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ABSTRACT
In this article, simulation of nanofluid flow and conjugated heat transfer in a micro-heat-exchanger is studied using the lattice Boltzmann method. Hot and cold streams enter the heat exchanger in opposite directions and heat transfer occurs between the two streams through a wall. The effect of nanoparticles volume fraction and diameter on the heat transfer and also the effect of viscous dissipation on the heat transfer performance are studied. Results show that increasing the nanoparticles volume fraction to φ = 5% causes 18% enhancement in the Nusselt number compared to the pure water. Also, increasing the nanoparticles diameter from 11 nm to 100 nm for φ = 5% results in 13.33% decrease in the Nusselt number. Finally, considering the viscous dissipation effect, reduction in the Nusselt number is observed.
Nomenclature
| C | = | lattice velocity |
| d | = | diameter (m) |
| ei | = | direction of lattice velocity |
| f | = | density distribution function |
| feq | = | density equilibrium distribution function |
| g | = | temperature distribution function |
| geq | = | equilibrium temperature distribution function |
| k | = | thermal conductivity (W/m.K) |
| Kb | = | Boltzmann constant (J/K) |
| L | = | mean free path (m) |
| M, N | = | number of lattices in the y and x directions, respectively |
| Nu | = | Nusselt number |
| Pr | = | Prandtl number |
| R | = | gas constant (J/K.mol) |
| Re | = | Reynolds number |
| t | = | time (s) |
| T | = | temperature (K) |
| U | = | macroscopic velocity in lattice scale |
| x, y | = | axial and vertical Cartesian coordinates, respectively |
| α | = | thermal diffusivity (m2/s) |
| θ | = | dimensionless temperature |
| µ | = | dynamic viscosity (kg/m.s) |
| υ | = | kinematic viscosity (m2/s) |
| ρ | = | density (kg/m3) |
| τ | = | collision relaxation time for flow |
| τθ | = | collision relaxation time for temperature |
| φ | = | nanoparticle volume fraction |
| ω | = | weight coefficient |
| Subscripts | = | |
| av | = | average |
| bf | = | base fluid |
| c | = | cold stream |
| H | = | hot stream |
| i | = | discrete lattice directions |
| in | = | inlet |
| nf | = | nanofluid |
| p | = | particles |
| x, y | = | x and y directions |
| w | = | wall |
Nomenclature
| C | = | lattice velocity |
| d | = | diameter (m) |
| ei | = | direction of lattice velocity |
| f | = | density distribution function |
| feq | = | density equilibrium distribution function |
| g | = | temperature distribution function |
| geq | = | equilibrium temperature distribution function |
| k | = | thermal conductivity (W/m.K) |
| Kb | = | Boltzmann constant (J/K) |
| L | = | mean free path (m) |
| M, N | = | number of lattices in the y and x directions, respectively |
| Nu | = | Nusselt number |
| Pr | = | Prandtl number |
| R | = | gas constant (J/K.mol) |
| Re | = | Reynolds number |
| t | = | time (s) |
| T | = | temperature (K) |
| U | = | macroscopic velocity in lattice scale |
| x, y | = | axial and vertical Cartesian coordinates, respectively |
| α | = | thermal diffusivity (m2/s) |
| θ | = | dimensionless temperature |
| µ | = | dynamic viscosity (kg/m.s) |
| υ | = | kinematic viscosity (m2/s) |
| ρ | = | density (kg/m3) |
| τ | = | collision relaxation time for flow |
| τθ | = | collision relaxation time for temperature |
| φ | = | nanoparticle volume fraction |
| ω | = | weight coefficient |
| Subscripts | = | |
| av | = | average |
| bf | = | base fluid |
| c | = | cold stream |
| H | = | hot stream |
| i | = | discrete lattice directions |
| in | = | inlet |
| nf | = | nanofluid |
| p | = | particles |
| x, y | = | x and y directions |
| w | = | wall |