Analysis of nonlinear heat exchange phenomena in natural convection cooled electronic systems

2016 ◽  
Vol 67 ◽  
pp. 15-20 ◽  
Author(s):  
Gilbert De Mey ◽  
Tomasz Torzewicz ◽  
Piotr Kawka ◽  
Andrzej Czerwoniec ◽  
Marcin Janicki ◽  
...  
Keyword(s):  
Natural Convection ◽  
Heat Exchange ◽  
Electronic Systems

scholarly journals Numerical study of the turbulent natural convection of nanofluids in a partially heated cubic cavity

2021 ◽  
pp. 57-57
Author(s):  
Zakaria Lafdaili ◽  
Sakina El-Hamdani ◽  
Abdelaziz Bendou ◽  
Karim Limam ◽  
Bara El-Hafad
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Heat Exchange ◽  
Metallic Nanoparticles ◽  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Stability Characteristic ◽  
Horizontal Strip ◽  
Turbulent Natural Convection

In this work we study numerically the three-dimensional turbulent natural convection in a partially heated cubic cavity filled with water containing metallic nanoparticles, metallic oxides and others based on carbon.The objective is to study and compare the effect of the addition of nanoparticles studied in water and also the effect of the position of the heated partition on the heat exchange by turbulent natural convection in this type of geometry, which can significantly improve the design of heat exchange systems for better space optimization. For this we have treated numerically for different volume fractions the turbulent natural convection in the two cases where the cavity is heated respectively by a vertical and horizontal strip in the middle of one of the vertical walls. To take into account the effects of turbulence, we used the standard turbulence model ? - ?. The governing equations are discretized by the finite volume method using the power law scheme which offers a good stability characteristic in this type of flow. The results are presented in the form of isothermal lines and current lines. The variation of the mean Nusselt number is calculated for the two positions of the heated partition as a function of the volume fraction of the nanoparticles studied in water for different Rayleigh numbers.The results show that carbon-based nanoparticles intensify heat exchange by convection better and that the position of the heated partition significantly influences heat exchange by natural convection. In fact, an improvement in the average Nusselt number of more than 20% is observed for the case where the heated partition is horizontal.

Unsteady Conduction in a Horizontal Solid Cylinder Cooled by Natural Convection: Alternate Lumped Criterion in Terms of the Solid Material

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Antonio Campo ◽  
Jaime Sieres
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Heat Exchange ◽  
Solid Body ◽  
Biot Number ◽  
The Body ◽  
Convection Heat ◽  
Lumped Model ◽  
Convective Coefficient ◽  
The Mean

Within the framework of the potent lumped model, unsteady heat conduction takes place in a solid body whose space–mean temperature varies with time. Conceptually, the lumped model subscribes to the notion that the external convective resistance at the body surface dominates the internal conductive resistance inside the body. For forced convection heat exchange between a solid body and a neighboring fluid, the criterion entails to the lumped Biot number Bil=(h¯/ks)(V/A)<0.1, in which the mean convective coefficient h¯ depends on the impressed fluid velocity. However, for natural convection heat exchange between a solid body and a fluid, the mean convective coefficient h¯ depends on the solid-to-fluid temperature difference. As a consequence, the lumped Biot number must be modified to read Bil=(h¯max/ks)(V/A)<0.1, wherein h¯max occurs at the initial temperature Ti for cooling or at a future temperature Tfut for heating. In this paper, the equivalence of the lumped Biot number criterion is deduced from the standpoint of the solid thermal conductivity through the solid-to-fluid thermal conductivity ratio.

Numerical simulation of natural convection in a porous cavity with internal hot and cold sources by lattice Boltzmann method

2021 ◽  
Author(s):  
Ying Zhang ◽  
Xuhui Huang ◽  
Yichen Huang ◽  
Meng Xu ◽  
Jie Lei
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchange ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Heat Transfer Performance ◽  
Size Ratio ◽  
Transfer Performance ◽  
Spacing Ratio ◽  
Boltzmann Method

Based on the non-orthogonal multiple-relaxation time lattice Boltzmann method (MRT-LBM), natural convection in a porous square cavity with a pair of isothermally hot and cold blocks inside has been studied numerically in the current study. The influence of arrangements (Case1, Case2, Case3, Case4, Case5), spacing ratio (S) and size ratio (A) of the hot and cold sources and the Rayleigh number (Ra) on the heat exchange efficiency has been studied. The results show that different arrangements produce different heat transfer effects. Hot and cold blocks placed horizontally (Case1) and hot block located in the upper left corner while cold block located in the bottom right corner (Case4) have better heat exchange performances than other three cases since the flow directions of hot and cold fluids are closer to that of heat transfer. Then the influence of spacing between blocks and size of blocks on heat transfer rate is further studied in Case1 and Case4. The heat transfer performance is improved with A increasing. Additionally, the variation of heat transfer performance with spacing is related to the arrangement and size ratio of blocks. For Ra=104, 105 and 106, the best heat transfer characteristic can be obtained in Case1 when S=0.05 and A=0.20. For Ra=107, Case4 exhibits the best heat transfer effect when S=0.35 and A=0.20.

scholarly journals Experimental tests for the occurence of convective heat transfer within the bed of rectangular steel profiles

2012 ◽  
Vol 33 (3) ◽  
pp. 84-95
Author(s):  
Rafał Wyczółkowski ◽  
Dorota Musiał
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Natural Convection ◽  
Heat Exchange ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Experimental Tests ◽  
Steel Sections

Abstract The paper describes tests intended to examine the occurrence of natural convection within the space occupied by 40×20 mm rectangular steel sections. Within these tests the bed of four layers of section was heated by the electric palate heater. Depending on the manner in which the heater was positioned, the tests were divided into two series. In the case of heating from above, the heat flowing through the bed is transferred only by conduction and radiation. When heating the bed from below, in addition to conduction and radiation, also a convective heat transfer will occur. Should this be the case, it will result in the intensification of the heat exchange. The results of measurements carried out have not demonstrated that the occurrence of any possible natural convection would influence the development of a temperature field in this type of charge.

scholarly journals Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity. Effect of Source Length, Position, Thermal Condition and Prandtl Number

2020 ◽  
Vol 38 (3) ◽  
pp. 722-737
Author(s):  
Abderrahmane Horimek ◽  
El-Amria Nekag
Keyword(s):  
Exchange Rate ◽  
Natural Convection ◽  
Heat Exchange ◽  
Heat Source ◽  
Prandtl Number ◽  
Thermal Conditions ◽  
Effect Analysis ◽  
Bottom Side ◽  
D Values ◽  
Good Heat

Cooling process of a heat source placed at the bottom side of a cold-walled cavity (TC) by means of natural convection has been studied numerically in this work. Two thermal conditions have been assumed at the source (q-imposed or T-imposed). The effects of Rayleigh number (Ra=10+3→10+6), source length (SL=0.1→1.0), source position (D) compared to left side, in addition to the effect of the number of Prandtl (Pr=0.71→10+2) were analyzed with ample details. For a source at the center of the bottom side, results showed an increase of flow and temperature disturbance with increasing Ra and/or SL, with an enhancement of both local and mean Nusselt numbers. Particular exceptions were noticed for high Ra values for the second heating type. For all considerations, the case of SL=0.1 makes an exception where a very good heat exchange rate is recorded. When the source is no longer centered, Clearer difference between this case and the previous one was recorded, especially for small D values. Very good heat exchange rate is recorded for D=0.0 for all considerations, with remarkable amount of difference compared the closest one to it, followed by a progressive decrease until the case of source at the center. Finally, Prandtl number (Pr) effect analysis showed an increase of the heat transfer rate with a clear amount from Pr=0.71 until Pr=5.0, followed by a slight increase for higher Pr values until stabilization for Pr>50.0. The good exploitation of the intervening parameters’ parameters, allows ensuring the best cooling of the source.

The effect of the temperature distribution along the perimeter of the boundary on the the flow in the convective Rayleigh-Benard cell

2011 ◽  
Vol 8 (1) ◽  
pp. 116-123
Author(s):  
V.L. Malyshev ◽  
E.F. Moiseeva ◽  
K.V. Moiseyev
Keyword(s):  
Natural Convection ◽  
Heat Exchange ◽  
Temperature Distribution ◽  
Incompressible Fluid ◽  
Viscous Incompressible Fluid ◽  
Maximum Speed ◽  
Two Dimensional ◽  
Rayleigh Benard ◽  
Dimensional Cell

This paper is devoted to the study of the natural convection of a viscous incompressible fluid in a two-dimensional cell with combined vertical and horizontal heating in symmetrical and asymmetrical cases; investigation of the dependence of the maximum speed and intensity of heat exchange on different heating regimes.

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