Constructal Placement of Discrete Heat Sources With Different Lengths in Vertical Ducts Under Natural and Mixed Convection

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Bugra Sarper ◽  
Mehmet Saglam ◽  
Orhan Aydin
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Hot Spot ◽  
Experimental Studies ◽  
Vertical Channel ◽  
Working Fluid ◽  
Heat Sources ◽  
Ansys Fluent ◽  
Cooling Performance ◽  
Spot Temperature

In this study, convective heat transfer in a discretely heated parallel-plate vertical channel which simulates an IC package is investigated experimentally and numerically. Both natural and mixed convection cases are considered. The primary focus of the study is on determining optimum relative lengths of the heat sources in order to reduce the hot spot temperature and to maximize heat transfer from the sources to air. Various values of the length ratio and the modified Grashof number (for the natural convection case)/the Richardson number (for the mixed convection case) are examined. Conductive and radiative heat transfer is included in the analysis while air is used as the working fluid. Surface temperatures of the heat sources and the channel walls are measured in the experimental study. The numerical studies are performed using a commercial CFD code, ANSYS fluent. The variations of surface temperature, hot spot temperature, Nusselt number, and global conductance of the system are obtained for varying values of the working parameters. From the experimental studies, it is showed that the use of identical heat sources reduces the overall cooling performance both in natural and mixed convection. However, relatively decreasing heat sources lengths provides better cooling performance.

Natural Convection From a Column of Flush Heat Sources in a Vertical Channel in Water

1990 ◽  
Vol 112 (4) ◽  
pp. 367-374 ◽  
Author(s):  
Y. Joshi ◽  
D. L. Knight
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Power Level ◽  
Experimental Studies ◽  
Vertical Channel ◽  
Input Power ◽  
Substrate Material ◽  
Temperature Measurements ◽  
Heat Sources ◽  
Single Column

Natural convection from a single column of eight in-line, rectangular heat sources flush mounted on one wall of a vertical channel immersed in water was examined. Input power to each heating element was varied from 0.2–2.0 W for channel spacings in the range of 1.5–15.0 mm, as well as with the shroud removed. Flow visualization in two mutually perpendicular vertical planes was carried out both with and without the shroud for each power level. Component temperature measurements were made using thermocouples embedded within the substrate. By suitably accounting for the increasing convected energy downstream, a single heat transfer correlation was obtained for all channel spacings larger than 3 mm. For smaller channel spacings, the component center temperatures increased substantially above the correlation. To investigate the effect of heater spacing, temperature measurements in the absence of shroud were also made with only selected components powered. As the spacing between successive heated components was increased to twice of the fully heated configuration, the upstream effects on component heat transfer become negligible. Further increase in spacing resulted in a weak enhancement in heat transfer downstream. Comparison of the present data with existing experimental studies and new computations revealed significant influence of the heater and substrate material thermal properties on the transport.

scholarly journals Turbulent mixed convection in heated vertical channel

2010 ◽  
Vol 14 (1) ◽  
pp. 125-135 ◽  
Author(s):  
Ameni Mokni ◽  
Hatem Mhiri ◽  
Palec Le ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Boundary Layers ◽  
Vertical Channel ◽  
Ambient Air ◽  
Forced Flow ◽  
Working Fluid ◽  
Heat Flow Rate ◽  
Maximum Heat ◽  
First Case

In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer enhancement obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Combined forced and free convection are studied in order to increase the cooling requirements. The study is conceded for two Rayleigh number. The first case corresponds to two separate boundary layers so the channel acts as two independent plates. For the second case the two boundary layers are attached. Calculations are carried out with air as the working fluid by changing the jet velocity in order to optimize the system to give the maximum heat flow rate over the chimney. The system of governing equations is solved with a finite volumes method and an implicit scheme. The results obtained show that the jet-wall activates the heat transfer, as does the drive of ambient air by the jet.

Computer Simulation of Mixed Convection of Alumina-Deionized Water Nanofluid Over Four In-Line Electronic Chips Embedded in One Wall of a Vertical Rectangular Channel

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Nalla Ramu ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Al2o3 Nanoparticles ◽  
Enhancement Factors

Abstract This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.

Conjugate Mixed Convection With Surface Radiation and Substrate Conduction in Laminar Channel Flow With Discrete Flush-Mounted Heat Sources

2010 ◽  
Author(s):  
Jing He ◽  
Anthony M. Jacobi
Keyword(s):  
Mixed Convection ◽  
Hot Spot ◽  
Surface Radiation ◽  
Bottom Surface ◽  
Heat Sources ◽  
Thick Substrate ◽  
Laminar Channel Flow ◽  
Uniform Temperature Field ◽  
Influence Of Substrate ◽  
High Reynolds

Thermal analysis employing a full conjugation model is performed in this study for laminar airflow in a parallel-plate channel with discrete flush-mounted heat sources. The numerical model accounts for mixed convection, surface radiation, and two-dimensional conduction in the substrate. The effects of Reynolds number, surface emissivity of walls and heat sources, as well as thickness and thermal conductivity of the substrate, are analyzed in detail. It is shown that participation of radiation brings the wall temperatures closer, and the trend of temperature variation along the top wall is drastically altered. Such effects are pronounced for black enclosures and diminished for high Reynolds numbers. The influence of substrate conductivity and thickness is very similar in that a large value for both parameters would facilitate redistribution of heat and tend to yield a uniform temperature field in the substrate. For highly conductive or thick substrate, the ‘hot spot’ cools down and may move upstream to the penultimate source. Radiation loss to the ambient increases with substrate conductivity and thickness due to the elevated temperature near the inlet and outlet, yet the total heat transfer over the bottom surface by convection and radiation remains unaltered.

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