ABSTRACT:
In electronic equipments, thermal management is indispensable
for its longevity and hence, it is one of the important topics of current
research. The dissipation of heat is necessary for the proper functioning of
these instruments. The heat is generated by the resistance encountered by
electric current. This has been further hastened by the continued
miniaturization of electronic systems which causes increase in the amount of
heat generation per unit volume by many folds. Unless proper cooling
arrangement is designed, the operating temperature exceeds permissible limit.
As a consequence, chances of failure get increased.
Increasing circuit density is driving advanced cooling systems
for the next generation microprocessors. Micro-Channel heat exchangers (MITE)
in silicon substrates are one method that is receiving considerable attention.
These very fine channels in the heat exchanger provide greatly enhanced
convective heat transfer rate and have been shown to be able to meet the
demands of the cooling challenge for the microprocessors for many generations
to come.
This work focused on laminar flow (Re=51, 84, 169) within
rectangular micro-channel with hydraulic diameter (86um) for single-phase
liquid flow. The influence of the thermo-physical -properties of the fluid on
the flow and heat transfer is investigated by evaluating thermo-physical
properties at a reference bulk temperature. The micro-heat sink model consists
of a (10 mm=10000um) long silicon substrate, with rectangular micro-channels,
(57um) wide and (180um) deep, fabricated along the entire length. Water at
(293k) is taken as working fluid. The results indicate that thermo-physical
properties of the liquid can significantly influence both the flow and heat
transfer in the micro-channel. The local heat transfer coefficient and averaged
NUSSELT number is calculated and plotted for Reynolds number (51, 84, and 169).
The results are verified for heat flux (50w/cm2, 90w/cm2,
and 150w/cm2). From these results we have taken the next
conclusions:
· A combined heat transfer convection-conduction within
the micro-channel is simulated according from the analyses of the temperature
profiles crossing in the same time the solid and the fluid. The diffuse heat
per conduction in the solid before attains the fluid per convection that is
vehicular to the exterior.
· The analyses of the Nusselt number show that the fluid
receives the big part of its heat in the inlet region of micro-channel, and if
the fluid advance in this channel; it heated. So, the difference between its
temperature and walls temperature decreased.
· The pressure drops calculated are agreed with the
theoretical and classical formulas.
Key words: conjugated heat transfer, viscous
dissipation, micro-channels, numerical simulation.
Nomenclature
Nomenclature :
Notations latines
Symboles Dénominations Unités
Dh
Cp Chaleur spécifique à p=cte J/Kg
4????
Diamètre hydraulique????h = m
????
2
????? Accélération gravitationnelle m/s
h Coefficient d'échange moyen W/m2 .K
m
2
q0 Densité De Flux Dégagée Par Le
Microprocesseur w/cm
T Température de fluide caloporteur k
U, V, W Composantes du vecteur de la vitesse d'écoulement
m/s
suivant x, y et z
|
~?
????
|
Vecteur de vitesse
|
x Largeur du micro-canal m
y Hauteur du micro-canal m
z Longueur du micro-canal m
Notations grecques
a diffusivité thermique m2/s
B coefficient de dilatation thermique du fluide 1/ k
K conductivité thermique du fluide W/m.K
3
ñ masse volumique du fluide Kg/m
u Viscosité dynamique du fluide kg/m.s
í Viscosité Cinématique du fluide
m2/s
???? La dissipation visqueuse J/m3.s
s-1
? Opérateur de vecteur Nabla
?2 Opérateur laplacien s-2
p pression N/m2
2
A surface m
t Temps s
Nombres adimensionnelles
Br Nombre de Brinkman
???????? Coefficient de frottement
Gr Nombre de grashof
Nu Nombre de Nusselt moyen
Ra
Re
Pr Nombre de Prandtl
Nombre de Rayleigt Nombre de Reynolds
Ri Nombre de Richardson
Indices
f Fluide
i interface
in Entrée
o Sortie
s Solide
| 
