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 |