Showing papers by "Josua P. Meyer published in 2007"
TL;DR: In this article, a three-dimensional micro-channel heat sink was designed to minimize the peak temperature from the walls to the coolant fluid by using the finite volume method, and numerical results showed that the degrees of freedom have a strong effect on the maximum thermal conductance.
126 citations
TL;DR: In this paper, the authors present a study of flow regimes, pressure drops, and heat transfer coefficients during refrigerant condensation inside a smooth, an 18° helical micro-fin, and a herringbone tube.
Abstract: This paper presents a study of flow regimes, pressure drops, and heat transfer coefficients during refrigerant condensation inside a smooth, an 18° helical micro-fin, and a herringbone tubes. Experimental work was conducted for condensing refrigerants R-22, R-407C, and R-134a at an average saturation temperature of 40 °C with mass fluxes ranging from 400 to 800 kg m −2 s −1 , and with vapour qualities ranging from 0.85 to 0.95 at condenser inlet and from 0.05 to 0.15 at condenser outlet. These test conditions represent annular and intermittent (slug and plug) flow conditions. Results showed that transition from annular flow to intermittent flow, on average for the three refrigerants, occurred at a vapour quality of 0.49 for the smooth tube, 0.29 for the helical micro-fin tube, and 0.26 for the herringbone tube. These transition vapour qualities were also reflected in the pressure gradients, with the herringbone tube having the highest pressure gradient. The pressure gradients encountered in the herringbone tube were about 79% higher than that of the smooth tube and about 27% higher than that of the helical micro-fin tube. A widely used pressure drop correlation for condensation in helical micro-fin tubes was modified for the case of the herringbone tube. The modified correlation predicted the data within a 1% error with an absolute deviation of 7%. Heat transfer enhancement factors for the herringbone tube against the smooth tube were on average 70% higher while against the helical micro-fin tube it was 40% higher. A correlation for predicting heat transfer coefficients inside a helical micro-fin tube was modified for the herringbone tube. On average the correlation predicted the data to within 4% with an average standard deviation of 8%.
98 citations
TL;DR: In this article, the energy-utilization over a 10-year period (1994-2003) has been analyzed for the South African industrial sector, which consumes more primary energy than any other sector of the economy.
66 citations
TL;DR: In this article, it was shown from the refrigerant condensation data that flow patterns have a strong influence on heat transfer and pressure drop, and compared to the performance of smooth tubes with helical wire inserts (with pitches of 5mm, 7.77mm and 11mm corresponding to helical angles of 78.2°, 72°, and 65.3°, respectively).
63 citations
TL;DR: In this paper, a capacitance sensor was developed for horizontal two-phase flow in small diameter tubes, and a test rig was constructed and a series of experiments were done with horizontal air-water flow in a 9 mm tube.
Abstract: Two-phase flow modelling is strongly dependent on flow patterns. For the purpose of objective flow pattern identification, a capacitance sensor was developed for horizontal two-phase flow in small diameter tubes. Finite element simulations were made during design to study the effect of vapour distribution, wall thickness and electrode angle. A test rig was constructed and a series of experiments was done with horizontal air–water flow in a 9 mm tube. The sensor test results are presented in time, amplitude and frequency domain. Flow regime characterization with the capacitance measurements is clearly possible.
61 citations
TL;DR: The information gained during this analysis brought to the four that the principle mode of mechanical failure for acetabular cups is overheating of the UHMWPE, mainly due to a lack of good and/or sufficient lubrication.
42 citations
TL;DR: This paper details a multigrid‐accelerated cut‐cell non‐conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow via a single equation set that describes sub‐, trans‐, and supersonic flows.
Abstract: This paper details a multigrid-accelerated cut-cell non-conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub-, trans-, and supersonic flows. Cut-cell technology is developed to furnish body-fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge-based vertex-centred finite volume method. An alternative dual-mesh construction strategy, similar to the cell-centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch-activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible–incompressible equation set on cut-cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.
19 citations
TL;DR: In this article, the mixing effectiveness of double-sided jets in crossflow was investigated using computational fluid dynamics and mathematical optimization techniques, and the results showed that changes in orifice size and spacing at a constant orifice-to-mainstream area ratio and momentum flux ratio have a significant influence on mixing effectiveness.
Abstract: Computational fluid dynamics and mathematical optimization were used to investigate the mixing effectiveness of jets in crossflow. A numerical model was developed, validated, and calibrated against experimental measurements of a temperature distribution at different cross-sectional planes downstream of an orifice injection plane. Good agreement was obtained when the ratio between momentum and species diffusivities was varied according to the jet-to-mainstream momentum flux ratio. Numerical optimization of various double-sided jet configurations followed, using a parametric approach. The results obtained showed that changes in orifice size and spacing at a constant orifice-to-mainstream area ratio and momentum flux ratio have a significant influence on mixing effectiveness. The optimum configuration compared favorably with an empirically defined relationship between orifice spacing and momentum flux ratio. Mathematical optimization was then combined with numerical methods to predict the optimum orifice configuration. The results showed the feasibility of using a gradient-based approximation method to allow, for a given set of parameters, the systematic adjustment of design variables to achieve improvement in performance.
17 citations
15 citations
TL;DR: Even for small problems, the developed solver outperforms Jacobi with local time-stepping in terms of computational time by a factor ranging between 30 and 1000, while having a total memory requirement of 1.9 times the aforementioned.
12 citations
Journal Article•
TL;DR: In this paper, numerical optimization results for three-dimensional heat and fluid flow in a rectangular micro-channel heat sink using water as the cooling fluid were reported. But the authors did not consider the effect of total volume fraction of the silicon wafer on the optimal aspect ratio and minimized maximum temperature.
Abstract: This paper reports numerical optimization results for three-dimensional heat and fluid flow in a rectangular micro-channel heat sink using water as the cooling fluid. The conducting heat sink consists of silicon wafer. Numerical simulation was conducted on a unit cell which is a micro-channel heat sink with a fixed volume of 0.9 mm3 and a fixed axial length of 10 mm. Geometric optimization was carried out to determine the optimal aspect ratio of a unit cell of a heat sink that minimized the overall maximum temperature and thus maximized the overall global thermal conductance. The effect of total volume fraction of the silicon wafer on the optimal aspect ratio and minimized maximum temperature was also studied. Results show that as the pressure drop increases, the minimized peak temperature decreases, and suggests that there is an optimal allocation of solid volume fraction for a fixed pressure drop. The behaviour of the optimized volume is in agreement with the constructal design method, where the objective is to minimize the peak temperature, subject to the constraints of fixed total volume and solid (silicon wafer) material.
TL;DR: In this paper, a vortex-centred finite volume numerical solver was developed, employing a fully implicit solution algorithm to obtain 3D temperature distributions, by comparing the peak temperatures obtained for a wide range of related cases, optimised cross-sectional shapes for particular input conditions were obtained.
Abstract: Purpose – This paper aims to investigate thermal geometric optimisation of rectangular heat conductive cooling structures within solid heat‐generating media for the purpose of minimising peak temperatures and enabling optimum use of spatial volume within integrated power electronics.Design/methodology/approach – A vortex‐centred finite volume numerical solver was developed, employing a fully implicit solution algorithm to obtain 3D temperature distributions. By comparing the peak temperatures obtained for a wide range of related cases, optimised cross‐sectional shapes for particular input conditions were obtained.Findings – Optimum shapes are dependent on seven identified parameters. In cases where a low percentage of volume is occupied by cooling structures, a high tendency exists for continuous thin cooling layers, as opposed to discrete rectangular cooling inserts, to present the best thermal behaviour. At higher volume percentages, the opposite is true.Practical implications – The reduced dimensions o...
Journal Article•
TL;DR: In this paper, a numerical approach is used to determine and compare steady-state thermal characteristics of this internal heat transfer augmentation scheme for two thermal boundary condition types, where a rectangular three-dimensional solid-state heat generating volume is externally cooled from its surface in either one or two orthogonal directions.
Abstract: This paper investigates the cooling ability of embedded solid-state, high-conductive layers in electronics applications. A numerical approach is used to determine and compare steady-state thermal characteristics of this internal heat transfer augmentation scheme for two thermal boundary condition types. The boundary conditions under investigation represent cases where a rectangular three-dimensional solid-state heat generating volume is externally cooled from its surface in either one or two orthogonal directions. Various material property and geometric parameters are considered. The numeric results are compared with predictions of a traditional planar conductivity approach. It is shown that a planar approach used for obtaining the thermal characteristics of a laminated composite structure over-simplifies the problem and only supplies an indication of the ultimate ideal cooling efficiency, which may be achieved, with cooling layers. This paper presents trends, which may be used to predict thermal characteristics more accurately for conditions where no thermal interfacial resistance is present.
TL;DR: In 2002, the first International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 2002) was held in the Kruger National Park, South Africa as discussed by the authors.
Abstract: In 2002, the first International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 2002) was hosted in the Kruger National Park, South Africa. In 2003, the second HEFAT confere...
01 Jan 2007
TL;DR: In this article, a probabilistic flow regime-based heat transfer coefficient during refrigerant condensation inside a smooth tube was presented, and a new time fraction-corrected flow regime based heat transfer correlation, heavily based on the Thome et al. correlation was developed for use in the Intermittent flow regime.
Abstract: This paper presents a study of probabilistic flow regime-based heat transfer coefficients during refrigerant condensation inside a smooth tube. Experimental work was conducted using refrigerant R-22, at an average saturation temperature of 40 o C, with mass fluxes ranging from 250650 kg/m 2 s, and with test section inlet vapor qualities ranging from 0.65 down to 0.10. These tests conditions represent mostly Intermittent flow, with some data points in the Annular and Stratified-wavy flow regimes. Utilizing time fraction data gathered in this experimental setup, a new time fraction-corrected flow regime-based heat transfer correlation, heavily based on the Thome et al. (J.R. Thome, J. El Hajal and A. Cavallini, Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, International Journal of Heat and Mass Transfer, 46:3365-3387, 2003) correlation was developed for use in the Intermittent flow regime. The modified correlation predicted the experimental data with a mean absolute deviation of 10%.
01 Jan 2007
TL;DR: In this article, the effect of void fraction and pressure drop on the aspect ratio, hydraulic diameter and peak temperature on the micro-channel heat sink was investigated, and the optimal configurations obtained numerically were compared with those obtained from approximate relationship using scale analysis and the trends are found to be in good agreement.
Abstract: This paper documents the geometric optimization of a three dimensional micro-channel heat sink with hydraulic diameter greater than 10μm. Two methods of analysis were used to perform the optimization; approximate relation using scale analysis and numerical method using a finite volume code. The micro-channel heat sink is treated as a combined unit. The effect of void fraction and pressure drop on the aspect ratio, hydraulic diameter and peak temperature on the micro-channel heat sink were investigated. The numerical simulation was carried out on a unit cell with volume of 0.9 mm3 and pressure differences between 10 kPa and 75 kPa. The optimal configurations obtained numerically were compared with those obtained from approximate relationship using scale analysis and the trends are found to be in good agreement.Copyright © 2007 by ASME
01 Jan 2007
TL;DR: In this paper, the authors extended the concept of generating the multi-scale structure for a finite-size flow system to three-dimensional heatgenerating plates with maximum heat transfer rate density.
Abstract: This paper extends the concept of generating the multi-scale structure for a finite-size flow system to three-dimensional heatgenerating plates with maximum heat transfer rate density. The fluid is forced through a given volume containing the heat generating plates by an applied pressure difference (ΔP). The heat-generating plates are arranged in a stack. This work consists of numerical simulation in a large number of flow configurations, one differing slightly from the next to determine the optimum plate spacing and maximum heat transfer rate density. The heat transfer rate density is further increased by inserting smaller three-dimensional plates between the bigger larger plates and optimising the whole structure. The effects of plate thickness and dimensionless pressure drop number on the resulting multi-scale structure are reported. The numerical results are found to be in good agreement with predicted results. NOMENCLATURE