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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 69, 2016 - Issue 6
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Original Articles

Molecular dynamic simulation: Studying the effects of Brownian motion and induced micro-convection in nanofluids

, , &
Pages 643-658 | Received 11 Mar 2015, Accepted 12 Aug 2015, Published online: 04 Jan 2016
 

ABSTRACT

Nanofluids are suspensions of nanoparticles into convectional heat transfer fluid to enhance the thermal conductivity of its base fluid. The roles of Brownian motion of nanoparticles and induced micro-convection in base fluid in enhancing the thermal conductivity of nanofluids were investigated using molecular dynamic (MD) simulation. The roles were determined by studying the effect of particle size on thermal conductivity and diffusion coefficient. Results show that the Brownian motion and induced micro-convection have insignificant effects on enhancing the thermal conductivity. The hydrodynamic effect is restricted by an amorphous-like interfacial fluid structure in the vicinity of the nanoparticle due to its higher specific area.

Nomenclature

d=

particle diameter, m

D=

diffusion coefficient, m2/s

E=

per atom energy for kinetic and potential, J

F=

force, N

g(r)=

radial distribution function

h=

average partial enthalpy, J

J=

heat current, J.m/s

k=

thermal conductivity, W/m.K

kB=

Boltzmann constant, 1.38 × 10–23 J/K

ke=

kinetic energy, J

MSD=

mean square displacement, m2

N=

total number of particles

pe=

potential energy, J

r=

displacement, m

t=

time, s

T=

temperature, K

v=

velocity, m/s

V=

volume, m3

Φ=

Lennard Jones potential, J

ε=

interaction strength, J

σ=

interatomic length scale, m

η=

dynamic viscosity, Pa.s

ø=

nanoparticles volume fraction, vol%

ρ=

mean number density, m−3

Subscripts=
Ar=

argon

B=

Brownian

Cu=

copper

f=

base fluid

i=

particle i

j=

particle j

nf=

nanofluid

p=

nanoparticle

α=

species α

Nomenclature

d=

particle diameter, m

D=

diffusion coefficient, m2/s

E=

per atom energy for kinetic and potential, J

F=

force, N

g(r)=

radial distribution function

h=

average partial enthalpy, J

J=

heat current, J.m/s

k=

thermal conductivity, W/m.K

kB=

Boltzmann constant, 1.38 × 10–23 J/K

ke=

kinetic energy, J

MSD=

mean square displacement, m2

N=

total number of particles

pe=

potential energy, J

r=

displacement, m

t=

time, s

T=

temperature, K

v=

velocity, m/s

V=

volume, m3

Φ=

Lennard Jones potential, J

ε=

interaction strength, J

σ=

interatomic length scale, m

η=

dynamic viscosity, Pa.s

ø=

nanoparticles volume fraction, vol%

ρ=

mean number density, m−3

Subscripts=
Ar=

argon

B=

Brownian

Cu=

copper

f=

base fluid

i=

particle i

j=

particle j

nf=

nanofluid

p=

nanoparticle

α=

species α

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