Thermal Management of Surface Mount Power Magnetic Components

1999 ◽  
Vol 122 (4) ◽  
pp. 323-327
Author(s):  
G. Refai-Ahmed ◽  
M. M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Power Loss ◽  
Numerical Study ◽  
Lower Surface ◽  
Experimental Results ◽  
Surface Mount ◽  
Conduction Heat Transfer ◽  
Magnetic Components ◽  
Underfill Material ◽  
Good Agreement

A numerical and experimental study of conduction heat transfer from low power magnetic components with gull wing leads was conducted to determine the effects of distributing the power loss between the core, the winding and the thermal underfill on the thermal resistance. The numerical study was conducted in the power loss ratio range of 0.5⩽PR⩽1.0, where the only active power loss was from the winding at PR=1. In addition, the effect of the thermal underfill material between the substrate and the lower surface of the magnetic package on the thermal performance of the magnetic device was also examined. For comparison, a test was conducted on a magnetic component at PR=1, without thermal underfill. This comparison revealed good agreement between the numerical and experimental results. Finally, a general model was proposed for conduction heat transfer from the surface mount power magnetic packages. The agreement between the model and the experimental results was within 8 percent. [S1043-7398(00)00704-0]

AN EXPERIMENTAL AND NUMERICAL STUDY OF HEAT TRANSFER IN A SIMULATED COLLECTOR FOR A SOLAR DRYER

1993 ◽  
Vol 17 (2) ◽  
pp. 145-160
Author(s):  
P.H. Oosthuizen ◽  
A. Sheriff
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Lower Surface ◽  
Local Heat ◽  
Electrical Heating ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Transfer Rates ◽  
Thermocouple Probe

Indirect passive solar crop dryers have the potential to considerably reduce the losses that presently occur during drying of some crops in many parts of the “developing” world. The performance so far achieved with such dryers has, however, not proved to be very satisfactory. If this performance is to be improved it is necessary to have an accurate computer model of such dryers to assist in their design. An important element is any dryer model is an accurate equation for the convective heat transfer in the collector. To assist in the development of such an equation, an experimental and numerical study of the collector heat transfer has been undertaken. In the experimental study, the collector was simulated by a 1m long by 1m wide channel with a gap of 4 cm between the upper and lower surfaces. The lower surface of the channel consisted of an aluminium plate with an electrical heating element, simulating the solar heating, bonded to its lower surface. Air was blown through this channel at a measured rate and the temperature profiles at various points along the channel were measured using a shielded thermocouple probe. Local heat transfer rates were then determined from these measured temperature profiles. In the numerical study, the parabolic forms of the governing equations were solved by a forward-marching finite difference procedure.

Forced Convection in a Porous Channel With Discrete Heat Sources

2000 ◽  
Vol 123 (2) ◽  
pp. 404-407 ◽  
Author(s):  
C. Cui ◽  
X. Y. Huang ◽  
C. Y. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Porous Channel ◽  
Heat Sources ◽  
Nusselt Numbers ◽  
Discrete Heat Sources ◽  
Flow Through ◽  
Good Agreement

An experimental study was conducted on the heat transfer characteristics of flow through a porous channel with discrete heat sources on the upper wall. The temperatures along the heated channel wall were measured with different heat fluxes and the local Nusselt numbers were calculated at the different Reynolds numbers. The temperature distribution of the fluid inside the channel was also measured at several points. The experimental results were compared with that predicted by an analytical model using the Green’s integral over the discrete sources, and a good agreement between the two was obtained. The experimental results confirmed that the heat transfer would be more significant at leading edges of the strip heaters and at higher Reynolds numbers.

Heat Transfer Evaluation for a Two-Pass Smooth Wall Channel: Stationary and Rotating Cases

2019 ◽  
Vol 142 (6) ◽  
Author(s):  
Mandana S. Saravani ◽  
Nicholas J. DiPasquale ◽  
Ahmad I. Abbas ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotational Speed ◽  
Numerical Study ◽  
Flow Behavior ◽  
Smooth Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

Abstract This study presents findings on combined effects of Reynolds number and rotational effect for a two-pass channel with a 180-deg turn, numerically and experimentally. To have a better understanding of the flow behavior and to create a baseline for future studies, a smooth wall channel with the square cross section is used in this study. The Reynolds number varies between 6000 and 35,000. Furthermore, by changing the rotational speed, the maximum rotation number of 1.5 is achieved. For the numerical investigation, large eddy simulation (LES) is utilized. Results from the numerical study show a good agreement with the experimental data. From the results, it can be concluded that increasing both Reynolds number and rotational speed is in favor of the heat transfer coefficient enhancement, especially in the turn region.

An Experimental Investigation of Heat Transfer in Variable Porosity Media

1985 ◽  
Vol 107 (3) ◽  
pp. 642-647 ◽  
Author(s):  
K. Vafai ◽  
R. L. Alkire ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Packed Bed ◽  
Volume Averaging ◽  
Experimental Results ◽  
Variable Porosity ◽  
Local Volume Averaging ◽  
Convection In Porous Media ◽  
Impermeable Boundary ◽  
Good Agreement

This paper presents an experimental investigation on the effects of a solid impermeable boundary and variable porosity on forced convection in porous media. Emphasis is placed on the channeling effects on heat transfer in packed beds. The local volume-averaging technique is used to establish the governing equations and a numerical scheme is developed which incorporates the boundary and variable porosity effects on heat transfer. The experimental results for the heat flux at the boundary are presented as a function of the pertinent variables in a packed bed. The Nusselt number is found to increase almost linearly with an increase in the Reynolds number based on the pore diameter. The experimental results are found to be in good agreement with the theoretical results which account for the variable porosity effects. A comparison between the numerical and the experimental results demonstrates the importance of boundary and variable porosity effects on heat transfer in variable porosity media.

scholarly journals Heat Transfer Enhancement and Hydrodynamic Characteristics of Nanofluid in Turbulent Flow Regime

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Mohammad Nasiri-lohesara
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Pure Water ◽  
Reynolds Numbers ◽  
Hydrodynamic Characteristics ◽  
Two Phase ◽  
Tube Heat Exchanger ◽  
Turbulent Flow Regime ◽  
Lower Slope ◽  
Good Agreement

Turbulent forced convection ofγ-Al2O3/water nanofluid in a concentric double tube heat exchanger has been investigated numerically using mixture two-phase model. Nanofluids are used as coolants flowing in the inner tube while hot pure water flows in outer tube. The studies are conducted for Reynolds numbers ranging from 20,000 to 50,000 and nanoparticle volume fractions of 2, 3, 4, and 6 percent. Results showed that nanofluid has no effects on fully developed length and average heat transfer coefficient enhances with lower slope than wall shear stress. Comparisons with experimental correlation in literature are conducted and good agreement with present numerical study is achieved.

Mixed Convection in a Horizontal Porous Duct With a Sudden Expansion and Local Heating From Below

1999 ◽  
Vol 121 (3) ◽  
pp. 653-661 ◽  
Author(s):  
Y. Yokoyama ◽  
F. A. Kulacki ◽  
R. L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Local Heating ◽  
Lower Surface ◽  
Porous Matrix ◽  
Sudden Expansion ◽  
Nusselt Numbers ◽  
Matrix Heat ◽  
Heating From Below

Results are reported for an experimental and numerical study of forced and mixed convective heat transfer in a liquid-saturated horizontal porous duct. The cross section of the duct has a sudden expansion with a heated region on the lower surface downstream and adjacent to the expansion. Within the framework of Darcy’s formulation, the calculated and measured Nusselt numbers for 0.1 < Pe < 100 and 50 < Ra < 500 are in excellent agreement. Further, the calculated Nusselt numbers are very close to those for the bottom-heated flat duct. This finding has important implications for convective heat and mass transfer in geophysical systems and porous matrix heat exchangers. The calculations were also carried out for glass bead-packed beds saturated with water using non-Darcy’s formula. The streamlines in the forced convection indicate that, even with non-Darcy effects included, recirculation is not observed downstream of an expansion and the heat transfer rate is decreased but only marginally.

Geometry Evaluation of Heat Transfer by Mixed Convention in Driven Cavities with Two Inserted Fins

2019 ◽  
Vol 396 ◽  
pp. 164-173 ◽  
Author(s):  
Priscila M. Rodrigues ◽  
Cicero C. de Escobar ◽  
Luiz Alberto Oliveira Rocha ◽  
Liércio André Isoldi ◽  
Elizaldo Domingues dos Santos
Keyword(s):  
Heat Transfer ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Lower Surface ◽  
Stable Stratification ◽  
Geometric Constraints ◽  
Driven Cavity ◽  
Geometric Configurations ◽  
Two Dimensional Flow ◽  
Volume Method

In this work, a numerical study of a flow with heat transfer by mixed convection are carried out. The objective is the geometric evaluation through the application of the Construtal Design and the exhaustive search method. The behavior of a lid-driven cavity with stable stratification subjected to an incompressible, laminar and two-dimensional flow is investigated. The cavity has two rectangular fins inserted in the lower surface. The problem is subject to three constrains: three geometric constraints: the area of the cavity, two fin areas. The investigated geometry has three degrees of freedom: the ratio between height and cavity length (H/L) and the ratio between height and length of each fin (H1/L1 and H2/L2). The effect of the fin geometry over spatial-averaged Nusselt (NuH) is investigated for Reynolds number (ReH) = 400 and Richardson (Ri) = 0.1. The conservation equations of mass, momentum and energy are tackled with Finite Volume Method (FVM) through the use of commercial software FLUENT. The results showed that the lower H2/L2 ratios resulted in higher NuH values. An increase in NuH value of approximately 49% between the worst and the best geometrical configuration was found, thus highlighting the importance of geometric evaluation on this kind of problem. It is concluded that for the problem addressed the best behavior is obtained when the fins have a small insertion into the cavity, thus avoiding the restriction of the main vortex flow. The results found highlight the importance of the geometric evaluation for the purpose of theoretical recommendation on the geometric configurations that lead to the best thermal performance.

Numerical Simulation of Thermal Performance of a High Aspect Ratio Thermal Energy Storage Device

2012 ◽  
Author(s):  
Jingde Zhao ◽  
Jorge L. Alvarado ◽  
Ehsan M. Languri ◽  
Chao Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Aspect Ratio ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Aspect Ratio ◽  
Numerical Study ◽  
Experimental Results ◽  
Heat Transfer Analysis

Heat transfer analysis of a high aspect ratio thermal energy storage (TES) device was carried out numerically. The three dimensional numerical study was performed to understand the heat transfer enhancement which results from internal natural convection in a high aspect ratio vertical unit. Octadecane was used as phase change material (PCM) inside TES system, which consisted of six corrugated panels filled with PCM. Each panel had a total of 6 tall cavities filled with PCM, which were exposed to external flow in a concentric TES system. Unlike traditional concentric-type TES devices where heat transfer by conduction is the dominant heat transport mechanism, the high aspect ratio TES configuration used in the study helped promote density-gradient based internal convection mechanism. The numerical model was solved based on the finite volume method, which captured the whole transient heat transfer process effectively. The time-dependent temperature profiles of the PCM inside a single TES panel are compared with the experimental results for two cases. Numerical and experimental results of the two cases showed a reasonable agreement. Furthermore, convection cells were formed and sustained when the PCM melted within the space between the solid core and the walls. The promising results of this numerical study illustrate the importance of internal natural convection on the speed of the PCM melting (charging) process.

Numerical Investigation of Heat Transfer and Cooling Effectiveness Within a LPT-Vane Cascade and its Comparison to Experimental Results

2012 ◽  
Author(s):  
Annette Beuermann ◽  
Andreas Pahs ◽  
Stefan Rochhausen
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Guide Vane ◽  
Numerical Data ◽  
Secondary Flows ◽  
Experimental Results ◽  
Cooling Effectiveness ◽  
Flow Angle ◽  
Film Cooling Effectiveness ◽  
Good Agreement

Gaps between stationary and rotating parts in turbines have to be fed with cooling air to keep metal temperatures below material limits. Reducing the coolant mass flow and analysing its impact on the flow field concerning aerodynamic and thermal data were the objectives of experiments, performed within the European research project AITEB. As part of this project, measurements of cooling effectiveness and heat transfer on the endwall of a low pressure turbine nozzle guide vane were performed at a low speed cascade wind tunnel at DLR Göttingen. Higher cooling mass flow rates increase secondary flows and subsequently heat transfer whilst metal temperatures are reduced due to larger coverage with coolant. It was also shown that heat transfer varies significantly with different flow angles. According to the experimentally investigated flow fields numerical studies were performed using the DLR code TRACE, a RANS-Solver for turbomachinery flows. TRACE simulations were done using the Wilcox k-ω turbulence modelling. The boundary conditions were taken from the experimental setup. In this paper the numerical data was analysed and compared with the experimental results regarding thermodynamics. The simulations confirmed a high influence of the flow angle. Within the flow regime affected by the injected coolant a good agreement between the numerical heat transfer results and the experimental data was observed. The qualitative and quantitative values were met after finding the optimum calculation parameters. Only in the region downstream of the throat area a different behaviour became obvious. Concerning film-cooling effectiveness quantitative differences between simulation and experiment were found whilst qualitative good agreement was observed.

Experimental Measurement of Water Evaporation Rates Into Air and Superheated Steam

1988 ◽  
Vol 110 (1) ◽  
pp. 237-242 ◽  
Author(s):  
M. Haji ◽  
L. C. Chow
Keyword(s):  
Heat Transfer ◽  
Superheated Steam ◽  
Evaporation Rate ◽  
Free Stream ◽  
Experimental Results ◽  
Water Evaporation ◽  
Analytical Prediction ◽  
Conduction Heat Transfer ◽  
Inversion Temperature ◽  
Analytical Results

The rates of evaporation of water from a horizontal water surface into a turbulent stream of hot air or superheated steam at different free-stream mass fluxes and modulated temperatures were experimentally measured. The pressure of the free stream was atmospheric. For steam, the experimental results are mostly within 10 percent of the available analytical results. Two previous experimental results are about 50 percent and 300 percent higher than the analytical results. For air, the measured evaporation rates are consistently higher than the analytical results. An estimate of the conduction heat transfer from the walls of the test section to water was made for several air tests. If the conduction heat transfer were subtracted from the total heat transfer, the measured evaporation rates are actually quite close to the analytical results. The present experiment also confirms the existence of a temperature, called the inversion temperature, below which the water evaporation rate is higher in air than in steam, but above which the opposite is true. The inversion temperature is in good agreement with the analytical prediction. The results for both air and superheated steam show that a certain scaled expression for the evaporation rate is independent of the free-steam mass flux, also in agreement with the analytical prediction.

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