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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 70, 2016 - Issue 6
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Original Articles

Thermal performance evaluation of the rotating U-shaped micro/mini/macrochannels using water and nanofluids

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Pages 650-672 | Received 14 Feb 2016, Accepted 20 Apr 2016, Published online: 18 Aug 2016
 

ABSTRACT

The thermal performance of the rotating U-shaped mini/micro/macrochannels is numerically investigated (Re = 125–20000). To compare the performance of different types of channels, the macrochannel passage with a square cross-section (D*D) is replaced by an array of parallel rectangular micro/mini channels with sides of D*D/12.5 (mini) and D*D/50 (micro). The results show that using nanofluid and converting the macrochannel to a parallel arrangement of minichannels considerably improve heat transfer enhancement and consequently a large volume reduction of up to about 70% for similar heat transfer. Also, in contrast to the macrochannel, adding ribs to the minichannels cannot improve their thermal performance.

Nomenclature

A=

heat transfer surface area, m2

Ac=

heat transfer cross-section area, m2

Cp=

heat capacity, kJ/kg · K

D=

side of the macrochannel cross section, m

Dm=

smaller side of micro/minichannel rectangular cross section, m

dh=

length scale of the channels, m

E=

thermal performance

e=

rib height, m

ϵijk=

permutation symbol

h=

convection heat transfer coefficient, W/m2 · K

k=

thermal conductivity, W/m · K

L1=

length of the straight passes with bend region, m

L2=

length of the straight passes without bend region, m

P=

pressure, Pa

p=

rib pitch, m

PP=

pumping power, W

ΔP=

pressure drop, Pa

q=

total heat transfer, W

q=

local heat flux, W/m2

R=

position vector from axis of rotation, m

r=

inner bend diameter, m

Re=

Reynolds number

Reω=

rotational Reynolds number

S=

path length, m

T=

temperature, K

T*=

scaled bulk temperature

u=

x-component of the fluid velocity, m/s

w=

rib width, m

x, y, z=

Cartesian coordinates, m

Greek Symbols=
θ=

convergence angle, °

ρ=

density, kg/m3

ϕ=

nanoparticle volume concentration, %

Ω=

angular velocity, rad/s

μ=

viscosity, Ns/m2

Subscripts=
0=

pure water flow at Re = 5,000

bf=

base fluid

CD=

convergence-divergence

i, j, k=

indices in x, y, z directions

in=

inlet

M=

macrochannel

m=

bulk

MCHS=

minichannel heat sink

mc=

microchannel

mn=

minichannel

nf=

nanofluid

np=

nanoparticle

pw=

pure water flow

R=

ribbed channel

ref=

reference condition

s=

smooth channel

st=

straight minichannel

w=

wall

Nomenclature

A=

heat transfer surface area, m2

Ac=

heat transfer cross-section area, m2

Cp=

heat capacity, kJ/kg · K

D=

side of the macrochannel cross section, m

Dm=

smaller side of micro/minichannel rectangular cross section, m

dh=

length scale of the channels, m

E=

thermal performance

e=

rib height, m

ϵijk=

permutation symbol

h=

convection heat transfer coefficient, W/m2 · K

k=

thermal conductivity, W/m · K

L1=

length of the straight passes with bend region, m

L2=

length of the straight passes without bend region, m

P=

pressure, Pa

p=

rib pitch, m

PP=

pumping power, W

ΔP=

pressure drop, Pa

q=

total heat transfer, W

q=

local heat flux, W/m2

R=

position vector from axis of rotation, m

r=

inner bend diameter, m

Re=

Reynolds number

Reω=

rotational Reynolds number

S=

path length, m

T=

temperature, K

T*=

scaled bulk temperature

u=

x-component of the fluid velocity, m/s

w=

rib width, m

x, y, z=

Cartesian coordinates, m

Greek Symbols=
θ=

convergence angle, °

ρ=

density, kg/m3

ϕ=

nanoparticle volume concentration, %

Ω=

angular velocity, rad/s

μ=

viscosity, Ns/m2

Subscripts=
0=

pure water flow at Re = 5,000

bf=

base fluid

CD=

convergence-divergence

i, j, k=

indices in x, y, z directions

in=

inlet

M=

macrochannel

m=

bulk

MCHS=

minichannel heat sink

mc=

microchannel

mn=

minichannel

nf=

nanofluid

np=

nanoparticle

pw=

pure water flow

R=

ribbed channel

ref=

reference condition

s=

smooth channel

st=

straight minichannel

w=

wall

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