lattice-Boltzmann model of two-phase flows, was employed. Macroscopic properties, such as surface tension (a) and contact angle (beta), were implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model was found to possess a linear relation between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The separate effects of the body force (gravity), gas injection rate, surface tension, and wettability were analyzed for both horizontal and vertical surfaces. It is shown that results of the lattice-Boltzmann modeling exhibit correct parametric dependencies of the departure diameter of bubbles generated on the horizontal surface on the above factors as previously established in experiments. For the case of bubble growth and departure on the vertical surface, the different effects of hydrodynamic parameters, except gas generation rate, were predicted.
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| 3. |
- Yang, Z. L., et al.
(author)
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Numerical simulation of bubbly two-phase flow in a narrow channel
- 2002
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In: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 45:3, s. 631-639
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Journal article (peer-reviewed)abstract
- An advanced numerical simulation method on fluid dynamics - lattice-Boltzmann (LB) method is employed to simulate the movement of Taylor bubbles in a narrow channel, and to investigate the flow regimes of two-phase flow in narrow channels under adiabatic conditions. The calculated average thickness of the fluid film between the Taylor bubble and the channel wall agree well with the classical analytical correlation developed by Bretherton. The numerical simulation of the behavior of the flow regime transition in a narrow channel shows that the body force has significant effect on the movement of bubbles with different sizes. Smaller body force always leads to the later coalescence of the bubbles, and decreases the flow regime transition time. The calculations show that the surface tension of the fluid has little effect on the flow regime transition behavior within the assumed range of the surface tension. The bubbly flow with different bubble sizes will gradually change into the slug flow regime. However, the bubbly flow regime with the same bubble size may be maintained if no perturbations on the bubble movement occur. The slug flow regime will not change if no phase change occurs at the two-phase interface.
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| 4. |
- Dovic, D., et al.
(author)
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Generalized correlations for predicting heat transfer and pressure drop in plate heat exchanger channels of arbitrary geometry
- 2009
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 52:19-20, s. 4553-4563
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Journal article (peer-reviewed)abstract
- Characteristics of the flow in chevron plate heat exchangers are investigated through visualization tests of channels with beta = 28 degrees and beta = 61 degrees. Mathematical model is then developed with the aim of deriving correlations for prediction off and Nu for flow in channels of arbitrary geometry (beta and 1511). Thermal and hydraulic characteristics are evaluated using analytical solutions for the entrance and fully developed regions of a sinusoidal duct adapted to the basic single cell. The derived correlations are finally adjusted so as to agree with experimental results from tests on channels with beta = 28 degrees and beta = 65 degrees. f and Nu calculated by the presented correlations are shown to be consistent with experimental data from the literature at Re = 2-10,000, beta = (15-67)degrees and b/l = 0.26-0.4.
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| 5. |
- Rundström, Daniel, et al.
(author)
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Large-eddy simulation of an impinging jet in a cross-flow on a heated wall-mounted cube
- 2009
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In: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 52:3-4, s. 921-931
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Journal article (peer-reviewed)abstract
- A large-eddy simulation (LES) is performed in order to predict the mean velocity field, the turbulence characteristics and the heat transfer rate of an impinging jet in cross-flow configuration on a heated wall-mounted cube. The WALE model was used to model the subgrid-scale tensor. The results from the LES are compared with a Reynolds stress model (RSM) and against earlier measurements with identical set-up. A comparison between the results from the predictions and the measurements shows that in general the LES has better agreement with the measurements compared to the RSM and particularly in the stagnation region of the impinging jet.
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| 6. |
- Song, Hong-Wei, et al.
(author)
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Thermal fatigue on pistons induced by shaped high power laser : Part II: Design of spatial intensity distribution via numerical simulation
- 2008
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 51:3-4, s. 768-778
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Journal article (peer-reviewed)abstract
- In the laser induced thermal fatigue simulation test on pistons, the high power laser was transformed from the incident Gaussian beam into a concentric multi-circular pattern with specific intensity ratio. The spatial intensity distribution of the shaped beam, which determines the temperature field in the piston, must be designed before a diffractive optical element (DOE) can be manufactured. In this paper, a reverse method based on finite element model (FEM) was proposed to design the intensity distribution in order to simulate the thermal loadings on pistons. Temperature fields were obtained by solving a transient three-dimensional heat conduction equation with convective boundary conditions at the surfaces of the piston workpiece. The numerical model then was validated by approaching the computational results to the experimental data. During the process, some important parameters including laser absorptivity, convective heat transfer coefficient, thermal conductivity and Biot number were also validated. Then, optimization procedure was processed to find favorable spatial intensity distribution for the shaped beam, with the aid of the validated FEM. The analysis shows that the reverse method incorporated with numerical simulation can reduce design cycle and design expense efficiently. This method can serve as a kind of virtual experimental vehicle as well, which makes the thermal fatigue simulation test more controllable and predictable.
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| 7. |
- Vynnycky, Michael, et al.
(author)
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An analytical and numerical study of coupled transient natural convection and solidification in a rectangular enclosure
- 2007
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 50:25-26, s. 5204-5214
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Journal article (peer-reviewed)abstract
- The transient process of the solidification of a pure liquid phase-change material in the presence of natural convection in a rectangular enclosure is considered both analytically and numerically. One vertical boundary is held at a temperature below the melting-point of the material, the other above; the horizontal boundaries are both assumed adiabatic. A nondimensional analysis of the problem, principally in terms of the Rayleigh (Ra) and Stefan (St) numbers, indicates that some asymptotic simplification is possible for materials often considered in the literature (water, gallium, lauric acid). This observation suggests a way to simplify the full problem when Ra >> 1 and St << 1, giving a conventional boundary value problem for the liquid phase and pointwise-in-space first-order ODEs for the evolution in time of the solidification front. The method is tested against full 2D finite-element-based transient numerical simulations of solidification. In addition, simpler approaches for determining the average thickness of the solid layer, based on boundary-layer and enclosure flow correlations, are also investigated.
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| 8. |
- Wiberg, Roland, et al.
(author)
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Heat transfer from a cylinder in axial turbulent flows
- 2005
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 48:8, s. 1505-1517
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Journal article (peer-reviewed)abstract
- Local convective heat transfer coefficients were measured on a two-diameter long cylinder in axial flows of air at conditions unexplored so far, by using thermochromic liquid crystals (TLC) coated on an electrically heated strip-foil consisting bonded to the external surfaces. The Reynolds numbers (Re) based on the cylinder diameter were between 8.9 x 10(4) and 6.17 x 10(5), and the flow in front of the cylinder was modified in some cases by the use of a turbulence generating grid, or by circular disc inserts of two sizes placed upstream of the cylinder. These created a major change in the local convective heat transfer coefficient distribution on the cylinder. Increase of the turbulence intensity from Tu < 0.1% to Tu = 6.7% at the same Re increased the average calculated Nusselt number Nu over the cylinder by 25%, and decreased the Nu non-uniformity over the surface. One of the flow modification inserts also reduced significantly the Nu non-uniformity. The position of flow reattachment was measured using tufts. Our heat transfer data agree well with the small amount if data published of others, when extrapolated to their conditions. Correlations between the Nu and Re in the form Nu = CRee were established and presented for the average Nu on the front, middle and rear cylinder surfaces, and the variation of the local exponent e was shown along the cylinder. Introducing a new technique, a TLC-coated heated flat plate mounted in the flow above the cylinder in the meridional plane was demonstrated to help visualize the flow field above the cylinder. A track of maximum convective coefficients on this plate was found similar in position to the stream line dividing the forward and backward flows in a case measured for the separated flow in a past study.
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| 9. |
- Pettersson, M, et al.
(author)
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Modelling of an electric IR heater at transient and steady state conditions Part I: model and validation
- 2000
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In: International Journal of Heat and Mass Transfer. - 0017-9310. ; 43:7, s. 1209-1222
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Journal article (peer-reviewed)abstract
- A model for an electric infrared (IR) heater has been developed. The model includes non-grey radiative heat transfer between the different parts of the IR heater, as well as conduction in reflector material and convective cooling of surfaces. The geometry is simplified into one dimension. Using IR module voltage, as the only input, the model predicts the temperature of heater components and cooling air, as well as the net radiation heat transfer to the surroundings at steady state and transient conditions. The model has been validated against both steady state and transient experimental results from a small electric IR heater. The model predictions are in good agreement with experimental data both regarding steady state results and the transient response over a wide range of voltages. (C) 2000 Elsevier Science Ltd. All rights reserved.
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| 10. |
- Pettersson, M, et al.
(author)
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Modelling of an electric IR heater at transient and steady state conditions Part II: modelling a paper dryer
- 2000
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In: International Journal of Heat and Mass Transfer. - 0017-9310. ; 43:7, s. 1223-1232
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Journal article (peer-reviewed)abstract
- A model for an electric infrared (IR) paper dryer has been developed. The model includes non-grey radiative heat transfer between the different parts of the IR heater, as well as conduction in reflector material and convective cooling of surfaces. Such heat transfer calculations are combined with energy balances to provide a system of equations that simulates the behaviour of an electric III dryer. Using IR module voltage as the only input, the model predicts the temperature of dryer components and cooling air, as well as the net radiation heat transfer to the paper sheet at steady state and transient conditions. The model has been used to investigate trends in efficiency and component temperature with changing voltage and paper grade. Emphasis has been on back reflector temperature and dryer efficiency. Also, the transients during start-up of an IR paper dryer have been investigated. The study indicates that the transients of the back reflector is important for the time needed to reach steady state heat flux at the paper sheet. (C) 2000 Elsevier Science Ltd. All rights reserved.
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