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Study of a new thin flat loop heat pipe for electronics

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Abstract

In this paper, a simple but detailed new theoretical model is developed for a thin loop heat pipe (LHP) to predict: the overall thermal resistance, the temperature distribution, the heat transfer rate, the heat leakage by conduction and the length of single and two-phase working fluid flows within the condenser. The theoretical results were confronted with experimental data of a mini flat LHP, manufactured using sintering and diffusion bonding processes. The working fluid used was water. A workbench, capable of simulating the actual operating conditions of a modern chip processor, with 1 cm2 of heat dissipating area, as found in smartphones and other electronic gadgets, was used to evaluate the LHP thermal performance. The tested LHP had dimensions of 76 x 60 x 1.6 mm3. The cold source was natural air convection to the surroundings. The device operated successfully in the orientations: horizontal, gravity-assisted, and against gravity. Tests were conducted until the evaporator reached 100°C, the limit temperature of electronics, resulting in overall thermal resistances of 0.37 °C/W, 0.47 °C/W and 0.44 °C/W, respectively. The model could successfully predict all steady-state operational parameters of the LHP with small deviations, proving to be suitable for designing new LHPs and other thin devices. The difference between predicted and measured resistances were within 5.64%, while between predicted and measured temperatures were within 3.30%. Lastly, the heat leak from the evaporator to the liquid line had a deviation of 16.62%. The LHP, although very thin, showed to be a good solution for cooling small electronic gadgets, such as mobile smartphones.

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Data Availability

The authors declare that the data supporting the findings of this study are available within the paper and its supplementary information files. Some supplementary data from the model and experimental results was uploaded.

Abbreviations

A :

area [m2]

B :

Chisholm parameter [-]

c :

specific heat [J/kg°C]

C :

Chisholm constant [-]

d :

diameter [m]

E :

Freidel parameter [-]

f :

friction factor [-]

F :

Freidel parameter [-]

Fr :

Froude number [-]

G :

mass velocity [kg/m2s]

g :

gravity acceleration [m/s2]

H :

Freidel parameter [-]

h :

heat transfer coefficient [W/m2K]

h lv :

latent heat of vaporization [J/kg]

I :

current [A]

J :

dimensionless vapor velocity [-]

K :

permeability [m2]

k :

thermal conductivity [W/m K]

L :

length [m]

ṁ:

mass flow rate [kg/s]

n :

Chisholm parameter [-]

Nu :

Nusselt number [-]

p :

pressure [Pa]

q :

heat transfer rate [W]

\(q"\) :

heat flux [W/ m2]

r:

radius [m]

Ra :

Rayleigh number [-]

Re :

Reynolds number [-]

Rh :

hydraulic resistance [Pa.s/kg]

R t :

thermal resistance [°C/W]

t :

thickness [m]

T :

temperature [°C]

U :

voltage [V]

V :

volume [m3]

W :

width [m]

We :

Weber number [-]

X :

Martinelli parameter [-]

Y :

Chisholm parameter [-]

z :

distance [m]

Z :

Shah’s correlating parameter

α :

thermal diffusivity [m2/s]

β :

coefficient of thermal expansion [1/K]

ɛ:

porosity [%]

Γ :

aspect ratio [-]

Δ:

difference [-]

δ:

uncertainty [-]

ζ :

roughness [µm]

θ :

contact angle [°]

κ :

surface area ratio [-]

μ :

dynamic viscosity [Pa.s]

v :

kinematic viscosity [m2/s]

ρ :

mass density [kg/m3]

σ :

surface tension [N/m]

υ:

specific volume [m3/kg]

ϕ :

phase [-]

φ :

channel aspect ratio [-]

χ :

vapor quality

ac :

active area

amb :

ambient

avg :

average

b :

barrier

c :

condenser

cap :

capillarity

ch :

channel

cs :

cross-section

eff :

effective

eq :

equivalent

ev :

evaporator

hl :

heat leak

h :

hydraulic

i :

internal

in :

inlet

ini :

initial

iso :

insulated

l :

liquid

ll :

liquid line

lo :

liquid only

p :

pressure

r :

reduced

sup :

superficial

t :

total

v :

vapor

vg :

vapor grooves

vo :

vapor inly

w :

wick

wf :

working fluid

1ϕ :

single-phase

2ϕ :

two-phase

FR :

Filling Ratio [%]

LHP :

Loop Heat Pipe

TP :

two-phase mixture

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Acknowledgments

The authors acknowledge FAPESC (Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina) for providing scholarship (grant number 3003/2021) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) for their financial support to the present research (grant number 423968/2018-1).

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Authors and Affiliations

  1. Heat Pipe Laboratory, Department of Mechanical Engineering, Federal University of Santa Catarina, Florianopolis, 88040-900, Brazil

    Kelvin Guessi Domiciano, Larissa Krambeck & Marcia Barbosa Henriques Mantelli

  2. Department of Physical-mechanical Engineering, Universidad Industrial de Santander, Bucaramanga, Colombia

    Juan Pablo Floréz Mera

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  1. Kelvin Guessi Domiciano
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  2. Larissa Krambeck
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Correspondence to Kelvin Guessi Domiciano.

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Domiciano, K.G., Krambeck, L., Mera, J.P.F. et al. Study of a new thin flat loop heat pipe for electronics. Heat Mass Transfer 59, 2035–2056 (2023). https://doi.org/10.1007/s00231-023-03381-9

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  • DOI: https://doi.org/10.1007/s00231-023-03381-9

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