Natural Convection Heat Transfer Characteristics of Simulated Microelectronic Chips

1987 ◽  
Vol 109 (1) ◽  
pp. 90-96 ◽  
Author(s):  
K.-A. Park ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Leading Edge ◽  
Thin Foil ◽  
Circuit Board ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Dimensional Boundary ◽  
The Heat Transfer Coefficient

Microelectronic circuits were simulated with thin foil heaters supplied with d-c power. The heaters were arranged in two configurations: flush mounted on a circuit board substrate or protruding from the substrate about 1 mm. Heat transfer coefficients (midpoint) were obtained with two heater heights (5 mm, 10 mm) and varying width (2 mm ∼ 70 mm), in water and R-113. The height effect for single flush heaters agrees qualitatively with conventional theory; however, even the widest heaters have coefficients higher than predicted due to leading edge effects. The heat transfer coefficient increases with decreasing width, with the coefficient for 2 mm being about 150 percent above that for 20 mm ∼ 70 mm. This is attributed to three-dimensional boundary layer effects. The protruding heaters have a coefficient about 15 percent higher. Data were obtained for in-line and staggered arrays of flush heaters with varying distance between heaters. Coefficients for the upper heaters are below those for lower heaters, with the differences diminishing as the vertical or horizontal spacing increases. For the protruding heaters, the upper heaters have higher coefficients than the lower heaters.

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Laser Doppler Velocimeter ◽  
Transfer Coefficients ◽  
Friction Coefficients ◽  
Heat Transfer Coefficients ◽  
Passage Vortex ◽  
Dimensional Boundary

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter (LDV). Friction coefficients obtained with the oil film interferometry (OFI) method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

Finite Element Predictions of Free Convection Heat Transfer Coefficients of Simulated Electronic Circuit Boards

1989 ◽  
Vol 111 (2) ◽  
pp. 129-134 ◽  
Author(s):  
C. Rajakumar ◽  
D. Johnson
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Convection Heat Transfer ◽  
Circuit Board ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heating Surfaces ◽  
Free Convection Heat ◽  
Microelectronic Components

A numerical simulation of the buoyancy-induced flow around microelectronic components mounted on a circuit board has been performed using the finite element method. The circuit board is modeled by a vertical plate on which rectangular strip heating surfaces are mounted. Computations have been performed in two-dimensional plane applying a simplifying assumption that the circuit board and the strip heating surfaces are infinitely long. The Navier-Stokes, the flow continuity and the energy equations for laminar flow have been considered in the finite element discretizations. Results of the computations are presented in the form of temperature contour plots and velocity vector plots in the flow field. The convection heat transfer coefficients at the surface of the microelectronic components are presented as a function of their height. The convection coefficients computed have been compared with experimental correlations of free convection heat transfer found in the literature.

Experimental Study on Transient Heat Transfer Enhancement for Helium Gas Flowing Over a Thin Twisted Plate

2014 ◽  
Author(s):  
Zhou Zhao ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Generation ◽  
Heat Input ◽  
Convection Heat Transfer ◽  
Transient Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Helium Gas ◽  
The Heat Transfer Coefficient

Transient forced convection heat transfer due to exponentially increasing heat input to a heater is important as a database for safety assessment of the transient heat transfer process in a Very High Temperature Reactor (VHTR). The knowledge of heat transfer enhancement using a heater with twisted configuration is also important for the high performance design of intermediate heater exchanger (IHX) in VHTR system. In this study, forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a short thin twisted plate with various helix angles was experimentally studied. A forced convection heat transfer experimental apparatus was used to measure the experimental data. The test heater was mounted horizontally along the center part of a circular test channel. Twisted plates were made of thin platinum plate with a thickness of 0.1 mm and width of 2 mm and 4 mm. The heat generation rates of the heater were controlled and measured by a heat input control system. The heat generation rate, Q̇, was raised with exponential function, Q̇ = Q0exp(t/τ). Where, t is time, and τ is period of heat generation rate. The mean temperature of the test heater was measured by resistance thermometry. The heat flux was obtained by the energy conservation equation. The test heater surface temperature was calculated from heat conduction equation of the heater. The transient heat transfer experimental data were measured for the periods ranged from 80 ms to 17 s and at a gas temperature of 303 K under 500 kPa. The flow velocities ranged from 4 m/s to 10 m/s. In the experiments, the twisted plates with different width were tested. The surface temperature and heat flux are increasing exponentially with the time. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than about 1 s. The heat transfer coefficients for total length of the twisted plate were compared with the values of flat plate which has the same width and thickness with the twisted one. The local mean heat transfer coefficients have been tested as well. The heat transfer coefficients of twisted plate are about 10% for 2 mm-width one and15% for 4 mm-width one higher than those of flat plate with same width at the quasi-steady state. And also, the heat transfer coefficients for the first half pitch are 24% higher than that for the total length of the same twisted plate. Therefore, an enhancement in the heat transfer coefficient for the twisted plate was clarified.

Simulation of Corrected Mass Flow and Non-Adiabatic Efficiency on a Turbocharger

2013 ◽  
Vol 388 ◽  
pp. 23-28
Author(s):  
A. Mohd Ibthisham ◽  
Srithar Rajoo ◽  
Amer Nordin Darus ◽  
Mazlan Abdul Wahid ◽  
Mohsin Mohd Sies ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mass Flow ◽  
Working Condition ◽  
Three Dimensional ◽  
Actual Condition ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Volume Method ◽  
The Heat Transfer Coefficient

The aim of this project is to evaluate turbine’s performance based on its actual condition. Holset H3B nozzles turbine geometry was used as simulation model. Turbine’s actual working condition was simulated using finite volume method (FVM). Three-dimensional Navier Stoke equations with heat convection loss via turbine volute are solved. The parameters studied are corrected mass flow and turbine’s efficiency at different heat transfer coefficients. Temperature difference within turbine’s volute is the major factor that deteriorates turbine’s efficiency. It is found that the higher the heat transfer coefficient, the lower turbine’s efficiency will be.

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

2015 ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Laser Doppler Velocimeter ◽  
Transfer Coefficients ◽  
Friction Coefficients ◽  
Heat Transfer Coefficients ◽  
Passage Vortex ◽  
Dimensional Boundary

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter. Friction coefficients obtained with the oil film interferometry method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

An Experimental Investigation of Free-Convection Heat Transfer From Rectangular-Fin Arrays

1963 ◽  
Vol 85 (3) ◽  
pp. 273-277 ◽  
Author(s):  
K. E. Starner ◽  
H. N. McManus
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Parallel Plates ◽  
Transfer Coefficients ◽  
Three Dimensional Flow ◽  
Fin Efficiency ◽  
Heat Transfer Coefficients ◽  
Vertical Arrays ◽  
Free Convection Heat

Average heat-transfer coefficients are presented for four fin arrays positioned with the base vertical, 45 degrees, and horizontal while dissipating heat to room air. The fins are analyzed as constant-temperature surfaces since the lowest fin efficiency encountered was greater than 98 percent. It was found that coefficients for the vertical arrays fell 10 to 30 percent below those of similarly spaced parallel plates. The 45-degree arrays yielded results 5 to 20 percent below those of the vertical. Two flow patterns were investigated for the horizontal arrays, and it was found that the coefficients could be reduced sharply by preventing three-dimensional flow.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

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