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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 |