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ABSTRACT
The heat transfer characteristics of condensation for R410A inside horizontal microfin tubes with 0° and 18° helical angles were investigated numerically. The numerical data fit well with the experimental results and with the empirical correlations. The results indicate that local heat transfer coefficients increase with increasing mass flux, vapor quality, and helical angle. The heat transfer enhancement in the helical microfin tubes is more pronounced at higher mass flux and vapor quality. The centrifugal force induced by the microfin with a 18° helical angle tends to spread the liquid from the bottom to the top, leading to a nearly symmetrical liquid–vapor interface during condensation. Swirling flows in the liquid phase are observed in the tube with the 18° helical angle, but the liquid phase tends to flow to the bottom due to gravity in the tube with the 0° helical angle.
Nomenclature
| Cp | = | specific heat capacity (J kg−1 K−1) |
| di | = | inner tube diameter (m) |
| e | = | Fin height (m) |
| E | = | specific sensible enthalpy (J kg−1) |
| F | = | volumetric body force (N m−3) |
| g | = | gravitational acceleration ( m s−2) |
| G | = | mass flux (kg m−2 s−1) |
| h | = | heat transfer coefficient ( W m−2 K−1) |
| hlv | = | latent heat of vaporization (J kg−1) |
| k | = | turbulent kinetic energy (m2 s−2) |
| m | = | mass source due to phase change (kg m−3 s−1) |
| MAD | = | mean average deviation (−) |
| MRD | = | mean relative deviation (−) |
| Ns | = | number of fins (−) |
| q | = | heat flux ( W m−2) |
| r | = | coefficient of mass source (s−1) |
| Re | = | Reynolds number (–) |
| T | = | temperature (K) |
| v | = | velocity ( m s−1) |
| x | = | vapor quality (−) |
| α | = | volume fraction (−) |
| β | = | helical angle (°) |
| θ | = | apex angle of the fin (°) |
| κ | = | curvature of the interface (m−1) |
| λ | = | thermal conductivity ( W m−1 K−1) |
| μ | = | dynamic viscosity (Pa s) |
| ρ | = | density (kg m−3) |
| σ | = | surface tension (N m−1) |
| ω | = | specific dissipation rate of turbulent kinetic energy (s−1) |
| Subscripts | = | |
| cal | = | results predicted by correlation |
| l | = | liquid phase |
| sat | = | saturation status |
| sim | = | results obtained by simulation |
| tp | = | two phase |
| v | = | vapor phase |
| wall | = | wall |
Nomenclature
| Cp | = | specific heat capacity (J kg−1 K−1) |
| di | = | inner tube diameter (m) |
| e | = | Fin height (m) |
| E | = | specific sensible enthalpy (J kg−1) |
| F | = | volumetric body force (N m−3) |
| g | = | gravitational acceleration ( m s−2) |
| G | = | mass flux (kg m−2 s−1) |
| h | = | heat transfer coefficient ( W m−2 K−1) |
| hlv | = | latent heat of vaporization (J kg−1) |
| k | = | turbulent kinetic energy (m2 s−2) |
| m | = | mass source due to phase change (kg m−3 s−1) |
| MAD | = | mean average deviation (−) |
| MRD | = | mean relative deviation (−) |
| Ns | = | number of fins (−) |
| q | = | heat flux ( W m−2) |
| r | = | coefficient of mass source (s−1) |
| Re | = | Reynolds number (–) |
| T | = | temperature (K) |
| v | = | velocity ( m s−1) |
| x | = | vapor quality (−) |
| α | = | volume fraction (−) |
| β | = | helical angle (°) |
| θ | = | apex angle of the fin (°) |
| κ | = | curvature of the interface (m−1) |
| λ | = | thermal conductivity ( W m−1 K−1) |
| μ | = | dynamic viscosity (Pa s) |
| ρ | = | density (kg m−3) |
| σ | = | surface tension (N m−1) |
| ω | = | specific dissipation rate of turbulent kinetic energy (s−1) |
| Subscripts | = | |
| cal | = | results predicted by correlation |
| l | = | liquid phase |
| sat | = | saturation status |
| sim | = | results obtained by simulation |
| tp | = | two phase |
| v | = | vapor phase |
| wall | = | wall |
