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ABSTRACT
This paper presents a numerical study of nanofluids condensation heat transfer inside a single horizontal smooth square tube. The numerical results are compared with the previous experimental predictions. The numerical results show that the heat transfer coefficient could be improved within 20% by increasing the volume fraction of Cu nanoparticle by 5% or by increasing the mass flux from 80 to 110 kg/m2 s. Reducing the hydraulic diameter of the microchannel from 200 to 160 µm leads to an increase in the condensation average heat transfer coefficient by 10%. A new correlation estimating the Nusselt number for the condensation of nanofluids or pure vapor is proposed. It predicts average condensation heat transfer with a good agreement with those computed.
Nomenclature
| A | = | area (m2) |
| Bo | = | boiling number |
| Ca | = | capillary number |
| Cp | = | specific heat (J/kg K) |
| D | = | hydraulic diameter (m) |
| f | = | friction factor |
| G | = | total mass flux (kg/s m2) |
| h | = | heat transfer coefficient (W/m2 k) |
| hfg | = | latent heat (J/kg) |
| L | = | annular condensation length (m) |
| l | = | length of the end part in condensation (m) |
| m | = | mass flux (kg/s) |
| P | = | pressure (Pa) |
| q | = | heat flux (Wm−2) |
| R | = | curvature radius (m) |
| Ref | = | film Reynolds number |
| U | = | velocity (m/s) |
| Xtt | = | Martinelli parameter |
| z | = | z-coordinate (m) |
| β | = | half of right angle (°) |
| δ | = | film thickness (m) |
| μ | = | dynamic viscosity (kg/m · s) |
| λ | = | thermal conductivity (W/m · K) |
| θ | = | contact angle (°) |
| ρ | = | density (kg m−3) |
| σ | = | surface tension coefficient (N m−1) |
| τ | = | shear stress (N · m−2) |
| Subscripts | = | |
| bf | = | base fluid |
| L | = | liquid |
| nf | = | nanofluid |
| p | = | particle |
| v | = | vapor |
| vl | = | liquid–vapor interface |
Nomenclature
| A | = | area (m2) |
| Bo | = | boiling number |
| Ca | = | capillary number |
| Cp | = | specific heat (J/kg K) |
| D | = | hydraulic diameter (m) |
| f | = | friction factor |
| G | = | total mass flux (kg/s m2) |
| h | = | heat transfer coefficient (W/m2 k) |
| hfg | = | latent heat (J/kg) |
| L | = | annular condensation length (m) |
| l | = | length of the end part in condensation (m) |
| m | = | mass flux (kg/s) |
| P | = | pressure (Pa) |
| q | = | heat flux (Wm−2) |
| R | = | curvature radius (m) |
| Ref | = | film Reynolds number |
| U | = | velocity (m/s) |
| Xtt | = | Martinelli parameter |
| z | = | z-coordinate (m) |
| β | = | half of right angle (°) |
| δ | = | film thickness (m) |
| μ | = | dynamic viscosity (kg/m · s) |
| λ | = | thermal conductivity (W/m · K) |
| θ | = | contact angle (°) |
| ρ | = | density (kg m−3) |
| σ | = | surface tension coefficient (N m−1) |
| τ | = | shear stress (N · m−2) |
| Subscripts | = | |
| bf | = | base fluid |
| L | = | liquid |
| nf | = | nanofluid |
| p | = | particle |
| v | = | vapor |
| vl | = | liquid–vapor interface |